A Control Strategy for Squat Assistance of Lower Limb Exoskeleton with Back Sensing

While many challenges remain with respect to the mechanical design of the lower limb exoskeleton, it is equally challenging and important to develop effective control strategies. The exoskeleton is a highly human-robot coupled system with a complex dynamic model and working environment, so it is crucial that the controller works in concert with the user intention without relying on imprecise models. This paper proposes a motion controller for a lower limb exoskeleton, aiming to perform collaborative squatting assistance with efficiency and flexibility. This control strategy is designed for our exoskeleton which is equipped with a force sensor on the back. The high-level control is a force-velocity admittance model estimating the human intention by the interaction force, and the low-level control is based on PD closed-loop velocity control with gravity compensation. Through experimental studies conducted with our exoskeleton, the feasibility and effectiveness of the control strategy are demonstrated.