Minimum Energy Control of Robot Manipulators Using a Simple Variable Stiffness Mechanism

This paper proposes a concept for the design and control of an energy saving manipulator utilizing passive elastic elements for energy storage. Firstly, we review our previously proposed method and the practical design of an energy saving manipulator briefly. This method reduces the energy consumption by using natural frequencies and eigenmodes of the system. Therefore, when the weights of the system are changed by transferring some objects or when the boundary conditions are changed, we should adjust stiffnesses of the system. Hence, in this paper, we propose a very simple variable stiffness mechanism that can change rotational stiffnesses around the manipulator joint axes. This mechanism makes it possible to adjust the natural frequencies and eigenmodes of the manipulator. A prototype 2DOF manipulator with the variable stiffness mechanism is developed by using the linear springs and the reaction wheels to verify the proposed method. Experimental results show the effectiveness of the proposed energy saving manipulator concept.