Continuous finite-time output torque control approach for series elastic actuator

Series elastic actuator (SEA) is widely used in robots that intelligently interact with humans, but unavoidably suffer from the influences brought by interactions, such as variations of the payload parameters and external disturbances. In order to address these challenges, this paper proposes a practical finite-time output feedback controller (FT-OFC) along with a finite-time extended state observers (FT-ESO) to generate the desired torque for SEA. Specifically, the dynamics of SEA system is analyzed and transformed firstly, through several coordinate transformations, into an integral-chain form. Based on this, we construct a new FT-ESO to estimate the uncertainties as well as the states of SEA system. Subsequently, a continuous terminal sliding-mode control scheme is introduced to synthesize the control law. Lyapunov-based analysis is provided to demonstrate that the equilibrium point of the closed-loop system is finite-time stable. The validity and superior performance of the proposed method are verified by a series of experiments carried out on a self-built SEA platform. (C) 2018 Elsevier Ltd. All rights reserved.