@article{miller_jernigan_abraham_buckner_2023, title={Comparison of Bolus Versus Dual-Syringe Administration Systems on Glass Yttrium-90 Microsphere Deposition in an In Vitro Microvascular Hepatic Tumor Model}, volume={34}, ISSN={["1535-7732"]}, DOI={10.1016/j.jvir.2022.07.032}, abstractNote={To utilize an in vitro microvascular hepatic tumor model to compare the deposition characteristics of glass yttrium-90 microspheres using the dual-syringe (DS) and traditional bolus administration methods.The microvascular tumor model represented a 3.5-cm tumor in a 1,400-cm3 liver with a total hepatic flow of 160 mL/min and was dynamically perfused. A microcatheter was placed in a 2-mm artery feeding the tumor model and 2 additional nontarget arteries. Glass microspheres with a diameter of 20-30 μm were administered using 2 methods: (a) DS delivery at a concentration of 50 mg/mL in either a single, continuous 2-mL infusion or two 1-mL infusions and (b) bolus delivery (BD) of 100 mg of microspheres in a single 3-mL infusion.Overall, the degree of on-target deposition of the microspheres was 85% ± 11%, with no significant differences between the administration methods. Although the distal penetration into the tumor arterioles was approximately 15 mm (from the second microvascular bifurcation of the tumor model) for all the cases, the distal peak particle counts were significantly higher for the DS delivery case (approximately 5 × 105 microspheres achieving distal deposition vs 2 × 105 for the BD case). This resulted in significantly higher deposition uniformity within the tumor model (90% for the DS delivery case vs 80% for the BD case, α = 0.05).The use of this new in vitro microvascular hepatic tumor model demonstrated that the administration method can affect the deposition of yttrium-90 microspheres within a tumor, with greater distal deposition and more uniform tumor coverage when the microspheres are delivered at consistent concentrations using a DS delivery device. The BD administration method was associated with less favorable deposition characteristics of the microspheres.}, number={1}, journal={JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY}, author={Miller, Samuel R. and Jernigan, Shaphan R. and Abraham, Robert J. and Buckner, Gregory D.}, year={2023}, month={Jan}, pages={11–20} }
 @article{zaccardo_buckner_2023, title={Saturation and duty cycle tolerant self-sensing for active magnetic dampers}, volume={200}, ISSN={["1096-1216"]}, DOI={10.1016/j.ymssp.2023.110567}, abstractNote={Traditional active magnetic damper (AMD) systems rely on external position sensors to measure the mover’s radial position, though these sensors add cost, complexity, failure modes, and potential sources of error due to the axial non-colocation of actuator and sensor. An alternate, so-called “self-sensing” approach seeks to exploit displacement-induced changes in electromagnet inductance to determine mover position; such techniques have been described in active magnetic bearing (AMB) and AMD literature since the 1980s. This paper details a novel, magnetic-saturation tolerant self-sensing approach for AMDs. The theoretical basis is presented; it is validated both experimentally and via a transient magnetic finite-element model. A position estimation error of 4.17 µm (0.164 mils) RMS is experimentally demonstrated over a typical mover position range and a theoretical bandwidth of 250 Hz is achieved.}, journal={MECHANICAL SYSTEMS AND SIGNAL PROCESSING}, author={Zaccardo, Victor M. and Buckner, Gregory D.}, year={2023}, month={Oct} }
 @article{shah_miller_jernigan_buckner_2022, title={A Permanent Magnet Synchronous Spherical Motor for High-Mobility Servo-Actuation}, volume={10}, ISSN={["2075-1702"]}, DOI={10.3390/machines10080612}, abstractNote={The development of direct-drive spherical motors offers a potential solution to the limitations of conventional multiple degree-of-freedom (DOF) actuators, which typically utilize single-DOF joints (rotational and/or prismatic), arranged in series or parallel and powered by multiple single-DOF actuators. These configurations can be accompanied by kinematic singularities, backlash, limited power density and efficiency, and computationally expensive inverse kinematics. This paper details the design, fabrication and experimental testing of permanent magnet synchronous spherical motors (PMSSM) for multi-DOF servo-actuation. Its stator-pole arrangement is based on a Goldberg polyhedron, with each pole comprised of hexagonal or pentagonal inner and outer plates. The stator geometry and winding configurations are optimized using electromagnetic finite element analysis. A custom-made controller board includes a microcontroller, servo drivers, a wireless serial interface, and a USB PC interface. Angular orientation is sensed using an inertial measurement unit in wireless communication with the microcontroller. A PID controller is implemented and demonstrated for time-varying reference trajectories.}, number={8}, journal={MACHINES}, author={Shah, Jay A. and Miller, Samuel R. and Jernigan, Shaphan R. and Buckner, Gregory D.}, year={2022}, month={Aug} }
 @article{perrin_jernigan_thayer_howell_leary_buckner_2022, title={Sensor Fusion with Deep Learning for Autonomous Classification and Management of Aquatic Invasive Plant Species}, volume={11}, ISSN={["2218-6581"]}, DOI={10.3390/robotics11040068}, abstractNote={Recent advances in deep learning, including the development of AlexNet, Residual Network (ResNet), and transfer learning, offer unprecedented classification accuracy in the field of machine vision. A developing application of deep learning is the automated identification and management of aquatic invasive plants. Classification of submersed aquatic vegetation (SAV) presents a unique challenge, namely, the lack of a single source of sensor data that can produce robust, interpretable images across a variable range of depth, turbidity, and lighting conditions. This paper focuses on the development of a multi-sensor (RGB and hydroacoustic) classification system for SAV that is robust to environmental conditions and combines the strengths of each sensing modality. The detection of invasive Hydrilla verticillata (hydrilla) is the primary goal. Over 5000 aerial RGB and hydroacoustic images were generated from two Florida lakes via an unmanned aerial vehicle and boat-mounted sonar unit, and tagged for neural network training and evaluation. Classes included “HYDR”, containing hydrilla; “NONE”, lacking SAV, and “OTHER”, containing SAV other than hydrilla. Using a transfer learning approach, deep neural networks with the ResNet architecture were individually trained on the RGB and hydroacoustic datasets. Multiple data fusion methodologies were evaluated to ensemble the outputs of these neural networks for optimal classification accuracy. A method incorporating logic and a Monte Carlo dropout approach yielded the best overall classification accuracy (84%), with recall and precision of 84.5% and 77.5%, respectively, for the hydrilla class. The training and ensembling approaches were repeated for a DenseNet model with identical training and testing datasets. The overall classification accuracy was similar between the ResNet and DenseNet models when averaged across all approaches (1.9% higher accuracy for the ResNet vs. the DenseNet).}, number={4}, journal={ROBOTICS}, author={Perrin, Jackson E. and Jernigan, Shaphan R. and Thayer, Jacob D. and Howell, Andrew W. and Leary, James K. and Buckner, Gregory D.}, year={2022}, month={Aug} }
 @article{upadhye_shah_liu_buckner_huang_2021, title={A Powered Prosthetic Ankle Designed for Task Variability - A Concept Validation}, ISSN={["2153-0858"]}, url={http://dx.doi.org/10.1109/iros51168.2021.9636324}, DOI={10.1109/IROS51168.2021.9636324}, abstractNote={Ankle joints play key roles in everyday locomotion, such as walking, stair climbing, and sit-to-stand. Despite the achievement in designing powered prosthetic ankles, engineers still face challenges to duplicate the full mechanics of ankle joints, including high torque, large range of motion (ROM), low profile, backdrivability, and efficiency, using electric motors and related transmissions. In this study, our goal was to develop a new active prosthetic ankle, Variable Spring embedded Motor-ball screw (VSeM) ankle, to meet all these requirements at the same time. Using a manually adjustable elastic element, which is parallel with our motor actuator, we can readjust the ROM of VSeM to handle all normal locomotion tasks. VSeM’s capability to mimic human ankle was validated through both bench tests and human subject tests.}, journal={2021 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS)}, publisher={IEEE}, author={Upadhye, Sameer and Shah, Chinmay and Liu, Ming and Buckner, Gregory and Huang, He}, year={2021}, pages={6153–6158} }
 @article{zaccardo_buckner_2021, title={Active magnetic dampers for controlling lateral rotor vibration in high-speed rotating shafts}, volume={152}, ISSN={["1096-1216"]}, DOI={10.1016/j.ymssp.2020.107445}, abstractNote={High-speed rotating machinery frequently operates supercritically, traversing self-excited resonance during startup and shutdown. The rotor's peak radial displacement often occurs during this critical transition, thus defining minimum clearances between the rotor and stator. Squeeze film dampers (SFDs) are frequently used to reduce lateral rotor vibration (LRV), but their passive nature imposes design and performance limitations. An alternate approach, the subject of this paper, employs active magnetic dampers (AMDs) to overcome the inherent tradeoffs associated with squeeze film dampers. This paper details the design, fabrication and experimental demonstration of an AMD for reducing LRV in a high-speed rotating shaft through its critical speed. A finite-element method (FEM) model of a high-speed flexible shaft with an AMD mounted proximal to a compliant bearing support is developed and parameterized using test data. Different actuator locations are evaluated using the FEM model, revealing that the primary mechanism for LRV reduction is the moment exerted about the compliant bearing. Performance of a SFD is simulated for comparison, revealing that the AMD more effectively reduces LRV. Peak radial deflection is reduced by an average of 79% through the shaft's first critical speed.}, journal={MECHANICAL SYSTEMS AND SIGNAL PROCESSING}, author={Zaccardo, Victor M. and Buckner, Gregory D.}, year={2021}, month={May} }
 @article{atay_bryant_buckner_2021, title={Control and Control Allocation for Bimodal, Rotary Wing, Rolling-Flying Vehicles}, volume={13}, ISSN={["1942-4310"]}, DOI={10.1115/1.4050998}, abstractNote={Abstract This paper presents a robust method for controlling the terrestrial motion of a bimodal multirotor vehicle that can roll and fly. Factors influencing the mobility and controllability of the vehicle are explored and compared to strictly flying multirotor vehicles; the differences motivate novel control and control allocation strategies that leverage the non-standard configuration of the bimodal design. A fifth-order dynamic model of the vehicle subject to kinematic rolling constraints is the basis for a nonlinear, multi-input, multi-output, sliding mode controller. Constrained optimization techniques are used to develop a novel control allocation strategy that minimizes power consumption while rolling. Simulations of the vehicle under closed-loop control are presented. A functional hardware embodiment of the vehicle is constructed onto which the controllers and control allocation algorithm are deployed. Experimental data of the vehicle under closed-loop control demonstrate good performance and robustness to parameter uncertainty. Data collected also demonstrate that the control allocation algorithm correctly determines a thrust-minimizing solution in real-time.}, number={5}, journal={JOURNAL OF MECHANISMS AND ROBOTICS-TRANSACTIONS OF THE ASME}, author={Atay, Stefan and Bryant, Matthew and Buckner, Gregory}, year={2021}, month={Oct} }
 @article{jenkins_atay_buckner_bryant_2021, title={Genetic Algorithm-Based Optimal Design of a Rolling-Flying Vehicle}, volume={13}, ISSN={["1942-4310"]}, DOI={10.1115/1.4050811}, abstractNote={Abstract This work describes a design optimization framework for a rolling-flying vehicle consisting of a conventional quadrotor configuration with passive wheels. For a baseline comparison, the optimization approach is also applied for a conventional (flight-only) quadrotor. Pareto-optimal vehicles with maximum range and minimum size are created using a hybrid multi-objective genetic algorithm in conjunction with multi-physics system models. A low Reynolds number blade element momentum theory aerodynamic model is used with a brushless DC motor model, a terramechanics model, and a vehicle dynamics model to simulate the vehicle range under any operating angle-of-attack and forward velocity. To understand the tradeoff between vehicle size and operating range, variations in Pareto-optimal designs are presented as functions of vehicle size. A sensitivity analysis is used to better understand the impact of deviating from the optimal vehicle design variables. This work builds on current approaches in quadrotor optimization by leveraging a variety of models and formulations from the literature and demonstrating the implementation of various design constraints. It also improves upon current ad hoc rolling-flying vehicle designs created in previous studies. Results show the importance of accounting for oft-neglected component constraints in the design of high-range quadrotor vehicles. The optimal vehicle mechanical configuration is shown to be independent of operating point, stressing the importance of a well-matched, optimized propulsion system. By emphasizing key constraints that affect the maximum and nominal vehicle operating points, an optimization framework is constructed that can be used for rolling-flying vehicles and conventional multi-rotors.}, number={5}, journal={JOURNAL OF MECHANISMS AND ROBOTICS-TRANSACTIONS OF THE ASME}, author={Jenkins, Tyler and Atay, Stefan and Buckner, Gregory and Bryant, Matthew}, year={2021}, month={Oct} }
 @article{elliott_ferguson_buckner_2021, title={The Cost-Sorted Distance Method for Identifying Minima Within Firefly Optimization Results: Application to Engineering Design}, volume={21}, ISSN={["1944-7078"]}, DOI={10.1115/1.4047554}, abstractNote={Abstract This paper provides a detailed description of the cost-sorted distance (CSD) method for visually and computationally identifying objective function minima within clustered population-based optimization results. CSD requires sorting the design vector population by cost and computing Euclidean distances between each pair of designs. It may be applied in conjunction with any population-based optimization method (e.g., particle swarm, genetic algorithm, simulated annealing, ant colony, firefly), but it is naturally compatible with the firefly algorithm (FA) because FA also requires the distances between each pair of design vectors and benefits from cost-sorting the population (the computational work required for CSD is a byproduct of FA). A modified FA is presented that uses CSD to more thoroughly search near potential minima and a systematic method for tuning the algorithm to reliably identify multiple minima is documented. The tuned algorithm's efficacy is demonstrated using a class of benchmark problems and a “real world” electromechanical design problem, where the identification of attractive design alternatives can be challenging.}, number={1}, journal={JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING}, author={Elliott, Christopher M. and Ferguson, Scott M. and Buckner, Gregory D.}, year={2021}, month={Feb} }
 @article{atay_bryant_buckner_2021, title={The Spherical Rolling-Flying Vehicle: Dynamic Modeling and Control System Design}, volume={13}, ISSN={["1942-4310"]}, DOI={10.1115/1.4050831}, abstractNote={Abstract This paper presents the dynamic modeling and control of a bi-modal, multirotor vehicle that is capable of omnidirectional terrestrial rolling and multirotor flight. It focuses on the theoretical development of a terrestrial dynamic model and control systems, with experimental validation. The vehicle under consideration may roll along the ground to conserve power and extend endurance but may also fly to provide high mobility and maneuverability when necessary. The vehicle uses a three-axis gimbal system that decouples the rotor orientation from the vehicle’s terrestrial rolling motion. A dynamic model of the vehicle’s terrestrial motion is derived from first principles. The dynamic model becomes the basis for a nonlinear trajectory tracking control system suited to the architecture of the vehicle. The vehicle is over-actuated while rolling, and the additional degrees of actuation can be used to accomplish auxiliary objectives, such as power optimization and gimbal lock avoidance. Experiments with a hardware vehicle demonstrate the efficacy of the trajectory tracking control system.}, number={5}, journal={JOURNAL OF MECHANISMS AND ROBOTICS-TRANSACTIONS OF THE ASME}, author={Atay, Stefan and Bryant, Matthew and Buckner, Gregory}, year={2021}, month={Oct} }
 @article{zaccardo_miller_buckner_2020, title={A large air gap magnetic levitator for intra-arterial positioning of a clinical microcatheter: design, fabrication, and preliminary experimental evaluation}, volume={4}, ISSN={["2366-598X"]}, DOI={10.1007/s41315-020-00124-5}, number={1}, journal={INTERNATIONAL JOURNAL OF INTELLIGENT ROBOTICS AND APPLICATIONS}, author={Zaccardo, Victor M. and Miller, Samuel R. and Buckner, Gregory D.}, year={2020}, month={Mar}, pages={122–131} }
 @article{weisler_miller_jernigan_buckner_bryant_2020, title={Design and testing of a centrifugal fluidic device for populating microarrays of spheroid cancer cell cultures}, volume={14}, ISSN={["1754-1611"]}, DOI={10.1186/s13036-020-0228-6}, abstractNote={In current cancer spheroid culturing methods, the transfer and histological processing of specimens grown in 96-well plates is a time consuming process. A centrifugal fluidic device was developed and tested for rapid extraction of spheroids from a 96-well plate and subsequent deposition into a molded agar receiver block. The deposited spheroids must be compact enough to fit into a standard histology cassette while also maintaining a highly planar arrangement. This size and planarity enable histological processing and sectioning of spheroids in a single section. The device attaches directly to a 96-well plate and uses a standard centrifuge to facilitate spheroid transfer. The agar block is then separated from the device and processed.Testing of the device was conducted using six full 96-well plates of fixed Pa14C pancreatic cancer spheroids. On average, 80% of spheroids were successfully transferred into the agar receiver block. Additionally, the planarity of the deposited spheroids was evaluated using confocal laser scanning microscopy. This revealed that, on average, the optimal section plane bisected individual spheroids within 27% of their mean radius. This shows that spheroids are largely deposited in a planar fashion. For rare cases where spheroids had a normalized distance to the plane greater than 1, the section plane either misses or captures a small cross section of the spheroid volume.These results indicate that the proposed device is capable of a high capture success rate and high sample planarity, thus demonstrating the capabilities of the device to facilitate rapid histological evaluation of spheroids grown in standard 96-well plates. Planarity figures are likely to be improved by adjusting agar block handling prior to imaging to minimize deformation and better preserve the planarity of deposited spheroids. Additionally, investigation into media additives to reduce spheroid adhesion to 96-well plates would greatly increase the capture success rate of this device.}, number={1}, journal={JOURNAL OF BIOLOGICAL ENGINEERING}, author={Weisler, Warren and Miller, Samuel and Jernigan, Shaphan and Buckner, Gregory and Bryant, Matthew}, year={2020}, month={Mar} }
 @article{atay_buckner_bryant_2020, title={Dynamic Modeling for Bi-Modal, Rotary Wing, Rolling-Flying Vehicles}, volume={142}, ISSN={["1528-9028"]}, DOI={10.1115/1.4047693}, abstractNote={Abstract This paper presents a rigorous analysis of a promising bi-modal multirotor vehicle that can roll and fly. This class of vehicle provides energetic and locomotive advantages over traditional unimodal vehicles. Despite superficial similarities to traditional multirotor vehicles, the dynamics of the vehicle analyzed herein differ substantially. This paper is the first to offer a complete and rigorous derivation, simulation, and validation of the vehicle's terrestrial rolling dynamics. Variational mechanics is used to develop a six degrees-of-freedom dynamic model of the vehicle subject to kinematic rolling constraints and various nonconservative forces. The resulting dynamic system is determined to be differentially flat and the flat outputs of the vehicle are derived. A functional hardware embodiment of the vehicle is constructed, from which empirical motion data are obtained via odometry and inertial sensing. A numerical simulation of the dynamic model is executed, which accurately predicts complex dynamic phenomena observed in the empirical data, such as gravitational and gyroscopic nonlinearities; the comparison of simulation results to empirical data validates the dynamic model.}, number={11}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Atay, Stefan and Buckner, Gregory and Bryant, Matthew}, year={2020}, month={Nov} }
 @article{atay_jenkins_buckner_bryant_2020, title={Energetic analysis and optimization of a bi-modal rolling-flying vehicle}, volume={4}, ISSN={["2366-598X"]}, DOI={10.1007/s41315-020-00119-2}, number={1}, journal={INTERNATIONAL JOURNAL OF INTELLIGENT ROBOTICS AND APPLICATIONS}, author={Atay, Stefan and Jenkins, Tyler and Buckner, Gregory and Bryant, Matthew}, year={2020}, month={Mar}, pages={3–20} }
 @article{jernigan_osborne_buckner_2020, title={Gastric artery embolization: studying the effects of catheter type and injection method on microsphere distributions within a benchtop arterial model}, volume={19}, ISSN={["1475-925X"]}, DOI={10.1186/s12938-020-00794-z}, abstractNote={Abstract Aims The objective of the study is to investigate the effect of catheter type and injection method on microsphere distributions, specifically vessel targeting accuracy. Materials and methods The study utilized three catheter types (a standard end-hole micro-catheter, a Surefire anti-reflux catheter, and an Endobar occlusion balloon catheter) and both manual and computer-controlled injection schemes. A closed-loop, dynamically pressurized surrogate arterial system was assembled to replicate arterial flow for bariatric embolization procedures. Four vessel branches immediately distal to the injection site were targeted for embolization. Embolic microspheres were injected into the model using these three catheter types and both manual and computer-controlled injections. Results Across all injection methods, the catheter effect on the proportion of microspheres to target vessels (vs. non-target vessels) was significant ( p = 0.005). The catheter effect on the number of non-target vessels embolized was nearly significant ( p = 0.059). Across all catheter types, the injection method effect was not statistically significant for either of two outcome measures (percent microspheres to target vessels: p = 0.265, number of non-target vessels embolized: p = 0.148). Conclusion Catheter type had a significant effect on targeting accuracy across all injection methods. The Endobar catheter exhibited a higher targeting accuracy in pairwise comparisons with the other two injection catheters across all injection schemes and when considering the Endobar catheter with the manifold injection method vs. each of the catheters with the manual injection method; the differences were significant in three of four analyses. The injection method effect was not statistically significant across all catheter types and when considering the Endobar catheter/Endobar manifold combination vs. Endobar catheter injections with manual and pressure-replicated methods.}, number={1}, journal={BIOMEDICAL ENGINEERING ONLINE}, author={Jernigan, Shaphan R. and Osborne, Jason A. and Buckner, Gregory D.}, year={2020}, month={Jun} }
 @article{kakaley_altieri_buckner_2020, title={Non-contacting measurement of torque and axial translation in high-speed rotating shafts}, volume={138}, ISSN={["1096-1216"]}, DOI={10.1016/j.ymssp.2019.106520}, abstractNote={This paper focuses on the development and experimental demonstration of a unique non-contacting Variable Reluctance (VR) sensor system that enables simultaneous estimation of torque, speed, and axial translation in high-speed rotating shafts. A novel tooth geometry is introduced featuring alternating slants on every third tooth of an otherwise standard toothed wheel. A novel torque and axial processing (TAP) algorithm allows axial translation to be extracted from the VR sensor measurements. Simulations confirm shaft speed, torque, and axial translation can be accurately estimated based on timing measurements. Experiments conducted on a high-speed driveshaft further validate the TAP approach and reveal that the accuracy of shaft torque estimation improves significantly with axial translation compensation.}, journal={MECHANICAL SYSTEMS AND SIGNAL PROCESSING}, author={Kakaley, Daniel E. and Altieri, Russell E. and Buckner, Gregory D.}, year={2020}, month={Apr} }
 @article{haigh_crews_wang_buckner_2019, title={Multi-Objective Design Optimization of a Shape Memory Alloy Flexural Actuator}, volume={8}, ISSN={["2076-0825"]}, DOI={10.3390/act8010013}, abstractNote={This paper presents a computational model and design optimization strategy for shape memory alloy (SMA) flexural actuators. These actuators consist of curved SMA wires embedded within elastic structures; one potential application is positioning microcatheters inside blood vessels during clinical treatments. Each SMA wire is shape-set to an initial curvature and inserted along the neutral axis of a straight elastic member (cast polydimethylsiloxane, PDMS). The elastic structure preloads the SMA, reducing the equilibrium curvature of the composite actuator. Temperature-induced phase transformations in the SMA are achieved via Joule heating, enabling strain recovery and increased bending (increased curvature) in the actuator. Actuator behavior is modeled using the homogenized energy framework, and the effects of two critical design parameters (initial SMA curvature and flexural rigidity of the elastic sleeve) on activation curvature are investigated. Finally, a multi-objective genetic algorithm is utilized to optimize actuator performance and generate a Pareto frontier, which is subsequently experimentally validated.}, number={1}, journal={ACTUATORS}, author={Haigh, Casey D. and Crews, John H. and Wang, Shiquan and Buckner, Gregory D.}, year={2019}, month={Feb} }
 @article{chanoit_pell_bolotin_buckner_williams_crenshaw_2019, title={Retraction mechanics of Finochietto-style self-retaining thoracic retractors}, volume={18}, ISSN={["1475-925X"]}, DOI={10.1186/s12938-019-0664-z}, abstractNote={Analyze the mechanics of Finochietto-style retractors, including the responses of thoracic tissues during thoracotomy, with an emphasis on tissue trauma and means for its reduction. Mechanical analyses of the retractor were performed, including analysis of deformation under load and kinematics of the crank mechanism. Thoracotomies in a porcine model were performed in anesthetized animals (7) and fresh cadavers (17) using an instrumented retractor. Mechanical analyses revealed that arm motion is a non-linear function of handle rotation, that deformation of the retractor under load concentrates force at one edge of the retractor blade, and that the retractor behaves like a spring, deforming under the load of retraction and continuing to force open the incision long after crank rotation stops. Experimental thoracotomies included retractions ranging from 50 to 112 mm over 30 to 370 s, generating maximum forces of 118 to 470 N (12–50 kgf). Tissue ruptures occurred in 12 of the 24 retractions. These ruptures all occurred at retraction distances wider than 30 mm and at forces greater than 122.5 N. Significant tissue ruptures were observed for nearly all retractions at higher retraction rates (exceeding ½ rotation of the crank per 10 s). The Finochietto-style retractor can generate large forces and some aspects of its design increase the probability of tissue trauma.}, journal={BIOMEDICAL ENGINEERING ONLINE}, author={Chanoit, Guillaume and Pell, Charles A. and Bolotin, Gil and Buckner, Gregory D. and Williams, Jeffrey P. and Crenshaw, Hugh C.}, year={2019}, month={Apr} }
 @article{miller_zaccardo_buckner_2018, title={A large air gap magnetic levitator for precise positioning of a clinical microcatheter: nonlinear modelling and control}, volume={2}, ISSN={["2366-598X"]}, DOI={10.1007/s41315-018-0077-3}, number={4}, journal={INTERNATIONAL JOURNAL OF INTELLIGENT ROBOTICS AND APPLICATIONS}, author={Miller, Samuel R. and Zaccardo, Victor M. and Buckner, Gregory D.}, year={2018}, month={Dec}, pages={462–469} }
 @article{kakaley_jolly_buckner_2018, title={An offset hub active vibration control system for mitigating helicopter vibrations during power loss: Simulation and experimental demonstration}, volume={77}, ISSN={["1626-3219"]}, DOI={10.1016/j.ast.2018.03.026}, abstractNote={Abstract In recent years, hub active vibration control (HAVC) technologies have been developed to attenuate blade pass frequency vibration on helicopters. While these systems provide superior vibration control with reduced weight compared to passive options, in the event of electrical power loss they can exacerbate the vibration problem in a manner that is problematic for helicopter and tiltrotor aircraft. This paper presents an offset hub active vibration control system (OHAVCS) designed to attenuate vibration during a power loss by offsetting the centers of rotation of two imbalance masses. The equations of motion for this system are developed using Lagrangian methods; analysis, simulation and experimental validation of these equations indicate that offsetting the imbalance masses effectively mitigates 1/Rev vibrations during a rotor hub power loss while continuing to cancel N/Rev vibrations during normal operation. These offsets create stabilizing centripetal torques that rotate each imbalance mass to a unique equilibrium angle. Experimental data also indicate that these offsets do not hinder control of the imbalance masses during normal (active) operation, though they do increase system power requirements.}, journal={AEROSPACE SCIENCE AND TECHNOLOGY}, author={Kakaley, Daniel E. and Jolly, Mark R. and Buckner, Gregory D.}, year={2018}, month={Jun}, pages={610–625} }
 @article{elliott_buckner_2018, title={Design optimization of a novel elastomeric baffle magnetorheological fluid device}, volume={29}, ISSN={["1530-8138"]}, DOI={10.1177/1045389X18799211}, abstractNote={This article details the design optimization of a novel magnetorheological fluid device, which incorporates a rolling elastomeric baffle to contain the fluid and minimize cost and complexity. The application considered here is an electronic joystick for a drive-by-wire construction machine, although designs for other semi-active applications could be similarly optimized. Performance is evaluated computationally and experimentally. A computationally efficient system model is developed and validated using finite element analysis to accurately predict the device’s magnetic flux characteristics. The design methodology is based on a variant of the firefly algorithm, which identifies promising initial designs, and conjugate gradient methods, which optimize these designs. A unique graphical method for interpreting the results of population-based firefly optimization is demonstrated. An experimental prototype, based on the optimized design, is tested and its data compared to simulation results.}, number={19}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Elliott, Christopher M. and Buckner, Gregory D.}, year={2018}, month={Nov}, pages={3774–3791} }
 @article{allred_churchill_buckner_2017, title={Real-time estimation of helicopter rotor blade kinematics through measurement of rotation induced acceleration}, volume={91}, ISSN={["0888-3270"]}, DOI={10.1016/j.ymssp.2017.01.003}, abstractNote={Abstract This paper presents a novel approach to monitoring rotor blade flap, lead-lag and pitch using an embedded gyroscope and symmetrically mounted MEMS accelerometers. The central hypothesis is that differential accelerometer measurements are proportional only to blade motion; fuselage acceleration and blade bending are inherently compensated for. The inverse kinematic relationships (from blade position to acceleration and angular rate) are derived and simulated to validate this hypothesis. An algorithm to solve the forward kinematic relationships (from sensor measurement to blade position) is developed using these simulation results. This algorithm is experimentally validated using a prototype device. The experimental results justify continued development of this kinematic estimation approach.}, journal={MECHANICAL SYSTEMS AND SIGNAL PROCESSING}, author={Allred, C. Jeff and Churchill, David and Buckner, Gregory D.}, year={2017}, month={Jul}, pages={183–197} }
 @inproceedings{malinga_ferguson_buckner_2016, title={Design optimization and analysis of a prescribed vibration system}, DOI={10.1115/detc2016-60096}, abstractNote={Advances in technology that come with increased system complexity have accentuated the intricacy of decision making in engineering design. This has stimulated a great deal of research in ways to incorporate decision analysis and multi-attribute decision-making theory in engineering problems. In this research, Conjoint Value Analysis is incorporated into a scheme that optimizes the design of a multi-attribute Prescribed Vibration System. The influence of designer preferences is investigated by comparing design alternatives that result from different preference rankings. Monte Carlo-based uncertainty and sensitivity studies are performed to support the design process by providing additional information on the candidate designs. By understanding how small changes in the values of optimized parameters influence the system attributes, sensitivity analysis and uncertainty analyses can be used as a design robustness measure. The overall choice of the design is therefore based not only on the performance objectives but also on the resulting system robustness, which is very valuable considering manufacturing variations and tolerance stacks.}, booktitle={Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2016, Vol 2b}, author={Malinga, B. and Ferguson, S. M. and Buckner, G. D.}, year={2016}, pages={353–360} }
 @article{malinga_buckner_2016, title={Design optimization of a prescribed vibration system using conjoint value analysis}, volume={48}, ISSN={["1029-0273"]}, DOI={10.1080/0305215x.2016.1157687}, abstractNote={This article details a novel design optimization strategy for a prescribed vibration system (PVS) used to mechanically filter solids from fluids in oil and gas drilling operations. A dynamic model of the PVS is developed, and the effects of disturbance torques are detailed. This model is used to predict the effects of design parameters on system performance and efficiency, as quantified by system attributes. Conjoint value analysis, a statistical technique commonly used in marketing science, is utilized to incorporate designer preferences. This approach effectively quantifies and optimizes preference-based trade-offs in the design process. The effects of designer preferences on system performance and efficiency are simulated. This novel optimization strategy yields improvements in all system attributes across all simulated vibration profiles, and is applicable to other industrial electromechanical systems.}, number={12}, journal={ENGINEERING OPTIMIZATION}, author={Malinga, Bongani and Buckner, Gregory D.}, year={2016}, pages={2090–2113} }
 @article{xu_jernigan_kleinstreuer_buckner_2016, title={Solid Tumor Embolotherapy in Hepatic Arteries with an Anti-reflux Catheter System}, volume={44}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-015-1411-7}, number={4}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Xu, Zelin and Jernigan, Shaphan and Kleinstreuer, Clement and Buckner, Gregory D.}, year={2016}, month={Apr}, pages={1036–1046} }
 @article{hoven_lam_jernigan_bosch_buckner_2015, title={Innovation in catheter design for intra-arterial liver cancer treatments results in favorable particle-fluid dynamics}, volume={34}, DOI={10.1186/s13046-015-0188-8}, abstractNote={Liver tumors are increasingly treated with radioembolization. Here, we present first evidence of catheter design effect on particle-fluid dynamics and downstream branch targeting during microsphere administrations. A total of 7 experiments were performed in a bench-top model of the hepatic arterial vasculature with recreated hemodynamics. Fluorescent microspheres and clinically used holmium microspheres were administered with a standard microcatheter (SMC) and an anti-reflux catheter (ARC) positioned at the same level along the longitudinal vessel axis. Catheter-related particle flow dynamics were analyzed by reviewing video recordings of UV-light illuminated fluorescent microsphere administrations. Downstream branch distribution was analyzed by quantification of collected microspheres in separate filters for two first-order branches. Mean deviation from a perfectly homogenous distribution (DHD) was used to compare the distribution homogeneity between catheter types. The SMC administrations demonstrated a random off-centered catheter position (in 71 % of experiments), and a laminar particle flow pattern with an inhomogeneous downstream branch distribution, dependent on catheter position and injection force. The ARC administrations demonstrated a fixed centro-luminal catheter position, and a turbulent particle flow pattern with a more consistent and homogenous downstream branch distribution. Quantitative analyses confirmed a significantly more homogeneous distribution with the ARC; the mean DHD was 40.85 % (IQR 22.76 %) for the SMC and 15.54 % (IQR 6.46 %) for the ARC (p = 0.047). Catheter type has a significant impact on microsphere administrations in an in-vitro hepatic arterial model. A within-patient randomized controlled trial has been initiated to investigate clinical catheter-related effects during radioembolization treatment.}, journal={Journal of Experimental & Clinical Cancer Research}, author={Hoven, A. F. and Lam, M. G. E. H. and Jernigan, S. and Bosch, M. A. A. J. and Buckner, G. D.}, year={2015} }
 @article{wiest_buckner_2015, title={Path optimization and control of a shape memory alloy actuated catheter for endocardial radiofrequency ablation}, volume={65}, ISSN={["1872-793X"]}, DOI={10.1016/j.robot.2014.10.019}, abstractNote={This paper introduces a real-time path optimization and control strategy for shape memory alloy (SMA) actuated cardiac ablation catheters, potentially enabling the creation of more precise lesions with reduced procedure times and improved patient outcomes. Catheter tip locations and orientations are optimized using parallel genetic algorithms to produce continuous ablation paths with near normal tissue contact through physician-specified points. A nonlinear multivariable control strategy is presented to compensate for SMA hysteresis, bandwidth limitations, and coupling between system inputs. Simulated and experimental results demonstrate efficient generation of ablation paths and optimal reference trajectories. Closed-loop control of the SMA-actuated catheter along optimized ablation paths is validated experimentally.}, journal={ROBOTICS AND AUTONOMOUS SYSTEMS}, author={Wiest, Jennifer H. and Buckner, Gregory D.}, year={2015}, month={Mar}, pages={88–97} }
 @article{allred_jolly_buckner_2015, title={Real-time estimation of helicopter blade kinematics using integrated linear displacement sensors}, volume={42}, ISSN={1270-9638}, url={http://dx.doi.org/10.1016/J.AST.2014.11.012}, DOI={10.1016/J.AST.2014.11.012}, abstractNote={A novel method for estimating helicopter rotor blade kinematics during flight is presented. Limitations of optical measurement approaches (which are incompatible with circulating dust and moisture) and kinematic approaches (which add additional mass and maintenance complications) are overcome by embedding linear displacement sensors into the spherical bearing hinge joint of a fully articulated rotor. Forward and inverse bearing kinematics for this multiple degree of freedom measurement platform are modeled using techniques developed for Gough–Stewart platforms. Displacement sensor orientations are optimized to ensure that the rotational and translational rotor blade displacement modes are distinguishable. Forward kinematic estimation methods, including Newton–Raphson and genetic algorithms, are derived to map sensor measurements to rotor blade displacements. Extensive computer simulations, validated by experimental testing of a prototype, confirm that these approaches provide accurate estimates of rotor blade motion. Estimation accuracy in excess of 99% is demonstrated for all three rotational degrees of freedom.}, journal={Aerospace Science and Technology}, publisher={Elsevier BV}, author={Allred, C. Jefferson and Jolly, Mark R. and Buckner, Gregory D.}, year={2015}, month={Apr}, pages={274–286} }
 @article{jernigan_osborne_mirek_buckner_2015, title={Selective Internal Radiation Therapy: Quantifying Distal Penetration and Distribution of Resin and Glass Microspheres in a Surrogate Arterial Model}, volume={26}, ISSN={1051-0443}, url={http://dx.doi.org/10.1016/J.JVIR.2015.02.022}, DOI={10.1016/j.jvir.2015.02.022}, abstractNote={To experimentally investigate the effects of microsphere density and diameter on distal penetration.A surrogate hepatic arterial system was developed to replicate the hemodynamics (pressures, flow rates, pulsatile flow characteristics) and anatomic geometry (vessel diameters) proximal and distal to the microsphere injection point. A planar tumor model, placed distal to the injection point, allowed visualization of deposited microspheres. Bland resin and glass microspheres, with physical characteristics approximating the characteristics of commercially available products, were injected into the surrogate system. Microsphere type, injection rate, systemic flow rate, and tumor model inclination were varied among tests (glass, n = 7; resin, n = 6) with replicates for 2 conditions. After injection, 254 micrographs were obtained at previously defined locations throughout the tumor model to document microsphere distributions. Average microsphere distributions and mass measurements of microspheres collected at the tumor outlet were analyzed to quantify distal penetration for each case.Across all test conditions, average penetration depths of resin microspheres were higher compared with glass microspheres (45.1 cm ± 11.8 vs 22.3 cm ± 9.9). The analysis of variance indicated that the observed difference between microsphere type (glass vs resin) was significant (P = .005, df = 1,2). The observed distance means did not differ significantly across flow rate or inclination angle.Penetration depths of resin microspheres were significantly higher than penetration depths of glass microspheres in the surrogate hepatic arterial system.}, number={6}, journal={Journal of Vascular and Interventional Radiology}, publisher={Elsevier BV}, author={Jernigan, Shaphan R. and Osborne, Jason A. and Mirek, Christopher J. and Buckner, Gregory}, year={2015}, month={Jun}, pages={897–904.e2} }
 @article{malinga_buckner_2015, title={ℒ1adaptive control of a shape memory alloy actuated flexible beam}, volume={3}, ISSN={2164-2583}, url={http://dx.doi.org/10.1080/21642583.2015.1082515}, DOI={10.1080/21642583.2015.1082515}, abstractNote={This paper details the synthesis of an 1 adaptive controller for a shape memory alloy (SMA) actuated flexible beam. The controller manipulates applied voltage, which alters SMA tendon temperature to track reference bending angles. Simulated and experimental results show that the 1 adaptive controller provides precise tracking of the reference trajectories and effectively compensates for the nonlinear hysteretic relationship between SMA Joule heating and bending angle without explicitly modelling these characteristics. A simulation model whose results closely resemble the experimental performance results is presented. As a first step towards the development of 1 adaptive control implementation guidelines, a complete description of the 1 control parameters and their correlation to tracking performance is presented.}, number={1}, journal={Systems Science & Control Engineering}, publisher={Informa UK Limited}, author={Malinga, Bongani and Buckner, Gregory D.}, year={2015}, month={Jan}, pages={460–471} }
 @article{wiest_buckner_2014, title={Indirect Intelligent Sliding Mode Control of Antagonistic Shape Memory Alloy Actuators Using Hysteretic Recurrent Neural Networks}, volume={22}, ISSN={["1558-0865"]}, DOI={10.1109/tcst.2013.2272420}, abstractNote={This paper presents the development of an indirect intelligent sliding mode control (IISMC) system for use with antagonistic shape memory alloy (SMA) actuators. The controller manipulates input voltages to a pair of offset antagonistic SMA tendons, resulting in heat-induced bending of a flexible beam. Hysteresis compensation is achieved using a pair of hysteretic recurrent neural networks, which map the nonlinear, hysteretic relationships between SMA temperatures and bending angle for each tendon. The sliding mode control law regulates tendon temperatures based on reference and measured bending angle. Additionally, the IISMC incorporates an antislack component to increase tendon responsiveness. Experimental results demonstrate precise tracking of periodic reference trajectories. The controller is robust to model uncertainty, disturbances, and parameter variations, with bending angle tracking results superior to those of an optimized proportional + integral controller.}, number={3}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Wiest, Jennifer Hannen and Buckner, Gregory D.}, year={2014}, month={May}, pages={921–929} }
 @article{archer_fang_ferguson_buckner_2014, title={Multi-Objective Design Optimization of a Variable Geometry Spray Fuel Injector}, volume={136}, ISSN={["1050-0472"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84903773146&partnerID=MN8TOARS}, DOI={10.1115/1.4026263}, abstractNote={This paper explores the simulation-based design optimization of a variable geometry spray (VGS) fuel injector. A multi-objective genetic algorithm (MOGA) is interfaced with commercial computational fluid dynamics (CFD) software and high performance computing capabilities to evaluate the spray characteristics of each VGS candidate design. A three-point full factorial experimental design is conducted to identify significant design variables and to better understand possible variable interactions. The Pareto frontier of optimal designs reveals the inherent tradeoff between two performance objectives—actuator stroke and spray angle sensitivity. Analysis of these solutions provides insight into dependencies between design parameters and the performance objectives and is used to assess possible performance gains with respect to initial prototype configurations. These insights provide valuable design information for the continued development of this VGS technology.}, number={4}, journal={JOURNAL OF MECHANICAL DESIGN}, author={Archer, J. R. and Fang, Tiegang and Ferguson, Scott and Buckner, Gregory D.}, year={2014}, month={Apr} }
 @inproceedings{hannen_buckner_2013, title={Indirect intelligent sliding mode control using hysteretic recurrent neural networks with application to a shape memory alloy actuated beam}, DOI={10.1115/smasis2012-7930}, abstractNote={This paper presents the development of an indirect intelligent sliding mode controller (IISMC) for shape memory alloy (SMA) actuators. The controller manipulates applied voltage, enabling temperature control in one or more SMA tendons, which are offset to produce bending in a flexible beam tip. Hysteresis compensation is achieved using a hysteretic recurrent neural network (HRNN), which maps the nonlinear, hysteretic relationships between SMA temperatures and bending angle. Incorporating this HRNN into a variable structure control architecture provides robustness to model uncertainties and parameter variations. Single input, single output and multivariable implementations of this control strategy are presented. Controller performance is evaluated using a flexible beam deflected by single and antagonistic SMA tendons. Experimental results demonstrate precise tracking of a variety of reference trajectories for both configurations, with superior performance compared to an optimized PI controller for each system. Additionally, the IISMC demonstrates robustness to parameter variations and disturbances.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, vol 1}, author={Hannen, J. C. and Buckner, G. D.}, year={2013}, pages={295–303} }
 @article{richards_dickey_kennedy_buckner_2012, title={Design and demonstration of a novel micro-Coulter counter utilizing liquid metal electrodes}, volume={22}, ISSN={0960-1317 1361-6439}, url={http://dx.doi.org/10.1088/0960-1317/22/11/115012}, DOI={10.1088/0960-1317/22/11/115012}, abstractNote={This paper describes the design and demonstration of a novel, easily fabricated micro-Coulter counter utilizing liquid metal electrodes. Fluid and electrode channels were fabricated simultaneously in a single lithographic patterning step. Eutectic gallium?indium (EGaIn) was injected into the device to form functional electrodes in a cross-channel parallel configuration. Functionality of the device was demonstrated at an ac excitation frequency of 5?kHz using a polymer microsphere suspension and simple post-processing techniques. The device successfully detected particles, exhibiting an output response proportional to particle size. EGaIn was demonstrated to be an effective micro-fluidic electrode material and provided a novel approach for the fabrication of a functional micro-Coulter counter.}, number={11}, journal={Journal of Micromechanics and Microengineering}, publisher={IOP Publishing}, author={Richards, A L and Dickey, M D and Kennedy, A S and Buckner, G D}, year={2012}, month={Sep}, pages={115012} }
 @article{crews_buckner_2012, title={Design optimization of a shape memory alloy-actuated robotic catheter}, volume={23}, ISSN={["1530-8138"]}, DOI={10.1177/1045389x12436738}, abstractNote={In this article, we present a method for optimizing the design of a shape memory alloy–actuated robotic catheter. Highly maneuverable robotic catheters have the potential to revolutionize the treatment of cardiac diseases such as atrial fibrillation. To operate effectively, the catheter must navigate within the confined spaces of the heart, motivating the need for a tight bending radius. The design process is complicated by the shape memory alloy’s hysteretic relationships between strain, stress, and temperature. This article addresses the modeling and optimization of both a single-tendon and antagonistic tendon robotic catheter using COMSOL Multiphysics Modeling and Simulation software. Several design variables that affect the actuator behavior are considered; these include the shape memory alloy tendon radius and its prestrain, the shape memory alloy tendon offset from the neutral axis of the flexible beam, the flexible beam radius and elastic modulus, and the thermal boundary condition between the shape memory alloy tendon and the beam. A genetic algorithm is used to optimize the radius of curvature of the two catheter designs. Both a single-crystal and polycrystalline models are implemented in COMSOL and are experimentally validated.}, number={5}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Crews, John H. and Buckner, Gregory D.}, year={2012}, month={Mar}, pages={545–562} }
 @article{richards_kleinstreuer_kennedy_childress_buckner_2012, title={Experimental Microsphere Targeting in a Representative Hepatic Artery System}, volume={59}, ISSN={["1558-2531"]}, DOI={10.1109/tbme.2011.2170195}, abstractNote={Recent work employing the computational fluid-particle modeling of the hepatic arteries has identified a correlation between particle release position and downstream branch distribution for direct tumor-targeting in radioembolization procedures. An experimental model has been constructed to evaluate the underlying simulation theory and determine its feasibility for future clinical use. A scaled model of a generalized hepatic system with a single inlet and five outlet branches was fabricated to replicate the fluid dynamics in the hepatic arteries of diseased livers. Assuming steady flow, neutrally buoyant microspheres were released from controlled locations within the inlet of the model and the resulting output distributions were recorded. Fluid and particle transport simulations were conducted with identical parameters. The resulting experimentally and simulation-derived microsphere distributions were compared. The experimental microsphere distribution exhibited a clear dependence on injection location that correlated very strongly with the computationally predicted results. Individual branch targeting was possible for each of the five outputs. The experimental results validate the simulation methodology for achieving targeted microsphere distributions in a known geometry under constant flow conditions.}, number={1}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Richards, Andrew L. and Kleinstreuer, Clement and Kennedy, Andrew S. and Childress, Emily and Buckner, Gregory D.}, year={2012}, month={Jan}, pages={198–204} }
 @inproceedings{jernigan_fortney_fahmy_buckner_2012, title={Implementing effective low-cost laboratory experiments into a distance engineering program}, DOI={10.1115/imece2010-40938}, abstractNote={This paper details the successful and inexpensive implementation of remote laboratory experiments into a control systems course using readily available hardware and software. The custom-made experiments include an inverted pendulum, a platform leveling system, a ball and beam apparatus, and an aerodynamic beach ball levitation system, each implemented in a separate course offering. With each laboratory, the control objective is to regulate a physical parameter, (pendulum angle, platform orientation, ball position, etc.) by manipulating voltage to a drive component (DC motor, linear actuator, blower, etc.). Engineering software commonly used in controls courses (MATLAB/Simulink and LabView) coupled with dedicated hardware (xPC Target and NI Compact Rio) provide the controller platforms, while Microsoft NetMeeting and standard Internet video conferencing equipment are used to interface the distance-learning students with the laboratory equipment. Both local students at North Carolina State University’s campus in Raleigh and distance students at the University of North Carolina at Asheville and Craven Community College in Havelock, NC complete the laboratory experiments. In a student survey, distance students participating in the remote labs rated the experience as favorably as local students. Course grades, including design project grades, were similar between the two groups.}, booktitle={Proceedings of the ASME International Mechanical Engineering Congress and Exposition (IMECE 2010), vol 6}, author={Jernigan, S. R. and Fortney, B. and Fahmy, Y. and Buckner, G. D.}, year={2012}, pages={87–94} }
 @article{hannen_crews_buckner_2012, title={Indirect intelligent sliding mode control of a shape memory alloy actuated flexible beam using hysteretic recurrent neural networks}, volume={21}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/21/8/085015}, abstractNote={This paper introduces an indirect intelligent sliding mode controller (IISMC) for shape memory alloy (SMA) actuators, specifically a flexible beam deflected by a single offset SMA tendon. The controller manipulates applied voltage, which alters SMA tendon temperature to track reference bending angles. A hysteretic recurrent neural network (HRNN) captures the nonlinear, hysteretic relationship between SMA temperature and bending angle. The variable structure control strategy provides robustness to model uncertainties and parameter variations, while effectively compensating for system nonlinearities, achieving superior tracking compared to an optimized PI controller.}, number={8}, journal={SMART MATERIALS AND STRUCTURES}, author={Hannen, Jennifer C. and Crews, John H. and Buckner, Gregory D.}, year={2012}, month={Aug} }
 @inproceedings{haigh_crews_wang_buckner_2012, title={Modeling and experimental validation of shape memory alloy bending actuators}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, vol 2}, author={Haigh, C. D. and Crews, J. H. and Wang, S. Q. and Buckner, G. D.}, year={2012}, pages={79–87} }
 @inproceedings{crews_buckner_2012, title={Multi-objective design optimization of a shape memory alloy actuated robotic catheter}, DOI={10.1115/smasis2011-5037}, abstractNote={In this paper, we present a method for optimizing the design of a shape memory alloy (SMA) actuated robotic catheter. The robotic catheter is designed for use in endocardial ablation procedures, where “trackability” (bending flexibility) and “pushability” are desirable but conflicting catheter traits, leading to a multi-objective optimization problem. The catheter uses SMA tendons for internal actuation, which create a bending moment about a central structure. The design of SMA actuators is often non-intuitive and complicated due to the material’s hysteretic dependence on stress and temperature. The modeling and design difficulties increase when considering antagonistic SMA actuation, which is the case for the robotic catheter. The catheter is optimized using a genetic algorithm coupled with COMSOL Multiphysics Modeling and Simulation software. The objective functions are formulated in order to improve bending flexibility and pushability. Bending flexibility is quantified by radius of curvature. Pushability is a more subjective characteristic that depends on axial stiffness and friction, but for optimization purposes, it is quantified using axial stiffness and the surface area of the catheter. Several design variables that affect the catheter behavior are considered; these include the SMA tendon diameter and its pre-strain, the offset of the SMA tendon from the neutral axis of the central structure, and the central structure’s diameter and elastic modulus.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 2011), vol 1}, author={Crews, J. H. and Buckner, G. D.}, year={2012}, pages={381–389} }
 @article{purser_richards_cook_osborne_cormier_buckner_2011, title={A Novel Shape Memory Alloy Annuloplasty Ring for Minimally Invasive Surgery: Design, Fabrication, and Evaluation}, volume={39}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-010-0126-z}, abstractNote={A novel annuloplasty ring with a shape memory alloy core has been developed to facilitate minimally invasive mitral valve repair. In its activated (austenitic) phase, this prototype ring has comparable mechanical properties to commercial semi-rigid rings. In its pre-activated (martensitic) phase, this ring is flexible enough to be introduced through an 8-mm trocar and easily manipulated with robotic instruments within the confines of a left atrial model. The core is constructed of 0.50 mm diameter NiTi, which is maintained below its martensitic transition temperature (24 °C) during deployment and suturing. After suturing, the ring is heated above its austenitic transition temperature (37 °C, normal human body temperature) enabling the NiTi core to attain its optimal geometry and stiffness characteristics indefinitely. This article summarizes the design, fabrication, and evaluation of this prototype ring. Experimental results suggest that the NiTi core ring could be a viable alternative to flexible bands in robot-assisted minimally invasive mitral valve repair.}, number={1}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Purser, Molly F. and Richards, Andrew L. and Cook, Richard C. and Osborne, Jason A. and Cormier, Denis R. and Buckner, Gregory D.}, year={2011}, month={Jan}, pages={367–377} }
 @article{lien_fang_buckner_2011, title={Hysteretic neural network modeling of spring-coupled piezoelectric actuators}, volume={20}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79956193310&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/20/6/065007}, abstractNote={This paper discusses the development of a high-fidelity, computationally efficient model for spring-coupled piezoelectric stack actuators. The model is based on a hysteretic recurrent neural network (HRNN), and aims to balance computational tractability with physical intuition. Previous work has detailed the development and experimental validation of an HRNN model for unloaded piezoelectric actuators. This paper extends the modeling approach to incorporate coupling with linear springs, and discusses training techniques based on genetic algorithms, which provide advantages over the previously employed Levenberg–Marquardt methods in terms of accuracy and model complexity. The resulting models are computable in real time. Model validity is established by comparison with a rate-dependent threshold-discrete Prandtl–Ishlinskii model.}, number={6}, journal={SMART MATERIALS AND STRUCTURES}, author={Lien, J. P. and Fang, Tiegang and Buckner, Gregory D.}, year={2011}, month={Jun} }
 @article{crews_mattson_buckner_2011, title={Multi-objective control optimization for semi-active vehicle suspensions}, volume={330}, ISSN={["1095-8568"]}, DOI={10.1016/j.jsv.2011.05.036}, abstractNote={In this paper we demonstrate a method for determining the optimality of control algorithms based on multiple performance objectives. While the approach is applicable to a broad range of dynamic systems, this paper focuses on the control of semi-active vehicle suspensions. The two performance objectives considered are ride quality, as measured by absorbed power, and thermal performance, as measured by power dissipated in the suspension damper. A multi-objective genetic algorithm (MOGA) is used to establish the limits of controller performance. To facilitate convergence, the MOGA is initialized with popular algorithms such as skyhook control, feedback linearization, and sliding mode control. The MOGA creates a Pareto frontier of solutions, providing a benchmark for assessing the performance of other controllers in terms of both objectives. Furthermore, the MOGA provides insight into the remaining achievable gains in performance.}, number={23}, journal={JOURNAL OF SOUND AND VIBRATION}, author={Crews, John H. and Mattson, Michael G. and Buckner, Gregory D.}, year={2011}, month={Nov}, pages={5502–5516} }
 @article{jernigan_chanoit_veeramani_owen_hilliard_cormier_laffitte_buckner_2010, title={A laparoscopic knot-tying device for minimally invasive cardiac surgery☆}, volume={37}, ISSN={1010-7940}, url={http://dx.doi.org/10.1016/j.ejcts.2009.09.024}, DOI={10.1016/j.ejcts.2009.09.024}, abstractNote={Intracorporeal suturing and knot tying can complicate, prolong or preclude minimally invasive surgical procedures, reducing their advantages over conventional approaches. An automated knot-tying device has been developed to speed suture fixation during minimally invasive cardiac surgery while retaining the desirable characteristics of conventional hand-tied surgeon's knots: holding strength and visual and haptic feedback. A rotating slotted disc (at the instrument's distal end) automates overhand throws, thereby eliminating the need to manually pass one suture end through a loop in the opposing end. The electronic actuation of this disc produces left or right overhand knots as desired by the operator.To evaluate the effectiveness of this technology, seven surgeons with varying laparoscopic experience tied knots within a simulated minimally invasive setting, using both the automated knot-tying tool and conventional laparoscopic tools. Suture types were 2/0 braided and 4/0 monofilament.Mean knot-tying times were 246+/-116 s and 102+/-46 s for conventional and automated methods, respectively, showing an average 56% reduction in time per surgeon (p=0.003, paired t-test). The peak holding strength of each knot (the force required to break the suture or loosen the knot) was measured using tensile-testing equipment. These peak holding strengths were normalised by the ultimate tensile strength of each suture type (57.5 N and 22.1N for 2/0 braided and 4/0 monofilament, respectively). Mean normalised holding strengths for all knots were 68.2% and 71.8% of ultimate tensile strength for conventional and automated methods, respectively (p=0.914, paired t-test).Experimental data reveal that the automated suturing device has great potential for advancing minimally invasive surgery: it significantly reduced knot-tying times while providing equivalent or greater holding strength than conventionally tied knots.}, number={3}, journal={European Journal of Cardio-Thoracic Surgery}, publisher={Oxford University Press (OUP)}, author={Jernigan, Shaphan R. and Chanoit, Guillaume and Veeramani, Arun and Owen, Stephen B. and Hilliard, Matthew and Cormier, Denis and Laffitte, Bryan and Buckner, Gregory}, year={2010}, month={Mar}, pages={626–630} }
 @article{lien_york_fang_buckner_2010, title={Modeling piezoelectric actuators with Hysteretic Recurrent Neural Networks}, volume={163}, ISSN={["0924-4247"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78049473465&partnerID=MN8TOARS}, DOI={10.1016/j.sna.2010.08.013}, abstractNote={This paper describes the application of Hysteretic Recurrent Neural Networks (HRNNs) to the modeling of polycrystalline piezoelectric actuators. Because piezoelectric materials exhibit voltage/strain relationships that are hysteretic and rate-dependent, the HRNN is composed of neurons with activation functions that incorporate these characteristics. Individual neurons are shown to agree with existing models of ideal single-crystal piezoelectric behavior. The combination of many such neurons into a network allows prediction of the heterogeneous behavior of polycrystalline materials. This model is shown to approximate the strain and polarization of an unloaded commercial stack actuator at multiple loading rates. A comparison is made to a recurrent Radial Basis Function Network model, and the HRNN is demonstrated to more accurately generalize across data sets. The model is further shown to execute on a PC platform at rates over 100 Hz, fast enough to support its application to real-time control.}, number={2}, journal={SENSORS AND ACTUATORS A-PHYSICAL}, author={Lien, J. P. and York, Alexander and Fang, Tiegang and Buckner, Gregory D.}, year={2010}, month={Oct}, pages={516–525} }
 @article{richards_cook_bolotin_buckner_2009, title={A Dynamic Heart System to Facilitate the Development of Mitral Valve Repair Techniques}, volume={37}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-009-9653-x}, abstractNote={Objective: The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair. Methods: A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images. Results: For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure. Conclusions: The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.}, number={4}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Richards, Andrew L. and Cook, Richard C. and Bolotin, Gil and Buckner, Gregory D.}, year={2009}, month={Apr}, pages={651–660} }
 @article{chung_lim_buckner_2009, title={A Learning Method for Multivariable PID Control Synthesis Based on Estimated Plant Jacobian}, volume={7}, ISSN={["2005-4092"]}, DOI={10.1007/s12555-009-0506-z}, number={5}, journal={INTERNATIONAL JOURNAL OF CONTROL AUTOMATION AND SYSTEMS}, author={Chung, Byeong-Mook and Lim, Yoon-Kyu and Buckner, Gregory D.}, year={2009}, month={Oct}, pages={737–744} }
 @article{purser_richards_cook_osborne_cormier_buckner_2009, title={Evaluation of a Shape Memory Alloy Reinforced Annuloplasty Band for Minimally Invasive Mitral Valve Repair}, volume={88}, ISSN={["1552-6259"]}, DOI={10.1016/j.athoracsur.2009.04.133}, abstractNote={<h3>Purpose</h3> An in vitro study using explanted porcine hearts was conducted to evaluate a novel annuloplasty band, reinforced with a two-phase, shape memory alloy, designed specifically for minimally invasive mitral valve repair. <h3>Description</h3> In its rigid (austenitic) phase, this band provides the same mechanical properties as the commercial semi-rigid bands. In its compliant (martensitic) phase, this band is flexible enough to be introduced through an 8-mm trocar and is easily manipulated within the heart. <h3>Evaluation</h3> In its rigid phase, the prototype band displayed similar mechanical properties to commercially available semi-rigid rings. Dynamic flow testing demonstrated no statistical differences in the reduction of mitral valve regurgitation. In its flexible phase, the band was easily deployed through an 8-mm trocar, robotically manipulated and sutured into place. <h3>Conclusions</h3> Experimental results suggest that the shape memory alloy reinforced band could be a viable alternative to flexible and semi-rigid bands in minimally invasive mitral valve repair.}, number={4}, journal={ANNALS OF THORACIC SURGERY}, author={Purser, Molly F. and Richards, Andrew L. and Cook, Richard C. and Osborne, Jason A. and Cormier, Denis R. and Buckner, Gregory D.}, year={2009}, month={Oct}, pages={1312–1316} }
 @inproceedings{veeramani_crews_buckner_2009, title={Hysteretic recurrent neural networks: A tool for modeling hysteretic materials and systems}, volume={18}, number={7}, booktitle={Smart Materials & Structures}, author={Veeramani, A. S. and Crews, J. H. and Buckner, G. D.}, year={2009} }
 @article{veeramani_crews_buckner_2009, title={Hysteretic recurrent neural networks: a tool for modeling hysteretic materials and systems}, volume={18}, ISSN={0964-1726 1361-665X}, url={http://dx.doi.org/10.1088/0964-1726/18/7/075004}, DOI={10.1088/0964-1726/18/7/075004}, abstractNote={This paper introduces a novel recurrent neural network, the hysteretic recurrent neural network (HRNN), that is ideally suited to modeling hysteretic materials and systems. This network incorporates a hysteretic neuron consisting of conjoined sigmoid activation functions. Although similar hysteretic neurons have been explored previously, the HRNN is unique in its utilization of simple recurrence to 'self-select' relevant activation functions. Furthermore, training is facilitated by placing the network weights on the output side, allowing standard backpropagation of error training algorithms to be used. We present two- and three-phase versions of the HRNN for modeling hysteretic materials with distinct phases. These models are experimentally validated using data collected from shape memory alloys and ferromagnetic materials. The results demonstrate the HRNN's ability to accurately generalize hysteretic behavior with a relatively small number of neurons. Additional benefits lie in the network's ability to identify statistical information concerning the macroscopic material by analyzing the weights of the individual neurons.}, number={7}, journal={Smart Materials and Structures}, publisher={IOP Publishing}, author={Veeramani, Arun S and Crews, John H and Buckner, Gregory D}, year={2009}, month={Jun}, pages={075004} }
 @article{jernigan_fahmy_buckner_2009, title={Implementing a Remote Laboratory Experience Into a Joint Engineering Degree Program: Aerodynamic Levitation of a Beach Ball}, volume={52}, ISSN={["1557-9638"]}, DOI={10.1109/TE.2008.924217}, abstractNote={This paper details a successful and inexpensive implementation of a remote laboratory into a distance control systems course using readily available hardware and software. The physical experiment consists of a beach ball and a dc blower; the control objective is to make the height of the aerodynamically levitated beach ball track a reference trajectory by manipulating the voltage to the blower. MATLAB/Simulink coupled with xPC target serve as the controller platform, while microsoft netmeeting and standard Internet video conferencing equipment are used to interface the distance-learning students with the laboratory equipment. Both local students at North Carolina State University's campus in Raleigh and distance students at the University of North Carolina at Asheville completed the laboratory experiment. In a student survey, distance students participating in the lab remotely rated the experience as favorably as local students. Course grades, including the design project grade, were similar between the two groups.}, number={2}, journal={IEEE TRANSACTIONS ON EDUCATION}, author={Jernigan, Shaphan R. and Fahmy, Yusef and Buckner, Gregory D.}, year={2009}, month={May}, pages={205–213} }
 @inproceedings{purser_cormier_buckner_cook_bolotin_2008, title={Annuloplasty band with shape memory alloy stiffener}, booktitle={Medical Device Materials IV}, author={Purser, M. and Cormier, D. and Buckner, G. and Cook, R. and Bolotin, G.}, year={2008}, pages={231–236} }
 @article{zohni_buckner_kim_kingon_maranchi_siergiej_2008, title={Effects of adhesion layers on the ferroelectric properties of lead zirconium titanate thin films deposited on silicon nitride coated silicon substrates}, volume={516}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2007.10.130}, abstractNote={Abstract We have investigated the addition of silicon nitride (Si 3 N 4 ) thin films into sol–gel deposited lead zirconium titanate (PZT) stacks and quantified the effects of various adhesion layers on the ferroelectric characteristics of these stacks. Although previous research has investigated issues related to the adhesion characteristics of PZT films, this research considers four specific adhesion layers deposited onto a silicon nitride coated substrate: zirconium (Zr), zirconium dioxide (ZrO 2 ), titanium (Ti) and tantalum (Ta), and compares experimental characteristics of each. Adhesion layer thicknesses of 15 nm and 25 nm were tested with pyrolysis temperatures of 600 °C and 650 °C. For many of the adhesion layers, the remnant polarization P r and capacitance–voltage (C–V) characteristics are similar to conventional PZT stacks deposited onto silicon dioxide (SiO 2 ) coated substrates, but only Ta withstands the thermal processing required for PZT deposition.}, number={18}, journal={THIN SOLID FILMS}, author={Zohni, Omar and Buckner, Gregory and Kim, Taeyun and Kingon, Angus and Maranchi, Jeff and Siergiej, Richard}, year={2008}, month={Jul}, pages={6052–6057} }
 @article{bean_chanoit_jernigan_bolotin_osborne_buckner_2008, title={Evaluation of a novel atrial retractor for exposure of the mitral valve in a porcine model}, volume={136}, ISSN={["1097-685X"]}, DOI={10.1016/j.jtcvs.2008.08.030}, abstractNote={ObjectivesTo describe a novel atrial retractor and compare 2 methods of intraoperative left atrial retraction for minimally invasive mitral valve repair.MethodsLeft atrial retraction was performed on 5 swine cadavers to evaluate performance (percent of mitral valve annulus accessible), complications encountered, ease of use, and surgical time for the minimally invasive atrial retractor and a HeartPort atrial retractor.ResultsEstimated accessibilities were 93.0% (standard error = 3.2) and 92.7% (standard error = 3.3) for the HeartPort and minimally invasive atrial retractor retractors, respectively, with a difference of 0.3% (standard error = 2.2%, P = .8832, df = 34). Tissue damage occurred in 1 case for the minimally invasive atrial retractor and 2 cases for the HeartPort retractor. The mean surgical times for retractor placement and mitral valve annulus exposure were 107.4 and 39.2 seconds for the HeartPort and minimally invasive atrial retractor retractors, respectively, with a difference of 68.2 seconds (P = .0092, df = 4).ConclusionsThe minimally invasive atrial retractor is a suitable alternative for atrial retraction compared with standard techniques of retraction. It provides comparable exposure of the mitral valve annulus, is less time consuming to place, provides subjectively more working volume within the left atrium, and has the advantage of minimal atriotomy incision length and customizable retraction. To describe a novel atrial retractor and compare 2 methods of intraoperative left atrial retraction for minimally invasive mitral valve repair. Left atrial retraction was performed on 5 swine cadavers to evaluate performance (percent of mitral valve annulus accessible), complications encountered, ease of use, and surgical time for the minimally invasive atrial retractor and a HeartPort atrial retractor. Estimated accessibilities were 93.0% (standard error = 3.2) and 92.7% (standard error = 3.3) for the HeartPort and minimally invasive atrial retractor retractors, respectively, with a difference of 0.3% (standard error = 2.2%, P = .8832, df = 34). Tissue damage occurred in 1 case for the minimally invasive atrial retractor and 2 cases for the HeartPort retractor. The mean surgical times for retractor placement and mitral valve annulus exposure were 107.4 and 39.2 seconds for the HeartPort and minimally invasive atrial retractor retractors, respectively, with a difference of 68.2 seconds (P = .0092, df = 4). The minimally invasive atrial retractor is a suitable alternative for atrial retraction compared with standard techniques of retraction. It provides comparable exposure of the mitral valve annulus, is less time consuming to place, provides subjectively more working volume within the left atrium, and has the advantage of minimal atriotomy incision length and customizable retraction.}, number={6}, journal={JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY}, author={Bean, Eric and Chanoit, Guillaume and Jernigan, Shaphan and Bolotin, Gil and Osborne, Jason and Buckner, Gregory}, year={2008}, month={Dec}, pages={1492–1495} }
 @article{lu_choi_buckner_tammi_2008, title={Linear parameter-varying techniques for control of a magnetic bearing system}, volume={16}, ISSN={["1873-6939"]}, DOI={10.1016/j.conengprac.2008.01.002}, abstractNote={In this paper, a linear parameter-varying (LPV) control design method is evaluated experimentally on an active magnetic bearing (AMB) system. A speed-dependent LPV model of the AMB system is derived. Model uncertainties are identified using artificial neural networks, and an uncertainty weighting function is approximated for LPV control synthesis. Experiments are conducted to verify the robustness of LPV controllers for a wide range of rotational speed. This LPV control approach eliminates the need for gain-scheduling, and provides better performance than the traditional proportional-integral-derivative control for high-speed operation.}, number={10}, journal={CONTROL ENGINEERING PRACTICE}, author={Lu, Bei and Choi, Heeju and Buckner, Gregory D. and Tammi, Kari}, year={2008}, month={Oct}, pages={1161–1172} }
 @article{veeramani_buckner_owen_cook_bolotin_2008, title={Modeling the dynamic behavior of a shape memory alloy actuated catheter}, volume={17}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/17/01/015037}, abstractNote={In this paper we investigate the transient behavior of a simple active catheter: a central tube actuated by a single nitinol tendon enclosed by an outer sleeve. Dynamic models are developed to characterize the transient behavior and optimize the design of an experimental prototype. The bending mechanics are derived using a circular arc model and are experimentally validated. Nitinol actuation is described using the Seelecke–Muller–Achenbach model for single-crystal shape memory alloys using experimentally determined parameters. The dynamic characteristics of this active catheter system are simulated and compared with experimental results. Joule heating is used to generate tip deflections, which are computed in real time using a dual-camera imaging system. The effects of outer sleeve thickness on heat transfer and transient response characteristics are studied.}, number={1}, journal={SMART MATERIALS AND STRUCTURES}, author={Veeramani, Arun S. and Buckner, Gregory D. and Owen, Stephen B. and Cook, Richard C. and Bolotin, Gil}, year={2008}, month={Feb} }
 @article{bolotin_buckner_jardine_kiefer_campbell_kocherginsky_raman_jeevanandam_2007, title={A novel instrumented retractor to monitor tissue-disruptive forces during lateral thoracotomy}, volume={133}, ISSN={["1097-685X"]}, DOI={10.1016/j.jtcvs.2006.09.065}, abstractNote={ObjectiveAcute and chronic pain after thoracotomy, post-thoracotomy pain syndrome, is well documented. The mechanical retractors used for the thoracotomy exert significant forces on the skeletal cage. Our hypothesis was that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces. This would provide equivalent exposure with significantly reduced forces and tissue damage and thus less post-thoracotomy pain.MethodsA novel instrumented retractor was designed and fabricated to enable real-time force monitoring during surgical retraction. Eight mature sheep underwent bilateral thoracotomy. One lateral thoracotomy was retracted at a standard clinical pace of 5.93 ± 0.80 minutes to 7.5 cm without real-time monitoring of retraction forces. The other lateral thoracotomy was retracted to the same exposure with real-time visual force feedback and a consequently more deliberate pace of 9.87 ± 1.89 minutes (P = .006). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure.ResultsFull lateral retraction resulted in an average force of 102.88 ± 50.36 N at the standard clinical pace, versus 77.88 ± 38.85 N with force feedback (a 24.3% reduction, P = .006). Standard retraction produced peak forces of 450.01 ± 129.58 N, whereas force feedback yielded peak forces of 323.99 ± 127.79 N (a 28.0% reduction, P = .009). Systolic blood pressure was significantly higher during standard clinical retraction (P = .0097), and rib fracture occurrences were reduced from 5 to 1 with force feedback (P = .04).ConclusionsUse of the novel instrumented retractor resulted in significantly lower average and peak retraction forces during lateral thoracotomy. Moreover, these reduced retraction forces were correlated with reductions in animal stress and tissue damage, as documented by lower systolic blood pressures and fewer rib fractures. Acute and chronic pain after thoracotomy, post-thoracotomy pain syndrome, is well documented. The mechanical retractors used for the thoracotomy exert significant forces on the skeletal cage. Our hypothesis was that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces. This would provide equivalent exposure with significantly reduced forces and tissue damage and thus less post-thoracotomy pain. A novel instrumented retractor was designed and fabricated to enable real-time force monitoring during surgical retraction. Eight mature sheep underwent bilateral thoracotomy. One lateral thoracotomy was retracted at a standard clinical pace of 5.93 ± 0.80 minutes to 7.5 cm without real-time monitoring of retraction forces. The other lateral thoracotomy was retracted to the same exposure with real-time visual force feedback and a consequently more deliberate pace of 9.87 ± 1.89 minutes (P = .006). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure. Full lateral retraction resulted in an average force of 102.88 ± 50.36 N at the standard clinical pace, versus 77.88 ± 38.85 N with force feedback (a 24.3% reduction, P = .006). Standard retraction produced peak forces of 450.01 ± 129.58 N, whereas force feedback yielded peak forces of 323.99 ± 127.79 N (a 28.0% reduction, P = .009). Systolic blood pressure was significantly higher during standard clinical retraction (P = .0097), and rib fracture occurrences were reduced from 5 to 1 with force feedback (P = .04). Use of the novel instrumented retractor resulted in significantly lower average and peak retraction forces during lateral thoracotomy. Moreover, these reduced retraction forces were correlated with reductions in animal stress and tissue damage, as documented by lower systolic blood pressures and fewer rib fractures.}, number={4}, journal={JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY}, author={Bolotin, Gil and Buckner, Gregory D. and Jardine, Nicholas J. and Kiefer, Aaron J. and Campbell, Nigel B. and Kocherginsky, Masha and Raman, Jai and Jeevanandam, Valluvan}, year={2007}, month={Apr}, pages={949–954} }
 @article{pandurangan_buckner_2007, title={Assessment of damage detection methods in GRID-LOCK (R) structures}, volume={21}, ISSN={["0888-3270"]}, DOI={10.1016/j.ymssp.2006.10.004}, abstractNote={Bonded metallic GRID-LOCK® structures are being adopted for a variety of aerospace applications due to their structural efficiency and damage tolerance. However, effective damage detection in these structures is complicated by a lack of interior access. In this paper, the feasibility of various non-destructive evaluation (NDE) techniques for detecting the presence, location, and magnitude of damage in GRID-LOCK® is investigated. Experiments conducted on a GRID-LOCK® test structure reveal that vibration-based damage detection and optical nde methods are superior to ultrasonic C-scans in detecting disbond defects. Finite-element analysis (FEA) is used to interpret experimental results and highlight the advantages of alternate NDE approaches.}, number={5}, journal={MECHANICAL SYSTEMS AND SIGNAL PROCESSING}, author={Pandurangan, Pradeep and Buckner, Gregory D.}, year={2007}, month={Jul}, pages={2185–2197} }
 @article{pandurangan_buckner_2007, title={Defect identification in GRID-LOCK (R) joints}, volume={40}, DOI={10.1016/j.ndtient.2006.12.006}, number={5}, journal={NDT & E International}, author={Pandurangan, P. and Buckner, G. D.}, year={2007}, pages={347–356} }
 @article{pandurangan_buckner_2007, title={Defect identification in GRID-LOCK® joints}, volume={40}, ISSN={0963-8695}, url={http://dx.doi.org/10.1016/j.ndteint.2006.12.006}, DOI={10.1016/j.ndteint.2006.12.006}, abstractNote={Damage detection in aircraft structures is conducted using a variety of nondestructive evaluation (NDE) techniques, including visual inspection, ultrasonic inspection, eddy current inspection, radiography and optical methods. These techniques are well established and have distinct advantages and limitations. Optical NDE methods show significant promise for variety of aerospace structural components, including inspection of bonded metallic GRID-LOCK® structures. In this paper, a full-field surface slope measurement technique (shearography) is utilized to confirm the effectiveness of optical NDE. Two bond defects (one disbond and one weak bond) are incorporated into a GRID-LOCK® test structure and internal pressurization results in qualitative indications of damage on the shearograms. Because accurate characterization of structural defects is critical for flight safety, a quantitative nondestructive evaluation (QNDE) method using a scanning optical probe is also explored. This QNDE method involves use of radial basis function networks (RBFNs) trained and validated using finite element analysis nodal displacements.}, number={5}, journal={NDT & E International}, publisher={Elsevier BV}, author={Pandurangan, Pradeep and Buckner, Gregory D.}, year={2007}, month={Jul}, pages={347–356} }
 @article{jernigan_buckner_eischen_2007, title={Finite element modeling of the left atrium to facilitate the design of an endoscopic atrial retractor}, volume={129}, ISSN={["1528-8951"]}, DOI={10.1115/1.2801650}, abstractNote={Abstract With the worldwide prevalence of cardiovascular diseases, much attention has been focused on simulating the characteristics of the human heart to better understand and treat cardiac disorders. The purpose of this study is to build a finite element model of the left atrium (LA) that incorporates detailed anatomical features and realistic material characteristics to investigate the interaction of heart tissue and surgical instruments. This model is used to facilitate the design of an endoscopically deployable atrial retractor for use in minimally invasive, robotically assisted mitral valve repair. Magnetic resonance imaging (MRI) scans of a pressurized explanted porcine heart were taken to provide a 3D solid model of the heart geometry, while uniaxial tensile tests of porcine left atrial tissue were conducted to obtain realistic material properties for noncontractile cardiac tissue. A finite element model of the LA was constructed using ANSYS™ Release 9.0 software and the MRI data. The Mooney–Rivlin hyperelastic material model was chosen to characterize the passive left atrial tissue; material constants were derived from tensile test data. Finite element analysis (FEA) models of a CardioVations Port Access™ retractor and a prototype endoscopic retractor were constructed to simulate interaction between each instrument and the LA. These contact simulations were used to compare the quality of retraction between the two instruments and to optimize the design of the prototype retractor. Model accuracy was verified by comparing simulated cardiac wall deflections to those measured by MRI. FEA simulations revealed that peak forces of approximately 2.85N and 2.46N were required to retract the LA using the Port Access™ and prototype retractors, respectively. These forces varied nonlinearly with retractor blade displacement. Dilation of the atrial walls and rigid body motion of the chamber were approximately the same for both retractors. Finite element analysis is shown to be an effective tool for analyzing instrument/tissue interactions and for designing surgical instruments. The benefits of this approach to medical device design are significant when compared to the alternatives: constructing prototypes and evaluating them via animal or clinical trials.}, number={6}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Jernigan, S. R. and Buckner, G. D. and Eischen, J. W.}, year={2007}, month={Dec}, pages={825–837} }
 @article{zohni_buckner_kim_kingon_maranchi_siergiej_2007, title={Investigating thin film stresses in stacked silicon dioxide/silicon nitride structures and quantifying their effects on frequency response}, volume={17}, ISSN={["0960-1317"]}, DOI={10.1088/0960-1317/17/5/026}, abstractNote={We have investigated the frequency shift caused by thin film stresses in silicon nitride (Si3N4) and silicon dioxide (SiO2) layers used during the fabrication of lead zirconium titanate (PZT) microelectromechanical (MEMS) devices. The films are deposited via thermal oxidation and low pressure chemical vapor deposition onto bare silicon wafers. Although previous research has reported stresses in these films, this paper introduces approaches to measure, model and predict the effects of these stresses on the frequency response of MEMS devices. Thin film stresses in each layer of a PZT stack are measured using a curvature measurement system, and these measurements are correlated to finite element analysis results and experimental vibration data. These comparisons illustrate the significance of the thin film stresses and their effect on the mechanical behavior of MEMS devices, in particular that as the membrane structures get thinner the frequency shift becomes much larger.}, number={5}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Zohni, Omar and Buckner, Gregory and Kim, Taeyun and Kingon, Angus and Maranchi, Jeff and Siergiej, Richard}, year={2007}, month={May}, pages={1042–1051} }
 @article{saadat_buckner_noori_2007, title={Structural system identification and damage detection using the intelligent parameter varying technique: An experimental study}, volume={6}, ISSN={["1741-3168"]}, DOI={10.1177/1475921707081980}, abstractNote={The unique capabilities of the intelligent parameter varying (IPV) technique for structural system identification and damage detection have been previously documented via comparative simulations. An intelligent parameter varying (IPV) approach for non-linear system identification of base excited structures. International Journal of Non-Linear Mechanics, 39(6), 993—1004; Saadat, S., Noori, M.N., Buckner, G.D., Furukawa, T.D. and Suzuki, Y. (2004). Structural health monitoring and damage detection using an intelligent parameter varying (IPV) technique. International Journal of Non-Linear Mechanics, 39(10), 1687—1697). These simulations demonstrate the effectiveness of IPV in detecting the existence and location of damage in base excited structures, and conclude that accuracy is not compromised by the introduction of realistic structural nonlinearities and ground excitation characteristics. This study presents an experimental verification of the IPV technique for structural system identification and damage detection. A scaled three-story, base-excited structure is designed and fabricated for these experiments. The structure is excited using a displacement-controlled shake table, and damage is introduced by triggering the release of cross-bracing tendons, i.e., inducing sudden changes in the restoring forces. Experimental results using harmonic and recorded earthquake excitation data clearly demonstrate the effectiveness of this IPV technique.}, number={3}, journal={STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL}, author={Saadat, Soheil and Buckner, Gregory D. and Noori, Mohammad N.}, year={2007}, month={Sep}, pages={231–243} }
 @article{bolotin_buckner_campbell_kocherginsky_raman_jeevanandam_maessen_2007, title={Tissue-disruptive forces during median sternotomy}, volume={10}, DOI={10.1532/hsf98.20071121}, abstractNote={Acute and chronic pain after median sternotomy is common and often underestimated. The mechanical retractors used for median sternotomy exert significant forces on the skeletal cage. We hypothesized that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces, functions that may provide equivalent exposure with significantly reduced forces and tissue damage, and thus, less postoperative pain.We developed a novel instrumented retractor designed to enable real-time force monitoring during surgical retraction and then tested it by performing median sternotomies on 16 mature sheep. For 8 of these median sternotomies, retraction was performed to 7.5 cm at a standard "clinical pace" of 7.25 +/- 0.97 minutes without real-time monitoring of retraction forces. For the other 8 median sternotomies, we performed retraction to the same exposure using real-time visual force feedback and, consequently, a more deliberate pace of 12.05 +/- 1.73 minutes (P <.001). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure.Full retraction resulted in an average force of 102.99 +/- 40.68 N at the standard clinical pace, compared to 64.68 +/- 17.60 N with force feedback (a 37.2% reduction, P = .021). Standard retraction produced peak forces of 368.79 +/- 133.61 N, whereas force feedback yielded peak forces of 254.84 +/- 75.77 N (a 30.9% reduction, P = .1152). Heart rate was significantly higher during standard clinical retraction (P = .025).Use of the novel instrumented retractor resulted in lower average and peak retraction forces during median sternotomy. Moreover, these reduced retraction forces correlated to a reduction in animal stress, as documented by heart rate.}, number={6}, journal={Heart Surgery Forum}, author={Bolotin, G. and Buckner, G. D. and Campbell, N. B. and Kocherginsky, M. and Raman, J. and Jeevanandam, V. and Maessen, J. G.}, year={2007}, pages={E487–492} }
 @article{lawrence_buckner_mirka_2006, title={An adaptive system identification model of the biomechanical response of the human trunk during sudden loading}, volume={128}, ISSN={["0148-0731"]}, DOI={10.1115/1.2165696}, abstractNote={Sudden loading injuries to the low back are a concern. Current models are limited in their ability to quantify the time-varying nature of the sudden loading event. The method of approach used six males who were subjected to sudden loads. Response data (EMG and kinematics) were input into a system identification model to yield time-varying torso stiffness estimates. The results show estimates of system stiffness in good agreement with values in the literature. The average root mean square error of the model’s predictions of sagittal motion was equal to 0.1deg. In conclusion, system identification can be implemented with minimal error and used to gain more insight into the time-dependent trunk response to sudden loads.}, number={2}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Lawrence, BM and Buckner, GD and Mirka, GA}, year={2006}, month={Apr}, pages={235–241} }
 @article{buckner_choi_gibson_2006, title={Estimating model uncertainty using confidence interval networks: Applications to robust control}, volume={128}, ISSN={["1528-9028"]}, DOI={10.1115/1.2199855}, abstractNote={Robust control techniques require a dynamic model of the plant and bounds on model uncertainty to formulate control laws with guaranteed stability. Although techniques for modeling dynamic systems and estimating model parameters are well established, very few procedures exist for estimating uncertainty bounds. In the case of H∞ control synthesis, a conservative weighting function for model uncertainty is usually chosen to ensure closed-loop stability over the entire operating space. The primary drawback of this conservative, “hard computing” approach is reduced performance. This paper demonstrates a novel “soft computing” approach to estimate bounds of model uncertainty resulting from parameter variations, unmodeled dynamics, and nondeterministic processes in dynamic plants. This approach uses confidence interval networks (CINs), radial basis function networks trained using asymmetric bilinear error cost functions, to estimate confidence intervals associated with nominal models for robust control synthesis. This research couples the “hard computing” features of H∞ control with the “soft computing” characteristics of intelligent system identification, and realizes the combined advantages of both. Simulations and experimental demonstrations conducted on an active magnetic bearing test rig confirm these capabilities.}, number={3}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Buckner, Gregory D. and Choi, Heeju and Gibson, Nathan S.}, year={2006}, month={Sep}, pages={626–635} }
 @article{pandurangan_buckner_2006, title={Vibration analysis for damage detection in metal-to-metal adhesive joints}, volume={46}, ISSN={["1741-2765"]}, DOI={10.1007/s11340-006-8736-y}, number={5}, journal={EXPERIMENTAL MECHANICS}, author={Pandurangan, P. and Buckner, G. D.}, year={2006}, month={Oct}, pages={601–607} }
 @article{stevens_buckner_2005, title={Actuation and control strategies for miniature robotic surgical systems}, volume={127}, DOI={10.1115/1.2098892}, abstractNote={During the past 20years, tremendous advancements have been made in the fields of minimally invasive surgery (MIS) and minimally invasive, robotically assisted (MIRA) cardiac surgery. Benefits from MIS include reduced pain and trauma, reduced risks of post-operative complications, shorter recovery times, and more aesthetically pleasing results. MIRA approaches have extended the capabilities of MIS by introducing three-dimensional vision, eliminating hand tremors, and enabling the precise articulation of smaller instruments. These advancements come with their own drawbacks, however. Robotic systems used in MIRA cardiac procedures are large, costly, and do not offer the miniaturized articulation necessary to facilitate tremendous advancements in MIS. This paper demonstrates that miniature actuation can overcome some of the limitations of current robotic systems by providing accurate, repeatable control of a small end effector. A 10× model of a two link surgical manipulator is developed, using antagonistic shape memory alloy wires as actuators, to simulate motions of a surgical end-effector. Artificial neural networks are used in conjunction with real-time visual feedback to “learn” the inverse system dynamics and control the manipulator endpoint trajectory. Experimental results are presented for indirect, on-line learning and control. Manipulator tip trajectories are shown to be accurate and repeatable to within 0.5mm. These results confirm that SMAs can be effective actuators for miniature surgical robotic systems, and that intelligent control can be used to accurately control the trajectory of these systems.}, number={4}, journal={Journal of Dynamic Systems, Measurement, and Control}, author={Stevens, J. M. and Buckner, G. D.}, year={2005}, pages={537–549} }
 @article{lawrence_mirka_buckner_2005, title={Adaptive system identification applied to the biomechanical response of the human trunk during sudden loading}, volume={38}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2004.09.038}, abstractNote={Epidemiological evidence indicates that sudden loading of the torso is a risk factor for low back injury. Accurately quantifying the time-varying loading of the spine during sudden loading events and how these loading profiles are affected by workplace factors such as fatigue, expectation, and training can potentially lead to intervention strategies that can reduce these risks. Electromyographic and trunk motion data were collected from six male participants who performed a series of sudden loading trials with varying levels of expectation (no preview, 300-ms audible preview), fatigue (no fatiguing exertion preceding sudden load, short duration/high intensity fatiguing exertion preceding sudden load), and training (untrained, trained). These data were used as inputs to an adaptive system identification model wherein time-varying lower back stiffness, torque, work, and impulse magnitudes were calculated. Results indicated that expectation significantly increased peak and average stiffness by 70% and 113%, respectively, and significantly decreased peak torque, work, and impulse magnitudes by 36%, 50%, and 45%, respectively. Training significantly decreased peak torque and work by 25% and 34%, respectively. The results also showed a significant interaction between expectation and training wherein training had a positive effect during the trials with preview but no effect during the trials with no preview (increased peak stiffness by 17% and decreased impulse magnitude by 43%).}, number={12}, journal={JOURNAL OF BIOMECHANICS}, author={Lawrence, BM and Mirka, GA and Buckner, GD}, year={2005}, month={Dec}, pages={2472–2479} }
 @article{kuniholm_buckner_nifong_orrico_2005, title={Automated knot tying for fixation in minimally invasive, robot-assisted cardiac surgery}, volume={127}, ISSN={["1528-8951"]}, DOI={10.1115/1.2055307}, abstractNote={Cardiovascular disease (CVD) is perhaps the most significant worldwide health issue. While open-heart surgery remains the predominant treatment, significant advancements have been made in minimally invasive surgery (MIS) and minimally invasive robot-assisted (MIRA) surgery. MIRA techniques offer many advantages over open-heart procedures and have extended the capabilities of MIS. However, these benefits come at the cost of increased operating times due to time spent tying knots. The additional bypass time limits patient access and is the most significant barrier to the adoption of MIRA techniques. This research seeks to overcome this barrier by designing a device for MIRA cardiac procedures that automates the knotting of sutures. If this task can be automated while ensuring the delivery of high-quality knots, great progress can be made in transforming the field. MIRA cardiac procedures can move from novel procedures performed by a select group of surgeons on a limited pool of patients to a viable alternative available to the majority of patients with CVD. In this research we propose a design for a self-contained device that delivers a locking knot. Results suggest that consistent knots can be delivered at a time savings of 12.5% and 26.4% over manual knots for trained and untrained users of a surgical robot, respectively.}, number={6}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Kuniholm, JF and Buckner, GD and Nifong, W and Orrico, M}, year={2005}, month={Nov}, pages={1001–1008} }
 @article{dixit_buckner_2005, title={Sliding mode observation and control for semiactive vehicle suspensions}, volume={43}, ISSN={["1744-5159"]}, DOI={10.1080/00423110412331290455}, abstractNote={This paper investigates the application of robust, nonlinear observation and control strategies, namely sliding mode observation and control (SMOC), to semiactive vehicle suspensions using a model reference approach. The vehicle suspension models include realistic nonlinearities in the spring and magnetorheological (MR) damper elements, and the nonlinear reference models incorporate skyhook damping. Since full state measurement is difficult to achieve in practice, a sliding mode observer (SMO) that requires only suspension deflection as a measured input is developed. The performance and robustness of sliding mode control (SMC), SMO, and SMOC are demonstrated through comprehensive computer simulations and compared to popular alternatives. The results of these simulations reveal the benefits of sliding mode observation and control for improved ride quality, and should be directly transferable to commercial semiactive vehicle suspension implementations.}, number={2}, journal={VEHICLE SYSTEM DYNAMICS}, author={Dixit, RK and Buckner, GD}, year={2005}, month={Feb}, pages={83–105} }
 @article{saadat_buckner_furukawa_noori_2004, title={An intelligent parameter varying (IPV) approach for non-linear system identification of base excited structures}, volume={39}, ISSN={["0020-7462"]}, DOI={10.1016/S0020-7462(03)00091-X}, abstractNote={Health monitoring and damage detection strategies for base-excited structures typically rely on accurate models of the system dynamics. Restoring forces in these structures can exhibit highly non-linear characteristics, thus accurate non-linear system identification is critical. Parametric system identification approaches are commonly used, but require a priori knowledge of restoring force characteristics. Non-parametric approaches do not require this a priori information, but they typically lack direct associations between the model and the system dynamics, providing limited utility for health monitoring and damage detection. In this paper a novel system identification approach, the intelligent parameter varying (IPV) method, is used to identify constitutive non-linearities in structures subject to seismic excitations. IPV overcomes the limitations of traditional parametric and non-parametric approaches, while preserving the unique benefits of each. It uses embedded radial basis function networks to estimate the constitutive characteristics of inelastic and hysteretic restoring forces in a multi-degree-of-freedom structure. Simulation results are compared to those of a traditional parametric approach, the prediction error method. These results demonstrate the effectiveness of IPV in identifying highly non-linear restoring forces, without a priori information, while preserving a direct association with the structural dynamics.}, number={6}, journal={INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS}, author={Saadat, S and Buckner, GD and Furukawa, T and Noori, MN}, year={2004}, month={Aug}, pages={993–1004} }
 @article{saadat_noori_buckner_furukawa_suzuki_2004, title={Structural health monitoring and damage detection using an intelligent parameter varying (IPV) technique}, volume={39}, ISSN={["1878-5638"]}, DOI={10.1016/j.ijnonlinmec.2004.03.001}, abstractNote={Abstract Most structural health monitoring and damage detection strategies utilize dynamic response information to identify the existence, location, and magnitude of damage. Traditional model-based techniques seek to identify parametric changes in a linear dynamic model, while non-model-based techniques focus on changes in the temporal and frequency characteristics of the system response. Because restoring forces in base-excited structures can exhibit highly non-linear characteristics, non-linear model-based approaches may be better suited for reliable health monitoring and damage detection. This paper presents the application of a novel intelligent parameter varying (IPV) modeling and system identification technique, developed by the authors, to detect damage in base-excited structures. This IPV technique overcomes specific limitations of traditional model-based and non-model-based approaches, as demonstrated through comparative simulations with wavelet analysis methods. These simulations confirm the effectiveness of the IPV technique, and show that performance is not compromised by the introduction of realistic structural non-linearities and ground excitation characteristics.}, number={10}, journal={INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS}, author={Saadat, S and Noori, MN and Buckner, GD and Furukawa, TD and Suzuki, Y}, year={2004}, month={Dec}, pages={1687–1697} }
 @article{buckner_2002, title={Intelligent bounds on modeling uncertainty: Applications to sliding mode control}, volume={32}, ISSN={["1094-6977"]}, DOI={10.1109/TSMCC.2002.801350}, abstractNote={Robust control techniques such as sliding mode control (SMC) require a dynamic model of the plant and bounds on modeling uncertainty to formulate control laws with guaranteed stability. Although techniques for modeling dynamic systems and estimating model parameters are well established, very few procedures exist for estimating uncertainty bounds. In the case of SMC design, a conservative global bound is usually chosen to ensure closed-loop stability over the entire operating space. The primary drawbacks of this conservative, hard computing approach are excessive control activity and reduced performance, particularly in regions of the operating space where the model is accurate. In this paper, a novel approach to estimating uncertainty bounds for dynamic systems is introduced. This soft computing approach uses a unique artificial neural network, the 2-Sigma network, to bound modeling uncertainty adaptively. This fusion of intelligent uncertainty bound estimation with traditional SMC results in a control algorithm that is both robust and adaptive. Simulations and experimental demonstrations conducted on a magnetic levitation system confirm these capabilities and reveal excellent tracking performance without excessive control activity.}, number={2}, journal={IEEE TRANSACTIONS ON SYSTEMS MAN AND CYBERNETICS PART C-APPLICATIONS AND REVIEWS}, author={Buckner, GD}, year={2002}, month={May}, pages={113–124} }
 @article{pichot_kajs_murphy_ouroua_rech_hayes_beno_buckner_palazzolo_2001, title={Active magnetic bearings for energy storage systems for combat vehicles}, volume={37}, ISSN={["0018-9464"]}, DOI={10.1109/20.911846}, abstractNote={Advanced energy storage systems for electric guns and other pulsed weapons on combat vehicles present significant challenges for rotor bearing design, Active magnetic bearings (AMBs) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favorably integrate into high-speed flywheel systems. The Department of Defense Combat Hybrid Power Systems (CHPS) program serves as a case study for magnetic bearing applications on combat vehicles. The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 318 kg (700 lb), 20000 rpm rotor. To minimize CHPS flywheel size and mass, a topology was chosen in which the rotating portion of the flywheel is located outside the stationary components. Accordingly, magnetic bearing actuators are required which share this configuration. Because of inherent low loss and nearly linear force characteristics, UT-CEM has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance, a nonrotating bearing test fixture was designed and built which permits measurement of static and dynamic force. An AMB control system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. This paper discusses bearing system requirements, actuator and controller design, and predicted performance; it also compares theoretical vs. measured actuator characteristics.}, number={1}, journal={IEEE TRANSACTIONS ON MAGNETICS}, author={Pichot, MA and Kajs, JP and Murphy, BR and Ouroua, A and Rech, BM and Hayes, RJ and Beno, JH and Buckner, GD and Palazzolo, AB}, year={2001}, month={Jan}, pages={318–323} }
 @article{buckner_schuetze_beno_2001, title={Intelligent feedback linearization for active vehicle suspension control}, volume={123}, ISSN={["0022-0434"]}, DOI={10.1115/1.1408945}, abstractNote={Effective control of ride quality and handling performance are challenges for active vehicle suspension systems, particularly for off-road applications. Off-road vehicles experience large suspension displacements, where the nonlinear kinematics and damping characteristics of suspension elements are significant. These nonlinearities tend to degrade the performance of active suspension systems, introducing harshness to the ride quality and reducing off-road mobility. Typical control strategies rely on linear, time-invariant models of the suspension dynamics. While these models are convenient, nominally accurate, and tractable due to the abundance of linear control techniques, they neglect the nonlinearities and time-varying dynamics present in real suspension systems. One approach to improving the effectiveness of active vehicle suspension systems, while preserving the benefits of linear control techniques, is to identify and cancel these nonlinearities using Feedback Linearization. In this paper the authors demonstrate an intelligent parameter estimation approach using structured artificial neural networks that continually “learns” the nonlinear parameter variations of a quarter-car suspension model. This estimation algorithm becomes the foundation for an Intelligent Feedback Linearization (IFL) controller for active vehicle suspensions. Results are presented for computer simulations, real-time experimental tests, and field evaluations using an off-road vehicle (a military HMMWV). Experimental results for a quarter-car test rig demonstrate 60% improvements in ride quality relative to baseline (non-adapting) control algorithms. Field trial results reveal 95% reductions in absorbed power and 65% reductions in peak sprung mass acceleration using this IFL approach versus conventional passive suspensions.}, number={4}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Buckner, GD and Schuetze, KT and Beno, JH}, year={2001}, month={Dec}, pages={727–733} }
 @article{buckner_2001, title={Intelligent sliding mode control of cutting force during single-point turning operations}, volume={123}, ISSN={["1528-8935"]}, DOI={10.1115/1.1366683}, abstractNote={A novel intelligent control architecture has been developed to regulate cutting forces during single-point turning operations. A self-adapting Sliding Mode Controller (SMC) accounts for parameter variations and unmodeled dynamics in the cutting process. A unique artificial neural network, the 2-Sigma network, statistically bounds modeling uncertainties between a low-order, linear dynamic model and the actual cutting process. These uncertainty bounds provide “localized” gains for the SMC, thus reducing excess control activity while maintaining performance. Initially, the 2-Sigma networks are trained off-line using experimental data from a variety of operating conditions. In the final implementation, the 2-Sigma networks are updated on-line, allowing the SMC to respond to parameter variations and unmodeled dynamics. Experiments conducted on a CNC lathe demonstrate the exceptional performance and robustness of this control system.}, number={2}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Buckner, GD}, year={2001}, month={May}, pages={206–213} }