JP2003029179A - Laser scanning device and imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multibeam scanning device which employs a general-purpose semiconductor laser as a beam light source and is manufactured at a low cost, has little decrease in light quantity thereby enables provision of a clear image. SOLUTION: A plurality of light beams B1 and B2 , emitted from semiconductor lasers 11a and 11b which are a plurality of laser light sources, are deflected and scanned using a single polygon mirror 12, refraction action is given to the plurality of light beams B1 and B2 light beams in the subscanning direction, by passing the beams through an angle correction lens 14 in the optical path and the distance in the subscanning direction of the light beams B1 and B2 is made so as to have a prescribed pitch on a photoreceptor drum 220.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital copying machine,
The present invention relates to a laser scanning device used in a writing system of an electrophotographic image recording device such as a laser printer or a laser facsimile, and more particularly to a multi-beam scanning device for simultaneously scanning a photosensitive member with a plurality of light beams to improve a recording speed. It is about.

[0002]

2. Description of the Related Art In a laser scanning device used in a writing system of an electrophotographic image recording device such as a digital copying machine, a laser printer, a laser facsimile, a plurality of light beams are scanned as a means for improving the recording speed. There has been proposed a multi-beam scanning device which simultaneously records a plurality of lines.

In such a multi-beam scanning device, it is necessary to provide a plurality of laser light emitting means for scanning a plurality of light beams. Further, the plurality of light beams are made to approach the photosensitive member and are scanned. There is a need to.

However, when a semiconductor laser emitting means such as a laser diode generally used as the laser emitting means is used, the size of the laser emitting means itself is large, so that the laser emitting means arranged adjacent to each other are arranged. The distance of the interval becomes wide, and the plurality of emitted light beams cannot be brought close to each other at the time of emission.

Further, it is possible to provide a laser emitting means capable of emitting a light beam in close proximity by using a special semiconductor laser, but in this case, the cost of the laser emitting means increases and the mounting accuracy is high. Need.

Therefore, conventionally, there is a method of arranging a plurality of laser emitting means using general-purpose laser diodes and using a beam splitter such as a prism or a half mirror to bring the light beams emitted from the laser emitting means close to each other. A method of bringing the light beams close to each other using the beam splitter will be described below with reference to FIG.

In the configuration of FIG. 8, the first laser diode 101a and the second laser diode 101b are arranged adjacent to each other, and the first light beam 102a is emitted from the laser diode 101a and the second laser diode 101a is emitted. The second light beam 102b is emitted from 101b. Also, the first and second light beams 102a.
2b are emitted so as to be parallel to each other.

The above first and second laser diodes 1
The beam splitter 103 is provided downstream of 01a and 101b.
Are arranged, the first light beam 101a is reflected by the reflection mirror 103, and then the first light beam 101a
Is incident from the incident surface 103a of the
The light reflected by is emitted from the emission surface 103d. In addition, the second light beam 101b is incident from the second incident surface 103b of the beam splitter, and is transmitted / reflected surface 103.
The light transmitted by c is emitted from the emission surface 103d.

The exit surface 10 of the beam splitter 103
First and second light beams 102a emitted from 3d
102b is in a state of being in close proximity, and is then deflected by the deflecting surface 106 of the polygon mirror, and
7 is irradiated on the surface.

[0010]

However, in the above-mentioned conventional configuration, in order to bring the light beam emitted from the laser emitting means close to each other, the beam splitter 103 is used, and the transmission / reflection surface 103c of the beam splitter 103 is used. Transmission / reflection characteristics are used. Therefore, the amount of light of the first and second light beams 102a and 102b is reduced to about half when passing through the beam splitter 103.

For this reason, a laser light emitting means having an energy more than twice as much as the light quantity required for writing on the photoconductor 107 is required, and the effect of cost reduction by using a general-purpose laser diode for the light emitting means is sufficient. There is a problem that you can not get it. In addition, there is a problem that a clear image cannot be obtained because the position of the light beam is displaced, the image forming position on the photosensitive member is displaced, or the beam spot is deformed.

The present invention has been made in order to solve the above-mentioned problems, and its purpose is to use a general-purpose semiconductor laser, which is low in cost, has a small decrease in light quantity, and produces a clear image. It is to provide a multi-beam scanning device that can obtain

[0013]

In order to solve the above problems, the laser scanning device of the present invention deflects a plurality of light beams emitted from a plurality of laser light sources by a single rotating polygon mirror. In the laser scanning device for scanning, the light beams are refracted in the sub-scanning direction orthogonal to the main scanning direction deflected by the rotary polygon mirror, so that the light beams are moved in the optical axis direction. Further, an angle correction means is provided for correcting the angle of the light beam so that the distance in the sub-scanning direction becomes a predetermined pitch at a position separated by a predetermined distance.

According to the above arrangement, the plurality of light beams emitted from the plurality of laser light sources are deflected by the single rotating polygon mirror and scanned in the main scanning direction, and at the same time, are arranged in the optical path. By passing through the angle correction means, a refraction action is given in the sub-scanning direction, and the distance in the sub-scanning direction can be set to a predetermined pitch at positions separated by a predetermined distance in the optical axis direction.

Thus, when a general-purpose semiconductor laser is used as the laser light source, first, a plurality of light beams emitted at a predetermined distance in the sub-scanning direction are brought close to each other. It is not necessary to pass through optical components such as mirrors and prisms that utilize the reflection / transmission effect. Therefore, the light quantity of the light beam emitted from the laser light source is reduced, and the cost of the laser scanning device can be reduced by using a general-purpose semiconductor laser.

The laser scanning device is generally used as an exposing means in an electrophotographic image forming apparatus. In this case, the position separated by a predetermined distance in the optical axis direction means the light on the surface of the photoconductor. The irradiation position of the beam, and the predetermined pitch in the distance in the sub-scanning direction is the line pitch in the sub-scanning direction corresponding to the set resolution of the image forming apparatus.

Further, in the laser scanning device, a plurality of light beams emitted from the plurality of laser light sources are emitted in a state of being inclined with respect to each other in the sub-scanning direction, and are converged in an incident optical path toward the rotary polygon mirror. It is preferable to have a configuration.

That is, in the case where the plurality of light beams are emitted as parallel light and are incident on the rotary polygon mirror, the plurality of light beams incident on the rotary polygon mirror are equal to the arrangement intervals of the semiconductor lasers. Will be provided in the sub-scanning direction. Therefore, the length of the rotary polygon mirror in the sub-scanning direction, that is, the thickness of the rotary polygon mirror also increases in accordance with the interval of the light beam in the sub-scanning direction. In this case, in order to stably perform high-speed rotation of the rotary polygon mirror, it is necessary to upsize the rotary polygon mirror and its motor, which causes a problem of increasing the size and cost of the laser scanning device.

On the other hand, according to the above configuration, the light beam emitted from the semiconductor laser is first tilted in the sub-scanning direction, so that the plurality of light beams are focused to some extent on the reflecting surface of the rotary polygon mirror. Therefore, it is possible to suppress the thickness of the rotary polygon mirror and prevent the laser scanning device from increasing in size.

Further, in the laser scanning device, the plurality of light beams are focused and irradiated on the reflecting surface of the rotary polygon mirror so that the distances in the sub-scanning direction are substantially the same, and the angle correcting means is provided. , Is arranged on the downstream side of the optical path of the light beam with respect to the rotating polygon mirror, refracts a plurality of light beams that diverge in the sub-scanning direction after being reflected by the rotating polygon mirror, and forms an angle so that these light beams converge with each other. It can be configured to correct.

According to the above arrangement, the plurality of light beams are focused and irradiated on the reflecting surface of the rotary polygonal mirror so that the distances in the sub-scanning direction are substantially the same, so that the thickness of the rotary polygonal mirror is increased. Can be minimized, which contributes to downsizing of the laser scanning device.

Further, in this case, although the plurality of light beams immediately after being reflected by the rotary polygon mirror proceed in the directions in which they diverge from each other, the angle correction means is arranged downstream of the rotary polygon mirror in the optical path. The angle can be corrected in the direction in which these diverging light beams are refocused.

In the laser scanning device, the plurality of light beams are focused and irradiated so as to be reflected on the reflecting surface of the rotary polygon mirror at positions separated by a predetermined distance in the sub-scanning direction. The angle correction means is arranged on the downstream side of the optical path of the light beam with respect to the rotary polygon mirror, and is adapted to receive a plurality of light beams focused in the sub-scanning direction after being reflected by the rotary polygon mirror. A plurality of light beams that are incident at a predetermined pitch close to each other in the sub-scanning direction are refracted (focusing effect by a convex lens) to the means, and these light beams travel substantially parallel to each other while maintaining the above predetermined pitch. The angle may be corrected so as to form a beam.

According to the above arrangement, the plurality of light beams are focused and irradiated on the reflecting surface of the rotary polygon mirror, so that the thickness of the rotary polygon mirror can be suppressed and laser scanning can be performed. Contributes to downsizing of the device.

Further, in this case, the plurality of light beams immediately after being reflected by the rotating polygonal mirror further proceed in the direction of converging with each other, and come into the state of being closest to each other at the time of incidence on the angle correcting means, and refraction of the angle correcting means Due to the action (divergence effect of the concave lens), the angles of these light beams are corrected so that they become substantially parallel light beams that travel while maintaining the above-mentioned predetermined pitch. As a result, the size of the lens used for the angle correction means can be reduced, and the cost of the lens can be reduced.

Further, in the laser scanning device, the angle correction means has an arcuate longitudinal axis which is a set of points at an equal distance from the beam reflection point of the rotary polygon mirror, and with respect to the longitudinal axis. It is preferable that the vertical cross section has the same shape at each scanning position.

According to the above construction, the incident position of the light beam in the sub-scanning direction on the incident surface of the angle correction means is constant in the sub-scanning direction without depending on the deflection angle of the rotary polygon mirror. The shape of the cross section orthogonal to the longitudinal axis can be made the same for all scanning directions, the lens used for the angle correction means can be easily designed, and the scanning line pitch on the photoconductor Misalignment does not occur easily.

In the laser scanning device, the angle correction means corrects the light beam scanned by the rotary polygon mirror at a constant angular velocity in the main scanning direction so that the light beam is scanned at a constant velocity, and It is preferable that the lens has a function of at least one of the cylindrical lenses that corrects the surface tilt caused by the rotating polygon mirror.

According to the above arrangement, the lens used for the angle correction means has at least one function of the fθ lens and the cylindrical lens, so that the number of optical components can be reduced and the laser scanning device can be reduced. The cost merit in is increased.

Further, in the laser scanning device, the angle correction means is arranged on the upstream side of the optical path of the light beam with respect to the rotary polygon mirror, and a plurality of light beams focused in the sub-scanning direction are incident. The angle correction means refracts a plurality of light beams incident at a predetermined pitch close to each other in the sub-scanning direction, and the light beams travel substantially parallel to each other while maintaining the predetermined pitch. The angle can be corrected so that the light beam has a different shape.

According to the above arrangement, the plurality of light beams emitted from the plurality of laser light sources are arranged at the upstream side of the optical path of the rotary polygon mirror and are collected at a predetermined pitch close to each other at the position of the angle correction means in the sub-scanning direction. It is supposed to be illuminated. And
The light beam passing through the angle correction means travels on and after the optical path including the rotary polygon mirror as substantially parallel light which maintains a positional relationship of being close to each other.

In this case, since the light beam passing through the angle correction means is the incident beam before being deflected and scanned by the rotary polygon mirror, the angle correction means considers the change of the incident position of the scanning beam in the main scanning direction. There is no need, and the lens design becomes easier, and the size of the lens becomes smaller, so that the cost of the lens can be reduced.

Further, in order to solve the above-mentioned problems, the image forming apparatus of the present invention has an exposing means for writing an electrostatic latent image on a photosensitive drum, as described in any one of claims 1 to 7. It is characterized by using a laser scanning device.

According to the above structure, a general-purpose semiconductor laser can be used as a laser light source in the laser scanning device used as the exposing means, and the cost of the laser scanning device can be reduced.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 shows a schematic configuration of the digital copying machine 1 according to this embodiment. The digital copying machine 1 is roughly composed of a document reading section 110 and an image forming section 210.

The document reading section 110 is configured to scan and read an image of a document placed on the document table 111 below the document table 111. As a mechanism therefor, the first scanning unit 112 is used. , The second scanning unit 11
3, an optical lens 114, and a CC that is a photoelectric conversion element
It has a D line sensor 115.

The first scanning unit 112 is composed of an exposure lamp unit for exposing the surface of the original document, a first mirror for reflecting a reflected light image from the original document in a predetermined direction, and the like. The second scanning unit 113 uses the CCD line sensor 11 to reflect the reflected light from the document reflected from the first mirror.
It is composed of a second mirror and a third mirror which lead to No. 5. The optical lens 114 forms an image of reflected light from the document on the CCD line sensor 115.

Further, the document reading section 110 can be provided with an automatic document feeder 116 on a document table 111 made of transparent glass on the upper surface thereof. Automatic document feeder 116
Is an apparatus for automatically feeding a plurality of originals set on the original set tray one by one onto the original table 111. In the configuration including the automatic document feeder 116, the document reading unit 110 causes the image of the document automatically conveyed by the automatic document feeder 116 to be at a predetermined exposure position by the operation related to the automatic document feeder 116. Can be read.

The original image read by the original reading unit 110 is sent as image data to an image data input unit (not shown), and after the image data is subjected to a predetermined image processing, it is stored in the memory of the image processing unit. Then, the image in the memory is read according to the output instruction and transferred to the laser writing unit 222 of the image forming unit 210.

The image forming section 210 includes a photosensitive drum 22.
A charger 221 that charges the photosensitive drum 220 to a predetermined potential around 0, and a light beam that is turned on / off according to the image data is applied to the charged photosensitive drum 220 to statically charge the photosensitive drum 220. A laser writing unit 222 that writes an electrostatic latent image, and a developing device 22 that supplies toner to the electrostatic latent image formed on the photoconductor drum 220 to visualize the electrostatic latent image.
3, a transfer device 224 that transfers the toner image formed on the surface of the photoconductor drum 220 to a recording sheet, a static eliminator 225 that removes charges on the photoconductor drum 220, and an excess that remains on the photoconductor drum 220 after transfer. A cleaning device 226 for collecting various toners is provided.

A fixing unit 227 is arranged on the discharge side of the image forming section 210, that is, on the downstream side of the photoconductor drum 220. The recording paper on which the image is transferred is sent to the fixing unit 227 and the image (toner image) is transferred. ) Is fixed on the recording paper.

On the discharge side of the image forming section 210, a switchback conveying path 228 for reversing the front and back of the recording paper to form an image again on the back surface of the recording paper is provided further downstream of the fixing unit 227. A post-processing device 240 that performs stapling processing and the like on the formed recording paper and that has an elevating tray 241 is provided. Fixing unit 2
The recording paper on which the toner image has been fixed at 27 passes through a switchback path 228 as necessary, and then is guided to a post-processing device 240 by a paper discharge roller 229, where a predetermined post-processing is performed. After that, it is discharged.

Further, the paper feeding portion for feeding the recording paper to the transfer position of the photoconductor drum 220 is arranged below the image forming portion 210, and has a multi-stage paper feeding tray portion having paper cassettes 251 to 253. A manual feed tray 254 and a duplex unit 255 are provided. Sheets fed from the multi-stage sheet feed tray section, the manual feed tray 254, and the duplex unit 255 are conveyed to the transfer position via the sheet feed conveyance path 256.

The duplex unit 255 is connected to a switchback path 228 for reversing the recording paper, and is used when images are formed on both sides of the recording paper. Double-sided unit 2
Reference numeral 55 has a configuration in which it can be replaced with a normal paper cassette, and it is also possible to replace the duplex unit 255 with a normal paper cassette.

The laser scanning device according to the present invention is the laser writing unit 222 in the digital copying machine 1 described above.
Applied to. The laser scanning device according to this embodiment will be described below in detail.

The laser scanning device, as shown in FIG. 1, emits a light beam in accordance with image data read from a memory or image data transferred from an external device, the light beam, etc. It is composed of a polygon mirror 12 that deflects angular velocity.

The laser light source 11 is composed of two semiconductor lasers 1.
1a and 11b are provided, and the structure is such that two light beams can be emitted. Here, the light beam emitted from the semiconductor laser 11a is the light beam B ₁ , and the semiconductor laser 1
The light beam emitted from 1b is referred to as a light beam B ₂ . The light beams B ₁ and B ₂ are deflected by the polygon mirror 12 and irradiated while scanning the surface of the photoconductor drum 220 in the main scanning direction.

In the following description, the light beam B ₁ ·
In each of B ₂ , the optical path from the laser light source 11 to the polygon mirror 12 is called an incident beam optical path, and the optical path from the polygon mirror 12 to the photosensitive drum 220 is called an outgoing beam optical path. In addition, a light beam in the incident beam optical path is called an incident beam, and an optical component arranged in the incident beam optical path is called an incident optical system, and a light beam in the outgoing beam optical path is called an outgoing beam and an optical beam arranged in the outgoing beam optical path. The component is called an output optical system.

The incident optical system guides the incident beam emitted from the laser light source 11 to the polygon mirror 12 and shapes the incident beam to have a rectangular sectional shape. Therefore, as the incident optical system, a collimator lens, an aperture, and a cylindrical lens are sequentially arranged from the upstream side (laser light source 11 side) to the downstream side (polygon mirror 12 side) in the incident beam optical path.

The collimator lens is a laser light source 11
Laser diode 11a. The substantially conical light beam diffused and emitted from 11b is converted into a parallel beam. The aperture is composed of a plate-shaped member having a rectangular opening in its substantially central portion, and is shaped so that the cross section of the light beam whose cross section perpendicular to the optical axis is substantially circular is rectangular. The cylindrical lens condenses the light beam in the sub-scanning direction (direction perpendicular to the optical axis and the generatrix of the cylindrical lens) on the reflecting surface of the polygon mirror 12.

In FIG. 1, in the incident optical system, the collimator lens, the aperture, and the cylindrical lens are arranged as an incident optical unit 13 formed by unitizing them. In addition, the incident optical unit 13
Are provided corresponding to the semiconductor lasers 11a and 11b, respectively.

Due to the action of the incident optical system, the incident beam incident on the reflecting surface of the polygon mirror 12 is focused on the reflecting surface of the polygon mirror 12 as a light beam focused only in the sub-scanning direction. Further, it is preferable that the focusing line on which the incident beam is focused is near the center in the height direction on the reflecting surface of the polygon mirror 12.

On the other hand, the output optical system is the polygon mirror 12
The outgoing beam reflected by each of the reflecting surfaces is guided to the photoconductor drum 220, and the outgoing beam is reflected by the photoconductor drum 220.
The beam spot when illuminating the top has a predetermined size,
It acts so that the photosensitive drum 220 is scanned at a constant speed. For this reason, in the emission optical system, the angle correction lens 14, the fθ lens 15, the long cylindrical lens 1 are arranged from the upstream side (polygon mirror 12 side) to the downstream side (photosensitive drum 220 side) in the emission beam optical path.
6 and an exit folding mirror 17 are provided.

The fθ lens 15 is the polygon mirror 1
When the photosensitive drum 220 is irradiated with the outgoing beam that moves at the constant angular velocity due to the constant angular velocity motion of 2, the beam spot is converted so that the beam spot moves at the constant linear velocity on the main scanning line. The long cylindrical lens 16 corrects the surface tilt of the polygon mirror 12 by the action related to the cylindrical lens in the incident optical system. Then, the emission folding mirror 17 reflects the emission beam after passing through the long cylindrical lens and guides it to the photoconductor drum 220. As a result, the emitted beam reaches the photosensitive drum 220 through different optical paths depending on the position of the twelve reflecting surfaces in the rotation direction.

The outgoing beam is deflected and scanned by the rotation of the polygon mirror 12, and the outgoing beam for scanning the width used for image formation on the photosensitive drum 220, that is, the main scanning line (hereinafter, this outgoing beam is used). The spatial region through which the beam is called the main scanning beam) is the main scanning beam region.

Each of the semiconductor lasers 11a and 11b
Light beam B emitted from it₁・ B ₂The main scanning beam
The areas are the same, but a different space is used for the sub-scanning direction.
Passes through the photoconductor drum 220 in close proximity (predetermined resolution
Irradiation is performed at an interval of one line pitch).

Therefore, in the above laser scanning device, the optical axes of the incident beams of the light beams B ₁ and B ₂ emitted from the semiconductor lasers 11a and 11b are not parallel to each other, and the polygon mirror 12 is used. In the outgoing beam after the reflection, the angle of the light beams B ₁ and B _{2 in} the sub-scanning direction is corrected by passing through the angle correction lens 17. As a result, the light beams B ₁ and B ₂ are irradiated on the photosensitive drum 220 in close proximity.

The light beams B ₁ and B ₂ are applied to the photosensitive drum 2
A method for irradiating in close proximity on 20 will be described below with reference to FIGS. In the following description, the direction corresponding to the optical axis direction of the laser scanning device is the X direction, the direction corresponding to the main scanning direction is the Y direction, and the direction corresponding to the sub scanning direction is the Z direction.

General-purpose laser diodes are used as the semiconductor lasers 11a and 11b provided in the laser scanning device. In a general-purpose laser diode, the light beam B ₁ · emitted by the volume of the laser diode itself
Since B ₂ cannot be brought close to each other at the time of emission, by arranging the semiconductor lasers 11a and 11b at a predetermined angle in the sub-scanning direction (Z direction), the polygon mirror 1
The light beams B ₁ and B ₂ are made to enter the two reflection points P ₀ in close proximity to each other.

At this time, the semiconductor lasers 11a and 11b
Assuming that the inclination angles of θ are θ ₁ and θ ₂ with respect to the rotating surface of the polygon mirror 12, the outgoing beam reflected by the polygon mirror 12 is incident on the incident surface of the angle correction lens 14 as shown in FIG. It is incident on the point P ₁ or P ₂ . Note that θ ₁ and θ ₂ do not necessarily have to be at the same angle, but if θ ₁ and θ ₂ are at the same angle, the divergence angle of the outgoing beam after being reflected by the polygon mirror 12 is the same. This is preferable because the angle correction lens 14 can be easily designed.

In the structure shown in FIG. 3, the angle correction lens 14 is used.
The incident surface of is a convex surface having a refraction effect only in the sub-scanning direction, and the light beams B ₁ and B ₂ are angle-corrected by the refraction effect of the incident surface, and have a predetermined resolution pitch when reaching the photoconductor drum 220. It is focused so that there is an interval.

In the angle correction lens 14 shown in FIG.
Although the incident surface side is a convex surface, the present invention is not limited to this, and the emitting surface side may be a convex surface, or both the incident surface side and the emitting surface side may be a convex surface. Further, the fθ lens 15 arranged downstream of the angle correction lens 14 does not change the inclination angle of the light beams B ₁ and B ₂ with respect to the sub scanning direction.

The angle correction lens 14 has an arcuate longitudinal axis as shown in FIG. 4, and the distance from the reflection point P ₀ of the polygon mirror 12 to the incident surface of the angle correction lens 14 is , Are designed to have the same distance L at all scanning line positions. This is for the following reason.

As shown in FIG. 5A, the semiconductor laser 1
Light beam B ₁ or B emitted from 1a or 11b
₂ is deflected from the deflection point P ₀ on the polygon mirror 12 and swung by an angle α in both directions of the main scanning direction from the scanning line corresponding to the center of the image, so that the maximum degree of deflection is 2α. Further, the distance from the deflection point P ₀ to the angle correction lens 14 in the X-axis direction is L, and the intersection point with the scanning line corresponding to the image center on the incident surface of the angle correction lens 14 is point Q ₁ and the above point Q. A straight line that passes through ₁ and is parallel to the Y-axis direction is a straight line R ₁ , and a curve whose distance from the deflection point P ₀ is the same distance L for each deflection angle is a curve R ₂ . Furthermore, the curve R _{2 at the} deflection angle α
The upper position is point Q ₂ and the position on the straight line R ₁ is point Q ₃ . At this time, the distance from the deflection point P ₀ to the point Q ₂ is L, and the distance from the deflection point P ₀ to the point Q ₃ is L / cos α.

Here, when the deflection angle is 0 (scan line corresponding to the center of the image), as shown in FIG. 5B, the emission angle of the emission beam in the Z-axis direction with respect to the reflecting surface of the polygon mirror 12 is set. and theta, straight 'If the point Q _1' R ₁ and the street Z axis an intersection between a plane parallel to the said output beam points Q ₁ the distance between the X-Y plane (i.e., the point Q ₁ -Q The distance between ₁ ') is Ltan θ.

Further, when the deflection angle is α, as shown in FIG.
As shown, output to the reflecting surface of the polygon mirror 12
The output angle of the beam in the Z-axis direction is θ, and the curve R₂Through
Point at the intersection of the curved surface parallel to the Z axis and the output beam
Q₂If ', point Q ₂'And the distance between the XY plane
(That is, point Q₂-Q₂'Distance between) is Lta
nθ. Also, the straight line R₁Through the plane parallel to the Z axis and above
Point Q at the intersection with the outgoing beam₃If you say'poi
Don't Q₃'And the XY plane (ie, point Q
₃-Q₃The distance between'is Ltan θ / cos α.

That is, when the incident surface of the angle correction lens 14 is formed along the straight line R ₁ , the incident position of the outgoing beam with respect to the incident surface of the angle correction lens 14 in the Z direction differs depending on the deflection angle. On the other hand, when the incident surface of the angle correction lens 14 is formed along the curve R ₂ , the Z-direction incident position of the outgoing beam with respect to the incident surface of the angle correction lens 14 does not depend on the deflection angle. , Z is constant in the Z direction, which facilitates lens design. That is, the angle correction lens 14 has an arcuate longitudinal axis, and the shape of the cross section orthogonal to the longitudinal axis can be made the same in all scanning directions.

In the laser scanning device described above, the light beams B ₁ and B ₂ are irradiated so as to be condensed on the reflection surface of the polygon mirror 12, and diverge after being reflected by the polygon mirror 12. . The angle correction lens 14 refocuses the light beams B ₁ and B ₂ diverging in the sub-scanning direction to bring them closer to each other on the photosensitive drum 220.
Here, a convex lens having a focusing action in the sub-scanning direction is used.

However, the present invention is not limited to this, and a configuration as shown in FIG. 6 is also possible. That is, in the configuration shown in FIG. 6, the light beams B ₁ and B ₂ emitted from the semiconductor lasers 11a and 11b are
The light is not condensed on the polygon mirror 12 in the sub-scanning direction, but is condensed at the position of the angle correction lens 14 '. Then, the angle correction lens 14 'is
Unlike the angle correction lens 14 of FIG. 3, it has the power of a diverging lens (concave lens).

As a result, the light beams B ₁ and B ₂ passing through the angle correcting lens 14 ′ irradiate the photoconductor drum 220 while maintaining the positional relationship in which they are close to each other and proceeding as substantially parallel light in the subsequent optical paths. To be done. In the configuration of FIG. 6 above,
Since the incident points of the light beams B ₁ and B ₂ with respect to the angle correction lens 14 ′ are almost one point in the sub-scanning direction, the cost advantage can be obtained by downsizing the angle correction lens 14 ′ and the lens Design becomes easy.

As in the configuration of FIG. 3, the light beam B is
_{When 1} · B ₂ is incident on the reflecting surface of the polygon mirror 12 at one point in the sub-scanning direction, the incident point position and angle correction of the light beams B ₁ · B _{2 on} the polygon mirror 12 in the sub-scanning direction are corrected. It is preferable that the center line of the lens 14 coincides. Similarly, the light beam B ₁ ·
B ₂ is ₂ in the sub-scanning direction on the reflecting surface of the polygon mirror 12.
When the light is incident at a point, it is preferable that the center position of the incident point of the light beams B ₁ and B ₂ of the polygon mirror 12 and the center line of the angle correction lens 14 ′ coincide with each other in the sub-scanning direction. As a result, the incident positions of the light beams B ₁ and B _{2 on} the angle correction lens 14 or 14 ′ are the same distance from the lens center, which facilitates the lens design of the angle correction lens 14 or 14 ′.

As a modified example of FIG. 6, when a dispersion lens (concave lens) is used as the angle correction lens, as shown in FIG. 7, the angle correction is performed on the upstream side of the polygon mirror 12, that is, on the incident beam optical path. It is also possible to arrange the lens 14 ″.

In the configuration shown in FIG. 7, the semiconductor laser 11a-1
The light beams B ₁ and B ₂ emitted from 1b are designed to be condensed at the position of the angle correction lens 14 ″, and the light beams B ₁ and B that pass through the angle correction lens 14 ″.
Numeral ₂ is a substantially parallel light which maintains a positional relationship of being close to each other, and is irradiated onto the photoconductor drum 220 along the optical path thereafter including the polygon mirror 12.

Further, in the configuration of FIG. 7, the angle correction lens 1
The light beams B ₁ and B ₂ passing through 4 ″ are incident beams before being deflected and scanned by the polygon mirror 12. Therefore, the angle correction lens 14 ″ is the angle correction lens 14 / in FIG. It is not necessary to consider the change in the incident position of the scanning beam in the main scanning direction as in 14 ', and the lens design becomes easier. That is, like the angle correction lens 14 · 14 ′, the distance from the reflection point P ₀ of the polygon mirror 12 to the incident surface of the angle correction lens 14 · 14 ′ is an arc shape so as to be equal at all scanning line positions. The shape having the longitudinal axis of 1 does not have to be formed.

In the laser scanning device according to this embodiment,
The distance in the sub-scanning direction of the light beams B ₁ and B ₂ on the photoconductor drum 220 is set according to the resolution pitch in the image forming unit 210. For example, a resolution of 400 dpi
, The scanning beam interval on the surface of the photoconductor drum 220 is 63.5 μm, the resolution is 600 dpi, 42.3 μm, and the resolution is 800 dpi, 3
The distance between the light beams B ₁ and B ₂ is set so as to be 1.8 μm.

As described above, according to the present invention,
In a scanning device using a multi-beam, a plurality of light beams emitted from semiconductor lasers having different heights in the sub-scanning direction are made incident on a polygon mirror 12 to be deflected, and after being reflected by the polygon mirror 12, an angle correction lens By passing 14 through, it is possible to perform exposure to the resolution pitch set on the photoconductor drum 220.

According to the present invention, a general-purpose semiconductor laser can be used as the light source of the light beam for scanning the photosensitive drum, and moreover, the reduction of the light quantity can be reduced and a highly accurate image can be obtained.

Further, in the laser scanning device according to this embodiment, the light beams B ₁ and B ₂ initially emitted from the semiconductor lasers 11a and 11b are emitted while being inclined with respect to each other in the sub-scanning direction. The present invention is not limited to this and may be emitted as light beams parallel to each other.

[0080] Semiconductor When the light beam B ₁ · B ₂ from the laser 11a · 11b is emitted is a parallel light beam with each other, the light beam B ₁ · at an angle correction lens 14 which is located downstream of the polygon mirror 12 B It is possible to refract the emitted beam of ₂ and bring the light beams B ₁ and B ₂ close to each other on the photoconductor drum 220. However, in this case, the light beams B ₁ and B ₂ incident on the polygon mirror 12 are
Since the semiconductor lasers 11a and 11b have the same spacing in the sub-scanning direction as the layout spacing, the polygon mirror 12
In the sub-scanning direction, that is, the thickness of the polygon mirror 12 becomes large, and in order to stably perform high-speed rotation of the polygon mirror 12, it is necessary to enlarge the polygon mirror 12 and the polygon motor. There are problems that the device becomes large and the cost increases.

On the other hand, like the above laser scanning device, the light beams B ₁ and B ₂ emitted from the semiconductor lasers 11a and 11b are _first tilted in the sub-scanning direction, and on the reflecting surface of the polygon mirror 12, By converging to a certain extent, it is possible to prevent the polygon mirror 12 and the polygon motor from increasing in size.

The laser scanning device according to the present invention is not limited to the configuration described above, but can be configured as follows.

In the laser scanning device for injecting a plurality of semiconductor lasers into the polygon mirror, the incident angles from the plurality of semiconductor lasers into the polygon mirror are not parallel to the polygon mirror deflection surface, but are incident at an angle. By the angle correction lens that arranges a plurality of reflected laser light (divergent light) near the polygon mirror,
It is possible to obtain a configuration in which two laser beams corresponding to the design pitch are obtained on the drum surface.

As a result, the laser light emitted from the plurality of semiconductor lasers is directly incident on the polygon mirror without passing through the half mirrors and prisms, so that the light quantity is not reduced so that a general-purpose semiconductor laser can be used. Therefore, the cost of the scanning device can be reduced.

In the laser writing device, the function of the angle correction lens can be incorporated into the fθ lens to have a lens having the integrated function. in this way,
By incorporating the function of the angle correction lens into the fθ lens and integrating the functions, the angle correction lens and the fθ lens can be molded with one lens, so that the cost merit is increased. It is possible to adopt a configuration in which the incident angles from the top to the polygon mirror are the same with respect to the deflection surface of the polygon mirror, and the light is incident on the polygon mirror from above and below. As a result, the divergence angle of the light beam to the lens after the reflection by the polygon mirror becomes the same, so that the lens shape becomes simple and it is easy to set the design pitch on the drum surface.

In the laser writing device, the incident points from the plurality of semiconductor lasers to the polygon mirror may be incident on the polygon mirror at one point or in an overlapping manner in the vertical direction (sub scanning direction). . This simplifies the lens shape and makes it easy to set the design pitch on the drum surface.

In the laser writing device, the distance in the deflection surface direction from the polygon mirror surface to the angle correction lens may be the same within the use range of the deflection angle. This simplifies the lens shape, makes it easy to set the design pitch on the drum surface, and prevents pitch deviation from occurring.

In the above laser writing device, the incident points from the plurality of semiconductor lasers to the polygon mirror are incident on the polygon mirror at two points in the vertical direction, and one point or over at the incident side surface of the angle correction lens. It is possible to adopt a configuration in which the lens is wrapped and transmitted through the lens to obtain a designed pitch on the drum surface. As a result, the plurality of light beams are collected at almost one point on the angle correction lens, which facilitates lens design. Also, it is easy to set the design pitch on the drum surface.

With respect to the vertical positional relationship of the laser writing device, the vertical position on the polygon mirror surface of one point or a plurality of laser beams which are incident in an overlapping manner may be substantially coincident with the lens axis center. . This makes the lens design easy because the vertical plane of the polygon mirror and the vertical plane of the lens axis center substantially coincide with each other.

In the vertical positional relationship of the laser writing device, the center position of a plurality of laser beams incident at two points in the vertical direction on the polygon mirror surface and the lens axis center may be substantially aligned. it can. This makes the lens design easy because the vertical plane of the polygon mirror and the vertical plane of the lens axis center substantially coincide with each other.

In the laser writing device, incident light from a plurality of semiconductor lasers to the polygon mirror is imaged on the polygon mirror, and a light beam is spread on the incident side surface of the incident angle correction lens. can do. As a result, the image is formed when the two laser beams hit the polygon mirror, so that the polygon mirror thickness can be minimized.

In the laser writing device, incident light from a plurality of semiconductor lasers to the polygon mirror may be imaged on the incident side surface of the incident correction lens. As a result, the two laser beams form an image on the entrance side surface of the entrance correction lens, and the output image becomes clear.

In the laser writing device, the incident light positions on the polygon mirror surface from the plurality of semiconductor lasers can be matched or overlapped with each other in the scanning direction. As a result, in the optical design, the deflection points on the polygon mirror are the same on the left and right with respect to the positional relationship of the plurality of beams, so that the densities at the ends of the deflected image are likely to match.

In the above laser writing device, the positions of the first semiconductor laser and the second semiconductor laser in the emitting direction may coincide with or overlap with each other when viewed from the deflection surface direction. As a result, the polygon mirror surface deflection points match or overlap when viewed from the deflection surface direction, which facilitates lens design. Further, the densities in the image main scanning direction are likely to match.

In the laser writing apparatus, the angle correction lens has the function of the fθ lens for converting the constant angular velocity of the polygon mirror into the constant linear velocity and the function of the long cylindrical lens that acts to determine the sub-scanning beam diameter. It can be configured. As a result, the function of another lens is incorporated in the angle correction lens, which is a cost advantage.

[0096]

As described above, the laser scanning device of the present invention imparts a refracting action to the plurality of light beams in the sub-scanning direction orthogonal to the main scanning direction deflected by the rotary polygon mirror. Thus, an angle correction means for correcting the angle of the light beam is provided so that the light beam has a predetermined pitch in the sub-scanning direction at a position separated by a predetermined distance in the optical axis direction. is there.

Therefore, the plurality of light beams emitted from the plurality of laser light sources are given a refracting action in the sub-scanning direction by passing through the angle correction means arranged in the optical path, and a predetermined number in the optical axis direction. The distance in the sub-scanning direction becomes a predetermined pitch at positions separated by a distance.

Thus, in order to bring a plurality of light beams emitted at a predetermined distance in the sub-scanning direction close to each other,
Since it is not necessary to pass through optical components such as half mirrors and prisms that utilize the reflection / transmission action, and the amount of light beam reduction is small, it is possible to use a general-purpose semiconductor laser and reduce the cost of the laser scanning device. The effect that it can be achieved is produced.

Further, in the laser scanning device, the plurality of light beams emitted from the plurality of laser light sources are emitted in a state of being inclined with respect to each other in the sub-scanning direction, and are converged in the incident optical path toward the rotary polygon mirror. It is preferable to have a configuration.

Therefore, by first tilting the light beam emitted from the semiconductor laser in the sub-scanning direction, the plurality of light beams can be focused to some extent on the reflecting surface of the rotating polygon mirror, and the rotating polygon surface can be converged to some extent. It is possible to suppress the thickness of the mirror and prevent the laser scanning device from becoming large.

Further, in the laser scanning device, the plurality of light beams are focused and irradiated on the reflecting surface of the rotary polygon mirror so that the distances in the sub-scanning direction are substantially the same, and the angle correction means , Is arranged on the downstream side of the optical path of the light beam with respect to the rotating polygon mirror, refracts a plurality of light beams that diverge in the sub-scanning direction after being reflected by the rotating polygon mirror, and forms an angle so that these light beams converge with each other. It can be configured to correct.

Therefore, the plurality of light beams are focused and irradiated on the reflecting surface of the rotating polygonal mirror so that the distances in the sub-scanning direction are substantially the same, so that the thickness of the rotating polygonal mirror is minimized. Therefore, there is an effect that it contributes to downsizing of the laser scanning device.

Further, in the laser scanning device, the plurality of light beams are focused and irradiated so as to be reflected on the reflecting surface of the rotary polygon mirror at positions separated by a predetermined distance in the sub-scanning direction. The angle correction means is arranged on the downstream side of the optical path of the light beam with respect to the rotary polygon mirror, and is adapted to receive a plurality of light beams focused in the sub-scanning direction after being reflected by the rotary polygon mirror. A plurality of light beams that are incident at a predetermined pitch close to each other in the sub-scanning direction are refracted (focusing effect by a convex lens) to the means, and these light beams travel substantially parallel to each other while maintaining the above predetermined pitch. The angle may be corrected so as to form a beam.

Therefore, by focusing and irradiating the plurality of light beams on the reflecting surface of the rotating polygon mirror,
The thickness of the rotary polygon mirror can be suppressed, which contributes to downsizing of the laser scanning device, and the plurality of light beams reflected by the rotary polygon mirror are brought into the state of being closest to each other at the time of incidence on the angle correction means. By doing so, it is possible to reduce the size of the lens used for the angle correction means and reduce the cost of the lens.

Further, in the laser scanning device, the angle correction means has an arcuate longitudinal axis which is a set of points that are equidistant from the beam reflection point of the rotary polygon mirror, and with respect to the longitudinal axis. It is preferable that the vertical cross section has the same shape at each scanning position.

Therefore, since the incident position of the light beam in the sub-scanning direction on the incident surface of the angle correcting means is constant in the sub-scanning direction, the lens used for the angle correcting means can be easily designed, and Thus, there is an effect that the pitch shift of the scanning lines on the photoconductor does not easily occur.

In the laser scanning device, the angle correction means corrects the light beam scanned by the rotary polygon mirror at a constant angular velocity in the main scanning direction so that the light beam is scanned at a constant velocity, and It is preferable that the lens has a function of at least one of the cylindrical lenses that corrects the surface tilt caused by the rotating polygon mirror.

Therefore, the number of optical components can be reduced, and the cost merit in the laser scanning device can be increased.

Further, in the laser scanning device, the angle correction means is arranged on the upstream side of the optical path of the light beam with respect to the rotary polygon mirror, and a plurality of light beams focused in the sub-scanning direction are incident. The angle correction means refracts a plurality of light beams incident at a predetermined pitch close to each other in the sub-scanning direction, and the light beams travel substantially parallel to each other while maintaining the predetermined pitch. The angle can be corrected so that the light beam has a different shape.

Therefore, since the light beam passing through the angle correction means is the incident beam before being deflected and scanned by the rotary polygon mirror, the angle correction means considers the change of the incident position of the scanning beam in the main scanning direction. There is no need, and the lens design becomes easier, and the lens size is reduced, so that the cost of the lens can be reduced.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a perspective view showing a schematic configuration of a laser scanning device.

FIG. 2 is a sectional view showing a schematic configuration of an image forming apparatus to which the laser scanning device is applied as an exposing unit.

FIG. 3 is an explanatory diagram showing an example of an optical path of an outgoing beam after being reflected by a polygon mirror in the laser scanning device.

FIG. 4 is an explanatory diagram showing an incident optical path of an outgoing beam after being reflected by a polygon mirror to an angle correction lens in the laser scanning device.

5 (a) to 5 (c) are explanatory views showing a consideration regarding the design of the angle correction lens. FIG.

FIG. 6 is an explanatory diagram showing an example of an optical path of a light beam in the laser scanning device.

FIG. 7 is an explanatory diagram showing an example of an optical path of an incident beam before being reflected by a polygon mirror in the laser scanning device.

FIG. 8 is an explanatory diagram showing an optical path of an incident beam before being reflected by a polygon mirror in a conventional laser scanning device.

[Explanation of symbols]

11a / 11b Semiconductor laser (laser light source) 12 Polygon mirror (rotating polygon mirror) 14 Angle correction lens (angle correction means) 15 fθ lens 16 Long cylindrical lens (cylindrical lens) 220 Photosensitive drum 222 Laser writing unit (laser scanning device) , Exposure means) B ₁ · B ₂ light beam

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Ono             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Tetsuji Ito             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Tetsuya Nishiguchi             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Hisashi Yamanaka             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2C362 AA07 AA10 BA04 BA48 BA86                 2H045 AA01 BA02 BA22 BA33 CA03                 5C051 AA02 CA07 DA02 DB02 DB22                       DB24 DB30 DC04 DC07 EA03                       FA01                 5C072 AA03 BA02 HA02 HA06 HA13                       HA20 HB08 XA01 XA05

Claims (8)

[Claims] 1. A laser scanning device for deflecting and scanning a plurality of light beams emitted from a plurality of laser light sources with a single rotating polygon mirror, wherein the rotating polygon mirror is used for the plurality of light beams. By giving a refracting action in the sub-scanning direction orthogonal to the deflected main scanning direction, the light beam has a predetermined pitch in the sub-scanning direction at a position separated by a predetermined distance in the optical axis direction. A laser scanning device comprising an angle correction means for correcting the angle of the light beam. 2. A plurality of light beams emitted from the plurality of laser light sources are emitted in a state of being inclined with respect to each other in the sub-scanning direction, and are converged in an incident optical path toward the rotary polygon mirror. Item 2. A laser scanning device according to item 1. 3. The plurality of light beams are focused and irradiated on the reflecting surface of the rotating polygonal mirror so that the distances in the sub-scanning direction are substantially equal to each other, and the angle correcting means is provided on the rotating polygonal mirror. On the other hand, it is arranged on the downstream side of the optical path of the light beam, and refracts a plurality of light beams that diverge in the sub-scanning direction after being reflected by the rotating polygon mirror, and performs an angle correction so that these light beams converge with each other. The laser scanning device according to claim 2. 4. The plurality of light beams are focused and irradiated so as to be reflected on a reflecting surface of the rotary polygon mirror at a position separated by a predetermined distance in the sub-scanning direction, and the angle correcting means includes A plurality of light beams, which are arranged on the downstream side of the optical path of the light beam with respect to the rotating polygon mirror and are focused in the sub-scanning direction after being reflected by the rotating polygon mirror, are incident on the angle correction means. A plurality of light beams that are incident at a predetermined pitch close to each other in the scanning direction are refracted, and the light beams are angle-corrected so that the light beams become substantially parallel light beams that travel while maintaining the predetermined pitch. The laser scanning device according to claim 2. 5. The angle correction means has an arcuate longitudinal axis that is a set of points that are equidistant from a beam reflection point of the rotary polygon mirror, and has a cross-sectional shape perpendicular to the longitudinal axis. 5. The laser scanning device according to claim 3, wherein the laser scanning device has the same shape at each scanning position. 6. The angle correcting means corrects a light beam scanned at a constant angular velocity in the main scanning direction by the rotary polygon mirror so that the light beam is scanned at a constant velocity, and a surface tilt caused by the rotary polygon mirror. 6. The laser scanning device according to claim 3, wherein the laser scanning device is a lens that also has at least one of the functions of a cylindrical lens that corrects. 7. The angle correction means is arranged on the upstream side of the optical path of the light beam with respect to the rotary polygon mirror, and a plurality of light beams focused in the sub-scanning direction are incident thereon. The angle correction means refracts a plurality of light beams incident at a predetermined pitch that are close to each other in the sub-scanning direction so that the light beams become substantially parallel light beams that travel while maintaining the predetermined pitch. 3. The laser scanning device according to claim 2, wherein the angle is corrected. 8. An electrophotographic image forming apparatus, wherein the laser scanning device according to any one of claims 1 to 7 is used as an exposing means for writing an electrostatic latent image on a photosensitive drum. .