An Intelligent Exoskeleton for Lower Limb Rehabilitation

ABSTRACT A lightweight adjustable exoskeleton is designed to exercise human legs of varying size and weights. The exoskeleton is actuated by three DC motors at the hip, knee, and ankle. An experimental setup with motor controllers, power supplies, a controlled board, and a computer is developed for closed loop control. A sliding mode control law is designed and implemented to exercise an articulated mannequin leg. It is shown that the exoskeleton is able to adapt to external forces making it suitable to aid in the human leg rehabilitation process. 1 INTRODUCTION Rehabilitation is a required but difficult process for patients trying to recover the full control of their hips, knees, or other parts of their body. Some of the most important types of rehabilitation include neuromuscular rehabilitation for neutrally impaired patients due to spinal cord injury and muscle/ligament rehabilitation for patients with hip, knee, or ankle replacement surgery. Spinal cord is capable of relearning the ability to walk through proper training even when cut off from the brain [1, 2]. A large proportion of people with spinal cord injury who sustain motor incomplete lesions can regain some recovery in their walking ability. Symmetrical movements of lower extremities consistent with normal physiological gait patterns provide critical sensory cues necessary for maintaining and enhancing walking ability [3]. While procedures such as hip replacement surgery can be very beneficial, the best way to maximize those benefits is through proper rehabilitation. The American Academy of Physical Medicine and Rehabilitation says as Baby Boomers age, the number of total hip replacements is expected to increase by more than 60 percent in the next 30 years. Physical therapy is extremely important in the overall outcome of any joint replacement surgery. The goals of physical therapy are to prevent contractures, improve patient education, and strengthen muscles through controlled exercises. Contractures result from scarring of the tissues around the joint. Contractures do not permit full range of motion, and therefore impede mobility of the replaced joint. A promising solution for rehabilitation of patients with spinal cord injury, those with joint replacement surgery, and many other mobility-impaired patients, is to design exoskeletal devices. It has already been shown that motorized robotic-assisted devices can be very helpful in training individuals to regain their walking ability following motor incomplete spinal cord injury [4]. Exoskeletal devices have the potential to be used during sitting, standing, and walking stages of rehabilitation. The study of the exoskeletal power assist systems was first initiated in the late 1960’s on a 30-DOF full-body exoskeleton which was called Hardiman [5]. Another early suggested exoskeleton was a 7-DOF man-amplifying arm with two-axis (universal) joints [6]. Exoskeletal systems have also been suggested as rehabilitative tools. A driven gait orthosis has been developed that can move patient’s legs on a treadmill [7]. Another device has been developed to provide walking aid for people with gait disorder [8]. This device has a hybrid control system that consists of posture and power-assist control based on biological feedback. The actuators are DC servomotors generating assist moments at the hip and the knee joints. 1 Copyright © 2010 by ASME