Fast terminal sliding mode control of harmonic drive system considering nonlinear attributes

Precision positioning performance is degraded by nonlinear effects of dynamic error and flexibility with harmonic drive systems. To compensate for dynamic error in the presence of nonlinear flexibility in high precision tracking, the nonlinear dynamic equation with dynamic error of harmonic drive is established by Lagrange method. Then, it is inverted to the state equation for control design. The nonlinear term is introduced into the design of the sliding mode based on the idea of terminal sliding mode control. Then, Fast terminal sliding mode controller is designed and the asymptotical stability of the system is guaranteed using Lyapunov method. The control scheme not only guarantees the convergence of the output tracking error in a finite time period but keeps the state of the system always at the terminal sliding surface. Simulation results show that the controller realize complete compensation of output errors with fast transient response. It is verified the feasibility of the control scheme.