Bilateral Drive Gear : a Highly Backdrivable Reduction Gearbox for Robotics - Yasutaka Fujimoto

Talk from the IROS 2021 workshop:
From gears to direct drive: Recent trends and opportunities in actuation
Website: www.ram.eemcs....
Abstract:
In collaborative robots and assist robots, safety must be guaranteed during contact with humans. However, the conventional reduction gearbox has low backdrivability, and when the robot contacts a worker or a user, an excessive reaction force may be generated, which is dangerous. In this research, we developed reduction gearboxes and servo motors with sufficiently high forward-driving efficiency and backward-driving efficiency without adding additional elements such as torque sensors. The actuators we have developed are safe, compact, and energy efficient. It is composed of a reduction gearbox and a servo motor, having advantages of compact and high power density, and high backdrivability.
In this work, we firstly focused on the reduction gearbox. We have proposed a method that maximizes the power transmission efficiency of the compound planetary reduction gearbox where the profile shift coefficients and the number of teeth are optimized under some conditions. We have succeeded in developing an extremely high-efficiency compound planetary gearbox, Bilateral Drive Gear, that exceeds 90% in both forward-driving efficiency and backward-driving efficiency by the proposed method. As for its performance, the forward-driving efficiency is +20% higher than that of a harmonic gear, which has almost the same reduction ratio, torque capacity, and weight. Backward-driving efficiency is +30% higher and reverse-drive starting torque is less than 1/300. The gearbox is back-driven with very little force, which is not possible with conventional reduction gearboxes. These can be realized by investigating the structure of the gearbox focusing on the driving efficiency and developing the optimization method of the design parameters.
Based on the proposed method, we prototyped reduction gearboxes of 1/16 to 1/1007 and showed that all of them can be back-driven. In addition, we have successfully reduced the backlash of the gearbox to 1 arcmin by allowing small deformation of the ring gears, which makes the proposed gearbox applicable to high-precision positioning systems. The gearbox keeps more than 80% of forward and backward driving efficiencies. For application to powered exoskeletons, a knee assist-type exoskeleton using the proposed gearboxes was prototyped, and it was shown that the knee torque under the assist control can be accurately estimated by the observer without using the torque sensor thanks to its small reverse-drive starting torque. In addition, we proposed a high-density motor with a structure that cools the windings by ventilating the air by the rotation of the rotor, and based on magnetic field analysis and thermo-fluid analysis, it has four times high-power density compared with the conventional motor. By developing the high-power density actuator as described above and demonstrating outstanding performance especially for the proposed gearbox, we believe the actuators are able to apply to various practical robotic applications.

[@BarkanUgurlu]

Excellent work from Prof. Fujimoto. Thank you for the informative talk

[@moses5407]

is this available? are design files available?

[@luckyshadowtux]

Very informative

[@taesuyoon]

what does the 'N' means at 19:11 ??

[@glenswada]

Great stuff, thank you.

[@jamesmatheson9624]

very impressive