Study Of Eliminating Image Rotation Control Based On Altitude-azimuth Telescope

Large optical telescope is the important optical equipment for space target detecting and tracking. The Altitude-azimuth mount structure is widely used for its good mechanical properties. But this structure telescope has the field rotation problem in the tracking process. As a result, except the point in the field center, others rotate around the field center in the image. This brings inconvenience for real-time target recognition and image processing afterwards. In order to obtain high quality and real target image, it is necessary to compensate the field rotation of the Altitude-azimuth telescope.Firstly, reasons for the Altitude-azimuth telescope image rotation are studied. The field rotation angle caused by the Altitude-azimuth structure and the reflect mirror system is calculated in the function of altitude angle and azimuth angle of the telescope, so the field rotation angle is obtained. Several commonly used eliminating image rotation methods for telescope are studied. Then the optical elimination method for rotation is applied in this paper. Analyze the properties of the telescope field rotation and put forward the guideline for the eliminating rotation turntable design and control system design. Secondly, commonly used servo controllers at present are analyzed. ARM9core board and CPLD bottom board pattern controller is adopted in this paper. Linux2.6operating system is transplanted to the ARM9platform and the eliminating rotation turntable control is achieved in Linux operating system. The cross compile environment between the host and the controller is built. This provides conditions for device driver and application program development under Linux system. Linux device driver design, application program design and CPLD program design, including PWM wave generation, CPLD bidirectional data bus and serial receiver etc are discussed in detail.Finally, the control system is modeled and system model parameters are identified. The incremental PID control algorithm is adopted and PID parameters are adjusted in MATLAB. The experiments result shows that there exists "dead zone" phenomenon when the velocity passes zero and large speed fluctuation while constant velocity tracking due to the turntable friction. This influences the control precision of the system. First of all the friction model parameters are identified based on LuGre friction model, then the friction compensation is added to the system in this paper, thus the control system precision can satisfy the requirement.