|Budget Amount *help
¥6,300,000 (Direct Cost: ¥6,300,000)
Fiscal Year 2002: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 2001: ¥4,300,000 (Direct Cost: ¥4,300,000)
Applying self-sensing technique to active magnetic bearings (AMBs) is very promising. Our group has been studying active magnetic bearings working in liquid nitrogen. When normal AMBs are used in liquid nitrogen, they do not work well. The displacement sensors for the AMBs do not work due to the low temperature of liquid nitrogen. In order to use displacement sensors working in liquid nitrogen, very expensive sensors which are especially developed would have to be bought. We have developed a displacement sensor for the AMBs used at the temperature of liquid nitrogen. In this study, the displacement sensors are evaluated not only in liquid nitrogen, but also in air. Dynamics of the self-sensing AMBs are also discussed.
The self-sensing AMBs consist of a rotor (shaft), a pair of AMBs with four electromagnets, and a driving motor. The rotor consisted of a pair of iron parts for the AMBs, and measures 24 mm in diameter, 160 mm long and 0.37 kg in weight. The driving motor was a PM-type moto
r which consisted of a rotor with permanent magnet (PM), Four electromagnets for driving, and Hall sensors for detecting the rotation angle. The motor spun without any mechanical contacts.
The principle of the self-sensing sensors is based on a differential transformer. The AMB has upper and lower electromagnets with four coils. Two primary coils of the upper electromagnet are excited by the PWM amplifiers. The induced voltage is led to the two secondary coils for sensing displacements. From the results, the relationship between output voltage and vertical rotor displacement at liquid nitrogen temperature is linear in the displacement range from -0.3 to 0.3 mm.
The dynamics of the self-sensing AMBs were studied. Impulse responses for the AMBs were investigated. As a result, damped free-vibration curves are observed in impulse responses. The vibration curves seem to decrease exponentially. From these results, the self-sensing AMBs are useful for suppressing the rotor vibrations - even in the low temperature environment. Less