Two-Handed Human Reach Prediction Models for Ergonomic Evaluation

Abstract

As an essential function of computerized ergonomic evaluation models based on digital human models, realistic simulation or prediction of human reach profiles is of great importance. Although several human-modeling efforts have been made to provide the capability of reach simulation, most studies have been limited to the reach of a single extremity. A variety of activities of human operators, however, frequently involve simultaneous positioning of two or more extremities to different target positions. Such a multiple reach problem cannot be satisfactorily resolved by means of conventional single-extremity reach models because formulation of the problem as a series of single reaches rarely yields accurate trajectory of human-reach profiles due to interactions of multiple extremities. In this research, a two-handed reach prediction model was developed. The human upper body was modeled as a seven-link system with 13 degrees of freedom, being regarded as a redundant open kinematic chain with two end-effectors. As a way of solving the two-handed reach problem, the resolved motion method was adopted among several inverse kinematics methods as the technique is fit for real-time redundancy control. The method is also capable of incorporating the joint range availability criterion as a cost function to minimize excessive deviations of body joints from their neutral positions. Real human-reach profiles were compared to those obtained from the prediction model and were found to be statistically similar. The methodology is expected to be applicable to the reach simulation of both upper and lower extremities without algorithmic difficulties. (C) 2010 Wiley Periodicals, Inc.