Impedance control with structural compliance and a sensorless strategy for contact tasks

Abstract

This study proposes an actuator whose design relies on a coordinated approach to control and hardware design: impedance control is supplemented with the introduction of a spring-damper coupler between the actuator and reference (ground). The coupler between the actuator and reference has the effect of further reducing the impedance apparent to the environment. Unlike traditional series elastic actuation, where the deformation of a physical spring coupler introduced between an actuator and link is fed back for control, our coupler is located between actuator and reference and its deformation is not fed back for control. The proposed control further employs time-delay estimation to account for the system dynamics that include both the physical and virtual couplers and to realize accurate and robust control over end-effector position and contact forces. We present a simple method for estimating interaction forces and regulating the contact force without a priori knowledge of the environment. A numerical simulation demonstrates the efficacy of the proposed approach.