A nonsingular terminal sliding algorithm for swing and stance control of a prosthetic leg robot

Abstract

The design of swing and stance control for path following of a prosthetic leg robot subject to uncertain dynamics and exterior disturbances is a serious issue, which affects the development of wearable robots. In wearable robots, parametric uncertainties and external disturbances are unavoidable problems. This problem is associated with practical engineering of wearable robots due to the actual swing and stance situations, where the combination of contact and tracking control objectives is highly complex. This paper proposes two novel finite-time controllers for a prosthetic leg robot with three degree-of-freedom. A prosthetic leg robot should emulate hip vertical displacement, thigh and knee angles according to human gaits in the presence of ground friction force and external disturbances. For the swing phase, a nonsingular fast terminal sliding mode control method is designed to track the reference trajectories fast and in the finite time without any non-singularity problem and chattering phenomenon. Moreover, the other designed controller can deal with input saturation by using a hyperbolic tangent function and an auxiliary system. For the stance phase, an impulse momentum sliding mode control scheme is introduced which allows the prosthetic leg robot to emulate the mechanics of human walking. Using the proposed controller, the robot imitates the patient momentum exchange and weight transfer in the stance phase. The proposed techniques cause the transition between contact and off-contact phases and contact phase itself. Finally, the simulation results verify the efficiency of the provided technique. In our future work, we will focus on employing this technique to a practical prosthesis legged robot.