Adaptive Interactive PID Supervisory Control of the Macro-micro Parallel Manipulator

Abstract

The supporting,orientating and trajectory tracking mechanism of the five hundred meter aperture spherical radio telescope (FAST) consists of a macro-micro parallel manipulator system. The macro parallel manipulator (feed cabin) driven by the large span flexible cables assures the large reachable workspace,while the micro parallel manipulator (Stewart platform) driven by the delicate electrical cylinders realizes the precision of the end-effector and expands the servo bandwidth. In order to decrease the impact of the flexibility of the macro parallel manipulator on the precision of the end-effector,a decoupled tracking and prediction algorithm based on the principle of parallel mechanisms is presented. This algorithm is used to predicate the future position and orientation of the feed cabin. Then the adaptive interactive PID controller,which utilizes the adaptive interactive algorithm to adjust the parameters of conventional PID controller,is devised as the supervisory controller in the joint space of the Stewart platform. The supervisory controller generates the control commands in the upper level of the electrical cylinders. Besides,in the lower level of the electrical cylinders,the digital servo filters with feedforward are employed to track the desired trajectory accurately. The experiments of the FAST50 m field model validate the effectiveness of the adaptive PID supervisory controller,accompanied with the motion predication of the feed cabin. The macro-micro parallel manipulator system can obtain the satisfactory positioning and orientating precision with the desired tracking velocity.