Precise External Torque Estimation for Two-Inertia System Considering Modeling Errors

Precise force/torque detection is required to realize precise force/torque control in flexible mechanisms (e.g. geared industrial robots, ball-screw driven stages). Since applying force/torque sensors introduces several disadvantages such as high cost and lowering system rigidity, sensorless estimation methods for a plant with a resonant mode have been proposed. For the sensorless load-side external force/torque estimation for a two-inertia system with a load-side encoder, mainly there are two methods, which have pros and cons in terms of the robustness against the modeling errors in the motor side or the transmission part. This paper proposes a novel design of the load-side external force/torque observer which combines the two conventional observers for more precise estimation even under modeling error effects. Also, through the theoretical analyses of the observer with/without a joint torque sensor, an advantage and limitation of applying a joint torque sensor for external force/torque estimation are revealed. The analyses are validated by simulations and experiments.