Design of nominal parameters for robust sensorless force control based on disturbance observer

The paper proposes a parameter design of a reaction force observer (RFOB) under existence of modeling error/parameter fluctuation. Observer-based sensorless-force-control is a good approach to reduce phase lag in control systems. Hence, the performance improvement can be easily attained by such a technique. However, the RFOB does not always guarantee accuracy of estimated value and adds incorrect compliance on the system. Due to insufficient report about RFOB design, its calibration is conducted based on the designer’s own experience. To calibrate the RFOB and achieve the correct force control quantitatively, the structure of the observer-based force control and physical interpretation of control loops should be revealed simply. The paper presents a condition to achieve the correct force control and design methodology of observers, thereby, providing a robust performance against parameter variation.