JP2002023086A - Laser scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser scanning device where all laser beams are image- formed on a face to be scanned and the laser beams are easily controlled as the laser scanning device which simultaneously scans a plurality of scanning lines. SOLUTION: The laser beams which are emitted from the semiconductor laser devices 13 and 14 and whose polarization directions are orthogonal to each other are synthesized by a polarization maintaining coupler 11 through polarization maintaining fibers 12 and 15. The beam is led to a light emitting point 10 and is emitted on the optical axis of a collimator lens 9 by means of a polarization maintaining fiber 16. The laser beam collimated by the collimator lens 9 is dispersed in a subscanning direction by a Savart plate 7 while it is converged on the mirror face of a rotary polygonal mirror 6 in a cylindrical lens 8. The dispersed laser beams 18 and 19 individually scan a scanning line on a photosensitive body 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser scanning device for forming an image on a surface to be scanned while scanning a laser beam, and more particularly to a laser scanning device for simultaneously scanning a plurality of scanning lines.

[0002]

2. Description of the Related Art In recent years, the resolution of an image forming apparatus used for a copying machine, a printer, a facsimile or the like has been increased, and the number of scanning lines for forming an image has been increasing and the density has been increasing. There is also a strong demand for higher speeds, and it is necessary to increase the scanning speed to achieve both.

However, in a laser scanning device,
There is a limit to improving the scanning speed by increasing the rotation speed of the polygon mirror that deflects the laser beam. For this reason, a multi-beam system has been proposed in which a plurality of scanning lines are simultaneously scanned using a plurality of laser beams that can be independently modulated. For example, in an image forming apparatus described in Japanese Patent Application Laid-Open No. 5-294005, a plurality of laser beams are emitted from a semiconductor laser array and scanning is performed simultaneously.

That is, a plurality of laser beams emitted from a semiconductor laser array are adjusted into parallel beams by a collimator lens, and then deflected by a rotating polygon mirror.
Each beam is condensed at a different position in the sub-scanning direction on the surface to be scanned via the scanning lens.

[0005]

However, in the above-described image forming apparatus, the principal ray of each laser beam is farther from the optical axis of the collimator lens. In particular, as the principal ray is farther from the optical axis of the collimator lens, the aberration becomes larger. Therefore, there is a problem that the laser beam does not form an image on the surface to be scanned, and a latent image is not normally formed on the surface to be scanned.

Further, since the focusing positions of the laser beams on the surface to be scanned are different from each other in the main scanning direction, the timing for starting the scanning is different for each laser beam, and the control of the laser beam is complicated. There are also problems. The present invention has been made in view of the above-described problems, and in a laser scanning device that simultaneously scans a plurality of scanning lines, all laser beams are imaged on a surface to be scanned.
It is another object of the present invention to provide a laser scanning device that can easily control a laser beam.

[0007]

In order to achieve the above object, a laser scanning device according to the present invention is provided with an independently modulated 2
In a laser scanning device that scans a surface to be scanned with two laser beams at predetermined intervals in the sub-scanning direction, two laser beams whose polarization directions are orthogonal to each other are combined to form a laser beam traveling in the same direction. Synthesizing means, collimating means for collimating the synthesized laser beam, and combining the synthesized laser beam according to the polarization direction.
And a spectroscopic means for splitting the light into a laser beam.

That is, the combined laser beam is emitted only from the same object point and enters the collimating means. Further, the collimating means is a collimator lens, and the principal ray of the combined laser beam is made to coincide with the optical axis of the collimator lens. The combined laser beam is guided from the combining unit to the collimating unit using an optical fiber that preserves the polarization state of the incident light.

A laser scanning device according to the present invention comprises a deflecting means for deflecting an optical path of the laser beam in a main scanning direction by reflecting the laser beam, and a laser beam in a sub-scanning direction on a reflection surface of the deflecting means. A light condensing means for condensing the beam is provided, and the spectroscopic means is arranged in the optical path from the light condensing means to the deflecting means.

A deflecting means for deflecting the optical path of the laser beam in the main scanning direction by reflecting the laser beam, and a condensing means for condensing the laser beam in the sub-scanning direction on a reflecting surface of the deflecting means are provided. The light splitting means is provided on the optical path from the collimating means to the light collecting means, and splits the combined laser beam into two non-parallel laser beams.

[0011] Further, the invention is characterized in that a lens having a positive refractive power in the sub-scanning direction is provided as the light condensing means. Further, the light condensing means includes a first lens having a positive refractive power in the sub-scanning direction and a second lens having a negative refractive power in the sub-scanning direction. The light is refracted by the second lens after being refracted by the first lens, so that the light is condensed on the reflection surface of the deflecting means, the distance between the spectroscopic means and the first lens, and The distance between the first lens and the second lens is variable.

Further, the spectroscopic means is a Savart plate. Further, the spectroscopic means is a polarizing prism.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the laser scanning device according to the present invention will be described below with reference to the drawings. (Embodiment) As shown in FIG. 1, a laser scanning device 1 includes an optical fiber 12 in an optical path of a laser beam from two semiconductor laser devices 13 and 14 to a photosensitive drum 2.
15, optical coupler 11, optical element 12, 15, 11, 16, 10, such as cylindrical lens 8, rotary polygon mirror 6, etc.
9, 8, 7, 6, 5, and 4.

The semiconductor laser devices 13 and 14 are individually modulated according to an image formed on a scanning line, and emit laser beams of linearly polarized light, respectively. The optical coupler 11 is a known polarization preserving coupler that can combine two beams while maintaining the polarization state of incident light.
The optical coupler 11 includes optical fibers 12 and 15 for receiving a laser beam and an optical fiber 16 for emitting a combined laser beam.

The optical fibers 12, 15 and 16 are known polarization preserving fibers that propagate while preserving the polarization state of the incident light, and the incident side ends of the optical fibers 12 and 15 are connected to the semiconductor laser devices 13 and 14, respectively. And optically coupled. The optical fiber 16 emits the laser beam such that the principal ray of the combined laser beam coincides with the optical axis of the collimator lens 9. A light emitting point 10 at which the optical fiber 16 emits a laser beam is disposed at a focal position of the collimator lens 9.

A collimator lens 9, which is one of the subsequent optical components, collimates the two combined laser beams, and a cylindrical lens 8 focuses the laser beam on the mirror surface of the rotary polygon mirror 6. A Savart plate 7 is provided in an optical path between the cylindrical lens 8 and the rotary polygon mirror 6. The Savart plate 7 has a configuration in which two birefringent materials are superimposed, and splits an incident laser beam only in the sub-scanning direction by birefringence as shown in FIG. That is, the Savart plate is arranged so that the main rays of the two split laser beams are scanned on the surface to be scanned with the phases thereof being aligned in the main scanning direction.

The rotary polygon mirror 6 is driven to rotate at high speed by a pulse motor (not shown), and separates the two split laser beams in the main scanning direction at a speed proportional to the product of the rotation speed and the number of mirror surfaces. Scan to. The scanned laser beam is irradiated on the photosensitive drum 2 through the toroidal lens 5 and the scanning lens 4. In addition, the toroidal lens 5
Is for preventing the rotary polygon mirror 6 from tilting down together with the cylindrical lens 8, and the scanning lens 4 is for scanning the laser beam on the photosensitive drum at a constant speed. Further, an SOS sensor 3 is provided between the scanning lens 4 and the photosensitive drum 2 and at a start end side of the main scanning via an SOS mirror 17, and detects a scanning start timing.

FIG. 3 shows the structure of the semiconductor laser devices 13 and 14. The semiconductor laser devices 13 and 14 include a cylindrical housing and a laser diode 2 provided in the housing.
8. It is composed of a light guide lens 29 and a polarizing filter 31,
Optical fibers 12 and 15 are connected. The housing has a cylindrical body 20 and a cylindrical optical connector 26 connected via a cylindrical coupler 23 so as to be slidable only, as understood from the drawing. The coupler 23, the cylindrical body 20, and the optical connector 26 are provided with annular convex portions 21, 25 formed on the outer peripheral surface of the coupler 23, and the annular concave portion 2 formed on the inner peripheral surface of the cylindrical body 20, the optical connector 26.
2 and 24 are fitted, and the cylindrical body 20 and the optical connector 26 can be relatively rotated in the direction of arrow 27 in the figure.

The cylindrical body 20 has a laser diode 28 attached to the inner surface of the end, and a flange 30 provided inside.
A light guide lens 29 is attached to the light source. The coupler 23 has a polarizing filter 31 attached to the inner peripheral surface, and the optical connector 26 is a connector (jack) for connecting the optical fibers 12 and 15. In order to prevent the optical fibers 12 and 15 from rotating with respect to the optical connector 26, the shape of the connector is an SC type which is a known shape, and the polarization directions of the laser beams emitted from the optical fibers 12 and 15 are the same. I keep it. When the interval between the laser beams 18 and 19 separated as described above is specifically obtained, for example, when the two birefringent materials constituting the Savart plate are quartz and each has a thickness of 2 mm, the light is separated. The interval between the chief rays of the laser beam is about 20 μm. Since the split laser beam translates, it keeps substantially the same interval in the vicinity of the rotary polygon mirror 6. If the magnification of the optical system composed of the toroidal lens 5 and the scanning lens 4 is set to twice, the interval in the sub-scanning direction on the photoreceptor will be about 40 μm. Scanning line density is 600d
In the case of pi, since the interval between the scanning lines is about 40 μm, two adjacent scanning lines can be scanned simultaneously.

As described above, according to the laser scanning apparatus of the present embodiment, the two laser beams are combined by the optical coupler into one laser beam, so that the principal ray of the laser beam is transmitted to the collimator lens. Since it can be made coincident with the optical axis, aberration can be suppressed and a latent image can be correctly formed on the surface to be scanned. Further, since the laser beam is separated using the Savart plate, the interval between the separated laser beams can be reduced, and the aberration can be suppressed even after the separation.

Further, since the Savart plate is arranged so that the main rays of the split laser beam are translated in the same phase in the main scanning direction, the focusing position of the laser beam on the surface to be scanned is determined by the sub-scanning. In the main scanning direction, only the directions can be separated from each other. Therefore, the timing of starting the scanning of the laser beam becomes the same, and the timing of starting the scanning of the laser beam can be controlled in the same manner as in the case of the single beam, so that the control of the laser beam is easy.

In the image forming apparatus described in the above publication, since the semiconductor laser array is used, if even one light emitting point fails, the entire semiconductor laser array must be replaced. In the scanning device, an individual semiconductor laser device is provided for each laser beam, so that only a failed semiconductor laser device can be replaced, which is economical.

In this embodiment, since the laser beam emitted from the laser diode and the combined laser beam are guided in a desired direction by the optical fiber, the optical fiber is bent to reduce the size of the apparatus. can do. Furthermore, since a laser beam is emitted from the same light emitting point using an optical fiber, only the position of the light emitting point needs to be controlled when the chief ray of the laser beam is aligned with the optical axis of the collimator lens. Easy to match.

In general, a laser beam spreads at a large angle from a light-emitting point. However, in the image forming apparatus disclosed in the above-mentioned publication, since the principal ray of the laser beam is separated from the optical axis of the collimator lens, the effective beam of the laser beam is increased. There is a problem that a part of the bundle protrudes outside the aperture of the collimator lens, and the amount of light irradiated on the surface to be scanned decreases. However, according to the laser scanning device of the present embodiment, the principal ray of the laser beam is made coincident with the optical axis of the collimator lens to minimize the projection of the effective ray bundle outside the aperture of the collimator lens. The loss of the amount of light irradiated on the scanning surface can be minimized. (Modifications) The present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and the following modifications can be made. .

In the above embodiment, the case where the Savart plate is used as the spectral means has been described. However, similar effects can be obtained by using a polarizer other than the Savart plate instead of the Savart plate. As a polarizer, for example, a variable Savart plate, a Wollaston prism (Wollaston prism)
prism or Rochon prism
prism), but the present invention can be carried out using a polarizing prism or a polarizing plate other than these.

The present invention can also be implemented in a polarizer that disperses incident light into non-parallel outgoing light in accordance with the direction of deflection. FIG. 4 is an optical path diagram showing an optical path until the laser beam emitted from the light emitting point 10 is condensed on the mirror surface of the rotary polygon mirror 6 when the polarizer is used. In FIG. 4, a laser beam emitted from a light emitting point 10 is a collimator lens 9.
After the light is collimated, the light enters the polarizer 32.
The laser beam incident on the polarizer 32 is split in the sub-scanning direction according to the polarization direction, and is split into parallel laser beams 33 and 3.
The light is incident on a cylindrical lens 8 and is condensed on a mirror surface 6 of a rotary polygon mirror.

The polarizer that splits the incident light into outgoing light that is not parallel to each other according to the polarization direction includes the Wollaston prism and the Rochon prism described above. However, the present invention can be implemented by using a polarizer that splits incident light into outgoing light that is not parallel to each other according to the polarization direction. As another modification, a variable Savart plate can be used instead of the Savart plate of the above embodiment.

FIG. 5 is an optical path diagram showing the optical path of the principal ray until the laser beam emitted from the light emitting point 10 reaches the mirror surface of the rotary polygon mirror 6 when a variable Savart plate is used as a polarizer. . In FIG. 5, a laser beam emitted from a light emitting point 10 is collimated by a collimator lens 9 and then enters a variable Savart plate 35 via a cylindrical lens 8. The laser beam incident on the variable Savart plate 35 is split in the sub-scanning direction in accordance with the polarization direction, converted into parallel laser beams 38 and 39, and collected on the mirror surface 6 of the rotating polygon mirror.

In FIG. 5, the variable Savart plate 35
Is composed of two Savart plates 36, 37, displaces the Savart plate 36 in the direction of arrow A, and
7 is displaced in the direction of arrow C, the laser beam 38,
39 can be increased in the sub-scanning direction. Conversely, when the Savart plate 36 is displaced in the direction of arrow B and the Savart plate 37 is displaced in the direction of arrow D, the distance between the laser beams 38 and 39 can be reduced.

With such a configuration, the interval between scanning lines on the surface to be scanned can be adjusted, so that the scanning line density can be adjusted. Therefore, the image quality can be increased by increasing the scanning line density as required by the user, or the image forming speed can be increased by decreasing the scanning line density.
Even in the case of using a polarizer that disperses the incident light into non-parallel output light, if the following configuration is adopted,
Scan line spacing can be adjusted.

FIG. 6 shows an optical path until the laser beam emitted from the light emitting point 10 is converged on the mirror surface of the rotary polygon mirror 6 when the polarizer is used. In particular, the interval between scanning lines is adjusted. FIG. 4 is an optical path diagram showing a case where the setting is enabled. In FIG. 6, a laser beam emitted from a light emitting point 10 and collimated by a collimator lens is split into two laser beams 41 and 42 by a polarizer 32, and then is split into a cylindrical lens 8 having a positive refractive power and a negative lens. Is condensed on the mirror surface of the rotary polygon mirror 6 by the cylindrical lens 40 having a refractive power of

In this configuration, when the distance between the polarizer 32 and the cylindrical lens 8 is increased, the laser beam 4
When the distance between the polarizer 32 and the cylindrical lens 8 is reduced, the laser beam 41,
42 can be reduced. As described above, when the cylindrical lens 8 is operated, the distance between the cylindrical lens 8 and the cylindrical lens 40 is adjusted to adjust the laser beams 41 and 42 so that the rotary polygon mirror 6 is always used.
Light can be collected on the mirror surface of. More specifically, when increasing the interval between the laser beams 41 and 42, the cylindrical lens 40 is moved away from the cylindrical lens 8, and when decreasing the interval between the laser beams 41 and 42, the cylindrical lens 40 is adjusted. By approaching the cylindrical lens 8, the laser beams 41 and 42 can be always focused on the mirror surface of the rotary polygon mirror 6.

Further, in the above embodiment, the laser beam is synthesized by using the polarization preserving coupler.
As shown below, the images may be synthesized using a half mirror. FIG. 7 is a configuration diagram of a semiconductor laser device using a half mirror. In FIG. 7, a semiconductor laser device 43 includes laser diodes 44 and 51, light guiding lenses 45 and 50 for guiding laser beams from the laser diodes to an optical fiber 48, polarizing filters 46 and 49 for converting the laser beam into linearly polarized light, and a half mirror. 47 are provided.
The optical fiber 48 is a polarization maintaining fiber.

In FIG. 7, a laser beam emitted from a laser diode 44 is focused by a light guide lens 45 so as to be incident on an optical fiber 48. Light guide lens 4
The laser beam emitted from 5 is converted into linearly polarized light by the polarization filter 46, passes through the half mirror 47, and enters the optical fiber 48. On the other hand, the laser beam emitted from the laser diode 51 similarly passes through the light guide lens 50 and the polarizing filter 49, is reflected by the half mirror, and enters the optical fiber 48. The other end of the optical fiber 48 is arranged such that the principal ray of the laser beam emitted therefrom coincides with the optical axis of the collimator lens 9 and the emission point of the laser beam is located at the focal point of the collimator lens 9.

Although not shown, the laser diode 4
The polarization filters 4 and 51 and the polarization filters 46 and 49 are held rotatably about the optical axes of the light guide lenses 45 and 50, respectively, and by rotating these, the polarization direction of the laser beam is adjusted. Although it is desirable that the semiconductor laser devices 13 and 14 of the above-described embodiments use laser diodes having the same characteristics, laser diodes having different characteristics can form a latent image on the surface to be scanned of the photosensitive member. Can be used. The laser diode 44,
The same applies to 51.

[0036]

As described above, according to the present invention,
Since the two laser beams are combined to form a laser beam traveling in the same direction, the principal ray of the combined laser beam can be made coincident with the optical axis of the collimator lens. Therefore, the influence of aberration and the loss of light amount can be suppressed to the minimum, so that the formation of a normal latent image can be prevented from being hindered.

In the same manner, conventionally, the position was adjusted for each laser diode in order to make the laser beam appropriately enter the collimator lens. However, according to the present invention, only the position of the light emitting point is adjusted. If this is the case, the combined laser beam can be appropriately incident on the collimator lens. In addition, since the combined laser beam is split using the birefringence of the polarizer, the interval between the split laser beams can be reduced. As a result, two adjacent scanning lines can be scanned simultaneously.

Further, while the distance between the laser beams in the sub-scanning direction has been adjusted by rotating the semiconductor laser array about the optical axis of the collimator lens, according to the present invention, the polarizer is used. Since the interval between the laser beams can be changed by operation and adjustment, the adjustment sensitivity is small and fine adjustment can be easily performed. For the same reason, even if the incident position of the combined laser beam on the collimator lens fluctuates, the interval between the separated laser beams can be kept constant.

Further, since the laser beam is split only in the sub-scanning direction and the phase is matched in the main scanning direction, the timing for starting the scanning of the laser beam can be matched. Therefore, only one laser beam is SOS
What is necessary is just to detect with a sensor, and control of a laser beam is easy. Further, since the laser beam is guided to the collimator lens using the polarization maintaining fiber, the polarization maintaining fiber can be bent to reduce the size of the apparatus.

Further, according to the present invention, the interval between the split laser beams is adjusted by using a variable Savart plate or a cylindrical lens, so that the scanning line density can be adjusted. Further, in the laser scanning device of the present invention, a laser diode is provided for each semiconductor laser device, and when a laser diode fails, only the failed laser diode or only the failed semiconductor laser device can be replaced, so that economy is reduced. It is a target.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a laser scanning device according to an embodiment of the present invention.

FIG. 2 is an optical path diagram of a laser beam in the laser scanning device.

FIG. 3 is a sectional perspective view of a semiconductor laser device in the laser scanning device.

FIG. 4 is an optical path diagram of a laser beam in a laser device using a polarizing prism according to a modification of the present invention.

FIG. 5 is an optical path diagram of a laser beam in a laser device according to a modification of the present invention using a variable Savart plate.

FIG. 6 is an optical path diagram of a laser beam in a laser device according to a modification of the present invention using two cylindrical lenses.

FIG. 7 is a configuration diagram illustrating a configuration of an optical coupler using a half mirror.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser scanning device 2 Photoconductor 3 SOS sensor 4 Scanning lens 5 Toroidal lens 6 Rotating polygon mirror 7 Savart plate 8 Cylindrical lens having positive refractive power 9 Collimator lens 10 Light emitting point 11 Optical coupler 12, 15, 16, 48 Optical fiber 13, 14 Semiconductor laser device 17 SOS mirror 28, 44, 51 Laser diode 29, 45, 50 Light guide lens 31, 46, 49 Polarizing filter 32 Polarizer 35 Variable Savart plate 40 Cylindrical lens 47 having negative refractive power 47 Half mirror

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 AA43 AA48 AA49 BA25 BA58 BA69 BA84 BA86 DA03 2H045 AA01 BA22 BA33 CB65 DA02 2H049 BA05 BA42 BB03 BC21 5C072 AA03 BA04 DA03 DA04 DA07 HA02 HA06 HA10 HA13 HB06 HB08 HB08

Claims (10)

[Claims] 1. A laser scanning apparatus for scanning a surface to be scanned with two independently modulated laser beams at predetermined intervals in a sub-scanning direction, wherein two laser beams having polarization directions orthogonal to each other are used. Combining means for combining into a laser beam traveling in the same direction; collimating means for collimating the combined laser beam; and combining the combined laser beam with two in accordance with the polarization direction.
A laser scanning device, comprising: a spectroscopic unit that splits the light into a laser beam. 2. The laser scanning device according to claim 1, wherein the combined laser beams are emitted only from the same object point and enter the collimating unit. 3. The laser scanning device according to claim 1, wherein the collimator is a collimator lens, and the principal ray of the combined laser beam is made to coincide with an optical axis of the collimator lens. . 4. The combined laser beam according to claim 1, wherein the combined laser beam is guided from the combining unit to the collimating unit using an optical fiber that preserves a polarization state of incident light. A laser scanning device according to any one of the above. 5. By reflecting the laser beam,
Deflecting means for deflecting the optical path of the laser beam in the main scanning direction; and condensing means for condensing the laser beam in a sub-scanning direction on a reflection surface of the deflecting means; The laser scanning device according to any one of claims 1 to 4, wherein the laser scanning device is provided in the middle of an optical path from the light source to the deflection means. 6. By reflecting the laser beam,
Deflecting means for deflecting the optical path of the laser beam in the main scanning direction; and condensing means for condensing the laser beam in the sub-scanning direction on a reflecting surface of the deflecting means. The laser according to any one of claims 1 to 4, wherein the laser beam is disposed in the optical path to the light condensing means and splits the combined laser beam into two non-parallel laser beams. Scanning device. 7. The laser scanning device according to claim 5, wherein a lens having a positive refractive power in a sub-scanning direction is provided as the light condensing unit. 8. The light condensing means includes a first lens having a positive refractive power in a sub-scanning direction and a second lens having a negative refractive power in a sub-scanning direction, and the light is separated by the spectral means. The laser beam is applied to the first
The light is refracted by the second lens after being refracted by the second lens, and is condensed on the reflection surface of the deflecting means. The distance between the spectroscopic means and the first lens, and the first The laser scanning device according to claim 7, wherein a distance between a lens and the second lens is variable. 9. The laser scanning device according to claim 4, wherein said spectral means is a Savart plate. 10. The laser scanning device according to claim 5, wherein said spectral unit is a polarizing prism.