Optimization-based differential kinematic modeling exhibits a velocity-control strategy for dynamic posture determination in seated reaching movements

We proposed a velocity control strategy for dynamic posture determination t hat underlay an optimization-based differential inverse kinematics (ODIK) a pproach for modeling three-dimensional (3-D) seated reaching movements. In this modeling approach, a four-segment seven-DOF linkage is employed to rep resent the torso and right arm. Kinematic redundancy is resolved efficientl y in the velocity domain via a weighted pseudoinverse. Weights assigned to individual DOF describe their relative movement contribution in response to an instantaneous postural change. Different schemes of posing constraints on the weighting parameters, by which various motion apportionment strategi es are modeled, can be hypothesized and evaluated against empirical measure ments. A numerical optimization procedure based on simulated annealing esti mate the weighting parameter values such that the predicted movement best f its the measurement. We applied this approach to modeling 72 seated reachin g movements of three distinctive types performed by six subjects. Results i ndicated that most of the movements were accurately modeled (time-averaged RMSE < 5 degrees) with a simple time-invariant four-weight scheme which rep resents a time-constant, inter-joint motion apportionment strategy. Modelin g error could be further reduced by using less constrained schemes, but not ably only for the ones that were relatively poorly modeled with a time-inva riant four-weight scheme. The fact that the current modeling approach was a ble to closely reproduce measured movements and do so in a computationally advantageous way lends support to the proposed velocity control strategy. ( C) 1998 Published by Elsevier Science Ltd. All rights reserved.