Lateral Vibration Control of Flexible Rotor Levitated by Magnetic Bearing Using Laminated Piezoelectric Actuator

When the high-speed rotor suffers whirl vibration of bending mode natural frequency, the thrust disk mounted on its shaft end is subject tq both lateral and rotational vibration. With the rotor riding on a magnetic bearing, there is danger that the gap between the thrust disk mounted on the rotor and the stator yoke becomes uneven in a circumferential direction so that moment may occur from circumferentially unbalanced magnetic pull between them, thus inducing bending mode natural vibration. Two methods are conceivable for solving this problem and utilizing the thrust bearing to control lateral vibration. (1) One method is by splitting the thrust coil in a circumferential direction according to the gap between the thrust disk and the stator yoke to control lateral vibration. (2)The other method is by inserting a laminated piezoelectric actuator between the thrust casing and the thrust yoke and adding moment to the thrust disk by slanting the thrust yoke by the piezoelectric actuator, thus controlling lateral vibration. This paper discusses the attempt made to control the 1st bending natural vibration of the flexible rotor by the second method. Considering that this attempt resulted in reduction of the gain of the open loop transfer function of the system at the 1st bending natural frequency, this mathod can be considered effective in lateral vibration control. The gain at the natural frequency was reduced by approximately 3dB by compensating the radial sensor signal for phase lead and adding feedback to the piezoelectric actuator.