A Non-Singular Terminal Sliding Mode Control Approach for a 7 Degree-of-Freedom Hydraulic Manipulator

This paper presents an approach for non-singular terminal sliding mode control of a 7-DOF hydraulic manipulator. Three sliding mode reaching laws including the tan hyperbolic function and a continuous power law are designed, analysed using the Lyapunov stability theory and simulated. The derivation makes use of component-wise notation to aid in coupling the multichannel inputs to the hydraulic subsystem. The performance of three control sliding surfaces, with the coupled dynamics of the manipulator links are investigated. Dynamics of the hydraulic actuator are derived along with analysis of the joint geometry to relate the control inputs to joint torques. The derived analytical model of the manipulator is validated using experimental data. Finally, the three NTSMC variants using the validated 7-DOF model of the hydraulically actuated robot are analysed/compared in MATLAB/Simulink environment.