JPH0562175U - Polygon mirror motor - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent deterioration of the supporting function of the dynamic pressure bearing and maintain the rotation accuracy of the polygon mirror at high accuracy. Then, the deterioration of the scanning accuracy of the laser beam due to the abnormal rotation of the polygon mirror is eliminated. [Structure] A cover 7a for covering the polygon mirror 1,
The cover member 6 supporting 7b is formed integrally with the bearing member 5 so that distortion due to the difference in thermal expansion does not occur near the bearing member 5 when the rotor 2 rotates.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a polygon mirror motor used as an optical scanning device such as a laser beam printer or a facsimile. More specifically, the present invention relates to a support structure for a cover that covers a polygon mirror in a polygon mirror motor.

[0002]

[Prior Art]

 Figure 2 shows the principle of a laser beam printer as an example of a device that uses a polygon mirror motor. Generally, a laser beam printer 20 includes a laser beam emitting device 21 such as a semiconductor laser, a control device 22 for controlling laser emitting timing of the laser beam emitting device 21, and a polygon mirror 31 for scanning the laser beam. It is composed of a mirror motor 30, a lens / mirror system 23, and a photosensitive drum 24 whose surface is imaged by a laser beam.

As shown in FIG. 3, for example, the polygon mirror motor 30 is configured between a polygon mirror 31, a rotor 32 mounted with the polygon mirror 31 and rotating, and an outer peripheral surface of the rotor 32. And a substantially cylindrical bearing member 34 that rotatably supports the rotor 32 via the dynamic pressure bearing 33, and the bearing member 34 is fitted to the outer periphery of the bearing member 34 to serve as another device member (not shown). The cover member 35 is attached and covers the polygon mirror 31.

The cover member 35 is provided with a translucent cover 36 a in a window portion 35 a located on the optical path of the laser beam, and a dustproof cover 36 b closing an opening 35 b for fitting with the bearing member 34. There is. The cover member 35 is fixed to the flange portion 34a of the bearing member 34 with a tightening screw (not shown) or the like. Then, the cover member 35 is fixed to another device member (not shown) with a tightening screw or the like, so that the polygon mirror 31 is installed at a predetermined position on the optical path of the laser beam.

Inside the rotor 32, a motor section 37 for rotationally driving the rotor 32 is formed. The motor section 37 is composed of a stator coil 38 wound around a center pole 40 fixed to the bearing member 34 side, and a rotor magnet 39 fixed to the inner peripheral surface of the rotor 32. A gap of several microns to several tens of microns is formed between the outer peripheral surface of the rotor 32 and the inner peripheral surface of the bearing member 34, and the outer peripheral surface of the rotor 32 (or the inner peripheral surface of the bearing member 34) moves. A pressure generating groove 41 is provided to form a dynamic pressure bearing 33, which supports the rotor 32 by the dynamic pressure generated during rotation.

[0006]

[Problems to be solved by the device]

 However, in the conventional polygon mirror motor shown in FIG. 3, a cover member 35 separate from the bearing member 34 is fitted around the bearing member 34, and the covers 36a and 36b are fixed to the cover member 35. Therefore, the following problem occurs. That is, the bearing member 34 expands due to the heat generated in the dynamic pressure bearing 33 during the rotation of the rotor 32 and the heat generated by the motor, but the contact thermal resistance to the cover member 35, which is separate from the bearing member 34, is large. The thermal expansion is almost nonexistent, or even less than that of the bearing member 34. Due to this difference in thermal expansion, the thermal expansion of the bearing member 34 is hindered and the inner peripheral surface facing the dynamic pressure bearing 33 is distorted, and the smoothness of the dynamic pressure bearing 33 consisting of a gap of only a few microns to a few tens of microns. However, there is a possibility that such a support function may be deteriorated, that seizure may occur, or that the rotation axes of the rotor 32 and the polygon mirror 31 may fluctuate, resulting in a reduction in scanning accuracy of the laser beam (deterioration of print quality).

An object of the present invention is to provide a polygon mirror motor which prevents deterioration of the supporting function of a dynamic pressure bearing and maintains the rotation accuracy of the polygon mirror with high accuracy. More specifically, the present invention aims to solve the deterioration of scanning accuracy when a polygon mirror motor is used in a laser scanning system.

[0008]

[Means for Solving the Problems]

 In order to achieve such an object, the present invention forms a dynamic pressure bearing between a polygon mirror, a rotor supporting the polygon mirror, and an outer peripheral surface of the rotor to rotatably support the rotor. In a polygon mirror motor, a bearing member, a motor unit for rotating the rotor, and a cover member that holds the bearing member and can be attached to another device member and that includes a cover that covers the polygon mirror are provided. The cover member and the bearing member are integrally formed of the same material.

[0009]

[Action]

 Therefore, even if the dynamic pressure bearing portion or the motor portion generates heat due to the rotation of the rotor, the bearing member and the cover member integrally formed with the bearing member are affected by the same thermal expansion, and there is no difference in thermal expansion between them. .. Moreover, since the cover member is separated from the part where the cover member is fixed to the other device member and the heat generating part, the influence of strain due to the difference in thermal expansion generated in the fixed part does not reach the inner peripheral surface of the bearing member. Do not change the bearing clearance of the hydrodynamic bearing.

[0010]

【Example】

 Hereinafter, the configuration of the present invention will be described in detail based on the embodiment shown in FIG.

FIG. 1 shows an embodiment of a polygon mirror motor to which the present invention is applied. This polygon mirror motor includes a polygon mirror 1, a rotor 2 that supports and rotates the polygon mirror 1, a motor unit 3 that drives the rotor 2 to rotate, and a dynamic pressure between the outer peripheral surface of the rotor 2. A bearing member 5 forming the bearing 4 and a cover member 6 integrally formed of the same material as the bearing member 5 are included.

As the bearing member 5, for example, it is preferable to use aluminum or an aluminum alloy, which is easy to perform precision processing, and a surface treatment for improving its wear resistance is disclosed, for example, disclosed in JP-A-63-235719. Has been surface treated. Similarly, on the rotor 2 side, aluminum or aluminum alloy is used, and the surface thereof is appropriately surface-treated. As shown in the figure, the rotor 2 has a bottomed cylindrical shape in which the polygon mirror 1 can be mounted on one of the shaft ends, and the polygon mirror 1 is fixed to the bottom portion through a spring washer so that no distortion occurs. There is. Grooves 12 for generating dynamic pressure are formed on the outer peripheral surface 2a of the rotor 2 (or the inner peripheral surface of the bearing member 5), and a dynamic pressure bearing 4 is formed between the rotor 2 and the bearing member 5. There is. The dynamic pressure bearing 4 is configured such that a gap of several microns to several tens of microns is formed between the outer peripheral surface of the rotor 2 and the inner peripheral surface of the bearing member 5, and a fluid generated in the groove 12 during rotation is formed. The dynamic pressure supports the rotor 2 in the radial direction. In addition to the air of this embodiment, a liquid or any other suitable fluid can be used as the dynamic pressure fluid.

The motor unit 3 includes, for example, a stator coil 10 wound around a center pole 8 fixed to the bearing member 5 side via a stator core 9, and a yoke (not shown) on the inner peripheral surface of the rotor 2. The magnet 11 is fixed through the magnet 11 and the excitation current is controlled by, for example, a brushless control method to obtain rotation.

The cover member 6 is for covering the polygon mirror 1 to protect it from dust and for installing the entire polygon mirror motor on another device member (not shown). In the case of the present embodiment, the cover member 6 is formed integrally with the bearing member 5, so that the range is not clear, but it means the region outside the cylindrical portion facing the rotor 2. A cover 7a for covering the window portion 6a located on the optical path and a dustproof cover 7b for closing the opening 6b used when the polygon mirror 1 is mounted are attached to the cover member 6 with a screw 13 or the like. The other polygon mirror 1 is protected from dust. Of these covers 7a and 7b, at least the cover 7a on the optical path is made of a translucent material such as glass. Therefore, the laser beam enters through an entrance (not shown), is reflected by the polygon mirror 1 at a predetermined angle, and then exits through the window portion 6a. The cover member 6 is fixed to another device member (not shown) with a tightening screw or the like so that the polygon mirror 1 is installed at a predetermined position on the optical path of the laser beam. Further, reference numeral 14 is a through hole for inserting a mounting screw or the like.

The polygon mirror motor configured as described above operates as follows.

When the rotor 2 is rotated by energizing the motor section 3, the coaxial polygon mirror 1 is rotated to prepare for scanning. As the rotor 2 rotates at high speed, dynamic pressure is generated in the dynamic pressure bearing 4 between the outer peripheral surface of the rotor 2 and the inner peripheral surface of the bearing member 5, and heat is generated in that portion. Further, also in the motor section 3, heat is generated by a stator coil or the like. This heat is transmitted to and cooled by the bearing member 5 and the cover member 6 integrally formed of the same material. At the same time, the heat causes thermal expansion of the bearing member and the cover member 6, but since they continuously expand, no distortion occurs in the inner surface of the bearing member 5, or the amount of distortion is significantly reduced. Therefore, the smooth support function of the dynamic pressure bearing 4 is not deteriorated, and the rotor 2 and the polygon mirror 1 continue to rotate to a certain extent.

[0017]

[Effect of the device]

 As is clear from the above description, in the polygon mirror motor of the present invention, the cover member for supporting the cover for covering the polygon mirror is integrally formed with the bearing member, so that the heat generated in the vicinity of the bearing member when the rotor rotates. Since the strain due to the difference in expansion does not occur, the bearing gap of the dynamic pressure bearing is maintained and the smooth support function does not deteriorate. Therefore, it is possible to prevent the rotor from wobbling and seizure, and when used in a laser beam scanning device, it is possible to prevent a reduction in the scanning accuracy of the laser beam and improve the printing quality.

Further, when the bearing member and the cover member are provided separately, the manufacturing tolerances of the respective members are overlapped with each other and strain is applied to the bearing member side during assembly to reduce the accuracy of the gap of the dynamic pressure bearing. However, in the case of the present invention, it is possible to prevent the occurrence of distortion during such mounting or assembling.

Further, since the bearing member 5 and the cover member 6 are integrally formed to reduce the number of parts, it is possible to reduce the manufacturing cost and the labor of parts management.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a polygon mirror motor of the present invention in which a bearing member, a cover member, and a part of a rotor are sectioned.

FIG. 2 is a system principle diagram of a laser beam printer.

FIG. 3 is a partial vertical cross-sectional view of a conventional polygon mirror motor.

[Explanation of symbols]

 1 polygon mirror 2 rotor 3 motor part 4 dynamic pressure bearing 5 bearing member 6 cover member 7a, 7b cover

Claims (1)

[Scope of utility model registration request] 1. A bearing member for rotatably supporting the rotor by forming a dynamic pressure bearing between a polygon mirror, a rotor that fixes and supports the polygon mirror at a shaft end, and an outer peripheral surface of the rotor. A polygon mirror motor comprising: a motor unit that rotationally drives the rotor; and a cover member that holds the bearing member and can be attached to another device member and that includes a cover that covers the polygon mirror. A polygon mirror motor characterized in that the bearing member and the bearing member are integrally formed of the same material.