Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-01-16
2003-11-25
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06653756
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to magnetic bearing devices, and more particularly to a magnetic bearing device for magnetically levitating a rotary body by contactlessly supporting the body with a plurality of magnetic bearings with respect to an axial direction and two radial directions orthogonal to each other and to the axial direction.
Already known as such magnetic bearing devices are those having five control axes, i.e., a control axis in an axial direction and two control axes respectively in two radial directions at each of two locations in the axial direction.
Magnetic bearing devices of the five-axis control type comprise an axial magnetic bearing for contactlessly supporting a rotary body with respect to the direction of axial control axis, two radial magnetic bearings for contactlessly supporting the rotary body with respect to the two directions of radial control axes orthogonal to each other at each of the two locations in the axial direction, and protective bearings (touchdown bearings) serving as mechanical restraining means for mechanically determining the movable ranges of the rotary body in the axial direction and the radial directions. The axial magnetic bearing comprises a pair of electromagnets so arranged as to hold the rotary body at opposite sides thereof in the direction of axial control axis for magnetically attracting the body. Each of the radial magnetic bearings comprises a pair of electromagnets so arranged as to hold the rotary body at opposite sides thereof in the direction of radial control axis concerned for magnetically attracting the body. Furthermore, the magnetic bearing device comprises a position detector serving as position detecting means for detecting the position of the rotary body with respect to the direction of each of the five control axes, and an electromagnet controller serving as electromagnet control means for controlling the pair of electromagnets for the control axis based on the result of detection of the position by the position detector. The position detector in the direction of axial control axis comprises one axial position sensor opposed to the end face of the rotary body to be detected from the direction of axial control axis. The position detector in the direction of each radial control axis comprises a pair of radial position sensors opposed to the rotary body and so arranged as to hold the body at opposite sides thereof in the direction of the control axis. The electromagnet controller comprises a proportional operation unit, differential operating unit and integral operating unit.
With respect to the direction of each control axis, the magnetic bearing device described has a mechanical central position for the movable range determined by the protective bearings, a magnetic central position relative to the positions of the electromagnets of the magnetic bearing, and central position relative to the sensors, i.e., relative to the positions of the position sensors. The mechanical central position in the direction of each control axis is the position of center of the movable range determined by the protective bearings. The magnetic central position with respect to the direction of each control axis is the position of the center of the pair of electrode magnets as arranged in the direction of the control axis. The central position relative to the sensor in the direction of the axial control axis is such that the gap (clearance) between the position detecting end face of the rotary body and the axial position sensor has a predetermined value. The central position relative to the sensors in the direction of each radial control axis is the position of center of the pair of radial position sensors as arranged in the direction of the control axis. The magnetic bearing device is so designed that the mechanical central position, the magnetic central position and the central position relative to the sensors are all in coincidence, whereas an error is likely to occur between the centers owing to manufacturing errors or assembling errors.
With the conventional magnetic bearing device, the electromagnets of the magnetic bearings are so controlled that the rotary body will be held at the central position relative to the sensors which is the designed central position, that is, the center of the rotary body will be at the central position relative to the sensors. Accordingly, the rotary body can not be held at the mechanical central position if the central position relative to the sensors is not in coincidence with the mechanical central position. When the difference of the mechanical central position of the rotary body from the central position relative to the sensors is great in this case, the clearance between the rotary body and the protective bearing diminishes locally to result in troubles.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic bearing device capable of magnetically levitating a rotary body approximately at the mechanical central position of the device easily.
The present invention provides a magnetic bearing device for magnetically levitating a rotary body by contactlessly supporting the body with magnetic attraction of pairs of electromagnets with respect to an axial direction and two radial directions orthogonal to each other and to the axial direction, the rotary body having movable ranges in the three supporting directions determined by mechanical restraining means, the magnetic bearing device being characterized in that the device comprises a pair of electromagnets so arranged as to hold the rotary body at opposite sides thereof in the direction of each of control axes in the respective three supporting directions, means for detecting the position of the rotary body in the direction of the control axis and electromagnet control means having at least an integral operation unit for controlling the electromagnets based on the result of detection of the position by the position detecting means, the electromagnet control means comprising a target levitated position setting means for setting as a target levitated position of the rotary body in the direction of the control axis the position of the rotary body corresponding to the median of an integral output which is the output of the integral operation unit when the rotary body is magnetically levitated in the vicinity of one of limit positions in the direction of the control axis determined by the mechanical restraining means and an integral output of the integral operation unit when the rotary body is magnetically levitated in the vicinity of the other limit position.
The pair of electromagnets to be used for each control axis are usually identical in characteristics. The electromagnet control means supplies to each electromagnet an energizing current comprising the combination of a predetermined steady-state current and a control current which varies depending on the position of the rotary body in the direction of the control axis. The steady-state current values for the pair of electromagnets are equal to each other, and the control currents therefor are equal to each other in absolute value but opposite in sign.
In the case where no force other than the magnetic attraction of the electromagnets acts on the rotary body as in the case of a horizontal control axis, and when the rotary body is contactlessly supported at a position with respect to the direction of the control axis, the magnetic attracting forces of the two electromagnets on the rotary body are equal to each other. Further the magnetic attraction of each electromagnet is in proportion to the square of the magnitude of the energizing current of the electromagnet and in inverse proportion to the size of the gap between the electromagnet and the rotary body. When the rotary body is supported at the magnetic central position, the gaps between the rotary body and the respective electromagnets are equal to each other in size, with the result that the energizing current values of the respective electromagnets are equal to each other. Thus, th
Kameno Hironori
Taniguchi Manabu
Ueyama Hirochika
Koyo Seiko Co. Ltd.
Le Dang
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