Powered Orthosis for Lower Limbs -Its Structure and Control-

Abstract

This paper describes a powered orthosis for lower limbs which restores the gait of locomotion of disabled persons, such as paraplegics, with its structure and control as well as its clinical experiments. The powered orthosis supports the patient's weight, and it has four electrohydraulic digital actuators to motorize hip and knee joints, as well as sensors to detect joint angles and plantar contacts. Each joint angle is controlled by a microcomputer such that an appropriate gait pattern is restored for a stable, powered level walk. This second prototype of the powered orthosis has been designed and developed for testing on patients in order to determine its effectiveness. For the control of this orthosis, the gait pattern is generated by a 16-bit master microcomputer using the preprogrammed pattern which is synthesized with 20 parameters; six 8-bit slave microcomputers measure and control joint angles. A new type of digital actuator was developed specifically for this purpose. In addition, a desktop microcomputer is used for the change of parameters as well as for the dialogue with the master computer. The orthosis weighs only 19.5kg, and the hydraulic power unit 68kg. Clinical experiments of this prototype are conducted on two paraplegics. A powered walk of 6.0 sec/step is realized for the first time, and then 4.5 sec/step for approximately 10 meters.