An Adaptive Reaction Force Observer Design

In this paper, a new adaptive design method is proposed for reaction force observer (RFOB)-based robust force control systems. It is a well-known fact that an RFOB has several superiorities over a force sensor such as higher force control bandwidth, stability improvement, force-sensorless force control, and so on. However, there are insufficient analysis and designmethods for an RFOB-based robust force control system; therefore, its stability and performance highly depend on designers own experiences. To overcome this issue, a new stability analysis and a novel adaptive design method are proposed for RFOB-based robust force control systems. In the proposed adaptive design method, the design parameters of the robust force control system, i.e., the bandwidths of disturbance observer (DOB) and RFOB, the nominal and identified inertias in the design of DOB and RFOB, respectively, and the force control gain, are adjusted automatically by using an adaptive control algorithm which is derived by estimating the plant parameters and environmental impedance. The proposed adaptive design method provides good stability and performance by considering the design constraints of a DOB. The validity of the proposals is verified by simulation and experimental results.