JPH09193453A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regenerate a high-quality image in both main scan and subscan directions. SOLUTION: A group of vertical linear images with a reference density Do and a three pixel width is formed to detect a density Dv1 and a group of horizontal linear images is formed to detect a density Dh1 (100-110). n electric current value for forming a horizontal linear image is increased and decreased until the density Dv1 coincides with the density Dh1, and the electric current value is stored when both densities meet each other (112-120). A group of vertical linear images with a reference density Do and 3, 5 pixel widths is likewise formed to detect a density Dv2 and a group of horizontal linear images is formed to detect a density Dha (122-128). Further, an electric current value for forming a horizontal linear image is increased and decreased until the density Dv2 coincides with the density Dha, and the electric current value is stored when both densities meet each other (130-138). Consequently, it is possible to maintain the balance between the image width in a main scan direction and the image width in a subscan direction by switching the intensity of a laser beam at the end part of the subscan 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 that forms an image by scanning a light beam.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser beam printer, a digital copying machine or a facsimile, a light beam such as a laser beam emitted from a gas laser or a semiconductor laser is predetermined by a rotating polygon mirror. Direction, main scanning is performed, and the light beam reflected by the rotating polygon mirror is moved in a direction orthogonal to a predetermined direction on the image forming surface of the photoconductor or the like, or an element such as a galvanomirror The light beam is deflected by the sub scanning. As an optical system for converging a light beam deflected by a polygon mirror in a state of constant velocity linear motion, an optical system including an fθ lens or the like is mainly used.

Therefore, the light beam is main-scanned (deflected) in a predetermined direction by the rotation of the polygon mirror, and the photosensitive member is exposed after the scanning speed is corrected by the fθ lens.
The photoconductor is formed, for example, in a cylindrical shape, and is rotated by step drive or rotated at a constant speed. By the rotation of the photoconductor, the exposed portion of the photoconductor is scanned in the direction substantially orthogonal to the main scanning direction, so the rotation of the photoconductor corresponds to the sub-scanning. By performing these main scanning and sub-scanning, the photoconductor can be exposed two-dimensionally. An image can be formed (exposed) on the photoconductor by turning on / off the light beam in synchronization with the main scanning and the sub-scanning.

As described above, in the image forming apparatus for forming an image by performing the main scanning and the sub-scanning with the light beam, the main scanning direction is 1
By controlling the on / off of the light beam during the main scanning, the resolution and gradation can be improved.

For example, there is known an image forming apparatus for forming an image by so-called pulse width modulation, which controls the blinking time of the light beam with respect to the light beam scanning at a constant speed in the main scanning direction (Japanese Patent Application Laid-Open No. 2000-242242). (See Japanese Laid-Open Patent Publication No. 62-233979). In this image forming apparatus, in order to maintain high gradation, the minimum pulse width and the maximum pulse width are determined according to the image processing characteristics of the apparatus, and the pulse width of the input digital image signal is adjusted. Therefore, the position of the image can be set in the main scanning direction.

However, according to this technique, the signal having the adjustable pulse width in the pulse width modulation is limited by the predetermined period determined according to the pixel size. Further, the pulse width modulation is reflected in image formation in the main scanning direction,
It cannot be applied to image formation in the sub-scanning direction. That is, in the sub-scanning direction, since the exposure is intermittently performed in each main scanning by stepwise driving or rotating the photosensitive member at a constant speed, the resolution in the sub-scanning direction cannot be improved. In order to improve the resolution in the sub-scanning direction, it is possible to step-drive the photoconductor with a small amount of movement or move the photoconductor at a low speed, but this leads to an increase in the image forming time, Not at all.

In order to solve this problem, the light beams are scanned and exposed so that the adjacent light beams partially overlap with each other, and the intensity of the light beams is changed (intensity modulation) to form an image in the sub-scanning direction. A technique for controlling the width is known (see Japanese Patent Laid-Open No. 6-91929). In this technique, by setting the intensity of the light beam at the end in the sub-scanning direction, the position of the image end in the sub-scanning direction is controlled, and the transition of the formed image is spatially set with high spatial position setting accuracy. doing.

By using these image forming apparatuses, images to be formed can be set with desired positional accuracy in both the main scanning direction and the sub scanning direction, and high quality images can be reproduced.

[0009]

However, in the case where the position setting of the image to be formed in the main scanning direction is realized by the on / off control of the light beam as in the conventional image forming apparatus, the main scanning direction and the sub scanning direction are Even when trying to form an image with the same width, due to the conditions such as the fluctuation of the scanning speed of the light beam and the developing process for making the image visible,
The formed images are formed with different widths.

Further, the intensity of the light beam is changed (intensity modulation).
Then, in the image forming apparatus that controls the image width in the sub-scanning direction,
With respect to the intensity change when the intensity of the light beam is changed due to changes in characteristics such as the beam diameter of the light beam, the scanning pitch, the sensitivity of the photoconductor, the intensity of the light beam (light intensity), and the development potential during development processing due to changes over time. The amount of change in the image width in the sub-scanning direction changes.

Therefore, in the conventional image forming apparatus, even if an image having the same width in the main scanning direction and the sub scanning direction is formed, the formed image varies in both the main scanning direction and the sub scanning direction. Therefore, the quality of the obtained image is deteriorated.

In view of the above facts, an object of the present invention is to obtain an image forming apparatus capable of reproducing an image with high image quality in both the main scanning direction and the sub scanning direction.

[0013]

In order to achieve the above object, an image forming apparatus of the present invention comprises a light beam emitting means for emitting a light beam, and scanning exposure of the light beam in a predetermined main scanning direction. Scan exposure is performed in the sub-scanning direction that intersects the main scanning direction, and a light beam having a predetermined beam diameter larger than the scanning interval when scanning in the sub-scanning direction is made to partially overlap adjacent light beams in the sub-scanning direction. Scanning light condensing means for condensing on the photoconductor, emission time changing means for changing the emission time of the light beam, intensity changing means for changing the intensity of the light beam, and an exposure unit in the main scanning direction. The amount of change in the position of the boundary due to the control of the emission time of the light beam at the predetermined position in the main scanning direction on the photoconductor when forming the boundary with the unexposed portion, and the sub-scan corresponding to the boundary in the main scanning direction. Direction dew The emission time so that the change amount of the boundary position due to the control of the intensity of the light beam at the predetermined position in the sub-scanning direction on the photoconductor when the boundary between the unexposed part and the unexposed part is substantially equal to And a control means for controlling the strength changing means.

According to a second aspect of the present invention, the control means forms the boundary so that an image in which the image width in the main scanning direction and the image width in the sub scanning direction substantially match each other is formed on the photoconductor. The intensity of the light beam corresponding to can be set.

As described in claim 3, a first region having a plurality of line segments having a predetermined length and a constant width in the sub-scanning direction, and a predetermined length and a constant width in the main scanning direction. It is possible to previously detect the average density of each of the second areas in which a plurality of line segments are formed, and set the intensity of the light beam corresponding to the boundary so that the detected average densities substantially match. .

According to the image forming apparatus of the present invention, the boundary between the exposed portion and the unexposed portion in the main scanning direction is formed by controlling the emission time of the light beam at the predetermined position in the main scanning direction on the photoconductor. The amount of change in position is controlled so as to substantially match the amount of change in position of the boundary in the sub-scanning direction corresponding to the boundary in the main scanning direction, which is formed by controlling the intensity of the light beam. In this way, at the boundaries between the exposed and unexposed portions in the main scanning direction and the sub-scanning direction, the amounts of change in the positions of the boundaries due to control match. Therefore, since the boundary can be formed with a change amount that is substantially the same in both the main scanning direction and the sub scanning direction, both the main scanning direction and the sub scanning direction can be set in substantially the same position, The quality of the resulting image is improved.

As described in claim 2, the control means corresponds to the boundary so that an image in which the image width in the main scanning direction and the image width in the sub scanning direction substantially match is formed on the photoconductor. The intensity of the light beam can be set. Therefore, an image in which the image width in the main scanning direction and the image width in the sub scanning direction substantially match is always formed on the photoconductor with the image width substantially matching. By doing so, the image width in either the main scanning direction or the sub-scanning direction cannot change, so that the quality of the obtained image is improved.

Further, as described in claim 3, a first region in which a plurality of line segments having a predetermined length and a constant width are formed in the sub-scanning direction, and a predetermined length and a constant width in the main scanning direction are provided. The average density of each of the second region and the second region in which a plurality of line segments are formed is detected in advance. Each average density represents the tendency of the image in the main scanning direction and the sub scanning direction. Therefore,
By setting the intensity of the light beam corresponding to the boundary so that the detected average densities are substantially the same, it is possible to form a good image in which the image width does not change in either the main scanning direction or the sub scanning direction. You can

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an optical scanning device 40 which constitutes an exposure section of a laser printer which is an image forming apparatus according to this embodiment. Optical scanning device 4 of the present embodiment
Reference numeral 0 denotes a laser light source 42, and a collimator lens 44 and a polygon mirror 4 are provided on the emission side of the laser light source 42.
6 are arranged in order. The laser light source 42 is connected to a control device 58 (details will be described later) including a microcomputer. The polygon mirror 4
6 is rotated at a constant speed by a control device 58 in a predetermined direction (arrow B direction in FIG. 1). Therefore, the laser beam emitted from the laser light source 42 is collimated by the collimator lens 44 and is rotated by the polygon mirror 46 to be main-scanned (deflected) in a predetermined direction (direction of arrow M in FIG. 1) on the photoconductor.

An fθ lens 48 is provided on the reflection side of the polygon mirror 46 to correct the incident laser beam to a constant scanning speed, and a reflection mirror 56 is provided downstream of the fθ lens 48. There is. This reflection mirror 5
A cylindrical photoconductor 54 is provided on the reflection side of 6.
Therefore, the scanning speed of the laser beam scanned by the polygon mirror 46 is corrected by the fθ lens 48, and then the photoconductor 54 is exposed through the reflection mirror 56. A linear scanning line is formed on the photoconductor 54 by the main scanning of the laser beam.

The photosensitive member 54 is rotated stepwise or at a constant speed in a predetermined direction (the direction of arrow A in FIG. 1) by the controller 58. Therefore, on the photoconductor 54, the laser beam is scanned by the rotation of the photoconductor 54 in a direction substantially orthogonal to the main scanning direction at the time of main scanning, and is sub-scanned.

In order to detect the image signal write timing signal (SOS) in the main scanning direction on the photoconductor 54, a position constituted by the pickup mirror 50 and the sensor 52 is located in the laser beam scanning region outside the photoconductor region. A detection sensor is provided.

The information (image) recorded on the photoreceptor 54 is visualized by developing means (not shown), and a visible image is formed on a copying material such as paper by transferring and fixing means (not shown). As the photosensitive member 54, a silver salt photographic photosensitive film may be used in addition to the electrophotographic photosensitive material, but it is desirable that the photosensitive characteristics exhibit high gamma characteristics.

Further, the image forming apparatus of this embodiment is provided with a density sensor 64 for detecting the density of the image from one side edge portion (on the left side of the paper in FIG. 1) of the photoconductor 54 ( Details will be described later).

As shown in FIG. 2, the control device 58 includes a laser driving device 6 including a microcomputer.
6 is provided. The laser driving device 66 is connected to a memory 68 for storing reference density Do and calibration data, which will be described later, as well as image data (all pixel data for one image). In this memory 68, reference density Do and calibration data, which will be described later, are stored in advance. Also,
The memory 68 stores all pixel data (image data) for one image supplied from an image data output device such as a host computer (not shown).

The laser driving device 66 has a function of performing pulse width modulation for generating a signal having a pulse width corresponding to pixel data and light intensity modulation for generating a signal of light intensity corresponding to pixel data ( It will be described later in detail), and is connected to the laser light source 42. The laser light source 4 has a pulse width and a light intensity corresponding to the signal output from the laser driving device 66.
2 is driven.

A density sensor 64 for detecting the density of the photoconductor is connected to the laser driving device 66.
The density sensor 64 may be a potential detector for detecting the latent image potential. In this case, the detected latent image potential value is converted into the density value of the image to be visualized, and this converted value is used as the density value. Further, the density value detected by the density sensor 64 may be an average density value in a minute area, or may be an average density value in units of a predetermined area.

A sensor 52 is connected to the laser driving device 66 via a synchronization detector 70. The memory 6 is synchronized with the synchronization signal output from the synchronization detector 70.
The image data is transmitted from 8 to the laser driving device 66.

As shown in FIG. 3, a laser driving device 66.
Includes a pulse signal processor 10. The pulse signal processor 10 is a circuit that generates a pulse signal for on / off controlling the laser light source 42 according to the input image data ID. The first input terminal 10J of the pulse signal processor 10 is connected to the memory 68 so that the image data ID is input. The second input terminal 10K is
It is connected to the sensor 70 so that a synchronization signal is input.

Although not shown, the pulse signal processor 10 includes a digital-analog converter, a generator for generating a screen signal having a triangular waveform, a comparator for comparing the input signal with the screen signal, and the like. The input digital image data ID is sequentially converted into an analog signal corresponding to the gradation (density) of the image data ID for each pixel for a predetermined time for one pixel, and this is compared with a screen signal. When the screen signal is larger than the analog signal, the pulse signal PW which is at the high level is output.
As the pulse signal PW is input, the pulse signal P
The output end 10Q that outputs W is connected to the control end 38G of the switch circuit 38. The switch circuit 38 becomes conductive when the high-level pulse signal PW is input.

Further, the pulse signal processor 10 has a signal S for operating switches 32, 34 and 36 which will be described later.
A selector 10A for outputting 1, S2 and S3 is provided. Although details will be described later, in order to output any one of the signals S1, S2, S3 from the selector 10A when calibrating the image width in the main scanning direction and the image width in the sub scanning direction,
The selector signal S is connected to the control terminal 10G of the pulse signal device 10.
The concentration processor 12 is connected so that E is input.

The concentration processor 12 is configured to include a microcomputer (not shown), and will be described later.
In order to make the image widths in the main scanning direction and the sub-scanning direction substantially coincide with each other, the laser light source 42 supplies a current corresponding to the density of the image end portion.
It is a circuit that performs processing for outputting to.

The input terminal and output terminal of the concentration processor 12 are connected to an input / output device of a microcomputer (not shown). The first input terminal 12J of the density processor 12 is connected to the memory 68 so that the reference density Do is input, and the second input terminal 12K is connected to the sensor 70 so that the synchronization signal is input. The input terminal 12M of is connected to the density sensor 64 so that the detected density Dx is input.

Further, the first output terminal 12 of the concentration processor 12
Q is connected to the reference end 14S of the comparator 14, and the second output end 12P is connected to the comparison end 14C of the comparator 14. The density processor 12 outputs the input reference density Do as the output signal D1 and the density Dx from the density sensor 64 as the output signal D2. The comparator 14 compares the signals input to the reference terminal 14S and the comparison terminal 14C, and compares the signals input to the reference terminal 14S with the comparison terminal 14S.
The difference value of the signal input to C is output as the comparison result. The output terminal 14Q of the comparator 14 is connected to the input terminal 16J of the up / down counter 16.

The up / down counter 16 is a counter circuit that raises or lowers the count value to the value of the comparison result according to the sign and the value of the input comparison result. That is, when D1> D2, the up / down counter 16
Increases the count value and stops at the value of the comparison result. On the other hand, when D1 <D2, it is lowered. The up-side output end 16U and the down-side output end 16D of the up-down counter 16 are equivalently connected to the respective input sides of the DA converters 18, 20, 22 for converting the input digital signal into an analog signal. There is. Therefore, the DA converter 18,
A digital signal having the same value output from the up / down counter 16 is input to each of 20 and 22.

The control terminals 18G, 20G and 22G of the DA converters 18, 20 and 22 are independently connected to the control output terminal F of the concentration processor 12. Concentration processor 1
From the control output terminal F of No. 2, the corresponding DA converters 18, 2
The latch signals R1, R2 and R3 are output to the control terminals of 0 and 22. Each of the DA converters 18, 20, and 22 includes a latch circuit (not shown), and each latch circuit (not shown) includes a concentration processor 12 to control ends 18G and 20G.
The value (output from the up / down counter 16) when the latch signals R1, R2, R3 are input to 22G is latched.

The output end 18Q of the DA converter 18 is connected to the control end 26G of the power supply 26 whose output current value is variable, and the power supply 26 outputs a current having a current value Ic1 corresponding to the analog value output from the DA 18. Output. Similarly, the output end 20Q of the DA converter 20 is connected to the control end 28G of the power supply 28, and the power supply 28 outputs the current of the current value Ic2 corresponding to the analog value output from the DA 20 and the DA converter 22.
The output end 22Q of the power supply 30 is connected to the control end 30G of the power supply 30, and the power supply 30 outputs a current having a current value Ic3 corresponding to the analog value output from the DA 22.

The output end 26Q of the power supply 26 is connected to the input end 38J of the switch circuit 38 via the switch 32. Similarly, the output end 28Q of the power supply 28 is connected to the input end 38J of the switch circuit 38 via the switch 34, and the output end 30Q of the power supply 30 is connected to the input end 38J of the switch circuit 38 via the switch 36. . Each of these switches 32, 34, 36 has a pulse signal processor 1
Signals S1, S2, S output from the selector 10A of 0
It operates (conducts) by 3.

Therefore, these switch circuits 32, 34,
The output sides of the switches 36 are commonly connected to the input end 38J of the switch 38, and the output side of the switch 38 is connected to the laser light source 42. Therefore, one of the selector signals (S1, S2, S3) is selected. ) Corresponding to the power supply 26,
A current output from any of the power sources 28 and 30 is switched by the switch 38 by the pulse width of the pulse signal PW output from the pulse signal processor 10 and is supplied to the laser light source.

The above-mentioned power sources are not limited to three as described above, but may be two, three, or five or more.

Here, the control of the image width in the main scanning direction and the control of the image width in the sub scanning direction will be described.

First, the case where the image width in the main scanning direction is controlled by changing the blinking time of the laser light will be described. FIG. 4 shows a partial image view of a text image formed when the laser light source 42 is driven with lighting times of three types of pulse widths in the main scanning direction and sub-scanning is performed four times with the same lighting time. .

As shown in FIG. 4A, when a main scan is performed in which a laser beam of a predetermined intensity is lit for a time ta, and four sub-scans are performed in the same lighting time, one main scan is performed. The laser light that exposes the photoconductor by scanning has a Gaussian shape indicated by the solid line 80 _a1 , and the photoconductor 54 is continuously exposed to the position of the laser light indicated by the solid line 80 _ax . Therefore, the laser light of the light energy indicated by the broken line 82 of the intensity where they are combined is exposed.

At this time, the exposure energy is the development threshold value Io.
Assuming that the portion exceeding the above is visualized by the development, as shown in the lower column of FIG. 4A, the image visualized after the development by the laser light by the four sub-scans is in the main scanning direction. , An oblique line portion including a range of the length La from the end portion P _a1 formed by the laser beam having the shape shown by the solid line 80 _a1 to the end portion P _ax formed by the laser beam having the shape shown by the solid line 80 _ax . Further, as shown in FIG. 4B, when the main scanning is performed in which the laser light of a predetermined intensity is lit for the time tb and the sub-scanning is performed four times in the same lighting time, the solid line 80 _b1 is used. From the Gaussian-shaped laser light shown, the solid line 8
The photosensitive member 54 is continuously exposed in the main scanning direction by the laser beam indicated by 0 _bx . In this case, as shown in the lower column of FIG. 4 (B), the image to be visualized after development, the solid line 80 from the end portion P _b1 formed by the laser beam having the shape shown by the solid line 80 _b1
The shaded portion includes the range of the length Lb up to the end portion P _bx formed by the laser beam having the shape indicated by _bx .

Similarly, as shown in FIG.
Main scanning is performed by turning on the intense laser light for time tc
When sub-scanning is performed four times with the lighting time of, each solid line
80 _c1The solid line 80 from the Gaussian-shaped laser beam shown in
_cxThe photosensitive member 5 is continuously exposed in the main scanning direction by the laser beam indicated by.
4 is exposed. In this case, it is shown in the lower column of FIG. 4 (C).
As you can see, the image that becomes visible after development is the solid line 80_c1Shape shown by
End P formed by a laser beam_c1To solid line 80_cx
End P formed by the laser beam having the shape _cxFor up to
The shaded portion includes the range of the length Lc.

As described above, by changing the pulse width for turning on the laser light source, the end position of the image in the main scanning direction can be changed. By changing the pulse width of the laser light in this manner, the edge portion (edge position) of the image, that is, the image width in the main scanning direction can be controlled.

At this time, since the laser beam for exposing the photosensitive member has a predetermined beam diameter, the laser beam has a pulse width corresponding to the scanning time converted on the photosensitive member to obtain a predetermined image width in the main scanning direction. When the light source is turned on, the exposed area becomes larger due to the beam diameter, and the image width becomes slightly longer. That is,
The line image in the sub-scanning direction having a predetermined image width in the main scanning direction becomes thick.

Next, a case will be described in which the image width in the sub-scanning direction is controlled by changing the intensity (intensity modulation) of the laser light that exposes the end portion in the sub-scanning direction. In FIG.
A partial image view of an image formed when the main scanning is performed three times in the sub-scanning at the scanning pitch PT is shown.

As shown in FIG. 5 (1), the three laser beams in the same sub-scanning direction have the same intensity (intensity Ia according to the current value Ic1 shown in FIG. 5 (2)), and the solid line 8 indicates the same.
It becomes the Gaussian shape shown by 0 ₁ , 80 ₂ , 80 ₃ ,
The photoconductor 54 is exposed to a laser beam of the light energy indicated by the broken line 82 of the combined intensity of the photoconductor 54. At this time, it is assumed that the portion where the exposure energy exceeds the development threshold value Io is exposed by the development, and exposure is performed for a time t ₁ ,
The image that is revealed after development by the third laser beam (Gaussian-shaped laser beam shown by the solid line 80 ₃ on the right side of the paper surface of FIG. 5) is an end portion formed by the second laser beam in the sub-scanning direction. becomes the hatched portion including the length range L ₁ from P ₁ to the end portion Pa, which is formed by the third laser beam (Fig. 5 (3) refer).

When the intensity of the third laser beam is decreased from the intensity Ia to the intensities Ib, Ic, and Id in this order, the position of the end (the right end in FIG. 5) where the combined exposure energy exceeds the development threshold Io is determined. It changes (moves from right to left in FIG. 5 (1)). Therefore, when the exposure is performed with the intensity Ib for the time t ₂ ,
The image that becomes visible after development by the third laser light is a shaded portion including the range of the length L ₂ from the end P ₁ to the end Pb, and if the time t ₃ is exposed with the intensity Ic, the third laser light Therefore, the image that becomes visible after development becomes a shaded portion including the range of the length L ₃ from the end P ₁ to the end Pc, and the time t
_{When the third and} subsequent portions are exposed with the intensity Id, the image that becomes visible after the development by the third laser beam becomes a shaded portion including the range of the length L ₄ from the end P ₁ to the end Pd (FIG. 5 (3)). reference). In this way, as the intensity of the laser light is reduced stepwise, the right edge of the image formed changes stepwise,
By changing the light intensity, the edge position of the text image can be changed from right to left. In this way, by changing the intensity of the laser light, the edge portion (edge position) of the image, that is, the edge portion position in the sub-scanning direction can be controlled.

FIG. 6 shows the calculation results of the relationship between the intensity of the laser beam and the end position of the third laser beam when the beam diameter and the scanning pitch are changed. In the figure,
The dotted line shows the result when the ratio between the beam diameter in the sub-scanning direction and the scanning pitch is 1.0. This ratio is a value obtained by dividing the beam diameter of the laser light represented by the full width at half maximum by the scanning pitch. Similarly, the solid line shows the result when the ratio is 1.36, and the alternate long and short dash line shows the result when the ratio is 2.0.

As described above, when the ratio changes, the relationship between the intensity of the laser beam at the end in the sub-scanning direction and the end position changes.
Therefore, when an image end portion is formed within the scanning pitch range, the formed end portion position changes according to the above ratio. For example, when the resolution is 800 dpi (dots / inch), the scanning pitch PT is about 0.032 mm,
When the beam diameter of the laser light is a full width at half maximum of 0.064 mm, the ratio is 2.0 (the characteristic indicated by the one-dot chain line in FIG. 6). In this case, the central position of the scanning pitch is 0.016 (=
When attempting to position the end position at 0.032 / 2) mm, the peak of the laser light intensity becomes about 0.4. When the scanning pitch PT is 0.044 mm (ratio 1.
36, the characteristic shown by the solid line in FIG. 6) The peak of the laser light intensity is about 0.53, and the scanning pitch PT is 0.032 mm.
At this time (ratio 1.0, characteristic indicated by the dotted line in FIG. 6), the peak of the laser light intensity is 0.68. Therefore, when trying to position the image end in the center of the scanning pitch PT,
It is necessary to set the intensity of the laser light that exposes the edge of the image to different numerical values depending on the difference in beam diameter. Therefore, the laser beams are arranged adjacent to each other on the photoconductor so that the images are continuous in the sub-scanning direction. Therefore, if the beam diameter of the laser beam corresponding to the scanning pitch PT determined from the resolution is determined, a predetermined image width is obtained in the sub-scanning direction. Therefore, when the intensity of the laser beam at the edge is changed, the edge position becomes short and the image width becomes short. That is, the line image in the main scanning direction having a predetermined image width in the sub scanning direction becomes thin.

Further, as can be understood from FIG. 6, by increasing this ratio, the linear characteristic is approximated, and by selecting the ratio of the beam diameter in the sub-scanning direction and the scanning pitch, the intensity of the laser beam The relationship with the position in the sub-scanning direction can be set linearly.

FIG. 7 shows an image formed by vertical and horizontal 5 × 5 pixels which is a corner portion of an image when the image widths of the image width in the main scanning direction and the image width in the sub scanning direction are adjusted stepwise. showed that. That is, the pixels at the ends in the main scanning direction (pixels in the region Ar1 in FIG. 7) form an image by adjusting the lighting time (pulse width), and the pixels at the ends in the sub-scanning direction (region Ar in FIG. 7).
Pixels within 2) form an image by adjusting the intensity of laser light. The adjustment of the pulse width and the intensity is performed by weighting each pixel. That is, in the example of FIG.
1, the weight of each pixel not included in Ar2 is 1, and the pixels 90A, 90B, 9 in the area Ar1 at the end portion in the main scanning direction.
0C, 90D, and 90E pixels include 1, 0.75, 0.
Pixels 90F, 90G, 90H, and 90 in the area Ar2 are attached in order of the weights of 5, 0.25, and 0 in the sub-scanning direction.
1, 0.75, 0.5, 0.2 for each pixel of I, 90E
Weights of 5 and 0 are added in order. Of the pixels included in the regions Ar1 and Ar2, only the pixel 90E is weighted in the main scanning direction and the sub-scanning direction, but the other pixels are weighted in either the main scanning direction or the sub-scanning direction. Is attached.

Each pixel in the area Ar1 is exposed with a lighting time (pulse width) substantially proportional to the weight, and each pixel in the area Ar2 is exposed with a laser beam intensity substantially proportional to the weight. As a result, an image in which the image width is reduced by approximately 1/4 in proportion to the weight in each direction should be formed. Area A at the end in the main scanning direction due to pulse width modulation
At r1, although a bulge due to the beam diameter of the laser light occurs to some extent (see FIG. 4), the position of the end portion approximately proportional to each weight is reproduced. However, at the end portion in the sub-scanning direction (the lower end portion on the paper surface of FIG. 7), it is reproduced at an uneven position with respect to the pixel weight due to the characteristic shown in FIG. Therefore, the balance between the image widths in the main scanning direction and the sub scanning direction is lost, and the image quality is degraded.

Here, the present inventor conducted an experiment in the case where the development threshold value was changed when the ratio of the laser beam intensity and the end position was constant (1.36), and The characteristics shown in 8 were obtained. In the figure, the solid line shows the result when the development threshold is 0.14, the one-dot chain line shows the result when the development threshold is 0.5, the dotted line shows the result when the development threshold is 0.75, The two-dot chain line shows the result when the development threshold is 1.0, and the three-dot chain line shows the result when the development threshold is 1.15. As can be understood from this result, as the development threshold increases, the exposed image portion gradually decreases, and the edge position becomes shorter. Therefore, it is understood that the end position changes when the developing conditions such as the time-dependent change and the temperature change change.

Considering the above points, the operation of the image forming apparatus of the present embodiment for maintaining the balance of the image widths in the main scanning direction and the sub-scanning direction and obtaining high image quality will be described. In the following description, an image extending in the sub-scanning direction, which is formed when the main scanning is performed so that the laser light source is turned on at a predetermined position in the main scanning direction, and the sub-scanning is called a vertical line image, is continuous. An image extending in the main scanning direction, which is formed when the main scanning is performed so that the laser light source is turned on and the sub scanning is performed a predetermined number of scanning pitches, is called a horizontal line image.

In this embodiment, a horizontal line image group consisting of a plurality of horizontal line images formed on the photoconductor 54 in a predetermined pattern (see the lower column of FIG. 10A) and a vertical line image consisting of a plurality of vertical line images. Image widths in the main scanning direction and the sub scanning direction are corrected by correcting the intensity of the laser light forming the end of the horizontal line image so that the densities of the respective regions of the group (see the upper column of FIG. 10A) become equal. To maintain the balance of.

First, when the image forming apparatus is powered on,
The image width correction routine shown in FIG. 9 is executed in the density processor 12 of the laser driving device 66, and in step 100, the entire surface of the photoconductor 54 is exposed to form a solid image having the same density on one surface.

In this step 100, the concentration processor 12
Reads the reference density Do, outputs the reference density Do as the output signal D1, and activates only the DA converter 18 with the latch signal R1. As a result, the DA converter 1
A current Ic1 corresponding to the analog signal from 8 is output from the power supply 26. At this time, the selector signal SE is output to the pulse signal processor 10 so that only the signal S1 is output from the pulse signal processor 10. As a result, the switch 32 is brought into a continuous conduction state (ON state), and the laser light source 38 is brought into a continuous lighting state (entire writing) by the current output from the power source 26. The density of the solid image thus formed is detected by the density sensor 64, and the density processor 12 outputs this density Dx as an output signal D2. As a result, the density D detected as the reference density Do in the comparator 14
x is compared, the output of the up / down counter 16 is increased or decreased until the detected density Dx becomes equal to the reference density Do, and the above processing is repeatedly executed.

In the next step 102, step 100
In the case of the solid image, the power source 26 which is the drive current of the laser light source when the reference density Do and the detected density Dx match
The latch signal R1 is output in order to hold the current value Ic1. For example, the latch signal is switched to inactivate the DA converter, and the value at the time of this switching is latched. As a result, the DA converter 18 receives the reference concentration Do.
In order to form a solid image with the
The digital value to output a current of 1 is latched.

In the next step 104, as shown in the pattern 92 of FIG. 10A, continuous lighting of three pixels (shaded area) and continuous extinction of three pixels (white area) are repeated for the main scanning. The same operation is performed for each sub-scan to form a vertical line image group. In this case, the laser light source 42 is driven by the current Ic1 output from the power supply 26. Next, step 1
At 06, the density of the formed vertical line image group is detected by the density sensor 64. The density of this vertical line image group is an average density obtained within a predetermined rotation time of the photoconductor, and this average density is stored in a storage device (not shown) as the density Dv1 of the vertical line image group. In the next step 108, FIG.
As shown in the pattern 94 of (A), it is possible to continuously turn on the light in the main scanning direction by the three sub scans 94A, 94B, 94C and turn off the light continuously by the next three sub scans 94D, 94E, 95F. Repeating is repeated in the sub-scanning direction to form a horizontal line image group. In this case, the laser light source 42 is driven by the current Ic1 output from the power supply 26. The sub-scan 94D functions to adjust the image width of the horizontal line image group, and the laser light source 42 is switched to be driven by the current Ic2 output from the power source 28. next,
In step 110, the density (average density) of the formed horizontal line image group is detected by the density sensor 64, and this average density is stored as the density Dh1 of the horizontal line image group.

Next, in step 112, the densities Dv1 and Dh1 are read from a storage device (not shown), and Dv1 = D
If the judgment is negative, and if the judgment is negative, the length of the image width of the horizontal straight line group is judged based on the shading.
At 4, it is determined whether Dh1 <Dv1. Dh1 <Dv1
In the case of, in order to increase the image width of the horizontal line image group, the current Ic2 output from the power source 28 is increased in step 118, and in the case of Dh1> Dv1, the image width of the horizontal line image group is decreased. The current Ic2 output from the power supply 28 is reduced. In this case, the density processor 12 outputs the vertical line image density as the output signal D1 and the density detected by the density sensor 64 as the output signal D1.
2 and outputs only the DA converter 20 to the latch signal R2.
Activate with. As a result, the current Ic2 corresponding to the analog signal from the DA converter 20 is output from the power supply 28. At this time, the selector signal SE is output to the pulse signal processor 10 so that only the signal S2 is output from the pulse signal processor 10 when performing the sub scan corresponding to the sub scan 94D. As a result, the switch 34 is turned on only when the sub-scanning corresponding to the sub-scanning 94D is performed, and the intensity of the laser light is changed to form an image. The density of the solid image thus formed is detected by the density sensor 64, the vertical line image density is compared with the detected horizontal line image density Dx in the comparator 14, and the detected horizontal line image density Dx is the vertical line image density. The output of the up / down counter 16 is increased / decreased until it becomes equal to, and the above processing is repeatedly executed.

On the other hand, when the affirmative determination is made in step 112, the densities match and the image widths of the horizontal line image group and the vertical image line group match, so in the next step 120, the power supply 28
The latch signal R2 is output in order to hold the current value Ic2. As a result, the DA converter 20 latches the digital value for outputting the current of the current value Ic2 from the power supply 28 to form the horizontal line image group and the vertical image line group having the matched image width.

By the above processing, the intensity of the end portion in the sub-scanning direction for obtaining the image width in the sub-scanning direction, which corresponds to the image width of a plurality of pixels to be formed in the main scanning direction, can be set. The following process is a process for making the image width in the main scanning direction and the image width in the sub scanning direction substantially coincide with each other when positioning the image end portion between the predetermined scanning pitches.

In step 122, since a vertical line image for 3.5 pixels is formed, as shown in a pattern 96 of FIG. 10B, a scanning time 96 for 3 pixels for one main scan is 96.
A, 96B and 96C are continuously turned on, and the scanning time 96D for one adjacent pixel is pulse width modulated corresponding to 0.5 pixel and the scanning time 96E and 96F for two pixels.
Is repeatedly turned off in the main scanning direction and then similarly performed for each sub-scanning to form a vertical line image group having a width of 3.5 pixels. In this case, the laser light source 42 is driven by the current Ic1 output from the power supply 26. Next, step 124
In, the density of the formed vertical line image group (average density)
Is detected by the density sensor 64, and this average density is stored in a storage device (not shown) as the density Dv2 of the vertical line image group.
In the next step 126, the pattern 98 of FIG.
As shown in, the sub-scanning 98A, 98B, 9 is performed three times consecutively.
The horizontal line image group is formed by repeating the continuous lighting in the main scanning direction at 8C and the continuous extinguishment at the next three successive sub scannings 98D, 98E and 98F in the sub scanning direction. In this case, the laser light source 42 is driven by the current Ic1 output from the power supply 26. Note that, similarly to the above, the sub-scan 98D functions to adjust the image width of the horizontal line image group, and the laser light source 42 is switched to be driven by the current Ic3 output from the power source 30. Next, in step 128, the density of the formed horizontal line image group (average density) is detected by the density sensor 64, and this average density is stored as the density Dh2 of the horizontal line image group. Next, at step 130, the densities Dv2, Dh are read from a storage device (not shown).
2 is read to determine whether or not Dv2 = Dh2. When a negative determination is made, it is determined at step 114 whether or not Dh2 <Dv2 because the length of the image width of the horizontal straight line group is determined based on the shading. When Dh2 <Dv2, the image width of the horizontal line image group is increased, so that the current Ic3 output from the power supply 30 is increased in step 136, and when Dh2> Dv2, the image width of the horizontal line image group is decreased. In step 134, the current Ic3 output from the power supply 30 is reduced. In this case, the density processor 12 outputs the vertical line image density as the output signal D1 and the density sensor 64.
The density detected in step 2 is output as the output signal D2, and only the DA converter 22 is activated by the latch signal R3. Thus, the current I corresponding to the analog signal from the DA converter 22
c3 is output from the power supply 30. At this time, the sub-scan 98
The pulse signal processor 10 when performing the sub-scan corresponding to D
From the selector signal SE so that only the signal S3 is output from
Is output to the pulse signal processor 10. As a result, the switch 36 is turned on only when the sub-scanning corresponding to the sub-scanning 98D is performed, and the intensity of the laser light is changed to form an image. The density of the solid image thus formed is detected by the density sensor 64, the vertical line image density is compared with the detected horizontal line image density Dx in the comparator 14, and the detected horizontal line image density Dx is the vertical line image density. The output of the up / down counter 16 is increased / decreased until it becomes equal to, and the above processing is repeatedly executed.

On the other hand, when the determination in step 130 is affirmative, the densities match and the image widths of the horizontal line image group and the vertical image line group match, so in the next step 138, the power source 30
The latch signal R3 is output to hold the current value Ic3. As a result, the DA converter 22 latches the digital value for causing the power supply 30 to output the current of the current value Ic3 in order to form the horizontal line image group and the vertical image line group of 3.5 image width.

By the above processing, the strength of the end portion in the sub-scanning direction for obtaining the 3.5 image width in the sub-scanning direction, which corresponds to the 3.5 image width to be formed in the main scanning direction, can be set. . Therefore, the intensity of the end portion in the sub-scanning direction can be set corresponding to the predetermined image width to be formed in the main scanning direction.

Therefore, by switching the intensity of the laser beam corresponding to the end portion in the sub-scanning direction to the intensity set by the above-mentioned current, it is possible to maintain the balance between the image width in the main scanning direction and the image width in the sub-scanning direction. Becomes

As described above, according to the image forming apparatus of the present embodiment, the densities of the vertical line image and the horizontal line image are detected, and the lasers at the end portions in the sub-scanning direction are detected so that the respective densities match. By changing the light intensity, it is possible to match the image width of the vertical line image and the image width of the horizontal line image, so when forming an image with the same image width in both the main scanning direction and the sub-scanning direction. In addition, it is possible to maintain the balance between the image width in the main scanning direction and the image width in the sub scanning direction. Therefore, the fluctuations of the image end portions in the main scanning direction and the sub scanning direction can be matched and reproduced, and a high-quality image can be obtained.

Further, since the difference in fluctuation of the image width between the main scanning direction and the sub-scanning direction is eliminated, the image width can be controlled with a higher precision than the scanning pitch which is predetermined structurally or by design, and a higher quality image can be obtained. Can be obtained.

Further, the densities of the formed vertical line image and the horizontal line image are detected, and the intensity of the laser beam at the end portion in the sub-scanning direction is changed so that the respective densities coincide with each other. Since the image width of the image and the image width of the horizontal line image are matched, even if the development threshold value changes, the image width can be controlled according to the changed development threshold value.
Higher quality images can be obtained regardless of the developing conditions.

In this embodiment, the image width of the horizontal line image is adjusted with reference to the image width of the vertical line image. However, the present invention is not limited to this, and the image width of the horizontal line image is not limited to this. The image width of the vertical line image may be adjusted with reference to. Further, the image width of the horizontal line image and the image width of the vertical line image may be adjusted with reference to a predetermined image width.

[0075]

As described above, according to the present invention, the emission time of the light beam at the predetermined position in the main scanning direction on the photosensitive member when the boundary between the exposed portion and the unexposed portion in the main scanning direction is formed. The amount of change in the position of the boundary by the control of and the light beam at the predetermined position in the sub-scanning direction on the photoconductor when forming the boundary between the exposed portion and the unexposed portion in the sub-scanning direction corresponding to the boundary in the main scanning direction Since the ejection time and the intensity are controlled so that the change amount of the boundary position due to the control of the intensity of the image and the intensity of the image are substantially matched, it is possible to suppress the variation between the image edge portion in the main scanning direction and the image edge portion in the sub scanning direction. Therefore, there is an effect that a high quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a control device.

FIG. 3 is a block diagram showing a schematic configuration of a laser driving device.

FIG. 4 is an explanatory diagram for explaining a phenomenon of image width reproduction in the main scanning direction by pulse width modulation.

FIG. 5 is an explanatory diagram for explaining a phenomenon of image width reproduction in the sub-scanning direction when the intensity of the laser beam at the end portion in the sub-scanning direction is modulated.

FIG. 6 is a diagram showing the relationship between the intensity of laser light and the end position in the sub-scanning direction.

FIG. 7 is a horizontal and vertical direction 5 for explaining the process of adjusting the image width.
It is an image figure which shows the partial image formed with x5 pixel.

FIG. 8 is a diagram showing the relationship between the intensity of laser light and the position of the image edge when the development threshold is changed.

FIG. 9 is a flowchart showing a flow of an image width correction routine in the laser driving device.

10A and 10B are diagrams showing a vertical line image and a horizontal line image formed by the image forming apparatus. FIG. 10A shows an image width of 3 pixels, and FIG. 10B shows an image width of 3.5 pixels.

[Explanation of symbols]

 40 Optical Scanning Device 42 Laser Light Source 58 Control Device 66 Laser Driving Device

Claims (3)

[Claims] 1. A light beam emitting device for emitting a light beam, and scanning exposure of the light beam in a predetermined main scanning direction and scanning exposure in a sub scanning direction intersecting the main scanning direction, and the sub scanning direction. Scanning light condensing means for condensing a light beam having a predetermined beam diameter larger than the scanning interval when scanning on the photoconductor so that a part of the adjacent light beams in the sub-scanning direction are overlapped, and the light beam is emitted. An emission time changing means for changing the time, an intensity changing means for changing the intensity of the light beam, and a main scanning direction on the photoconductor when forming a boundary between an exposed portion and an unexposed portion in the main scanning direction. The amount of change in the position of the boundary by controlling the emission time of the light beam at the predetermined position, and the photoconductor when forming the boundary between the exposed portion and the unexposed portion in the sub-scanning direction corresponding to the boundary in the main scanning direction. Upper sub-scan And the amount of change in the boundary positions by controlling the intensity of the light beam at a predetermined position of the direction, but the image forming apparatus having a control means for controlling the injection time changing means and intensity changing means so as to substantially coincide, the. 2. The intensity of the light beam corresponding to the boundary is formed so that an image in which the image width in the main scanning direction and the image width in the sub scanning direction substantially match each other is formed on the photoconductor. The image forming apparatus according to claim 1, wherein: 3. A first region in which a plurality of line segments of a predetermined length and a constant width are formed in the sub-scanning direction, and a second region in which a plurality of line segments of a predetermined length and a constant width are formed in the main scanning direction. 2. The image according to claim 1, wherein the average density of each area and the area is detected in advance, and the intensity of the light beam corresponding to the boundary is set so that the detected average densities substantially match. Forming equipment.