Research On Modal Decoupling Control For Multi-dimensional Force Loading System Of Electro-hydraulic Drive Parallel Mechanism

With the advancement and development of science and technology,multi-dimensional force loading is widely used in the fields of complex mechanical environment simulation,recurring rehabilitation therapy,and mechanical properties testing of mechanical parts.The electro-hydraulic driven multi-dimensional force loading parallel mechanism has the advantages of strong bearing capacity,high precision,high rigidity,and uniformity of errors,which can meet the requirements of multiple degree of freedom(DOF),different strengths and different loading frequencies.However,the flexible load and the physical space structure of parallel mechanism lead to the strong coupling of the respective output forces of the multi-dimensional force loading system.It is difficult to achieve independent control of the respective channels.Therefore,the force/torque reproduction accuracy is reduced,and the performance of multi-dimensional force loading is affected.This paper proposes a new control strategy,modal space sliding mode controller,which aims to achieve multi-dimensional force loading decoupling in the physical space.The modal space sliding mode controller can effectively compensate the amplitude attenuation and phase lag during the loading process,and suppress the chattering caused by the sliding mode control in the physical space.The main research of this study is as followings:(1)The kinematics forward and inverse solution model of parallel mechanism is established.Considering the flexible load,the dynamic model of rigid-flexible hybrid parallel mechanism is established.A dynamic model of servo valve controlled asymmetric hydraulic cylinder is established.The strong dynamic coupling between the output forces of each DOF is analyzed,which lays a foundation for the establishment of modal space.(2)Considering the load stiffness of the flexible load mapped to each joint space,the modal space is established by using the theory of vibration mechanics.Based on the analysis of the characteristics of each modal channel,the modal space channel conditions required for the decoupling of multi-dimensional force loading in physical space are studied.(3)From the perspective of structural block diagram,how to design a non-diagonal controller matrix in physical space based on modal space PI control is studied.To further improve the tracking performance of each modal channel,combined with the independent design characteristics of each modal channel in modal space,a modal space sliding mode controller is proposed.Using the linearized feedback method,the sliding mode control rate is designed in the modal space.The stability of the modal space sliding mode controller is proved by Lyapunov function.(4)The independent characteristics of each channel in the modal space established in this paper are verified.The decoupling characteristics of multi-dimensional force loading in physical space are verified by the consistent dynamic performance of modal channels.The proposed modal space sliding mode controller that can realize multi-dimensional force decoupling and improve dynamic tracking performance is verified in this paper.