Modeling of force sensing and validation of disturbance observer for force control

Controlling robots in contact with environment is the important problem in industry applications. In order to solve the instability in force control, the velocity feedback gain is enlarged. The system becomes unstable with small velocity feedback gain, and robot´s response becomes slow with large one. Since there is trade-off between stability and responsivity, it is thought that force control by robots is difficult. In the conventional force control, great many researches have paid attention to develop novel force control systems and implemented force sensors to detect external force. This paper shows that feedback of the value of force sensor makes attainment of force control difficult. The novel analysis technique of force control that force sensor is modeled by 2 mass resonant system is shown. Force control is attainable with the construction of the easiest force control system by feedback the value of reaction torque observer. Sensor-less force control is the one of the fundamental techniques for evolution of human-cooperating robot, tele-robotics, robotic virtual reality and so on. The numerical and experimental results show viability of the proposed method.