Safeness of a robot arm using ultrasonic motors with high responsiveness and backdrivability

We propose a robot arm using ultrasonic motors and demonstrate its characteristics such as high responsiveness and backdrivability, which are important characteristics in the view of the safety. The high responsiveness allows the robots to avoid collision against any objects and backdrivability makes the robots have compliance to unexpected actions of people. In this paper, we clarify the responsiveness and backdrivability of the ultrasonic motors experimentally. For the demonstration, we build a prototype robot arm having three joints which are all directly coupled to the output axis of the ultrasonic motors. In the experiments, the robot showed the responsiveness less than a few milliseconds, torque control such as if torsion spring model, and the backdrivability as a free joint. We discuss the safety control strategy using these characteristics..