Development of a Real-Time Tunable Spring – Toward Independent Control of Position and Stiffness of Joints –
Takuya Umedachi*, Yasutake Yamada**, and Akio Ishiguro*
*Department of Electrical and Communication Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
**Logistic & Automation Division, Murata Machinery, Ltd., 2 Nakajima, Hashizume, Inuyama, Aichi 484-8502, Japan
Traditionally, robot control has been done typically by “highly precise control algorithms”: their joint angle trajectories are accurately determined at any time with vast amount of computation. This, however, causes serious problems, particularly in terms of adaptability and energy efficiency. On the other hand, an extreme approach has been gaining a lot of attention recently. A good instantiation is the passive dynamic walker, driven only by exploiting the intrinsic dynamics of its mechanical system. However, mechanical system is not everything as well as control system is not everything: “well-balanced” coupling between control and mechanical systems should be considered. In addition, the “meeting point” between the two systems should be varied according to the environment encountered. In light of these facts, this study particularly focuses on the stiffness of robots’ joints, since this strongly contributes to tuning the dominance relationship between control and mechanical systems. More specifically, the aim of this study is to develop a “Real-time tunable spring” that can smoothly change its elasticity without changing its natural length, allowing robot’s joints to change their position and stiffness independently.
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