Adaptive robust output force tracking control of pneumatic cylinder while maximizing/minimizing its stiffness

MENG De-yuan(孟德远), TAO Guo-liang(陶国良), BAN Wei(班伟), QIAN Peng-fei(钱鹏飞)

(State Key Laboratory of Fluid Power and Mechatronic Systems (Zhejiang University), Hangzhou 310027, China)

Abstract:The system considered in this work consists of a cylinder which is controlled by a pair of three-way servo valves rather than a four-way one. Therefore, the cylinder output stiffness is independently controllable of the output force. A discontinuous projection based adaptive robust controller (ARC) was constructed to achieve high-accuracy output force trajectory tracking for the system. In ARC, on-line parameter adaptation method was adopted to reduce the extent of parametric uncertainties due to the variation of friction parameters, and sliding mode control method was utilized to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbance. Furthermore, output stiffness maximization/minimization was introduced to fulfill the requirement of many robotic applications. Extensive experimental results were presented to illustrate the effectiveness and the achievable performance of the proposed scheme. For tracking a 0.5 Hz sinusoidal trajectory, maximum tracking error is 4.1 N and average tracking error is 2.2 N. Meanwhile, the output stiffness can be made and maintained near its maximum/minimum.

Key words:servo-pneumatic systems; output force control; cylinder output stiffness; sliding mode control; adaptive control