Estimation of Antagonistic Output Ratios Based on Force Distribution at End Effector of Limb

In this paper, a method is proposed to estimate the detailed muscular strength of a human limb. The detailed muscular strength discussed in this paper is not the strength produced by coordinated muscle actions but the joint torque generated by each muscle group classified according to its function. It is assumed that a human limb is modeled as a two-link manipulator actuated by three pairs of six muscle groups. Although the model theoretically derives the output force distribution at an end effector from the joint torques, the joint torques are not calculated directly from the distribution. The antagonistic ratios of the output forces at the end effector are introduced to solve this problem. However, the estimation results cannot be compared with actual values in a real environment because it is impossible to measure the output of only a certain muscle in a noninvasive way. Instead, simulations and experiments using a robotic arm demonstrate that the proposed method estimates the output ratios of muscle groups with a satisfactory accuracy.