JP2003170623A - Imaging method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form high-quality images without a color shift regardless of a deviation of the detected registration position. <P>SOLUTION: An image for position detection is formed on an image carrier or on a transfer material carrier with the use of an imaging means (S1). The position of the formed image for position detection is detected (S2). Image processing is changed (S5 and S6) to process images in accordance with the detected result (S4). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus for inputting an image signal to form an image on a recording medium.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electrophotographic apparatuses have been advanced in speed, function, and color, and various types of printers have been put on the market.

From the viewpoint of increasing the speed of a printer, research and development of a tandem type apparatus for arranging a plurality of electrophotographic units for forming images of different colors in series and driving them simultaneously to form an image are advanced. The color image forming apparatus of this type has a wide potential for business use because it can form a color image at high speed. In this tandem type image forming apparatus, a new limitation is imposed for forming a good image as in the conventional apparatus.

The tandem type image forming apparatus is roughly classified into an intermediate transfer type and an electrostatic transfer belt type. In the former case, toner images of a plurality of colors are once formed on the intermediate transfer body by superimposing (primary transfer), and then secondary transfer is collectively performed on a transfer paper to form a final image. On the other hand, in the latter device, the transfer paper is attracted to the electrostatic transfer belt, and the toner images are superposed on the transfer paper to form an image. Each of these methods has its advantages and disadvantages, and the method using an intermediate transfer member is characterized in that it is unlikely to be affected by the thickness or surface property of the transfer paper at the time of primary transfer color superposition. Further, the electrostatic transfer belt has a characteristic that deterioration of an image can be suppressed because transfer is required only once.

However, in any method,
Since different color images are formed by different image forming units, there is a drawback that the registration for each color is difficult to match. There is concern about unevenness. Therefore, in order to improve such a problem, the following two methods are widely known and adopted in many color printers.

(Method 1) A registration error (hereinafter, registration error) is corrected. Specifically, a toner pattern (registration pattern) for resist detection is formed on an intermediate transfer body or an electrostatic transfer belt, and this is read by an optical sensor, and based on the read result, the image writing start position is determined. The misregistration is corrected by feeding back the adjustment.

(Method 2) Image processing is used to make color shade variation and color unevenness inconspicuous. For example, when the systematic dither method (hereinafter, dither method) is used as the halftone reproduction means,
Use a dither pattern that is resistant to color unevenness and density fluctuations. More specifically, there are methods such as reducing the number of dither lines, giving directionality to dot growth, or setting different screen angles for each color.

[0008]

However, the following problems may occur in the color image forming apparatus having the above structure.

(Problem 1) The correction of registration as described above requires a high level of technology, and if such a function is to be incorporated, the cost and size of the apparatus will increase.

A more specific description will be given below. The registration misalignment is roughly classified into a misalignment in the sub-scanning direction (paper transport direction), a misalignment in the main scanning direction (laser scanning direction), a misalignment in the main scanning magnification, and a misalignment in the main scanning direction (SKEW). . Among them, the misregistration in the sub-scanning direction can be adjusted by adjusting the scanning line writing timing from the TOP signal which is the synchronization signal of the page, and the misregistration in the main scanning direction can be the BD (beam The write start timing from the (detection) signal to the laser may be adjusted, and both can be adjusted relatively easily. However, in order to correct the deviation in the main scanning magnification, it is necessary to provide a means for adjusting the image clock for each color, which cannot be easily performed. Further, in order to adjust the skew SKEW of the tilt in the main scanning direction, a means for correcting the position of the exposure means (for example, a lens), a means for adjusting the position of the image forming unit, etc. are required, and the cost of the apparatus is reduced. It will invite up.

Further, in addition to the uneven registration occurring uniformly over the entire surface of the image, there are also uneven registration errors occurring within the image.
This includes, for example, unevenness in thickness in the circumferential direction of the intermediate transfer belt or the electrostatic transport belt, registration error due to eccentricity of an image carrier such as a photosensitive drum, or a belt driving roller.
In order to improve this kind of misregistration, a means for finely controlling the speed of the drive motor for the photoconductor or the belt is required, but this also requires a difficult technique.

Further, even if the registration is corrected by using the complicated control means as described above,
Correct correction is not always possible. The cause of such a phenomenon is that the toner pattern for resist detection is not well formed (for example, the pattern is faint), or the intermediate transfer belt or the electrostatic transport belt is damaged, It is possible that the scratch is erroneously detected as a detection pattern. Needless to say, if the registration correction is not performed normally, tint variation or tint unevenness will occur in the image.

(Problem 2) As described above, when image processing is used to suppress variation in tint and unevenness in tint, new image deterioration may occur. For example, if the number of dither lines is reduced, the resolution of the image will decrease. Also, when the direction of dot growth is given,
The dot reproducibility of highlights will decrease. Further, when the screen angles of the respective colors are made different, a moire pattern may occur due to the interference of the screens. In any case, such image processing brings about an adverse effect of image deterioration. Therefore, such image processing is effective because it can suppress color unevenness and density fluctuation when the registration is deteriorated, but when the registration is good, it only deteriorates the image quality and is not always suitable. I can't say.

The present invention has been made in view of the above-mentioned conventional example, and an image for adjusting the registration position is formed on the image forming image carrier or the transfer material carrying member, and the position of the formed image is formed. It is an object of the present invention to provide an image forming method and apparatus capable of forming a high-quality image free from color misregistration by detecting a color difference and changing image processing according to the detected misregistration position.

[0015]

In order to achieve the above object, the image forming apparatus of the present invention has the following configuration.
That is, an image forming apparatus for inputting an image signal to form an image on a recording medium, the image processing unit executing image processing on the input image signal, and the image signal processed by the image processing unit. An image forming unit that forms an image on a recording medium based on the image forming unit, a unit that forms a position detection image on the image carrier or a transfer material carrier using the image forming unit, and a position of the position detection image And a control unit that controls to change the image processing in the image processing unit according to the detection result of the position detection unit.

In order to achieve the above object, the image forming method of the present invention includes the following steps. That is, it is an image forming method of inputting an image signal to form an image on a recording medium, which comprises an image processing step of executing image processing on the input image signal, and an image signal processed in the image processing step. An image forming step of forming an image on a recording medium based on
A step of forming a position detection image on an image carrier or a transfer material carrier; a position detection step of detecting the position of the position detection image; and an image processing step according to the detection result of the position detection step. And a control step of controlling the image processing to change.

[0017]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the present embodiment, a method will be described in which an optimum image can be provided by changing the screen ruling in accordance with the detection result of the registration detecting section regardless of the registration shift amount.

FIG. 1 is a block diagram illustrating a main part of a color image forming apparatus according to an embodiment of the present invention.
In order to speed up the color image output, this color image forming apparatus stacks a plurality of photoconductors corresponding to different colors and sequentially multiplies toner images (this is generally 4 It is called the drum tandem method).

The color image forming apparatus receives print data from the host computer 1000, the printer controller 100 receives and decodes the print data, and outputs the print data to the pulse width modulation circuit 200, which corresponds to a printer engine. It controls the operation of the recording unit. The control unit 10
0 controls the operations of the printer controller 100 and the pulse width modulation circuit 200, and switches the control of the image processing in the printer controller 100 according to the signal from the registration sensor 9.

In FIG. 1, a plurality of image forming units Y, M, C and K (yellow unit, magenta unit, cyan unit and black unit in this order) are provided, and an intermediate transfer belt 50 is provided longitudinally through each image forming unit. It is arranged. Each image forming unit Y, M, C, K includes
Cylindrical photoconductors (photosensitive drums) 1Y, 1M, 1C, and 1K as electrostatic latent image carriers are supported so as to be rotatable in the arrow directions. 2Y, 2M, 2C and 2K are primary chargers, which are arranged to face the photosensitive drums 1Y, 1M, 1C and 1K, respectively. Laser exposure units 3Y, 3M, 3C, and 3K are primary chargers 2Y, 2M, and
Photosensitive drums 1Y, 1M, 1C, 1K for 2C, 2K
The photoreceptor is exposed on the downstream side in the rotation direction of. Four
Y, 4M, 4C and 4K are developing units containing yellow, magenta, cyan and black toners, respectively.
They are arranged further downstream than the exposure units 3Y, 3M, 3C and 3K so as to be adjacent to the respective photosensitive drums.

The intermediate transfer belt 50 includes a driving roller 51,
The tension roller 52 and the secondary transfer counter roller 53 are stretched and conveyed by three rollers.

The images visualized on the photosensitive drums 1Y, 1M, 1C and 1K are transferred to the primary transfer rollers 6Y and 6Y.
Each of M, 6C, and 6K sequentially transfers to the intermediate transfer belt 50, and once forms a reversed full-color image on the intermediate transfer belt 50. Then, the secondary transfer roller 54 collectively transfers (secondarily transfers) the transfer material P such as recording paper. The transfer residual toner (waste toner) remaining on the intermediate transfer belt 50 is cleaned by the cleaner 7 of the intermediate transfer belt 50.

The operation of the image forming apparatus configured as described above will be described by taking the image forming unit Y as an example.

The photosensitive drum 1Y has a photo-semiconductive layer on the surface of a conductive substrate such as aluminum and rotates in the direction of arrow a. Then, the surface is uniformly negatively charged by the primary charger 2Y, and then exposed by the laser exposure unit 3Y to form an electrostatic latent image corresponding to the original. The developing device 4Y performs development using negatively charged toner,
A toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 1Y. The toner image thus formed on the surface of the photosensitive drum 1Y is transferred to the intermediate transfer belt 50.

The above operation is performed in each image forming unit at a predetermined timing, the toner image formed on each photosensitive drum is held on the intermediate transfer belt 50, and then the transfer material P is transferred by the secondary transfer roller 54. Will be transferred at once. The transfer material P on which the toner image is transferred in this manner is supplied to the fixing device 8 and is heated and pressed to be fixed, whereby a full-color image is obtained.

Further, two registration detection optical sensors (hereinafter referred to as registration sensors) 9 are arranged on the left and right sides (main scanning direction) so as to face the intermediate transfer belt 50.

The color image forming apparatus according to the present embodiment has a resolution of 600 dpi for each color, and each dot can perform multi-value output of 8 bits (256 gradations).

A method of generating a multi-valued image output will be described below.

The print image data output from the host computer 1000 is the printer controller 100.
In this way, image development, color conversion, and halftone processing are performed, and each color is output as an 8-bit digital image signal of 600 dpi. The output image signal is then converted into a binary laser drive signal by the pulse width conversion circuit 200, and then input to the laser exposure units 3Y, 3M, 3C and 3K.

FIG. 2 is a block diagram showing details of the pulse width conversion circuit 200 according to the present embodiment. Below, FIG.
Follow along.

First, the printer controllers 100 to 8
Bit (0 to 255 gradations) digital image signal 301
Is generated. Next, this digital image signal 301
Is a digital-analog converter (D / A converter) 20
1 and is converted into the analog image signal 302, and then supplied to one input of the comparator 205.

On the other hand, the reference clock signal 304 generated from the oscillator 202 is supplied to the timing signal generating circuit 203, and from this timing signal generating circuit 203, the printer controller 100 and the digital-analog are used as the transfer pixel clock of the digital image signal. Converter 2
01 is supplied. At the same time, the timing signal generation circuit 2
A screen clock 305 is generated from 03 and is supplied to the pattern signal generator 204. The pattern signal generator 204 generates a pattern signal (triangular wave signal) 26 having the screen clock 305 as a synchronization signal and is supplied to the other input of the comparator 205. The comparator 205 compares the pattern signal 306 with the analog image signal 302. For example, when the analog image signal 302 is larger, it is “0”, and vice versa.
When 2 is smaller, the binary image signal 307 of “1”
To occur. That is, the pattern signal 306 is pulse-width modulated by the analog image signal 302. This pulse-width-modulated binary image signal is supplied to each corresponding laser exposure unit, and is used here as an ON / OFF control signal for emission of the semiconductor laser. The control unit 110 is
When registering a registration pattern, the D / A converter 201
Image data corresponding to the registration pattern is output to form a registration pattern on the intermediate transfer belt 50.

Next, the print controller 100 will be described.

FIG. 3 is a block diagram showing the configuration of the printer controller 100 according to this embodiment. The printer controller 100 includes a control circuit 101 and an image processing unit 102. The control circuit 101 performs various communications with the host computer 1000 and the printer engine, and controls the image processing unit 102 according to the communications commands.

The image processing unit 102 includes an image expansion circuit / color conversion circuit 103 and a halftone processing circuit 104.
In this embodiment, multi-value dither conversion is used for the halftone processing. Here, the switching of the image processing according to the present embodiment is performed based on a plurality of types of dither matrix data stored in the ROM 105, based on the halftone processing circuit 10.
4 is performed by selecting the optimum dither matrix data.

The control unit 110 is a ROM 111 for storing the CPU 1110, its program, various control data, and the like.
1, a RAM 1112 for storing various data when the CPU 1110 executes the control processing, and stores a program for executing the control processing shown in a flowchart described later.

Next, the structure and characteristics of the registration sensor 9 will be described.

FIG. 4 shows a registration sensor 9 according to this embodiment.
It is a figure which shows the structure of.

As shown in FIG. 4, the registration sensor 9 is
A light emitting element 91 such as an LED and a light receiving element 92 such as a photodiode are provided. The infrared light from the light emitting element 91 is applied to the registration pattern Q on the intermediate transfer belt 50, and the specularly reflected light therefrom is received by the light receiving element. The position of the registration pattern Q is detected by measuring at 92.

FIG. 5 is a diagram for explaining the output characteristics of the registration sensor 9.

This characteristic is shown by the curve A, and the output of the sensor 9 (the amount of light received by the photodiode 92) decreases as the amount of toner applied increases. This is because when the amount of toner on the intermediate transfer belt 50 increases, the irradiation light is diffused by the toner, and at the same time, the surface of the intermediate transfer belt 50, which is the base, is hidden and the intermediate transfer belt 50 is hidden.
This is because the specular reflection light from is reduced.

The main configuration of the color image forming apparatus according to this embodiment has been described above.

Next, a method of detecting the registration shift amount will be described.

FIG. 6 is a diagram for explaining the positional relationship between the registration sensor 9 and the registration pattern.

Two registration sensors 9 are arranged in the left and right direction in the main scanning direction so that the registration patterns formed on the left and right sides of the intermediate transfer belt 50 can be detected. Each of the registration patterns P-Y, P-M, P-C, and P-K is
This is a registration pattern for detecting registration in the sub-scanning direction, and in order, yellow, magenta, cyan,
Formed with black toner. Further, each of the V-shaped registration patterns S-Y, S-M, S-C, and S-K is a registration pattern for detecting registration in the main scanning direction, and yellow, magenta, and It is formed with cyan and black toners.

A method of calculating the registration shift using such a registration pattern will be described in detail with reference to FIG.

First, registration detection in the sub-scanning direction will be described.

In the figure, Q represents an actually formed registration pattern for registration detection in the sub-scanning direction, and Q'is
A registration pattern formed when the registration shift is "0" is shown. Here, when the timing at which the registration sensor 9 detects the registration pattern Q is T and the timing at which the ideal registration pattern is to be detected is T ', the registration deviation dp in the sub-scanning direction is shown.
Can be calculated by the following formula.

Dp = (TT ') × ps Here, ps represents the moving speed of the intermediate transfer belt.

Next, registration detection in the main scanning direction will be described.

In the figure, S represents an actually formed registration pattern for registration detection in the main scanning direction, and S'is
A registration pattern formed when the registration shift is "0" is shown. The registration pattern S for detecting the registration in the main scanning direction is a V-shaped pattern composed of two lines intersecting at an angle of 90 degrees, and the angle of the line portion is about 45 with respect to the sub-scanning direction. It is degree. Since this pattern passes the registration sensor 9 twice, the first passage timing is T1, and the second passage timing is T2. Similarly, assuming that the timings at which the ideal registration pattern S'should be detected are T1 'and T2', the registration shift ds in the main scanning direction.
Can be calculated by the following formula.

Ds = {(T2'-T1 ')-(T2-T
1)} × ps × 1/2 Next, a method for detecting the time when the registration pattern passes through the registration sensor 9 will be described with reference to FIG.

In FIG. 8, reference numeral 800 denotes a sensor output when the registration pattern passes through the registration sensor 9. When the registration sensor 9 is detecting a pattern other than the registration pattern (the base of the intermediate transfer belt 50), the amount of specularly reflected light incident on the photodiode 92 is large, so the output of the sensor 9 is large and the output of the registration sensor 9 is constant. Has become. Further, when the registration pattern passes through the registration sensor 9, the amount of regular reflection light incident on the photodiode 92 is reduced by the toner, and the output of the registration sensor 9 is reduced. After that, the output 800 of the registration sensor 9 is output as a digital signal 801 through a comparison circuit (not shown). In the figure, a dotted line 802 represents the threshold value of the comparison circuit, and the output signal 801 from the comparison circuit is turned on when the output of the sensor 9 is less than or equal to the threshold value 802. Then, the center T of the portion where the signal 801 is turned on is set as the registration pattern detection timing.

The above is the description of the registration deviation amount detecting method in the image forming apparatus according to the first embodiment.

Next, the image processing in the first embodiment will be described. As described above, in the first embodiment, multivalued dither is used for the halftone processing. In the first embodiment, two types of multi-valued dither matrices are used.

9A to 9C are diagrams for explaining the first dither matrix according to the first embodiment. still,
This dither matrix is used when the registration shift amount is small.

FIG. 9A shows a dither pattern, and the numbers indicate the dot generation order. This dither matrix has a total of 9 dots of 3 dots × 3 dots as one pixel, and is a fatting type (dot concentrated type) pattern that grows in a spiral (spiral shape) from the center. The image forming apparatus according to the first embodiment is
Since this has a resolution of 00 dpi, the screen ruling is 200 (lpi) when this dither pattern is used. FIG. 9B shows a dither threshold matrix, and the numbers correspond to the thresholds for each dot. It should be noted that this dither matrix is an eight-value dither having seven threshold values per dot. Further, FIG. 9C shows the correspondence between each threshold value and the output image data. The first embodiment
Then, the same dither pattern is used for all Y, M, C, and K colors.

FIGS. 10A to 10C show the first embodiment.
It is a figure showing the 2nd dither matrix which concerns on. This dither matrix is used when the registration shift amount is large, and is a pattern advantageous for color unevenness and tint change due to the registration shift. On the other hand, there is a demerit that the resolution becomes low.

FIG. 10A shows a dither pattern. This dither matrix has a total of 36 dots of 6 dots × 6 dots as one pixel, and like the first dither matrix, it is a fattening type (dot concentration). Type)
It is a pattern. When this dither pattern is used, the screen ruling is 100 (lpi). Figure 10
(B) represents a dither threshold matrix. still,
This dither matrix is a ternary dither with two threshold values per dot. Further, FIG. 10C shows the correspondence between each threshold value and the output image data. Furthermore, the first
Similarly to the dither pattern, the second dither pattern is Y,
The colors of M, C, and K are common.

Next, the reason why the second dither pattern is more advantageous than the first dither pattern for color unevenness and tint variation will be described.

FIG. 11A and FIG. 11B are diagrams for explaining the tint variation when the first dither pattern shown in FIG. 9 is used. In this figure, the image is 44%
A halftone pattern (4 dots of 9 dots are recorded) is used.

In the figure, the O marks represent the dots recorded in the first color, and the X marks represent the dots recorded in the second color. Further, FIG. 11A shows a case where there is no misregistration between the first color and the second color, and the dots of each color are correctly superimposed and recorded. On the other hand, FIG.
The case where the second color dot is shifted upward (in the sub-scanning direction) by one dot is shown. As is clear from this figure, in FIG. 11A showing the case where there is no registration deviation, all the dots are superimposed, whereas in the case of FIG. Only it will not overlap. This difference is recognized as a tint variation.

On the other hand, FIG. 12A and FIG.
It is a figure explaining the tint change when the 2nd dither pattern shown in FIG. 10 is used. As the image, a halftone pattern of 44% (9 dots of 36 dots are recorded) is used as in the case of using the first dither pattern.

FIG. 12A shows a case where there is no misregistration between the dots of the first color and the dots of the second color, and FIG.
Indicates a case where the second color dot is displaced by one dot in the upward (sub-scanning) direction. As you can see from this figure, this second
If the dither pattern is used, 75% of the dots are overlapped even when there is a registration shift, so it can be said that the dither pattern is more advantageous than the first dither pattern in which only 50% of the dots are overlapped under the same conditions with respect to the tint variation.

Although only the misregistration between the two colors has been described here, the same can be realized in the case of four colors.

In the first embodiment described above, only the effect on the registration deviation in the vertical direction (sub-scanning direction) has been described. However, the registration deviation in the main scanning direction, the deviation in the main scanning magnification, and the inclination in the main scanning direction are described. Similar effects can be obtained for deviations (SKEW).

Next, the features of the first embodiment,
A control process of changing the image process according to the registration shift amount will be described with reference to the flowchart of FIG.

First, the control process is started by calculating the registration shift amount. Therefore, the timing of performing the control according to the first embodiment is a case where the registration deviation amount may change. Specifically, it is executed when the power of the main body of the image forming apparatus according to the first embodiment is turned on, and when the photoconductor or the intermediate transfer belt is replaced. Alternatively, the process may be performed after every predetermined number of prints or when the environment in which the apparatus is installed is significantly changed, such as temperature or humidity.

FIG. 13 shows the CPU 1 of the control unit 110 described above.
6 is a flowchart showing a control process executed by 110.

First, in step S1, the intermediate transfer belt 50
A registration pattern is formed on the top. This registration pattern is u
As described above with reference to FIG. The first embodiment
Then, one set of registration patterns shown in FIG. 6 is formed to detect the registration shift. Of course, a plurality of sets of this registration pattern may be formed, and the registration shift amount calculated from each set may be averaged. Next, in step S2, after the registration sensor 9 detects the registration pattern, the registration sensor 9 is used to detect the position of the registration pattern (T described in FIG. 8). Then, the process proceeds to step S3, and the registration shift amount is calculated based on the detection result of the registration pattern. The method of calculating the registration shift amount has already been described with reference to FIGS. 7 and 8.

Next, in step S4, which of the first dither pattern and the second dither pattern is to be used is determined according to the registration deviation amount obtained in step S3. In the first embodiment, as the registration deviation amount, the maximum registration deviation amount between the colors is set as the registration deviation amount of the image forming apparatus.

More specifically, since the color image forming apparatus according to this embodiment has image planes of four colors Y, M, C, and K, there are six registration deviation amounts between the colors ( Y
-M, Y-C, Y-K, M-C, M-K, C
-6 ways between K). In the first embodiment, the registration deviation amount in the sub-scanning direction and the registration deviation amount in the main scanning direction are calculated independently. Further, the calculation of the registration deviation amount is performed on the left and right sides of the intermediate transfer belt 50. There are four types of registration deviation amounts (right main scanning direction, left main scanning direction, right sub scanning direction,
Left sub-scanning direction). Therefore, the calculated misregistration amount is
There are a total of 24 ways (6 x 4 ways). Of these 24 types of registration deviation amounts, the largest one is set as the registration deviation amount of this image forming apparatus.

In step S4, it is determined whether or not the above-described registration deviation amount (maximum registration deviation amount) exceeds 50 μm. If the registration deviation amount is 50 μm or less, the process proceeds to step S5 and the printer controller 100 is instructed. First
Instruct to select the dither pattern.

On the other hand, in step S4, the registration shift amount is 50 μm.
If m or more, it is determined that there is a high possibility that tint variation and tint unevenness will occur, and the process proceeds to step S6 to instruct the printer controller 100 to select the second dither pattern.

It should be noted that it is preferable that the threshold value for determining the registration deviation amount (50 μm in the first embodiment) be an optimum value for each image forming apparatus according to the present embodiment.

As described above, in the first embodiment,
By changing the number of screen lines used for recording in accordance with the registration detection result, an optimum image can be provided regardless of the registration shift amount.

In the first embodiment, the number of screen lines is switched by using the multi-value dither for the halftone processing.
However, the method of switching the screen frequency is not limited to this, and another method (PWM method or the like) may be used.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the second embodiment, a case will be described in which the optimum image is provided regardless of the registration shift amount by changing the dot growth direction of the halftone processing according to the detection result of the registration detection unit. In the second embodiment, the specific direction (the sub-scanning direction in the second embodiment)
It is preferable to apply the present invention to an image forming apparatus that tends to have a large registration deviation.

Hereinafter, the color image forming apparatus according to the second embodiment of the present invention will be described in detail with reference to the drawings.
The color image forming apparatus used in the second embodiment and the method for detecting the registration shift amount are substantially the same as those in the first embodiment, and the description of the common configuration and method will be omitted.

First, image processing in the image forming apparatus according to the second embodiment of the present invention will be described. Also in this case, as in the first embodiment, multi-value dither is used for the halftone processing. Note that the second embodiment also uses two types of multivalued dither matrices, and the first dither matrix in the second embodiment is the same as the first dither matrix used in the first embodiment. , The description is omitted.

FIGS. 14A to 14C are diagrams for explaining the second dither matrix according to the second embodiment.

This dither matrix is used when the registration shift amount in the sub-scanning direction is large.
Although the pattern is caused by misregistration, the pattern is advantageous for color unevenness and tint change. On the other hand, since the dot concentration in the highlight portion is weaker than that in the first dither matrix, there is a demerit that the highlight reproducibility is deteriorated.

FIG. 14A shows the dither pattern of the second dither matrix. This dither matrix has 3 dots × 3 dots, which is 9 dots in total, as one pixel, as in the first dither matrix. . On the other hand, the dot growth direction has directionality, and more specifically, it is a pattern that grows vertically in the sub-scanning direction. FIG. 14B shows a dither threshold matrix. Also, FIG. 14 (c)
Represents the correspondence between each threshold value and the output image data. Further, like the first dither pattern, the second dither pattern is also common to each color.

Next, the second dither pattern is used rather than the first dither pattern.
The reason why the dither pattern is advantageous for color unevenness and tint variation will be described.

First, the tint variation when the first dither pattern is used is as described above with reference to FIG. Briefly, when there is a 1-dot registration deviation in the sub-scanning direction, the dot superposition rate becomes 50% (44
% For halftone images).

On the other hand, FIGS. 15 (a) and 15 (b) show
It is a figure explaining the tint variation when a 2nd dither pattern is used. As the image, as in the case of using the first dither pattern, a halftone pattern of 44% (4 dots among 9 dots are recorded) is used.

FIG. 15A shows a case where there is no misregistration between the first color dot and the second color dot.
(B) shows a case where the second color dot is displaced by one dot in the upward (sub-scanning) direction. As can be seen from this figure, if this second dither pattern is used, 100% of the dots will overlap even if there is misregistration. Therefore, under the same conditions as in the first dither pattern, only 50% of the dots will overlap. Can also be said to be advantageous for color variation.

Although only the misregistration between the two colors has been described here, it goes without saying that the same applies to the case of four colors.

Next, the control of the second embodiment will be described with reference to the flowchart of FIG. The control process is started in the same manner as in the first embodiment, and is executed when the power of the main body is turned on and when the photoconductor or the intermediate transfer belt is replaced.

FIG. 16 is a flow chart for explaining the dither pattern selection processing in the image forming apparatus according to the second embodiment of the present invention, and the program for executing this processing is stored in the ROM 1111 of the control unit 110 described above. .

Steps S11 to S1 of this process
The process of No. 3 is performed in steps S1 to S of FIG.
This is similar to the process of 3.

First, in step S11, a registration pattern is formed on the intermediate transfer belt 50. Then step S
In step 12, the registration pattern on the intermediate transfer belt 50 is detected, and the registration sensor 9 is used to detect the position of the registration pattern. Then, the process proceeds to step S13, the registration shift amount is calculated, and the registration shift amount is calculated from the detection result.

Then, the process proceeds to step S14 and step S1.
The selection judgment of the dither pattern is made according to the registration shift amount calculated in 3. Here, as in the case of the above-described first embodiment, the maximum registration deviation amount between the respective colors is set as the registration deviation amount of the image forming apparatus, and when the registration deviation amount (maximum registration deviation amount) exceeds 50 μm, the tint variation, When it is determined that there is a high possibility that color unevenness will occur, the process proceeds to step S15 for determining the directionality of the registration deviation amount. If the registration shift amount is 50 μm or less, the process proceeds to step S16, and the first dither pattern (central growth) is performed.
Select.

In step S15, the maximum value of the registration deviation amount in the sub-scanning direction and the maximum value of the registration deviation amount in the main-scanning direction are compared, and if the former exceeds twice the latter, that is, (in the sub-scanning direction) Registration deviation amount) / (Registration deviation amount in the main scanning direction)> 2
In this case, it is determined that the registration shift has the directivity in the sub-scanning direction, and the process proceeds to step S17 to select the second dither pattern.

In the second embodiment, the directionality judgment threshold value is set to "2", but it is preferable to set it to the optimum value according to the image forming apparatus applicable to the present embodiment.

As described above, according to the second embodiment, by changing the dot growth direction of the halftone processing according to the detection result by the registration detecting means, an optimum image can be provided regardless of the registration shift amount. it can.

[Third Embodiment] In the third embodiment, an optimum image is provided irrespective of the registration shift amount by changing the screen angle of the halftone processing according to the detection result of the registration detecting means. The method will be described.

The third embodiment of the present invention will be described below with reference to the drawings. The color image forming apparatus and the registration deviation amount detecting method used in the third embodiment are substantially the same as those in the first embodiment, and the configuration of the color image forming apparatus is the same as that in the first embodiment. Is similar to
The description is omitted.

First, the image processing according to the third embodiment will be described. Here, as in the case of the above-described first embodiment, multivalued dither is also used for halftone processing in this embodiment. In the third embodiment, two types of multivalued dither matrices are used, but the first dither matrix in the third embodiment is the same as the first dither matrix used in the first embodiment, The description is omitted.

Next, the second dither matrix will be described. In the third embodiment, the dither matrix having a different screen angle for each image plane of each color is used as the second dither matrix.
By using it as a dither matrix, color unevenness and tint variation are prevented. Therefore, this second dither matrix becomes independent for each of Y, M, C, and K. The dither matrix used for the yellow plane is the same as the first dither matrix.

Next, the magenta dither matrix is shown in FIG.
7 (a) and FIG. 17 (b), which will be described in detail below.

FIG. 17A shows the pattern of the second dither matrix, and this dither matrix is
10 dots are 1 pixel. FIG. 17 (b) shows
It is a figure which shows the application state of the repetition of the dither matrix with respect to the input image plane. This makes it possible to add a screen angle to the output image (in this case, 18.4).
Every time). The ROM for storing the dither pattern stores at least one unit of dither matrix as shown in FIG. 17A, or as shown in FIG. The dither matrix of may be stored.

FIG. 18A shows the threshold matrix of this second dither matrix, and FIG. 18B shows the correspondence between each threshold and the output image data.

Next, the cyan dither matrix will be described with reference to FIGS. 19 (a), 19 (b), 20 (a) and 20 (b).

FIG. 19A shows a pattern of the second dither matrix for cyan, and this dither matrix has 10 dots as one pixel, and has a shape symmetrical with the dither pattern for magenta. FIG. 19
(B) is a diagram showing a state in which the dither matrix is repeatedly applied to the input image plane, and the screen angle in this case is -18.4 degrees.

FIG. 20A shows the threshold matrix of this second dither matrix, and FIG. 20B shows the correspondence between each threshold and the image data to be output.

Next, regarding the second dither matrix of black K, FIGS. 21A, 21B, 22A, and 22B.
Will be explained.

FIG. 21A shows a black dither pattern, and this dither matrix has 8 dots as 1 pixel. FIG. 21B is a diagram showing a state in which the dither matrix is repeatedly applied to the input image plane, and the screen angle in this case is 45 degrees.

FIG. 22A shows the threshold matrix of the second dither matrix, and FIG. 22B shows the correspondence between each threshold and the output image data.

The four (Y, M, C, K) colors and four types of patterns are combined to form the second dither pattern. Generally, a dither pattern in which the screen angle is different for each color is effective in preventing color unevenness and tint variation, but it also has a drawback that a moire pattern may occur due to screen interference. is there.

Next, control in the color image forming apparatus according to the third embodiment of the present invention will be described with reference to the flowchart of FIG.

FIG. 23 is a flow chart for explaining the dither pattern selection processing in the image forming apparatus according to the third embodiment of the present invention, and the program for executing this processing is stored in the ROM 1111 of the control unit 110 described above. .

The process is started in the same manner as in the first embodiment, and is executed when the power source of the image forming apparatus main body is turned on and when the photoconductor or the intermediate transfer belt 50 is replaced.

Steps S21 to S2 of this process
The process of No. 4 is performed in steps S1 to S of FIG.
This is the same as the processing of 4.

In step S24, if the registration deviation amount (maximum registration deviation amount) exceeds 50 μm, the tint variation,
It is judged that there is a high possibility that color unevenness will occur, and the step S
In step 26, the second dither pattern (Y, M, C and K have different screen angles) is selected. On the other hand, when the registration shift amount is 50 μm or less, the process proceeds to step S25, and the first dither pattern (screen angle is constant) is selected.

As described above, according to the third embodiment, according to the detection result of the registration detecting means,
By changing the screen angle of the halftone processing, an optimum image can be formed regardless of the registration shift amount.

[Fourth Embodiment] In the fourth embodiment, registration correction is performed according to the detection result of the registration detection means, and if the registration correction is not normally completed, the image processing method is changed. As a result, it is possible to prevent variation in tint and unevenness in tint due to misregistration.

The fourth embodiment of the present invention will be described below with reference to the drawings. Since the color image forming apparatus and the registration deviation amount detecting method used in the fourth embodiment are substantially the same as those in the first embodiment, the description of the configuration and the method thereof will be omitted.

Next, the image processing according to the fourth embodiment will be described. Here, the multi-value dither is used for the halftone processing as in the first embodiment. In the fourth embodiment, two types of multi-valued dither matrices are used.
Furthermore, the first dither matrix according to the fourth embodiment is
This is similar to the first dither matrix used in the first embodiment described above. The second dither matrix is also the same as the second dither matrix used in the above-described first embodiment, and the description thereof will be omitted.

FIG. 24 is a flow chart for explaining the processing in the image forming apparatus according to the fourth embodiment of the present invention.
A program that executes this process is stored in the ROM 1111 of the control unit 110 described above.

This processing is started in the same manner as in the first embodiment, and is executed when the power source of the image forming apparatus main body is turned on and when the photoconductor or the intermediate transfer belt 50 is replaced. Further, steps S31 to S3 of this process
The process of No. 3 is performed in steps S1 to S of FIG.
Since it is the same as the processing of 3, the description thereof will be omitted.

In step S34, registration correction is executed. Here, the misregistration in the sub-scanning direction is corrected by adjusting the scanning line writing timing from the TOP signal corresponding to the vertical synchronizing signal, and the misregistration in the main scanning direction is corrected from the BD signal corresponding to the horizontal synchronizing signal. Correct by adjusting the laser writing timing. Then, the process proceeds to step S35, and similarly to step S31 described above, a registration pattern is formed again on the intermediate transfer belt 50. Next, in step S36, the registration sensor 9 is used, and in step S37, as in step S32,
The position of the registration pattern formed on the intermediate transfer belt 50 is detected. Then, the process proceeds to step S37, and step S3
In the same manner as 3, the registration deviation amount after registration correction is calculated.
Then, the process proceeds to step S38, and in accordance with the registration deviation amount obtained in step S37, as in the case of the above-described first embodiment, the maximum registration deviation amount between the respective colors is set as the registration deviation amount of the image forming apparatus after registration correction. Shift amount (maximum registration shift amount) is 50
See if it exceeds μm. If k exceeds 50 μm, it is determined that the registration correction is not normally performed, and the process proceeds to step S40, where the second dither pattern (100 (lp
i)) is selected. On the other hand, when the registration deviation amount is 50 μm or less, the process proceeds to step S39, it is determined that the registration correction is normally completed, and the first dither pattern (200 (lpi)) is selected.

As described above, according to the fourth embodiment, the registration correction is performed according to the detection result of the registration detection means, and when the registration correction is not normally performed, the image processing method is performed. By changing, it is possible to prevent variation in tint and unevenness in tint due to misregistration.

In the fourth embodiment, in order to judge whether the registration correction is normally completed,
The misregistration amount is detected again, and depending on the size of the misregistration amount,
Although the dither pattern is selected, the judgment may be made by other methods. Specifically, when the registration deviation amount detected before the registration correction exceeds the registration correction possible range, or when the registration pattern cannot be accurately detected, it is determined that the registration correction has ended abnormally. May be.

Further, in the above-described embodiments, the method of using a screen frequency different from that of the first dither matrix as the second dither matrix has been described, but as in the second and third embodiments, the dither growth direction and There is no problem even if dither matrixes with different screen angles are used.

The present invention can be applied not only to the tandem type color image forming apparatus described in the embodiments but also to other type color image forming apparatuses.

In the present embodiment, an example of performing image processing for preventing tint variation and color unevenness caused by an increase in the registration shift amount has been described, but it is related to the registration shift amount. If there are other (correlated) defects in image formation, it is within the scope of the present invention to use image processing for preventing or reducing the image defects.

Even when the present invention is applied to a system composed of a plurality of devices (eg, host computer, interface device, reader, printer, etc.), a device composed of one device (eg, copying machine, facsimile device, etc.) ) May be applied.

Further, an object of the present invention is to supply a storage medium (or recording medium) recording a program code of software for realizing the functions of the above-described embodiment to a system or apparatus, and to supply a computer of the system or apparatus ( Alternatively, it can be achieved by the CPU or MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiment are realized, but also an operating system (OS) running on the computer is executed based on the instruction of the program code. This also includes a case where a part or all of the actual processing is performed and the processing realizes the functions of the above-described embodiments.

Furthermore, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted in the computer or the function expansion unit connected to the computer, based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs some or all of the actual processing,
The case where the functions of the above-described embodiments are realized by the processing is also included.

As described above, according to the present embodiment, an optimum image is provided regardless of the registration shift amount by changing the dither matrix used for image processing according to the detection result of the registration pattern detection means. be able to.
In the above-described embodiment, the number of screen lines is switched by using multi-value dither for halftone processing. However, the method of switching the screen frequency is not limited to this, and another method (for example, PWM method) may be used. In that case, in the configuration of FIG. 2, the control unit 110 outputs a request to the timing signal generation circuit 203 to change the phase or cycle of the screen clock 305, and the pattern signal generator 204 outputs the request. By changing the cycle and / or the phase of the pattern signal 306 to be generated, the screen ruling and the screen angle can be changed.

[0133]

As described above, according to the present invention, an image for adjusting the registration position is formed on an image carrier for image formation or a transfer material carrier, and the position of the formed image is adjusted. There is an effect that a high-quality image having no color shift can be formed by detecting and changing the image processing according to the detected shift in the registration position.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a pulse width conversion circuit according to the present embodiment.

FIG. 3 is a block diagram showing a configuration of a printer controller according to the present embodiment.

FIG. 4 is a diagram showing a configuration of a registration sensor according to the present embodiment.

FIG. 5 is a diagram illustrating output characteristics of the registration sensor according to the present embodiment.

FIG. 6 is a diagram illustrating a positional relationship between a registration sensor and a registration pattern according to the present embodiment.

FIG. 7 is a diagram illustrating a method of calculating a registration deviation amount according to the present embodiment.

FIG. 8 is a diagram illustrating a method for detecting the position of a registration pattern.

FIG. 9 is a diagram illustrating a first dither matrix used in the embodiment of the present invention.

FIG. 10 is a diagram illustrating a second dither matrix used in the first embodiment of the present invention.

FIG. 11 is a diagram for explaining tint variation when the first dither pattern is used in the first embodiment, FIG.
FIG. 6A is a diagram showing an example of dot recording when there is no dot deviation between the first and second colors, and FIG. 9B is a diagram showing an example of recording dots when deviation occurs.

FIG. 12 is a diagram for explaining the effect when the second dither pattern is used in the first embodiment, (a) shows an example of dot recording when there is no dot shift between the first color and the second color, FIG. 9B is a diagram showing an example of recording dots when deviation occurs.

FIG. 13 is a flowchart showing processing in the color image forming apparatus according to the first embodiment of the present invention.

FIG. 14 is a diagram illustrating a second dither matrix used in the second embodiment of the present invention.

FIG. 15 is a diagram illustrating an effect when a second dither pattern is used in the second embodiment, in which (a) shows the first color and the second color.
An example of dot recording when there is no dot deviation between the colors and
FIG. 6B is a diagram showing an example of recording dots when vertical displacement occurs.

FIG. 16 is a flowchart showing processing in the color image forming apparatus according to the second embodiment of the present invention.

FIG. 17 is a diagram illustrating a second dither matrix for magenta used in the third embodiment of the present invention.

FIG. 18 is a (b) diagram showing a threshold matrix (a) of a second dither matrix for magenta in the third embodiment and correspondence between each threshold and image data to be output.

FIG. 19 is a diagram illustrating a second dither matrix for cyan used in the third embodiment of the present invention.

FIG. 20 is a diagram (b) showing the correspondence between the threshold value matrix (a) of the second dither matrix for cyan and the respective threshold values and the output image data in the third embodiment.

FIG. 21 is a diagram illustrating a second dither matrix for black used in the third embodiment of the present invention.

FIG. 22 is a diagram (b) showing the correspondence between the threshold value matrix (a) of the second dither matrix for black and the respective threshold values and the output image data in the third embodiment.

FIG. 23 is a flowchart showing processing in the color image forming apparatus according to the third embodiment of the present invention.

FIG. 24 is a flowchart showing processing in the color image forming apparatus according to the fourth embodiment of the present invention.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/405 H04N 1/40 C 5C079 1/52 D 1/60 1/46 B 1/40 BF term (reference) 2C362 BA52 BA66 BA68 BA71 CA03 CA04 CA09 CA18 CA22 CA39 2H027 DA09 EA18 EB04 EC03 EC07 EC20 EE02 FD08 ZA07 2H030 AA01 AB02 AD13 BB02 BB23 BB42 5C074 AA10 BB03 NN0717NN0707NN0717NN070719NN0707NN19070719NN070719190707191907019NN0707019NN0707019FF07EE19 FF19EE19 FF19EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF19EE07 FF07EE19 FF07EE19 FF19EE07 FF19EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 FF07EE19 EF07 WHEN WHITE WHEN PP58 PP74 PQ08 PQ12 PQ22 TT03 5C079 HB03 KA03 LA24 LC04 LC14 LC20 MA01 MA11 NA03 PA03

Claims (22)

[Claims] 1. An image forming apparatus for inputting an image signal to form an image on a recording medium, the image processing unit executing image processing on the input image signal, and the image processing unit processed by the image processing unit. An image forming unit that forms an image on a recording medium based on an image signal; a unit that forms a position detection image on an image carrier or a transfer material carrier using the image forming unit; An image forming apparatus comprising: a position detection unit that detects a position; and a control unit that controls the image processing in the image processing unit to be changed according to a detection result of the position detection unit. 2. The image forming apparatus according to claim 1, wherein the control unit changes the screen ruling of the halftone processing by the image processing unit. 3. The image forming apparatus according to claim 1, wherein the control unit changes a screen angle of halftone processing by the image processing unit. 4. The image forming apparatus according to claim 1, wherein the control unit changes a dot growth direction of halftone processing by the image processing unit. 5. The image forming apparatus according to claim 1, wherein the image processing unit executes image processing on the input image signal by using a dither matrix. 6. The image forming apparatus according to claim 1, wherein the image processing unit executes image processing by PWM on an input image signal. 7. The image carrier or transfer material carrier carries images corresponding to different colors, and the position detection image is provided for each carrier corresponding to each color of the image carrier or transfer material carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed on the image forming apparatus. 8. The image carrier or the transfer material carrier carries images corresponding to different colors, and the control means carries out an image on the carrier corresponding to each color of the image carrier or the transfer material carrier. The image forming apparatus according to claim 7, wherein the image processing in the image processing unit is changed according to the amount of positional deviation. 9. The image carrier or the transfer material carrier carries images corresponding to different colors, and the control means carries out an image on the carrier corresponding to each color of the image carrier or the transfer material carrier. The image forming apparatus according to claim 5, wherein the dither matrix used in the image processing unit is selected for each color in accordance with the amount of positional deviation. 10. The apparatus according to claim 1, further comprising position correction means for correcting the image forming position by the image forming means according to the position of the position detection image detected by the position detecting means. The image forming apparatus described. 11. The image forming apparatus according to claim 1, wherein the image forming apparatus is a laser beam printer. 12. An image forming method for inputting an image signal to form an image on a recording medium, comprising: an image processing step of executing image processing on the input image signal; and an image processing step performed in the image processing step. An image forming step of forming an image on a recording medium based on an image signal, a step of forming a position detection image on an image carrier or a transfer material carrier, and a position detection step of detecting the position of the position detection image. And a control step of controlling so as to change the image processing in the image processing step according to the detection result of the position detection step. 13. The image forming method according to claim 12, wherein in the control step, the screen ruling of the halftone processing in the image processing step is changed. 14. The image forming method according to claim 12, wherein in the control step, a screen angle of halftone processing in the image processing step is changed. 15. The image forming method according to claim 12, wherein in the control step, the dot growth direction of the halftone processing in the image processing step is changed. 16. The image processing step, wherein the image processing is executed on an input image signal by using a dither matrix.
The image forming method according to item. 17. The image forming apparatus according to claim 12, wherein in the image processing step, image processing is executed on the input image signal by PWM. 18. The image bearing member or the transfer material bearing member,
An image corresponding to a different color is carried, and the position detection image is formed for each carrier corresponding to each color of the image carrier or the transfer material carrier.
The image forming method according to any one of 2 to 17. 19. The image carrier or the transfer material carrier is
Each of the control means carries an image corresponding to a different color, and the control means performs the image processing in the image processing step in accordance with the amount of displacement of the image position of the image carrier or the transfer material carrier corresponding to each color of the image carrier. The image forming method according to claim 12, wherein the image forming method is changed. 20. The image bearing member or the transfer material bearing member,
The images corresponding to different colors are carried, and in the control step, the dither used in the image processing step is used in accordance with the deviation amount of the image position on the carrier corresponding to each color of the image carrier or the transfer material carrier. The image forming method according to claim 16, wherein a matrix is selected for each color. 21. The method according to claim 10, further comprising a position correction step of correcting the image forming position in the image forming step according to the position of the position detection image detected in the position detecting step. The image forming method described. 22. A program for executing the image forming method according to any one of claims 12 to 21 is stored. A computer-readable storage medium.