抄録
A pneumatic actuator tends to be applied to the more rigorous motion control in addition to conventional simple works, and some PID or optimal control pneumatic servo systems have already been proposed. To design these control systems, the mathematical model describing system dynamics must be known beforehand. However, the exact modeling and identification of system parameters are difficult due to various inherent nonlinearities in a pneumatic system. Moreover, the system parameters depend on the operating conditions so strongly that the satisfactory response can not always be obtained with the constant gain controller.
In this study, to cope with these problems an adaptive control scheme, which can adjust its own gains by using estimated system parameters to realize the desired response, is employed in the electro-pneumatic servo system comprising a pneumatic cylinder and electro-pneumatic proportional control valves. The control law is designed with the adaptive pole-placement method applicable to also a non-minimum phase system often encountered in a discrete-time control using a digital computer. The air low stiffness makes a pneumatic system fairly sensitive to frictional or external load force, resulting in a decreased position control accuracy. For dealing with these forces, the conventional adaptive poleplacement control scheme is expanded to consider them as an unknown deterministic disturbance.
From various experimental examinations, the following is verified. The adaptive control can make the pneumatic servo system enough robust to achieve the identical desired response independently of the operating conditions such as a mass load, an operating pressure, a desired position and so on. Further, the effect of considering the disturbance remarkably appears at being subject to the external force. This expanded control method can be satisfied with also the positioning accuracy.
