Abstract
The accuracy of ordinary magnetic bearings is not high enough because displacement sensors used for feed-back are inaccurate. The aim of the paper is to clarify limitations of the positioning accuracy of an object of an electromagnetic levitation system in which a flux density sensor and a current sensor are used for estimat-ing the displacement of the object. First, a displacement estimation method using flux density and current signals in an electromagnet is discussed. Then a non-contact positioning system controlled by electromag-nets, Hall elements and current sensors is introduced. The system is provisionally positioned with a precision displacement sensor. Comparison of the resolution, frequency characteristics and measurement range is made between the estimated displacement and the output of the precision sensor to evaluate the accuracy of the estimation. After that, the object is controlled using the estimated displacement as the feedback signal and the accuracy and stability of the estimated displacement are examined. The experimental results show that the resolutions of estimated displacement and positioning were 0.25 μm, the positioning range was more than ± 100 μm, and the stability of positioning due to the ambient temperature variation was 3.0 μm/°C.
