@article{zhang_tran_huang_2019, title={Admittance Shaping-Based Assistive Control of SEA-Driven Robotic Hip Exoskeleton}, volume={24}, ISSN={["1941-014X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85085177698&partnerID=MN8TOARS}, DOI={10.1109/TMECH.2019.2916546}, abstractNote={This paper presents an admittance shaping-based assistive control for a series elastic actuator (SEA) driven robotic hip exoskeleton that can assist individuals with hip muscle weakness to restore normative mobility. The motivation for this paper is to develop a unified controller framework for designing an SEA-driven hip exoskeleton to assist walking and enhance gait stability. The controller design aims to modify the dynamic response of a coupled human-exoskeleton system, i.e., the relationship between the net muscle torque exerted by the human and the resulting angular motion, to ensure strong human-exoskeleton synergy to provide the effective assistance. This controller was preliminarily evaluated on a healthy subject walking on a treadmill at a speed of 1.0 m/s. Results showed that the exoskeleton can effectively provide walking assistance to the human by reducing electromyography (EMG) activation and increasing agility during locomotion. Specifically, EMG was reduced 3.3%–38% when walking with the hip exoskeleton when compared to walking without wearing the hip exoskeleton. In addition, timing of the maximum hip flexion angle increased by 10% (moved from 42% to 32% of gait cycle) when the controller had an inertia compensation of 60%. The faster onset of the maximum flexion angle will allow the wearer to more quickly generate reactive steps when trying to avoid a fall. Future work will aim to apply the hip exoskeleton to persons having hip muscle weakness or other musculoskeletal impairment, to restore hip movement and enough hip force to walk normally.}, number={4}, journal={IEEE-ASME TRANSACTIONS ON MECHATRONICS}, author={Zhang, Ting and Tran, Minh and Huang, He}, year={2019}, month={Aug}, pages={1508–1519} }
 @article{zhang_huang_2019, title={Design and Control of a Series Elastic Actuator With Clutch for Hip Exoskeleton for Precise Assistive Magnitude and Timing Control and Improved Mechanical Safety}, volume={24}, ISSN={1083-4435 1941-014X}, url={http://dx.doi.org/10.1109/tmech.2019.2932312}, DOI={10.1109/TMECH.2019.2932312}, abstractNote={Transparency and guaranteed safety are important requirements in the design of wearable exoskeleton actuators for individuals who have lower limb deficits but still maintain a certain level of voluntary motor control. Specifically, precision in torque delivery timing and magnitude, robustness, disturbance rejection, and repeatability are desired in the actuator design and control. Motivated by these needs, this study aims to develop a series of elastic actuators with clutch (SEAC) that can precisely generate the desired assistance in terms of both timing and torque magnitude for a wearable hip exoskeleton and guarantee the wearer's safety at the same time. The proposed mechanical design improves actuator transparency and safety by a mechanical clutch that automatically disengages the transmission when needed. A new torque control for the SEAC, based on singular perturbation theory with flexible compensation techniques, is proposed to precisely control the assistive torque by rejecting the undesired human motion disturbance. The mechanical design of the proposed device and the design of a singular perturbation control algorithm are discussed, and the SEAC performance is verified by experiments. Experimental results, derived from a test with a human subject, are presented to demonstrate the precision of the assistive torque and timing control of the SEAC while interacting with a human wearer.}, number={5}, journal={IEEE/ASME Transactions on Mechatronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Zhang, Ting and Huang, He}, year={2019}, month={Oct}, pages={2215–2226} }
 @article{zhang_huang_2018, title={A Lower-Back Robotic Exoskeleton}, volume={25}, ISSN={["1558-223X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85047189327&partnerID=MN8TOARS}, DOI={10.1109/mra.2018.2815083}, abstractNote={A lower-back exoskeleton prototype designed to provide back support for industrial workers who manually handle heavy materials is presented in this article. Reducing spinal loads during these tasks can reduce the risk of work-related back injuries. Biomechanical studies show that compression of the lumbar spine is a key risk factor for musculoskeletal injuries. To address this issue, we present a wearable exoskeleton designed to provide back support and reduce lumbar spine compression. To provide effective assistance and avoid injury to muscles or tendons, we apply a continuous torque of approximately 40 Nm on both hip joints to actively assist both hip abduction/adduction (HAA) and hip flexion/extension (HFE). Each actuation unit includes a modular and a compact series-elastic actuator (SEA) with a clutch. The SEA provides mechanical compliance at the interface between the exoskeleton and the user, and the clutches can automatically disengage the torque between the exoskeleton and the user. These experimental results show that the exoskeleton can lower lumbar compression by reducing the need for muscular activity in the spine. Furthermore, powering both HFE and HAA can effectively reduce the lumbar spinal loading user experience when lifting and lowering objects while in a twisted posture.}, number={2}, journal={IEEE ROBOTICS & AUTOMATION MAGAZINE}, author={Zhang, Ting and Huang, He}, year={2018}, month={Jun}, pages={95–106} }
 @article{zhang_tran_huang_2018, title={Design and Experimental Verification of Hip Exoskeleton With Balance Capacities for Walking Assistance}, volume={23}, ISSN={["1941-014X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85040563606&partnerID=MN8TOARS}, DOI={10.1109/tmech.2018.2790358}, abstractNote={Most current hip exoskeletons emphasize assistance for walking rather than stability. The goal of this paper is to develop a novel, high-power, self-balancing, and passively and software-controlled actively compliant hip exoskeleton that can assist with movement and maintain balance in both the sagittal and frontal planes. The developed hip exoskeleton includes powered hip abduction/adduction and hip flexion/extension joints. Each actuation unit employs a modular and compact series elastic actuator (SEA) with a high torque-to-weight ratio. It provides mechanical compliance at the interface between the exoskeleton and the wearer to ensure safety and a natural gait in the coupled wearer-exoskeleton system. A new balance controller based on the extrapolated center of mass concept is presented for maintaining walking stability. This controller reacts to perturbations in balance and produces a compliant guidance force through a combination of the passive elasticity of the SEA and active compliant control based on adaptive admittance control. The function of the hip exoskeleton is not to override human control, but rather to involve the wearer in movement control in order to avoid conflicts between wearer and exoskeleton. Our preliminary experiments on a healthy subject wearing the hip exoskeleton demonstrate the potential effectiveness of the proposed hip exoskeleton and controller for walking balance control.}, number={1}, journal={IEEE-ASME TRANSACTIONS ON MECHATRONICS}, author={Zhang, Ting and Tran, Minh and Huang, He}, year={2018}, month={Feb}, pages={274–285} }
 @article{zhang_jiang_liu_2018, title={Design and Functional Evaluation of a Dexterous Myoelectric Hand Prosthesis With Biomimetic Tactile Sensor}, volume={26}, ISSN={["1558-0210"]}, DOI={10.1109/tnsre.2018.2844807}, abstractNote={This paper presents the design, tactile sensor, characterization, and control system of a new dexterous myoelectric hand prosthesis to overcome the limitations of state-of-the-art myoelectric prostheses (e.g., limited functionality, controllability, and sensory feedback). Our dexterous myoelectric hand allows independent finger movement and thumb abduction/adduction, with a motor for each finger and an additional motor for the thumb (i.e., six total motors). Each fingertip has a biomimetic tactile sensor with 13 tactile units, each of which can detect normal and tangential forces. The hand controller uses an electromyography pattern recognition controller and a tactile sensor feedback-based grasping controller to automatically and dynamically adjust the finger grasp force to prevent objects from slipping. This closed-loop controller structure will allow users to safely and effectively grasp complex objects with varying densities and shapes. In addition, the electronic hardware is integrated into the hand, and the pattern recognition controller can be implemented in the hand embedded system.}, number={7}, journal={IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING}, author={Zhang, Ting and Jiang, Li and Liu, Hong}, year={2018}, month={Jul}, pages={1391–1399} }
 @inproceedings{zhang_huang_2017, title={Enhancing gait balance via a 4-DoFs wearable hip exoskeleton}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85049976192&partnerID=MN8TOARS}, DOI={10.1109/werob.2017.8383824}, abstractNote={One limitation of the current lower-limb exoskeletons is that they do not provide the function of maintaining the lateral stability. During walking, beyond the forward step length regulated by hip flexion/extension (HFE), adaptation of the step width, which can be adjusted by hip abduction/adduction (HAA) motions, is also crucial for walking stability. Biomechanical studies have indicated that the step width and the mediolateral foot placement at the end of each step can be estimated based on the center of mass (CoM), which is assumed to be located at the pelvis. The extrapolated center of mass (XCoM) is obtained by vertically projecting the CoM's position to the ground in the direction of its velocity. The present study is to develop a novel, high-power, self-balancing, and passively and software-controlled actively compliant hip exoskeleton that can assist with movement and maintain balance in both the sagittal and frontal planes.}, booktitle={2017 International Symposium on Wearable Robotics and Rehabilitation (WEROB)}, author={Zhang, T. and Huang, He}, year={2017}, pages={23–24} }