Digital Hand Model Reconstructing the Morphology and Posture

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The purposes of the present study were (1)to obtain representative 3D hand forms covering the variations in the Japanese hand morphology, and (2)to reconstruct grasping postures for a digital hand model. The following results were obtained.1.A method was proposed to obtain the rotation axis of finger joints from MRI images taken in 3 different postures. Bone surfaces were extracted, and the rotation axis was calculated from the relative position of 2 adjacent bones. It was found that rotation axes of metacarpo-pharangeal and proximal and distal inter-phalangeal joints were not parallel, and that the direction of the rotation axis relative to the proximal bone changes according to the flexion angle.2.A method was proposed to obtain an individual link structure modeled from optical motion capture data. Using the link model, postures to grasp 5 cylinders of different diameter were captured. The captured data was utilized to generate postures required to grasp cylinders of arbitrary diameter between the captured ones. When a posture is reconstructed, the strategy for grasping a cylinder was taken into consideration.3.A generic hand model was created from CT images of a male subject taken in 3 different postures. The generic model consists of the surface polygon models of the skin and bones, link structure, and functional rotation centers.4.From the hand dimensions measured on 100 male and female subjects, hand dimensions of 9 members of a boundary family were calculated. Shape models of the 9 virtual hands were created by deforming the generic model so that the dimensions of the generic model become identical to those of each of virtual forms.5.Bone lengths were measured from X-ray films obtained in a previous study, and analyzed for the allometry of link lengths