Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-01-17
1998-09-08
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 61, H02K 709, B23Q 1110
Patent
active
058049002
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to magnetic bearing spindle devices for use as machine tools.
Throughout the specification, the term "front" refers to the left-hand side of each of the drawings, and the term "rear" to the opposite side thereof.
BACKGROUND ART
The spindle devices for use as machine tools include antifriction bearing spindle devices in addition to magnetic bearing spindle devices. Magnetic bearing spindle devices comprise as arranged within a housing a spindle, motor, radial magnetic bearings, an axial magnetic bearing, radial sensors, an axial sensor and touchdown bearings. The spindle is adapted to be supported contactlessly by the radial magnetic bearings and the axial magnetic bearing relative to the housing. Antifriction bearing spindle devices comprise a spindle, motor and antifriction bearings which are arranged with a housing. The spindle is rotatably supported by the antifriction bearings relative to the housing. Magnetic bearing spindle devices have the advantages over antifriction bearing spindle devices that the spindle can be greater in diameter, given higher rigidity and driven at a higher speed with a diminished bearing loss.
For some kinds of work, there arises a need to apply a cooling-working fluid to the workpiece from the front end of the spindle for cooling the workpiece and the tool. To fulfill the need, an antifriction bearing spindle device is proposed which has a cooling-working fluid channel extending through the spindle axially thereof, and a tubular cooling-working fluid supply member fixed to the rear end of the housing and connected to the spindle by a rotary joint. The rotary joint comprises a pipe member attached to the rear end of the spindle and housed in an outer frame fixed to the supply member, and an annular seal member fitted in a clearance between the pipe member and the outer frame to provide a sealed structure. In the case of the antifriction bearing spindle device, the spindle is always in a fixed position radially thereof, so that the cooling-working fluid can be readily prevented from leaking from the joint of the fluid supply member and the spindle in the manner described as by an oil seal. Moreover, the working fluid, even if leaking in a small amount, will produce no adverse effect on the entire device.
With the magnetic bearing spindle device, however, the spindle at a halt differs from the spindle in operation in its position with respect to the radial and axial directions. Accordingly, even if the spindle has a cooling-working fluid channel extending axially therethrough, with a tubular cooling-working fluid supply member fixed to the rear end of the housing, the spindle can not be connected to the fluid supply member by a rotary joint. Since sealing means of the contact type, if used, fails to permit high-speed rotation of the spindle, it appears possible to insert the fluid supply member into the fluid channel of the spindle with a clearance formed around the member, whereas it is then impossible to completely prevent leakage of the working fluid. Furthermore, leakage of the working fluid, if occurring, gives rise to an insulation failure especially when the fluid is soluble in water, causing damage to the motor, magnetic bearing, sensor or the like and leading to a malfunction of the entire magnetic bearing spindle device.
An object of the present invention is to provide a magnetic bearing spindle device free of the foregoing problems.
DISCLOSURE OF THE INVENTION
The present invention provides a magnetic bearing spindle device which comprises a spindle disposed within a housing, magnetic bearings for contactlessly supporting the spindle relative to the housing while the spindle is in rotation, and mechanical touchdown bearings for supporting the spindle in contact therewith when the spindle is initiated into rotation and when the spindle is brought to a halt, the magnetic bearing spindle device being characterized in that the spindle is formed with a cooling-working fluid channel extending axially therethrough.
When a
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Taniguchi Manabu
Ueyama Hirochika
Koyo Seiko Co. Ltd.
Mullins B.
Stephan Steven L.
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