Experimental Evaluation of a Quasi-direct-drive Actuator with a 3D-printed Planetary Gear Reducer

Abstract

When electromagnetic motors are used as actuators for robots, the reduction gear is an essential component in most cases. The mechanical design choices increase if we can fabricate the custom-made reduction gear. The performance of the robot also increases because of the optimized reduction ratio. Moreover, the rapid progress of the 3D printing technology allows us to develop the reduction gear at a low cost agilely. However, most of the previous development remains at the proof-of-concept level, and quantitative evaluation of the 3D printed reduction gear is insufficient. In this paper, we fabricated a quasi-direct-drive actuator with a 3D-printed planetary gear reducer. The planetary gear reducer consists of resin molded parts by Fused Filament fabrication. We quantitatively measured its performances such as 1) transmission efficiency of static torque, 2) joint stiffness, 3) the effect of temperature on stiffness, 4) the influence of the 3D printing parameters on stiffness and strength, and 5) durability against a continuous operation. The prototype actuator unit demonstrated a sinusoidal joint movement for 46 hours, where its maximum output torque and frequency were 19.6 Nm and 0.1 Hz, respectively.