Independent stiffness and force control of antagonistic pneumatic artificial muscles joint

Abstract

With the extensive development of the robotics research, the actuator source of the robot has been extensively studied. The traditional motor and cylinder drive have big stiffness, it is easier to hurt the operator. The PAM is more compliance, and it have high force-to-weight ratio and safety[1]. Based on these characteristics, researchers take in-depth study of PAMs. PAM can generate contraction force by compressing gas. It is used in medical, rehabilitation and robotics[2-5]. The first woven PAM was designed by American physician Joseph L. McKibben in the 1950s[6]. In the last decade, international scholars have got some achievements[7]. Ching-ping Chou et al. established the static model of McKibben type PAM[8]. Based on the mathematical model, Repperger et al. designed a nonlinear feedback controller to control the single PAM system[9]. However a single PAM system can't provide simultaneous tension and pressure. So, Caldwell et al. designed a PID controller for controlling the position of a group of antagonistic PAMs joint[10]. Bong-Soo Kang analyzed force characteristic of antagonistic PAMs joint by sliding control[11]. In order to provide compliance to enhance the intrinsic safety of human or robot interaction, several researchers have developed variable stiffness of PAMs. The modulation of actuator output stiffness and force can serve several purposes in robotic applications.

Sensor-less Angle and Stiffness Control of Antagonistic PAM Actuator Using Reference Set

“…In the case of rehabilitation, the stiffness prescribed by physiotherapists changes according to the treatment phase; thus, it must be adjusted step-by-step. There have been several studies on a model-based stiffness or compliance control using a PAM actuator [4,[9][10][11][12][13][14][15][16][17][18], and some of the studies are as follows. Cao et al [16] proposed model-based angle-compliance control to develop a robotic gait rehabilitation device.…”

“…The contribution of this study is that the proposed sensor-less angle/stiffness control method using a UKF represents a novel approach in robotics. Moreover, it does not require any encoder, which previous relevant studies [4,[9][10][11][12][13][14][15][16][17][18] have relied upon, to achieve simultaneous control. This sensor-less angle/stiffness control approach can realize a low-cost, lightweight actuator that ensures safe contact with humans and environments.…”