JP2743858B2 - Optical printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical printer, and more particularly to an optical printer such as a laser printer or a laser plotter capable of high-speed printing.

[0002]

2. Description of the Related Art As an example of an optical printer, an optical printer which performs printing by scanning a light beam on a photoreceptor with a polygon mirror has been widely known (for example, Japanese Patent Application Laid-Open No. 61-15119). JP-A-61-5631
No. 6).

FIG. 3 is a schematic view of an optical system of an optical printer using a conventional polygon mirror. FIG. 3A is a schematic side view, and FIG. 3B is a schematic top view. In order to simplify the drawing and show the basic principle of the optical system, the polygon mirror surface is actually a reflecting surface, but is shown as a transmitting surface in the drawing.

As shown in FIGS. 3 (a) and 3 (b), a conventional optical printer comprises a semiconductor laser 1, a collimator lens 2, a first cylindrical lens 4, a polygon mirror having a surface 6, an fθ lens 7 and a It comprises two cylindrical lenses 8.

The operation of this conventional optical printer will be described. The light emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2 and is scanned by a first cylindrical lens 4 in a sub-scanning direction (perpendicular to the scanning direction by a polygon mirror). Only on the polygon mirror surface 6. This is to correct the "vibration" of the light beam in the sub-scanning direction due to the inclination of each surface of the polygon mirror.

The light beam reflected by the polygon mirror surface 6 is focused on a recording surface 9 by an fθ lens 7 and a second cylindrical lens 8. By rotating the polygon mirror surface 6, the light beam is deflected, so that main scanning is performed in the line direction, and sub-scanning is performed by moving the recording surface 9 in a direction orthogonal to the main scanning direction. In this manner, an electrostatic latent image corresponding to image information is formed as a set of dots on the recording surface 9 serving as a photoreceptor, and is subjected to development and transfer processes to form an image on recording paper. Is recorded.

[0007]

In the above-mentioned conventional optical printer, the printing speed is determined by the rotation speed of the polygon mirror. This rotational speed has a limit due to the performance of the motor and mechanical destruction of the rotating optical system. In this optical printer, the pixel density may be switched. Usually, the degree of the pixel density is dpi (dot per inch: the number of dots per inch) or lpi
(Line per inch: the number of main scanning lines per inch in the sub-scanning direction).

Here, it is assumed that, in a certain optical printer, printing and image formation in the normal mode are performed by dots indicated by black circles corresponding to pixel sizes as shown in FIG. At this time, when printing and image formation are performed at a pixel density of 1/2 of the normal mode, the size of the dots forming the pixels (the condensing diameter of the laser beam) is increased as shown in FIG. A method of exposing is conceivable.

On the other hand, as shown in FIG. 4C, exposure is performed twice in the main scanning direction and the sub-scanning direction while keeping the focused diameter of the laser beam in the normal mode, and one pixel is formed by four dots. With this configuration, high-definition and clear printing and image formation are possible. However, FIG. 4 (c) with one beam
Such a method lowers the printing and image forming speed at half the pixel density of the normal mode as compared with the method of FIG. 4B.

Therefore, conventionally, as a means for solving the above-mentioned decrease in printing speed, a plurality of condensed beams are formed on a recording surface.
A method of scanning a line at a time is conceivable. As a method for realizing this, a method using a multi-beam semiconductor laser having a plurality of light emitting points as a light source has been conventionally proposed (for example, Japanese Patent Application Laid-Open No. 5-167809).

However, at present, a multi-beam semiconductor laser used as a light source in this conventional optical printer is difficult to obtain, and some of the lasers which are practically used are less expensive than ordinary semiconductor lasers. There is a problem that it is quite expensive.

The present invention has been made in view of the above points,
It is an object of the present invention to provide an optical printer that can increase the printing speed at the time of high-definition printing with a low pixel density by using a normal one-beam semiconductor laser.

[0013]

In order to achieve the above-mentioned object, the present invention focuses a single laser beam modulated and output from a semiconductor laser on a photoreceptor and scans the same in a main scanning direction. In an optical printer that forms an image on a photoconductor by moving the photoconductor in a sub-scanning direction orthogonal to the scanning direction, an optical system position in which a single laser beam modulated and output from a semiconductor laser is divergent light or convergent light Further, a birefringent substance having an optical axis such that ordinary light and extraordinary light are separated in the sub-scanning direction is arranged.

[0014] In addition, the birefringent material of the present invention has means for arbitrarily inserting a single laser beam into the optical path and retracting the birefringent substance out of the optical path. And a mode in which printing is performed using a single laser beam.

[0015]

Further, since the present invention has a half-wave plate for adjusting the plane of polarization of the incident laser beam of the birefringent substance, the intensity of ordinary light and extraordinary light on the photoreceptor can be adjusted to be the same. Desirable.

[0017]

According to the present invention, a single optical beam modulated and output from a semiconductor laser is placed at an optical system position where it is divergent light or convergent light, so that the ordinary optical axis and the extraordinary light are separated in the sub-scanning direction. Since a refractive material is arranged, a single laser beam is divided into two in the sub-scanning direction: ordinary light and extraordinary light.
The laser beam can be converted into two laser beams and irradiated on the photoconductor. Therefore, 1/1 of the normal mode printing in FIG.
In the case of printing at a print density of 2, the sub-scanning speed is twice that in normal mode printing, and the printing shown in FIG.

Here, the insertion position of the birefringent substance is the position of the optical system where the light is divergent light or convergent light. This is because the light is focused on a point.

Further, when the birefringent material of the present invention is constituted by a single parallel plate of birefringent crystals, it can be constructed at a low cost, and a plurality of parallel plates of birefringent crystals or birefringent each having a tapered surface. When a crystal plate is used, the problem of the difference in light-collecting characteristics between two beam spots can be solved. Therefore, the present invention is used in an optical system in which the difference in light-collecting characteristics between two beam spots due to a difference in optical path length on the recording surface is problematic. be able to.

[0020]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an optical system according to an embodiment of the optical printer according to the present invention. 2, the same components as those in FIG. 2 are denoted by the same reference numerals. As shown in the schematic side view of FIG. 1A and the schematic top view of FIG.
It comprises a semiconductor laser 1, a collimating lens 2, a half-wave plate 3, a first cylindrical lens 4, a Savart plate 5, a polygon mirror having a surface 6, an fθ lens 7, and a second cylindrical lens 8.

The polygon mirror surface 6 is actually a reflection surface, but is shown as a transmission surface in order to simplify the drawing and show the basic principle of the optical system. In the present embodiment, the Savart plate 5 is disposed at a position between the first cylindrical lens 4 and the polygon mirror surface 6 as an optical system position at which the laser beam from the semiconductor laser 1 is convergent light. 1/1 between the collimating lens 2 and the first cylindrical lens 4
It is characterized in that the two-wavelength plate 3 is inserted.

The Savart plate 5 is a widely used optical component composed of two birefringent plates, as will be described later, and can be easily obtained like a half-wave plate. In this embodiment, the Savart plate 5 is configured to be freely inserted and retracted (removed) with respect to the optical path of the laser beam. Although not shown in FIG. 1, the insertion / retraction (removal) means can be mechanically inserted or removed by means suitable for the individual design at the time of designing the optical printer, for example, an arm or a linkage. Further, the optical axis of the Savart plate 5 is arranged so that ordinary light and extraordinary light after passing through the Savart plate 5 are separated in the sub-scanning direction.

In this embodiment, the half-wavelength plate 3 is configured to be rotated by a rotating means (not shown). When the half-wave plate 3 is rotated, the polarization direction of the laser beam incident on the Savart plate 5 is rotated. Accordingly, the distribution ratio between the ordinary light and the extraordinary light is adjusted. The intensity of the beam spot can be adjusted. In the case of this embodiment, two laser beams of simultaneous modulation are applied to the same photosensitive material, so that the two laser beams are halved so that the spot intensities are equal so that there is no difference in print density. The amount of rotation of the plate 3 is adjusted.

Next, the operation of this embodiment will be described.
The laser beam emitted from the semiconductor laser 1 with its intensity modulated according to the image information is converted into parallel light by the collimator lens 2, and then the polarization direction is rotationally adjusted by the half-wavelength plate 3, and the first The light passes through the cylindrical lens 4 and enters the Savart plate 5. Here, when the Savart plate 5 is inserted into the optical path, the output power of the semiconductor laser 1 is increased so that the intensity of the laser spot on the recording surface 9 becomes the same as that when the Savart plate 5 is removed. You.

The two laser beams, ordinary light and extraordinary light, extracted from the Savart plate 5 are adjusted to have the same intensity by adjusting the amount of rotation of the half-wave plate 3 so that the printing density difference on the recording surface 9 does not occur. In addition, the light is condensed by the first cylindrical lens 4 on the polygon mirror surface 6 or in the vicinity thereof only in the sub-scanning direction.

The two laser beams reflected by the polygon mirror surface 6 are focused on a recording surface 9 by an fθ lens 7 and a second cylindrical lens 8. By rotating the polygon mirror surface 6 as in the conventional case, the two laser beams are simultaneously deflected in the same direction, the main scanning is performed in the line direction, and the recording surface 9 is moved in the direction orthogonal to the main scanning direction. By doing so, sub-scanning is performed. In this manner, an electrostatic latent image corresponding to image information is formed as a set of dots on the recording surface 9 serving as a photoreceptor, and is subjected to development and transfer processes to form an image on recording paper. Is recorded.

According to this embodiment, the two laser beams separated in the sub-scanning direction are simultaneously focused on the recording surface 9 by using the one-beam ordinary semiconductor laser 1. The Savart is designed so that the distance between the laser beam spots on the recording surface 9 is the two pixel pitches adjacent to each other in the sub-scanning direction in the normal mode, and is appropriately approached or separated in consideration of the sensitivity of the photosensitive material. By variably setting the thickness of the plate 5 or the material of the photosensitive material, FIG.
High-definition printing with a printing density of 1/2 shown in FIG. 4C can be performed at twice the sub-scanning speed as when printing in the normal mode shown in FIG. That is, according to the present embodiment, it is possible to increase the printing speed of the low-print-density portion as compared with a normal one-beam optical printer while maintaining high definition.

When the Savart plate 5 is retracted (removed) out of the optical path of the laser beam emitted from the semiconductor laser 1, it can be operated as an optical printer for performing printing with one beam as in the related art. it can.

In the present embodiment, the Savart plate 5 is used as a birefringent substance for converting one beam into two beams. However, the present invention is not limited to this, and another birefringent substance may be used. This will be described with reference to FIG. 2. FIG. 2 (a) shows a single birefringent plate 11, and the separation interval between two laser beams of ordinary light and extraordinary light obtained through the birefringent plate 11 is determined. Is determined by the plate thickness.

When one birefringent plate 11 is used, a difference in optical path length between two laser beams occurs. However, a difference in light-collecting characteristics of two beam spots on the recording surface due to the difference in optical path length causes a problem. When used in an optical system that does not need to be used, there is a feature that it can be configured at the lowest cost.

Further, the Savart plate 5 is a 2
Since the Savart plate 5 can be used to solve the above-mentioned problem of the difference in the light-collecting characteristics of the two beam spots, the two beam spots on the recording surface due to the optical path length difference are formed. Can be used for an optical system in which the difference in light-collecting characteristics is a problem.

Further, as shown in FIG. 2 (c), birefringent members 14 and 15 in which two birefringent plates each having a tapered surface are adhered to each other are arranged opposite to each other, and are movable in the direction A in the figure. The variable Savart plate described above can be used instead of the Savart plate 5, and in this case, the separation interval between the two laser beams can be made variable.

Further, in the above embodiment, the half-wave plate 3
Is used to adjust the intensity of the two laser beam spots, but this is not always necessary. When the semiconductor laser 1 is rotated around its optical axis as a rotation axis, the same Adjustments are possible.

[0034]

As described above, according to the present invention,
By placing a birefringent substance with an optical axis that separates ordinary light and extraordinary light in the sub-scanning direction, at the optical system position where a single laser beam modulated and output from a semiconductor laser is divergent or convergent light. Because a single laser beam is converted into two laser beams, an ordinary light and an extraordinary light, separated in the sub-scanning direction and irradiated onto the photoconductor, a normal semiconductor laser can be used without using a multi-beam semiconductor laser. The printing speed of the low-pixel-density portion can be made higher than before, and high-definition printing can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic view of an optical system according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing each example of a main part of the present invention.

FIG. 3 is a schematic diagram of an optical system as an example of a conventional optical printer.

FIG. 4 is an explanatory diagram of a pixel configuration on a recording surface.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 collimating lens 3 1/2 wavelength plate 4 first cylindrical lens 5 Savart plate 6 polygon mirror surface 7 fθ lens 8 second cylindrical lens 9 recording surface

Claims (2)

(57) [Claims] 1. A laser beam modulated and output from a semiconductor laser is focused on a photosensitive member and is scanned in a main scanning direction, and the photosensitive member is moved in a sub-scanning direction orthogonal to the main scanning direction. An optical printer that forms an image on the photoconductor, wherein the single laser beam modulated and output from the semiconductor laser is located at an optical system position where the single laser beam is divergent light or convergent light, and the normal light in the sub-scanning direction is abnormal. A birefringent material having an optical axis separated from light is arranged , and the birefringent material is
The insertion of a single laser beam into the optical path and the
An optical printer comprising means for arbitrarily evacuating . 2. A single laser beam modulated and output from a semiconductor laser is focused on a photosensitive member, scans in a main scanning direction, and moves the photosensitive member in a sub-scanning direction orthogonal to the main scanning direction. An optical printer that forms an image on the photoconductor, wherein the single laser beam modulated and output from the semiconductor laser is located at an optical system position where the single laser beam is divergent light or convergent light, and the normal light in the sub-scanning direction is abnormal. A birefringent material having an optical axis that separates light from light is arranged , and the birefringent material is incident on the birefringent material.
By rotating and adjusting the polarization direction of the laser beam,
1/2 wavelength plate for adjusting the distribution ratio of ordinary light and extraordinary light
Is disposed in the optical path on the incident side of the birefringent substance.
Optical printer to butterflies.