Development of ankle-less active lower-limb exoskeleton controlled using finite leg function state machine

Abstract

An electric-powered lower-limb exoskeleton (HLEX-v2) was developed to provide walking assistance to the elderly. It was semianthropomorphically designed with two passive hip roll/yaw joints and two active hip/knee flexion/extension joints with an ankle-less foot. The gait phases of a pilot were estimated through a shoe insole embedded with two force sensing resistors–one to detect the pilot’s toe-contact and another to sense the heel-contact–to generate assistive torques at each active joint. The estimated gait phase indicated that the proposed controller commanded torques at hip and knee joints to achieve control tasks assigned from a developed finite leg function state machine (FLFSM). In the FLFSM, the controlled leg’s task was determined based on estimated gait phases of the leg itself and the contralateral leg. The impedance control and feed forward torque control were low-level control actions for handling force-interaction with the ground. The currents applied to each actuator were regulated with a PI controller based on current feedback sensing to increase the torque exertion bandwidth of the actuators. The proposed walking assistive torque generation control was implemented on the HLEX-v2. Experimental walking data for the robot were collected to verify the effectiveness of the exoskeleton with the walking assistance scheme.