JP2000181172A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of correcting a deviation of scanning line with accuracy below the scanning line pitch unit even in the case of correcting the positional deviation of the gradation image, at a low cost and high speed. SOLUTION: This image forming device 10 is provided with resist detecting devices 44A and 44B respectively detecting each color mark formed on a transfer belt 42. The resist detecting device 44A is, allowed to use a position of the resist mark of the K color as a reference, to detect the positional deviation of another color, and to output into the image processing part 12 as resist data. In the image processing part 12, based on the resist data, the device is allowed to control exposing light quantity so as to make correction quantity of light beams with regard to the sub-scanning direction within 45% of the scanning pitch or in the range of 55% to 100%. Thus, even in the case of correcting the gradation image, the image can be reproduced in excellent accuracy.

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 photosensitive member with a light beam.

[0002]

2. Description of the Related Art Conventionally, there has been known an image forming apparatus which includes a plurality of light beam scanning devices for scanning with a light beam such as a laser beam and forms a color image. As such an image forming apparatus, each color (for example, black: K,
A light beam scanning device, a photoconductor, and the like provided for each of cyan (C), magenta (M), and yellow (Y);
2. Description of the Related Art There is an image forming apparatus in which a toner image of each color formed by each photoconductor is sequentially transferred onto a transfer belt in a superimposed manner, and then collectively transferred onto a sheet to obtain a color image.

The above-described light beam scanning device includes a laser diode (hereinafter, referred to as LD) for outputting a light beam, and a laser diode driver (hereinafter, referred to as LDD).
And outputs a light beam corresponding to the image data. Then, the light beam output from the LD is collimated by a collimator lens, and is incident on a polygon mirror via a cylinder lens or the like. After that, the light beam deflected by the polygon mirror makes the scanning speed constant by the f · θ lens, and performs main scanning on the charged photoconductor. The sub-scanning is performed by rotating the photoconductor at a constant speed in a direction orthogonal to the main scanning direction, and two-dimensional exposure is performed.
The exposed portion of the photoreceptor is applied with toner by a developing device, and the toner images of each color are sequentially transferred to a transfer belt by a transfer device, and then are collectively transferred to a sheet.

A light beam that scans each photoconductor is exposed at predetermined intervals determined by the moving speed of the transfer belt and the distance between the photoconductors. When the image data for each photoconductor is the same, or in an ideal state, the image positions of all colors on the transfer belt all overlap. However, in practice, the optical beam scanning device is displaced due to misalignment of optical components, misalignment of a photoconductor mounting portion, distortion of the entire device, or the like.

In order to correct the scanning position deviation, a predetermined image (hereinafter, referred to as a registration mark) is written at a predetermined position, and a registration detection device detects the registration mark position for each photoconductor and detects the position. There is known a technique for correcting a scanning position shift (registration shift) by moving or deforming an optical component or the like constituting a light beam scanning device based on information (JP-A-63-271275, etc.). ). However, in order to correct the scanning position by mechanical means, an actuator such as a stepping motor or a solenoid is required, which is generally expensive and has poor maintainability.

In order to solve this problem, various techniques have been proposed in which electric data processing and the amount of exposure light and exposure timing are devised without using a mechanical correction mechanism.

For example, Japanese Patent Application Laid-Open No. 4-326380 has means for indicating a deviation between an ideal scanning position and an actual scanning position, and at least a recording pattern to be exposed, There has been proposed a configuration in which either the amount or the exposure timing is corrected, and the scanning position is corrected in pixel units or less.

However, the technique described in Japanese Patent Application Laid-Open No. Hei 4-326380 is a registration correction technique that considers only line / text images. For example, when a gradation image is to be corrected, density unevenness or the like occurs. There's a problem.

When correcting the inclination or the bending of the scanning line, the correction amount in the sub-scanning direction needs to be different depending on the main scanning position. Is moved and corrected to reproduce a uniform density gradation image, the reproduction density becomes uneven depending on the main scanning position as shown in FIG. The cause will be described.

Generally, reproduction of a gradation image in an electrophotograph is realized by adjusting the lighting state of each pixel of a screen matrix in which a plurality of pixels are combined. When a dither screen and an error diffusion screen are used, a screen matrix or a part of the screen matrix is an image having only one pixel OFF portion (hereinafter, 1off).
For example, a pattern shown in FIG. 16 can be taken. When an angled line screen is used, a pattern including a 1off image, for example, as shown in FIG. 17 can be taken.

If the correction of a text image according to the prior art described above is applied to a gradation image as it is, and these 1off images are to be reproduced by correcting a positional shift of a distance corresponding to, for example, 0.5 scanning pitch, the following is required. Although it is possible to slightly lower the development density in a portion corresponding to the portion, there is a problem that a complete off portion cannot be formed and the portion is crushed. This problem will be described.

FIG. 6A shows an example of gradation image data. As shown in FIG. 6A, the weight of the image data in the sub-scanning direction (corresponding to the light beam exposure amount, that is, the image density) is 100 (ON) −.
0 (OFF) -100 (ON) -0 (OFF) ... That is, a 1off image exists every other pixel.

A plurality of pixels forming an image are formed by irradiating light so that adjacent light spots partially overlap in a chain. For example, as shown in FIG. 6B, the exposure energy given to six pixels along the line AA in FIG. 6A is the exposure energy given to six pixels individually. It becomes the combined exposure energy of the scanning light (shown by a thick line in the figure).

In order for the toner to adhere, as shown in FIG. 6B, an exposure energy not less than a certain exposure energy (development threshold value; for example, 0.6) is required, and is not less than the development threshold value. The toner adheres to a range of the following to form one pixel. An image exposed and developed with the exposure energy distribution as shown in FIG. 6B is as shown in FIG.

In a text image, a line image is usually formed from a plurality of adjacent pixels. Therefore, in a combined exposure energy distribution obtained by combining exposure energies for a plurality of pixels forming a line image, the magnitude of the exposure energy The line image formation position can be shifted by changing the exposure energy of the scanning light for forming the edge portion of the line image so that the edge position in the range equal to or higher than the upper development threshold value is shifted by the amount of position shift. it can.

However, this conventional text image correction method is applied to a 1off image shown in FIG.
For example, if it is attempted to correct and reproduce a positional deviation corresponding to a distance corresponding to 0.5 scanning pitch, as shown in FIG. 8C, the image is developed at a uniform low density and the OFF portion is not reproduced (hereinafter referred to as 1off collapse). ). This is because, when a conventional correction method for a text image is applied, when correcting a positional shift of 0.5 scanning pitch, the weight of the image data is reduced as shown in FIG.
This is because the exposure distribution is changed as shown in FIG. 8A and the exposure distribution becomes as shown in FIG. 8B, and the amount of exposure is uniformly insufficient over the entirety.

For the above reasons, when the gradation image is moved in the sub-scanning direction, the 1off portion in the above-described screen configuration is crushed, and the density varies. For example, as shown in FIG. 18, the relationship between the gradation level and the reproduction density (hereinafter referred to as gradation linearity) changes depending on the image movement amount in the sub-scanning direction. When different corrections are made, even if an attempt is made to reproduce a gradation image having a uniform density, unevenness occurs in the reproduction density.

Japanese Patent Application Laid-Open No. 9-39294 discloses that in order to correct this density unevenness, the positional deviation of a scanning line is corrected.
Although a configuration having a density shift correction unit for correcting density fluctuation when a gradation image is reproduced is described, basically, in the sub-scanning direction, position shift correction is performed in units of a scanning pitch, so that an angled It cannot be applied to a line screen, and further has the problem that the outline of a text image, a line image, and a gradation image rattles.

Further, as a method of correcting the density shift, the modulation data of the target dot of the image data subjected to the position shift correction is determined so that the density shift is reduced from the state of the modulation signals of a plurality of adjacent dots. In addition, there is a problem that a density shift correction unit using a look-up table or the like is required, and the circuit scale and processing time increase.

Further, it is not possible to perform image position movement and image position movement using intensity modulation in the sub-scanning direction with an accuracy equal to or less than the scanning pitch.

[0021]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is possible to accurately and accurately correct a scanning line shift at a scanning line pitch unit or less at a low cost and at a high speed. An object of the present invention is to provide an image forming apparatus capable of faithfully reproducing any of a line drawing, a text image, and a gradation image by the same data processing method.

[0022]

According to a first aspect of the present invention, an image is formed by scanning and exposing a photosensitive member with a light beam in a main scanning direction and a sub-scanning direction intersecting the main scanning direction in accordance with image data. Input means for inputting an amount of positional deviation of a scanning line formed by main scanning and sub-scanning from a reference line, and a first position to be exposed based on the input amount of positional deviation. And the second position adjacent to the first position to be exposed in the sub-scanning direction and the second position calculated by the adjacent scan are calculated, and the first position exposure value is calculated. And the calculated amount of exposure at the second position is determined so that the actual amount of exposure at the first and second positions is different from the calculated value of exposure at the first and second positions. Correction means for correcting

According to the first aspect of the present invention, there is provided an image forming apparatus for forming an image by scanning and exposing a photosensitive member with a light beam in a main scanning direction and a sub-scanning direction intersecting the main scanning direction in accordance with image data. , The input means inputs the amount of positional deviation of the scanning line formed by the main scanning and the sub-scanning from the reference line. As the input means, for example, a sensor for detecting the amount of displacement can be employed, but an input device such as a reading device or a keyboard which stores and reads the amount of displacement in a storage device may be used.

The correcting means calculates the exposure value of the first position to be exposed (to be exposed) based on the positional shift amount input by the input means, and calculates the first position to be exposed and the first position in the sub-scanning direction. An exposure calculation value at a second position at an adjacent second position and an adjacent scan by an adjacent scan is obtained, and a relationship between the exposure calculation value at the first position and the exposure calculation at the second position is obtained. In other words, when the exposure is performed using the calculated exposure value at the first position and the calculated exposure value at the second position to correct the position shift, the corrected image almost exactly reproduces the original image. Ask if the relationship makes it impossible to do so.

Then, the actual exposure amount at the first position and the second position is corrected so as to have a different relationship from the calculated value of the exposure amount at the first position and the second position. That is, the correction is performed so that the actual exposure amount at the first position and the actual exposure amount at the second position have different exposure amounts. For example, the exposure amount at the first position and the exposure amount at the second position after the correction have the same exposure amount, so that the corrected image does not have a uniform density.

According to a third aspect of the present invention, the correction means sets a distance between the adjacent first position and the second position in the sub-scanning direction as a scanning pitch, and sets the corrected image movement amount to the scanning pitch. 0% or more of the pitch and less than 45% or more than 55% of the scanning pitch and 10%
It is preferable that the correction be made to be within 0%. This makes it possible to accurately correct the positional deviation in units equal to or less than the scanning pitch, and also to correct the image including the above-described 1off image by 1off.
The original image can be reproduced almost faithfully without the occurrence of the f collapse. This correction may be performed by controlling the lighting time and lighting timing of the light beam.

[0027] Further, the correction by the correction means is performed according to claim 4.
As described above, N is an odd number of 3 or more, the interval between the adjacent first position and the second position in the sub-scanning direction is a scanning pitch, and the corrected image movement amount is the scanning pitch. It is preferable to make the unit 1 / N.

According to a second aspect of the present invention, there is provided an image forming apparatus for forming an image by scanning and exposing a photosensitive member with a plurality of light beams in a main scanning direction and a sub-scanning direction intersecting the main scanning direction in accordance with image data. An input means for inputting a shift amount of a scanning line formed by a main scan and a sub-scan from a reference line, and an exposure amount calculation of a first position to be exposed based on the input shift amount. And a second position adjacent to the first position to be exposed in the sub-scanning direction and an exposure calculation value at a second position by adjacent scanning are calculated, and the exposure calculation value at the first position and the second position are calculated. A correction for obtaining a relationship between the calculated exposure value of the position and the actual exposure amount of the first position and the second position so as to have a different relationship from the calculated value of the exposure amount of the first position and the second position. Means.

According to the second aspect of the present invention, an image is formed by scanning and exposing a plurality of light beams to a photoreceptor in a main scanning direction and a sub-scanning direction intersecting the main scanning direction in accordance with image data. In the forming apparatus, the input unit inputs a positional shift amount of a scanning line formed by main scanning and sub-scanning from a reference line. Further, the reference line can be any one of the scanning lines formed by scanning the plurality of light beams.

The correction means calculates the exposure value of the first position to be exposed (to be exposed) based on the positional shift amount input by the input means, and calculates the first position to be exposed and the sub-scanning direction. An exposure calculation value at a second position at an adjacent second position and an adjacent scan by an adjacent scan is obtained, and a relationship between the exposure calculation value at the first position and the exposure calculation at the second position is obtained. In other words, when the exposure is performed using the calculated exposure value at the first position and the calculated exposure value at the second position to correct the position shift, the corrected image almost exactly reproduces the original image. Ask if the relationship makes it impossible to do so.

Then, the actual exposure amount at the first position and the second position is corrected so as to have a different relationship from the calculated value of the exposure amount at the first position and the second position. That is, the correction is performed so that the actual exposure amount at the first position and the actual exposure amount at the second position have different exposure amounts. For example, the exposure amount at the first position and the exposure amount at the second position after the correction have the same exposure amount, so that the corrected image does not have a uniform density.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the correcting means is provided at a third position adjacent to the first position in the sub-scanning direction and at the third position. Third position adjacent to the second position and opposite to the sub-scanning direction
The exposure amount at the position and the exposure amount at the fourth position adjacent to the second position in the sub-scanning direction and the fourth position adjacent to the first position in the sub-scanning direction are calculated from the calculated exposure amount. Is also corrected to the increased value.

According to the fifth aspect of the invention, for example, when the image at the first position is on, the image at the second position is off, and the images at the third and fourth positions are on, When reproducing predetermined image data, an exposure amount at a third position adjacent to the first position in the sub-scanning direction and at a third position adjacent to the second position in the sub-scanning direction, A fourth position adjacent to the second position in the sub-scanning direction and a fourth position adjacent to the first position in the sub-scanning direction.
The exposure at the position is increased to a value that is larger than the calculated exposure, for example, a value that is larger than the exposure corresponding to a predetermined maximum density. Thereby, 1 of
The width of the f-image portion can be set to a substantially ideal width.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to the drawings. Hereinafter, a case where the present invention is applied to a so-called tandem type color image forming apparatus will be described.

FIG. 1A shows a color image forming apparatus 10 according to the present embodiment. The color image forming apparatus 10 includes an image processing unit 12 and converts the input image data into a laser modulation signal for each of four colors (K (black), C (cyan), M (magenta), and Y (yellow)). Are output to the light beam scanning device 14K, the light beam scanning device 14C, the light beam scanning device 14M, and the light beam scanning device 14Y, respectively.

The light beam scanning device 14K is an LDD 16K
And modulates the light beam emitted from the LD 18K (see also FIG. 2) by the laser modulation signal output from the image processing unit 12, and scans the photosensitive member 20K.

FIG. 2 shows the configuration of the light beam scanning device 14K. The light beam scanning devices 14C, 14C
Since the configuration is the same for M and 14Y, the description is omitted.

The light beam scanning device 14K includes an LD 18K. The light beam emitted from the LD 18K is converted into parallel light by the collimating lens 22, passes through the cylinder lenses 24 and 26, and returns to the polygon mirror 30 by the return mirror 28. Folded in the direction.

The polygon mirror 30 has a regular polygonal column shape and is rotated at a substantially constant angular velocity in the direction A in the figure by a motor (not shown). The light beam incident on the reflection surface of the polygon mirror 30 is deflected in a predetermined direction. , Fθ lens 32,
The light passes through 34 and is returned by the cylinder mirror 36 in the direction of the return mirror 38. The light beam that has been turned in the direction of the photoconductor 20K by the turning mirror 38 performs main scanning on the photoconductor 20K via the window glass 40.

The photoreceptor 20K is rotated at a substantially constant angular velocity in the direction of arrow B in the figure, whereby sub-scanning is performed. Toner exposed on the photoreceptor 20K in this manner is attached with toner by a developing unit (not shown), and the attached toner is transferred by a transfer unit (not shown) in FIG.
The image is transferred to the transfer belt 42 traveling in the direction.

Hereinafter, similarly, the light beam scanning device 14
M, 14C, and 14K, so that the photoconductors 20M, 20C, and 20
By scanning on K, toner images of cyan, magenta, and yellow are transferred to the transfer belt 42, and a color image is formed on the transfer belt 42.

The image forming apparatus 10 forms a registration mark for each color as shown in FIG. 1B at both ends in the width direction of the transfer belt 42 in order to detect a positional shift of the scanning line of each color. . In the case where the registration marks of the respective colors are in an ideal state in which no displacement occurs, FIG.
As shown in FIG. 3, they are formed at intervals D in the sub-scanning direction. The registration marks of the respective colors are detected by registration detection devices 44A and 44B disposed on the downstream side in the traveling direction of the transfer belt 42 and at both ends in the width direction of the transfer belt 42.

The registration detecting device 44A measures the time from the detection of the K color registration mark to the detection of the C color registration mark, based on the position of the K color registration mark. Similarly, the registration detection device 44B measures the time from the detection of the K registration mark to the detection of the C registration mark.

Based on the measured time and the moving speed of the transfer belt 42, the distance DL between the colors K and C in the sub-scanning direction at the left end of the transfer belt 42 and the sub-scanning direction at the right end of the transfer belt 42 in FIG. Distance D between K color and C color
M is calculated, and a deviation L (= D−D) at the left end of the transfer belt 42 from a predetermined ideal scanning position is calculated.
L) and the shift amount M (= D) at the right end of the transfer belt 42.
−DM) is calculated and output to the image processing unit 12 as registration data. This is performed similarly for the M color and the Y color. Note that the reference scanning line is not limited to the K color and may be another color.

FIG. 4 shows a schematic configuration of the image processing section 12. The image processing unit 12 includes a shift correction coefficient calculating unit 46.
It has. The shift correction coefficient calculator 46 calculates shift correction coefficients a and b based on the C color resist data output from the resist detection devices 44A and 44B. The shift correction coefficients a and b are calculated as follows.

A = ML, b = L (1) The calculated shift correction coefficients a and b are output to the main arithmetic unit 48. The main operation unit 48 calculates a shift correction amount dy based on the shift correction coefficients a and b. This deviation correction amount dY
Can be defined as follows, where X is the main scanning position.

DY = a.X + b (2) The main operation unit 48 is connected to the line memory 50 and the line memory 52, and receives the input image data D _0.
The data D ₂ obtained by performing a predetermined calculation based on the deviation correction amount dY is output to the line-in memory 50 and the data D _F2 is output to the line memory 52 (details will be described later). The line memories 50 and 52 are so-called FIFO (first in first out) memories. And the line memory 5
From 0, a laser modulation signal modulated according to the data D _F2 is output to the LDD 16K.

Although not shown in FIG. 4 for the sake of simplicity, the image processing section 12 includes line memories for M and Y in addition to the line memories 50 and 52 for C color. I have.

Next, the relationship between the amount of pixel movement and the amount of exposure will be described.

FIG. 19A shows ON-O in the sub-scanning direction.
An exposure profile of a pattern following FF-ON-OFF..., And FIG. 19B shows a relationship between a pixel movement amount and an exposure amount. In FIG. 19A, an image is formed in a section where the exposure amount is equal to or more than the development threshold. Here, ON-OFF-ON-OFF in the sub-scanning direction
.. Are faithfully reproduced as shown in FIG.
1 (OFF part) and W2 (ON part) must be equal. ON-OFF-ON-OF in the sub scanning direction
If it is attempted to move the pattern following F... By controlling at least one of the light beam exposure amount, lighting time, and lighting timing, ΔP (difference between the minimum exposure amount and the development threshold) is 19B, as shown in FIG. 19B, the value becomes 0 when the image movement amount becomes approximately 0.45 pixels regardless of the beam diameter. That is, when ΔP becomes 0, the 1off image is not reproduced and is collapsed. Also, when the image movement amount is 0.55 pixels, it is equal to the case where the image movement amount is -0.45 pixels, so that 0.45 to 0.55 (0.5 ± 0.
05) It can be seen that when the image is moved by one pixel, 1off collapse occurs.

Next, the operation of this embodiment will be described. In the following, for the sake of simplicity, a description will be given of a case where the positional shift of the C color is corrected, and the description of the correction of other colors will be omitted. As described above, the image movement amount (correction amount) in the sub-scanning direction is 0.45 to 0.45.
A description will be given of a case where a 1/3 scanning pitch is set so as not to be 0.55 (0.5 ± 0.05) pixels, and a shift correction range is set to one line.

First, registration marks of each color are formed on the transfer belt 42, and when the registration marks move in the sub scanning minus direction, the registration detection devices 44A and 44B
The registration marks are detected in the order of color and C color.

The registration detecting device 44A measures the time from the detection of the K color registration mark to the detection of the C color registration mark, based on the position of the K color registration mark. Similarly, the registration detection device 44B measures the time from the detection of the K registration mark to the detection of the C registration mark.

From the measured time and the moving speed of the transfer belt 42, the distance DL between the K color and the C color in the sub-scanning direction at the left end of the transfer belt 42 and the K color in the sub-scanning direction at the right end of the transfer belt 42 are calculated. The distance DM between the C colors is calculated.

Then, a shift amount L (= D-DL) at the left end of the transfer belt 42 from a predetermined ideal scanning position.
And the shift amount M (= D−D) at the right end of the transfer belt 42.
M) is calculated, and is registered as image data in the image processing unit 12.
Is output to the deviation correction coefficient calculator 46.

The shift correction coefficient calculator 46 calculates shift correction coefficients a and b according to equation (1) and outputs the calculated shift correction coefficients a and b to the main calculator 48.

Next, the control executed in the main arithmetic section 48 will be described with reference to the flowchart shown in FIG.

In step 100 shown in FIG. 5, the shift correction coefficients a and b calculated by the shift correction coefficient calculator 46 are input. In the next step 102, the main scanning direction position X is set to 0 (the left end side in FIG. 3), and in the next step 1
In step 04, the calculation of equation (2) is performed from the shift correction coefficients a and b input in step 100 to calculate the shift correction amount dY.

Then, in step 106, a correction amount dYs to be actually used for correction is set according to the deviation correction amount dY. This dYs is set as follows.

(1) 0 ≦ dY <0.333− (0.33
3 × 0.5): dYs = 0 (2) 1 / 3- (0.333 × 0.5) ≦ dY <0.6
In the case of 67− (0.333 × 0.5): dYs = 0.333 (3) 0.667− (0.333 × 0.5) ≦ dY <
In the case of 0.667+ (0.333 × 0.5): dYs = 0.667 (4) In the case other than the above (1) to (3): dYs = 1 As described above, dYs is 45 to 45 in the scanning pitch. Instead of 55%, 0 (0/3), 0.333 (1/3), 0.66
7 (2/3) and 1 (3/3), and the image movement resolution in the sub-scanning direction is set to 1/3 scanning pitch unit. Note that 1 /
The scanning pitch is not limited to three scanning pitch units, but is a scanning pitch of 45 to 55.
It is sufficient that the scanning pitch unit does not become%.

That is, for example, even when the original deviation correction amount dY corresponds to 50% of the scanning pitch, the above (2)
Under the conditions shown in (1), the actual correction amount dYs becomes 1/3 of the scanning pitch.

In the next step 108, the image data D ₀
Enter the inputs data D _F1 from the line memory 50. The line memory 50 is initially cleared to zero. In the next step 110, determined from the data D ₀ and data D _F1 entered as follows _{D 1, D 2, D F2} .

D ₁ = D ₀ × (1−dYs) (3) D ₂ = D ₀ × dYs (4) D _F2 = D _F1 + D ₁ (5) Next step 112 Then, the data D ₂ obtained in step 110 is output to the line memory 50 and the data D _F2 is output to the line memory 52. As described above, the line memory 50 stores the data corresponding to the line immediately before the line corresponding to the data stored in the line memory 52. Then, in the next step 114, the main scanning position X is incremented by one, and in a step 116, it is determined whether or not the processing for one line has been completed. If the processing for one line has not been completed, the result in step 116 is negative, and the processing returns to step 104 to repeat the same processing as described above until the data processing for one line is completed. If the processing for one line has been completed, the result in Step 116 is affirmative, and the routine proceeds to Step 118.

In step 118, it is determined whether the processing for one page has been completed. If the processing for one page has not been completed, the result in step 118 is NO, and step 1
02 and the same processing as above is repeated. This is repeated until the processing for one page is completed.

As described above, the amount of misregistration is detected based on the reference registration mark formed on the transfer belt 42, and the amount of correction for this misregistration is determined by the scan pitch of 45 to 45.
By keeping it within the range of 55%, FIG.
Even when the image shown in FIG. 7C is corrected, the corrected image data is as shown in FIG. 7A, and the exposure amount profile is as shown in FIG. 7B. For this reason, the image after development is as shown in FIG. 7C, and it is possible to prevent the 1off collapse as shown in FIG. 8C. FIG.
In (A), the line whose image data is “67” is the first line.
The line where the position and the image data are “33” respectively correspond to the second position.

Further, it is possible to improve the accuracy of the beam exposure position without increasing the precision of the mechanism of the laser optical system, and the same is applied to any image data of a line drawing, a text image, and a gradation image. It is possible to reproduce an image with high accuracy by the data processing method described above. In addition, since the data processing unit does not need to use a look-up table or the like, it can have a simple circuit configuration and can perform high-speed processing.

In this embodiment, the correction in the case where the scanning line is inclined with respect to the reference line has been described. However, if the configuration is further provided with more registration marks and registration detecting devices in the main scanning direction, the scanning can be performed. It is also possible to correct for line bending.

In this embodiment, since the shift correction range is set to 0 to 1 scan line, the number of line memories of the main processing unit is two. However, if more line memories are provided, more scan lines are provided. Can be corrected. [Second Embodiment] The following describes a second embodiment of the present invention. The configuration other than the image processing unit is the same as that of the first embodiment, and a detailed description thereof will be omitted.

FIG. 9 shows a schematic configuration of the image processing section 12 '. The same parts as those of the image processing unit 12 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The image processing section 12 ′ includes an intensity correction coefficient calculation section 54. The intensity correction coefficient calculator 54 includes a shift correction coefficient a calculated by the shift correction coefficient calculator 46,
b is input. Further, the intensity correction coefficient calculating unit 54 includes:
Further, image data D ₊₂ , ₊₁ line memory data D ₊₁ ,
0 line memory data D ₀₀ , -1 line memory data D
_-1 and -2 line memory data D- ₂ are input. In addition,
Data other than the image data D _{+ 2} each include an intensity correction coefficient (details will be described later). Then, after D ₀ , D _A , D _B , D _C , and D _D are respectively determined from the input data according to conditions described later, D ₀ is determined by the main arithmetic unit 4.
To 8, D _A -2 line memory 56 f, D _B -1 line memory 58 F, D _C 0 line memory 60 f, D _D is input +1 line memory 62 f respectively.

Next, as an operation of the second embodiment, control executed in the intensity correction coefficient calculating section 54 will be described with reference to a flowchart shown in FIG.

In step 200 shown in FIG. 10, the deviation correction coefficients a and b calculated by the deviation correction coefficient
Enter In the next step 202, the main scanning direction position X
Is set to 0, and in the next step 204, from the deviation correction coefficients a and b input in step 200, the calculation of the equation (2) is performed to calculate the deviation correction amount dY.

Then, in step 206, the image data D ₊₂ , ₊₁ line memory data D ₊₁ , 0 line memory data D ₀₀ , -1 line memory data D _-1 , -2 line memory data D _-2 and the image data For data other than D _{+ 2} , an intensity correction coefficient corresponding to each data is input. The -2 line memory 56, the -1 line memory 58, the 0 line memory 60, and the +1 line memory 62
Is initially cleared to zero.

The next step 208 is as follows:
Output data D₀, D_A, D_B, D _C, D_DDetermine
You.

(1) (0 <dY <1) and (D ₀₀ = OFF, D ₊₂ ≠ OFF, D ₊₁ ≠ OFF, D _-1で
OFF, when the D _-2 ≠ OFF) (where, OFF is set to 0 as an _{example): D 0 ··· (D -2} , intensity correction _{coefficient: NML) D A ··· (D} -1, strength Correction coefficient: UP) D _B ... (D ₀₀ , intensity correction coefficient: DOWN) D _C ... (D ₊₁ , strength auxiliary coefficient: DOWN) _DD ... (D ₊₂ , intensity correction coefficient : UP) (2) In cases other than (1) D ₀ ... (D _-2 , intensity correction coefficient: not changed) D _A ... (D _-1 , intensity correction coefficient: not changed) D _B ... (D ₀₀ , intensity correction coefficient: not changed) D _C ... (D ₊₁ , intensity correction coefficient: not changed) D _D ... (D ₊₂ , intensity correction coefficient: NML) , DOWN = 0.7, NML = 1.0, UP =
1.3.

[0076] In this data step 210 obtained in, D ₀ is the main operating unit, D _A -2 line memory 56 f, D _B -1 line memory 58 F, D _C 0 line memory f 60, D _D is output as +1 line memory 62 f.

In the next step 212, the main scanning position X is incremented by one, and in a step 214, it is determined whether or not the processing for one line has been completed. If the processing for one line has not been completed, the result in step 214 is negative, and the processing returns to step 204 to repeat the same processing as described above until the processing for one line is completed. If the processing for one line has been completed, the result in step 214 is affirmative, and the routine proceeds to step 216.

In step 216, it is determined whether the processing for one page has been completed. If the processing for one page has not been completed, the determination in step 216 is negative, and the processing returns to step 202 and the same processing as described above is repeated. This is repeated until the processing for one page is completed.

Next, the control executed in the main arithmetic section 48 will be described with reference to the flowchart shown in FIG. Note that a detailed description of a portion that performs the same processing as the flowchart illustrated in FIG. 5 will be omitted.

Steps 300 to 304 are the same as steps 100 to 106 in FIG. After determining the dYs at step 306, the next step 308 inputs the image data D _0, inputs the data D _F1 from the line memory 50. The line memory 50 is initially cleared to zero. Then, the next step 310
From the input data D ₀ and data D _F1 , D ₁ , D ₂
Is calculated according to the equations (3) and (4).

In the next step 312, D _F2 is obtained as follows.

(1) When the intensity correction coefficient is UP D _F2 = 1.3 × (D _F1 + D ₁ ) (2) When the intensity correction coefficient is DOWN D _F2 = 0.7 × (D _F1 + D ₁ ) ( 3) When the intensity correction coefficient is NML: D _F2 = 1.0 × (D _F1 + D ₁ ) The D ₂ determined in this manner is stored in the line memory 50.
_F2 is output to the line memory 52, respectively. Step 3
16 to 320 are steps 212 to 21 in FIG.
6 is the same as the processing of FIG.

Image data obtained by correcting an image in which the image data pattern in the sub-scanning direction is ON-ON-OFF-ON-ON as described above, ie, ideal O
The data of ± 1 pixel is multiplied by 0.7 with respect to the FF section, and the ideal O
FIG. 12A shows image data when the data of ± 2 pixels is 1.3 times that of the FF section.

In FIG. 12A, the line where the image data is “47” is the first position, and the image data is “23”.
Is the second position, the line that is 130 adjacent to the first position when the image data is "130" is the third position, and the line that is 130 adjacent to the second position and the image data is 130 is the fourth position. Respectively. For comparison, FIG.
FIG. 14A shows image data obtained by processing according to the flowchart shown in FIG. 5, and FIG. 14A shows ideal OF data.
The image data when only the data of ± 1 pixel in the F section is multiplied by 0.7 is shown. The exposure profile along the line AA shown in FIG. 13A is as shown in FIG. 13B, and the image to be developed is an image as shown in FIG. 13C. In this case, as shown in FIG. 13C, the OFF portion of the image to be developed is smaller than the ideal OFF portion width.

The exposure profile along the line AA shown in FIG. 14A is as shown in FIG.
The image to be developed is an image as shown in FIG. In this case, as shown in FIG. 14C, the OFF portion of the image to be developed is wider than the ideal OFF portion width.

On the other hand, the exposure profile along the line AA shown in FIG. 12A is as shown in FIG. 12B, and the image to be developed is an image as shown in FIG. Becomes In this case, as shown in FIG. 12C, the OFF portion of the image to be developed has a substantially ideal OFF portion width.

As described above, the exposure amount of the pixel at a position shifted by one pixel before and after the ideal OFF portion is reduced, and the exposure amount of the pixel at a position shifted by two pixels before and after the ideal OFF portion is increased. The width of the portion can be made almost ideal.

Further, by performing the correction as described above, it is possible to improve the accuracy of the beam exposure position without increasing the accuracy of the mechanism of the laser optical system, and it is possible to reproduce an image with high accuracy. . In addition, since the data processing unit does not need to use a look-up table or the like, it can have a simple circuit configuration and can perform high-speed processing.

In this embodiment, a case has been described where ± 1 pixel data is 0.7 times the ideal OFF portion and ± 2 pixels data is 1.3 times the ideal OFF portion. However, it is not limited to this.

In this embodiment, the correction in the case where the scanning line is inclined with respect to the reference line has been described. However, if the configuration is further provided with more registration marks and registration detection devices in the main scanning direction, the scanning can be performed. It is also possible to correct for line bending.

In this embodiment, since the shift correction range is set to 0 to 1 scan line, the number of line memories of the main processing unit is two. However, if more line memories are provided, more scan lines are provided. Can be corrected.

[0092]

As described above, according to the present invention, the correction means calculates the exposure value at the first position and the exposure value at the second position on the basis of the displacement amount input by the input means. And the actual exposure at the first and second positions is corrected so as to have a different relationship from the calculated exposure at the first and second positions. This has the effect that an image can be reproduced with high accuracy even in the case of correction.

[Brief description of the drawings]

FIG. 1A is a schematic configuration diagram of an image forming apparatus.
(B) is a plan view of the transfer belt as viewed from above.

FIG. 2 is a schematic configuration diagram of a light beam scanning device.

FIG. 3 is a diagram for explaining position shift detection.

FIG. 4 is a schematic configuration diagram of an image processing unit according to the first embodiment.

FIG. 5 is a flowchart illustrating a flow of control executed in a main processing unit according to the first embodiment.

FIGS. 6A to 6C are diagrams illustrating an example of image data, an exposure energy profile, and an image to be developed.

FIGS. 7A to 7C are diagrams showing image data, an exposure energy profile, and an image to be developed in the present invention.

FIGS. 8A to 8C are diagrams showing conventional image data, a profile of exposure energy, and an image to be developed.

FIG. 9 is a schematic configuration diagram of an image processing unit according to the second embodiment.

FIG. 10 is a flowchart illustrating a flow of control executed in an intensity correction calculation unit according to the second embodiment.

FIG. 11 is a flowchart illustrating a flow of control executed in a main processing unit according to the second embodiment.

12A to 12C are diagrams illustrating an example of image data, an exposure energy profile, and an image to be developed in the present invention.

13A to 13C are diagrams illustrating an example of image data, an exposure energy profile, and an image to be developed for comparison with the case of FIG. 12;

14A to 14C are diagrams illustrating an example of image data, an exposure energy profile, and an image to be developed for comparison with FIG.

FIG. 15 is a diagram for explaining uneven reproduction density of a gradation image when the inclination of a scanning line is corrected.

FIG. 16 is a diagram illustrating an example of a screen matrix of a dither or error diffusion screen.

FIG. 17 is a diagram illustrating an example of an angled line screen image.

FIG. 18 is a diagram illustrating a relationship between a gradation level and a reproduction density when an image is moved in the sub-scanning direction.

FIG. 19A is a diagram showing a profile of exposure energy. (B) is a diagram showing a relationship between an image movement amount and an exposure amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image processing part (correction means) 14 Light beam scanning device 16 Laser diode driver 18 Laser diode 20 Photoconductor 42 Transfer belt 44 Registration detection apparatus (Input means)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 1/04 H04N 1/04 DF term (reference) 2C362 AA03 BA04 BA51 BA68 BA71 CA18 CA23 CA39 2H027 DA38 EB04 EC03 EC06 EC20 ED06 ED24 EE02 EE07 EF09 2H030 AA01 AB02 AD12 BB02 BB16 BB23 BB44 BB56 5C072 AA03 BA02 BA04 CA02 CA06 CA14 DA02 HA02 HA09 JA07 UA12 UA13 VA07

Claims (5)

[Claims] 1. An image forming apparatus for forming an image by scanning and exposing a photosensitive member with a light beam in a main scanning direction and a sub-scanning direction intersecting the main scanning direction in accordance with image data, the image forming apparatus comprising: Input means for inputting an amount of positional deviation of the scanning line from the reference line, a calculated amount of exposure at a first position to be exposed based on the input amount of positional deviation, and a first position to be exposed And a second-position exposure calculation value at the second position adjacent to the sub-scanning direction, and a second-position exposure calculation value obtained by the adjacent scanning, and a relationship between the first-position exposure calculation value and the second-position exposure calculation value. And the first
An image forming apparatus comprising: a correction unit configured to correct an actual exposure amount at the position and the second position so as to have a different relationship from the calculated exposure amount value at the first position and the second position. 2. An image forming apparatus for forming an image by scanning and exposing a photosensitive member with a plurality of light beams according to image data in a main scanning direction and a sub-scanning direction intersecting the main scanning direction. Input means for inputting an amount of displacement of the scanning line formed from the reference line, a calculated value of an exposure amount at a first position to be exposed based on the inputted amount of displacement, A second position adjacent to the first position in the sub-scanning direction and a second position exposure calculation value obtained by adjacent scanning are obtained, and the first position exposure calculation value and the second position exposure calculation value are calculated. And the first
An image forming apparatus comprising: a correction unit configured to correct an actual exposure amount at the position and the second position so as to have a different relationship from the calculated exposure amount value at the first position and the second position. 3. The correction unit according to claim 1, wherein a distance between the adjacent first position and second position in the sub-scanning direction is a scanning pitch, and a corrected image movement amount is equal to or more than 0% of the scanning pitch and is not more than 45%. % Or 5 of the scanning pitch
3. The image forming apparatus according to claim 1, wherein the correction is performed so as to be larger than 5% and within 100%. 4. A correction by the correction means, wherein N is an odd number of 3 or more, and an interval between the adjacent first position and second position in the sub-scanning direction is a scanning pitch, and the corrected image movement amount is 4. The image forming apparatus according to claim 1, wherein 1 is a unit of 1 / N of the scanning pitch. 5. 5. An exposure amount at a third position adjacent to the first position in the sub-scanning direction and at a third position adjacent to the second position in the sub-scanning direction, and 2
Correcting the exposure amount at a fourth position adjacent to the position in the sub-scanning direction and the fourth position adjacent to the first position opposite to the first position in the sub-scanning direction to a value increased from the calculated exposure amount. The image forming apparatus according to any one of claims 1 to 4, wherein: