Novel endeffector stiffness control by biarticular muscle in robot manipulator

This paper reveals the advantage of the biarticular muscle which has been said to play an important role in human's motion control and applies it to the robot manipulator control. Biarticular muscle changes the energy flow in muscles resulting in efficient motion and help stabilizing the posture of the human body. These advantages are analyzed and reflected to the control of a robot manipulator. In order to analyze these characteristics, we adopt three-pair six-muscle model of human arm including biarticular muscles and derive simple relationship between an endeffector force/position and three muscle torques based on the absolute angle of two joints, and muscle characteristic which has viscoelasticity is modeled as PD position feedback control. Based on these modeling, the relationship between the stiffness in the workspace and in the muscle torque space is calculated and simulated to verify the characteristics and roles of the biarticular muscle. The derived equations and simulations verify that a new feedback control introducing the biarticular muscle can stabilize the motion of the endeffector more efficiently.