JP2001337283A - Laser beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam scanner of a multibeam light source unit type which is small in the increased number of parts, is simple in structure, is high in density, speed and image quality and is low in a cost. SOLUTION: Cylinder lenses 3a and 3b are respectively held or fixed to bases 12a and 12b. The bases 12a and 12b are slid and energized upward by compression springs 14. The bases are guided by guide members 15 and guides 12c projecting form the bases 12a and 12b so as not to incline with the optical axis. Adjusting screws 13a and 13b are tightened or loosened with respect to receiving parts 13c, by which the bases 12a and 12b are made movable in a vertical direction and the distance y3 of the optical axis centers of the cylinder lenses with respect to the true optical axis is made adjustable. The deterioration in the optical characteristics is prevented by correcting this value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to a laser beam scanning device used as exposure means for forming an electrostatic latent image on a photoreceptor by a digital copying machine, a plain paper facsimile, or the like.

[0002]

2. Description of the Related Art
In an image forming apparatus (hereinafter referred to as a machine) equipped with a laser beam scanning device using a laser beam, such as a laser printer, a digital copying machine, and a plain paper facsimile, the pixel density (dp
i) of 300 to 400 dpi, which is not very high density, was mainly used. However, recently, the market demand for image quality is particularly severe, and the pixel density is 1200 dpi.
Machines exceeding the above are put on the market, and high-speed machines with high-density image quality are becoming mainstream in the future.

In order to meet such demands, the following 3
There are two ways to respond. One is to keep the rotation speed of an optical deflector (hereinafter, polygon motor) unchanged, and instead reduce the rotation speed of the photoreceptor to cope with this. 6
If a machine with a pixel density of 1200 doi is to be made based on a pixel density of 00 dpi, the rotational speed of the photoconductor is set to 600 dpi while the rotational speed of the polygon motor remains at 600 dpi.
Making it half of i results in a machine with a pixel density of 1200 dpi. The second is to increase the rotation speed of the polygon motor to cope with the problem. Since the theory is the same as that of the first corresponding content, the description is omitted. The third is to use two or more laser light sources to cope with the problem. This can be achieved without reducing the rotation speed of the photosensitive member and without increasing the rotation speed of the polygon motor.

A disadvantage of the first countermeasure is that the speed of the photoreceptor is reduced, so that the printing speed is reduced, which is not suitable for high-speed operation. A disadvantage of the second countermeasure is that since the rotation speed of the polygon motor increases, noise, vibration, and an increase in the temperature inside the apparatus become technical issues. Another disadvantage of the third countermeasure is that the configuration is complicated by using two or more laser light sources, and the number of components increases because optical elements are required for each laser light source, and the light control system is also complicated at the same time. In addition to this, a mechanism for mechanically adjusting the interval between the two beams in the sub-scanning direction is required. For example, if the pixel density is 1200 dpi, the beam interval on the drum surface is 21.1.
Adjust to 7 μm (25.4 mm ÷ 1200)
dpi). However, in the future, it is predicted that the above-described multi-beam light source unit will become mainstream and will be compatible with high density, high speed, and high image quality.

In the case of a conventional multi-beam light source unit, in the case of two beams, a laser beam is synthesized by an optical prism and irradiated onto a mirror surface of a polygon motor. However, the cost of the optical prism is extremely high and is not suitable for a low-cost printer. As a cost reduction measure, an optical prism-less multi-beam light source unit has been proposed, and this method is becoming the mainstream of the multi-beam light source unit.

However, a disadvantage of this method is that, since the light beam interval in the main scanning direction is wider than that of the light source unit combining the optical prisms, the light of the cylindrical lens that narrows the light spot in the sub-scanning direction when the beam interval is adjusted. There is a possibility that the optical path may be deviated from the axial center position, thereby increasing the light spot and significantly deteriorating the optical imaging performance.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multi-beam light source unit type laser beam scanning apparatus which has a simple structure, high density, high speed, high image quality and low cost, with the number of parts added as small as possible. And

[0008]

According to a first aspect of the present invention, there is provided a laser beam scanning apparatus comprising:
A laser light source, a cylinder lens system that converges a light beam from the laser light source in the sub-scanning direction and forms a long line image in the main scanning direction, and a light deflector having a deflecting / reflecting surface near the image forming position of the line image A scanning imaging optical system for condensing a light beam deflected by the optical deflector as a light spot on a surface to be scanned, and a laser in the sub-scanning direction disposed between the cylinder lens system and the optical deflector. A laser beam scanning device having a beam shaping means for blocking light around the light beam and a cylinder lens for narrowing a light spot in the sub-scanning direction with respect to the optical deflector, comprising two or more laser light sources; Each optical path intersects on the deflecting / reflecting surface of the deflector, and the beam condensing interval in the sub-scanning direction to converge as a light spot on the surface to be scanned at regular intervals in the main scanning direction and the sub-scanning direction To To allow integer, characterized by comprising independently provided the cylinder lens for each optical path.

According to a second aspect of the present invention, in order to achieve the above object, the cylinder lens is provided so that the optical axis can be adjusted in the sub-scanning direction.

According to a third aspect of the present invention, in order to achieve the above object, the cylinder lens can be adjusted by an optical axis adjustment mechanism provided independently in the sub-scanning direction in each optical path. And

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the overall configuration of an example of a laser beam scanning device to which the present invention is applied. The laser beam scanning device includes an optical housing 1 having an open upper surface, a cover (not shown) for closing the upper surface of the optical housing 1, and a light source unit (laser beam generator) fixed to a side surface of the optical housing 1 to oscillate a laser beam. Means) 2, an aperture (beam shaping means) not shown,
Cylinder lenses (first focusing means) 3a, 3b, polygon motor (deflection scanning means) 4, scanning lens (imaging means) 5, and opening 6 formed in optical housing 1 as an emission port. It is composed.

The light source unit 2 is an example of a laser beam generating means, and includes a laser diode, a laser diode support holder, a collimator lens for adjusting the position of the laser diode and fixing the laser beam to a substantially parallel light beam, and a laser diode. It comprises a laser drive substrate 7 for supplying and controlling current for light emission.

The beam converted into a parallel light beam by the light source unit 2 is beam-shaped by an aperture having a rectangular, oval, or elliptical shape in order to obtain a desired spot diameter (a beam after passing through the beam shaping means). Then, the light is made incident on the cylinder lenses 3a and 3b, which are the first light condensing means, and is narrowed in the sub-scanning direction. A polygon motor 4 as deflection scanning means is provided at the position of the image forming point of this beam, and the scanning beam reflected on each mirror surface (six surfaces in the figure) passes through the scanning lens 5.

The scanning lens 5 is designed to have an fθ characteristic as a main scanning characteristic. In the sub-scanning direction, the image forming point and the image plane formed by the cylinder lenses 3a and 3b, which are the first condensing means, are conjugated. The lens is designed to have surface tilt correction characteristics so as to satisfy the following condition, and is generally constituted by a plurality of lens groups (shown as a single lens in the figure).

These parts are housed in the optical housing 1 with a predetermined positional accuracy. As means for fixing each component, pressing with a leaf spring, bonding, snap-fitting, and the like are well known, and any fixing method may be used although not shown. The opening 6 may be always open, but in many cases the entire surface of the opening is closed with dustproof glass for dust protection. Irradiation of the beam to the photoconductor 8 is performed in the scanning direction (the direction of the arrow X in the figure) as shown in the drawing.

FIG. 2 is a perspective view showing an example of a two-beam light source unit and beam irradiation on the photosensitive member 8. FIG.
(A) and (B) are optical prism synthesis methods, and (C) and (C)
(D) shows an optical prismless system.

In FIGS. 2A and 2B, beams L3 and L4 emitted from laser diodes 9c and 9d are converted into collimated light beams by collimating lenses 10c and 10d, respectively, and shaped by an aperture (not shown). L4
Goes straight through the optical prism 11, and the beam L3
At 1 the beam is combined with the beam L4. Two beams L3, L4
Is about 2-3 m in the main scanning direction immediately after the optical prism 11
at a distance of about m on the mirror of the polygon motor 5, and on the surface of the photoconductor 8, the main scanning direction x2 and the sub-scanning direction y
Irradiation at a distance of 2.

2 (C) and 2 (D), beams L1 and L2 emitted from laser diodes 9a and 9b are converted into collimated light beams by collimating lenses 10a and 10b, respectively, and shaped by an aperture (not shown). Immediately after the unit, the two beams are approximately 10 to 12 in the main scanning direction.
Although the distance is about mm, the distance intersects at a distance of 0 mm on the mirror of the polygon motor 5, and the light is irradiated on the surface of the photoconductor 8 at a distance of x1 in the main scanning direction and y1 in the sub-scanning direction.

That is, in the optical prismless system, the cylinder lenses 3a and 3b can be divided because the distance between the beams is farther from the main scanning direction, but in the optical prism combining system, the cylinder lenses 3c can be divided because the distance between the beams is short. Cannot be split. In addition, the distance y2 between the sub-scanning beams on the surface of the photoconductor 8 of the optical prism combining method is rotationally adjusted (in the direction of the arrow in the drawing) with the beam L4 as the center X2. The distance y1 between the sub-scanning beams on the surface of the photoreceptor 8 of the optical prismless system is the beam L
The rotation is adjusted (in the direction of the arrow in the figure) about the middle X1 of the distance between L1 and L2.

FIG. 3 is a plan view (A) of the cylinder lens optical axis adjusting mechanism in one embodiment of the laser beam scanning device according to the present invention, a side sectional view (B) along the arrow BB line,
It is a front view (C). The cylinder lenses 3a, 3b are held or fixed to the bases 12a, 12b by bonding or pressing with a leaf spring (not shown), bonding, snap-fitting, or the like. The bases 12a and 12b are configured to be slid in the upward direction in the figure by a compression spring 14, and are guided by a guide member 15 and a guide 12c protruding from the bases 12a and 12b so as not to be inclined with respect to the optical axis. I have.

Then, the adjusting screws 13a and 13b are
By tightening or loosening c, the bases 12a and 12b are movable in the vertical direction of the arrow in the figure, and the distance y3 of the center of the cylinder lens optical axis with respect to the true optical axis becomes the adjustment width, and this value is corrected. This prevents deterioration of optical characteristics. As shown, the two beams L1 and L2
Can be adjusted for each optical path (cylinder lens optical axis) of the light sources.

FIG. 4 is a perspective view showing an optical path for correcting an optical axis shift in a cylinder lens for sub-scanning beam adjustment in one embodiment of the laser beam scanning apparatus according to the present invention. Assuming that the light emitting point A1 does not have a positional shift due to a dimensional variation of components, the optical axis center A of the cylinder lens 3a
1 '. The distance between two light emitting points is l
In this case, the center of rotation for adjusting the distance between beams in the sub-scanning direction is the point X1 at the position of 1/2. When the rotation is adjusted with this position as the center X1, the light emitting point A1 is at B1, the light emitting point A2 is at B2, and the optical paths passing through the cylinder lenses 3a and 3b are at B1 'and B2', respectively. A range of adjustment of the distance occurs.

[0023]

As described above, the laser beam scanning device according to the present invention is compatible with a laser beam device having a plurality of beams because the cylinder lens is provided independently of the optical path. Since the optical axis adjustment mechanism is provided for each beam in the sub-scanning direction, there is an effect that a high quality image can be obtained without significantly impairing optical characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall configuration of an example of a laser beam scanning device to which the present invention is applied.

FIGS. 2A and 2B are perspective views showing an example of a two-beam light source unit and beam irradiation to a photoconductor 8; FIGS. 2A and 2B are optical prism combining systems; FIGS. 2C and 2D are optical prisms; Shows the less-less method.

FIG. 3 is a plan view (A), a side sectional view (B), and a front view (C) of the cylinder lens optical axis adjusting mechanism in one embodiment of the laser beam scanning device according to the present invention. is there.

FIG. 4 is a perspective view showing an optical path of optical axis shift correction by a cylinder lens for sub-scanning beam adjustment in one embodiment of the laser beam scanning device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 optical housing 2 light source unit (laser beam generating means) 3a, 3b cylinder lens (first focusing means) 3c cylinder lens 4 polygon motor (deflection scanning means) 5 scanning lens (imaging means) 6 aperture 7 laser drive board 8 Photoconductor 9a, 9b, 9c, 9d Laser diode 10a, 10b, 10c, 10d Collimating lens 11 Optical prism 12a, 12b Base 12c Guide 13a, 13b Adjusting screw 13c Receiving part 14 Compression spring 15 Guide member L1, L2, L3, L4 beam

Claims (3)

[Claims] 1. A laser light source, a cylinder lens system for converging a light beam from the laser light source in a sub-scanning direction to form a long line image in a main scanning direction, and deflecting and reflecting near the image forming position of the line image A light deflector having a surface, a scanning imaging optical system for converging a light beam deflected by the light deflector as a light spot on a surface to be scanned, and disposed between the cylinder lens system and the light deflector; In a laser beam scanning device having a beam shaping means for blocking light around a laser beam in the sub-scanning direction and a cylinder lens for narrowing a light spot in the sub-scanning direction to the optical deflector, two or more laser light sources are used. The optical paths cross each other on the deflecting / reflecting surface of the optical deflector, and are condensed as light spots on the surface to be scanned at regular intervals in the main scanning direction and the sub-scanning direction. Bee A laser beam scanning apparatus, wherein a laser beam condensing interval is adjustable, and said cylinder lens is provided independently for each optical path. 2. The laser beam scanning device according to claim 1, wherein said cylinder lens is provided so that an optical axis can be adjusted in a sub-scanning direction. 3. The optical system according to claim 1, wherein the cylinder lens is adjustable by an optical axis adjusting mechanism provided independently in a sub-scanning direction in each optical path.
Laser beam scanning device.