Tao Guoliang

Zhu Xiaocong

Cao Jian

State Key Laboratory of Fluid Power
Transmission and Control,

Zhejiang University,

Hangzhou 310027, China

Abstract: A parallel manipulator joint driven by three pneumatic muscles and its posture control strategy are presented. Based on geometric constraints and dynamics, a system model is developed through which some influences on dynamic response and open-loop gain are analyzed including the supply pressure, the initial pressure and the volume of pneumatic muscle. A sliding-mode controller with a nonlinear switching function is applied to control posture, which adopts the combination of a main method that separates control of each muscle and an auxiliary method that postures error evaluation of multiple muscles, especially adopting the segmented and intelligent adjustments of sliding-mode parameters to fit different expected postures and initial states. Experimental results show that this control strategy not only amounts to the steady-state error of 0.1º without overshoot, but also achieves good trajectory tracking.

Key words: Pneumatic muscle  Parallel manipulator joint  Sliding-mode controller   Posture control