Abstract
The pneumatic muscle actuator (PMA) has been widely applied in the researches of rehabilitation robotic devices for its high power to weight ratio and intrinsic compliance in the past decade. However, the high nonlinearity and hysteresis behavior of PMA limit its practical application. Hence, the control strategy plays an important role in improving the performance of PMA for the effectiveness of rehabilitation devices. In this paper, a PMA-based knee exoskeleton based on ergonomics is proposed. Based on the designed knee exoskeleton, a novel proxy-based sliding mode control (PSMC) is introduced to obtain the accurate trajectory tracking. Compared with conventional control approaches, this new PSMC can obtain better performance for the designed PMA-based exoskeleton. Experimental results indicate good tracking performance of this controller, which provides a good foundation for the further development of assist-as-needed training strategies in gait rehabilitation.
Highlights
The knee joint is the most susceptible joint of the lower limb joint for human beings [1]
Movement impairment of knee joint, which is commonly characterized by spastic muscle tone or leg muscle weakness, may have a great influence on the activities of daily life (ADL)
The soft actuators such as the pneumatic artificial muscles (PMA), shape memory alloys, and the electroactive polymer actuators play an important role in the design of soft exoskeletons [15,16,17,18]
Summary
The knee joint is the most susceptible joint of the lower limb joint for human beings [1]. The utilization of soft actuators, soft structural materials, and soft sensors have improved the performance of exoskeletons [10,11,12,13,14] The soft actuators such as the pneumatic artificial muscles (PMA), shape memory alloys, and the electroactive polymer actuators play an important role in the design of soft exoskeletons [15,16,17,18]. To improve the accuracy of joint trajectory tracking for a PMA-based exoskeleton, various control strategies have been studied in recent decades. Shen applied an SMC to the designed PMA-based servo system to obtain robust control [33]. Based on the designed knee exoskeleton, a novel PSMC is introduced to obtain the accurate trajectory tracking. Compared with conventional control approaches, this new PSMC can obtain better performance for the designed PMA-based exoskeleton.
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