Actuator gear train design and material selection method for collaborative robots

Collaborative robots are industrial robots especially designed for interaction with humans and their work environments. Traditional actuators usually have high stiffness, stable structure, long life, and high repeatability, but are quite heavy, expensive, energy consuming, and suffer from slow response. For collaborative robots, a new kind of actuator gear train with relatively high performance and accuracy, lightweight, low cost, and quick response to the environment, is needed. In this research, a complete design method for collaborative robot actuator gear trains has been developed, including an actuator structure study, gear train type choice, gear train parameter optimization and standardization, gear train performance evaluation, and material selection. Different form traditional gear train design method, which only determines gear teeth numbers according to reduction ratio requirements, the optimization design developed in this research seeks to achieve the best gear train performance based on the optimum assignment of all input parameters. An exhaustive method is applied determine the constraint relationships between the input parameters and the design requirements. Several assumptions are made for the input parameters to simplify the design process process and improve computational efficiency. The parameters are assumed to be continuous instead of discrete at first. After design optimization, the diametral pitch, number of teeth and face width are standardized. For original robot actuator gear train design, the material is usually chosen from metal alternatives. However, the gear train can be made of various materials, including steel, cast irons, nonferrous alloys, and even plastics. Materials with lower density and lower cost, among other properties, can significantly improve gear train performance once basic strength and fatigue limit requirements are met. Material selection based on the material properties directly can confuse the designer, so a material selection process based the final gear train performance (torque capacity, weight, torque density, inertia, and responsiveness) to support meaningful and effective selection. The ELECTRE III multiple criteria decision analysis method is used to compare material alternatives to facilitate material selection.