A powered lower limb exoskeleton supplemented with FES for gait assistance in paraplegic patients

Abstract

This thesis presents the design, implementation and testing of a lower limb exoskeleton that allows paraplegic patients to stand and walk. The device is supplemented with functional electrical stimulation (FES) at the quadriceps muscles to obtain the physiological benefits provided by FES and increase the extensive torque available at the knee joints. The wearable robot is a five link mechanism consisting of a hip piece that is attached around the lower torso, two thigh pieces and two shank pieces respectively strapped to the thighs and shanks of the user. The device has powered hip and knee joints with all the actuation and transmission contained in the thigh pieces. The thigh pieces also contain the distributed embedded system while the battery is carried in the back of the hip piece. The device is designed to be used with ankle foot orthoses to stabilize the ankle joints and forearm crutches that allow the user to maintain the balance. All the sensors and instrumentation are contained in the device that is controlled by the user by postural commands that affect the center of pressure of the user-robot system. The general control is structured in two levels: the lower level is an angular position PD controller around the joints while the higher level is a state machine that coordinates the four joints to perform the different maneuvers. The device was tested by a T10 ASIA A (complete) paraplegic patient who by using the exoskeleton was able to perform sit to stand, stand to sit and walking maneuvers. When compared with long leg braces the efficacy of the device was significantly high and the walking difficulty perceived by the user was significantly less. The energy provided by the motors in sit to stand and stair climbing maneuvers was significantly reduced when FES was used.