HTSD-enhanced decoupled ADRC for Stewart platform via modal space design

Purpose The purpose of this study is to reduce dynamic tracking errors caused by internal coupling and external disturbances in the electro-hydraulic Stewart parallel platform. An enhanced decoupled active disturbance rejection control (EDADRC) method is proposed to improve control performance. Design/methodology/approach First, the kinematic and dynamic models of the Stewart parallel platform are established, followed by a modal analysis. Then, a novel high-order tangent sliding-mode differentiator (HTSD) is designed for active disturbance rejection control (ADRC). Finally, the modal decoupling method is applied to ADRC. Findings Experimental verification shows that the dynamic tracking errors of EDADRC are reduced by 0.617 compared to modal space proportional-integral-derivative (MSPID). The overshoot caused by external disturbances are reduced by 0.953 compared to linear active disturbance rejection control. Originality/value A novel HTSD is constructed using a hyperbolic tangent function to replace the traditional tracking differentiator (TD) in ADRC, significantly enhancing noise suppression and enabling high-quality acquisition of the original signal. For the first time, the modal decoupling method is applied to ADRC to design an EDADRC with stability analysis. This achieves control channel decoupling, simplifies controller parameter tuning and optimization and significantly improves system dynamic response.