A Bi-Criterion Model for Human Arm Posture Prediction

The human arm may be considered to be a redundant mechanism given a pointing task. As a result, multiple arm configurations can be used to complete a pointing task in which the tip of the index finger is brought to a preselected point in space. A kinematic model of the human arm with four degrees of freedom (DOF) and the synthesis of two criteria were developed as an analytical tool for studying position tasks. The two criteria were: (1) minimizing angular joint displacement (Minimal Angular Displacement (MAD)) and (2) averaging limits of the shoulder joint range (Joint Range Availability (JRA)). Joint angles predicted by a weighted model synthesizing the MAD and JRA criteria was linearly correlated (slope=0.97; r=0.81) with experimental data compared to individual criteria (MAD slope=0.76; r=0.67 or JRA slope=1; r=0.56). The partial contributions to the synthesized criterion were 70% MAD and 30% JRA. Solving the inverse kinematics problem of articulated redundant serials mechanism such as the human or robotic arm has applications in fields of human-robot interaction and wearable robotics, ergonomics, and computer graphics animation. Keywords— human arm, redundancy, pointing task, kinematics, optimization.