JPH0719093B2 - Image recording method - Google Patents

Description

The present invention relates to an image recording method in an optical scanning electrophotographic recording device.

[Conventional technology]

Generally, in an optical scanning electrophotographic recording apparatus such as a laser printer, while a beam optically modulated by image information is main-scanned, a photosensitive member that is sub-scanned is sequentially exposed to form an electrostatic latent image. The electrostatic latent image is formed and visualized by toner development or the like to obtain a recorded image.

For example, in the optical scanning electrophotographic recording apparatus disclosed in Japanese Patent Laid-Open No. 56-8112, a character code signal for one page read from a magnetic tape and written at a predetermined address of a page memory is converted into 32 × 32 dots. A character pattern (which can be reproduced by 32 beam scans) is applied to a stored character generator. Then, every time the beam is scanned, a modulation signal is taken out from the character generator and applied to the beam modulator, and the beam is main-scanned while the laser beam is modulated by the beam modulator, and the beam is scanned on the photoconductor. Form a latent image. Then, this electrostatic latent image is developed with toner.

As described above, the optical system of the laser printer that performs main scanning with the laser beam for recording becomes complicated.

Therefore, in order to simplify the light source and the optical system, a fluorescent dot array tube in which phosphors are arranged in an array in the main scanning direction in a pixel unit is used as a light source, and the generated light modulated according to image information is imaged. Light that forms an electrostatic latent image by exposing it on the surface of a photoconductor that is sub-scanned through an optical system, and develops the latent image by toner development to perform recording according to image information. A scanning electrophotographic recording device has been proposed (see Japanese Patent Laid-Open No. 58-108864).

However, in such an optical scanning electrophotographic recording device,
There is a problem in that the potential of the electrostatic latent image formed by exposure is shallow and the electrostatic contrast tends to be weak due to the use of a minute light emitting phosphor as the light source.

Also, as described above, whether the main scanning of the laser beam,
Regardless of whether the fluorescent dot array tubes arranged in an array in the main scanning direction are used as the light source, this type of image recording method causes latent image formation due to the rising and falling edges of the modulated beam. In the area, it is difficult to obtain a desired potential distribution at the boundary between the image portion to which toner or the like is to be made visible and the non-image portion not to be made visible. Therefore, it is difficult to improve the quality of the recorded image.

For example, in positive-positive recording in which a non-exposed portion not irradiated with a beam is visualized as an image portion,
It is known that the image quality is deteriorated by the development that "the image becomes thin" (see the above-mentioned JP-A-56-8112).

Further, the present inventor has found that at the boundary between the image part and the non-image part, the resolution of the image obtained by visualization becomes insufficient because a sufficient potential difference or potential contrast between both parts cannot be obtained. In the case of a document image, we also found a problem that the sharpness of the visualized characters may be lost.

Incidentally, in order to solve the problem of "image thinning" in the positive-positive recording, the above-mentioned Japanese Patent Laid-Open No.
In the '8112 publication, the width of the modulation pulse obtained based on the 32 × 32 dot character pattern is changed so that the width of the unexposed portion on the photoconductor on the image portion in the main scanning direction is relatively wide. An image recording method has been proposed. According to this image recording method, the problem that "the image becomes thin" in the positive-positive recording can be solved. However, as will be described later in detail, in the invention of this known image recording method, the light generated by the minute light emitting segment by each pixel unit arranged in the main scanning direction, which is the premise of the present invention, corresponds to the image information. It modulates according to the pulse width, and the modulated light is
Even if it is simply applied to an optical scanning type electrophotographic recording device which records according to image information by exposing through a focusing optical system to a pre-charged photoconductor surface that is fed in the sub-scan direction, the above sufficient resolution is obtained. It is not possible to achieve the effect of obtaining

[Problems to be Solved by the Invention]

The present invention has been made in view of the above background, and an object thereof is to provide an image recording method in an optical scanning electrophotographic recording apparatus capable of recording an image with high resolution. .

〔Constitution〕

FIG. 1 shows a schematic structure of an optical scanning electrophotographic recording apparatus to which the image recording method of the present invention can be applied. In FIG. 1, the optical scanning electrophotographic recording apparatus is configured such that each phosphor is turned on in a line in the main scanning direction on a pixel-by-pixel basis in the fluorescent dot array tube 1 in accordance with the binary image information BS.
By turning off, the minute emission beam is directly modulated. The modulated minute emission beam is uniformly charged by the charger 3 and is sub-scanned to be fed in a drum-shaped photoreceptor 4.
The surface is irradiated through the imaging optical system 2 to sequentially perform exposure line by line. The electrostatic latent image formed by this exposure is visualized by toner adhesion or the like by the developing device 5, and this visualized image is transferred to the recording paper 7 by the transfer device 6 in the transfer section. In addition,
Reference numeral 8 in the drawing denotes a cleaner for cleaning the toner remaining on the surface of the photoconductor 4 after transfer.

Fig. 2 shows that phosphors are provided in the face glass 11 in pixel units.
A specific configuration example of the fluorescent dot array tube 1 in which 12 are arranged in an array and the driving ICs 13 are integrally incorporated on the same substrate 15 together with the terminals 14 is shown. Further, as the light source, instead of the fluorescent dot array tube 1 as described above, an LED in which pixels are arranged in an array may be used.

The image recording method of the present invention is the image recording method in the optical scanning electrophotographic recording apparatus as shown in FIG. A means capable of changing the pulse width corresponding to the image information that modulates the light emitted from the light emitting segment is used. Then, at the boundary between the image part and the non-image part, the power of the exposure beam is controlled by controlling the pulse width of the light modulation corresponding to the image information so that the latent image potential difference between both parts is sufficiently large and the potential contrast is sufficiently high. Is changed appropriately. Specifically, in the sub-scanning of the light beam,
At the boundary between the image part and the non-image part, unlike the part other than the boundary, the ratio of the light beam exposure time to the one-pixel scanning time in the sub-scanning direction (hereinafter referred to as pixel frequency duty).
To be within a certain appropriate range. This gives the optimum scanning conditions of the light beam so that a recorded image with sufficient resolution can be obtained.

Hereinafter, with reference to FIGS. 3 to 6, the relationship between the pixel frequency duty and the image resolution at the boundary between the image part and the non-image part, and the appropriate range of the pixel frequency duty for obtaining a good image resolution Will be described.

FIG. 3 shows a latent image potential distribution on the photoconductor in the sub-scanning direction for a pattern exposed every other pixel in the sub-scanning direction (a striped pattern repeating every black and white line extending in the main scanning direction). It is a characteristic diagram. In this characteristic diagram, the horizontal axis represents the relative distance that is a value obtained by removing the distance from a certain reference position in the sub-scanning direction by the pixel pitch, and the vertical axis represents the relative distance on the photoconductor with respect to the potential of the photoconductor when the exposure energy is zero. The relative potential, which is the ratio of the latent image potential of each part, is taken. Then, as a parameter, the pixel frequency duty is changed in the range of 10 to 150%, and the latent image potential distribution is shown for the pattern exposed by using the beam of each pixel frequency duty.

This pattern is a striped pattern in which black-and-white lines (extending in the main scanning direction) alternate in the sub-scanning direction, and is a pattern that gives a minimum interval between black lines exposed every other pixel in the sub-scanning direction. . Therefore, it is the most difficult pattern to ensure good potential difference and potential contrast of both parts at the boundary between the image part and the non-image part, as well as the image resolution, and conversely, it is the best pattern for evaluating these. It can be said that the pattern.

As is clear from this characteristic diagram, the valley of the relative potential gradually decreases as the pixel frequency duty increases, and the crest of the relative potential gradually decreases accordingly. And, the difference between the valley and the peak of the relative potential that not only affects the image quality itself but also the potential contrast of both parts at the boundary between the image part and the non-image part,
It changes according to the pixel frequency duty. Therefore, the pixel frequency duty is one of the conditions for improving the potential difference and the potential contrast of both parts at the boundary, and by extension, the resolution of an image obtained by visualizing this pattern and the sharpness of characters. Recognize.

Further, in FIG. 3, when a level a which is an example of the relative potential of the visualization level (corresponding to the developing bias value used in the developing device) in positive-positive recording is used and the pixel frequency duty is 100% It is also understood that the black line width b and the white line width c are shown as an example depending on the pixel frequency duty (of course, each line width b, c also depends on the visualization level). . Therefore, the pixel frequency duty, together with the visualization level,
It can also be seen that this is one of the conditions for setting the black and white line widths to appropriate values.

Further, in this characteristic diagram, the relative distance in the sub-scanning direction on the horizontal axis corresponding to the boundary between pixels in the sub-scanning direction is an integer (for example,
2.0) corresponds to the inclination of the latent image potential on the photoconductor at the above-mentioned boundary and corresponds to the density gradation at the boundary as will be described later with reference to FIGS. 5 and 6. Of the image portion and the sharpness of the edge of the image portion determines the potential difference between the image portion and the non-image portion and the magnitude of the potential contrast at the boundary. The inclination of the characteristic line in such a portion changes from an increasing tendency to a decreasing tendency as the pixel frequency duty increases in the range of 10% to 150%,
The pixel frequency duty that gives the peak is 10 to 150%
It can be seen from the fact that the proper value exists within the range of the pixel frequency duty.

Here, in selecting an appropriate value of the pixel frequency duty, first, from the viewpoint of exposure unevenness in the main scanning direction, the ratio of the beam diameter to the pixel pitch in the main scanning direction (hereinafter referred to as the relative beam diameter) is set. It is necessary to specify the appropriate range. That is, linear stripes generated in the sub-scanning direction of a recorded image due to exposure unevenness in the main scanning direction (in the method of visualizing the non-exposed portion, linear stripes of the color of the visualized material (toner) in the non-image portion, Further, in the method in which the exposed portion is visualized, it is necessary to set the relative beam diameter so that a linear stripe due to the color of the recording paper does not appear in the image portion.

FIG. 4 is a characteristic diagram showing the relationship between the exposure unevenness in the main scanning direction and the relative beam diameter when all the lines in the sub scanning direction are exposed. In this characteristic diagram, the horizontal axis represents the relative beam diameter, and the vertical axis represents the peak of the surface potential of the photoconductor when the above exposure is performed with respect to the surface potential of the photoconductor when the exposure energy is zero (potential of the underexposed portion). ) Is taken as the relative potential of each. From the viewpoint of preventing exposure unevenness in the main scanning direction, the relative potential shown in this figure is set to about 0.2.
It has been found desirable to do the following: Therefore, it can be seen from the figure that it is desirable to set the relative beam diameter to a value of about 1.0 (lower limit value) or more.

Next, under the condition that the relative beam diameter is set to about 1.0 or more, a sufficient potential difference and potential contrast between the image part and the non-image part are obtained at the boundary between the image part and the non-image part for the pattern of FIG. Can get good resolution of
An appropriate range of pixel frequency duty will be described.

FIG. 5 shows the ratio of the potential difference between peaks and valleys (hereinafter referred to as relative potential difference) to the surface potential of the photoconductor when the exposure energy is zero, and the exposure pattern of FIG. It is a characteristic view which shows the relationship with the pixel frequency duty of the existing beam. In this characteristic diagram, the vertical axis represents the relative potential difference and the horizontal axis represents the pixel frequency duty.
Further, as a parameter, the relative beam diameter of the beam used for exposure of the pattern is changed, and the above relationship is shown for the pattern exposed using the beam of each relative beam diameter. Regarding this relative potential difference, the greater this is, the greater the difference between the density of the visualized material (toner) in the image area and the density of the non-image area becomes, resulting in a clearer image (sharp image of light and shade). From this viewpoint, it has been found that it is desirable that the relative potential difference has a value of about 0.6 or more. Therefore, this about 0.
Since a relative potential difference of 6 or more is secured, and the relative beam diameter of the exposure beam is set to about 1.0 or more,
The shaded area in the figure, that is, 10 to 110% is the appropriate range of pixel frequency duty.

Furthermore, FIG. 6 shows the exposure pattern of FIG.
Potential contrast (expressed as (potential of peak-potential of valley) / (potential of peak + potential of valley) from potential of peak and valley in FIG. 3)) and pixel of beam used for exposure of the above pattern It is a characteristic view which shows the relationship with a frequency duty. In this characteristic diagram, the vertical axis represents the potential contrast and the horizontal axis represents the pixel frequency duty. Also, as a parameter,
The above relationship is shown for the pattern exposed by using the beam of each relative beam diameter by changing the relative beam diameter of the beam used for the exposure of the pattern. Regarding this potential contrast, the larger this is, the larger the density gradient at the boundary between the image portion and the non-image portion becomes,
It is possible to obtain a sharp image of the image part edge (sharp image of the image part edge) in which the density changes more rapidly at this boundary part, and from this point of view, the value of the potential contrast can be about 60% or more. Proved to be desirable. Therefore, since the potential contrast of about 60% or more is secured and the relative beam diameter of the exposure beam is set to about 1.0 or more, the shaded portion in the figure, that is, 20 to 140% is the pixel frequency duty. It becomes the proper range of.

From the relationship between FIG. 5 and FIG. 6 described above, the pixel frequency duty for obtaining the sufficient resolution of the image and the potential contrast at the boundary between the image part and the non-image part can be sufficiently secured. It can be said that the range of 20 to 110%, that is, the range in which the pixel frequency duty Td satisfies the following equation.

0.2 ≦ Td ≦ 1.1 Therefore, in the image recording method of the present invention, in exposure by irradiating the photoconductor with the light beam modulated according to the pulse width corresponding to the image information through the imaging optical system in the main scanning direction. The exposure beam diameter is set to a predetermined value so that the relative beam diameter of is within 1.0 or more, and the pixel frequency duty Td satisfies the above formula at the boundary between the image part and the non-image part. The pulse width of light modulation corresponding to the image information is changed. As a result, it is possible to perform image recording with a high contrast and a high resolution regardless of whether positive-positive recording that visualizes an unexposed portion or negative-positive recording that visualizes an exposed portion. Experimentally, in recording that visualizes the non-exposed portion, the pixel frequency duty is 60
The best image could be obtained at 70%.

In the above description, only the pixel frequency duty that greatly affects the quality of the recorded image is focused, but the quality of the recorded image is determined by many other factors such as scanning speed, beam power, and visualization potential. Therefore, in order to obtain a higher quality image, it is necessary to select an appropriate value of the pixel frequency duty after considering each of these factors.

Although various means are conceivable as means for specifically carrying out the present invention, they are not particularly shown here, but the exposure time with respect to one pixel scanning time at the boundary between the image portion and the non-image portion according to the image information. It can be easily executed by changing the ratio of, that is, the pulse width of the image information.

〔The invention's effect〕

As described above, according to the image recording method of the present invention, the exposure beam diameter is set to a predetermined value so that the relative beam diameter in the main scanning direction falls within the range of about 1.0 or more, and the image portion and the non-image portion are At the boundary, by changing the pulse width of the light modulation corresponding to the image information so that the ratio of the exposure time by the light beam to the one-pixel scanning time in the sub-scanning direction becomes a predetermined value within the range of 0.2 to 1.1, It is possible to sufficiently secure the potential difference and the potential contrast between the image portion and the non-image portion at the boundary.
Therefore, the resolution is high, and it is possible to prevent the edge portion of the image from being blurred and impairing the sharpness of the image as in the conventional case.

For example, even when the linear image portions are close to each other at a minute interval, such as the character "Todoroki" shown in FIG. 7, it is possible to satisfactorily record in a small size such as 6 points. In other words, when recording a character of "Todoroki" with a size of 6 points at 300 dpi, only the "car" portion is enlarged in FIG. 7, and the grid is also shown to show the pixel size. A portion where white and black lines are lined up for each pixel occurs in the sub-scanning direction indicated by arrow d. According to the recording method of the present invention, good resolution can be ensured even in a pattern that is exposed every other pixel in the sub-scanning direction as described above, and even in a pattern that is the most difficult to obtain. it can.

The invention of an image recording method disclosed in the above-mentioned Japanese Patent Laid-Open No. 56-8112 for solving the problem of "image thinning" in positive-positive recording is described in the main scanning direction, which is the premise of the present invention. The light emitted from the minute light emitting segment by each pixel unit arranged is modulated according to the pulse width corresponding to the image information, and the modulated light is imaged on the surface of the pre-charged photosensitive member which is sub-scanned and fed. Even if it is simply applied to an optical scanning type electrophotographic recording apparatus that performs recording according to image information by exposing through a light source, it is preferable even when the black and white lines are lined up for each pixel as described above. It is not possible to obtain the effect that the resolution can be obtained.

Hereinafter, this point will be specifically described with reference to FIG. FIG. 8 shows the latent image potential distribution in the main scanning direction when the exposure pattern of FIG. 3 is formed by using the beams with pixel frequency duty of 100%, 60%, and 10%, respectively. This is the same as FIG. 3. In addition, FIG. 8 also shows a pulse e for beam modulation (exposure with H, non-exposure with L) and beam spots f and g in the case of image frequency duty of 100% in positive-positive recording. There is.

When the image frequency duty is 100%, the beam spot f generated at the point of the relative distance 1.0 in the sub-scanning direction when the pulse e is turned on moves in the sub-scanning direction indicated by the arrow d, and the pulse e is turned off. The same relative distance of 2.0
Disappears at the point. Then, as the pulse e is turned on again, a beam spot occurs at the same relative distance of 3.0,
This moves to the same relative distance of 4.0 and disappears. By the movement of the beam spot during this period, the beam intensity distribution (Gaussian distribution) at each value of the moving beam spot is shown.
The energy to be exposed is spatially integrated as shown in FIG. The potential of the charged photoreceptor is attenuated according to the energy. As a result, as shown in FIG. 8, a relative potential distribution from the point of the same relative distance of 1.0 to the same relative distance of 4.0 at the image frequency duty of 100% is obtained.
9 (b) and 9 (c) schematically show the state of exposure by moving the beam spot as in FIG. 9 (a), for the case of image frequency duty of 10% and 60%, which will be described later. It is shown.

Here, when the pixel frequency duty is 100%, the visualization level corresponding to the relative potential of level h shown in the characteristic diagram of the latent image potential distribution in FIG. 8 is set (corresponding to this relative potential. When the developing bias is set to), only the portion having the width i is visualized in the portion having the relative distance of 2.0 to 3.0 corresponding to the image portion. Therefore, the visible image pattern P1 as shown in FIG. 8 is obtained. The phenomenon in which the developed width is narrower than the width corresponding to the image portion of the pulse e is the above-mentioned phenomenon of "the image becomes thin".

On the other hand, when exposure is performed at an image frequency duty of 10%, for example, the beam spot f generated at the same relative distance of 1.0 moves to a point of the same relative distance of 1.1 (a point moved by 10% of one pixel from the same relative distance of 1.0). Disappears, then the same relative distance
It occurs at the point of 3.0, moves to the same relative distance of 3.1, and disappears.
Due to the movement of the beam spot during this period, the exposed energy is spatially integrated as shown in FIG. 9B, and the image frequency duty is 10% as shown in FIG.
In the case of, the relative potential distribution from the point of the same relative distance of 1.0 to the same relative distance of 4.0 is obtained.

As is clear from the latent image potential distribution when the image frequency duty is 10%, the visualization level is 100% above the duty.
In the case of%, the potential becomes higher than the relative potential corresponding to the visualization level at all points at the same relative distance, and all points are visualized. As a result, it is not an image in which white and black lines are lined up, but the visualization pattern 2 in FIG.
The image is recorded as a continuous black image.
That is, it is not possible to exhibit the resolution enough to record an image in which white and black lines are lined up for each pixel. Then, the image recording method disclosed in the above-mentioned Japanese Patent Laid-Open No. 56-8112, that is, by changing the width of the modulation pulse, the width in the main scanning direction of the non-exposed portion on the photosensitive member which becomes the image portion is made relatively small. The invention of the image recording method is to widen only by modulating the light generated by the minute light emitting segment by each pixel unit arranged in the main scanning direction, which is the premise of the present invention, according to the pulse width corresponding to the image information. Then, the modulated light is simply applied to an optical scanning type electrophotographic recording device for performing recording according to image information by exposing the precharged photoconductor surface, which is sub-scanned and fed, through an imaging optical system. In this case, such an embodiment that leads to the same result as the recording when the image frequency duty is 10% is included.

On the other hand, according to the image recording method of the present invention, good resolution can be obtained even in the pattern in which the best resolution is most difficult to be obtained, which is exposed every other pixel in the sub-scanning direction as described above. For example, when the image frequency duty is 60%, for example, a portion indicated by the width j in FIG. 8 is visualized, and portions not visualized remain at both ends of the portion in the sub-scanning direction. Therefore, an image in which white and black lines are lined up can be recorded as shown as a visualization pattern 3 in FIG.

[Brief description of drawings]

FIG. 1 is a simplified configuration diagram showing an optical scanning type electrophotographic recording device using a fluorescent dot array tube as a light source. FIG. 2 is a perspective view showing a configuration example of a fluorescent dot array tube. FIG. 3 is a characteristic diagram of relative potential with respect to relative distance for a pattern exposed every other pixel in the sub-scanning direction. FIG. 4 is a characteristic diagram of the relative potential with respect to the relative beam diameter when the entire line in the sub-scanning direction is exposed. FIG. 5 is a characteristic diagram of relative potential difference with respect to pixel frequency duty for a pattern exposed every other pixel in the sub-scanning direction. FIG. 6 is a characteristic diagram of potential contrast with respect to pixel frequency duty. FIG. 7 is an explanatory diagram of an example of a recorded image. FIG. 8 is an explanatory diagram of the relationship between the movement of the beam spot and the latent image potential. FIG. 9 is an explanatory diagram of the state of exposure by moving the beam spot. 1 ... Fluorescent dot array tube 2 ... Imaging optical system 3 ... Charging device 4 ... Photoconductor 5 ... Developing device 6 ... Transfer device 7 ... Recording paper 8 ... Cleaner

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04N 1/23 103 A 9186-5C 1/29 Z 9186-5C

Claims (1)

[Claims] 1. Light generated by a minute light emitting segment for each pixel unit arranged in the main scanning direction is modulated in accordance with a pulse width corresponding to image information, and the modulated light is pre-charged by sub-scan feed. In an optical scanning type electrophotographic recording apparatus for performing recording according to image information by exposing the exposed photoconductor surface through an imaging optical system, the relative beam diameter, which is the ratio of the diameter of the exposure beam to the pixel pitch, and the exposure Relative potential difference, which is the ratio of the potential difference between the peak of the photoconductor surface potential and the valley of the peak in the pattern in which the pixel to be exposed and the pixel not to be exposed are in the sub-scanning direction, and the surface potential of the photoconductor when the exposure energy is zero, and The potential contrast between the peaks and valleys,
From the relationship between the three, the relative beam diameter in the main scanning direction is almost 1.
The exposure beam diameter is set to a predetermined value so that it falls within the range of 0 or more, and at the boundary between the image portion and the non-image portion in the sub-scanning direction, the exposure by the minute light emission segment for one pixel scanning time in the sub-scanning direction is performed. By changing the pulse width of the light modulation corresponding to the image information so that the time ratio becomes a predetermined value within the range of 0.2 to 1.1, the boundary between the image part and the non-image part becomes sharp An image recording method characterized by.