Large stroke and high precision pneumatic-piezoelectric hybrid positioning control using adaptive discrete variable structure control

This paper investigates a novel large stroke and high precision pneumatic-piezoelectric hybrid positioning control system that contains a pneumatic servo cylinder and a piezoelectric servo actuator combined in cascade. The pneumatic servo cylinder serves to positioning with high speed and large stroke; the piezoelectric actuator positions in fine stroke for compensating the influence of friction force so as to achieve large stroke, high response and high positioning accuracy. The overall control systems have complex dual-input single-output (DISO). For that, the control strategies of the pneumatic controller and the piezoelectric controller are designed and verified in experiments, respectively, using adaptive discrete variable structure control (ADVSC) theorem. The ADVSC developed in this paper combines self-tuning adaptive control and discrete variable structure control so that the control parameters can be adapted on-line for achieving an optimum sliding surface and reducing the chattering phenomenon of variable structure control. Subsequently, the pneumatic-piezoelectric hybrid positioning control is implemented, which test results clarify that the positioning accuracy of the novel pneumatic-piezoelectric hybrid positioning system can reach 0.1 μm, the resolution limit of the position sensor used in this investigation, with high response for the positioning strokes of 10 mm, 180 mm and multi-step 0-50-100-50 mm.