BSA – Bi-Stiffness Actuation for optimally exploiting intrinsic compliance and inertial coupling effects in elastic joint robots

Dennis Ossadnik, Mehmet C. Yildirim, Fan Wu, Abdalla Swikir, Hugo T. M. Kussaba, Saeed Abdolshah and Sami Haddadin
2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2022)

Abstract

Compliance in actuation has been exploited to generate highly dynamic maneuvers such as throwing that take advantage of the potential energy stored in joint springs. However, the energy storage and release could not be well-timed yet. On the contrary, for multi-link systems, the natural system dynamics might even work against the actual goal. With the introduction of variable stiffness actuators, this problem has been partially addressed. With a suitable optimal control strategy, the approximate decoupling of the motor from the link can be achieved to maximize the energy transfer into the distal link prior to launch. However, such continuous stiffness variation is complex and typically leads to oscillatory swing-up motions instead of clear launch sequences. To circumvent this issue, we investigate decoupling for speed maximization with a dedicated novel actuator concept denoted Bi-Stiffness Actuation. With this, it is possible to fully decouple the link from the joint mechanism by a switch-and-hold clutch and simultaneously keep the elastic energy stored. We show that with this novel paradigm, it is not only possible to reach the same optimal performance as with power-equivalent variable stiffness actuation, but even directly control the energy transfer timing. This is a major step forward compared to previous optimal control approaches, which rely on optimizing the full time-series control input.

@inproceedings{ossadnik2022BSA,
	title={BSA - Bi-Stiffness Actuation for optimally exploiting intrinsic compliance and inertial coupling effects in elastic joint robots},
	author={Dennis Ossadnik, Mehmet C. Yildirim, Fan Wu, Abdalla Swikir, Hugo T. M. Kussaba, Saeed Abdolshah and Sami Haddadin},
	booktitle={2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2022).},
	year={2022},
	organization={IEEE}
}