Comparison of Characteristics of Internal Planetary Gear Reducer with Epitrochoid Curve using Metal and 3D Printed Parts

The demand for industrial robots has recently increased and is expected to continue to grow. In addition, efforts toward the United Nations' Sustainable Development Goals and carbon neutrality are gaining momentum worldwide. In this paper, we evaluate lightweight reduction gears developed for improving the energy efficiency of robots. To reduce robot weight, it is necessary to replace conventional metal materials with lightweight materials such as composite materials and resins. However, in general, weight reduction tends to reduce stiffness, resulting in a decrease in the speed and precision performance required for industrial robots. We evaluate the applicability of replacing metal parts with plastic materials made using a fused deposition modeling 3D printer. The evaluation was conducted using a drive unit, which has a significant impact on the power and position control performance of a robot. In addition, a gear with a low reduction ratio, which is generally considered to have high backdrivability, is developed to incorporate into robots that work side-by-side with humans. Onyx resin, with a density less than half that of metal, was used to make the plastic parts. The use of resin for the case that encloses the gears significantly contributes to weight reduction and has only a small effect on torsional stiffness and hysteresis loss. Since the resin case is easily deformed, it allows for errors caused by metal machining, resulting in smooth rotation and improved torque transmission efficiency.