Large stroke and high precision pneumaticpiezoelectric hybrid positioning control using adaptive discrete variable structure control, Mechatronics, v 15, n 5, June, p 523-545
- M. H. Chiang, C. C. Chen, T. N. Tsou
INTRODUCTION The pneumatic control systems have played the important roles in the industrial automation equipments owing to the following advantages low cost, clean of the working environments, easy in power transfer, and so on. In recent years, high accuracy and high speed systems are growing up rapidly, and are important in high-tech industry. However, the precise position control of a pneumatic cylinder is very difficult due to the compressibility of air, nonlinear behavior of the air flow rate through the servo valve, the friction force between the cylinder and the piston, and the stick slip effect at the low speed of the system. The traditionally pneumatic control systems are only controlled to carry out simple on-off position and speed control by using programmable logic controller. The high precision control cannot be reached through onoff logic controller so that the modern control strategies are essential. Pandian et al  proposed practical design for the position and trajectory control of pneumatic actuators based on the sliding mode control approach. Shih and Ma  developed a control law which combines the sliding mode and modified differential PWM (M-D-PWM) control method to control the position of a pneumatic rodless cylinder. The control accuracy of the pneumatic cylinder is always under 0.1 mm. Furthermore, K.R. Pai and M.C. Shih  designed velocity compensator to overcome the stick-slip effect of the pneumatic table and the pneumatic table has the positioning accuracy of 20 nm. Piezoelectric actuators have been developed in recent years and already applied in pneumatic precision positioning control. Chiang et al  investigated pneumatic-piezoelectric hybrid positioning control system and the positioning accuracy can reach 100 nm. These papers mainly research the horizontal precision positioning control, but fewer papers study the vertical precision positioning control under loading effect. This paper is mainly to study the precision performance of positioning to the vertical pneumatic cylinder under vertical loading. In this paper, the friction force and the vertical loading have the great effect on the positioning accuracy. The hybrid fuzzy sliding mode controller with loading compensator is developed and implemented in the microcomputer to control the position of the vertical pneumatic cylinder under vertical loading in the study. Regarding the simulation of loading force, it can be accomplished by controlling the pressure of the load cylinder using pneumatic proportional valve.