JP2004223767A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device which can obtain images not different in the density from images without being treated by a vertical scanning position adjustment, by making a density of a one dot width horizontal line constant. <P>SOLUTION: A synchronous detector 11 detects beams of an LD 7, and sends a detection signal to a memory control circuit 12. The memory control circuit 12 outputs image data from a line memory to a pattern detection process circuit 3 on the basis of the synchronous detection signal. The pattern detection process circuit 3 sends to an LUT circuit, a code corresponding to density information of three pixels in total, namely, a pixel at a main scanning direction position to be recorded in the 600 dpi binary image data, and its upper and lower two pixels, and a vertical scanning shift amount inputted from a vertical scanning registration shift detecting part. The LUT circuit 4 sends a pulse width and a pulse position signal to a PWM circuit 5, and the PWM circuit 5 sends a PWM signal to an LD driver on the basis of the received pulse width and pulse position signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a digital copying machine and a laser printer, and more particularly to adjustment of a forming position in a sub-scanning direction.
[0002]
[Prior art]
In a conventional image forming apparatus, an image portion on a photoreceptor is irradiated with laser light, and toner is adhered to the irradiated portion to form an image. This is an electrophotographic system using a so-called negative / positive process system. In the conventional method, the input image data is converted into a double resolution to correct the registration deviation below the sub-scanning pitch in the sub-scanning direction, the registration deviation correction is performed on the double-resolution data, and the corrected height is corrected. In the resolution data, data of the original resolution is generated and recorded from the bias of the density distribution in the unit area with four pixels corresponding to one pixel at the original resolution as a unit area. Further, in the conventional method, the position of forming an image in the sub-scanning direction is adjusted by controlling each exposure amount in a plurality of main scans.
[0003]
Further, there are the following prior arts as prior arts.
A first image that requires a halftone representation of color material image data for each color is detected from a position shift detection pattern formed in the same transfer area by the photoconductor of each color, and the amount of positional shift with respect to a reference pixel position is detected. The image is separated into data and second image data that does not require halftone expression, detects a displacement of the drive of the scanning light emitted based on the second image data, and controls the direction to eliminate the displacement. There is a forming device (see Patent Document 1).
[0004]
The first and second photodetectors for detecting the light beam before and after the writing scan range on the main scanning line and the polygon mirror from the light beams detected by the first and second photodetectors. A write clock generation circuit that measures a scan time of the light beam for each surface and changes a write clock in accordance with the measurement result; the write clock generation circuit detects the light beam by the first photodetector; The scanning time is measured by counting a predetermined reference clock until detection by the second photodetector (see Patent Document 2).
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-158707 [Patent Document 2]
JP-A-2002-267961
[Problems to be solved by the invention]
However, when correcting a registration shift below the sub-scanning pitch, it is ideal that the image recorded by the corrected data has the same attributes (density, line width, etc.) other than the sub-scanning position. For example, it is desirable that the density and line width of all the one-dot-width horizontal lines be constant when the one-dot-width horizontal lines are output while changing the sub-scanning position in various ways.
[0007]
If the image density differs depending on the sub-scanning position adjustment amount, there is a problem that the image density changes depending on the region when the sub-scanning position adjustment amount differs depending on the main scanning position or when the sub-scanning position adjustment amount differs depending on the sub-scanning position. . In particular, when a color image is formed by superimposing a plurality of color toner images on a medium, the hue changes.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and in a case where a resist deviation equal to or less than a sub-scanning pitch is adjusted by controlling each exposure amount in a plurality of main scans, even if the sub-scanning adjustment amount is changed, one dot is required. An object of the present invention is to provide an image forming apparatus capable of obtaining an image in which the density does not change from an image in which the sub-scanning position is not adjusted by making the density of the width horizontal line constant.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to claim 1 scans a recording medium with a light beam and forms an image on the recording medium. First detecting means for detecting a pixel recorded by the means and a main scanning position, second detecting means for detecting a pixel, a pixel and a main scanning position where the sub-scanning position is one scan before, and a sub-scanning position after the one scanning. Calculating means for calculating the light output rank to be output to the recording pixel from the on / off information of the three pixels and the desired sub-scanning direction shift amount smaller than the sub-scanning pitch; Output means for outputting light of a corresponding exposure amount to a position of a pixel recorded by the recording means.
[0010]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the first detecting means detects that the pixel and the main scanning position are the same.
[0011]
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the second detecting means is such that the sub-scanning position is the same as the pixel before the one scanning, and the pixel is the same as the main scanning position. I do.
[0012]
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the output unit has a comparison unit that determines an exposure amount corresponding to the light output rank by comparing the density of the test pattern. I do.
[0013]
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the comparing unit determines the exposure amount corresponding to the light output rank when the power of the image forming apparatus is turned on from off. It is characterized by the following.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
Next, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a configuration of the image forming apparatus of the present invention.
The image forming apparatus according to the present invention includes a line memory 1, a sub-scanning registration shift detecting unit 2, a pattern detection processing circuit 3, an LUT circuit 4, a PWM circuit 5, an LD driver 6, an LD 7, a polygon mirror 8, a lens 9, a photosensitive drum. 10, a synchronization detector 11, and a memory control 12.
[0015]
Next, the operation in the embodiment of the present invention will be described.
FIG. 1 shows the configuration (for one color) of the image forming apparatus. A beam emitted from an LD (laser diode) 7 is scanned in the main scanning direction by a polygon mirror 8 that rotates at a constant speed, is imaged on a surface of a photosensitive drum 10 via a lens 9, and a transfer material on which an image is transferred. Is output. The sub-scanning pitch P of the beam from the LD 7 on the surface of the photosensitive drum 10 is 600 dpi (42 μm). The main scanning writing pitch is also 600 dpi.
[0016]
The synchronization detector 11 includes a photoelectric conversion element and a signal waveform shaping circuit, detects a beam from the LD 7, and sends a detection signal to the memory control circuit 12. The memory control circuit 12 outputs image data from the line memory 1 to the pattern detection processing circuit based on the synchronization detection signal 11. The pattern detection processing circuit 3 receives the density information of three pixels including the pixel at the main scanning position to be printed and the upper and lower two pixels in the binary image data of 600 dpi and the input from the sub-scanning registration deviation detecting unit 2. It is sent to the code LUT circuit 4 corresponding to the sub-scanning shift amount (−3 / 4P to + 3 / 4P).
[0017]
As a method of detecting a sub-scanning resist shift, a shift detecting pattern of a color whose sub-scanning resist shift amount is to be detected is first drawn on a transfer medium, and then a shift detecting pattern of a reference color (BK) is overwritten. When there is no sub-scanning resist shift between the two colors, the two shift detection patterns exactly overlap each other, and the shift detection pattern of the color to be detected detects the reference color based on the reflected light intensity of the transfer medium surface.
The sub-scanning registration deviation detecting unit 2 is provided at the position shown in FIG. 2 for three colors separated in the main scanning direction, and detects sub-scanning registration deviations of Y, C, and M colors.
[0018]
The LUT circuit 4 sends a preset pulse width and pulse position signal to the PWM circuit 5 corresponding to the code sent from the pattern detection processing circuit 3.
The PWM circuit 5 sends a PWM signal to the LD driver 6 based on the received pulse width and pulse position signal. The PWM signal is output in synchronization with the video clock signal (600 dpi frequency). The used PWM circuit 5 can output a pulse signal in which the pulse width and the pulse start position are set at 1/64 resolution of the writing cycle within the writing cycle of 600 dpi.
[0019]
The LD driver 6 supplies a drive current to the LD when receiving the “ON” signal and an offset current to the LD when receiving the “OFF” signal.
3A and 3B show width codes (light output ranks) generated by the pattern detection processing circuit 3 in accordance with the density information of the image data and the sub-scanning shift amount. The pulse width W corresponding to the width code is set in the LUT (shown in (c) of FIG. 3). The pulse start position in the write cycle is determined from the following equation.
Pulse start position = (write cycle-pulse width W) / 2
[0020]
As shown in FIG. 4, the test pattern to be output to set the pulse width W corresponding to the width code has a width code generated by the pattern detection processing circuit 3 when the sub-scanning shift amount is different. different. The pattern shown in FIG. 4 is a part of the test pattern, and the actually output pattern size is 20 mm × 20 mm.
[0021]
FIG. 5 is a flowchart showing a procedure for setting the pulse width W.
W0 to W4 in the drawing represent W corresponding to five classes (width codes = 0 to 4). W0 corresponds to a case where all the image data of the target three pixels are 0. When an optical pulse is output at this time, an unnecessary image is drawn on a white background of the image. W0 is fixed at 0 because so-called soiling may occur.
[0022]
Next, the procedure for setting the pulse width W will be described.
First, W0 = 0 and initial values of W1 to W4 are set (step S1). Next, a test pattern is output (step S2), and it is determined whether the density of the shift 0 line is appropriate (step S3). If the density of the shift 0 line is not appropriate (step S3 / NO), the W4 value is adjusted, and the process returns to before step S2. If the density of the shift 0 line is appropriate (step S3 / YES), a test pattern is output (step S5).
[0023]
Next, it is determined whether or not the densities of the shift 0 line and the shift 1/2 line are the same (step S6). If the densities of the shift 0 line and the shift 1/2 line are not the same (step S6 / NO), the W2 value is adjusted (step S7), and the process returns to before step S5. When the densities of the shift 0 line and the shift 1/2 line are the same (step S6 / YES), provisional values of W0, W2, W4 to W3, W1 which have already been set are set (step S8). Next, a test pattern is output (step S9).
[0024]
Next, it is determined whether or not the density of the shift 0 line and the shift 1/4 line are the same, and whether or not the sub scanning position of the shift 1/4 line is intermediate between the shift 0 line and the shift 1/2 line. Perform (Step S10). When the shift 0 line and the shift 1/4 line have the same density and when the sub scanning position of the shift 1/4 line is halfway between the shift 0 line and the shift 1/2 line (step S10 / YES), the processing ends. It becomes. If the densities of the shift 0 line and the shift 1/4 line are not the same and the sub-scanning position of the shift 1/4 line is not in the middle of the shift 0 line and the shift 1/2 line (step S10 / NO), W3, The W1 value is adjusted (step S11), and the process returns to step S9.
[0025]
The LUT in which the pulse width corresponding to the width code C is set by the processing operation of FIG. 5 is as follows.
The test pattern image shown in FIG. 4 was output to the transfer material using the LUT, and the result of the visual evaluation was as follows:
The density of the 1-dot width horizontal line is appropriate. The density of the 1-dot width horizontal line (shift amount 0, 1 / 4P, 1 / 2P, 3 / 4P) is the same. 1dot-width horizontal line (shift amount 0, 1 / 4P, 1). / 2P, 3 / 4P) changes continuously in the sub-scanning position. If the LUT setting is not appropriate, a density difference occurs when an image having a different sub-scanning position adjustment amount is output.
[0026]
The generalized method of calculating the width code is as follows. Even if the input data is multi-valued, the LUT is created in the same procedure.
Sub-scanning pitch: P
Adjustment step: P / M (M is an integer)
The range of the adjustment amount j is − (M−1),... + (M−1)
j is an integer. The range of the density value Dk is 0,... Dkmax.
Dk is an integer, and k represents a sub-scanning position.
k:-is the sub-scanning position before the recording pixel k: 0 is the sub-scanning position of the recording pixel k: + is the sub-scanning position width code C after the recording pixel is
When j ≦ 0, C = M · D ₀ + (D ₀ −D ₊ ) · j
When j ≦ 0, C = M · D ₀ + (D ₋₋ D ₀ ) · j
The domain of C is 0,..., Dkmax · M.
[0027]
(Second embodiment)
FIG. 6 is a flowchart illustrating the processing operation of the image forming apparatus.
First, when the power is turned on (step S20), process conditions are set (step S21). Next, LUT setting is performed (step S22), and a standby state is set (step S23). Here, the image formed at the sub-scanning position and the image formed at the intermediate position between the two sub-scannings when the LUT (pulse width setting corresponding to the code) is continuously used once are defined as photosensitive drums. Although the density varies due to a change in the characteristics with time or a decrease in the amount of light due to the aging degradation of the LD, the density does not differ by setting the LUT each time the power of the image forming apparatus is turned on.
[0028]
【The invention's effect】
As is clear from the above description, since the light of the exposure amount to be output to the recording pixel is controlled based on the density information of the three consecutive pixels in the sub-scanning direction and the desired shift amount in the sub-scanning direction, It can be changed by an amount smaller than the scanning position pitch.
Further, since the density is determined by comparing the exposure amount corresponding to the light output rank to be output to the recording pixel and the density of the test pattern, the density of the image can be kept constant even when images having different sub-scanning position adjustment amounts are output.
Further, since the LUT setting is performed every time the power supply of the image forming apparatus is turned on, the image density difference due to the sub-scanning position adjustment amount due to the temporal change in the characteristics of the photosensitive drum and the decrease in the light amount due to the temporal deterioration of the LD is reduced. Does not occur.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating input image data and width code output according to the embodiment of the present invention.
FIG. 4 is a diagram showing a test pattern according to the embodiment of the present invention.
FIG. 5 is a diagram illustrating a processing operation of the image forming apparatus according to the embodiment of the present invention.
FIG. 6 is a diagram illustrating a processing operation of the image forming apparatus according to the embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1 line memory 2 sub-scanning resist deviation detecting unit 3 pattern detection processing circuit 4 LUT circuit 5 PWM circuit 6 LD driver 7 LD
8 Polygon mirror 9 Lens 10 Photoreceptor drum 11 Synchronization detector 12 Memory control circuit

Claims (5)

In an image forming apparatus that scans a recording medium with a light beam and forms an image on the recording medium,
Storage means for recording pixels;
First detection means for detecting the pixel and the main scanning position recorded by the recording means,
A second detection unit for detecting a pixel whose sub-scanning position is one scan before, the pixel, and the main scanning position;
Calculating means for calculating an optical output rank to be output to the pixel from the on / off information of three pixels of which the sub-scanning position is after one scan and a desired sub-scanning direction shift amount smaller than the sub-scanning pitch; ,
An output unit that outputs light having an exposure amount corresponding to a predetermined light output rank to a position of the pixel recorded by the recording unit. The image forming apparatus according to claim 1, wherein the first detecting unit detects that the pixel and the main scanning position are the same. 2. The image forming apparatus according to claim 1, wherein the second detection unit is configured such that the pixel at which the sub-scanning position is one scan before is the same as the pixel and the main scanning position. 3. The image forming apparatus according to claim 1, wherein the output unit includes a comparison unit that determines an exposure amount corresponding to the light output rank by comparing a density of a test pattern. The image forming apparatus according to claim 4, wherein the comparing unit determines the exposure amount corresponding to the light output rank when the power of the image forming apparatus is turned on from off.

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