Development of a knee joint assistive-mechanism adapted for bilateral roll-back motion

Abstract

To reduce the deployment cost of walking rehabilitation after surgery, a structure of knee joint assistive-mechanism that is adapted for bilateral roll-back motion has been proposed. This has two grooved cams which are not coincident with the locus of the knee joint’s imaginary rotation center. However, these generate the self-locking in case of the same motion directions of each follower roller. A design condition has been shown for avoiding these self-locking. X-ray fluoroscopy of a prototype mechanism is used to evaluate the misalignment between the rotation centers of the knee and knee joint mechanism. Then, a load test prototype was used to test the roll-back motion under rated-torque, and some differences in the characteristics of the right and left knee-assistive motions were investigated. Based on roll-back motion data obtained from the Japanese people with an average height, a maximum displacement of 15 mm and an angle of 55° is used for the prototype mechanisms’ imaginary rotation centers, and their cam shapes are generated using asymmetrical modified trapezoid motion curves. The results show that the proposed mechanism can be rotated smoothly to generate the exact knee roll-back motion and that its characteristics for right and left knee-assistive motions are almost identical.