液驱并联机构多维力加载系统滑模解耦控制

Sliding mode decoupling control for electro-hydraulic multidimensional force loading system with parallel mechanism

针对液驱并联机构多维力加载系统频响低、耦合力强、参数时变和模型摄动的问题,提出一种改进的滑模控制策略以提高系统响应速度与输出精度。首先,建立多维力加载系统刚柔混合动力学模型与液压系统模型,推导不同位姿下系统闭环传递函数,分析各通道间耦合力产生机理。其次,考虑多维力加载系统模型实际质量矩阵和刚度矩阵的不确定性,提出名义矩阵补偿方法。基于系统补偿模型,构建滑模控制器名义模型,进而利用力跟踪误差确定控制器二阶滑模面,探索滑模面收敛条件,分析控制参数对力跟踪误差收敛速度的影响。在此基础上,采用线性化反馈技术,确定滑模控制律。最后,根据李雅普诺夫定理分析提出的控制结构稳定性,得到渐进稳定的充分条件。研究结果表明:在工作频段,相较于传统PI控制,滑模控制的多维力加载系统通道间耦合力范围减小86.5%,耦合力矩范围减小66%;广义质量矩阵和广义刚度矩阵的非对角性是多维力加载系统产生耦合力的主要因素,改进的滑模控制器能够克服多维力加载系统的建模误差,提高系统的动态响应速度及对外部扰动的鲁棒性。

Aiming at the problems of low frequency response,strong coupling force,time-varying parameters and model perturbation in the electro-hydraulic multi-dimensional force loading system with parallel mechanism,an improved sliding mode control strategy was proposed to improve the response speed and output precision of the system.Firstly,the rigid-flexible hybrid dynamic model and hydraulic system model of the multi-dimensional force loading system were established,and the closed-loop transfer function of the system in each posture was derived.Then the coupling force generation mechanism between each channel was analyzed.Secondly,considering the uncertainty of the actual mass matrix and stiffness matrix of the multi-dimensional force loading system model,a nominal matrix compensation method was proposed.Based on the system compensation model,the nominal model of the sliding mode controller was constructed.Then the second-order sliding mode surface of the controller was determined by the force tracking error.Furthermore,the convergence conditions of the sliding mode surface was explored.The influence of the control parameters on the convergence rate of the force tracking error was analyzed.On this basis,the sliding mode control law was determined by linear feedback technology.Finally,according to Lyapunov theorem,the sufficient condition of asymptotic stability was obtained.The results show that in the working frequency band,compared with the traditional PI control,the coupling force range and the coupling torque range among the channels of multi-dimensional force loading system by sliding mode control reduce by 86.5%and 66%,respectively.The non-diagonality of generalized mass matrix and generalized stiffness matrix is the main factor of coupling force in multi-dimensional loading system.The improved sliding mode controller can not only overcome the modeling error of multi-dimensional loading system,but also improve the dynamic response speed of the system and the robustness against the external disturbances.