JP2003118161A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of outputting a high resolution image exhibiting an excellent halftoning over the entire region from a highlight region to a high gray level region. SOLUTION: Imaging is performed by irradiating a photosensitive drum with light beams having different spot diameters in the sub-scanning direction. An image is written with a light beam having a small spot diameter in the highlight region, the light beam having a small spot diameter is then gradually combined with a light beam having a larger spot diameter, and an image is written with light beams of all spot diameters in the high gray level region. The pitch W of scanning lines, the maximum spot diameter D1 and the minimum spot diameter D2 preferably satisfy a relation D2<W<D1. Furthermore, the ratio of arbitrary spot diameters is preferably not smaller than 1.2. Spot diameter of the light beam in the main scanning direction is preferably smaller than the pitch in the sub-scanning direction or not larger than 1/2 of the pitch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus used in, for example, a copying machine, a printer, a facsimile, a plate making system and the like.

[0002]

2. Description of the Related Art As a high-speed, high-quality image forming apparatus, a copying machine and a laser beam printer which employ an electrophotographic system are known. In recent years, digital contents have become commonplace in offices and homes, and thus the demand for higher image quality of such an electrophotographic image forming apparatus has further increased.

In this electrophotographic image forming apparatus, an image carrier is irradiated with light by a laser beam or the like, and an image is recorded according to the amount of light irradiated at that time. It is possible to form any image up to an image including a halftone such as a photograph. In the case of binary recording of characters, figures, etc., a sufficiently fine image can be obtained by performing binary recording at 600 dpi or 1200 dpi by adjusting the image exposure to the resolution of the printer. Further, when reproducing the halftone density, it is possible to reproduce a good halftone density by adopting a dither method, a density pattern method or the like. Further, an image forming apparatus of a pulse width modulation system (PWM system) has been proposed which forms a halftone in each pixel with high resolution without lowering the recording density. This PWM type image forming apparatus forms halftone pixels by modulating the irradiation time of a laser beam by an image signal, and can form an image with high resolution and high gradation. Particularly suitable for forming.
That is, according to the PWM method, the area gradation of the dots formed by the beam spot can be performed for each pixel, and the halftone can be expressed without lowering the resolution. However, in the above-described PWM type image forming apparatus, when the pixel density is further increased, the pixels become relatively small with respect to the beam spot diameter, and thus it is impossible to obtain sufficient gradation by exposure time modulation. There was a problem. Therefore, in order to improve the resolution while maintaining the gradation, it is necessary to make the beam spot diameter smaller. (Here, the beam spot diameter is 1 / e from the peak light amount of a laser optical spot having a substantially Gaussian distribution.
It is a diameter at a light quantity of ² , and will be hereinafter referred to as "diameter in the main scanning direction x diameter in the sub scanning direction". ) For example, the relationship between the spot size and the wavelength is represented by “spot size ∝K · F · λ”, and by using the blue light emitting semiconductor laser (405 nm, 420 nm) which has been put on the market in recent years, the red semiconductor laser which has been conventionally used. (6
80 nm, 780 nm), it is possible to reduce the laser spot diameter to about 1/2 by using the same optical system as the conventional product. At this time, K: constant, F: F number,
λ: wavelength.

By using a blue light emitting semiconductor laser, it is possible to form a laser spot light having a small diameter, and particularly by performing faithful area gradation control from highlight to halftone, high-definition image recording becomes possible.

[0005]

By reducing the spot size of the laser writing system as described above, it is possible to realize high definition of an image from highlight to halftone, but in the high density region, As shown in FIG. 14, a small spot size causes a gap, resulting in a problem that sufficient gradation cannot be obtained in the high density region as shown in Conventional Example 2 of FIG.

For example, when an image is recorded at a resolution of 600 dpi by using an optical spot of 21 × 21 μmφ, as shown in FIG. 14, a high-definition output image is obtained by faithful area gradation control in the image area from highlight to halftone. Although it is obtained, the recording pixel is 42.3μ in the high density area.
One dot of 600 dpi of m square cannot be completely filled, and sufficient gradation cannot be obtained in the high density region as shown in Conventional Example 2 of FIG. 7 (here, Conventional Example 1 of FIG. The case of 55 × 65 μmφ is shown).

At this time, the recording resolution is doubled to 1200 dp.
When set to i, 21 for a recording pixel of 21.2 μm square
By performing image drawing with a spot light of x21 μmφ, good image output can be performed in all areas from the highlight to the high density area as shown in FIG. However, since the recording density increases, the number of scans increases and the output speed of the printer decreases.

The present invention has been made in order to solve the problems of the prior art, and an object thereof is to output a high-definition image having excellent gradation in the entire area from highlight to high density. Image forming apparatus.

[0009]

In order to achieve the above object, the present invention provides a photoconductive image carrier, a charging means for uniformly charging the image carrier, and a surface of the image carrier after charging. An exposure unit that forms an electrostatic latent image by imagewise exposure; a developing unit that attaches toner to the electrostatic latent image to form a toner image;
In an image forming apparatus including a transfer unit that transfers the toner image onto a transfer material, the exposure unit emits a light beam, and the emitted light beam is spotted on the image carrier. A scanning image forming means for forming an image and scanning the spot-shaped light to form a scanning line, wherein the light imaged on the image carrier has a different spot shape for each scanning line. Characterize.

The light emitting means emits a plurality of light beams,
It is preferable that the scanning image forming unit forms an image of each of the plurality of light beams on the same image carrier.

It is preferable that the scanning image forming means includes means for varying the spot shape of one light beam emitted from the light emitting means for each scanning line.

It is preferable that the plurality of light beams are sequentially used for image drawing in a direction substantially orthogonal to the scanning line.

It is preferable that the means for varying the spot shape of the one light beam for each scanning line has a function of defocusing the light beam emitted from the light emitting means.

The means for varying the spot shape of the one light beam for each scanning line preferably includes an actuator for moving the position of the optical means for guiding the light beam emitted from the light emitting means.

It is preferable that the ratio of any two spot diameters of the plurality of lights having different spot shapes formed on the image carrier is 1.2 or more.

It is preferable that the light beams having different spot shapes have different spot diameters in a direction substantially orthogonal to the scanning line.

With respect to the pitch W of the scanning lines, the spot diameter D1 of the maximum spot light of the plurality of light beams and the spot diameter D2 of the first spot light are D2 <W <D
It is preferable to satisfy 1.

It is preferable that the diameter of 1 / e ² of the peak intensity of the spot light in the direction along the scanning line is smaller than the pitch of the scanning line.

It is preferable that the diameter of 1 / e ² of the peak intensity of the spot light in the direction along the scanning line is smaller than 1/2 of the pitch of the scanning line.

It is preferable that the diameter of 1 / e ² of the peak intensity of the spot light in the direction along the scanning is equal to or less than 1/2 of the pixel size of the recording resolution.

It is preferable that the highlight region is drawn by using the laser spot having the smallest diameter among the spot lights having different spot shapes.

The light emitting means is 400 nm to 500 nm.
It is preferable to include a blue semiconductor laser having an emission wavelength of.

In the present invention, an image is drawn by using a small spot light in the highlight area, and image formation is advanced by combining it with a gradually increasing spot light, and all spot light is used in the high density area. By performing image drawing, high-definition and stable image output can be performed in the highlight area, and sufficient image density can be obtained without gaps even in the high-density area, and all areas from the highlight to the high density can be obtained. It is possible to output a high-definition image with excellent gradation.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a diagram showing a configuration of an exposure unit of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing a flow from data processing to a laser control unit in the apparatus, and FIG. FIG. 3 is a diagram showing an outline of an overall configuration of the same device.

First, the schematic configuration of the image forming apparatus 100 according to the embodiment of the present invention will be described with reference to FIG. The image forming apparatus 100 includes a photosensitive drum 101, a charging device 102 arranged around the photosensitive drum 101, an image exposing device 107, and a developing device 10.
9, an electrophotographic recording device including a transfer charger 104, a fixing device 105, and a cleaning member 106.

The surface of the photosensitive drum 101 as an image carrier is uniformly charged by a charger 102 as a charging means, and the charged surface on the downstream side in the rotation direction of the photosensitive drum 101 is an image exposure device 107 as an exposing means. The light beam scanned by is emitted through the reflection mirror 108.
An electrostatic latent image is formed on the surface of the photosensitive drum 101 by the light beam. Toner held on the developing cylinder 103 of the developing device 109 as a developing unit further downstream in the rotation direction of the photosensitive drum 101 is attached to the electrostatic latent image and developed as a toner image. The toner image is transferred onto a sheet 110 as a material to be transferred by a transfer charger 104 as a transfer unit arranged below the photosensitive drum 101. The sheet 101 on which the unfixed toner image is transferred is conveyed to the fixing device 105, and is heated and pressed to fix the unfixed toner image. The toner remaining on the photosensitive drum 101 is removed by the cleaning member 106.

The photosensitive drum 101 may be of a function separation type having a two-layer structure such as a charge generating layer and a charge transporting layer with a conductive supporting substrate as the lowermost layer, or a single layer type.

As the charging method, a corona charging method using a corona charger composed of a wire and an electric field control grid,
A roller charging method in which a direct current or a superimposed bias of direct current and alternating current is applied to a charging roller which is brought into contact with the image bearing member to charge the image carrier is exemplified. Optical system 107 as exposure means
There are scanner-type devices that use semiconductor lasers, those that perform image exposure on LEDs through SELFOC lens (trademark), which is a light concentrating device, and other optical devices such as EL devices and plasma light-emitting devices. Systems can also be used.

In the developing system, a magnetic one-component non-contact developing system in which magnetic toner is conveyed by magnetic force and fly-developed on the image bearing member in the developing nip without contact, or in contact with the image bearing member in the developing nip Non-contact development of non-magnetic one component in which non-magnetic toner is regulated by a blade and charged, and is carried on a developing sleeve and is carried in the developing nip in a non-contact manner to develop the toner in a non-contact manner. Method, or a non-magnetic one-component contact development method in which development is carried out by contacting the image carrier at the development nip, similarly non-magnetic toner is mixed with a carrier which is magnetic powder, and similarly conveyed to the development nip by the development sleeve for development processing. Various developing methods such as a two-component developing method for carrying out can be used.

As the transfer method, a transfer method using electric force or mechanical force can be used. A corona transfer method that uses a corona wire to apply a DC bias that has a polarity opposite to the charging polarity of the toner is used as a method for transferring using electrical force. 10 ⁵ ~ 1
A roller transfer method in which a roller having a member having an electric resistance value of 0 ¹² Ω on the surface layer is brought into contact with the roller and a bias having a polarity opposite to that of the toner is applied thereto is used.

In the present invention, as the image exposure device 107, that is, as an optical device for performing image exposure, a scanner type optical system using a blue laser light emitting element capable of laser oscillation of short wavelength light and capable of reducing the diameter of an optical spot. To use. As shown in FIG. 1, the image exposure device comprises a plurality of semiconductor laser parts 11 and 12 as light emitting means, a polygon mirror 20 rotating at a high speed, and an f-θ lens group 21, and the semiconductor laser parts 11 and 12 are As shown in FIG. 2, the laser driver 25 receives the time-series digital image signals output from the image processing unit 24 of the image reading apparatus or the personal computer that performs image processing on the input data 30. , 26 according to the light emission signal.
The laser beams emitted from the semiconductor laser units 11 and 12 are made into substantially parallel light by the collimator lenses 14 and 15, and are condensed on the polygon mirror 20 by the cylindrical lenses 17 and 18, and are rotated at a constant speed. The light is reflected and deflected on the upper side, and an image is formed in a spot shape on the photosensitive drum 22 by the fθ lens group 21.
3 is scanned at a constant speed. The scanning of the laser beam on the image plane at this time is performed by sequentially scanning a plurality of laser beams in the sub-scanning direction.

The present invention is characterized in that spot lights having different spot diameters are used for a plurality of laser beams. For example, when an image is drawn by two laser beams as shown in FIG. The relationship between the diameter C3 in the sub-scanning direction at 1 / e ² from the peak intensity of C1 and the diameter A3 in the sub-scanning direction at 1 / e ² from the peak intensity of the small spot light A1 is the scanning pitch in the sub-scanning direction. Is defined as W, the relationship of A3 <W <C3 is satisfied. Using the above configuration, a sub-matrix is formed by combining a small spot light and a large spot light as a set as shown in FIG. 5, and gradation drawing is performed. For example, recording density 400 dpi
And two scanning lines having a small light spot and a large light spot as a set, and P at 200 dpi in the main scanning direction.
Perform WM drawing. At this time, by starting dot growth from a scanning portion having a small spot, high-definition drawing of a highlight area becomes possible, and an image can be drawn with a large spot even in a high-density area. It realizes output.
At this time, the number of scanning lines having the plurality of spot diameters may be three or more, and it is also possible to perform image drawing by changing the spot shape of one laser beam for each scanning line. Furthermore, the method of dot growth is not limited to the embodiment of the present specification, and it is of course possible to perform image drawing with a small diameter spot even in a halftone region. In particular, when an image is drawn using a plurality of scanning lines having three or more kinds of spot diameters, it is possible to draw an image with spot light having a small diameter up to a relatively high density area.

Further, in the two spot lights having different spot diameters as described above, the spot diameter ratio is preferably 1.2 or more. The ratio of the two spot diameters is 1.
If it is smaller than 2, the functional separation by the two spot lights cannot be sufficiently performed in the highlight region and the high concentration region, and the effect of such functional separation is achieved by setting the spot diameter ratio to 1.2 or more. Appears.

The spot diameter of the spot light in the main scanning direction is preferably smaller than the spot diameter in the sub scanning direction. Such a balance between the spot diameter of the spot light in the main scanning direction and the spot diameter in the sub scanning direction is important when controlling the line width in the vertical and horizontal directions. For example, when using spot light having the same spot diameter in the main scanning direction and the spot diameter in the sub-scanning direction to fill a certain pixel with area gradation, the dot becomes horizontal because it scans for a certain period of time. I will end up. In other words, if such a spot light is used to output a vertical line and a horizontal line using the same data, the vertical line becomes thicker. In order to eliminate this imbalance, it is desirable that the spot diameter of the spot light in the main scanning direction is smaller than the spot diameter in the sub scanning direction as described above, and it is particularly preferable that the spot diameter is 1/2 or less. .

The spot diameter of the spot light in the main scanning direction is preferably smaller than the pitch W in the sub scanning direction. This is because if the spot diameter in the main scanning direction is larger than the pitch W in the sub scanning direction, sufficient gradation reproduction cannot be performed, and there is no point in increasing the resolution in the sub scanning direction.

(First Embodiment) A first embodiment of the present invention will be described below.

In the present invention, an optical device for image exposure is
Using two laser beams of blue laser light emitting elements 11 and 12 as a semiconductor laser part capable of laser oscillation with a wavelength of 05 nm and capable of reducing the diameter of an optical spot, these two laser beams are used as shown in FIG. The spot diameter in the sub-scanning direction on the image plane of each laser beam is 40
Small spot light A2 of μm (A3) and 87 μm (C
3) Two scanning lines A1 and C1 of the large spot light C2
To draw an image. At this time, spot lights A2 and C
The diameters A3 and C3 of 2 in the sub-scanning direction are adjusted so that the entire surface can be filled up and image exposure can be performed when an image is drawn at a desired recording pitch. Although the diameter in the main scanning direction is arbitrary, it is desirable that the diameter is smaller than that in the sub scanning direction, and it is further desirable that it is 2/3 or less of the recording pixel size.

The emitted light beam is collimator lens 1
After being collimated by the lenses 4 and 15, the light passes through the spot adjusting lens, is condensed and reflected by the cylindrical lenses 17 and 18 on the polygon mirror 20 which is a rotary deflecting device, and is condensed again by the fθ lens group 21. And image plane 2 at a constant speed
2 is moved in the scanning direction 23.

In this embodiment, the print resolution is 400 dpi, and the PW of 200 dpi in the main scanning direction is set as shown in FIG.
Data is printed by M driving, a sub-matrix is formed by combining a small spot light and a large spot light as a set, and dots are grown from a scanning portion having a small spot in the order shown in the drawing to thereby create a highlight area. High-definition drawing is possible, and an image can be drawn with a large spot even in a high-density area. Therefore, high-definition image output is realized over the entire density area. FIG. 6 shows an image of the print pattern in the highlight area when this embodiment is used. Further, in FIG. 5, the dot growth method when the pixel is divided into four has been described, but the number of recording gradations and the growth method are not limited to this.

As a result of outputting an image with the above-described structure, it is possible to perform reliable area gradation not only from the highlight to the halftone area but also from the halftone to the high density area as compared with the conventional example. It is possible to obtain the gradation curve as in Example 1. By obtaining such a gradation curve, sufficient gradation latitude is secured in the image area from highlight to halftone, where density stability is most important, and high-definition image output with small output density fluctuations is secured. Can be realized.

(Second Embodiment) A second embodiment of the present invention will be described below.

In the present invention, as shown in FIG. 8, three blue lasers are emitted as a semiconductor laser portion capable of oscillating a laser beam having a wavelength of 405 nm in an optical device for image exposure and capable of reducing an optical spot diameter. Elements 11, 12,
13 is used to output the emitted light beam to the collimator lens 1
After being collimated by 4, 15, and 16, collimated by the cylindrical lenses 17, 18 and 19 on the polygon mirror 20 which is a rotation deflecting device, and condensed again by the fθ lens group 21, and at a constant speed. In the scanning direction 2 on the image plane 22
Move to 3. Blue laser light emitting device 11, 12, 1
As shown in FIG. 9, 3 receives an input of a time-series digital image signal output from an image processing unit 24 such as a computer unit of an image reading apparatus or a personal computer that performs image processing on the input data 30, The laser driver 25, 2
Blinks according to the light emission signals of 6, 27.

The spot diameter of these three laser beams in the sub-scanning direction on the image plane is 30 as shown in FIG.
A small spot light A4 of μm (A6) and 50 μm (B
6) Image drawing is performed by the scanning lines A5, B5, and C5 composed of three kinds of spot light, that is, the inner spot light B4 and the large spot light C4 of 100 μm (C6). At this time, the diameters A6 of the spot lights A4, B4, and C4 in the sub-scanning direction,
B6 and C6 are adjusted so that when the image is drawn at the desired recording pitch, the entire surface is filled up and image exposure is possible. The diameter in the main scanning direction is arbitrary, but it is preferably smaller than that in the sub scanning direction, and more preferably 1/2 or less of the recording pixel size. Further, when an image is drawn with three scanning lines, it is necessary to appropriately adjust the recording position of the scanning lines in the sub-scanning direction according to the spot diameter of each scanning line. As in this embodiment, the diameters of the small, medium, and large spot lights in the sub-scanning direction are A6 = 30 μm and B6 = 50, respectively.
In the case of a scanning line consisting of .mu.m and C6 = 100 .mu.m, for example, the recording position is as shown in FIG. 10, the scanning position of the scanning line A5 is 15 .mu.m apart from the center of the scanning position at A7 and the scanning line B5.
The distance B7 from the center of the scanning position of 13 μm, the scanning line C5
By performing the image drawing while shifting the distance C7 from the center of the scanning position of 10 μm in the illustrated direction, it is possible to irradiate the entire image surface with light even in the high density region.

In this embodiment, the print resolution is 400 dpi, and the PW is 200 dpi in the main scanning direction as shown in FIG.
Data is printed by M drive, and a sub-matrix is formed by making a set of three scanning lines having three kinds of small, medium, and large spot light, and dots are grown from a scanning portion having a small spot in the order shown. By doing so, it is possible to perform high-definition drawing in the highlight area, and it is possible to perform image drawing in a large spot even in the high-density area. Therefore, high-definition image output is realized over the entire density area. FIG. 12 shows an image of the print pattern in the highlight area when using this embodiment. Further, in FIG. 11, the dot growth method when the pixel is divided into six has been described, but the number of recording gradations and the growth method are not limited to this. As a result, compared to the conventional example, not only from the highlight to the halftone area, but also from the halftone to the high density area, reliable area gradation can be performed,
It is possible to obtain the gradation curve as in the second embodiment of FIG. By obtaining such a gradation curve, a sufficient gradation latitude is secured in the image area from highlight to halftone where stability of density is most important,
It is possible to realize a high-definition image output with a small output density fluctuation.

(Embodiment 3) The third embodiment of the present invention will be described below.

In this embodiment, the defocus characteristic of the optical system is used as a means for drawing an image using spot light having a different spot diameter for each scanning line in the first embodiment. Specifically, as shown in FIG. 13, the spot diameter adjusting lens 32 as an optical means is moved in parallel with the light flux of a single laser beam by using an electromagnetic induction type servomotor as an actuator. The above is defocused to obtain spot lights having different spot diameters.

In this embodiment, the spot diameter in the main scanning direction is kept at 30 μm, the diameter of the small spot light in the sub scanning direction is 40 μm, and the diameter of the large spot light is adjusted to 80 μm. Image drawing was performed by the same method.

As a result of outputting an image with the above-described configuration, it is possible to perform reliable area gradation not only in the highlight and halftone regions but also in the halftone and high density regions as compared with the conventional example. It is possible to obtain the gradation curve as in Example 1. By obtaining such a gradation curve, sufficient gradation latitude is secured in the image area from highlight to halftone, where density stability is most important, and high-definition image output with small output density fluctuations is secured. Can be realized.

[0050]

As described above, according to the present invention, an image is drawn by using a small spot light in the highlight area, and the image is formed by combining the spot light with a gradually increasing spot light to obtain a high density image. In the area, image drawing can be performed using all the spot lights. By performing image formation in this way, it is possible to perform high-definition and stable image output in the highlight area, and also to obtain sufficient image density without gaps even in the high-density area, and the It is possible to output a high-definition image with excellent gradation in all areas up to the density.

[0051]

[Brief description of drawings]

FIG. 1 is a diagram illustrating an exposure unit according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a flow of a laser control unit from data processing of the present invention.

FIG. 3 is a diagram showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 4 is a diagram illustrating a beam drawing method according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating a dot growth method of a printing unit according to the first embodiment of the present invention.

FIG. 6 is an image diagram of a highlight area when an image is drawn in the embodiment of the present invention.

FIG. 7 is a graph showing the relationship between gradation data and density.

FIG. 8 is a diagram illustrating an exposure unit according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating the flow of data processing and laser control according to the second embodiment of the present invention.

FIG. 10 is a diagram illustrating a beam drawing method according to the second embodiment of the present invention.

FIG. 11 is a diagram illustrating a dot growth method of a printing unit according to the second embodiment of the present invention.

FIG. 12 is an image diagram of a highlight area when an image is drawn in the second embodiment of the present invention.

FIG. 13 is a diagram illustrating an exposure unit according to a third embodiment of the present invention.

FIG. 14 is a diagram illustrating a problem of a conventional example.

FIG. 15 is a diagram illustrating a problem of the conventional example.

[Explanation of symbols]

11,12,13 Laser chip 14, 15, 16 Collimator lens 17,18,19 Cylindrical lens 20 polygon mirror 21 fθ lens group 22 Image carrier 23 scanning direction 24 Image processing unit 25,26,27 Laser driver 31 Focus adjustment section 32 Focus adjustment lens 33 Focus servo motor 101 image carrier 102 primary charger 103 developer carrier 104 Transfer charger 105 Fixer 106 cleaner 107 Image exposure device 109 developer 110 recording paper

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C362 AA03 AA21 AA22 AA29 AA35                       AA37 BA56 BA67 CA10 CA14                 2H076 AB05 AB06 AB09 AB12 AB22                       AB76 EA05 EA16                 5C074 BB26 CC22 DD05 DD14 EE02                       FF05 HH02

Claims (14)

[Claims] 1. A photoconductive image carrier, a charging unit for uniformly charging the image carrier, and an exposing unit for exposing the surface of the image carrier after charging to form an electrostatic latent image. In an image forming apparatus including a developing unit that attaches toner to the electrostatic latent image to form a toner image, and a transfer unit that transfers the toner image to a transfer material, the exposure unit emits a light beam. And a scanning image forming unit that forms a scanning line by scanning the spot-like light and forming a scanning line on the image carrier with the emitted light beam. An image forming apparatus, wherein the light imaged on has a different spot shape for each scanning line. 2. The light emitting means emits a plurality of light beams, and the scanning image forming means forms an image of each of the plurality of light beams on the same image carrier.
The image forming apparatus according to item 1. 3. The image according to claim 1, wherein the scanning image forming unit includes a unit that makes the spot shape of one light beam emitted from the light emitting unit different for each scanning line. Forming equipment. 4. The image forming apparatus according to claim 2, wherein the plurality of light beams are sequentially used for image drawing in a direction substantially orthogonal to the scanning line. 5. The means for varying the spot shape of the one light beam for each scanning line has a function of defocusing the light beam emitted from the light emitting means. Image forming device. 6. The means for varying the spot shape of the one light beam for each scanning line includes an actuator for moving the position of an optical means for guiding the light beam emitted from the light emitting means. The image forming apparatus according to claim 5. 7. The ratio of any two spot diameters among a plurality of lights having different spot shapes imaged on the image carrier is 1.2 or more. The image forming apparatus according to any one of 1. 8. The light having different spot shapes comprises:
The image forming apparatus according to claim 1, wherein spot diameters in a direction substantially orthogonal to the scanning line are different. 9. The spot diameter D1 of the maximum spot light and the spot diameter D2 of the first spot light of the plurality of light beams with respect to the pitch W of the scanning lines satisfy D2 <W <D1. The image forming apparatus according to any one of claims 1 to 8, which is characterized. 10. The image according to claim 1, wherein a diameter at 1 / e ² of a peak intensity of the spot light in a direction along a scanning line is smaller than a pitch of the scanning line. Forming equipment. 11. The diameter of 1 / e ² of the peak intensity of the spot light in the direction along the scanning line is smaller than 1/2 of the pitch of the scanning line.
The image forming apparatus according to item 0. 12. The diameter of 1 / e ² of the peak intensity of the spot light in the direction along the scanning is 1/2 or less of the pixel size of the recording resolution.
10. The image forming apparatus according to any one of 9 to 9. 13. The image forming apparatus according to claim 1, wherein a highlight area is drawn by using a laser spot having the smallest diameter among the spot lights having different spot shapes. 14. The light emitting means is 400 nm to 500 nm.
The image forming apparatus according to claim 1, further comprising a blue semiconductor laser having an emission wavelength of nm.