JPH0675185A - Scanning optical device - Google Patents

Abstract

PURPOSE:To diminish the increase of the loss torque of the high-speed rotating body of a rotary polygon mirror and the increase of power consumption, to prevent the contamination of dust or a galling phenomenon by vibration or the like from occurring and to prevent accuracy from being deteriorated. CONSTITUTION:A rotary sleeve 22 consisting of a ceramic material is engaged around a fixed shaft 21 consisting of the ceramic material in freely rotatably and a fixing member 23 consisting of a metallic material is fixed around the sleeve 22. Besides, the rotary polygon mirror and a driving magnet 26 are fitted to the fixing member 23. A driving motor is constituted by arranging a stator 28 at the position opposed to the magnet 26 in a motor housing 27 where the shaft 21 is fixed. A permanent magnet 30 is arranged on the lower side of the sleeve 22 and a permanent magnet 31 which is faced to the magnet 30 in a top and bottom direction is arranged to the shaft 21. By the repulsive force of both magnets 30 and 31, load in a thrust direction is supported.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device in a recording device using a light beam such as a laser beam, which incorporates a rotary polygon mirror for scanning the light beam onto, for example, a photosensitive member.

[0002]

2. Description of the Related Art In recent years, it has been required in a scanning optical apparatus of this type to rotate a rotary polygon mirror at a high speed or with high accuracy. A bearing that rotates by contact is used.

FIG. 5 shows a deflection scanning device of a conventional laser beam printer using a hydrodynamic bearing which is one of such non-contact bearings. The rotary shaft 1 and the sleeve 2 are rotatably fitted to each other, and a thrust plate 3 is arranged at a lower end portion of the sleeve 2 together with a fixed plate 4 and fixed to an outer cylinder 5. A flange 6 is fixed to the rotary shaft 1, and a rotary polygon mirror 7 is fixed to an upper portion of the flange 6,
A yoke 9 to which a drive magnet 8 is fixed is fixed to a lower portion of the flange 6, and a stator 10 fixed to the outer cylinder 5 is arranged at a position facing the drive magnet 8 to form a drive motor. There is.

Here, the thrust plate 3 is provided with a shallow groove 11 on the surface facing the end of the rotary shaft 1 to form a dynamic thrust bearing. Further, on the outer peripheral surface of the rotary shaft 1, herringbone-shaped shallow grooves 14 are engraved at two positions facing the inner peripheral surface of the sleeve 2, and further, in a spiral shape such that a lubricating fluid flows through the dynamic pressure thrust bearing. A shallow groove 15 is engraved. Further, the inner surface of the sleeve 2 has a shallow groove 14 and a shallow groove 15.
The stability of the lubricating fluid is ensured by providing the small-diameter hole 17 in the diametrical direction as well as providing the concave portion 16 at a position facing the intermediate portion. Further, similarly, a clearance portion 18 is formed on the inner surface of the sleeve 2 at a position facing the intermediate portion of the two shallow grooves 14, and faces the intermediate portion between the lower shallow groove 14 and the dynamic pressure thrust bearing portion. An escape portion 19 is formed at the position so that the loss of the fluid bearing portion is reduced.

In addition to such a fluid dynamic bearing, a bearing device using a ceramic material has been recently used.

[0006]

However, in the above-mentioned conventional example, in order to obtain a high-speed and high-precision deflection scanning device,
It has the following drawbacks.

(1) In a fluid dynamic bearing using oil, grease or the like as the fluid, the viscous resistance of the fluid increases as the speed increases, the loss torque increases, heat generation increases, and power consumption increases.

(2) A hydrodynamic bearing that uses a fluid such as air is difficult to handle because it is vulnerable to the contamination of dust and moisture, and when it is contacted by vibration or the like while rotating at high speed. Is likely to cause a so-called galling phenomenon.

(3) In the case of a bearing using a ceramic material, it is difficult to mount a rotating polygon mirror and the like, and the coefficient of thermal expansion of the material is greatly different. The accuracy will be deteriorated if the above occurs.

The object of the present invention is to solve the above-mentioned drawbacks, to reduce loss torque and power consumption even at high speed rotation, to prevent the occurrence of a galling phenomenon due to the inclusion of dust or vibration, and to stabilize the accuracy. It is to provide a scanning optical device that can be held physically.

[0011]

A scanning optical device according to the present invention for achieving the above-mentioned object is rotatably fitted to each other in a scanning optical device in which a rotary polygon mirror is rotated to deflect and scan a light beam. The fixed shaft and the rotating sleeve to be fitted together are made of a ceramic material, and the drive magnet and the rotating polygon mirror are attached to a metal member fixed to the outer periphery of the rotating sleeve.

[0012]

In the scanning optical device having the above structure, when the rotary polygon mirror is fixed and the rotary sleeve rotates at high speed, an air film is formed between the rotary sleeve and the rotary shaft, and the load in the thrust direction is permanent. Since it is supported by the repulsive force of the magnet, the rotating sleeve rotates without contact.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. 1 and 2 show a first embodiment,
A rotary sleeve 22 is rotatably fitted around a fixed shaft 21 and is made of a ceramic material. A fixed member 23 made of a metal material such as aluminum or brass is attached to the outer circumference of the rotary sleeve 22 by a known means such as shrink fitting, and a rotary polygon mirror 24 is attached to the fixed member 23 by a leaf spring 25. It is fixed, and the drive magnet 26 is fixed by means such as adhesion.
The fixed shaft 21 is fixed to a motor housing 27, and a motor substrate 29 on which a stator 28 and electric parts are attached is installed in the motor housing 27 at a position facing the drive magnet 26 to form a drive motor. Further, while the permanent magnet 30 is arranged below the rotary sleeve 22, a permanent magnet 31 is arranged on the fixed shaft 21 so as to face the permanent magnet 30 in the vertical direction.
1 repels each other and supports a load in the thrust direction.

Here, the rotary sleeve 2 is driven by the drive motor.
When the rotating sleeve 2 is rotated, an air film is formed between the fixed shaft 21 and the rotating sleeve 22, so that the rotating sleeve 2 is contactless.
2 and the rotary polygon mirror 24 can be driven to rotate. When the rotary polygon mirror 24 is rotated by the drive motor,
As shown in FIG. 2, the laser beam L emitted from the laser unit 33 arranged in the optical box 32 is reflected by the rotary polygon mirror 24, then condensed by the lens group 34, and deflected onto the photoconductor 35. To scan.

With the above construction, the rotating side of the deflection scanning device can be completely rotated without contact with the fixed side, and only air is interposed between the fixed shaft 21 and the rotating sleeve 22. Therefore, even when rotating at high speed, the increase in loss torque is small, the heat generation is small, and the power consumption is small. Further, since the fixed shaft 21 and the rotary sleeve 22 are formed of a ceramic material, the galling phenomenon is less likely to occur even if dust or the like is mixed in or if they are contacted by vibration or the like during high speed rotation. .
In particular, when high-strength silicon nitride (Si ₃ N ₄ ) is used as the ceramic material forming the fixed shaft 21 and the rotary sleeve 22, the galling phenomenon may occur due to its excellent wear resistance and strength. Extremely small.

Further, since the fixing member 23 made of a metal material is fixed to the outer circumference of the rotary sleeve 22 and the rotary polygon mirror 24 and the drive magnet 26 are fixed to the fixing member 23, the accuracy due to the difference in the coefficient of thermal expansion is high. Since the deterioration is small and the shape of the rotary sleeve 22 made of a ceramic material is simple, high-precision machining is easy and it is advantageous in terms of cost. Further, since the fixing member 23 made of a metal material fixed to the outer periphery of the rotary sleeve 22 is easy to process, the drive magnet 26 can be attached at a desired position, and the processing accuracy can be made high. it can. The position of the center of gravity of the rotating body can be freely designed to some extent by changing the shape of the fixing member 23, and it is easy to set it near the ideal bearing center.

FIG. 3 shows a second embodiment, and the same members as those in FIG. 1 having the same functions are designated by the same symbols.
A groove 36 is provided in the fixed shaft 21 made of a ceramic material in the vicinity of the center of the portion fitted into the rotary sleeve 22.

By providing the groove 36 in this way, since there are two air films formed between the fixed shaft 21 and the rotary sleeve 22 during rotation, it is possible to reduce whirling in the moment direction. Becomes Also, the groove 36
The processing may be performed before firing the ceramic, and the processing cost does not increase.

FIG. 4 shows a third embodiment. In this case, the fixed shaft 21 has a double structure in which an outer tube 21b made of a ceramic material is fixed around a core shaft 21a made of a metal material. .

With such a structure, the amount of expensive ceramic material used can be reduced, and even when the groove 36 at the center of the bearing portion described in the second embodiment is provided, the outer tube made of ceramic material is used. 21b is divided into two and fixed,
If the outer periphery is ground in the later processing, the accuracy will not deteriorate.

Although the above embodiments have been described by taking the inner rotor type deflection scanning device, which is advantageous for high-speed rotation, as an example, the present invention can be applied to other outer rotor type and surface facing type devices. Is possible.

[0022]

As described above, in the scanning optical device according to the present invention, since the rotary sleeve rotates around the fixed shaft in a non-contact manner, less heat is generated even at high speed rotation, and loss torque and power consumption are reduced. The increase is also small. In addition, it is unlikely that the galling phenomenon due to the mixing of dust or the like or the vibration will occur. Further, since the rotary polygon mirror and the drive magnet are fixed to the fixed member made of a metal material fixed to the outer periphery of the rotary sleeve, the accuracy deterioration due to the difference in the coefficient of thermal expansion can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a plan view of an optical box.

FIG. 3 is a sectional view of a second embodiment.

FIG. 4 is a sectional view of a third embodiment.

FIG. 5 is a cross-sectional view of a conventional example.

[Explanation of symbols]

 21 fixed shaft 21a shaft core 21b outer tube 22 rotary sleeve 23 fixed member 24 rotary polygon mirror 25 leaf spring 26 drive magnet 27 motor housing 28 stator 29 motor substrate 30, 31 permanent magnet

Claims (4)

[Claims] 1. A scanning optical device for deflecting and scanning a light beam by rotating a rotary polygon mirror, wherein a fixed shaft and a rotary sleeve which are rotatably fitted to each other are made of a ceramic material and fixed to an outer periphery of the rotary sleeve. A scanning optical device in which a drive magnet and the rotary polygon mirror are attached to the metal member. 2. The scanning optical device according to claim 1, wherein a groove is provided on the outer circumference of the fixed shaft near the center of the fitting portion between the fixed shaft and the rotary sleeve. 3. The scanning optical device according to claim 1, wherein an outer peripheral portion of the fixed shaft is made of a ceramic material, and a core shaft made of a metal material is provided therein. 4. The scanning optical device according to claim 1, wherein the ceramic material is silicon nitride.