High accuracy eliminating image rotation control system for optical telescope

When an optical telescope tracks dim celestial bodies, the camera requires a long-time exposure to obtain clear target images. Due to the self-rotation of the Earth, for an alt-azimuth telescope, this will result in a rotation of the field of view. To counteract the rotation, an eliminating image rotation mechanism (EIRM) is required. This paper introduces a new EIRM, which is low cost and easy to install. Due to the unavoidable backlash and nonlinearity of stepper motor, the accurate model of EIRM is difficult to obtain. In order to improve the control accuracy of EIRM, a novel control algorithm based on sigmoid function and speed feed-forward is proposed. Control experiments based on proportional integral (PI) control, Fuzzy-PI and proposed controller were conducted, and the results showed that the proposed algorithm has the smallest tracking error. Lastly, the mechanism is installed on a 1.2-meter aperture optical telescope, and the observation results further demonstrate the effectiveness of this method.