Toward Inherently Safer Human-Robot Interaction Using Compliant Actuators With High Torque-to-Inertia Ratios and Low Torque-to-Stiffness Ratios

Existing robots rely on external sensors to detect and prevent potential human-robot collisions. However, with the growing demand for complex and high-speed human-robot interaction, robots with inherently safer actuators are becoming more desirable. Such robots offer robust protection against excessive impact force even when external sensors fail or become unavailable. Robot actuators with low reflected inertia and low effective stiffness are necessary to achieve mechanically safer human-robot interaction. This paper presents novel compliant actuators with high torque-to-inertia ratios and low torque-to-stiffness ratios without compromising the output torque and output stiffness of an actuator. Comparisons with existing actuators demonstrate that a robot with the proposed compliant actuators has a much lower effective mass sensed at the end-effector. Impact analysis is presented to verify the effectiveness of high torque-to-inertia ratios and low torque-to-stiffness ratios. To assess the performance of the proposed robot, a pose repeatability experiment is conducted, which shows that the end-effector position control precision is comparable to existing stiff robots despite the inherent compliance of the actuators. These compliant actuators can be used to build various human-friendly robots and are expected to improve the safety and reliability of human-robot interaction.