JP3388333B2 - Light beam scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device, and more particularly, to a light beam scanning device for scanning and irradiating light from a light source onto an irradiation object through a cylindrical lens and an optical deflector.

[0002]

2. Description of the Prior Art Data sent from a host device is directly OP
C (Organic Photoconductio
A light beam scanning device is used to create a printing plate by laser drawing on (n: organic photoconductor). In this case, an electrophotographic method is adopted as the recording method, and charging and drawing processing are performed in the process, and a plane scanning optical system is provided as the recording optical system.

An example of such a plane scanning optical system is shown in FIG. In FIG. 5, the light from the light source 1 by the semiconductor laser is a collimator lens 2 and a cylindrical lens 3.
It is irradiated to the polygon mirror 4 which is an optical deflector via
Horizontal deflection is performed. This deflected light is reflected by the fθ lens 5
The light is emitted to the cylinder mirror 6 via the and is vertically deflected. The light that has been two-dimensionally scanned in this way is irradiated onto the photosensitive material 13.

FIG. 6 shows a light beam scanning device disclosed in Japanese Patent Laid-Open No. 3-2817, and the same parts as those in FIG. 5 are designated by the same reference numerals. Referring to FIG. 6, the light from the light source 1 is generated by a rotatable collimated beam diameter diaphragm plate 14,
The polygon mirror 4 is irradiated with light through the ND filter 15 for attenuating light and the cylindrical lens 3, and is horizontally deflected. The deflected light is transmitted to the plurality of fθ lenses 5
The light is applied to the photosensitive material 13 via.

[0005]

As a linear density of an image used in a newspaper company or the like, a low density of 454 LPI (Lin) is used.
e per Inch) and high density 909 LPI are mixed.

For this reason, in the example of FIG. 5, when the density is low, the scanning is performed twice so that the beam diameter at the time of high density has one line data width (see FIG. 4B), and the low density and high density are obtained. It is necessary to guarantee the image quality so that the resolution is the same as the density. That is, when the density is low, scanning is performed twice, so that the execution speed is halved and the recording time becomes long.

In the example of FIG. 6, when the recording density is switched, the diameter of the light spot on the photosensitive material 13 in the horizontal scanning direction (main scanning direction) is changed by the rotation speed of the polygon mirror 4 and the light emission timing of the light source 1. The diameter in the vertical scanning direction (sub-scanning direction) is changed according to the tilt amount of the diaphragm plate 14.

That is, at the time of high density recording, the diaphragm plate 14
The amount of light blocking is reduced by reducing the tilt amount of
Light is attenuated by the filter 15, and when recording at low density,
The amount of light blocking is increased by increasing the tilt amount of the diaphragm plate 14, and the ND filter 15 is removed from the optical path to allow light to pass.

In the case of such a system, when a semiconductor laser is used, the beam diameters in the sub-scanning direction are not the same at a fixed diaphragm due to variations in the divergence angle of the element, and the width of the diaphragm plate must be adjusted. is necessary. In addition, the ND filter 15 needs to be appropriate because it does not have a constant value even when the amount of light varies due to the diaphragm.

Further, using the diaphragm plate 14 means that
Since the beam diameters at the high-density and low-density image forming positions are changed, there is a drawback that the resolution of the low density is reduced.

An object of the present invention is to provide a light beam scanning device capable of eliminating a decrease in scanning speed and resolution.

[0012]

According to the present invention, there is provided a light beam scanning device for scanning and irradiating an object to be irradiated with light from a light source through a cylindrical lens and an optical deflector, the light source and the cylindrical lens. Is provided between and
An optical beam scanning device comprising: a movable filter means capable of switching between two plates and an optical attenuator by an external drive; and a birefringent plate provided between the cylindrical lens and the optical deflector. can get.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The operation of the present invention will be described. The semiconductor laser is a linearly polarized light, and its attention is paid to the fact that the phases are aligned. The beam is separated into two by a λ / 2 plate and a birefringent plate by using an optical phenomenon, and a low density double beam is used. Scanning is possible with a single scan. ND during high-density scanning
A filter is inserted in the optical path instead of the λ / 2 plate and the polarization direction is restored to one beam.

In this case, the ND filter has a transmittance of 50.
%, It is possible to obtain an image energy on the surface of the photosensitive material which is equivalent to that when the beam is split into two beams, and the transmittance is 5
It is sufficient to use one type of 0% ND filter.

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

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and the same portions as those in FIG. 5 are designated by the same reference numerals. In FIG. 1, only parts different from those in FIG. 5 will be described.
A movable filter unit 7 is provided between the collimator lens 2 and the cylindrical lens 3, and a birefringent plate 8 is provided between the cylindrical lens 3 and the polygon mirror 4. The other structure is the same as that of FIG. 5, and the description thereof is omitted.

The movable filter 7 is movable in the direction of arrow A in a plane orthogonal to the optical axis, as shown in FIG.
As shown in (B), a λ / 2 plate 9 and an ND filter (transmittance 50%) 10 are attached.

The light emitted from the semiconductor laser 1 becomes a parallel light flux by the collimator lens 2. The polarization direction of the laser light is fixed as a light source, and for convenience sake, the vibration wave in the direction perpendicular to the surface of the optical base 100 is treated as a P wave and the vibration wave in the horizontal direction is treated as an S wave.

The light P wave emitted from the collimator lens 2 passes through the λ / 2 plate 9 selected by the movable filter portion 7 (see FIG. 2).
(State of (A)). The λ / 2 plate 9 has a function of changing the polarization direction of λ / 2, and therefore, the λ / 2 plate 9 is polarized by 45 ° with respect to the optical base 100, and thus the λ / 2 plate 9 is 22.5 with respect to the P wave.
It is arranged to tilt.

The light that has passed through the λ / 2 plate 9 passes through the cylindrical lens 3 and then enters the birefringent plate 8 such as quartz or calcite having a large birefringence effect and is transmitted therethrough. In this process, the light polarized at 45 ° is split into the extraordinary ray 11 and the ordinary ray 12 due to the birefringence phenomenon. Therefore, it is outputted as two separated beams of P wave and S wave which are parallel to each other.

At this time, the birefringent plate 8 is arranged so that two waves are separated in the sub-scanning direction (direction orthogonal to the main scanning direction by the polygon mirror 4).

The two separated beams are deflected by the polygon mirror 4 and are focused on the image forming surface which is the photosensitive surface on the photosensitive material 13 via the fθ lens 5 and the cylindrical mirror 6.

Here, the separation distance d of the two separated lights in the birefringent plate 8 is as shown in FIG. 3, d = [(1 / n ² −1 / ne ² ) / {2 (sin ² φ / ne ² + cos ² φ / n 0 ² )}] (sin ² φ) t ... (1).

Here, n0 is the refractive index for the ordinary ray 12, ne is the refractive index for the extraordinary ray 11, t is the thickness of the birefringent plate 8, and φ is the angle of the optical axis of the birefringent plate 8.

Further, the above d is also determined by the magnification of the fθ lens 5 and the cylindrical mirror 6. As a result, the separation distance d of the two separated beams 17 (see FIG. 1) on the image plane is determined by setting the plate thickness t of the birefringent slope 8 by the equation (1).

Since the two separated lights differ only in the polarization direction, they have the same beam shape and energy density on the image plane, and become a twin beam 17. Therefore, low density 4
When scanning 54 LPI, λ / 2 of the movable filter unit 7
By arranging the plate 9 and the birefringent plate 8 on the optical axis, two beams are formed, and when scanning the high-density 909 LPI, the movable filter unit 7 is moved by a drive system (not shown) to obtain λ / 2.
By switching from the plate 9 to the ND filter 10, the emitted P wave passes through the birefringent plate 8 as an ordinary ray 12 as it is, so that the beam is not separated and enters the polygon mirror 4, and the fθ lens 5 and the cylindrical mirror 6 The light is focused on the image forming position via.

Here, since the ND filter 10 completely separates the light amount into two, a filter that transmits 50% is set,
The power when splitting into two beams and the power when not splitting are the same.

FIG. 4A shows two-beam scanning by one-time scanning according to the present embodiment, and FIG.
1-beam scanning by one time scanning is shown, both are 454L
This is a case of obtaining a PI width system.

[0029]

By adopting such a configuration, it becomes possible to scan at a speed twice that of the conventional one without changing the image quality, and the λ / 2 plate 9 and the ND filter 10 of the movable filter section 7 are selected. By doing so, switching between 2 beams and 1 beam becomes possible, and high-density 909 LPI scanning becomes possible as in the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2A is a diagram showing a state of a light beam when transmitted through a λ / 2 plate, and FIG. 2B is a diagram showing a state of a light beam when transmitted through an ND filter.

3 is a ray diagram of light passing through a birefringent plate.

FIG. 4A shows a scanning beam of an embodiment of the present invention,
(B) is a diagram showing a conventional scanning beam.

FIG. 5 is a diagram showing an example of a conventional light beam scanning device.

FIG. 6 is a diagram showing another example of a conventional light beam scanning device.

[Explanation of symbols]

1 Light source (semiconductor laser) 2 Collimator lens 3 Cylindrical lens 4 polygon mirror 5 fθ lens 6 Cylindrical mirror 7 Movable filter section 8 Birefringent plate 9 λ / 2 plate 10 ND filter 11 extraordinary rays 12 ordinary rays 13 Sensitive materials 100 optical base

Claims (3)

(57) [Claims] 1. A light beam scanning device for scanning and irradiating light from a light source onto an object to be irradiated through a cylindrical lens and an optical deflector, the λ / 2 plate being provided between the light source and the cylindrical lens. And a light attenuator that can be switched by an external drive, and a birefringence plate provided between the cylindrical lens and the light deflector. 2. A low density scan is performed by switching to select a λ / 2 plate of the movable filter means, and a high density scan is performed by switching to select an optical attenuator of the movable filter means. The light beam scanning device according to claim 1, wherein 3. The light beam scanning device according to claim 2, wherein the optical attenuator has an attenuation amount of 50%.