The Study On Tracking And Control Technology Of Optical Telescope For Quantum Communication

As the key technology in a telescope project of Chinese academy of sciences, the tracking precision and speed stability of the tracking and control system of optical telescope for quantum communication, determines the stability of satellite-to-ground quantum communication link. Based on a 1.2m aperture telescope developed by the institute of optics and electronics, the main factors influencing the speed stability of the telescope tracking and control system were analyzed, and the corresponding compensation method and control strategies were put forward.The establishing process of quantum communication link was discussed. The component units, the working principle of each unit and the role each played in the telescope coarse tracking control system were analyzed in detail. The design of controller hardware platform of the telescope was introduced. And the measuring method of controlled plant and the block diagram of coarse tracking control system is given. From disturbance causes, existing disturbance compensation technology, problems existing in the compensation technology and the influence of the disturbance to the speed stability of the telescope, respectively, the encoder subdivision error and friction torque disturbance are analyzed.For the problem that non-linear photoelectric encoder subdivision error directly influences the telescope tracking accuracy and speed stability, a position measuring method based on subdivision error compensation algorithm was proposed. Compare and analysis the existing encoders, and one type encoder was selected. The angle measuring principle of the grating moire fringe technology and subdivision technology was discussesed. Mathematical analysis was done for subdivision signals. Combined with practical engineering experience, six types of subdivision error sources were summed up. Further mathematical analysis on subdivision error sources was done, and that there is a proportion relationship between subdivision error sources and subdivision signals in angle period was concluded, which can be used for the determination of error sources. Subdivision error compensation algorithm based on the position control system was put forward. And the infulence of subdivision error on the telescope control system was analyzed. And two types of telescope coarse control system model was proposed, the Model I: the subdivision error compensation algorithm applying only to the of the speed loop of the controller; Model II: the subdivision error compensation algorithm was applied both in the speed loop and position loop at the same time. Both models were analyzed and compared. In actual engineering, Elevation exists arcsec level jitter problem. The method that analyze the jitter problem from the time domain, frequency domain and spatial domain respectively was put forward. The characteristics of this disturbance was found out. Combined with proportion relationship between subdivision error sources and subdivision signals in angle period, DC subdivision error compensation was proposed. In the telescope elevation tracking system, the subdivision error compensation model II wass carried out, a maximum position error reduced by half.In view of the nonlinear friction torque reducing the speed stability of the optical quantum telescope, a high-precision LuGre parameters identification method based on PSO is proposed and its application model is given. The Characteristics of friction and the existing friction models were analyzed and the LuGre model is chosen as the compensation model of friction through comparison. A high-precision disturbance observer measuring method of friction torque is proposed. Then, particle swarm optimization(PSO) algorithm was given in detail, and the method of LuGre friction model parameters identification using PSO was proposed. Finally, combined with LuGre friction model, high-precision disturbance observer measuring friction torque and PSO LuGre friction model parameters identification algorithm, a new compensation method was put forward and its corresponding friction torque compensation controller is designed. Friction torque compensation controller was applied to the telescope azimuth control, and reverse motion maximum tracking error is only 40.6% of the tracking error before compensation, while the positive movement maximum tracking error become 34.5% of the racking error before compensation at low speed or zero-crossing.In order to enhance the disturbance rejection ability and speed stability of optical telescope, a new control strategy of fuzzy sliding mode control(FSMC) was put forward. SMC theory and its invariance to disturbance was given and proved. Main solution was given for the chattering problem of SMC. Then, the fuzzy control system theory and constituent part was studied. As the controlled plants, a SMC controller is designed based on the servo platform of Azimuth and Elevation.And a sliding mode controller based on fuzzy controller switching gain adjustment was designed. With telescope azimuth as the controlled plant, the measured the subdivision error and friction torque were input into as a disturbance. The designed FSMC was applied to Azimuth. Through simulation, the FSMC designed in this paper can be used to enhance the system ability to resist interference and restrain the chattering.Through actual test and simulation, two kinds of disturbance compensation method and one kind control strategy was proposed, which improved to be effective in disturbance rejection and speed stability for tracking and control system of the optical telescope for quantum communication, and have reference value for other control platforms.