Development of an energy-saving manipulator with bi-articular muscle-like variable stiffness mechanism

Abstract

The authors have previously proposed a control method that can significantly reduce the energy consumption of the robot manipulator using passive storage elements such as springs. Based on the optimal control theory, the optimal design method of the spring is established and its effectiveness is verified by experiment. In the previous researches, a spring was added to each joint and its stiffness was adjusted to save energy. On the other hand, in this paper, we introduce a stiffness variable mechanism that simulates bi-articular muscles acting across two joints. We first derive the equations of motion of a manipulator with a new variable stiffness mechanism based on multibody dynamics approach and analyze its characteristics. Then, an algorithm for obtaining an optimal spring stiffness is proposed, and finially its effectiveness is confirmed by numerical simulation.