Study On Control Method Of Three-axis Turntable Servo System Based On Decoupling And Sliding Mode Control

Three-axis turntable is the special test equipment for inertial navigation device, itsaccuracy directly determines the accuracy of inertial navigation device which influences theperformance of various types of spacecraft, and it has great importance to the nationalaeronautics and space cause. With the development of aerospace technology, the demandfor the performance of the aircraft and weapons has become higher and higher, so theaccuracy of the inertial navigation devices has higher requirements. The three-axis turntable,as the test device of the inertial navigation device, requires higher precision than the devicebeing tested; it also faces the challenges of high precision, high acceleration.When more than one axis of three-axis turntable is moving at the same time, the framewill produce centrifugal force and Coriolis force which will influence each axis throughtorque and reaction torque. As a result, the three-axis turntable has become a complexsystem with nonlinear coupling which is difficult to control; it will reduce the dynamicperformance and the accuracy of three-axis turntable. Therefore, the decoupling ofthree-axis is very important to the performance of turntable. Firstly, the mathematicalmodel of three-axis turntable is set up using the knowledge of dynamic, in order to obtainthe differential equations of three-axis turntable. Aiming at the above problems, we design adecoupling control law based on feedback linearization, and use the Simulink to build thesystem model; it can be seen from the simulation results, the nonlinear decoupling controllaw proposed in this paper has a good effect, which can limit the coupling effect in anacceptable range; so, the three-axis turntable is divided into three independent SISOsystems.Secondly, a time-vary sliding mode control algorithm based on the mathematicalmodel is designed; replacing traditional sliding mode surface with time-vary sliding modesurface which makes the system state is always moving in the sliding mode surface,eliminating the problem of weak robustness in the reaching phase of traditional slidingmode control. We introduce the integral term into the design which can effectively weakenthe chattering and reducing the steady state error. And we divide time-varying slidingsurface into two parts which can velocity up the response of system. Finally, the controlalgorithm proposed in this paper is verified by experiments on three-axis turntable, theresults of the experiments are compared with PID control and conventional sliding mode control. The experimental results show that: compared with PID control and conventionalsliding mode control, this algorithm can decouple the system and track the reference signalfaster with better robustness.Thirdly, an iterative learning control algorithm based on the mathematical model isdesigned; and considering the situations of parameter uncertainty and parametertime-varying, in order to improve the precision during the period of tracking periodicanticipant input, the method of parameter adaptive is introduced; the convergence analysisof the adaptive parameter iterative learning control algorithm is carried out; finally, theexperiments are carried out on the three-axis turntable in order to verify the controlalgorithm proposed in this paper. Compared with the parameter fixed iterative learningcontrol law, the turntable can track the target signal faster and has a stronger robustness tothe uncertain disturbance.