Torque-sensorless Impedance Control for an Actuator with Compound Planetary Gearbox for reducing External Contact Force

In recent years, the demand for collaborative robots has been increasing. As collaborative robots must be safe against contact. The purpose of this research was to develop robots that can perform tasks involving contact in collaboration with humans. A torque sensor is generally used to detect the external force at contact, but can reduce the rigidity of the robot. Thus, in this paper, we propose impedance control without a torque sensor for an actuator comprising a motor and reduction gear. Position-control-based impedance control was applied to the proposed method, and the torque can be estimated without a torque sensor using a highly efficient reduction gear. In addition, an external-force feedback gain is introduced for position-control-based impedance control and an external contact force reduction method is realized based on the angular transmission error of the reduction gear. From experiments, the proposed method achieved both position control and force control. As a result, the external contact force was reduced by approximately 10%.