Observer-based backstepping control of a 6-dof parallel hydraulic manipulator

• Integrate the mechanical part and hydraulic dynamics of Stewart platform in the backstepping control scheme.
• The proposed nonlinear observer provides a real-time forward kinematics solution for parallel manipulators.
• The proposed scheme can achieve direct posture control.
• The rigorous stability analysis for overall system is presented.
• Comparisons with a well-tuned platform׳s PID controller and sliding mode controller in the experimental results.
• The case with extra payload demonstrates the performance of the controller being applied on driving simulator.

In this paper, a backstepping control strategy is proposed to control the 6-dof parallel hydraulic manipulator (Stewart platform) while incorporating an observer-based forward kinematics solver. Different from conventional control methods, the proposed control considers not only the platform dynamics but also the dynamics of the hydraulic actuator. One feature of this work is employing the observer-based forward kinematics solution to achieve the posture tracking goal successfully only with the measurement of actuators lengths. When designing the controller of hydraulic actuators, the friction compensation is applied to improve the performance. The stability of the whole system is thoroughly proved to ensure convergence of the control errors. Simulations and experimental results are presented to validate the hereby proposed results.