JP2002059588A - Image forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method and an image forming device that is miniaturized by reducing the number of parts, prevents an occurrence of image irregularity by matching scanning positions by using one polygon mirror and can increase printing speed. SOLUTION: The image forming device is structured so as to form simultaneously a latent image by exposing laser light to a plurality of charged photosensitive bodies 13, 14, 15 and 16 and print by causing electrostatically a color toner to stick or transfer and is comprised of a selective reflection means 4 made up of a laser light source 1, a polygon mirror 2, an Fθ lens 3 and a mirror and liquid crystal shutters 9, 10, 11 and 12 for exposure to light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus, and more particularly, to a method in which a charged photosensitive member is exposed to a laser beam to form a latent image, and a color toner is electrostatically attached or transferred. And an image forming apparatus for performing printing.

[0002]

2. Description of the Related Art Conventionally, as a means for forming a latent image on a photoreceptor, a fluorescent lamp is used as an exposure light source, and an image forming apparatus which controls light exposed by a liquid crystal shutter (abbreviated as exposure light as appropriate). Has been used.

This image forming apparatus, as shown in FIG.
An exposure unit 100 includes a fluorescent lamp 101 serving as an exposure light source, a liquid crystal shutter array 102 that blocks or transmits exposure light in response to an external signal, and a light source that focuses light passing through the liquid crystal shutter array 102 on a photoconductor. The configuration includes a selfoc lens 103.

The image forming apparatus forms an open / close arrangement line by line on the liquid crystal shutter array 102 in response to an external signal, and exposes the liquid crystal shutter array 102 with light emitted from the fluorescent lamp 101. At this time, the light passing through the liquid crystal shutter array 102 is exposed. Is focused on the photoreceptor by the selfoc lens 103 to form a fine latent image.

However, since the conventional image forming apparatus uses a fluorescent lamp as an exposure light source, the fluorescent lamp has insufficient light emission intensity, instability of light emission and uneven intensity distribution, and a fluorescent substance in the fluorescent lamp. In addition, the liquid crystal shutter array needs to be equipped with a selfoc lens in order to focus exposure light on the photoreceptor, resulting in a complicated structure.

In order to solve these disadvantages, an image forming apparatus using a laser light source as an exposure light source has been developed and put into practical use. In recent years, various color image forming apparatuses using a laser light source as an exposure light source have been developed and put into practical use.

[0007] These color image forming apparatuses have in common that they use a photoreceptor and a laser light source. However, three or four photoconductors are used, and for these photoconductors,
A configuration using a laser light source, an Fθ lens and a polygon mirror, respectively, or a configuration using a laser light source, an Fθ lens and a polygon mirror for three or four exposure positions on one photoconductor, respectively There are various types of color image forming apparatuses.

However, these color image forming apparatuses have a drawback in that it is difficult to make the light emission characteristics of a plurality of laser light sources uniform. As one of the color image forming apparatuses which solves such a defect, Japanese Patent Application Laid-Open No. Hei 11-91164 discloses an image in which a single laser light source simultaneously exposes a plurality of photosensitive drums by using a half mirror and a liquid crystal shutter. A forming apparatus is disclosed.

This image forming apparatus is, as shown in FIG.
The output light from one laser light source 201 is split by using a plurality of half mirrors 203, 205, and 207, and the split light is modulated by liquid crystal shutters 211, 212, and 213. Then, the polygon mirrors 217, 218, and 219 are used. Scanning on photosensitive members (photosensitive drums 220, 221, 222).

As described above, the conventional image forming apparatus overcomes the drawback that the use of one laser light source 201 makes it difficult to make the emission characteristics of a plurality of laser light sources uniform.

[0011]

However, this color image forming apparatus requires the same number of Fθ lenses and polygon mirrors as the number of photoconductors or a plurality of exposure locations on one photoconductor. There is a problem that it is necessary to secure a space for installing parts, and the size cannot be reduced.

Further, in this color image forming apparatus, since a plurality of polygon mirrors are used, the plane directions of the plurality of polygon mirrors during operation are not aligned, so that the positions of optical scanning do not match, and image unevenness occurs. There was such a problem.

Furthermore, since the liquid crystal shutter passes through the liquid crystal shutter before entering the polygon mirror, the liquid crystal shutter needs an opening / closing switching speed equal to the switching speed of the laser light emitting element, and the printing speed cannot be increased. was there.

In order to solve the above problem, the present invention is reduced in size by reducing the number of parts, and
An object of the present invention is to provide an image forming method and an image forming apparatus which can prevent the occurrence of image unevenness and further increase the printing speed by matching the positions of optical scanning using one polygon mirror. .

In Japanese Patent No. 2738151,
For the purpose of increasing the printing speed, a printing device using a hologram element has been proposed. This technology uses a switching element that converts a laser beam from a laser light source into a spot-shaped beam, and converges the beam. Although this technique enables high-speed printing by providing a plurality of hologram elements in a one-to-one correspondence, the above-described problem cannot be solved.

[0016]

According to a first aspect of the present invention, there is provided an image forming method for simultaneously exposing a plurality of portions of a photoreceptor to form an image. A laser beam for simultaneously exposing a plurality of portions of the photoconductor is output, and the laser beam is scanned,
An element that focuses the scanned laser light on the photoreceptor, divides the scanned laser light into a plurality, blocks or transmits the divided laser light by an external signal, and modulates the intensity. Each light modulating means arranged in an array forms an array of light intensity modulation for one line in advance for one scan of the laser light, and the laser light divided into a plurality There is a method of scanning on the means.

With this arrangement, each light modulating means forms an array of light intensity modulation corresponding to a latent image for one line in advance for one scan of laser light, so In addition, compared to a light modulation unit that forms an array of light intensity modulation, the switching speed of opening and closing the light modulation unit can be reduced to 1 / (the number of dots in one line), and the image formation speed can be increased. Can be.

According to a second aspect of the present invention, there is provided an image forming method for forming an image by simultaneously exposing a plurality of portions of a photoreceptor to form latent images on the plurality of portions of the photoreceptor. A laser exposure unit for forming a laser beam, an optical scanning unit for scanning the laser beam output from the laser exposure unit, and a laser beam scanned by the optical scanning unit for focusing on the photoconductor. Lens, a light splitting means for splitting the laser light passing through the Fθ lens, and an output side of the light splitting means for blocking or transmitting each laser light split by an external signal. And a light modulation means in which elements for modulating the intensity are arranged in an array.

By doing so, the number of components of the laser light source, polygon mirror and Fθ lens can be reduced to one each, so that an installation space for the reduced components is not required.
The size can be reduced. Further, since one polygon mirror is used, the positions of the optical scanning can be matched, and the occurrence of image unevenness can be prevented.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the number of the light splitting means is equal to or greater than the number of the photoconductors or the number of a plurality of locations on one photoconductor. Are configured as selective reflection means composed of mirrors having predetermined transmittance and reflectance, respectively.

In this way, the laser beam can be split with high accuracy, and the optical path length of each split laser beam can be easily matched by adjusting the position of each mirror.

According to a fourth aspect of the present invention, in the image forming apparatus of the second or third aspect, the light modulating means is a liquid crystal shutter array.

In this way, it is possible to provide a light modulating means that can handle fine pixels.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the liquid crystal shutter array has a multilayer structure.

In this way, the control of exposure by the liquid crystal shutter array is not limited to ON / OFF control of total transmission or total blockage of laser light, and the amount of transmitted laser light can be controlled, and the latent image to be formed can be controlled. Can be provided with gradation.

According to a sixth aspect of the present invention, in the image forming apparatus of the fourth aspect, the liquid crystal shutter array is a liquid crystal element that changes the amount of transmitted laser light in response to an external signal. There is a configuration.

In this way, the transmitted light amount of the laser beam can be controlled by an external signal, so that the latent image to be formed can be provided with gradation.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the image forming method and the image forming apparatus of the present invention and their application examples will be described with reference to the drawings. First, the structure and operation of an image forming apparatus according to an embodiment of the present invention will be described.

[Embodiment of Image Forming Apparatus] FIG. 1 is a schematic view of a main part of an embodiment of an image forming apparatus according to the present invention. In FIG. 1, the image forming apparatus forms a latent image by exposing a plurality of charged photosensitive drums 13, 14, 15, 16 to a laser beam and electrostatically attaches or transfers color toner to perform printing. There is a configuration.

The image forming apparatus includes one laser light source 1 and one polygon mirror 2 for scanning the photosensitive drums 13, 14, 15, and 16 with the laser light output from the laser light source 1, A selective reflection comprising an Fθ lens 3 for passing the laser light reflected by the polygon mirror 2 and mirrors 5, 6, 7, and 8 having different reflectances and transmittances for splitting the laser light passing through the Fθ lens 3 Means 4 and the photosensitive drums 13, 14, 1 while blocking or transmitting the laser beam split by the selective reflection means 4.
Liquid crystal shutter array 9 for exposing 5 and 16
10, 11, and 12.

Here, the laser light source 1 outputs the output light a. This output light a has a plurality of photosensitive drums 1
It is equal to or greater than the sum of the laser beam intensities necessary for exposing 3, 14, 15, 16 respectively. The laser light source 1 always outputs laser light at a constant intensity except when not exposing any of the photosensitive drums 13, 14, 15, 16; that is, except when forming a white portion of an image. With this configuration, it is possible to prevent insufficient laser beam intensity and to stabilize the output intensity, so that a clear image can be formed.

Then, the output light a output from the laser light source 1 is reflected by the polygon mirror 2, enters the Fθ lens 3, and further enters the selective reflection means 4.

As shown in FIG. 2, the number of the selective reflection means 4 is equal to the number of the plurality of photosensitive drums 13, 14, 15, and 16, ie, four mirrors 5, 6, 7, and 8 are provided. The mirrors 5, 6, 7, and 8 are disposed so as to reflect the laser beam to the photosensitive drums 13, 14, 15, and 16, respectively.

Each of the mirrors 5, 6, 7, and 8 has a predetermined transmittance and reflectance. For example, the output light a incident on the selective reflection means 4 is first incident on the mirror 5. Then, 25% is reflected, 75% is transmitted, and the reflected light b (25% intensity of the output light a) and the transmitted light c (75% of the output light a) are transmitted.
% Strength). Then, the reflected light b is transmitted to the photosensitive drum 1
The transmitted light c proceeds to the liquid crystal shutter array 9 in the vicinity of 3, and the transmitted light c proceeds to the next mirror 6.

Subsequently, the transmitted light c enters the mirror 6 and
33% is reflected, 67% is transmitted, and becomes reflected light d (intensity of 25% of output light a) and transmitted light e (intensity of 50% of output light a). The transmitted light e travels to the next mirror 7.

Subsequently, the transmitted light e enters the mirror 7 and
50% is reflected, 50% is transmitted, and becomes reflected light f (intensity of 25% of output light a) and transmitted light g (intensity of 25% of output light a). Then, the reflected light f travels to the liquid crystal shutter array 11 near the photosensitive drum 15, and the transmitted light g travels to the next mirror 8.

Next, the transmitted light g enters the mirror 8.
The mirror 8 is a total reflection mirror, and is 100% of the transmitted light g.
Is reflected and becomes reflected light h. Then, the reflected light h travels to the liquid crystal shutter array 12 near the photosensitive drum 16.

The optical path length of each reflected light may be equal for each photosensitive drum. For example, the distance between the mirrors 5, 6, 7, and 8 in the selective reflection means may be shortened to reduce the optical path difference. Thus, each of the divided laser beams forms a latent image having a uniform pitch width on the photosensitive drums 13, 14, 15, and 16, so that the images are focused on the photosensitive drums 13, 14, 15, and 16. be able to. The correction of the optical path difference can be easily performed by shifting the positions of the photosensitive drums 13, 14, 15, and 16.

The liquid crystal shutter arrays 9, 10, 1
The liquid crystal shutter arrays 1 and 12 are provided near the photosensitive drums 13, 14, 15 and 16, and the reflected lights b, d, f and h divided by the selective reflection means 4 from the output light a at the same intensity. The photosensitive drums 13, 14, 15, and 16 are exposed by scanning on 9, 10, 11, and 12, respectively.

Here, the liquid crystal shutter arrays 9, 10,.
Reference numerals 11 and 12 denote an image for one line formed in advance for each scan of the laser beam, and the reflected light b, d, f, and h scan the image for one line, thereby forming a photosensitive drum. Latent images are formed on 13, 14, 15, and 16.
That is, the liquid crystal shutter arrays 9, 10, 11, 12
Controls exposure to the photosensitive drums 13, 14, 15, and 16.

Here, the liquid crystal shutter arrays 9, 10,
As shown in FIG. 3, a liquid crystal shutter array 9 (10, 11, 12) having a multi-layer structure may be used as 11, 12. In this way, the control of exposure by the liquid crystal shutter array 9 is not limited to on / off control of total transmission or total blockage of laser light, and the amount of transmitted laser light can be controlled. Can provide tonality.

Although not shown, a liquid crystal element capable of changing the amount of transmitted laser light by changing an externally applied voltage may be used for the liquid crystal portion of the liquid crystal shutter array. Even in such a case, the transmitted light amount of the laser beam can be controlled to give gradation to the latent image to be formed.

Further, the liquid crystal shutter arrays 9, 10, 1
It is preferable to dispose the first and second photosensitive drums at positions close to the photosensitive drums 13, 14, 15, and 16. In this case, a latent image having substantially the same definition as that of the liquid crystal shutter can be formed on the photosensitive member.

The image forming apparatus according to the above-described embodiment
Since a plurality of scanning lights are generated from one laser light source using the selective reflection means, a plurality of photosensitive members can be exposed simultaneously. In addition, each reflected light divided by the selective reflection means passes through each liquid crystal shutter array in which an array of light intensity modulation corresponding to one line of latent image is formed in advance for one scan of laser light. Since scanning is performed, latent images can be simultaneously formed on a plurality of photoconductors.

Further, an image forming apparatus (an image forming apparatus disclosed in Japanese Patent Application Laid-Open No.
In performing four-color development, one laser light source, four polygon mirrors, and four Fθ lenses are required. On the other hand, the image forming method and the image forming apparatus according to the present invention use one laser light source, one Since only one polygon mirror and one Fθ lens are required, the number of parts can be reduced.

As a result, a space for installing these components is not required, and the size of the image forming apparatus can be reduced accordingly. In addition, by using one polygon mirror, the positions of optical scanning can be matched,
The occurrence of image unevenness can be effectively prevented.

Further, each liquid crystal shutter array has:
An array of light intensity modulation corresponding to one line of latent image is formed in advance for one scan of laser light.
Compared with a liquid crystal shutter that forms an array of light intensity modulation for each number of dots in a line, the switching speed of opening and closing the liquid crystal shutter can be reduced to 1 / (number of dots in one line), resulting in higher printing speed. Can be achieved.

<Application Example of Image Forming Apparatus> Next, the structure and operation of an application example of the image forming apparatus of the present invention will be described. FIG. 4 is a schematic view of a main part of the image forming apparatus in an application example of the image forming apparatus of the present invention.

In the figure, the image forming apparatus uses a single photoreceptor belt 17 as a photoreceptor, and forms a latent image by exposing a plurality of portions of the photoreceptor belt 17 to laser light, thereby electrostatically forming a color image. The printing is performed by attaching or transferring toner.

In this image forming apparatus, one laser light source 1 and the laser light output from the laser light source 1 are
One polygon mirror 2 for exposing a laser beam to a plurality of portions of the photoreceptor belt 17, an Fθ lens 3 for passing the laser beam reflected by the polygon mirror 2, and a laser beam for passing through the Fθ lens 3 Reflection means 4 comprising mirrors 5, 6, 7, and 8 having different reflectivities and transmittances. It comprises liquid crystal shutter arrays 9, 10, 11, and 12 for exposing three exposure locations.

Here, in the image forming apparatus, for example, the distance between the mirrors 5, 6, 7, and 8 in the selective reflection means 4 may be reduced to reduce the optical path difference of each reflected light. With this configuration, the image forming apparatus allows the laser beams split by the selective reflection unit 4 to form latent images having an equal pitch width on four exposure locations (exposure locations for each color) on the photoreceptor belt 17. Once formed, the image can be focused on the photoreceptor belt 17. The optical path difference can be corrected by changing the inclination of the photosensitive belt 17.

Further, in the image forming apparatus, the liquid crystal shutter arrays 9, 10, 11, and 12 are arranged near four exposure locations on the photoreceptor belt 17, and similar to the embodiment shown in FIG. The reflected lights b, d, f, and h, which are divided into the same intensity from the output light a by the selective reflection means 4, scan these liquid crystal shutter arrays 9, 10, 11, and 12,
The four exposure locations on the photoreceptor belt 17 are exposed.

In the image forming apparatus, the liquid crystal shutter arrays 9, 10, 11, and 12 previously form an array of light intensity modulation corresponding to one line of latent image for one scan of laser light. Accordingly, by scanning the respective liquid crystal shutter arrays with the reflected light beams b, d, f, and h, a latent image can be simultaneously formed at four exposure locations on the photosensitive belt 17.

The liquid crystal shutter arrays 9, 10, 1
By disposing the photoreceptors 1 and 12 at positions close to the four exposure locations on the photoreceptor belt 17, a latent image having substantially the same definition as that of the liquid crystal shutter can be formed on the photoreceptor.
Other structures and operations are the same as those of the image forming apparatus according to the embodiment.

As described above, according to the present invention, the image forming apparatus comprises:
One photoreceptor belt is used as a photoreceptor, a latent image is formed by exposing a plurality of portions of the photoreceptor to laser light, and color toner is electrostatically attached or transferred to print. Even you can use it. Further, the image forming apparatus according to the application example can obtain the same effect as the image forming apparatus according to the embodiment.

Next, an embodiment of the image forming method of the present invention will be described with reference to FIG. "Embodiment of Image Forming Method" The image forming method according to the present invention is directed to an image forming method for simultaneously exposing a plurality of portions of a photoreceptor to form an image. Output. This state is a state in which the laser light source 1 outputs the output light a as shown in FIG.

Subsequently, the polygon mirror 2 scans the output light a. Here, by using only one polygon mirror 2, there is no need to secure a space for installing a plurality of polygon mirrors, and the image forming apparatus can be downsized accordingly. Further, it is possible to prevent image unevenness that occurs when a plurality of polygon mirrors are used.

Next, the Fθ lens 3 focuses the scanned laser beam on the photosensitive member. Here, by using only one Fθ lens 3, there is no need to secure a space for installing a plurality of Fθ lenses, and the image forming apparatus can be downsized accordingly.

Subsequently, the light splitting means splits the scanned laser beam into a plurality. Here, as light splitting means, mirrors 5, 6, having the same number of the plurality of photosensitive drums 13, 14, 15, 16 as having the predetermined transmittance and reflectance, respectively.
The selective reflection means 4 composed of 7 and 8 is used.

Next, each light modulating means in which elements for modulating the intensity by intercepting or transmitting the laser beam split by the signal from the outside and arranged in an array form is used in advance for one scanning of the laser beam. An array of light intensity modulation for one line is formed. Here, liquid crystal shutter arrays 9, 10, 11, and 12 are used as light modulating means.

In this way, the liquid crystal shutter arrays 9, 10, 11, and 12 form an array of light intensity modulation corresponding to one line of latent image in advance for one scan of laser light. For each number of dots in one line,
Compared with a light modulation unit that forms an array of light intensity modulation, the switching speed of opening and closing the light modulation unit can be reduced to 1 / (the number of dots in one line), and the image formation speed can be increased. .

Then, the laser light divided into a plurality scans each light modulating means. As described above, the laser light divided into a plurality is divided into the liquid crystal shutter arrays 9, 10, 11,
12 are simultaneously scanned, so that the photosensitive drums 13, 14, 1
5, 16 can be exposed simultaneously.

As described above, according to the image forming method of the present invention, the image forming apparatus can be downsized by reducing the number of components, and the positions of optical scanning can be matched using one polygon mirror. As a result, it is possible to prevent the occurrence of image unevenness and further increase the printing speed.

[0064]

As described above, the image forming method and the image forming apparatus of the present invention require one laser light source, one polygon mirror and one Fθ lens, and can reduce the number of parts. The image forming apparatus can be reduced in size. In addition, the image forming method and the image forming apparatus of the present invention can prevent the occurrence of image unevenness by using one polygon mirror to match the positions of optical scanning.

According to the image forming method and the image forming apparatus of the present invention, each liquid crystal shutter array forms an array of light intensity modulation corresponding to one line of latent image in advance for one scan of laser light. Therefore, when compared with a liquid crystal shutter (for example, an image forming method disclosed in Japanese Patent Application Laid-Open No. 11-91164) that forms an array of light intensity modulation for each dot number of one line, the switching speed of opening and closing the liquid crystal shutter is reduced. , 1 / (the number of dots in one line), and the printing speed can be increased.

Further, in the image forming method and the image forming apparatus according to the present invention, the liquid crystal shutter array is disposed at a position close to the photosensitive member, so that the latent image having the same definition as that of the liquid crystal shutter is provided. Can be formed on the photoreceptor.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view for explaining a selective reflection unit in the embodiment of the image forming apparatus of the present invention.

FIG. 3 is a schematic external view for explaining a liquid crystal shutter array in the embodiment of the image forming apparatus of the present invention.

FIG. 4 is a schematic view of a main part of the image forming apparatus in an application example of the image forming apparatus of the present invention.

FIG. 5 is an enlarged schematic cross-sectional view illustrating an exposure unit of an image forming apparatus in a conventional example.

FIG. 6 is a schematic diagram illustrating an exposure unit of a conventional color image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 polygon mirror 3 Fθ lens 4 selective reflection means 5, 6, 7, 8 mirror 9, 10, 11, 12 liquid crystal shutter array 13, 14, 15, 16 photosensitive drum 17 photosensitive belt 100 exposure unit 101 fluorescent lamp Reference Signs List 102 Liquid crystal shutter array 103 Selfoc lens 201 Laser light source 203, 205, 207 Half mirror 211, 212, 213 Liquid crystal shutter 217, 218, 219 Polygon mirror 220, 221, 222 Photosensitive drum

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/04 F term (reference) 2C162 AE21 AE28 AE47 AF01 FA05 FA08 FA18 FA44 FA49 FA50 2C362 BA51 BA56 BA67 BA86 BA87 DA09 2H045 AA01 BA26 BA34 DA02 2H076 AB02 AB16 AB21 DA16 EA05 EA06 2H088 EA40 HA21 HA28 MA16

Claims (6)

[Claims] 1. An image forming method for simultaneously exposing a plurality of portions of a photoconductor to form an image, comprising: outputting a laser beam for simultaneously exposing the plurality of portions of the photoconductor, and scanning the laser beam; An element that focuses the scanned laser light on the photoreceptor, divides the scanned laser light into a plurality, and blocks or transmits the divided laser light by an external signal to modulate the intensity. Each light modulating means arranged in an array forms an array of light intensity modulation for one line in advance for one scan of the laser light, and the laser light divided into a plurality An image forming method. 2. An image forming method for simultaneously exposing a plurality of portions of a photoreceptor to form an image, comprising: a laser exposing unit for forming a latent image on a plurality of portions of the photoreceptor; Optical scanning means for scanning the output laser light; an Fθ lens for focusing the laser light scanned by the optical scanning means on the photoconductor; and a laser beam passing through the Fθ lens. Light splitting means for splitting, and light provided on an output side of the light splitting means and arranged to form an array of elements that modulate the intensity by blocking or transmitting each laser beam split by an external signal. An image forming apparatus, comprising: a modulation unit. 3. The light splitting means according to claim 1, wherein said light splitting means is a selective reflecting means comprising a mirror having a predetermined transmittance and a reflectance equal to or more than the number of said photoconductors or the number of a plurality of portions of one photoconductor. The image forming apparatus according to claim 2, wherein: 4. An image forming apparatus according to claim 2, wherein said light modulating means is a liquid crystal shutter array. 5. The image forming apparatus according to claim 4, wherein said liquid crystal shutter array has a multi-layer structure. 6. The image forming apparatus according to claim 4, wherein the liquid crystal shutter array is a liquid crystal element that changes the amount of transmitted laser light according to an external signal.