On the Determination of Joint Motion Coupling for the Human Shoulder Complex 2008-01-1870

This paper presents a novel approach to determining the joint motion coupling relationship for the human shoulder complex. The human shoulder complex is the most sophisticated part in terms of degrees of freedom and motion. In the literature, different human shoulder biomechanical models have been developed for various purposes. Also, researchers have realized that there are constant movement relationships among the shoulder bones: the clavicle, scapula, and humerus. This is due to muscles and tendons that are involved in skeletal motions. These relationships, which are also called shoulder rhythm, entail joint motion coupling and joint limit coupling. However, the scope of this work is to determine the joint motion coupling relationship. This relationship is available in the literature, but it is an Euler-angle-based relationship. In the virtual human modeling environment, we cannot directly use this Euler-angle-based relationship. A novel approach is proposed to transfer Euler-angle-based coupling equations into a relationship based on the Denavit-Hartenberg (DH) method. A realistic shoulder complex model is built within Virtools. Euler angles are obtained for static positions with intervals of 15 degrees, and the elevation angle of the arm varied between 0 and 120 degrees. For a specific posture, we input the Euler angles to the shoulder complex model for each bone; then a set of DH joint angles can be determined. The new joint motion coupling relationship is obtained by polynomial, trigonometric and Fourier functions fitting of the DH joint angles using Mathematica. This DH-based joint motion coupling relationship can be used for posture and motion prediction.