JPH06328772A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To provide an image forming apparatus which can form an image by interpolating picture elements on a photosensitive material by changing the shape of a beam spot of an optical signal corresponding to an image signal. CONSTITUTION:An image forming apparatus for forming an image on a medium to be recorded by optical signals is equipped with a laser drive circuit 101 and a semiconductor laser unit 102 which emit a laser beam corresponding to an image signal, a mechanism part which forms an image by scanning a laser beam on a photosensitive drum 104, and a spot fairing lens 105 which expands a laser beam spot by lengthening by more than one scan perpendicularly to the laser beam scanning direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus which forms an image on a recording medium using a laser beam or an optical signal.

[0002]

2. Description of the Related Art In a commonly used image output device such as a laser beam printer, a laser beam emitted from a laser unit is deflected by a scanning mirror to scan a photosensitive drum for each dot line. do. That is, the photosensitive drum is rotated at a constant speed so that the deflected beam spot is irradiated to only one dot line by one scanning. At this time, since the photosensitive drum has already been charged, an electrostatic latent image is formed on the photosensitive drum by scanning the laser beam. This laser beam is turned on according to the print image such as a character pattern,
Since it is controlled so as to be turned off, the electrostatic latent image formed on the photosensitive drum becomes a dot pattern representing a character pattern or the like that coincides with the irradiation of the laser beam.

[0003]

However, in the above-mentioned conventional image output apparatus, the dot pattern is provided with a screen angle in order to obtain gradation, and pulse width modulation (P
WM) to set the horizontal resolution to the vertical resolution of 1
/ 2. As a result, the horizontal resolution is reduced.

The present invention has been made in view of the above-mentioned conventional example, and an image can be formed by interpolating pixels on the photoconductor by changing the shape of the beam spot of the optical signal according to the image signal. An object is to provide an image forming apparatus.

[0005]

In order to achieve the above object, the image forming apparatus of the present invention has the following constitution. That is, an image forming apparatus for forming an image on a recording medium by an optical signal, and a light generating unit for generating an optical signal according to the image signal, and a formation for forming an image by scanning the optical signal on the photoconductor. And means for expanding the beam spot of the optical signal by a plurality of scans in a direction substantially orthogonal to the scanning direction of the optical signal.

[0006]

In the above structure, an optical signal is generated according to the image signal, and when the optical signal is used to scan the photoconductor to form an image, the beam spot of the optical signal is moved in the scanning direction of the optical signal. Scanning is performed by expanding a plurality of scans in a substantially orthogonal direction. Thereby, it is possible to interpolate and record the pixels of the line surrounded by the two scanning lines.

[0007]

Embodiment 1 Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Before explaining this embodiment, the structure of the laser beam printer of this embodiment will be described with reference to FIG.

FIG. 9 is a sectional view showing the internal structure of the laser beam printer (LBP) 900 of this embodiment.
P900 is a data source not shown (host computer, etc.)
Character pattern registration and fixed form (form data)
It is configured to be able to register etc.

In FIG. 9, reference numeral 900 denotes an LBP main body, which inputs and stores character information (character code) supplied from an externally connected host computer or the like, form information, macro commands, and the like. A corresponding character pattern, form pattern, or the like is created according to the information, and an image is formed on a recording paper, which is a recording medium. Three
Reference numeral 00 denotes an operation panel on which various switches for operation and LED displays are arranged, and reference numeral 901 denotes a printer control unit for controlling the entire LBP 900 and analyzing character information supplied from the host computer. The printer control unit 901 mainly converts character information into a video signal of a corresponding character pattern to convert the laser drive circuit 101.
Output to.

A laser drive circuit (driver) 101 is a circuit for driving the semiconductor laser unit 102, and switches the semiconductor laser on and off in accordance with an input video signal. The laser light 904 is emitted from the rotary polygon mirror 10.
3 is swung in the left-right direction to scan on the photosensitive drum 104. As a result, an electrostatic latent image having a character pattern is formed on the photosensitive drum 104. This latent image is the photosensitive drum 104.
After being developed by the developing unit 907 around, the image is transferred to the recording paper. A cut sheet is used for this recording paper,
The cassette recording paper is stored in a paper cassette mounted on the LBP 900, and is taken into the apparatus by the paper feed roller 909 and the transport rollers 910 and 911, and the photosensitive drum 10
4 is supplied.

FIG. 1 is a block diagram of an embodiment which most prominently shows the gist of the present embodiment.

In the figure, 105 is a spot shaping lens. The laser drive circuit 101 drives the semiconductor laser unit 102 based on the input character pattern information to turn on / off the laser beam. At this time, the spot shaping lens 1 provided in front of the scanning mirror
With 05, the spot of the laser beam is shaped into an ellipse. The contents of this shaping will be described later. After that, the laser beam is polarized by the scanning mirror 103 to scan on the photosensitive drum 104. The photosensitive drum 104 is uniformly charged, and an electrostatic latent image (hereinafter referred to as an electrostatic image) is formed on the photosensitive drum 1 according to the exposure pattern.
It will be formed on 04.

FIG. 2 is a diagram schematically showing an electrostatic image drawn on the photosensitive drum 104. In the figure, the circle marks represent each pixel, but P should be set so that a combination of 2 dots and 1 dot is added so that a screen angle is provided to produce gradation.
ON / OFF of the semiconductor laser unit 102 is controlled by the WM. Therefore, the resolution in the main scanning direction (horizontal direction) is half that in the sub-scanning direction (vertical direction). In order to clearly show the difference in resolution at this time, in FIG. 3, when the resolution in the sub-scanning direction is 400 dpi (dots / inch), the horizontal resolution (200 dpi) and the vertical resolution (40 dpi) are set.
0 dpi).

In FIG. 2, L₁ ~ L₆ Is the main run
It shows the number of the inspection line, BL ₂ Is the scan line L₂ 
Beam spot, BL when scanning_Four Is the scan line
In L_Four Beam spots when scanning
Is showing. Of course BL₂ And BL_Four When is different from
Since it is scanned in the inter-zone, at the same time on the photosensitive drum 104
It does not exist, but it is the same for ease of understanding the following explanation.
Both are shown on the drawing.

The beam spot BL is shown on the left side of FIG.₂ When
BL_Four Energy in the sub-scanning direction (vertical direction) of
The intensity distribution (Gaussian distribution) is shown. Beam Spo
Energy intensity at the center of scanning_P Then that
The energy intensity of the scan line adjacent to
Minute E_P The beam shape is the beam shaping lens so that
It has been shaped by s 105. Beam spot BL
₂ And BL_Four Overlapping parts (indicated by diagonal lines in the figure)
The energy intensity of_P /
2 + E_P / 2 = E_P It is supposed to be. Therefore,
L₂ L during scanning₃The shaded part of is L_Four L during scanning₃ of
Each shaded area is exposed once
Line L₃ The shaded area of is interpolated by 1 dot pixel
become. L ₃ The shaded area is L₃ Dot 20 during scanning
It is located between 0 and the dot 201, and the pixel information originally
It is the part that does not meet the information, but in this case the running before and after that
Inspection line L₂ And L_Four Depending on the pixel information of line L₃ of
The pixel is interpolated at this position.

FIG. 4 is a diagram showing the case of solid black printing, in which the beam spot 400 is exposed when scanning the line L ₁ , and the beam spot 401 is exposed when scanning the line L ₃ . The part 402 where these two beam spots overlap is a part where the energy potential of the central part of each beam spot becomes 1/2, and the energy potential of the shaded part 402 becomes "1" by two scans, It becomes equal to the energy potential of the central part. In this way, the shaded portion 402 is irradiated with the laser beam having the same energy potential as the central portion of each beam spot, and dot data is formed here.

As described above, by forming the beam spots for three dot lines, dot data having the same energy potential as the central portion of the beam spots is formed in the portion where the beam spots overlap, so that the end portions overlap. The same dots as usual are formed on the exposed portion. As a result, as shown in FIG. 5, the resolution in the horizontal direction is originally 200 dpi, whereas the resolution in the horizontal direction is double (400 d).
pi).

Therefore, the resolution in the horizontal direction (main scanning direction) is apparently increased by this pixel interpolation.

It is most preferable for the purpose of this embodiment to shape the beam spot by setting the major axis of the beam spot to be the length of three scanning lines and the minor axis to be the length of one pixel. . (Second Embodiment) FIG. 6 is a block diagram showing a second embodiment of the present invention. In the figure, 601 is a pixel information detection unit, and 602 is a laser switching unit. It should be noted that the same numbers as those in FIG. 1 are assigned to the same processes as those in the above-described embodiment and the description thereof will be omitted.

When the beam spot is made up of 3 dot lines, as shown in FIG. 7, the pixel data located at the center of the beam spot 700 is a white dot (scan line L).
₁ ) and the pixel data located at the center of the beam spot 701 is a black dot (scan line L ₃ ), the end portions of these beam spots 700 and 701 (scan line L
₂ ) The energy potential of the scanning line L ₁ is “0” (that is, the beam is in an off state) and the scanning line L ₃ is 1/2 when the maximum value of the energy potential is “1”. (That is, the beam is turned on). L ₁ indicated by the shaded area on the scan line L ₂
The energy potential of the beam spot 703 formed at the position where the beam spots 700 and 701 of L ₃ and L ₃ respectively overlap is the sum of the energy potentials at the ends of the beam spots. Therefore, in this case, the energy potential of this spot 703 is 0 + 1/2 = 1/2, that is, the pixel data of the dot 703 indicated by the shaded area is gray.

When such a spot 703 is formed at the position indicated by 704, the edge portion of the character data is visually blurred. Therefore, when the pixel information detection unit 601 has different energy potentials in the central portions of the two beam spots of three dot lines (L _{1 to} L ₃ in this example) in the sub-scanning direction (vertical direction). That is, the case where the pixel data in the beam spots 700 and 701 on the line L ₁ of the first 1st dot and the line L ₃ of the last 3rd dot among the 3 dot lines differ is sequentially detected. To

That is, the pixel information detecting section converts the image data into three lines.
It has a buffer to store the input data, and the buffer of these 3 lines is
Compare images to determine if the image meets the above conditions
To do. Thus, the corresponding pixels on the first and third lines
Are detected to be different, line L₁ And L₃ of
Line L based on pixel data₂ Do not interpolate
Control signal 600 to output line L₂ Scan of
Sometimes the laser switching unit 602 causes the beam spot
The major axis and minor axis of the grate should be swapped 90 degrees. That is,
The major axis in the main scanning direction (horizontal direction) and the sub-scanning direction (vertical direction)
Shape the beam spot so that it has a short diameter
To do. As a result, the major axis direction is line L ₂ Line up
become.

This state is shown in FIG. In FIG. 8, as indicated by the shaded area, a dot having an energy potential of “1” is formed in the gap between the dot 800 and the dot 801, and pixel interpolation is performed by the same action as described above. In this way, blurring of the edge portion of the character data can be suppressed, and the horizontal resolution can be doubled as shown in FIG.

In this embodiment, the case where a laser beam is used as a light source has been described, but it is clear that the scope of application of the present invention is not limited to this. For example, OFT (optical fiber tube) is used. Even if the above is used, the gist of the present invention can be applied as it is.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program for implementing the present invention to a system or an apparatus.

As described above, according to this embodiment, the beam spot of the image forming apparatus such as a laser beam printer is vertically elongated in the vertical direction with respect to the main scanning direction, and the laser beam is projected onto the photosensitive drum once. By irradiating multiple dot lines by scanning and interpolating pixels at the positions corresponding to the ends of the beam spot on the photosensitive drum, it is possible to increase the horizontal resolution while maintaining gradation. become.

Further, the beam spot is adaptively switched to be horizontally long with respect to the main scanning direction so that the central portion and the end portion of the beam spot exist on the same dot line. By interpolating the pixels on the photosensitive drum by the two laser beams existing on the line, it is possible to suppress blurring of the edge portion of the character data, and various effects can be obtained.

[0029]

As described above, according to the present invention,
By changing the shape of the beam spot of the optical signal according to the image signal, the image can be formed by interpolating the pixels on the photoconductor, so that the resolution of the formed image can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a laser beam printer of this embodiment.

FIG. 2 is a diagram schematically showing an electrostatic image drawn on a photosensitive drum in the laser beam printer of this embodiment.

FIG. 3 is a diagram showing a resolution in a conventional image forming apparatus.

FIG. 4 is a diagram illustrating pixel interpolation during solid black printing.

FIG. 5 is a diagram showing a relationship between horizontal resolution and vertical resolution in the laser beam printer of this embodiment.

FIG. 6 is a block diagram showing a configuration of a laser beam printer according to a second embodiment of the present invention.

FIG. 7 is a diagram for explaining a problem caused by an interpolation pixel.

FIG. 8 is a diagram for explaining a beam spot of the second embodiment.

FIG. 9 is a structural cross-sectional view of the laser beam printer of this embodiment.

[Explanation of symbols]

 101 laser drive circuit 102 laser unit 103 scanning mirror 104 photosensitive drum 105 spot shaping lens 601 pixel information detection unit 602 laser switching unit

Claims (3)

[Claims] 1. An image forming apparatus for forming an image on a recording medium by an optical signal, comprising: a light generating unit for generating an optical signal according to the image signal; and an image by scanning the optical signal on a photoconductor. An image forming apparatus comprising: a forming unit that forms a beam spot of the optical signal; and an expanding unit that expands a beam spot of the optical signal by a plurality of scans in a direction substantially orthogonal to the scanning direction of the optical signal. 2. An image forming apparatus for forming an image on a recording medium by an optical signal, comprising: a light generating means for generating an optical signal according to the image signal; and an image detecting means for detecting a state of the image signal. Forming means for forming an image by scanning an optical signal on the photoconductor, and a beam spot of the optical signal depending on a detection state of the image detecting means, or a scanning direction of the optical signal or substantially orthogonal to the scanning direction. An image forming apparatus comprising: an expanding unit that expands a plurality of pixels in a direction in which the image is formed. 3. The image forming apparatus according to claim 1, wherein the beam spot is expanded into a substantially elliptical shape.