Force Sensorless Fine Force Control Based on Notch-Type Friction-Free Disturbance Observers

In order to realize force sensorless fine force control, this paper proposes a new notch-type friction-free disturbance observer (DOB) and a new notch-type friction-free reaction force observer (FFRFO). Generally, a force sensorless force control system is always influenced by the static friction phenomenon. In order to suppress the estimation error due to static friction, a force sensorless force control system uses a dither signal, and a friction free reaction force observer (FFRFO) is used to consider this dither signal. Since the high frequency gain charactheristics of conventional FFRFO are significantly higher than 0 dB, the entire force control system sometimes becomes unstable or produces oscillating responses. To overcome this problem, this paper proposes a new force sensorless control system using the notch-type friction free reaction force observer, whose inner system is the proposed acceleration control based on the notch-type friction free disturbance observer. The effectiveness of the proposed system is confirmed by experiments using an actual industrial robot.