Adaptive reaction torque/force observer design I

This paper proposes a new adaptive design method for the robust force control systems based on disturbance observer (DOB). A DOB is a robust control tool that is widely used in motion control applications. It can also be used to estimate environmental impedance by identifying system uncertainties and is called as reaction torque/force observer (RTOB/RFOB). A RTOB/RFOB has several superiorities over a force sensor such as higher bandwidth, sensorless force control, stability improvement etc., so it can be used in force control implementations effectively. However, there is no systematic analysis and design methods for a RTOB/RFOB based robust force control system; therefore, its stability and performance highly depend on designers own experiences. A new adaptive design method is proposed by estimating environmental impedance. It adjusts not only the force control gain, but also the bandwidths of a DOB and a RTOB/RFOB and the ratio between uncertain and nominal inertias. In this paper, it is assumed that environmental impedance can be modeled by considering only stiffness or damping. The validity of the proposal is verified by simulation and experimental results.