The Study On Anti-Load Disturbance Control Strategy For Parallel 6-DOF Platform

Because of strong bearing capacity,low motion inertia,large structural stiffness and high motion accuracy,the parallel 6-DOF platform has been widely used in motion simulators,parallel machine tools,parallel robots,ultra-precision machining equipment and other equipment.The existing research indicated that,in the process of the parallel 6-DOF platform working,the load of each drive rod is changing with the posture and load of the move platform constantly.As for motor-drive parallel 6-DOF platform,the load disturbance on the drive rod will directly affect the motor and impact rod's position output accuracy,which will cause the performance of the parallel 6-DOF platform decreases.In order to eliminate the impact of load disturbance on the platform,an anti-load disturbance control strategy for parallel 6-DOF platform was proposed.In this paper,the mechanical structure characteristics of the parallel 6-DOF platform are introduced.The mathematic relation between the stretching amount of the driving rod and the pose of the moving platform was established.At same time,the forward kinematics solution method was proposed by using the Newton-Taylor expansion method.Thus,kinematics model of platform was established.Then,the dynamic model of platform was established by using the Newton-Euler dynamic modeling method.The load's mathematical expression on each drive rod was derived and the variation law of the load on each drive rod was analyzed.Next,a three-closed-loop control system based on a second-order nonsingular terminal sliding mode load observer(SNTSMO)was proposed for the drive motor of parallel 6-DOF platform.The SNTSMO was designed to observe the torque output error,and then torque error can compensate into the current loop to reduce the speed fluctuation caused by load disturbance and enhance the anti-load disturbance ability of drive rod.Beside it,an incremental PID controller was designed for the parallel 6-DOF platform and the closed-loop control system of platform was built.Finally,the simulation model of the parallel 6-DOF platform was established using Matlab/Simulink and the anti-load disturbance control strategy we proposed was introduced into the simulation model.The simulation results show that the anti-load disturbance control strategy we proposed can reduce the influence of load disturbance on the motor-driven parallel 6-DOF platform and improve the working accuracy of the motor-driven parallel 6-DOF platform.It provides an important reference for the theoretical research and engineering application of the high performance parallel 6-DOF platform control system.