Contour Control Of Multi-axis Global Task Coordinate Frame Of Direct Drive H-type Platform

The direct drive H-type platform,which is composed of three permanent magnet linear synchronous motors(PMLSMs)has been widely used in industry due to its advantages of fast dynamic response and high precision machining.However,maintaining high contour accuracy in large curvature trajectory tracking is difficult due to the strong mechanical coupling between the redundant axes of the servo motion platform.To address this challenge,a contour control strategy is proposed in which the rigid-flexible coupling model of servo platform is established in a multi-axis global task coordinate frame(MGTCF)and combined with adaptive equivalent integral sliding mode control(AEISMC).The results demonstrate that the proposed approach can significantly improve the accuracy of contour tracking and the robustness of the system.In the actual motion of the direct drive H-type platform,the PMLSMs at both ends of the crossbeam are affected by the transverse reciprocating motion of the X-axis PMLSM actuator at the crossbeam.They are also affected by the load disturbance,the unbuilt modulus of the platform and other uncertain nonlinear factors,which leads to the dynamic mismatch of the two longitudinal PMLSMs and the deflection of the crossbeam.To capture these complex interactions,a three-degree-of-freedom rigid-flexible coupling model of the direct drive H-type platform based on the generalized coordinate system is established,the rotation mode of the crossbeam is defined and the complete dynamic constraint relationship between the driving axes is established.The positioning mode of the motion point at the platform model in the generalized coordinate system is given.Since the three-degree-of-freedom platform dynamic model does not match the traditional global task coordinate frame(GTCF),a multi-axis global task coordinate frame model based on the rigid-flexible coupling model of direct drive H-type platform is proposed in this thesis.In order to solve the problem of positioning point deviation,the curvature axis is introduced on the basis of the original contour error axis and the tracking path axis of GTCF,which ensures that the dynamic model of the platform is consistent with the MGTCF degree of freedom of the contour error calculation model.At the same time,taking the deflection angle of the crossbeam and the deflection angle of the coordinate axis as the performance index,the position coordinates of the motion point can be further defined in the contour error calculation model.MGTCF solves the constant constraint that the actual positioning point of GTCF is limited by its projection point along the normal direction of the desired profile,and modifies the local non-orthogonal quantity caused by incomplete decoupling between the axes.At the same time,an integral sliding mode is used as the contour controller to compare the contour tracking performance of MGTCF and GTCF in the expected trajectory with large curvature.The simulation results show that the tracking performance of MGTCF is better than that of GTCF in large curvature profile control.In order to compensate the unbuilt modulus in the dynamic model of the direct drive H-type platform and restrain the uncertainty of system parameters and uncertain nonlinear disturbance,the system adopts a contour control strategy combined with adaptive equivalent integral sliding mode.The simulation results show that the modeling method and control strategy proposed in this thesis can fully improve the contour tracking performance of the platform and ensure the robustness of the system.