Saturated nonlinear control of robots with series elastic actuators

In this paper, two saturated nonlinear control strategies are proposed for regulation of SEA-driven robots based on singular perturbation (SP) and Energy Shaping (ES). The SP-based saturated controller is designed with two saturated control terms for cascaded two subsystems, and the ES-based saturated controller is proposed by a saturated PD control term plus a static gravity compensator. In comparison of the two controllers, the SP-based saturated controller requires the stiffness being relative large, while the ES-based saturated controller requires accurate stiffness knowledge. Satisfaction of the control saturation is guaranteed by using the hyperbolic tangent function in controllers design. Asymptotical control stability is analyzed using the Hoppensteadts Theorem and the Krasovskii-LaSalle theorem, and the control effectiveness is illustrated by simulations and experiments.