Junichi Asama

Effects of Permanent-Magnet Passive Magnetic Bearing on a Two-Axis Actively Regulated Low-Speed Bearingless Motor

Performance comparisons in a bearingless motor with and without passive magnetic bearings (PMBs) are presented. The bearingless motor is actively controlled in two perpendicular-axes. The axial and conical movements are supported by PMBs. The experimental results are compared to the calculated ones by 3-D finite-element method. Effectiveness of PMBs is analytically and experimentally investigated in both static and dynamic tests. It is found that a rotational test is successful only with the PMBs.

Development of a Four-Axis Actively Controlled Consequent-Pole-Type Bearingless Motor

In this paper, a design-optimization method for a consequent-pole bearingless motor with a rather large air-gap length is presented. A rotor iron and permanent-magnet structure is proposed which enhances the suspension-force capability during startup. Magnetic saturation in the rotor-iron pole area is solved, and the stator iron is designed so that magnetic saturation is avoided. The design optimization is based on finite-element-method analysis. It is shown that startup is achieved from the touch-down condition in the experiments.

A design consideration of a novel bearingless disk motor for artificial hearts

A novel bearingless disk motor for a possible application of implantable centrifugal artificial hearts is proposed in this paper. To reduce a motor height, C-shaped stator cores with radially expanded coil windings are employed. End windings are not located in the axial direction. The motor height and an outer diameter are designed to be 10mm and 70mm, respectively. Magnetic suspension characteristics of the bearingless disk motor are analyzed by using finite element method. The design consideration of a suspension winding configuration has been discussed especially on radial suspension force variations. A prototype machine is fabricated and tested. Experimental results have provided the feasibility of the design of the bearingless disk motor.

Principle of a Novel Single-Drive Bearingless Motor With Cylindrical Radial Gap

In this paper, a novel single-drive bearingless motor with cylindrical radial air-gap is proposed. The single-drive bearingless motor has only one set of three-phase windings. It generates both torque and axial suspension force independently with only one three-phase inverter and one displacement sensor. Therefore, this single-drive bearingless motor has the advantages of low cost and small size. Only axial direction z-axis is actively positioned. The other axes, radial movements x and y, and tilting movements θ∞ and θy, are passively stable. In the proposed motor, the rotor is a cylindrical permanent magnet magnetized in a radial parallel direction. The stator consists of six C-shaped cores and one set of three-phase windings. The principles of the suspension force and torque generations by the dand q-axis currents, respectively, are shown. The proposed machine was fabricated and tested only to confirm the principles. In the experiments, start-up was successfully achieved. In an acceleration test up to 3600 r/min, stable magnetic suspension and speed regulation by the d- and q-axis current regulations were confirmed.

Basic characteristics of 150,000r/min switched reluctance motor drive

Developments of high speed motor drive have been described. A switched reluctance motor has been designed for 2 kW output at a rotational speed of more than 100,000 r/min. A test machine has been constructed based on the design. The iron parts are fabricated by 6.5% silicon steel, i.e., low iron loss material. The rotational speed of 150,000 r/min is reported experimentally. Fast and accurate controller has been developed using field programmable gate array device.

Development of a one-axis actively regulated bearingless motor with a repulsive type passive magnetic bearing

This paper describes a novel one-axis actively regulated bearingless motor with a spinning top-shaped rotor, which is intended for a use as a cooling fan. This motor requires only one set of three-phase winding and thus one three-phase inverter to realize both rotation and magnetic suspension, and thus it is dubbed a single-drive bearingless motor. An axial position of the rotor is actively regulated and radial and tilting motions are passively stabilized by the passive magnetic bearing. Torque and axial suspension force are regulated by q-axis and d-axis currents, respectively. In this paper, the structure and principle, design, and test results of the proposed bearingless motor are presented.

Influence of Rotor Skew in Induction Type Bearingless Motor

A prototype induction type bearingless motor has been developed with 4-axis active position regulation. In the developed motor, a problem of serious axial oscillation is observed during high acceleration and deceleration of shaft rotation. In the worst case, the shaft touched down and magnetic suspension was not possible. In this paper, the cause of the axial oscillation is presented. The axial shaft oscillation is shown to be caused by the skew of rotor conductors. One possible solution has been proposed and its effectiveness is verified in a prototype bearingless motor.

Suspension Characteristics Measurement of a Bearingless Motor

Bearingless PM motors which have additional suspension windings have been designed with 3D FEM. To verify satisfactions in practical application, a test machine has been built. In this paper, suspension force is measured with the static forces. Two experimental methods are proposed. It is proved that those procedures are suitable even if it is in limited conditions, only one shaft end can be used for static force applied. Furthermore, the relation of the suspension force and rotor rotational angle is shown.

Stator design of a multi-consequent-pole bearingless motor with toroidal winding

Multi-consequent-pole bearingless motors have been developed for low rotational speed and swinging stages used in monitoring system and vacuum process chambers. The motor has flat shape and two degrees of freedom are actively controlled in the radial x-y directions. The suspension windings have a novel structure of a toroidal coil wound around the stator yoke. The structure realizes a short axial length with compact coil end-windings. In this paper, the toroidal winding design is compared with conventional distributed winding design. The design process indicates a consideration of magnetic saturation in the stator yoke with three dimensional finite element analysis. A special design consideration for the stator yoke is required because of significant leakage flux caused by the toroidal winding. It is shown that a compact axial length is realized. It is also shown that a wide cross sectional area is required in the stator yoke compared with conventional distributed windings.

Design and test result of novel single-drive bearingless motor with cylindrical radial gap

In this paper, a novel single-drive bearingless motor with the cylindrical radial air-gap is proposed. The single-drive bearingless motor has only one set of three-phase windings. It generates both torque and axial suspension force independently with only one three-phase inverter and one displacement sensor. Therefore, the single-drive bearingless motors have the advantages of low cost and small size. Only axial direction z-axis is actively positioned. The other axes, radial movements x and y, and tilting movements θx and θy, are passively stable. In the proposed bearingless motor, the rotor is a cylindrical permanent magnet magnetized in a radial parallel direction. The stator consists of six C-shaped cores and one set of three-phase windings. The principles of the suspension force and the torque generations by the d- and q-axis currents, respectively, are shown. The test machine is fabricated and tested. In the experiments, the start-up is successfully achieved. In the acceleration test up to 3600 r/min, the stable magnetic suspension and the speed regulation by the d- and q-axis current regulation are confirmed.