| The high precision three-axis turntable is a kind of semi-physical simulation platform used for performance test of inertial navigation equipment.It can reduce the research cost of related components by simulating the air attitude of aircraft.In order to ensure the test accuracy of inertial navigation equipment,the turntable needs high control precision.Due to the nonlinear interference factors such as dynamic coupling and friction between the frames of the three-axis turntable,it is necessary to design a controller with high control precision and good low-speed performance.On the other hand,the system error and installation error of the circular grating will affect the accuracy of feedback of angle,so it’s necessary to adopt appropriate fitting method to calibrate the error of the circular grating.Focusing on the above two problems,thesis takes the high precision threeaxis turntable as the research object and aims to ensure the control accuracy and lowspeed performance.Relevant researches were carried out:(1)The mathematical model of torque motor and driver used in turntable was derived.The common error sources of turntable control were analyzed.The dynamics analysis of the three-axis turntable was carried out,and the coupling torque formula between the frames was deduced.The dynamics model of the three-axis turntable was built in simulink,and the dynamics decoupling simulation was carried out.It provided the basis of simulation for the research of control algorithms.(2)Aiming at the problem that the it is difficult to ensure the position accuracy and low-speed stability under the influence of various interference torques,the principle of active disturbance rejection control was analyzed first,and then a linear active disturbance rejection control and PID switching control algorithm was improved.In this algorithm,linear active disturbance rejection control and PID control can realize dynamic switching by designing position and speed switching conditions,and the control quantity will not change dramatically.The improved linear active disturbance rejection and PID switching control was applied to the turntable control,which gived full play to the respective characteristics of PID control and linear active disturbance rejection control,and improved the low-speed stability and dynamic performance of the system.(3)Aiming at the calibration problem of angle measurement errors of rotary circular grating,thesis firstly analyzed the source of the errors of angle measurement of circular grating,and then applied harmonic model to the least square fitting of the errors,including linear least square method and nonlinear least square method based on frequency domain analysis of angle measurement errors.An improved piecewise linear fitting method was proposed.The whole fitting interval was segmented by adaptive fitting interval growth function,and each segment was fitted with a polynomial of different order.The number of segments was reduced and the fitting efficiency and accuracy were improved.(4)The control strategy and calibration algorithm were verified by experiments.The rotary table test body was controlled by the developed high precision three-axis turntable control software,and the turntable position accuracy,speed accuracy,stability and system bandwidth were tested respectively.The results show that the designed control algorithm meets the requirements of relevant technical indexes.The angle measurement errors of circular grating were collected by optical tube and 23-sided prism.Calibration experiments were carried out with different calibration algorithms respectively,and the effectiveness of the fitting algorithms was verified by experiments. |
