Developing a 3-Dimensional Kinematic Model of the Hand for Ergonomic Analyses of Hand Posture, Hand Space Envelope, and Tendon Excursion.

The objective of the study is to develop a 3-dimensional kinematic model of the hand that predicts hand posture. A 3-dimensional kinematic model of the hand was built using Visual C++ environment and OpenGL graphics. The hand was modeled as open chains of rigid bodies with 25 DOF’s. The GUI of the model was designed to include human, object , and task attributes. A simple contact algorithm was applied to the model to find contacts between hand segments and object surface while rotating joint angles of fingers. Two different joint angle rotation algorithms – “variable rotation method” in which observed joint rotation rates were used, and “constant rotation method” in which all joints rotate at constant rates – were applied to the model. Joint angles of all fingers and thumb were measured for 16 subjects (11 males, 5 females) with motion capture system during a power grip and a pulp pinch grip. Three differently sized cylindrical objects were used. A sensitivity study was performed to investigate the effects of object size, object location, object orientation, hand size, and skin deformation on predicted postures. The average difference between predicted and measured joint angles ranged from -10.0o to 9.1o. The coefficient of determinant (R) between predicted and measured joint angles was 0.76 for the power grip and 0.88 for the pinch grip. The joint rotation algorithm affected prediction accuracy : application of the “variable rotation