Degrees of freedom coupling adapted to the upper limb of a digital human model

Abstract

The upper limbs of digital human models have many degrees of freedom. Moreover, their range of motion tends to be overestimated. In some conditions, the resulting kinematic chain may predict unrealistic postures. Many kinematic correlations or 'couplings' have been measured at the upper limb (ex. shoulder rhythm, sinus cone limits). So far, a few of them were adapted to digital human models. These models often use a simplified 'claviscapular' segment, which simplifies the shoulder girdle, (i.e., clavicle and scapula) as a single segment. This paper presents the development of a set of upper limb degree of freedom couplings for digital human models, adapted from experimental kinematic data that comes from different published studies. It is shown how these couplings improve the upper limb model by reducing its overestimated ranges of motion and reachable workspace and by improving its kinematic behaviour. The use of experimental data from a single group of subjects is the next step towards a more homogeneous upper limb coupling model.