Disturbance Compensation And Precision Control Techniques Of Tracking Gimbal On Telescope

The research direction of this article is based on 1.2m optical communication telescope in the quantum communication programme of Chinese academy. This telescope has both the quantum communication side and the astronomical observation side. This paper analyzes these factors that will change the precision of telescope. It is to make the telescope system obtain high pointing precision and tracking precision in the quantum communication side and the astronomical observation side. These factors include two fields: inner disturbances and outer disturbances. The inner disturbances have the model uncertainty, the torque fluctuation of motor, friction disturbance, drive backlash and so on. The wind disturbance is mainly the outer disturbance for the ground-based telescope. All of the disturbance factors will deteriorate seriously the tracking and observation performance of telescope system. This article will focus on the disturbance compensation and precision control techniques for the telescope system.At first, the dynamic model of telescope system is founded. And then it emphatically analyzes the three mainly factors that reduce the precision of telescope. The three mainly factors include friction disturbance, wind disturbance and drive backlash. The paper analyzes the influence that these disturbances bring telescope. And it introduces the mainly mathematical models of three disturbances. To restrain the friction disturbance and drive backlash, some compensation and control methods are introduced for the telescope system.A kind of multi-loops control method that combines the Internal Model Control(IMC) with acceleration loop is proposed in this paper. It is to restrain the wind disturbance and friction disturbance. First, it analyzes the meaning and the ability for disturbance restraining of acceleration loop. Then it measures the ability for disturbance restraining of the proposed control method. It is stated that the results of theory analysis are right. Simulatausly, by appling the low frequency disturbance in the telescope system and measuring the performance of telecope. They show that the performance of the proposed control method is better than the traditional double loops control method and the multi-loops control method with acceleration loop. Comparing with the traditional double loops control method, the tracking error of fixed point reduces fivefold when the acceleration loop is introduced. On the basis, the tracking error of fixed point reduces twofold again when the acceleration loop and IMC are introduced simulatausly.Since the acceleration loop needs to install a couple of acceleration sensors, it will increase the cost of system. Therefore, a kind of control method based on improved Extend State Observation(ESO) is proposed to restrain the model uncertainty and friction disturbance in this paper. In theory, it is stated that this control method is convergent. The proposed control method based on improved ESO is used in the telescope experiment platform. The experiments shows that the proposed control method has the better performance than traditional PI control method for reduce the turning error. The maximum turning error reduces thirty percent. Comparing with the linear Active Disturbance Rejection Control(ADRC) method, the maximum turning error reduces eleven percent.When the control method based on improved ESO is used in the system, there are still some bigger repeatability turning errors in the system. On the basis, a kind of Iterative Learning Control(ILC) method based on ESO is proposed in this paper. The ESO is used to change the nonlinear system to the approximate linear system. And the ILC is used to find the best control input signal for the system. The two control methods complement the others’ weakness. According to the experiment results, they show that this kind of control method has the excellent ability to reduce the turning error.Taking into consideration the development tendency of telescope in the future, this paper chooses the brushless DC servo motor and harmonic drive gear as the transmission mechanism of telescope. It analyzes the principle and characteristic of harmonic drive gear. The harmonic drive syetem is introduced detailly in this paper. And we found the dynamic model of harmonic drive system.This paper proposes two position control methods based on double speed loops: double PI speed loops and double PI-ESO speed loops. It is to restrain the nonlinear characteristics of flexibility, backlash and friction. In theory, this paper analyzed deeply the control performance of double speed loops. Nextly, by the simulation for harmonic drive model, it it stated that double speed loops can restrain nicely the deadzone characteristic in the system. Furthermore, to reduce the bigger turning error in the system, this paper uses the ESO to estimate and compensate the nonlinear disturbance. By combining the ESO with double speed loops control structure, it can furtherly enhance the precision of system. Finally, the performance of these control methods are compared in the harmonic drive experiment platform.Finally,this paper introduces the out-field experimental situation of 1.2m quantum communication telescope. These experiments include inhibition experiment of wind disturbance, sine guide experiment and tracking experiment of star.