Takahisa Ohji

Modeling and control of a new horizontal-shaft hybrid-type magnetic bearing

This paper reports on the development of a new horizontal-shaft hybrid-type magnetic bearing system. The bearing system will be used for a horizontal-shaft machine. The rotor is levitated due to the repulsive force between a stator and a rotor permanent magnet (PM). A lower cost and higher radial stiffness have been achieved by using a strontium-ferrite magnet on the rotor and an Nd-Fe-B PM above and below the rotor magnet. A finite-element analysis was performed to calculate the levitation force and radial stiffness. An upper stator magnet subtending an angle of 45/spl deg/ provides the best compromise between a large levitation force and radial stiffness. A model for the horizontal-shaft hybrid magnetic bearing system has been developed and includes the effect of the rotor dynamics and the electromagnetic forces. An integral servocontroller was designed to stabilize the axial position. The controller has been implemented in a digital signal processor. Experimental results performed on a prototype system are in agreement with the theoretical results.

Permanent magnet bearings for horizontal- and vertical-shaft machines: A comparative study

Two types of magnetic bearing systems employing permanent magnets to be used for vertical-shaft and horizontal-shaft machines, respectively, have been designed and fabricated in our laboratory. In this article we report a comparative evaluation of (i) the permanent magnet configuration and its effect on radial disturbance attenuation, (ii) magnetic losses and their effect on energy storage, and (iii) the off-state position of the rotor magnet in two types of bearing systems. Experimental results are presented.

Conveyance test by oscillation and rotation to a permanent magnet repulsive-type conveyor

Various applications of a single-axis controlled repulsive-type magnetic bearing have been proposed earlier. However, most conventional systems are equipped with a set of passive magnetic bearings and an active magnetic bearing. In this paper a new repulsive-type conveyor system with many passive magnetic bearing pairs is proposed. This system enables an easy rotation with negligible friction and soft conveyance by radial stiffness between the rotor and the stator permanent magnets. This paper also reports a conveyance test using ellipse motion of each shaft.

A new repulsive type magnetic bearing-modeling and control

This paper reports on the development of a new repulsive type magnetic bearing system whose radial bearing section makes good utilization of the repulsive forces between stator and rotor permanent magnets resulting in a simplified axial control scheme. The shape and configuration of the permanent magnet is the most critical component for satisfactory operation of this type of magnetic bearing. In this paper, modeling of the permanent magnets has been done with the help of finite element analysis and the nature of the repulsive forces and stiffnesses are estimated along the three directions. Using the forces and expressing the rotor dynamics the issue of modeling a real physical repulsive type magnetic bearing system is discussed. The controller has been configured around a digital signal processor. A prototype model has been designed and fabricated in our laboratory and experiments are carried out.

Permanent magnet configuration in repulsive type magnetic bearing for improved radial disturbance attentuation characteristics

This paper reports on the development of a repulsive type magnetic bearing system and the importance of permanent magnet (PM) configuration on the attenuation of radial disturbance. A new configuration of the permanent magnet of the bearing system resulting in improved stiffness characteristics in the radial direction has been described. Prototype models have been designed and developed in our laboratory and experiments carried out.

Disturbance attenuation and faster stabilization via permanent magnet placement on repulsive type magnetic bearing

Repulsive type magnetic bearings consisting of permanent magnets (PM) and controlled current electromagnets have the advantages of less number of electromagnets and simplified control circuit compared to active magnetic bearing. The system is a fundamentally unstable one and is very prone to disturbance. The shape and configuration of the permanent magnet has a strong influence on the stability of the system. Two models of repulsive type magnetic bearing have been designed and fabricated in our laboratory. Repulsive forces and stiffness characteristics for different PM configurations have been studied and suitable configuration have been chosen. This paper investigates a method of disturbance attenuation and faster stabilization via permanent magnet configuration on repulsive type magnetic bearing.