Position control considering passive stiffness of rubberless artificial muscle antagonistic drive system

Abstract

This paper describes position control considering passive stiffness of an antagonistic drive system using a rubberless artificial muscle. The rubberless artificial muscle is a pneumatic actuator similar to a McKibben type artificial muscle. The artificial muscle has a passive compliance characteristic that varies with inner pressure. Therefore, the antagonistic drive system can control the antagonistic position with tuning of passive compliance characteristics. As described in this paper, the system can be either rigid or soft according to the compliance characteristic of the actuator. As described herein, this study confirms the variable stiffness characteristic of the rubberless artificial muscle. Furthermore, a mathematical model is derived to show the relation between the passive stiffness and antagonistic force of the system. This report then explains the contraction displacement linearization system (CDLS), which decides the inner pressure based on the contraction displacement and contraction force. The CDLS performs linearization of the nonlinear characteristics of contraction displacement. The possibility of realizing the antagonistic position control with tuning passive stiffness of the antagonistic drive system was confirmed experimentally.

Detailed Dynamic Model of Antagonistic PAM System and Its Experimental Validation: Sensorless Angle and Torque Control With UKF

“…Therefore,P is obtained from u irrespective of A 0 . The equations of the seesaw motion (8) and the friction model ( 10) can be rewritten with τ − T f = 0 and…”

“…The characteristic compliance of a PAM actuator system plays an important role in its flexibility [7], [8]. [9] noted that the control bandwidth becomes smaller at low pressure, and therefore, PAM control becomes difficult.…”

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.…”

Independent stiffness and force control of antagonistic pneumatic artificial muscles joint

“…Guanghua Zong use the adjusting method to control stiffness of antagonistic PAMs joint [13], handles the stiffness control problem of a manipulator driven by a rubber actuator. Saito N proposed to control position and stiffness simultaneously by using of an antagonist pair of PAMs [14], Reported by the McKibben artificial muscle-activated robot arm with independent joint position and stiffness of the adaptive control.. Xiangrong Shen controlled the stiffness and force of cylinder [15], proposes a approach to the design of a robot actuator with physically variable stiffness. Although such studies provide an effective control regimen for PAM antagonistic joints, they do not achieve the goal of controlling the forces and stiffness of antagonistic PAMs.…”