Abstract
This paper describes one of the control methods which attain robust positioning performances of a parallel manipulator. Pneumatic cylinders are employed as a driving actuator by focusing on its rectilinear movement which makes it easy to construct a manipulator and high power/weight ratio and so on. In positioning control schemes of a parallel manipulator, almost of them are based on the inverse kinematics, a map from a position/orientation of the platform to displacement of links, since inverse kinematics has an analytic solution contrary to the serial link manipulator. This method has an advantage that a complicated manipulator's dynamics is not needed, but the influences of interaction force and manipulator's dynamics, which act as disturbances on the positioning servo, must be lowered to improve control performances. Basically pneumatic actuator is controlled by pressure, therefore if pressure would be generated so as to cancel the influence of disturbances, then disturbances would not affect on the control performances entirely. Therefore positioning control system employing 2 disturbance observers is constructed based on the pressure control. If dynamics of the platform could be adjusted based on the hand coordinate system, its field of use would be spread out extremely. In this study, a control system based on the hand coordinate system is also constructed. The validity of these control systems are confirmed through some experiments and analysis.
