Torque control of grasping force feedback using a series elastic actuator with an ultrasonic motor for a teleoperated surgical robot

In the context of teleoperated surgical robots, much research has been conducted into haptic feedback systems. Ultrasonic motors (USMs) are expected to be used as actuators for generating feedback torque because of their fast response and high torque–weight ratio. However, their nonlinear characteristics make control of the output torque difficult, leading to large spike-like torque errors during rotation reversal. One approach to counteracting this effect is to use series elastic actuators (SEAs). In this study, a force feedback system using an SEA with a USM was proposed. The spike-shaped errors in the output torque of the USM were reduced by up to 60 % by attaching an SEA to its output shaft. The dependence of the torque accuracy and the response time of the SEA on its spring constant were also examined. By introducing the SEA with a spring constant of 42.4 mN·m/°, it was indicated that the torque error of 14.8 mN·m and the response time of 9 ms could be simultaneously achieved. Finally, the force feedback system was applied to a teleoperated surgical robot, and the stiffness of the objects grasped by the robot was successfully fed back with the error of 0.65 % when grasping a sponge.