Contact and tracking hybrid control with impulse-momentum sliding surface and terminal sliding mode

The control system proposed in the paper is motivated by robotic testing of prosthetic legs, where a test robot is used to emulate the mechanics of walking. Previously, robust trajectory tracking of walking profiles was used on the test robot’s hip axes, both for swing and stance phases. For the stance phase, a tracking controller does not reproduce the dynamics of weight transfer and release during the swing-stance transitions of human walking. To address this problem, a novel contact mode controller is proposed which allows the test robot to emulate weight transfer and momentum exchange in the stance phase. The swing phase controller is still designed for tracking, but introduces a fast terminal sliding mode controller for rapid convergence to reference swing trajectories with small chattering. This paper introduces the concept of an impulse-momentum sliding surface and develops the control system for a one-degree-of-freedom electromechanical system moving in a vertical axis. A simulation study and a successful real-time implementation are described that illustrate the practical validity of the concept, which can be used in conjunction with more realistic walking models.