面向接触力调节的六自由度Stewart平台导纳-ESO固定时间滑模控制方法

Admittance-ESO-Based Fixed-Time Sliding Mode Control Method for Contact-Force Regulation of a Six-DOF Stewart Platform

摘要: 针对六自由度(6-DOF) Stewart平台在任意固定法向单侧接触中的跟踪精度下降和接触力峰值问题，提出导纳–扩张状态观测器固定时间滑模复合控制方法。导纳外环将法向力误差转化为位姿修正，固定时间滑模内环跟踪修正参考，扩张状态观测器(ESO)估计并前馈补偿加速度域集总扰动。考虑小误差重构和观测残差，将收敛结论限定为原点邻域内的实用收敛。在统一MATLAB框架下，将该方法与PD、传统滑模控制(SMC)和不含ESO的固定时间滑模控制(FT-SMC)进行自由空间、扰动、接触及参数不确定性对比。结果表明，所提方法在外扰以及动平台质量、转动惯量和支链质量同时增加10%的参数失配工况下Z向RMSE均为四种方法中最低；标称接触峰值由PD + 导纳的101.85 N降至71.76 N，末0.5 s平均绝对力误差趋近于零。FT-SMC类方法主要降低接触峰值，ESO主要改善外扰和平台参数失配下的跟踪精度。

Abstract: To address the degradation of tracking accuracy and the increase in contact force peaks of a six-degree-of-freedom (6-DOF) Stewart platform during arbitrary fixed normal unilateral contact tasks, an admittance-extended state observer (ESO)-based fixed-time sliding mode composite control method is proposed. The outer-loop admittance controller converts the normal force error into pose corrections, while the inner-loop fixed-time sliding mode controller tracks the modified reference trajectory. The extended state observer (ESO) estimates the lumped disturbances in the acceleration domain and provides feedforward compensation. Considering the reconstruction of small errors and observation residuals, the convergence property is established as practical convergence within a neighborhood of the equilibrium point. Within a unified MATLAB simulation framework, the proposed method is compared with proportional-derivative (PD) control, conventional sliding mode control (SMC), and fixed-time sliding mode control without ESO (FT-SMC) under free-space motion, external disturbances, contact conditions, and parameter uncertainties. The results demonstrate that the proposed method achieves the lowest RMSE in the z-direction among the four methods under external disturbances and parameter mismatch conditions, where the moving platform mass, rotational inertia, and limb masses are simultaneously increased by 10%. For the nominal contact condition, the peak contact force is reduced from 101.85 N obtained by the PD plus admittance controller to 71.76 N, and the mean absolute force error over the final 0.5 s approaches zero. The FT-SMC-based methods mainly contribute to reducing contact force peaks, whereas the ESO primarily improves tracking accuracy under external disturbances and platform parameter mismatches.