JPH06148552A - Dynamic pressure bearing motor - Google Patents

Abstract

PURPOSE:To provide the structure in which the shaft diameter of a part composing a dynamic pressure shaft bearing, and the diameter of a polygon mirror installing boss part can be small, and in which a shaft bearing surface and a mirror installation surface can be processed simultaneously easily. CONSTITUTION:A stator coil 7 composing a motor 6 is installed on an outer part of a shaft bearing member 2, a rotary magnet 8 is disposed on the outer side of it to be fixed to a rotary shaft 1, and at least part of the rotary shaft 1 is formed cylindrical having an inner side end surface 23 for only a pair of magnets 10, 11 composing a thrust magnetism shaft bearing 5 to be installed on the inner side of it, so that the rotary shaft 1 is supported contactlessly in the thrust direction, thereby the rotary shaft 1 formed compact in the smallest size possible securing the minimum space for containing the magnets 10, 11 as an inner space 22 in the rotary shaft 1, and making support possible by suction by a vacuum chuck from the inner side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor that supports a rotor with a dynamic pressure bearing. More specifically, the present invention relates to a rotor structure of a motor, such as a laser scanning motor or a high speed spindle motor, which incorporates a dynamic pressure bearing and rotates at a high speed.

[0002]

2. Description of the Related Art A laser scanning motor, a magnetic drum motor, a gyro motor, or a motor that rotates at high speed such as a high-speed spindle motor is capable of rotating at high speed. The hydrodynamic bearings that support the rotor and rotating shaft are used in. For example, a polygon mirror used as an optical scanning device such as a laser beam printer or a facsimile is attached to a rotary shaft supported by a dynamic pressure bearing so as to be rotatable at high speed.

The advantages of the optical scanning device using such a dynamic pressure bearing are that it can rotate at a high speed, has less unevenness in rotation, and has little runout of the rotating shaft. In particular, the fact that the polygon mirror has a small amount of surface wobbling (commonly referred to as surface tilt) associated with axial wobbling is an important item of the optical scanning device. In addition to the small swing of the rotating shaft, the squareness between the mirror mounting surface and the axis of the rotating shaft is an important factor. Therefore, in an optical scanning device that requires high accuracy, it is desirable to suppress the squareness error to 3 seconds or less.

By the way, as a cause of deteriorating the accuracy of the squareness of the mirror mounting surface, the outer peripheral surface of the rotary shaft (the outer peripheral surface of the boss portion for fitting the bearing surface and the polygon mirror) is processed and then temporarily covered. This is to remove the workpiece (rotary shaft) from the machine tool, set it again on a machine tool suitable for machining the mirror mounting surface, and shift to machining the mirror mounting surface. In a chuck mechanism for a workpiece having a round shaft shape of a normal machine tool, chucking accuracy varies, and an inclination of an axis center of about 3 seconds is within the range of the variation. Therefore,
In order to suppress this variation, after setting the rotary shaft, which is the workpiece, on the processing machine, it is preferable to process the bearing surface, the mirror mounting surface orthogonal thereto and the outer peripheral surface of the boss portion at the same time without resetting.

Conventionally, as a dynamic pressure bearing motor employing a rotary shaft capable of easily performing such simultaneous machining,
There is something like FIG. In this dynamic pressure bearing motor, the rotating shaft 101 has a cylindrical shape, and the motor is formed therein. The motor is composed of a magnet 103 fixed to an inner peripheral surface 124 of a cylindrical rotating shaft 101, and a stator coil 104 supported by a center pole 106 arranged inside the magnet 103. Stator coil 1
04 is usually wound around the core 105 and the center pole 1
Base member 10 mounted on the bearing member 102 side.
It is fixed at 7, etc. On the other hand, a groove 109 for dynamic pressure generation is formed on the outer peripheral surface 108 of the rotating shaft 101 as shown in FIG. 4, and a dynamic pressure bearing is formed between the groove 109 and the inner peripheral surface 110 of the cylindrical bearing member 102. Radial (radial) support. Further, a pressing plate 114 for fixing the polygon mirror 113 fitted in the boss portion 111 is attached to the upper end surface of the rotating shaft 101. Furthermore, the rotating shaft 10
The ring-shaped magnet 116 is attached to the space 115 inside the boss portion 111 that fixes the polygon mirror 113 of No. 1, and the rotary shaft 101 is thrust by the attraction force with the magnet 117 attached to the upper end of the center pole 106. A thrust magnetic bearing which is supported in a non-contacting direction is constructed.

As shown in FIG. 5, the rotary shaft 101 having such a structure is supported by suction from the inside by a vacuum chuck 120 inserted into a space 119 inside the rotary shaft 101. The vacuum chuck 120 has a tip surface 121.
Is pressed against the inner end surface 118 of the rotating shaft 101, and vacuum suction is performed by an intake hole 122 opening at that portion. The rotating shaft 101 is supported by a vacuum chuck 120, and the bearing surface 108, the mirror mounting surface 112, and the boss portion 11 are supported.
The outer peripheral surface of No. 1 (the inner peripheral guide surface of the mirror) is,
Finishing is simultaneously performed by the cutting tool 123 in a route such as b and c. Thereby, the bearing surface 1 of the rotating shaft 101
It is possible to obtain a very good perpendicularity between 08 and the mirror mounting surface 112.

[0007]

However, in such a structure, the motor is installed in the internal space 119 of the rotary shaft 101.
Because of the above configuration, the shaft diameter inevitably becomes large, and high speed rotation cannot be performed so much. That is, since the bearing loss and the heat generation amount due to the viscous resistance of the air present in the bearing gap during rotation are proportional to the cube of the diameter of the rotating shaft 101, a large driving force is required and heat generation is increased at high speed rotation. is there.

In the conventional structure, the polygon mirror 11 is used.
The boss portion 111 into which the polygon mirror 113 is fitted for accommodating the magnets 116 and 117 constituting the thrust magnetic bearing in the inner space 115 of the boss portion 111 to which 3 is attached.
There is no choice but to increase the diameter of the small polygon mirror 11
There is a limit for driving No. 3. That is, the small polygon mirror 113 cannot be fitted and attached to the boss portion 111 of the rotating shaft 101.

According to the present invention, the shaft diameter of the portion constituting the dynamic pressure bearing and the diameter of the boss portion to which the polygon mirror is attached are reduced, and the bearing surface and the mirror mounting surface are easily machined simultaneously. The purpose is to provide a motor.

[0010]

In order to achieve the above object, the present invention provides a cylindrical bearing member forming a part of a stator, and a rotary shaft forming a part of a rotor fitted in the bearing member and rotating. In a dynamic pressure bearing motor that configures a dynamic pressure bearing between and and supports the rotating shaft in the radial direction with the dynamic pressure bearing,
The stator coil that constitutes the motor is installed outside the bearing member, and the rotor magnet is arranged outside the bearing member to be fixed to the rotating shaft, while at least a part of the rotating shaft is formed into a cylindrical shape having an inner end surface, and the magnet is inside the The magnet is installed on the bearing member side so as to be opposed to the magnet, and the rotary shaft is not contacted in the thrust direction by the attractive force or repulsive force between the magnet fixed inside the rotary shaft and the magnet on the bearing member side. I will support you.

[0011]

Therefore, the internal space of the rotary shaft is sufficient if only the minimum space for accommodating the pair of magnets forming the thrust magnetic bearing can be secured, and the diameter of the rotary shaft can be reduced. Moreover, since the internal space of the rotating shaft has an internal end surface, the suction support by the vacuum chuck can be performed from the inside by utilizing the peripheral wall surface and the end surface of the internal space. Therefore, even if the rotating shaft has a small diameter, the chuck is supported by utilizing the internal space, and the outer peripheral surface of the bearing portion and the mirror mounting surface are machined at the same time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows a dynamic pressure bearing motor for a polygon mirror as an example of the dynamic pressure bearing motor of the present invention. This dynamic pressure bearing motor for a polygon mirror has a rotary shaft 1 to which a polygon mirror 3 is attached and which rotates, and a cylindrical bearing which houses the rotary shaft 1 and forms a dynamic pressure bearing 4 between the rotary shaft 1 and the rotary shaft 1. The member 2, the base member 9 that closes the bottom of the bearing member 2 and supports the column 20, the pair of magnets 10 and 11 that form the thrust magnetic bearing 5, and the drive unit / motor 6 fixed to the rotary shaft 1. The rotor magnet 8 and the stator coil 7 are mainly included.

The rotating shaft 1 has a boss portion 15 into which the polygon mirror 3 is fitted, a bearing portion 12 having a larger diameter than the boss portion 15, and a mirror mounting surface 14 for receiving the polygon mirror 3 at a boundary between these. And a pressing plate 16 is provided at the upper end so as to be attached by a tightening screw 17. Therefore, by fitting the polygon mirror 3 to the boss portion 15 and attaching the pressing plate 16, the polygon mirror 3 is pressed and fixed to the mirror attachment surface 14 in a state where the radial positioning of the polygon mirror 3 is performed. Further, on the outer peripheral surface (so-called bearing surface) of the bearing portion 12 of the rotating shaft 1,
For example, the groove for generating dynamic pressure is about 5 μm due to etching or the like.
It is formed with a depth of 20 μm, and a surface treatment for improving abrasion resistance, for example, the surface treatment disclosed in Japanese Patent Laid-Open No. 63-235719 is applied thereon. Further, the rotating shaft 1 has a cylindrical portion having an inner end surface 23 at least in part. For example, in the case of the present embodiment, the space 22 is provided inside the bearing portion 12 and the inner end surface 23 is formed. Further, the protrusion 16 of the pressing plate 16 is also provided inside the boss portion 15.
A recess 25 for accommodating a is formed. Further, a screw hole 27 into which the tightening screw 17 is screwed is provided in a partition wall 26 portion that divides the internal space 22 and the recess 24. The polygon mirror 3 is fitted into the boss portion 15,
A pressing plate 16 is placed on it and is fixed to the rotary shaft 1 by a tightening screw 17.

A ring-shaped magnet 10 is fixed to the peripheral wall surface 24 of the internal space 22 of the rotary shaft 1. Further, the magnet 11 is provided inside the magnet 11 so as to face the magnet 10.
Are arranged. The magnet 11 is fixed to a column 20 that is erected at the center of the base member 9.
The magnet 10 and the magnet 11 are arranged so as to attract each other, and constitute a thrust magnetic bearing 5 that supports the rotating shaft 1 in the axial direction in a non-contact manner by the attraction force.

A hub 18 is fixed to the stepped portion at the upper end of the bearing portion 12 of the rotary shaft 1 by, for example, press fitting. The hub 18 has a cup shape surrounding the stator coil 7 and the core 19 of the bearing member 2, and the rotor magnet 8 is attached to the inner peripheral wall surface of the peripheral portion thereof. The rotor magnet 8 is arranged so as to face the stator coil 7 and the core 19 in the radial direction of the rotating shaft 1.

The bearing member 2 is formed of an aluminum alloy or the like, and has a surface treatment for improving wear resistance, such as a wear resistant coating or a lubricious coating as disclosed in JP-A-63-235719. It is applied to the inner peripheral surface that constitutes the bearing surface. A core 19 made of a laminated plate is attached to the outer periphery of the bearing member 2, and the stator coil 7 is wound around the core 19.

A small vent hole 21 is opened in the base member 9, and an internal space 22 in the rotary shaft 1 which is substantially sealed between the bearing member 2 and the rotary shaft 1 and the base member 9 is used as an air damper. Make it work. The resistance to the entry and exit of air changes depending on the diameter and length (depth) of the vent hole 21.

In the rotary shaft 1 of the optical scanning device thus constructed, the motor 6 is arranged outside the bearing member 2 and the rotary shaft 1, and the magnets 10, 1 constituting the thrust magnetic bearing 5.
Since only 1 is arranged inside the rotary shaft 1, its size is reduced as necessary to the extent that the magnets 10 and 11 can be housed, but its shape is almost the same as that of the conventional rotary shaft shown in FIG. It hasn't changed. Therefore, for example, similarly to the conventional rotary shaft shown in FIG. 3, the inner peripheral surface 2 of the rotary shaft 1
4 and the inner end surface 23 are held by the vacuum chuck 120 as shown in FIG. 5, and then the outer peripheral surface of the bearing portion 12 and the mirror mounting surface 14 are processed at the same time, and the rotary shaft 1 having a good surface inclination.
Is obtained.

The above embodiment is one example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, as shown in FIG. 2, a pair of magnets 10 and 11 forming the thrust magnetic bearing 5 are installed so as to face each other in the thrust direction of the rotating shaft, and the facing surfaces of these magnets 10 and 11 repel each other. It is magnetized so as to form a pole and is supported in the thrust direction by the repulsive force.

[0021]

As is apparent from the above description, in the dynamic pressure bearing motor of the present invention, the stator coil constituting the motor is installed outside the bearing member, and the rotor magnet is arranged outside the stator coil. On the other hand, while at least a part of the rotary shaft is formed into a cylindrical shape having an inner end surface, a pair of magnets forming a thrust magnetic bearing is installed inside the rotary shaft to support the rotary shaft in the thrust direction in a non-contact manner. It is only necessary to secure the minimum space for accommodating the pair of magnets forming the thrust magnetic bearing as the internal space of the rotary shaft, and it is possible to reduce the diameter of the rotary shaft to the minimum required. Therefore, the dynamic pressure bearing motor of the present invention enables high speed rotation while suppressing bearing loss and heat generation. In addition, since the thrust magnetic bearing is arranged inside the rotary shaft and the drive motor is arranged outside the rotary shaft, the length of the rotary shaft can be shortened and the motor can be flattened.

Moreover, since the inner space of the rotating shaft has an inner end face, by utilizing the peripheral wall surface and the end face of this inner space, suction support by a vacuum chuck can be performed from the inside even if the rotating shaft has a small diameter. Thus, the outer peripheral surface of the bearing portion and the mirror mounting surface can be simultaneously processed. Therefore,
It is possible to obtain a mirror mounting surface with an extremely good squareness.

Further, according to the present invention, since it is not necessary to accommodate a pair of magnets for constituting the thrust magnetic bearing inside the boss portion to which the polygon mirror is attached, the shaft diameter of the boss portion can be made small and the size is small. It becomes possible to attach it even with the polygon mirror.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing an example of a dynamic pressure bearing motor of the present invention.

FIG. 2 is a central longitudinal sectional view showing another embodiment of the dynamic pressure bearing motor of the present invention.

FIG. 3 is a central longitudinal sectional view showing a conventional dynamic pressure bearing motor.

FIG. 4 is a front view showing the outer appearance of the rotor of the motor shown in FIG.

FIG. 5 is an explanatory view showing a finishing work of the outer peripheral surface and the mirror mounting surface of the rotor of FIG.

[Explanation of symbols]

 1 rotating shaft 2 bearing member 4 dynamic pressure bearing 5 thrust magnetic bearing 6 motor 7 stator coil 8 rotor magnet 10 magnet constituting thrust magnetic bearing 11 magnet constituting thrust magnetic bearing 22 inner space 23 inner end surface

Claims (1)

[Claims] 1. A dynamic pressure bearing is formed between a cylindrical bearing member forming a part of a stator and a rotating shaft forming a part of a rotor fitted into the bearing member and rotating, and the rotating shaft In a dynamic pressure bearing motor that is supported by the dynamic pressure bearing in the radial direction, a stator coil that constitutes the motor is installed outside the bearing member, and a rotor magnet is further arranged outside thereof to be fixed to the rotary shaft. At least a part of the rotating shaft is formed into a cylindrical shape having an inner end surface, a magnet is fixed to the inside of the rotating shaft, the magnet is installed on the bearing member side so as to face the magnet, and the magnet is fixed to the inside of the rotating shaft. A hydrodynamic bearing motor, wherein the rotating shaft is supported in the thrust direction in a non-contact manner by an attractive force or a repulsive force with a magnet on the bearing member side.