@article{driscoll_liu_huang_2023, title={1-D Manual Tracing Based on a High Density Haptic Stimulation Grid - a Pilot Effort}, ISSN={["2835-9518"]}, url={http://dx.doi.org/10.1109/whc56415.2023.10224505}, DOI={10.1109/WHC56415.2023.10224505}, abstractNote={Lower limb amputees lack the neurological path-ways needed for perception of how their prosthetic limbs are interacting with the environment, leading to a lack of confidence in their devices and reduced balancing capabilities. Sensory substitution methods, such as vibrotactile and electrotactile feedback applied to unaffected body segments offer a potential way to restore some of the lost information pathways. While high resolution haptic stimulation grids have become commercially available, few studies have tried to make use of these devices to provide more intuitive sensory substitution methods. This study developed an encoding approach, which is based on the illusory “phantom actuator” phenomenon, to convert 1-D position information to a wearer through a bHaptics Tactsuit. By evaluating performance of 1-D manual tracking task among 14 participants under the proposed approach and a traditional amplitude modulation approach, we demonstrated an improvement of velocity tracing accuracy (p=0.0375) with the proposed approach, although the proposed approach did not lead to significant improvement in the position tracing accuracy.}, journal={2023 IEEE WORLD HAPTICS CONFERENCE, WHC}, publisher={IEEE}, author={Driscoll, Brendan and Liu, Ming and Huang, He}, year={2023}, pages={375–381} }
 @article{alili_nalam_li_liu_feng_si_huang_2023, title={A Novel Framework to Facilitate User Preferred Tuning for a Robotic Knee Prosthesis}, volume={31}, ISSN={["1558-0210"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85147231065&partnerID=MN8TOARS}, DOI={10.1109/TNSRE.2023.3236217}, abstractNote={The tuning of robotic prosthesis control is essential to provide personalized assistance to individual prosthesis users. Emerging automatic tuning algorithms have shown promise to ease the device personalization procedure. However, very few automatic tuning algorithms consider the user preference as the tuning goal, which may limit the adoptability of the robotic prosthesis. In this study, we propose and evaluate a novel prosthesis control tuning framework for a robotic knee prosthesis, which could enable user preferred robot behavior in the device tuning process. The framework consists of 1) a User-Controlled Interface that allows the user to select their preferred knee kinematics in gait and 2) a reinforcement learning-based algorithm for tuning high-dimension prosthesis control parameters to meet the desired knee kinematics. We evaluated the performance of the framework along with usability of the developed user interface. In addition, we used the developed framework to investigate whether amputee users can exhibit a preference between different profiles during walking and whether they can differentiate between their preferred profile and other profiles when blinded. The results showed effectiveness of our developed framework in tuning 12 robotic knee prosthesis control parameters while meeting the user-selected knee kinematics. A blinded comparative study showed that users can accurately and consistently identify their preferred prosthetic control knee profile. Further, we preliminarily examined gait biomechanics of the prosthesis users when walking with different prosthesis control and did not find clear difference between walking with preferred prosthesis control and when walking with normative gait control parameters. This study may inform future translation of this novel prosthesis tuning framework for home or clinical use.}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Alili, Abbas and Nalam, Varun and Li, Minhan and Liu, Ming and Feng, Jing and Si, Jennie and Huang, He}, year={2023}, pages={895–903} }
 @article{liu_naseri_lee_hu_lewek_huang_2023, title={A simplified model for whole-body angular momentum calculation}, volume={111}, ISSN={["1873-4030"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144824437&partnerID=MN8TOARS}, DOI={10.1016/j.medengphy.2022.103944}, abstractNote={The capability to monitor gait stability during everyday life could provide key information to guide clinical intervention to patients with lower limb disabilities. Whole body angular momentum (Lbody) is a convenient stability indicator for wearable motion capture systems. However, Lbody is costly to estimate, because it requires monitoring all major body segment using expensive sensor elements. In this study, we developed a simplified rigid body model by merging connected body segments to reduce the number of body segments, which need to be monitored. We demonstrated that the Lbody could be estimated by a seven-segment model accurately for both people with and without lower extremity amputation.}, journal={MEDICAL ENGINEERING & PHYSICS}, author={Liu, Ming and Naseri, Amirreza and Lee, I-Chieh and Hu, Xiaogang and Lewek, Michael D. and Huang, He}, year={2023}, month={Jan} }
 @article{alili_nalam_fleming_liu_dean_huang_2023, title={Closed-Loop Feedback Control of Human Step Width During Walking by Mediolaterally Acting Robotic Hip Exoskeleton}, ISSN={["2153-0858"]}, DOI={10.1109/IROS55552.2023.10342127}, abstractNote={Maintaining balance during gait in the mediolateral direction requires more active motor control than in the anteroposterior direction. Step width modulation is a key strategy used by healthy individuals to achieve mediolateral walking balance, but it can be disrupted in populations with poor sensorimotor integration and weak hip abductors, such as the elderly, stroke patients, and people with lower limb amputation. Wearable hip exoskeletons have the potential to serve as assistive or rehabilitation devices for these populations, but there has been limited research on their appropriate usage. In this study, we successfully demonstrated the feasibility of controlling step width using a mediolaterally acting robotic hip exoskeleton. We were able to effectively adjust the user's step width by increasing or decreasing it to predefined targets through the regulation of admittance control parameters governing the device. The maximum average error to increase or decrease the step width was 1.2 cm. This research has the potential to facilitate the development of assistive and rehabilitation applications focused on enhancing the mediolateral gait balance of individuals with neurological impairments, elderly individuals, and amputees via the control of step width.}, journal={2023 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS)}, author={Alili, Abbas and Nalam, Varun and Fleming, Aaron and Liu, Ming and Dean, Jesse and Huang, Helen}, year={2023}, pages={6097–6102} }
 @article{naseri_liu_lee_huang_2023, title={Development and Online Validation of an Intrinsic Fault Detector for a Powered Robotic Knee Prosthesis}, ISSN={["2153-0858"]}, DOI={10.1109/IROS55552.2023.10342433}, abstractNote={Robotic prosthetic legs have the potential to significantly improve the quality of life for lower limb amputees to perform locomotion in various environments and task conditions. However, these devices lack the capability to recover from internal intrinsic control faults, which can lead to harmful consequences affecting the user's gait performance and eroding trust in these robotic devices. Therefore, a reliable fault detection system is necessary to detect intrinsic faults in a timely manner and provide a compensatory response to mitigate their effects. This paper focuses on designing an active fault detector for a robotic knee prosthesis and demonstrates its effectiveness in real time. The developed system utilizes a Gaussian Process model to estimate knee angular velocity, which is sensitive to intrinsic faults and relies on the difference between estimated velocity and the actual measurement to detect internal control faults. In an offline analysis, the developed detector demonstrated a higher detection rate, lower false alarm ratio, and faster detection time compared with the two approaches reported previously. An online demonstration was also conducted with a unilateral amputee participant and showed performance similar to that of offline analysis. We expect that this detector can be integrated into a fault tolerance strategy to enhance the reliability and safety of robotic prosthetic legs, enabling users to perform their everyday tasks with greater confidence.}, journal={2023 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS, IROS}, author={Naseri, Amirreza and Liu, Ming and Lee, I-Chieh and Huang, Helen}, year={2023}, pages={2158–2164} }
 @article{naseri_lee_huang_liu_2023, title={Investigating the Association of Quantitative Gait Stability Metrics With User Perception of Gait Interruption Due to Control Faults During Human-Prosthesis Interaction}, volume={31}, ISSN={["1558-0210"]}, DOI={10.1109/TNSRE.2023.3328877}, abstractNote={This study aims to compare the association of different gait stability metrics with the prosthesis users’ perception of their own gait stability. Lack of perceived confidence on the device functionality can influence the gait pattern, level of daily activities, and overall quality of life for individuals with lower limb motor deficits. However, the perception of gait stability is subjective and difficult to acquire online. The quantitative gait stability metrics can be objectively measured and monitored using wearable sensors; however, objective measurements of gait stability associated with human’s perception of their own gait stability has rarely been reported. By identifying quantitative measurements that associate with users’ perceptions, we can gain a more accurate and comprehensive understanding of an individual’s perceived functional outcomes of assistive devices such as prostheses. To achieve our research goal, experiments were conducted to artificially apply internal disturbances in the powered prosthesis while the prosthetic users performed level ground walking. We monitored and compared multiple gait stability metrics and a local measurement to the users’ reported perception of their own gait stability. The results showed that the center of pressure progression in the sagittal plane and knee momentum (i.e., residual thigh and prosthesis shank angular momentum about prosthetic knee joint) can potentially estimate the users’ perceptions of gait stability when experiencing disturbances. The findings of this study can help improve the development and evaluation of gait stability control algorithms in robotic prosthetic devices.}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Naseri, Amirreza and Lee, I-Chieh and Huang, He and Liu, Ming}, year={2023}, pages={4693–4702} }
 @article{naseri_liu_lee_liu_huang_2022, title={Characterizing Prosthesis Control Fault During Human-Prosthesis Interactive Walking Using Intrinsic Sensors}, volume={7}, ISSN={["2377-3766"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85133795882&partnerID=MN8TOARS}, DOI={10.1109/LRA.2022.3186503}, abstractNote={The physical interactions between wearable lower limb robots and humans have been investigated to inform effective robot design for walking augmentation. However, human-robot interactions when internal faults occur within robots have not been systematically reported, but it is essential to improve the robustness of robotic devices and ensure the user’s safety. This letter aims to (1) present a methodology to characterize the behavior of the robotic transfemoral prosthesis as an effective wearable robot platform while interacting with the users in the presence of internal faults, and (2) identify the potential data sources for accurate detection of the prosthesis fault. We first obtained the human perceived response in terms of their walking stability when the prosthesis control fault (inappropriate intrinsic control output/command) was emulated/applied in level-ground walking. Then the measurements and their features, obtained from the transfemoral prosthesis, were examined for the emulated faults that elicited a sense of instability in human users. The optimal features that contributed the most in separating faulty interaction from the normal walking condition were determined using two machine-learning-based approaches: One-Class Support Vector Machine (OCSVM) and Mahalanobis Distance (MD) classifier. The OCSVM anomaly detector could achieve an average sensitivity of 85.7% and an average false alarm rate of 1.7% with a reasonable detecting time of 147.6 ms for detecting emulated control errors among all subjects. The result demonstrates the potential of using machine-learning-based schemes in identifying prosthesis control faults based on intrinsic sensors on the prosthesis. This study presents a procedure to study human-robot fault tolerance and inform the future design of robust prosthesis control.}, number={3}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, author={Naseri, Amirreza and Liu, Ming and Lee, I-Chieh and Liu, Wentao and Huang, He}, year={2022}, month={Jul}, pages={8307–8314} }
 @article{shah_fleming_nalam_liu_huang_2022, title={Design of EMG-driven Musculoskeletal Model for Volitional Control of a Robotic Ankle Prosthesis}, volume={2022-October}, ISSN={["2153-0858"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85146352781&partnerID=MN8TOARS}, DOI={10.1109/IROS47612.2022.9981305}, abstractNote={Existing robotic lower-limb prostheses use autonomous control to address cyclic, locomotive tasks, but are inadequate in adapting to variations in non-cyclic and unpredictable tasks. This study aims to address this challenge by designing a novel electromyography (EMG)-driven musculoskeletal model for volitional control of a robotic ankle-foot prosthesis. The proposed controller ensures continuous control of the device, allowing users to freely manipulate the prosthesis behavior. A Hill-type muscle model was implemented to model a dorsiflexor and a plantarflexor to function around a virtual ankle joint. The model parameters for a subject specific model was determined by fitting the model to the experimental data collected from an able-bodied subject. EMG signals recorded from antagonist muscle pairs were used to activate the virtual muscle models. This model-based approach was then validated via offline simulations and real-time prosthesis control. Additionally, the feasibility of the proposed prosthesis control on assisting the user's functional tasks was demonstrated. The present control may further improve the function of robotic prosthesis for supporting versatile activities in individuals with lower-limb amputations.}, journal={2022 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS)}, author={Shah, Chinmay and Fleming, Aaron and Nalam, Varun and Liu, Ming and Huang, He}, year={2022}, pages={12261–12266} }
 @article{lee_fylstra_liu_lenzi_huang_2022, title={Is there a trade-off between economy and task goal variability in transfemoral amputee gait?}, volume={19}, ISSN={["1743-0003"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85126546016&partnerID=MN8TOARS}, DOI={10.1186/s12984-022-01004-8}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF NEUROENGINEERING AND REHABILITATION}, author={Lee, I-Chieh and Fylstra, Bretta L. and Liu, Ming and Lenzi, Tommaso and Huang, He}, year={2022}, month={Mar} }
 @article{yuan_bai_driscoll_liu_huang_feng_2022, title={Standing and Walking Attention Visual Field (SWAVF) task: A new method to assess visuospatial attention during walking}, volume={104}, ISSN={["1872-9126"]}, url={http://dx.doi.org/10.1016/j.apergo.2022.103804}, DOI={10.1016/j.apergo.2022.103804}, abstractNote={Visuospatial attention during walking has been associated with pedestrian safety and fall risks. However, visuospatial attention measures during walking remained under-explored. Current studies introduced a newly-developed Standing and Walking Visual Attention Field (SWAVF) task to assess visuospatial attention during walking and examined its reliability, validity, and stability. Thirty young adults completed a traditional computerized Attention Visual Field (AVF) task while sitting, and the SWAVF task under walking and standing settings. Nine participants also performed the SWAVF task under additional distraction conditions. Results showed good split-half reliability during standing (r = 0.70) and walking (r = 0.69), moderate concurrent validity with the sitting AVF task (r = 0.42), moderate convergent validity between the standing and walking settings (r = 0.69), good construct validity, and moderate rank-order stability (r = 0.53). Overall, the SWAVF task showed good psychometric properties. Potential applications to the evaluation of prosthetic and other exoskeleton devices, smart glasses, and ground-level traffic lights or signs were discussed.}, journal={APPLIED ERGONOMICS}, publisher={Elsevier BV}, author={Yuan, Jing and Bai, Xiaolu and Driscoll, Brendan and Liu, Ming and Huang, He and Feng, Jing}, year={2022}, month={Oct} }
 @article{lee_liu_lewek_hu_filer_huang_2022, title={Toward Safe Wearer-Prosthesis Interaction: Evaluation of Gait Stability and Human Compensation Strategy Under Faults in Robotic Transfemoral Prostheses}, volume={30}, ISSN={["1558-0210"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85139401676&partnerID=MN8TOARS}, DOI={10.1109/TNSRE.2022.3208778}, abstractNote={Although advanced wearable robots can assist human wearers, their internal faults (i.e., sensors or control errors) also pose a challenge. To ensure safe wearer-robot interactions, how internal errors by the prosthesis limb affect the stability of the user-prosthesis system, and how users react and compensate for the instability elicited by internal errors are imperative. The goals of this study were to 1) systematically investigate the biomechanics of a wearer-robot system reacting to internal errors induced by a powered knee prosthesis (PKP), and 2) quantify the error tolerable bound that does not affect the user’s gait stability. Eight non-disabled participants and two unilateral transfemoral amputees walked on a pathway wearing a PKP, as the controller randomly switched the control parameters to disturbance parameters to mimic the errors caused by locomotion mode misrecognition. The size of prosthesis control errors was systematically varied to determine the error tolerable bound that disrupted gait stability. The effect of the error was quantified based on the 1) mechanical change described by the angular impulse applied by the PKP, and 2) overall gait instability quantified using human perception, angular momentum, and compensatory stepping. The results showed that the error tolerable bound is dependent on the gait phase and the direction of torque change. Two balance recovery strategies were also observed to allow participants to successful respond to the induced errors. The outcomes of this study may assist the future design of an auto-tuning algorithm, volitionally-controlled powered prosthetic legs, and training of gait stability.}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Lee, I-Chieh and Liu, Ming and Lewek, Michael D. and Hu, Xiaogang and Filer, William G. and Huang, He}, year={2022}, pages={2773–2782} }
 @article{tu_li_liu_si_huang_2021, title={A Data-Driven Reinforcement Learning Solution Framework for Optimal and Adaptive Personalization of a Hip Exoskeleton}, volume={2021-May}, ISSN={["2577-087X"]}, url={http://dx.doi.org/10.1109/icra48506.2021.9562062}, DOI={10.1109/ICRA48506.2021.9562062}, abstractNote={Robotic exoskeletons are exciting technologies for augmenting human mobility. However, designing such a device for seamless integration with the human user and to assist human movement still is a major challenge. This paper aims at developing a novel data-driven solution framework based on reinforcement learning (RL), without first modeling the human-robot dynamics, to provide optimal and adaptive personalized torque assistance for reducing human efforts during walking. Our automatic personalization solution framework includes the assistive torque profile with two control timing parameters (peak and offset timings), the least square policy iteration (LSPI) for learning the parameter tuning policy, and a cost function based on a transferred work ratio. The proposed controller was successfully validated on a healthy human subject to assist unilateral hip extension in walking. The results showed that the optimal and adaptive RL controller as a new approach was feasible for tuning assistive torque profile of the hip exoskeleton that coordinated with human actions and reduced activation level of hip extensor muscle in human.}, journal={2021 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA 2021)}, publisher={IEEE}, author={Tu, Xikai and Li, Minhan and Liu, Ming and Si, Jennie and Huang, He}, year={2021}, pages={10610–10616} }
 @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} }
 @misc{yuan_cline_liu_huang_feng_2021, title={Cognitive measures during walking with and without lower-limb prosthesis: protocol for a scoping review}, volume={11}, ISBN={2044-6055}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85101189834&partnerID=MN8TOARS}, DOI={10.1136/bmjopen-2020-039975}, abstractNote={IntroductionTuning of lower-limb (LL) robotic prosthesis control is necessary to provide personalised assistance to each human wearer during walking. Prostheses wearers’ adaptation processes are subjective and the efficiency largely depends on one’s mental processes. Therefore, beyond physical motor performance, prosthesis personalisation should consider the wearer’s preference and cognitive performance during walking. As a first step, it is necessary to examine the current measures of cognitive performance when a wearer walks with an LL prosthesis, identify the gaps and methodological considerations, and explore additional measures in a walking setting. In this protocol, we outlined a scoping review that will systematically summarise and evaluate the measures of cognitive performance during walking with and without LL prosthesis.}, number={2}, journal={BMJ OPEN}, author={Yuan, Jing and Cline, Emily and Liu, Ming and Huang, He and Feng, Jing}, year={2021} }
 @article{popp_liu_huang_2021, title={Development of a Wearable Human-Machine Interface to Track Forearm Rotation via an Optical Sensor}, ISSN={["1558-4615"]}, url={http://dx.doi.org/10.1109/embc46164.2021.9629851}, DOI={10.1109/EMBC46164.2021.9629851}, abstractNote={The goal of this research was to develop an intuitive wearable human-machine interface (HMI), utilizing an optical sensor. The proposed system quantifies wrist pronation and supination using an optical displacement sensor. Compared with existing systems, this HMI ensures intuitiveness by relying on direct measurement of forearm position, minimizes involved sensors, and is expected to be long-lasting. To test for feasibility, the developed HMI was implemented to control a prosthetic wrist based on forearm rotation of able-bodied subjects. Performance of optical sensor system (OSS) prosthesis control was compared to electromyography (EMG) based direct control, for six able-bodied individuals, using a clothespin relocation task. Results showed that the performance of OSS control was comparable to direct control, therefore validating the feasibility of the OSS HMI.}, journal={2021 43RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY (EMBC)}, publisher={IEEE}, author={Popp, Fiona and Liu, Ming and Huang, He}, year={2021}, pages={7360–7363} }
 @article{tabor_agcayazi_fleming_thompson_kapoor_liu_lee_huang_bozkurt_ghosh_2021, title={Textile-Based Pressure Sensors for Monitoring Prosthetic-Socket Interfaces}, volume={21}, ISSN={["1558-1748"]}, url={https://doi.org/10.1109/JSEN.2021.3053434}, DOI={10.1109/JSEN.2021.3053434}, abstractNote={Amputees are prone to experiencing discomfort when wearing their prosthetic devices. As the amputee population grows this becomes a more prevalent and pressing concern. There is a need for new prosthetic technologies to construct more comfortable and well-fitted liners and sockets. One of the well-recognized impediments to the development of new prosthetic technology is the lack of practical inner socket sensors to monitor the inner socket environment (ISE), or the region between the residual limb and the socket. Here we present a capacitive pressure sensor fabricated through a simple, and scalable sewing process using commercially available conductive yarns and textile materials. This fully-textile sensor provides a soft, flexible, and comfortable sensing system for monitoring the ISE. We provide details of our low-power sensor system capable of high-speed data collection from up to four sensor arrays. Additionally, we demonstrate two custom set-ups to test and validate the textile-based sensors in a simulated prosthetic environment. Finally, we utilize the textile-based sensors to study the ISE of a bilateral transtibial amputee. Results indicate that the textile-based sensors provide a promising potential for seamlessly monitoring the ISE.}, number={7}, journal={IEEE SENSORS JOURNAL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tabor, Jordan and Agcayazi, Talha and Fleming, Aaron and Thompson, Brendan and Kapoor, Ashish and Liu, Ming and Lee, Michael Y. and Huang, He and Bozkurt, Alper and Ghosh, Tushar K.}, year={2021}, month={Apr}, pages={9413–9422} }
 @article{alili_nalam_li_liu_si_huang_2021, title={User Controlled Interface for Tuning Robotic Knee Prosthesis}, ISSN={["2153-0858"]}, url={http://dx.doi.org/10.1109/iros51168.2021.9636264}, DOI={10.1109/IROS51168.2021.9636264}, abstractNote={The tuning process for a robotic prosthesis is a challenging and time-consuming task both for users and clinicians. An automatic tuning approach using reinforcement learning (RL) has been developed for a knee prosthesis to address the challenges of manual tuning methods. The algorithm tunes the optimal control parameters based on the provided knee joint profile that the prosthesis is expected to replicate during gait safely. This paper presents an intuitive interface designed for the prosthesis users and clinicians to choose the preferred knee joint profile during gait and use the autotuner to replicate in the prosthesis. The interface-based approach is validated by observing the ability of the tuning algorithm to successfully converge to various alternate knee profiles by testing on two able-bodied subjects walking with a robotic knee prosthesis. The algorithm was found to converge successfully in an average duration of 1.15 min for the first subject and 2.31 min for the second subject. Further, the subjects displayed different preferences for optimal profiles reinforcing the need to tune alternate profiles. The implications of the results in the tuning of robotic prosthetic devices are discussed.}, journal={2021 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS)}, publisher={IEEE}, author={Alili, Abbas and Nalam, Varun and Li, Minhan and Liu, Ming and Si, Jennie and Huang, He}, year={2021}, pages={6190–6195} }
 @article{brandt_wen_liu_stallings_huang_2017, title={Interactions Between Transfemoral Amputees and a Powered Knee Prosthesis During Load Carriage}, volume={7}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/S41598-017-14834-7}, DOI={10.1038/S41598-017-14834-7}, abstractNote={Abstract}, number={1}, journal={Scientific Reports}, publisher={Springer Nature}, author={Brandt, Andrea and Wen, Yue and Liu, Ming and Stallings, Jonathan and Huang, He Helen}, year={2017}, month={Nov} }
 @article{huang_crouch_liu_sawicki_wang_2016, title={A cyber expert system for auto-tuning powered prosthesis impedance control parameters}, volume={44}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84944521097&partnerID=MN8TOARS}, DOI={10.1007/s10439-015-1464-7}, abstractNote={Typically impedance control parameters (e.g., stiffness and damping) in powered lower limb prostheses are fine-tuned by human experts (HMEs), which is time and resource intensive. Automated tuning procedures would make powered prostheses more practical for clinical use. In this study, we developed a novel cyber expert system (CES) that encoded HME tuning decisions as computer rules to auto-tune control parameters for a powered knee (passive ankle) prosthesis. The tuning performance of CES was preliminarily quantified on two able-bodied subjects and two transfemoral amputees. After CES and HME tuning, we observed normative prosthetic knee kinematics and improved or slightly improved gait symmetry and step width within each subject. Compared to HME, the CES tuning procedure required less time and no human intervention. Hence, using CES for auto-tuning prosthesis control was a sound concept, promising to enhance the practical value of powered prosthetic legs. However, the tuning goals of CES might not fully capture those of the HME. This was because we observed that HME tuning reduced trunk sway, while CES sometimes led to slightly increased trunk motion. Additional research is still needed to identify more appropriate tuning objectives for powered prosthetic legs to improve amputees' walking function.}, number={5}, journal={Annals of Biomedical Engineering}, author={Huang, He and Crouch, D. L. and Liu, M. and Sawicki, G. S. and Wang, D.}, year={2016}, pages={1613–1624} }
 @article{liu_wang_huang_2016, title={Development of an Environment-Aware Locomotion Mode Recognition System for Powered Lower Limb Prostheses}, volume={24}, ISSN={["1558-0210"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84963864628&partnerID=MN8TOARS}, DOI={10.1109/tnsre.2015.2420539}, abstractNote={This paper aimed to develop and evaluate an environment-aware locomotion mode recognition system for volitional control of powered artificial legs. A portable terrain recognition (TR) module, consisting of an inertia measurement unit and a laser distance meter, was built to identify the type of terrain in front of the wearer while walking. A decision tree was used to classify the terrain types and provide either coarse or refined information about the walking environment. Then, the obtained environmental information was modeled as a priori probability and was integrated with a neuromuscular-mechanical-fusion-based locomotion mode (LM) recognition system. The designed TR module and environmental-aware LM recognition system was evaluated separately on able-bodied subjects and a transfemoral amputee online. The results showed that the TR module provided high quality environmental information: TR accuracy is above 98% and terrain transitions are detected over 500 ms before the time required to switch the prosthesis control mode. This enabled smooth locomotion mode transitions for the wearers. The obtained environmental information further improved the performance of LM recognition system, regardless of whether coarse or refined information was used. In addition, the environment-aware LM recognition system produced reliable online performance when the TR output was relatively noisy, which indicated the potential of this system to operate in unconstructed environment. This paper demonstrated that environmental information should be considered for operating wearable lower limb robotic devices, such as prosthetics and orthotics.}, number={4}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Liu, Ming and Wang, Ding and Huang, He}, year={2016}, month={Apr}, pages={434–443} }
 @article{zhang_liu_huang_2015, title={Effects of Locomotion Mode Recognition Errors on Volitional Control of Powered Above-Knee Prostheses}, volume={23}, ISSN={["1558-0210"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84921025654&partnerID=MN8TOARS}, DOI={10.1109/tnsre.2014.2327230}, abstractNote={Recent studies have reported various methods that recognize amputees' intent regarding locomotion modes, which is potentially useful for volitional control of powered artificial legs. However, occasional errors in locomotion mode recognition are inevitable. When these intent recognition decisions are used for volitional prosthesis control, the effects of the decision errors on the operation of the prosthesis and user's task performance is unknown. Hence, the goals of this study were to 1) systematically investigate the effects of locomotion mode recognition errors on volitional control of powered prosthetic legs and the user's gait stability, and 2) identify the critical mode recognition errors that impact safe and confident use of powered artificial legs in lower limb amputees. Five able-bodied subjects and two above-knee (AK) amputees were recruited and tested when wearing a powered AK prosthesis. Four types of locomotion mode recognition errors with different duration and at different gait phases were purposely applied to the prosthesis control. The subjects' gait stabilities were subjectively and objectively quantified. The results showed that not all of the mode recognition errors in volitional prosthesis control disturb the subjects' gait stability. The effects of errors on the user's balance depended on 1) the gait phase when the errors happened and 2) the amount of mechanical work change applied on the powered knee caused by the errors. Based on the study results, “critical errors” were defined and suggested as a new index to evaluate locomotion mode recognition algorithms for artificial legs. The outcome of this study might aid the future design of volitionally-controlled powered prosthetic legs that are reliable and safe for practice.}, number={1}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Zhang, Fan and Liu, Ming and Huang, He}, year={2015}, month={Jan}, pages={64–72} }
 @article{zhang_liu_harper_lee_huang_2014, title={Engineering Platform and Experimental Protocol for Design and Evaluation of a Neurally-controlled Powered Transfemoral Prosthesis}, ISSN={["1940-087X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84940242678&partnerID=MN8TOARS}, DOI={10.3791/51059}, abstractNote={To enable intuitive operation of powered artificial legs, an interface between user and prosthesis that can recognize the user's movement intent is desired. A novel neural-machine interface (NMI) based on neuromuscular-mechanical fusion developed in our previous study has demonstrated a great potential to accurately identify the intended movement of transfemoral amputees. However, this interface has not yet been integrated with a powered prosthetic leg for true neural control. This study aimed to report (1) a flexible platform to implement and optimize neural control of powered lower limb prosthesis and (2) an experimental setup and protocol to evaluate neural prosthesis control on patients with lower limb amputations. First a platform based on a PC and a visual programming environment were developed to implement the prosthesis control algorithms, including NMI training algorithm, NMI online testing algorithm, and intrinsic control algorithm. To demonstrate the function of this platform, in this study the NMI based on neuromuscular-mechanical fusion was hierarchically integrated with intrinsic control of a prototypical transfemoral prosthesis. One patient with a unilateral transfemoral amputation was recruited to evaluate our implemented neural controller when performing activities, such as standing, level-ground walking, ramp ascent, and ramp descent continuously in the laboratory. A novel experimental setup and protocol were developed in order to test the new prosthesis control safely and efficiently. The presented proof-of-concept platform and experimental setup and protocol could aid the future development and application of neurally-controlled powered artificial legs.}, number={89}, journal={JOVE-JOURNAL OF VISUALIZED EXPERIMENTS}, author={Zhang, Fan and Liu, Ming and Harper, Stephen and Lee, Michael and Huang, He}, year={2014}, month={Jul} }
 @article{liu_zhang_datseris_huang_2014, title={Improving Finite State Impedance Control of Active-Transfemoral Prosthesis Using Dempster-Shafer Based State Transition Rules}, volume={76}, ISSN={0921-0296 1573-0409}, url={http://dx.doi.org/10.1007/S10846-013-9979-3}, DOI={10.1007/S10846-013-9979-3}, number={3-4}, journal={Journal of Intelligent & Robotic Systems}, publisher={Springer Science and Business Media LLC}, author={Liu, Ming and Zhang, Fan and Datseris, Philip and Huang, He}, year={2014}, month={Dec}, pages={461–474} }
 @article{liu_chelidze_2008, title={A new type of atomic force microscope based on chaotic motions}, volume={43}, ISSN={0020-7462}, url={http://dx.doi.org/10.1016/j.ijnonlinmec.2008.03.001}, DOI={10.1016/j.ijnonlinmec.2008.03.001}, abstractNote={Local flow variation (LFV) method of non-linear time series analysis is applied to develop a chaotic motion-based atomic force microscope (AFM). The method is validated by analyzing time series from a simple numerical model of a tapping mode AFM. For both calibration and measurement procedures the simulated motions of the AFM are nominally chaotic. However, the distance between a tip of the AFM and a sample surface is still measured accurately. The LFV approach is independent of any particular model of the system and is expected to be applicable to other micro-electro-mechanical system sensors where chaotic motions are observed or can be introduced.}, number={6}, journal={International Journal of Non-Linear Mechanics}, publisher={Elsevier BV}, author={Liu, Ming and Chelidze, David}, year={2008}, month={Jul}, pages={521–526} }