@article{kim_bryant_2024, title={Electrohydraulic System Analysis of Variable Recruitment Fluidic Artificial Muscle Bundles With Interaction Effects}, volume={146}, ISSN={["1528-9028"]}, DOI={10.1115/1.4064092}, abstractNote={Abstract}, number={3}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Kim, Jeong Yong and Bryant, Matthew}, year={2024}, month={May} }
 @article{mazzoleni_kim_bryant_2022, title={Control of a dynamic load emulator for hardware-in-the-loop testing of fluidic artificial muscle bundles}, volume={12041}, ISBN={["978-1-5106-4957-6"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2612920}, abstractNote={Fluidic artificial muscles (FAMs) have emerged as a viable and popular robotic actuation technique due to their low cost, compliant nature, and high force-to-weight-ratio. In recent years, the concept of variable recruitment has emerged as a way to improve the efficiency of conventional hydraulic robotic systems. In variable recruitment, groups of FAMs are bundled together and divided into individual motor units. Each motor unit can be activated independently, which is similar to the sequential activation pattern observed in mammalian muscle. Previous researchers have performed quasistatic characterizations of variable recruitment bundles and some simple dynamic analyses and experiments with a simple 1- DOF robot arm. We have developed a linear hydraulic characterization testing platform that will allow for the testing of different types of variable recruitment bundle configurations under different loading conditions. The platform consists of a hydraulic drive cylinder that acts as a cyber-physical hardware-in-the-loop dynamic loading emulator and interfaces with the variable recruitment bundle. The desired inertial, damping and stiffness properties of the emulator can be prescribed and achieved through an admittance controller. In this paper, we test the ability of this admittance controller to emulate different inertial, stiffness, and damping properties in simulation and demonstrate that it can be used in hardware through a proof-of-concept experiment. The primary goal of this work is to develop a unique testing setup that will allow for the testing of different FAM configurations, controllers, or subsystems and their responses to different dynamic loads before they are implemented on more complex robotic systems.}, journal={BIOINSPIRATION, BIOMIMETICS, AND BIOREPLICATION XII}, author={Mazzoleni, Nicholas and Kim, Jeong Yong and Bryant, Matthew}, year={2022} }
 @article{vemula_kim_mazzoleni_bryant_2022, title={Design, analysis, and validation of an orderly recruitment valve for bio-inspired fluidic artificial muscles}, volume={17}, ISSN={["1748-3190"]}, DOI={10.1088/1748-3190/ac4381}, abstractNote={Abstract}, number={2}, journal={BIOINSPIRATION & BIOMIMETICS}, author={Vemula, Dheeraj and Kim, Jeong Yong and Mazzoleni, Nicholas and Bryant, Matthew}, year={2022}, month={Mar} }
 @article{mazzoleni_kim_bryant_2022, title={Motor unit buckling in variable recruitment fluidic artificial muscle bundles: implications and mitigations}, volume={31}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665X/ac49d9}, abstractNote={Abstract}, number={3}, journal={SMART MATERIALS AND STRUCTURES}, author={Mazzoleni, Nicholas and Kim, Jeong Yong and Bryant, Matthew}, year={2022}, month={Mar} }
 @article{kim_mazzoleni_bryant_2021, title={Modeling of Resistive Forces and Buckling Behavior in Variable Recruitment Fluidic Artificial Muscle Bundles}, volume={10}, ISSN={["2076-0825"]}, DOI={10.3390/act10030042}, abstractNote={Fluidic artificial muscles (FAMs), also known as McKibben actuators, are a class of fiber-reinforced soft actuators that can be pneumatically or hydraulically pressurized to produce muscle-like contraction and force generation. When multiple FAMs are bundled together in parallel and selectively pressurized, they can act as a multi-chambered actuator with bioinspired variable recruitment capability. The variable recruitment bundle consists of motor units (MUs)—groups of one of more FAMs—that are independently pressurized depending on the force demand, similar to how groups of muscle fibers are sequentially recruited in biological muscles. As the active FAMs contract, the inactive/low-pressure units are compressed, causing them to buckle outward, which increases the spatial envelope of the actuator. Additionally, a FAM compressed past its individual free strain applies a force that opposes the overall force output of active FAMs. In this paper, we propose a model to quantify this resistive force observed in inactive and low-pressure FAMs and study its implications on the performance of a variable recruitment bundle. The resistive force behavior is divided into post-buckling and post-collapse regions and a piecewise model is devised. An empirically-based correction method is proposed to improve the model to fit experimental data. Analysis of a bundle with resistive effects reveals a phenomenon, unique to variable recruitment bundles, defined as free strain gradient reversal.}, number={3}, journal={ACTUATORS}, author={Kim, Jeong Yong and Mazzoleni, Nicholas and Bryant, Matthew}, year={2021}, month={Mar} }
 @article{mazzoleni_kim_bryant_2020, title={The Effect of Resistive Forces in Variable Recruitment Fluidic Artificial Muscle Bundles: A Configuration Study}, volume={11374}, ISSN={["1996-756X"]}, DOI={10.1117/12.2557907}, abstractNote={The use of soft, compliant actuators has recently gained research attention as a potential approach to improve human-robot interaction compatibility. Fluidic artificial muscles, or McKibben actuators, are a popular class of soft actuator due to their low cost and high force-to-weight ratio. However, traditional McKibben actuators face efficiency problems, as in most actuation schemes, the actuator is sized for the largest possible load, resulting in energy loss when operating at lower force regimes. To address this issue, our group has developed a bio-inspired actuation strategy called variable recruitment. In variable recruitment, actuators are placed within a bundle and can be sequentially activated depending on the required load. This strategy mimics the hierarchical architecture of mammalian muscle tissue and improves system efficiency and bandwidth while allowing for variable stiffness properties. Previous variable recruitment models and controllers assume that the force output of each actuator is independent and that these forces sum to provide the total bundle force. However, our recent work has shown that there is significant interaction between actuators within a bundle, particularly at lower recruitment states. This is because at these states, inactive or partially activated actuators resist bundle motion and reduce total force production. In this paper, we study these resistive effects at low recruitment states by considering two different variable recruitment configurations: a fixed-end configuration (with resistive forces) and a tendon configuration (designed with tendons to eliminate resistive forces). We then assess the tradeoffs between the two configurations. We found that while using the tendon configuration eliminates resistive forces, if we consider both configurations with the same overall system length, the tendon configuration has less overall system free strain because its FAMs have to be shorter than those of the fixed-end configuration. However, despite this difference in free strain, our results still show that the tendon configuration can have higher maximum load capacity and efficiency than the fixed-end configuration and that the specific application and system requirements will dictate the proper configuration choice.}, journal={BIOINSPIRATION, BIOMIMETICS, AND BIOREPLICATION X}, author={Mazzoleni, Nicholas and Kim, Jeong Yong and Bryant, Matthew}, year={2020} }