Validation of Human Three-Joint Arm's Optimal Control Model with Hand-Joint’s Feedback Mechanism Based on Reproducing Constrained Reaching Movements

Abstract

We have already formulated the human three-joint arm’s optimal control model with its hand-joint’s feedback mechanism and have clarified that the model is effective in reproducing human unconstrained reaching movements including the experimental fact that the hand-joint angle hardly changes over the entire movement. For validating the proposed model, this paper applies it to reproducing human constrained reaching movements in which the hand has to take a specified posture at the final point as in the case of holding a cup’s handle with fingertips. The following results were obtained: (1) the proposed model was able to move its hand joint despite the existence of the feedback mechanism preventing the hand-joint angle from changing; (2) the proposed model succeeded at reproducing the measured hand trajectories and the measured angular transition characteristics for the hand joint in most of the constrained reaching movements. These results suggest that the proposed model has the ability to simulate human reaching movements regardless of whether they are unconstrained or constrained, i.e., it can be a general and plausible model for the human three-joint arm's control mechanism. Moreover, it is computationally considered that the hand-joint’s angular transition characteristic depends on the average of the resultant torque around the hand joint over the entire movement.

Keywords

• three-joint arm
• optimal control model
• hand joint
• feedback torque
• constrained movement
• hand posture
• unconstrained movement
• angular transition
• resultant torque