JPH0919100A - Motor tightly sealed to reduced pressure state and its manufacture - Google Patents

Abstract

PURPOSE: To provide a polygon mirror motor tightly sealed to a state of reduced pressure with an extremely small windage loss which has a high rotating accuracy even at a high speed. CONSTITUTION: A magnetic fluid bearing, which utilizes magnetic fluid 9 for lubricating and sealing bearing 7 and 8, is used; a flange 5 is provided at an open end of a housing 5 having a bottom, and a cover capable of maintaining airtightness is arranged in the flange portion; and a polygon mirror motor 1 as a target is tightly sealed to a reduced pressure state within a pressure- reduced chamber without providing any special air vent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided with a bearing structure suitable for maintaining precision rotation, and particularly, it has a low power loss at a high speed rotation like a polygon mirror motor for a laser beam printer.
Moreover, the present invention relates to a motor that requires strict rotational accuracy.

[0002]

2. Description of the Related Art Recently, in OA laser beam printers, as the performance and performance of devices have been improved, polygon mirror motors for laser scanning used therein have been required to have high rotational accuracy. Conventionally, a ball bearing has been used for this motor, but a non-contact type fluid lubrication bearing has come to be used in terms of high speed and rotational fluctuation. Further, an air bearing and a magnetic fluid bearing having an excellent sealing property have been proposed and put into practical use under the conditions of use in a clean environment. In particular, magnetic fluid bearings are
Since the magnetic fluid has high viscosity, high bearing rigidity can be obtained with a small-diameter bearing, and damping performance against shaft vibration is good, and it is effective as a bearing device for high-precision rotation as disclosed in JP-A-1-320314 and JP-A-3-51514. It is disclosed in the publication.

[0003]

According to the above-mentioned prior art, the application of the fluid bearing has been proposed for the high speed and high precision rotation of the motor, and the magnetic fluid is used to enable the use in a clean environment. We are trying to achieve the purpose by using magnetic fluid bearings used for lubrication and sealing of bearings and dynamic pressure group type air bearings. In addition, recently, in the laser beam printer for OA, the number of revolutions is 30,000 r due to high speed and high definition of printing.
It requires a polygon mirror motor that can rotate at a high speed of at least min. The rotation speed of the polygon mirror motor is 30,000 r / mi
Above n, motors using either bearing will remarkably increase the windage loss of the rotor, the temperature rise due to heat generation of the motor cannot be ignored, and cannot be used unless forced cooling. However, in the OA laser beam printer, it is not possible to provide special cooling equipment for the motor in terms of the compactness of the main machine and the manufacturing cost, so it is necessary to reduce the windage loss of the rotor and suppress the temperature rise. The method of reducing the windage loss of the rotor is to fill the motor housing with dilute gas,
A method is known in which the pressure is reduced to reduce the density of gas in the housing and the housing is rotated.

Since the air bearing has a bearing action by utilizing the viscosity of air, a dilute gas having a density lower than that of air is filled in place of air to reduce the wind loss while maintaining the bearing action. However, it cannot be used in a depressurized environment because the bearing loses its function. The magnetic fluid bearing has a high sealing property against the magnetic fluid enclosed in the bearing portion due to its structure,
Moreover, since the bearing characteristics do not change in any environment, it is suitable for bearings of polygon mirror motors, but in order to maintain the interior of the motor housing in a special environment for a long period of time, it is necessary to devise a mechanism to ensure the inside and outside of the housing. Also,
Since the polygon mirror motor for OA is required to be mass-produced, compact, and low-priced, a simple method can be used to make the housings of a large number of motors at a time in the special environment described above and to secure a highly confidential motor. Must be manufactured.
Therefore, unless such a problem is solved, it is not possible to provide a polygon mirror motor having high reliability and low power loss. However, in the conventional pressure reducing motor, no specific consideration is given to the configuration of the motor including the manufacturing facility, the manufacturing method, and the facility, and the pressure reducing motor has not been put to practical use in mass-produced products. .

An object of the present invention is to provide a structure of a polygon mirror motor capable of maintaining a depressurized environment in the motor housing for a long period of time and a method of manufacturing a motor in which a plurality of motors are simply depressurized and assembled.

[0006]

According to the present invention, in order to achieve the above-mentioned object, a magnetic fluid bearing suitable for use in a reduced pressure state so as to maintain a low loss even in a high speed region and a highly accurate rotation. Is used for the polygon mirror motor configuration. That is, a radial bearing is arranged in a bottomed bearing chamber integrally formed with a motor housing, and a shaft rotatably supported by the radial bearing, a rotor attached to the shaft, and a magnetic field provided in the housing. A motor for driving a rotating coil with a coil for generation and a member constituting a magnetic circuit in the rotating body arranged to face the coil, wherein the shaft is provided at an open end of a bottomed bearing chamber. The magnetic fluid seal configured as described above is arranged, and a magnetic fluid is sealed in this bearing chamber to rotatably support the shaft by fluid lubrication, and the sealed magnetic fluid is sealed by the magnetic fluid seal. A cover that can maintain airtightness is arranged at the open end of the housing to easily assemble the motor in a depressurized state without using a special air vent for depressurizing the inside of the housing. It has the structure of a polygon mirror motor capable.

In a concrete method of manufacturing a polygon mirror motor according to the present invention, one or a plurality of the motors are installed in a chamber, and a movable rod arranged in the chamber can be used to maintain airtightness at the open end of the housing. The covers are set at intervals, the inside of the chamber is made airtight to a prescribed decompressed environment, and then the covers arranged at intervals at the open ends of the housing are pressed against the housing by the rods described above, and then inside the chamber. Is released to atmospheric pressure, and the inside of the motor housing is set to a reduced pressure environment.

[0008]

Since the structure is such that the inside of the polygon mirror motor housing can be depressurized without providing a special air vent for depressurization, the airtightness is high, the depressurized state can be maintained for a long time, and the motor can be operated with low loss. You can drive. Therefore, the motor according to the invention does not require special cooling. Further, since minute bubbles contained in the magnetic fluid can be degassed during depressurization, it is possible to suppress fluctuations in the rotation of the motor due to viscous friction in the bearing chamber. Further, since the polygon mirror motor according to the present invention is configured as a motor that can set a plurality of motors in the decompression chamber and can be in a decompressed state, it is possible to provide a low-cost motor excellent in mass productivity.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

A motor 1 shown in FIG. 1 is a polygon mirror motor having a polygon mirror for scanning a laser.

The housing 5 of the polygon mirror motor 1 shown in FIG. 1 is made of aluminum and has a bottomed bearing chamber 6 integrally formed therewith.
It has. In the bearing chamber 6, radial bearings 7 and 8 and a magnetic fluid seal 10 having a permanent magnet 11 are arranged above the radial bearing 7 with a space therebetween, and a magnetic fluid 9 is sealed therein. A lid 21 is provided below the radial bearing 8, and an O-ring 22 constitutes a bottomed housing which is kept airtight. This radial bearing 7,8
Supports a magnetically permeable shaft 2 with a magnetic fluid 9 so as to be rotatable by fluid lubrication. The magnetic fluid seal 10 forms a magnetic circuit of the magnetic fluid 9 sealed in the bearing chamber 6 by using the permanent magnet 11 and the shaft 2 so as to prevent the magnetic fluid 9 from flowing out of the bearing chamber 6. The polygon mirror 4 is fixed to the rotating body 3 fixed to the shaft 2 by screws 13. And
The axial load of the rotating member such as the rotating body 3 and the polygon mirror 4 is constituted by a permanent magnet 12a fixed to the outer periphery of the bearing chamber 6 and a permanent magnet 12b fixed to the inner periphery of the rotating body 3 for a magnetic thrust bearing. Supported by. A motor substrate 17 is fixed to the housing 5, and a coil 18 for generating a magnetic field is provided on the motor substrate 17. This coil 18
A permanent magnet 20 and a yoke 19 that form a magnetic circuit are provided in the rotating body 3 that is disposed so as to face the rotating body 3, and the rotating body 3 serves as a motor that is driven by a rotating magnetic field. The open end of the housing 5 is in the shape of a flange, and the cover 16 is fixed to the flange with a screw 14.
Airtightness is maintained by 5. The polygon mirror motor 1 thus configured has a structure in which the inside and the outside are kept airtight by a few O-rings, and the inside a can be maintained in a depressurized state for a long period of time without using a special air vent. The depressurization of the polygon mirror motor 1 is performed by the device shown in FIG.

FIG. 2 is a partial sectional view of equipment for manufacturing the polygon mirror motor 1 which is hermetically sealed in a depressurized state. The decompression chamber 23 includes a pedestal 24b and a casing 24a.
The polygon mirror motor 1 can be stored in plural units. The frame 24b is provided with a guide portion 30 for positioning the polygon mirror motor 1, and the polygon mirror motor 1 is set at this position. At this time, the housing 5 and the cover 16 are set on the mount 24b without using the screws 14. Then, in this state, the casing 24a is fixed to the pedestal 24b to form the decompression chamber 23 having high airtightness. Exhaust port 2 on casing 24a
5 and an intake port 26 are provided so that the inside of the chamber 23 can be depressurized to a prescribed pressure by a vacuum pump. When the pressure is reduced, the intake port 26 is closed by the valve 27.

After setting the polygon mirror motor 1,
The movable rod 28 provided on the casing 24a is moved until it comes into contact with the cover 16, and the rod 28 and the cover 16 are joined by the adhesive member 31. Then, the rod 28 is lifted to keep the clearance between the motor housing 5 and the flange portion of the cover 16 at a predetermined dimension h. Rod 28 and cover 16
Although the bonding method is shown here as an example,
Alternatively, magnetic attraction force, vacuum chuck, screw connection or the like may be used. In such a state, the chamber 23 is depressurized to a prescribed pressure with a vacuum pump. Since the wind loss of the polygon mirror motor 1 is determined by the degree of vacuum, it is 1/10 of the wind loss under the atmospheric pressure condition.
The pressure is reduced to 100 Torr or less for the following. It is necessary to set the degree of vacuum to a pressure at which contamination of the polygon mirror due to evaporation of the magnetic fluid does not occur. In the case of a polygon mirror motor, it is desirable to reduce the inner pressure b of the chamber to 10 Torr to 100 Torr.

While maintaining a predetermined depressurization condition, the cover 16 is pressed against the housing 5 using the rod 28, and the valve provided in the intake port is opened to open the chamber 23 to the atmospheric pressure. Even if the chamber 23 is opened to the atmospheric pressure, the inside of the polygon mirror motor 1 is kept airtight by the O-rings 15 and 22, so that the depressurized state can be maintained. After releasing the chamber to atmospheric pressure, the polygon mirror motor 1 is taken out from the chamber 23 and the cover 16 is attached to the housing 5 with the screw 1.
It is possible to complete the polygon mirror motor 1 that is fixed to the housing 5 by 4 and is hermetically sealed in a depressurized state. The housing 5 and the cover 16 of the polygon mirror motor 1 are made of aluminum castings. However, mold castings and die castings have blowholes inside. And the outside may communicate with each other and the reduced pressure may not be maintained. In order to prevent this, it is desirable to seal the housing 5 and the cover 16 with resin or the like.

The reason why the magnetic fluid is used in the polygon mirror motor according to the present invention is that the lubricating magnetic fluid sealed in the bearing portion has a simple structure by arranging a ring-shaped permanent magnet at the position shown in FIG. Since leakage can be prevented and the clearance formed by the permanent magnet 11 of the magnetic fluid seal part and the rotating shaft is set to a size of 0.05 mm to 0.1 mm even under reduced pressure, the evaporation of the magnetic fluid can be ignored. This is a small number and does not contaminate the polygon mirror 4. In terms of rotational performance, the polygon mirror motor can be supported with high accuracy and smoothness by supporting the shaft 2 with fluid lubrication by the magnetic fluid sealed in the bearing portion. Therefore, the magnetic fluid bearing according to the present invention uses the magnetic fluid for both lubrication and sealing of the bearing. A feature of the polygon mirror motor according to the present invention that is hermetically sealed in a depressurized state is that when the polygon mirror is rotated at a high speed under atmospheric pressure, the magnetic fluid is sealed in the bearing by rotation in a high speed rotation region of 20,000 r / min or more. Bubbles are entrained in the bearing, which enters the sliding surface of the bearing and causes fluctuations in viscous friction.
A Taylor vortex may be generated in the S part of the item to increase the rotation fluctuation. In the case of a decompression type motor, even minute bubbles contained in the magnetic fluid are degassed during decompression and no Taylor vortex is generated, so such a phenomenon does not occur and a polygon mirror motor with high rotation accuracy can be provided. .

[0016]

According to the present invention, since the polygon mirror motor is hermetically sealed in a depressurized state, it is possible to provide a polygon mirror motor which has a high rotational accuracy and a small loss and which does not require cooling.
Further, the polygon mirror motor according to the present invention is installed in a single chamber or in a plurality of chambers, and a cover capable of maintaining airtightness is provided at an open end of the housing with a movable rod arranged in the chamber at an interval to keep the airtight state. After the inside of the chamber is set to the specified depressurized environment, the cover placed at the open end of the housing is pressed against the housing by the rod, and then the inside of the chamber is released to the atmospheric pressure, so that the inside of the motor housing is depressurized to assemble. It is possible to provide a low-cost motor manufacturing method suitable for mass production.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a polygon mirror motor showing an embodiment of the present invention.

FIG. 2 is a partial sectional view of a polygon mirror motor manufacturing facility of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polygon mirror motor, 2 ... Axis, 4 ... Polygon mirror, 5 ... Housing, 6 ... Bearing chamber, 7, 8 ... Radial bearing, 9 ... Magnetic fluid, 10 ... Magnetic fluid seal, 23 ... Chamber.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H02K 21/24 F16J 15/40 A

Claims (3)

[Claims] 1. A radial bearing is disposed in a bottomed bearing chamber integrally formed in a non-magnetic housing, and a magnetically permeable shaft rotatably supported by the radial bearing is attached to the shaft. A rotating body, a coil for generating a magnetic field provided in the housing, and a member that constitutes a magnetic circuit are provided in the rotating body arranged to face the coil, and in a motor driven by a rotating magnetic field, a bottomed bearing chamber A magnetic fluid seal composed of the shaft is arranged at the open end, a magnetic fluid is sealed in the bearing chamber to form a magnetic fluid bearing that rotatably supports the shaft by fluid lubrication, and at the open end of the housing. The motor is constructed by arranging a cover capable of maintaining airtightness with a distance from the housing and pressing the cover against the housing of the motor under a reduced pressure condition to seal the inside of the housing. Motor sealed in a reduced pressure state to. 2. The motor sealed in a depressurized state according to claim 1, wherein the housing and the cover are made of aluminum, and the housing and the cover are coated with a resin or the like for sealing treatment. 3. A radial bearing is arranged in a bottomed bearing chamber integrally formed in a motor housing, and a shaft rotatably supported by the radial bearing, a rotor attached to the shaft, and A motor provided with a coil for generating a magnetic field provided in a housing and a member constituting a magnetic circuit in the rotating body arranged so as to face the coil and driven by a rotating magnetic field at an open end of the bearing chamber. A magnetic fluid seal configured with the shaft is arranged, a magnetic fluid is sealed in the bearing chamber to support the shaft rotatably by fluid lubrication, and airtightness can be maintained at the open end of the housing. The cover is set, the motor is installed in the chamber alone or in a plurality of chambers, and the movable rod arranged in the chamber is used to set a predetermined portion on the flange portion of the housing and the flange portion of the cover. After making the inside of the chamber, which has been set in a hermetically sealed state, with a gap, to a specified depressurized environment, the cover placed at the open end of the housing is pressed against the housing by the rod, and then the inside of the chamber is released to atmospheric pressure. A method of manufacturing a motor sealed in a depressurized state, characterized in that the inside of the motor housing is depressurized.