Choice of Muscular Forces for Motion Control of a Robot Arm with Biarticular Muscles

Abstract

The contribution of biarticular muscles to the control of robotic arms and legs has recently attracted great interest in the field of robotics. The advantages of using biarticular muscles under kinetic interaction with the external environment have been well studied; however, the contribution of the muscles to the motion control of articulated robot arms under no kinetic interaction appears to remain an unclear issue, especially for robot arms of which the muscles are directly anchored to their links, which induces a change in the moment arms to allow the muscles to generate joint torques and permit point-to-point motion control to their desired postures in a feedforward manner with constant muscular forces. This paper presents a case study in which the role of biarticular muscles in the motion control of an articulated robot arm was investigated, focusing on the feature of its redundancy actuation, which allows an arbitrary choice from infinite combinations of muscular forces, realizing motion control to a desired posture. The numerical analysis in this paper addresses three typical combination choices. Mappings from muscular forces to desired postures are calculated in the analysis of the three choices. The simulation results of motion control executed according to the three mappings are also analyzed. The analysis indicates the interesting results that biarticular muscles do not contribute to the desired postures and that a very weak dependence property of monoarticular muscles on the desired postures exists for a particular choice. The simulation results also demonstrate that the implementation of one choice results in a degraded motion control performance as compared with that of the two other choices.