Katsuhiko Izawa

Flywheel vibration isolation test using a variable-damping isolator

This study demonstrates the isolation performance of a variable-damping isolator using a bio-metal fiber (BMF) valve to enhance the pointing performance of observation satellites by isolating disturbances induced by reaction wheel assemblies. Vibration isolation tests of the variable-damping isolator were performed using an air-floating wheel disturbance detector to investigate whether the isolator can actually isolate flywheel vibration. In this paper, we first present a recently developed variable-damping isolator with low power consumption, and a reaction wheel disturbance detector, fabricated in a previous study, which detects low-frequency disturbances. Next, we describe the effectiveness of the variable-damping isolator based on flywheel vibration isolation test results.

Development of variable-damping isolator using bio-metal fiber for reaction wheel vibration isolation

This study focuses on the basic characteristics of a variable-damping isolator using a bio-metal fiber (BMF) valve to enhance the pointing performance of optical equipment on-board satellites. A variable-damping BMF valve isolator for isolating disturbances induced by reaction-wheel operation has been designed and fabricated. The opening and closing of the valve to change the damping of the isolator is implemented by using characteristic variation of the bio-metal fiber to the input electric current. The BMF isolator fabricated in this study has the advantages of being a simple variable-damping device with low power consumption, unlike conventional variable-damping devices, such as solenoid-valve-type oil dampers and ER or MR dampers. This paper presents the basic characteristics of the BMF isolator obtained from dynamic tests of the isolator.

Analysis of Dynamics Interaction Between Satellite and Magnetic Bearing Wheel (MBW) with Inclined Magnetic Poles(1st Report, Stability Analysis)

A Magnetic Bearing Wheel (MBW) with inclined magnetic poles has been developed. This paper deals with dynamics interaction between a satellite and the MBW. In the MBW-satellite system, the MBW rotor is coupled with the satellite by magnetic bearing forces and torques and there is some possibility that the magnetic bearing controller makes the satellite nutation unstable. In this paper, equations of motion of the MBW-satellite system are formulated by Kanes method and based on the stability analysis of this system, it is shown that both cross feedback control of rotor gimbal angle and integrator in the ordinary magnetic bearing controller are instability factors of the satellite nutation. However, this nutation is stabilized with cross feedback control of the satellite angular rate estimated by a minimal order observer from the magnetic bearing control torques. The effects of the disturbance feedback controller in our 3rd report on the system stability are also considered, and the results show that the system stability is not affected by the disturbance feedback controller.

Development of Magnetic Bearing Wheel (MBW) with Inclined Magnetic Poles (2nd Report, Analysis of Disturbance Factors and Motion of MBW)

A Magnetic Bearing Wheel (MBW) with inclined magnetic poles is under development. This paper deals with the analysis of disturbance factors and motion of MBW. In general, disturbance factors of a magnetic bearing is limited to rotor imbalance, and motion of the magnetic bearing is discussed under the action of synchronous disturbance force/moment caused by the imbalance. This imbalance is defined by the radial shift (static imbalance) and tilt (dynamic imbalance) of sensor detection surface against the principal inertial axis of rotor. However, besides the imbalance, there are actually other disturbance factors such as the radial shift and tilt of rotor core surface similar to sensor detection surface, and the distortion of those surfaces so that MBW generates synchronous and harmonic disturbances. In this paper, all disturbance factors of MBW is formulated, and the relation between each factor and disturbance force/moment is clarified. Moreover, it is clarified that there are forward and backward components to the direction of rotor spin in radial harmonic disturbances.