A 3K Planetary Gear Train with a flexure-based anti-backlash carrier for collaborative robots

Backdrivable joint actuators are critical to enhancing the human-robot interaction performance of collaborative robots. A Planetary Gear Train (PGT) with a high reduction ratio and high bidirectional transmission efficiencies is a promising gear reducer candidate for joint actuators. However, a conventional PGT normally has a large backlash resulting in low transmission accuracy and an uncontrollable dead zone, which hinders the applications in joint actuators. Utilizing the unique structural characteristic of the 3K-type PGT that its carrier is not partici-pated in the torque transmission, a novel flexure-based carrier with the adjustable preload and stiffness is proposed to significantly reduce backlash. To study the effects of the proposed carrier on the backlash of the 3K-type PGT, a kinetostatic model and a modified backlash model are formulated. Simulation results indicate that the carrier reduces backlash effectively, and the step dead zone caused by backlash is transformed into a low stiffness zone. The effectiveness of the proposed carrier is further verified by experimental results such that the backlash of the prototype is reduced from 10.97 arcmin to 0.47 arcmin significantly.