Variable Transmission With Actively Controllable Reduction Ratio

Abstract

Actuators that interact with the environment and humans require a variable reduction ratio to maintain high motor efficiency over various output loads. Actively controlled continuous variable transmission optimizes motor efficiency by changing the gear ratios at the desired time. This study presents the modeling, design, and characterization of a transmission capable of actively controlling the reduction ratio for robotic applications. Power transmission through the proposed compression mechanism using a compression spring without an external energy source enabled a compact design. The transmission ratio range (1:1 and 4.2:1) is determined through kinematic analysis of the toroidal drive design. The reduction ratio shifting module enabled a low power consumption during shifting (approximately 3.5 W) and static condition (approximately 0.2 W) through the nonbackdrivability and self-locking features of the worm gear. The characterization results showed good power transmission efficiency of 75% across the entire operating range. The system was equipped with overload protection features for slipping between the disk and roller, exhibiting a torque capacity of 2.4 N·m. Finally, we compare the performance of our proposed variable transmission with that of the existing system to demonstrate the applicability of our design to robot actuators.