Cable-Driven Actuation for Highly Dynamic Robotic Systems
Hwangbo, Jemin(ETH Zurich)
Spain | IROS 2018
2018-10-01 | 바로가기
Torque, Legged_locomotion, Resistance
Cited by 7
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2018 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Date of Conference: 1-5 Oct. 2018
Jemin Hwangbo, Vassilios Tsounis, Hendrik Kolvenbach Marco Hutter
Robotic Systems Lab, ETH Zurich
This paper presents the design and experimental evaluations of an articulated robotic limb called Capler-Leg. The key element of Capler-Leg is its single-stage cable-pulley transmission combined with a high-gap radius motor. Our cable-pulley system is designed to be as light-weight as possible and to additionally serve as the primary cooling element, thus significantly increasing the power density and efficiency of the overall system. The total weight of active elements on the leg, i.e. the stators and the rotors, contribute more than 60 % of the total leg weight, which is an order of magnitude higher than most existing robots. The resulting robotic leg has low inertia, high torque transparency, low manufacturing cost, no backlash, and a low number of parts. The Capler-Leg system itself, serves as an experimental setup for evaluating the proposed cable-pulley design in terms of robustness and efficiency. A continuous jump experiment shows a remarkable 96.5 % recuperation rate, measured at the battery output. This means that almost all the mechanical energy output during push-off is returned back to the battery during touch-down.
This paper presented a novel cable-pulley system and the derived single legged robotic limb, Capler-Leg. The proposed system has a gear ratio of 5 which is much lower than the transmissions in most legged robots. However, in conjunction with a high gap-radius motor, we show that the combined system is not just efficient, but also extremely powerful. We conducted several tests for torque tracking, and it was extremely accurate both for static and dynamic cases. We presented a high-jump test of 1.2 m only using 80 % of the torque capacity with an extra weight which is 50 % of the robot's weight. We also showed a longevity test of half a million cycles and proved that the cable is durable in practical scenarios. During the longevity test, Capler-Leg recuperated 96.5 % of the total mechanical power on average. This test shows that the transmission has extremely low friction. Therefore, we conclude that the proposed solution is very well-suited for legged robotics.
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