Development of an assistive instrument for lifting motion using driving springs

Abstract

To assist in lifting heavy weight objects from the floor, an assistive instrument that can be worn on the hip and knee joints has been developed. The instrument was driven by coil and flat spiral springs to operate for a long time. At this instrument, the assistive mechanism for the hip joint comprised a plate cam with a “sine-output” oscillating follower and a compression coil spring. The assistive mechanism for the knee joint comprised a non-circular gear, two grooved cams and a flat spiral spring. To eliminate the influence of abduction or adduction and a medial or lateral rotation, two types of freely rotating joints were attached to each of these mechanisms. Based on the analysis of the lifting motion of an object from the floor, it was concluded that the torque applied on the hip and knee joints depends on the individual differences in body height and a body weight, and can be estimated using a two dimensional model. A prototype of the proposed instrument was fabricated and tested. This instrument can be used to reduce the required muscle activities of the hip and knee joints by about 15% compared to while lifting without the instrument when subjected to a force of 98N by an object. Furthermore, the results showed that the assistive instrument exhibits sufficient performance in aiding the lifting motions.

Keywords

• assistive instrument
• lifting
• hip joint
• knee joint
• flexion
• extension
• driving spring