A Study of a PMAC-Based Astronomical-Telescope Control System and Its Application

A large-aperture astronomical telescope is a precision instrument and it is a great challenge to achieve needed performance of its control system. As the core unit the servo controller determines the performance of the control system. In this paper we describe a PMAC-based auto-control system of motion of an astronomical telescope. In particular, we have first studied the principle of PMAC servo control, the methods of tuning PID parameters, and the principle of a PMAC-based motion control system of an astronomical telescope. Based on the study we have designed the software and hardware of a PMAC-based motion control system of an astronomical telescope. The main characteristic of our auto-control system is that its servo control system uses a combination of the traditional PID feedback control algorithm and forward-feeding control algorithm, so that influences of external disturbances are effectively reduced. This makes the system to perform excellently under dynamic and static conditions. In addition, different methods of tuning PID parameters, such as the step-function tuning and the method combining velocity-measurement and step-function tunings,can yield satisfactory results. The control system overall has a good adaptability either to different driving motors or to different components for measurement of shaft angles. The control system has been applied to the 2.16m Astronomical Telescope at Xinglong. In this application the control system uses the IPC+PMAC double-CPU hierarchical control method. The method achieves telescope-interface operation/control through an industrial personal computer under a VC++ platform. Certain PMAC Pcomm32 interface functions are called by the method for these. The self-adaptive algorithm for adjusting PID parameters as incorporated in the system ensures stability of the system in its high-speed running mode, as well as high-level accuracies and efficiencies in its low-speed running mode. Our research and operational practice show that our telescope control system based on the PMAC has high control accuracies and fine versatility. We expect it to be usable in a variety of astronomical-telescope control systems.