Highly Efficient 2K-H Compound Planetary Reduction Gearbox Using Balancer

Abstract

In recent years, research on robots has been conducted all around the world to address the reduction of the working population and the shortages of care workers needed for the aging population and disaster-relief activities. Currently, harmonic and cycloid gearboxes are widely used as reduction gearboxes for the joints of robots. Harmonic gearboxes have a high reduction ratio and a small backlash and are compact and lightweight, but their efficiency and stiffness are low. Cycloid gearboxes have a high reduction ratio, small backlash, and high efficiency, but their size is too large. Furthermore, both gearboxes are very difficult to backdrive with a reduction ratio of 1/100. Thus, we focused upon planetary gearboxes and made a 3K compound planetary reduction gearbox, made more efficient by optimizing the numbers of teeth and the profile-shift coefficients. A reduction gearbox with a reduction ratio of 1/97 and an efficiency of 93% was realized and back driving was possible. Building on this, we aim to develop a highly efficient 2K-H compound planetary reduction gearbox to achieve higher efficiency than the 3K model. However, the 2K-H compound planetary reduction gearbox has high efficiency when there is only one planet gear, so the eccentricity of the planet gear must be considered. In this paper, we show the method and experimental result of canceling the eccentricity of the planet gear using a balancer after deriving the efficiency equation in the 2K-H compound planetary reduction gearbox and showing the efficiency result by optimizing the profile-shift coefficient.