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(2) A. Shimada, Y. Kishiwada, M. Fujita, and N. Arimura: “Sensor-less Control based on Observerbility Using Mechanical Spring”, The 47th Automatic Control Annual Joint Conference, 912 (2004)
(3) M. Arimura, A. Shimada, and M. Terauchi: “AC Servo Motor Position Sensor-less Control using Mechanical Springs”, The papers of technical Meeting on Industrial Instrumentation and Control, IEEJ, IIC-05-56 (2005) (in Japanese)