Generation of a Practical Reach Envelope with the Center of Rotation of the Shoulder Joint Considered

견관절의 회전중심점을 고려한 동작가능 영역의 생성

Shoulder joint is the most movable joint in human body with, at least, three degrees of freedom, since there are at least three bones and five joints involved in shoulder movement. Due to the complexity of the shoulder joint and the lack of appropriate anatomical data, modeling of the shoulder joint has been known to be extremely difficult. In many biomechanical models being used, shoulder joint is considered as a fixed point and it is also assumed that the shoulder joint does not noticeably move during the shoulder movement. However, such an assumption is not valid in real applications and causes inaccuracy, especially, in the area of workspace evaluation. The reachable area generated by a human becomes somewhat different from that of current models for those models fail to appropriately reflect the movement of shoulder joint's center of rotation. In this study, the location of the shoulder joint's center of rotation was obtained in relation to the location of humerus, on which a new model for reach envelope generation was developed for workspace evaluation. From the experiments conducted for three subjects, the initial location of the center of rotation was determined for each subject and subsequent changes in the instantaneous center of rotation were drawn as a function of flexion and abduction of the shoulder. Based on the regression analysis, the study suggested a new method for the generation of reach envelope. Comparisons were also made among real reach envelopes obtained from the experiment, the ones from the model, and the ones from the new method suggested in the study. As a result, the prediction errors incurred from the new method were significantly reduced when compared to the ones from the current approach.