The development of a robotic walk-assist device for rehabilitation in patients with lower extremity paralysis

For people who struggle to walk due to muscle weakness or partial paralysis of the lower limbs, walk-assist devices can help to regain mobility by improving muscle mass and function lost due to disuse. A walk-assist motorized knee joint was built by students at the University of Hartford to be used as a rehabilitative device for repetitive knee extension and flexion. The prototype is composed of a custom-built knee-ankle-foot orthotic with upright supports, mounted around the knee joint. A posterior-mounted electrical actuator contracts and extends when activated by the patient's own electromyography (EMG) signals, collected through sensors within the device. The degree of flexion and extension are controlled by output from an optical encoder, which measures knee joint angle during therapy. EMG activation thresholds varied among subjects (n=4), which requires on-site adjustability to the gain and/or coding to resolve for patient-specific differences in threshold activation. The actuator requires 24 volts of power to drive the device at the desired 25% gait speed (1.20 km/hr) with an error of 2.82+/-0.2° (n=3). The optical encoder had 4.1% error when detecting simulated joint angles between 30° and 120° (n=3). Functional testing of the walk-assist device in the Human Performance Laboratory revealed it can accurately control a desired 30° squatting motion to 28.9°+/-0.9 at a rate of 5.1°/sec, or approximately 27% normal speed. However, there were differences in center of pressure (mm), where a normal squatting motion showed 18% deviation from center of pressure, while the device-driven squat resulted in 65% deviation. This device is an effective and inexpensive solution for physical therapy in patients with lower limb paralysis who aim to regain muscle and improve gait.