JP2000227567A - Light beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light beam scanner that the accuracy of a spot diameter on a photoreceptor is enhanced and the image quality of a high-speed and high-density image forming device can be drastically improved by constituting an over-field type scanning system and the like so that the fitting position of a light source unit emitting a light beam toward a rotary polygon mirror can be adjusted in an optical axis direction. SOLUTION: In the over-field type scanning system, the divergent light beams are emitted from the light source unit 10, transmitted through an image forming lens system 5 and converted to the parallel light beams in a main scanning direction at the reflection surface of the rotary polygon mirror 4. When the unit 10 is assembled, it is moved in the optical axis direction while emitting the light beams and fixed by a fixing tool 52 after being adjusted so that the light beams become the parallel light beams on the mirror 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used for an image forming apparatus such as a laser beam printer and a laser facsimile.

[0002]

2. Description of the Related Art A light beam scanning device used in an image forming apparatus such as a laser beam printer or a laser facsimile reflects a light beam such as a laser beam by a rotating polygon mirror rotating at a high speed and deflects and scans the light beam. The scanning light is focused on a photoreceptor on a rotating drum to form an electrostatic latent image. Next, the electrostatic latent image on the photoreceptor is visualized into a toner image by a developing device, transferred to a recording medium such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording medium ( Print) is performed.

FIG. 8 shows a general underfield type light beam scanning device, and a laser driver 101a.
Laser light (light beam) generated from the semiconductor laser 101 driven by the laser beam is collimated in the lens barrel, condensed into a linear light beam by the cylindrical lens 102, and perpendicularly to the rotation axis by the rotating polygon mirror 103. The light beam is deflected and scanned in a predetermined direction (main scanning direction), and forms an image on a photosensitive member 106 on a rotating drum via an imaging lens system 104 and the like. The light flux formed on the photoreceptor 106 forms an electrostatic latent image in accordance with the main scanning by the rotation of the rotary polygon mirror 103 and the sub-scanning by the rotation of the rotating drum.

In this manner, the photosensitive drum 106 of the rotating drum
However, the writing position on the rotating drum may be shifted due to the division error of the reflection surface of the rotary polygon mirror 103. Therefore, the scanning light of the rotating polygon mirror 103 is reflected by the BD mirror 107 when reaching one end of the scanning surface, and is reflected by the BD sensor 1.
08 and converted into a scanning start signal by a controller (not shown). The semiconductor laser 101 starts write modulation after receiving the scanning start signal.

The imaging lens system 104 includes a spherical lens 104
a and a toric lens 104b, and a rotating polygon mirror 1
03 has a so-called fθ function of converting scanning light scanned at a constant angular velocity into scanning light scanned at a constant speed in the main scanning direction on the rotating drum.

[0006] In recent years, the speed of image forming apparatuses and the density of images have been increasing. However, in order to increase the speed, the number of rotations of the rotating polygon mirror must be increased, and the surface of the reflecting surface of the rotating polygon mirror must be increased. You need to increase the number.

Further, in order to increase the density of a point image (spot), it is required to narrow down the spot diameter of the point image formed on the photoreceptor minutely by an imaging lens system or the like. It is necessary to increase the diameter of the light beam incident on the rotating polygon mirror in consideration of aberrations. Therefore, each reflecting surface of the rotating polygon mirror must be enlarged. As a result, the diameter of the rotating polygon mirror must be increased. I can't avoid it.

However, when the large-diameter rotary polygon mirror is rotated at a high speed, the structure of the rotary polygon mirror itself is destroyed, the vibration and noise of the bearing and motor of the rotary polygon mirror, and the temperature rise due to heat generation. Is a major barrier in practical use.

Therefore, in order to avoid these problems,
An overfield type light beam scanning device shown in FIG. 7 has been developed. The over-field scanning system can dramatically reduce the circumferential width of the reflecting surface of the rotating polygon mirror, that is, the facet width, and can double the number of rotating polygon mirrors. Attention has been paid to the fact that a low-speed rotating polygonal mirror can achieve the same speed and density.

In addition, by increasing the number of surfaces of the rotary polygon mirror, the outer shape becomes close to a cylindrical shape, and the windage loss when rotating at high speed is reduced, which is an extremely great advantage from the viewpoint of low noise and energy saving. There is.

As shown in FIG. 7A, an overfield type scanning system is configured such that a laser beam generated from a semiconductor laser 201 driven by a laser driver 201a is transmitted by a cylindrical lens 202 only in the sub-scanning direction. The light is condensed, the beam shape is adjusted by a stop (not shown), and the light is turned back toward the reflection surface of the rotary polygon mirror 203 by the reflection mirror 202a. Reflection mirror 202
7A, the laser light is reflected upward from below the rotating polygon mirror 203 at a predetermined angle, for example, 1 ° with respect to a horizontal plane perpendicular to the rotation axis, as shown in FIG. The light passes through the lenses 204 a and 204 b of the lens system 204 and enters the reflecting surface of the rotary polygon mirror 203.

The rotary polygon mirror 203 reflects the laser light upward at the same angle as the above by the facet width of the reflection surface. The laser light deflected and scanned by the rotary polygon mirror 203 is again applied to each lens 204a, 204a of the imaging lens system 204.
The light passes through a condensing lens 205, passes through a condensing lens 205, and forms an image on a photosensitive member 206 on a rotating drum with a predetermined spot diameter. A point image (spot) formed on the photoconductor 206 is formed by the rotating polygon mirror 20.
The electrostatic latent image is formed by the main scanning by the rotation of No. 3 and the sub-scanning by the rotation of the rotating drum.

A part of the scanning light is introduced into a BD sensor 208 by a BD mirror 207, converted into a writing start signal for controlling a writing position in the main scanning direction by a processing circuit (not shown), and sent to a laser driver 201a.

In such an overfield type scanning system, incident light and outgoing light (scanning light) are separated by causing so-called oblique incidence of laser light incident on a rotary polygon mirror from below a horizontal plane. However, when the angle of oblique incidence is small, the spot shape on the photoconductor is uniform in the main scanning direction, and therefore, the image quality is good. Both must pass through the imaging lens system. As a result, the laser light incident on the rotating polygon mirror passes through two lenses of the imaging lens system and the like in addition to the lens and the cylindrical lens in the light source unit on the upstream side of the rotating polygon mirror,
It is unavoidable that these lenses affect the accuracy of the laser light incident on the reflecting surface of the rotary polygon mirror.

On the other hand, in recent years, even in the above-described underfield type scanning system, the laser light emitted from the light source unit is converted into convergent light, so that the optical path of the laser light to the photosensitive member is shortened. The technology to make the whole system compact has attracted attention.

[0016]

However, according to the above prior art, as described above, especially in an overfield type scanning system, the accuracy of the incident light of the rotary polygon mirror is controlled by the lens built in the light source unit. In addition, there is an unsolved problem that it is difficult to obtain a desired spot shape on the photoreceptor because it is affected by the arrangement position and lens shape of the imaging lens system lens and the like.

Further, since the distance from the light source unit to the rotary polygon mirror is fixed, the accuracy of the shape and arrangement position of a lens of an image forming lens system for reflecting the scanning light of the rotary polygon mirror, a reflecting mirror, and the like, and the arrangement position thereof. Can not obtain a spot diameter within a predetermined range on the photoreceptor.

In particular, in a scanning optical system (scanner unit) in which the spot diameter is reduced in order to increase the density of an image, a so-called defocusing method for obtaining a desired spot diameter on the surface of the photosensitive member, that is, the image plane. The allowable range was narrow, and it was necessary to reduce such restrictions.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unresolved problems of the related art, and has been described with reference to the attached position of a light source unit that generates a light beam toward a rotating polygon mirror in an overfield type scanning system or the like. A light beam scanning device that can be adjusted in the optical axis direction to improve the accuracy of the spot diameter on the photoreceptor, etc., and to greatly improve the image quality in image forming devices with higher speed and higher density The purpose is to provide.

[0020]

To achieve the above object, a light beam scanning device according to the present invention comprises a light source unit for generating a light beam, a rotary polygon mirror for deflecting and scanning the light beam, and a rotating polygon mirror. An imaging lens system that forms an image of the light beam on a photosensitive member via a polygon mirror; and a housing that supports the light source unit, the rotating polygon mirror, and the imaging lens system, wherein the light beam forms the image. A light beam scanning device configured to be incident on a reflection surface of the rotary polygon mirror through at least a part of a lens system, and to adjust a mounting position of the light source unit with respect to the housing in an optical axis direction. It is preferable that an attachment position adjusting means is provided.

A light source unit for generating a light beam; a rotary polygon mirror for deflecting and scanning the light beam; an image forming lens system for forming an image of the light beam on a photosensitive member via the rotary polygon mirror; A light beam scanning device comprising a unit, a housing supporting the rotating polygon mirror, and the imaging lens system, wherein the light source unit is configured to emit the light beam as divergent light or convergent light, The light beam scanning device may be provided with a mounting position adjusting means for adjusting a mounting position of the light source unit with respect to the housing in an optical axis direction.

It is preferable that the light source unit is a unit in which a light source for generating a light beam and a lens are unitized.

It is preferable that the light source unit is formed by unitizing a light source for generating a light beam, a lens, and a drive board for driving the light source.

It is preferable that the light source unit is configured so that the distance between the light source and the lens can be adjusted.

[0025]

If the light beam generated from the light source unit is not parallel light in the main scanning direction on the reflecting surface of the rotary polygon mirror, it is difficult to obtain a desired spot diameter on the photoreceptor. In (2), since the light beam passes through the lens of the imaging lens system on the upstream side of the rotary polygon mirror, it is difficult to obtain the accuracy of the incident light on the rotary polygon mirror due to the arrangement position and the lens shape. Therefore, before fixing the light source unit to a housing such as an optical box, the light source is generated along the mounting position adjusting means while generating a light beam and observing the light beam on the reflecting surface of the rotating polygon mirror or the spot on the photosensitive member. The light source unit is fixed to the housing after the unit is moved in the optical axis direction and adjusted so that the light beam incident on the rotary polygon mirror becomes parallel light in the main scanning direction.

On the other hand, in an underfield type scanning system or the like, the light beam emitted from the light source unit may be, for example, a convergent light instead of a parallel light in order to promote the miniaturization of the entire apparatus. In such a scanning system,
The spot diameter on the photoreceptor is significantly affected by the accuracy of the lens and the reflection mirror in the optical path from the light source unit to the photoreceptor. Therefore, while observing the spot diameter on the photoconductor, the mounting position of the light source unit is moved in the optical axis direction to adjust the distance to the rotary polygon mirror. In this manner, a predetermined spot diameter can be obtained with high accuracy and easily.

Even if the spot diameter is reduced for higher image quality, a predetermined spot diameter can be easily obtained with high accuracy, and high image quality can be realized.

In particular, in an underfield type scanning system which can cope with an increase in the speed of the image forming apparatus, a so-called collimation adjustment is performed by making the light beam incident on the rotary polygon mirror surely parallel as described above. It is also possible to prevent the allowable range of defocus from becoming small.

As a result, it is possible to realize an image forming apparatus having high image quality and capable of greatly accelerating high speed and high density.

[0030]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a light beam scanning device according to a first embodiment, which forms an image up to 300 mm in width in a main scanning direction and a sub-scanning direction with a pixel density of 1200 dpi on a recording paper or the like. This is an over-field type scanning system that can perform scanning.

The laser beam, which is a light beam generated from the semiconductor laser 1 as a light source of the light source unit 10, is
1 and its lens barrel 12 (see FIG. 3) to make divergent light having a predetermined divergence angle, adjust the beam shape by a stop 13, and condense the light only in the sub-scanning direction by a cylindrical lens 2; Is turned back toward the twelve rotating polygon mirror 4. The reflection mirror 3 is shown in FIG.
As shown in the figure, the laser beam is reflected upward from below the rotary polygon mirror 4 at an angle of, for example, 1 ° with respect to a horizontal plane perpendicular to the rotation axis, and is passed through the lenses 5a and 5b of the imaging lens system 5. The light is condensed on the reflecting surface of No. 4. The light source unit 1 is formed by a method described later so that the laser light focused on the reflection surface of the rotary polygon mirror 4 becomes parallel light in the main scanning direction.
The adjustment of the mounting position of 0 is performed.

The rotary polygon mirror 4 reflects the laser beam upward by the facet width of the reflection surface at the same angle of 1 ° as described above. The laser light deflected by the rotary polygon mirror 4 passes through the lenses 5a and 5b of the imaging lens system 5 again, is turned into a U-turn shape by a pair of reflection mirrors 6a and 6b whose reflection surfaces have a right angle, and is collected. After passing through the optical lens 7, it is turned back by the reflection mirror 8, and passes through the dustproof glass 9 to rotate the drum 2.
In the main and sub scanning directions, for example, about 45 μm
An approximately circular spot having a spot diameter of?
The spot formed on the photoreceptor in this manner forms an electrostatic latent image with the main scanning by the rotation of the rotary polygon mirror 4 and the sub-scanning by the rotation of the rotary drum 20.

In forming a latent image on a photoconductor, the timing of writing a latent image in the main scanning direction for each scanning line is a reference signal from the beam detector 21.
A part of the scanning light is separated by a reflection mirror 22 called a BD mirror, and focused on a beam detector 21 by a condenser lens 23.

FIG. 2 shows a digital copier 30 for forming an image on a transfer material based on a latent image formed on a photoreceptor. As described above, an electrostatic latent image is formed on the photoconductor on the rotating drum 20 based on the image information input via the CPU. The surface of the rotating drum 20 is uniformly charged by the primary charging means 33 before forming a latent image.

The latent image is developed by a developing device 34 with toner as a developer. On the other hand, the transfer material P such as recording paper stacked on the middle plate 36 in the paper supply cassette 35 is supplied with a paper supply roller 37 as a paper supply unit and a registration roller pair 39 stopped by a roller pair 38 as a conveyance unit. , Where the transfer material P is skewed. The registration roller 39, which has adjusted the timing of aligning the leading end position of the toner image on the rotating drum 20 with the leading end of the transfer material P, sends the transfer material P to the transfer section, where the transfer means 40 transfers the toner image of the photoconductor to the transfer material P. Transcribed above.

The transfer material P after the transfer is conveyed to the fixing section 42 by the conveying means 41, where the toner image is heated and fused to the transfer material P. Thereafter, the transfer material P is discharged to the paper discharge tray 43. The toner remaining on the photoconductor of the rotating drum 20 after the transfer is cleaned by the cleaning unit 44 and collected.

The light source unit 10, as shown in FIG.
A drive board 14 on which a laser driver for driving the semiconductor laser 1 is mounted, a lens barrel 12 containing a laser unit including the semiconductor laser 1 and a lens 11 are unitized by a holder 15, and the holder 15 is a housing. It is fitted in a V-shaped groove 51a, which is mounting position adjusting means formed parallel to the optical axis O on a support 51 constituting a part of a scanner case (optical box) 50 as a body. The holder 15 has a cylindrical portion 12a of the lens barrel 12 fitted on the inner peripheral surface, and has a V-shaped groove 5 on the outer peripheral surface.
1a and the flange portion 1 of the lens barrel 12
2b has a flange portion 15b to be connected thereto.

The holder 15 of the light source unit 10 is
1a, the mounting position of the light source unit 10 is adjusted so that the rotary polygon mirror 4 is irradiated with laser light that has become parallel light in the main scanning direction. The holder 15 is fixed by stopping.

The over-field scanning system according to the present embodiment realizes a high pixel density of 1200 dpi as described above, so that the spot diameter is particularly 52 μm.
If m exceeds m, the density of the image changes from a predetermined parameter, and the image quality is deteriorated such as lack of sharpness of the image.

FIG. 4 is a graph showing the relationship between the spot diameter and the defocus of the image plane in the scanning optical system according to one embodiment. In this graph, for the allowable limit value of the spot diameter of 52 μm, the image plane data is obtained from the data at each main scanning position of y = 0 and y = 150 where the center of the optical system in the main scanning direction (y direction) is 0. The allowable range of focus is ± 0.8 mm.

This value of ± 0.8 mm is a fraction of that of a conventional scanning system having a spot diameter of about 70 μm.

In such a scanning system, if the laser beam irradiated on the rotary polygon mirror is not parallel light in the main scanning direction, the allowable range is further narrowed, and it is difficult to realize a spot diameter within the limit value. Become.

Therefore, as described above, the holder is connected to the V of the support.
By moving the light source unit along the groove and adjusting the position of the entire light source unit in the optical axis direction, the light beam on the reflecting surface of the rotating polygon mirror is made parallel light in the main scanning direction, and a stable spot diameter on the image plane is obtained. It is configured to be obtained.

By performing the collimation adjustment by the light source unit in this manner, the spot diameter on the photosensitive member can be adjusted to a predetermined value with extremely high accuracy, and high image quality can be realized.

In addition, when a failure occurs in the laser unit or the laser driver, there is an advantage that the same good image can be formed by removing and replacing only the laser unit.

FIG. 5 shows a light beam scanning device according to the second embodiment. This is an underfield type scanning system, in which the semiconductor laser 6 as a light source of the light source unit 70 is used.
The laser light generated from the lens 1
(See FIG. 6), the light is converted into convergent light having a predetermined convergent angle, condensed only in the sub-scanning direction by the cylindrical lens 62, the beam shape is adjusted by a not-shown stop, and reflected by the six-side rotating polygon mirror 64 Focus on the surface.

The laser light reflected and deflected by the rotary polygon mirror 64 is applied to the lenses 65a and 65b of the imaging lens system 65.
And is turned back by the reflection mirror 66 to form an image on the photoreceptor of the rotating drum 80. The spot formed on the photoreceptor forms an electrostatic latent image with the main scanning by the rotation of the rotating polygon mirror 64 and the sub-scanning by the rotation of the rotating drum 80.

A part of the scanning light is introduced into the BD sensor 81 via the BD mirror 82 and the condenser lens 83.

The light source unit 70 is, as shown in FIG.
The semiconductor laser 61 is fixed to the laser holder 73 by press-fitting, and a drive board 74 on which a laser driver is mounted is mounted on the laser holder 73 by screws 76 via a spacer 75. A lens holder 74 to which the lens 71 is fixed is engaged with the inside of the cylindrical portion 72a of the lens barrel 72 by a screw portion 74a. The lens barrel 72 is in contact with a V-shaped groove of a support forming a part of the scanner case 90 which is a housing, as in the first embodiment. After adjusting the mounting position of the light source unit 70 in the optical axis direction along the V-shaped groove, the lens barrel 72 is fixed by the fixture 92.

The lens holder 74 holds the lens barrel 7 as described above.
2 and the lens holder 74 with respect to the lens barrel 72.
It is configured to be able to be turned in and out.

While observing with a not-shown observation device, a light beam having a predetermined divergence angle is emitted.
Turn the lens holder 74 to rotate the semiconductor laser 61 and the lens 7
Adjust the separation distance of 1.

The lens barrel 72 is made of iron and the lens holder 74
Is made of resin, so that the inside of the scanner unit and
Even if the temperature of the light source unit 70 rises, the semiconductor laser 61
And the distance between the lens 71 can be kept constant.

[0054]

Since the present invention is configured as described above, the following effects can be obtained.

By adjusting the position of the light source unit in the direction of the optical axis, the light beam incident on the reflection surface of the rotary polygon mirror can be adjusted, and the spot diameter on the image plane can be adjusted with high accuracy. Thereby, a high-quality and stable image can be formed.

Even if the light source unit is replaced, a stable and high-quality image can be formed similarly, and the compatibility of the light source unit is improved.

By adjusting the mounting position of the light source unit while measuring the spot diameter on the image plane, the spot diameter on the image plane can be easily adjusted to a predetermined size.

[Brief description of the drawings]

FIG. 1 shows a light beam scanning device according to a first embodiment, in which (a) is a schematic plan view and (b) is a schematic cross-sectional view.

FIG. 2 is a schematic diagram showing a digital copying machine using the light beam scanning device of FIG.

FIG. 3 is a perspective view showing a light source unit of the light beam scanning device of FIG.

FIG. 4 is a graph showing a change in spot diameter when an image forming position is defocused in one embodiment.

FIGS. 5A and 5B show a light beam scanning device according to a second embodiment, in which FIG. 5A is a schematic plan view and FIG. 5B is a schematic sectional view.

6 is a sectional view showing a light source unit of the light beam scanning device of FIG.

FIG. 7 illustrates an overfield scanning system according to a conventional example.

FIG. 8 illustrates an underfield scanning system according to another conventional example.

[Explanation of symbols]

 1,61 Semiconductor laser 2,62 Cylindrical lens 3,6a, 6b, 8,66 Reflecting mirror 4,64 Rotating polygon mirror 5,65 Imaging lens system 10,70 Light source unit 11,71 Lens 12,72 Lens tube 15 Holder 20, 80 Rotary drum 50, 90 Scanner case 51 Supporter 51a V-shaped groove 52, 92 Fixture

Claims (5)

[Claims] A light source unit for generating a light beam; a rotating polygon mirror for deflecting and scanning the light beam; an imaging lens system for forming an image of the light beam on a photosensitive member via the rotating polygon mirror; and the light source A unit for supporting the unit, the rotating polygon mirror, and the imaging lens system, wherein the light beam passes through at least a part of the imaging lens system and is incident on a reflection surface of the rotating polygon mirror. A light beam scanning device, comprising: a mounting position adjusting means for adjusting a mounting position of the light source unit with respect to the housing in an optical axis direction. 2. A light source unit for generating a light beam, a rotary polygon mirror for deflecting and scanning the light beam, an imaging lens system for forming an image of the light beam on a photosensitive member via the rotary polygon mirror, and the light source A light beam scanning device comprising a unit, a housing supporting the rotating polygon mirror, and the imaging lens system, wherein the light source unit is configured to emit the light beam as divergent light or convergent light, A light beam scanning device, further comprising: mounting position adjusting means for adjusting a mounting position of the light source unit with respect to the housing in an optical axis direction. 3. The light beam scanning device according to claim 1, wherein the light source unit is obtained by unitizing a light source for generating a light beam and a lens. 4. The light beam according to claim 1, wherein the light source unit is formed by unitizing a light source for generating a light beam, a lens, and a drive board for driving the light source. Scanning device. 5. The light beam scanning device according to claim 3, wherein the light source unit is configured to adjust a distance between the light source and the lens.