Research On Finite-time/Prescribed-time Control Of 3-DOF Air-bearing Simulator

In the process of aerospace technology development,in order to reduce the cost of aerospace experiments,a large number of ground simulation experiments need to be carried out in advance.With its low cost,long lasting time and small disturbance,the air-bearing test-bed can effectively verify the effect of the control algorithm on the spacecraft,and become an important part of auxiliary research on spacecraft rendezvous and docking,space target acquisition,satellite formation and other space missions.Compared with traditional asymptotic control,finite-time control has faster convergence speed,stronger robustness and higher convergence accuracy,and is widely used in spacecraft attitude control,robotic arm control and other fields.This paper mainly studies the finite-time control algorithm of the 3-DOF air-bearing test-bed,including Fixed-time Nonsingular Terminal Sliding Mode Control method and Parametric Lyapunov Equation Based Time-Varying Feedback Control method,the convergence time of the latter is given by the designer,and the saturation nonlinear characteristics of the actuator are considered in the design.First,we introduce the experimental environment,working principle and system parameters of the air-bearing test-bed.Then,according to the structure and movement characteristics of the air bearing table,the inertial coordinate system and the body coordinate system were established respectively,the dynamic models under the two coordinate systems were deduced,and the factors that produced the uncertainty of the model were analyzed.Next,we introduce the basic knowledge of finite-time control,design fixed-time controller based on terminal sliding mode for the air-bearing test-bed,analyze the convergence and robustness of the designed control algorithm and conduct simulation tests.Then we introduce the basic knowledge of the Parametric Lyapunov Equation,design a time-varying feedback controller that satisfies the input saturation of the actuator for the air bearing test-bed,analyze the bounded stability with interference,and conduct simulation tests.Finally,after completing the preparatory work such as thrust distribution and sensor data filtering,the typical motion forms of the air bearing test-bed including fixed point,straight line and ellipse are tested,and the control effect of the control algorithm is compared.The test results show that the two control algorithms have strong anti-interference and high tracking accuracy.In the PLETFC test,the output of the controller never exceeded the saturation limit,the control process was stable,the switching loss of the actuator was small,and the fuel cost was small.FNTSMC converges faster in fixed-point tests,but its control effect depends on the selection of parameters,and the controller output will be saturated briefly at the initial moment.