K. Ohnishi concluded that the conventional installation of sensor elements requires filtering and other processing, which is not convenient for practical applications. Therefore, they developed a Reaction Torque Observer (RTO) with force sensing feedback, which was used in a 6-axis industrial robot, by combining the characteristics of external disturbance observer to estimate the external force, and showed that this sensorless control can obtain the force value more easily.[1] B. Yalcin and K. Ohnishi used an external disturbance observer and a reaction force observer to implement Impedance Control, and combined it with Sliding Model Neural Network Control to quickly correct the environmental forces sensed by the robot.[2]
The reasons for selecting the Disturbance Observer in this research are as follows.
1.Compared with other anti-disturbance controllers, the parameters are simple and easy to design.
2.The inner loop and the outer loop can be designed separately, which has a high design freedom.
3. Decoupled by negative feedback, easy to understand and intuitive.
4. The characteristics of external disturbance can be estimated, and sensorless control can be used.
Citation
[1] S. Katsura, Y. Matsumoto and K. Ohnishi, "Modeling of Force Sensing and Validation of Disturbance Observer for Force Control," in IEEE Transactions on Industrial Electronics, vol. 54, no. 1, pp. 530-538, Feb. 2007, doi: 10.1109/TIE.2006.885459.
[2] B. Yalcin and K. Ohnishi, "Environmental Impedance Estimation and Imitation in Haptics by Sliding Mode Neural Networks," IECON 2006 - 32nd Annual Conference on IEEE Industrial Electronics, 2006, pp. 4014-4019, doi: 10.1109/IECON.2006.347716.