JP2004287309A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for improving the convenience of a user by performing image formation while maintaining readability or image quality as much as possible without stopping this device even when it is impossible to correct color deviation. <P>SOLUTION: This digital color copying machine is configured to perform disposition under the consideration of the convenience of a user by permitting color print when color deviation lies only in yellow when it is impossible to correct color deviation due to any factor as the result of the detection of color deviation with a resist pattern. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that forms a color image by superimposing a plurality of images.
[0002]
[Prior art]
In recent years, in the field of color image forming apparatuses, a plurality of image forming units are provided for the purpose of increasing the image forming speed, and each image forming unit forms an image of a different color on an image carrier such as a photosensitive drum. A so-called tandem type color image forming apparatus that forms a color image by sequentially transferring images onto a recording sheet conveyed by a recording sheet conveying body such as a transfer belt and superimposing the images is increasing. In a color image forming apparatus employing this method, when transferring and superimposing images of each color formed by each image forming unit, the transfer position of each image is shifted due to an attachment error of the image carrier or uneven rotation speed. As a result, color shift may occur.
[0003]
In order to prevent the occurrence of such color misregistration, a resist pattern having a predetermined shape is formed on each recording sheet transporting body by each image forming unit, and these are detected by a sensor or the like, and the amount of positional displacement between the resist patterns is calculated. In other words, so-called registration correction is performed in which the transfer position of the image by each image forming unit is corrected based on the positional shift amount.
[0004]
Furthermore, if the detection data of the resist pattern includes an erroneous detection due to a scratch on the recording sheet transporter, the registration correction is prohibited, a warning is given, the apparatus is stopped, and image formation is prohibited. Alternatively, there has been proposed an image forming apparatus that permits only image formation in a single color, or permits image formation only when the user acknowledges it (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-2002-351183
[0006]
[Problems to be solved by the invention]
However, in the image forming apparatus described in Patent Document 1, when the detection data of the resist pattern includes an erroneous detection, if the apparatus is stopped, a monochrome image without color shift may be formed. If the image cannot be formed and only the image formation of a single color is permitted, the image cannot be formed based on the color original, so that the user lacks flexibility and is inconvenient. In addition, if the user is notified and the image formation is permitted without performing the registration correction, there remains a problem in image quality and readability.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above problem and to perform image formation while maintaining readability and image quality as much as possible without stopping the apparatus even when color misregistration cannot be corrected. An object of the present invention is to provide an image forming apparatus capable of improving the image quality.
[0008]
[Means for Solving the Problems]
As a specific means for achieving the above object, the present invention according to claim 1 includes a plurality of image forming means for forming images of different colors, and the image of each color formed by each image forming means is provided. In an image forming apparatus capable of forming a color image by multiple transfer onto a transfer unit or a transfer material, a detection unit for detecting a color shift of a color image caused by a shift in a transfer position of any of the image forming units, and a detection unit Correction means for correcting a color shift based on the detection result by the detection means, and a case wherein the color shift detected by the detection means cannot be corrected, and the uncorrectable color shift is a predetermined one of the plurality of image forming means. And control means for permitting the formation of a color image when the image is caused only by the one-color image forming means, and prohibiting the formation of the color image otherwise.
[0009]
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the plurality of image forming units include image forming units that form cyan, magenta, and yellow images, and the predetermined one color is It is characterized by being yellow.
[0010]
According to a third aspect of the present invention, there are provided a plurality of image forming means for forming an image based on image data of different colors, and multiple transfer of the image of each color formed by each image forming means to a transfer means or a transfer material. An image forming apparatus capable of forming a color image by performing a color shift of a color image caused by a shift in a transfer position of any of the image forming means; A correcting unit that corrects the shift, and if the color shift detected by the detecting unit cannot be corrected, all the image data of different colors is replaced with image data of a predetermined one color, thereby forming an image of the one color image. And control means for controlling the formation.
[0011]
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the plurality of image forming units include image forming units that form cyan, magenta, yellow, and black images. It is characterized by being black.
[0012]
The present invention according to claim 5, further comprising a plurality of image forming means for forming images of different colors, wherein the image of each color formed by each of the image forming means is multi-transferred to a transfer means or a transfer material to perform color transfer. In an image forming apparatus capable of forming an image, detecting means for detecting a color shift of a color image caused by a shift of any transfer position of an image forming means, and correcting the color shift based on a detection result by the detecting means Correction means, and determination means for determining whether the original image is monochrome or color based on a predetermined determination condition, and when the color shift detected by the detection means cannot be corrected, the determination means Control means for changing the determination condition so as to be easily determined to be monochrome.
[0013]
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, when the color misregistration detected by the detection unit is uncorrectable, the control unit may add a color condition in addition to a change of the determination condition of the determination unit. It is characterized in that image formation is prohibited.
[0014]
[Action]
According to the image forming apparatus of the first aspect, when the color misregistration is uncorrectable, the uncorrectable color misregistration occurs only in a predetermined one of the plurality of image forming means. If this is the case, the formation of a color image is permitted. Otherwise, the formation of a color image is prohibited.
[0015]
According to the image forming apparatus of the third aspect, when the color misregistration cannot be corrected, all the image data of different colors are replaced with the predetermined one color image data, so that the image of the one color image is replaced. The formation takes place.
[0016]
According to the image forming apparatus of the present invention, when the color misregistration cannot be corrected, the determination condition of the monochrome / color determination unit is changed so that the monochrome / color determination unit is easily determined to be monochrome.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0018]
<First embodiment>
FIG. 1 is a schematic configuration diagram of a digital color copying machine 1 which is an image forming apparatus according to a first embodiment of the present invention. The digital color copying machine 1 has an image reader unit 100 for reading a document image, and an image printer unit 101 for reproducing image data read by the image reader unit 100.
[0019]
The image reader unit 100 includes a document glass 12 on which a document 11 is placed, an exposure lamp 13 for irradiating the document 11, a first mirror 14, a second mirror 15, a third mirror 16, and a reflected light that folds reflected light from the document 11. And a CCD sensor 18 that converts the collected light into an electric signal, and an image processing unit 19 that performs various processes on the converted electric signal.
[0020]
By irradiating the original 11 with the exposure lamp 13 while moving the first slider composed of the exposure lamp 13 and the first mirror 14 and the second slider composed of the second mirror 15 and the third mirror 16 in the direction of the arrow in the figure, The document reflected light incident on the CCD sensor 18 is converted into red, green, and blue electric signals by the CCD sensor 18 (hereinafter, red, green, and blue are represented as R, G, and B, respectively). , A / D conversion converts the analog signal into image data consisting of an RGB 8-bit digital signal.
[0021]
The image printer unit 101 includes an image control unit 20, an exposure scanning unit 30, an image processing unit 40, a paper feeding unit 50, and a fixing unit 60, and forms an image by a known electrophotographic method.
[0022]
The image control unit 20 performs well-known image processing such as shading correction, line-to-line correction, and scaling movement processing on the RGB image data output from the image processing unit 19, and then performs magenta, cyan, yellow, The image data is converted into image data of each of the reproduced colors of black (hereinafter, each of the reproduced colors of magenta, cyan, yellow, and black is represented as M, C, Y, and K, and the numbers of the components related to each of the reproduced colors are M, C, Y, and K). C, Y, and K are added as subscripts). The image data is temporarily stored in an image memory (not shown) in the image control unit 20 for each of the reproduced colors of M, C, Y, and K, and is then synchronized with supply of a recording sheet as a transfer material. It is read out for each scanning line, and at the same time becomes a drive signal for the LED arrays 42M to 42K.
[0023]
The exposure scanning unit 30 deflects light emitted from LED arrays 42M to 42K, which will be described later, by a polygon mirror 31 based on a driving signal output from the image control unit 20, and reflects the light by an fθ lens (not shown). The light is guided to the photosensitive drums 43M to 43K via the mirror groups 32M to 32K.
[0024]
The image processing unit 40 includes a recording sheet transport unit 44 in which a transfer belt 45 serving as a transfer unit is stretched around a driving roller 46 and a driven roller 47, and an upstream side (hereinafter, referred to as a recording sheet transport direction) facing the transfer belt 45. An image forming unit 41M of each color of M, C, Y, and K, which is an image forming unit arranged at a predetermined interval from the “upstream side” to the downstream side in the transport direction (hereinafter, simply referred to as “downstream side”). ~ 41K. Each of the image forming units 41M to 41K is a known unit including a photosensitive drum 43M to 43K, an LED array 42M to 42K for exposing and scanning the surface thereof, a charging charger, a developing unit, a transfer charger, and a cleaner. The image forming units 41M to 41K are main parts of an image forming unit 41K that forms an image using black toner and an image forming unit 41M to 41Y that forms an image using MCY color toner so that maintenance can be easily performed. Are unitized, and are detachable from the main body of the digital color copying machine 1 in units of each unit. The paper supply unit 50 includes paper supply cassettes 51, 52, and 53 for storing recording sheets having different sizes, pickup rollers 54, 55, and 56 for feeding out the recording sheets from the paper supply cassettes, and It includes a registration roller 57 and the like for setting a timing for sending the recording sheet to the transfer belt 45.
[0025]
Before the photosensitive drums 43M to 43K are subjected to exposure by the LED arrays 42M to 42K, residual toner on the surface is removed by a cleaner, and thereafter, the photosensitive drums are uniformly charged by a charging charger. As described above, the photosensitive drums 43M to 43K are exposed while being uniformly charged, and an electrostatic latent image is formed on the surface thereof. Each electrostatic latent image is developed by a developing device of each color, whereby M, C, Y, and K toner images are formed on the surfaces of the photosensitive drums 43M to 43K. The toner images of the respective colors are sequentially transferred onto the recording sheet conveyed by the transfer belt 45 by the electrostatic action of the transfer charger disposed on the back side of the transfer belt 45 at each transfer position. At this time, the image forming operation of the image forming unit for each color is performed with a timing shifted from the upstream side to the downstream side so that the toner image is transferred to the same position of the conveyed recording sheet in a superimposed manner. Is done.
[0026]
The recording sheet on which the toner images of each color have been multiplex-transferred is conveyed to a fixing unit 60 by a transfer belt 45, and is pressed under high heat by a fixing roller 61 having a heater therein, so that the toner particles are fused on the recording sheet surface. After being attached and fixed, the sheet is discharged to a sheet discharge tray 70.
[0027]
FIG. 2 is a block diagram showing the image controller 20 and its periphery in FIG. However, only the registration correction unit 200, which is an element related to registration correction, is shown. The registration correction related unit 200 generates a pattern data including data on a shape, a gradation (density) value, a formation position in a main scanning direction, and a formation timing (a formation position in a sub-scanning direction) of a resist pattern described later. A data generation unit 202, an engine control unit 201 that controls each unit of the image printer unit 101 so as to form a resist pattern in accordance with the pattern data, and a correction amount using the shift amount data measured by the pattern detection unit 48 as a detection unit. It comprises a color misregistration correction calculation unit 203 as a correction unit for calculating, and a registration correction control unit 204 as a control unit for executing various controls described later based on the calculated correction amount. Each of these components is functionally realized by processing executed by a CPU or the like constituting the image control unit 20 according to a predetermined computer program. Further, each of these components may be realized by a dedicated hardware logic circuit.
[0028]
Next, the processing executed by the registration correction unit 200 will be described with reference to the flowchart shown in FIG. In the first embodiment of the present invention, full color printing by MCYK is permitted when the deviation amount exceeds the correctable range only in Y, and otherwise, full color printing by MCYK is prohibited. Hereinafter, a flow until the printing is completed will be described.
[0029]
First, when a command to perform registration correction is issued from the image control unit 20 (YES in step S301), the pattern data generation unit 202 generates pattern data including data on the shape, formation position, and the like of the resist pattern (step S302). ). The timing for performing the registration correction can be arbitrarily selected from various timings, such as when the power is turned on, when an opening / closing door (not shown) is opened / closed, or when a print command is not issued for a long time.
[0030]
The engine control unit 201 controls each unit of the image printer unit 101 to form a resist pattern according to the pattern data on the recording sheet transport unit 44, which is a recording sheet transport area on the transfer belt 45. The formed resist pattern is detected by a pattern detection unit 48 such as a sensor, and the amounts of M, C, and Y deviations from K are measured based on the detection results (step S303).
[0031]
Various known methods can be employed for measuring the resist pattern and the amount of deviation. For example, as shown in FIG. 4, K, Y, C, and M linear resist patterns extending parallel to a direction (main scanning direction) orthogonal to the transfer direction of the transfer belt 45 are formed on the recording sheet transfer unit 44. Are formed at intervals of 1 mm in the transport direction (sub-scanning direction). The formed resist pattern is detected by the pattern detecting section 48 along with the rotation of the transfer belt 45. A clock of a predetermined frequency is counted by an oscillator (not shown), and the distance between the resist patterns is specified by the number of clocks (time) when the resist pattern of each color is detected. For example, if the distance between the resist pattern of K and the resist pattern of C is determined to be 2.03 mm in the unit of distance, the resist patterns of K and C should originally be formed at a timing of 2 mm. The shift amount is 2 (mm) −2.03 (mm) = − 0.03 (mm). The digital color copying machine 1 according to the present embodiment measures the amounts of shift of M, C, and Y with respect to K on the basis of K. For example, measures the amounts of shift of C, Y, and K with respect to M based on M. For example, the shift amount may be measured based on any other color.
[0032]
Returning to FIG. 3, next, the color misregistration correction calculation unit 203 calculates a correction amount using the measured misalignment amount data (step S304).
[0033]
At this time, when the shift amount is smaller than a preset threshold value R for determining whether correction is possible, that is, when the shift amount is within the correctable range (YES in step S305), the color shift correction is performed. The required image forming timings of the image forming units 41M to 41Y are corrected based on the correction amount calculated by the arithmetic unit 203, and printing is executed according to a job request from the user (YES in step S312) (step S313). .
[0034]
On the other hand, when the shift amount is larger than the threshold value R, that is, when the shift amount exceeds the correctable range (NO in step S305), and when only the Y exceeds the correctable range (YES in step S306), the registration The correction control unit 204 ignores the deviation (that is, without performing registration correction), and executes printing in accordance with the job request from the user (YES in step S312) (step S313). This is because Y is known to have the lowest visibility when the ground is white compared to other color schemes (pure color, white, black, gray, etc.). It is based on the idea that it is hardly noticeable even if it does not pose a problem in practical use.
[0035]
However, if the value exceeding the correctable range includes at least one of M and C in which color misregistration is noticeable (NO in step S306), a flag of registration correction calculation abnormality is set, and
The registration correction control unit 204 prohibits full-color printing by MCYK (step S307). At that time, a message such as "registration correction calculation error", "Please call a service person", or "Cannot print in full color" is displayed on the display device 110 (see FIG. 2) such as a display on the operation panel. Notify the user of the occurrence of the abnormality. In this state, there is a job request from the user (YES in step S308), and if the request is full-color printing (YES in step S309), the registration correction control unit 204 rejects printing (step S310). ). However, if the request from the user is other than full-color printing such as monochrome printing or mono-color printing using one or two of the MCY image forming units 41M to 41Y other than K (NO in step S309) ) Is executed (step S313).
[0036]
Note that the digital color copying machine 1 according to the present embodiment is capable of correcting the misregistration amount even when the color misregistration correction calculation unit 203 does not perform the calculation normally because the resist pattern is not correctly generated. The same processing as in the case of exceeding is performed. In short, whatever the cause, the above processing is performed when the generated color shift cannot be corrected.
[0037]
After the registration correction, if a registration correction command is issued again before the user requests a job (YES in step S301), the registration correction is repeated again (steps S302 to S304). At that time, when the correction was not completed normally at the previous registration correction, but the correction was completed normally when the registration correction was performed again (for example, an abnormal value was output due to a registration pattern detection error at the previous registration correction). Correction could not be performed, but this time it could be detected normally and could be corrected), the registration correction control unit 204 permits full-color printing, and displays the latest state on the display device 110. . On the other hand, when the registration correction command is not issued, the previous registration correction result is held.
[0038]
<Second embodiment>
Next, a second embodiment of the present invention will be described. The configuration of the digital color copying machine according to the second embodiment is the same as that of the digital color copying machine 1 according to the first embodiment shown in FIGS. In the digital color copying machine 1 according to the second embodiment of the present invention, all the MCY image data is replaced with K image data regardless of the MCY color in which the shift amount exceeds the correctable range. The setting of the image forming process is changed so as to print with K.
[0039]
Hereinafter, the flow of processing until printing is completed will be described with reference to the flowchart of FIG. In FIG. 5, the processing in steps S501 to S505 is the same as the processing in steps S301 to S305 in FIG. 3, and a description thereof will be omitted, and only different points will be described.
[0040]
In the digital color copying machine 1 according to the second embodiment, when the shift amount exceeds the correctable range (NO in step S505), the registration correction control unit 204 uses the switching device such as a selector to perform M, C, and Y. Are switched to K image data buses, and the setting is changed so that all M, C, Y, and K image data are printed in K (step S506). At this time, a message “Print all in black” is displayed on the display device 110 such as the operation panel to inform the user that the setting has been changed. In this state, if there is a job request from the user (YES in step S507), printing is performed in all colors black in accordance with the setting (step S508). On the other hand, when the shift amount is within the correctable range (YES in step S505), the setting of the MCYK image data is not changed.
[0041]
After the registration correction, if a registration correction command is issued again before the user requests a job (NO in step S507, YES in step S501), the processes of S501 to S506 are performed again as in the case of FIG. repeat.
[0042]
When the reference for measuring the shift amount is not K, and when the shift amount exceeds the correctable range is K, color printing is performed only by the MCY image forming units 41M to 41Y in addition to the above monocolor printing. May be.
[0043]
If the deviation exceeds the correctable range (NO in step S505), the registration correction control unit 204 decomposes the image data of the original into image data of each color of MCYK, and selects one of the image data according to the user's selection. It is also possible to perform color separation printing in which only the color is printed.
[0044]
Further, similarly to the first embodiment, when only the Y has a shift amount exceeding the correctable range, normal color printing is permitted, and in other cases, the setting of the image data is changed. You may do it.
[0045]
<Third embodiment>
A third embodiment of the present invention will be described. The configuration of the digital color copying machine according to the third embodiment is basically the same as that of the digital color copying machine 1 according to the first embodiment shown in FIGS. 1 and 2, except that the original is a monochrome original or a color original. The difference is that an automatic color selection function (ACS) for determining whether the document is a document is provided.
[0046]
In the digital color copying machine 1 according to the third embodiment of the present invention, regardless of the MCYK color in which the shift amount exceeds the correctable range, the threshold value used as the reference for ACS determination is increased from the normal threshold value α. The original is rewritten to a threshold value β that can be easily identified as monochrome.
[0047]
Here, the ACS determination method will be described. First, an arbitrary number of dots are extracted from the RGB image data obtained by scanning the document, and saturation data indicating the degree of vividness of each dot is obtained. Therefore, a difference max-min between the maximum value max of the saturation data and the minimum value min of the saturation data is obtained, and if the value of the difference max-min is larger than the threshold value, the document is determined to be a color document, and the threshold value is determined. If smaller, the document is determined to be a monochrome document. Therefore, the larger the threshold value, the more easily the document is determined to be monochrome. That is, the thresholds α and β have a relationship of α <β. Note that the determination method is not limited to the above method, and various known methods can be adopted.
[0048]
Hereinafter, the flow of processing until printing is completed will be described with reference to FIG. Note that the processing in steps S601 to S605 in FIG. 6 is the same as the processing in steps S301 to S305 in FIG. 3, and thus description thereof will be omitted, and only differences will be described.
[0049]
In the digital color copying machine 1 according to the third embodiment, when the shift amount exceeds the correctable range (NO in step S605), the registration correction control unit 204 changes the ACS threshold from the normal threshold α to monochrome. (Step S606). At this time, the display device 110 such as a display on the operation panel displays "The setting value of the color / monochrome determination is being changed" to notify the user that the ACS threshold has been changed. In this state, if there is a job request from the user (YES in step S607), the color / monochrome determination of the document is performed using the changed threshold value β, and printing is performed according to the determination result (step S607). S608). On the other hand, if the shift amount is within the correctable range (YES in step S605), the setting of the threshold α is not changed (step S609).
[0050]
After the registration correction, if a registration correction command is issued again before the user requests a job (NO in step S607, YES in step S601), the processes in steps S601 to S606 and S609 are performed again as in the case of FIG. Repeat the process.
[0051]
If the original is determined to be a color original in the ACS, it is desirable to prohibit full-color printing.
[0052]
Note that the present invention is not limited to a digital color copying machine, but is applicable to all image forming apparatuses that form a color image by superimposing a plurality of images, such as a printer and a facsimile. It is.
[0053]
【The invention's effect】
As described in detail above, in the image forming apparatus according to the first aspect of the present invention, the color image formation is prohibited when the color misregistration cannot be corrected for only yellow in which the color misregistration is inconspicuous. Therefore, the color image formation is not prohibited until the readability and the image quality are not substantially affected, and the usability for the user is improved.
[0054]
In the image forming apparatus according to the third aspect of the present invention, the image forming operation is not stopped even when the correction of the color misregistration is impossible, and all the image data of each color is replaced with image data of a predetermined one color. By printing in the one color, it is possible to form an image in an emergency evacuation state while maintaining readability even for a color original, thereby improving the usability for the user.
[0055]
In the image forming apparatus according to the fifth aspect of the present invention, the image forming operation is not stopped even when the color misregistration cannot be corrected, and the determination condition of the monochrome / color determination unit is changed so as to be easily determined to be monochrome. By doing so, it is possible to provide a printed matter in monochrome in a case where there is substantially no effect on readability and image quality even when printed in monochrome, such as a document image with a small number of color portions, and user convenience is improved.
[Brief description of the drawings]
FIG. 1 is a configuration sectional view of a digital color copying machine 1 according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a registration correction section 200 of the digital color copying machine 1 shown in FIG.
FIG. 3 is a flowchart illustrating a process flow until printing is completed in the digital color copying machine according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of a resist pattern.
FIG. 5 is a flowchart illustrating a process flow until printing is completed in a digital color copying machine according to a second embodiment of the present invention.
FIG. 6 is a flowchart illustrating a process flow until printing is completed in a digital color copying machine according to a third embodiment of the present invention.
[Explanation of symbols]
1: Digital color copier
100; Image reader unit
101: Image printer unit
11; manuscript
12; Original glass
13; fluorescent light
14; 1st mirror
15; second mirror
16; third mirror
17; lens
18; CCD sensor
19: Image processing unit
20; image control unit
30; exposure scanning section
31; polygon mirror
40; Image processing unit
41M to 41K; imaging unit
42M to 42K; LED array
43M to 43K; photoconductor drum
44; recording sheet transport section
45; transfer belt
46; drive roller
47; driven roller
48; pattern detection unit
50; paper feed unit
51-53; paper cassette
54-56; Pickup roller
57; registration roller
60; fixing unit
61; fixing roller
70; paper output tray
110; display device
200; resist correction related section
201; Engine control unit
202; pattern data generation unit
203: color misregistration correction calculation unit
204: registration correction control unit

Claims (6)

An image forming apparatus that includes a plurality of image forming units that form images of different colors, and that can form a color image by multiple-transferring each color image formed by each image forming unit to a transfer unit or a transfer material. ,
Detecting means for detecting a color shift of a color image caused by a shift of any transfer position of the image forming means;
Correction means for correcting the color misregistration based on the detection result by the detection means,
This is a case where the color shift detected by the detection means is uncorrectable, and the uncorrectable color shift is caused by only a predetermined one-color image forming means of the plurality of image forming means. Control means for permitting the formation of a color image in some cases and prohibiting the formation of a color image in other cases;
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the plurality of image forming units include image forming units that form images of cyan, magenta, and yellow, and the predetermined one color is yellow. apparatus. A plurality of image forming means for forming an image based on image data of different colors is provided, and a color image can be formed by multi-transferring each color image formed by each image forming means to a transfer means or a transfer material. In the image forming apparatus,
Detecting means for detecting a color shift of a color image caused by a shift of any transfer position of the image forming means;
Correction means for correcting the color misregistration based on the detection result by the detection means,
When the color misregistration detected by the detection means cannot be corrected, all the image data of the different colors is replaced with image data of a predetermined one color, so that an image is formed by the one color image. Control means for performing
An image forming apparatus comprising: 4. The image forming apparatus according to claim 3, wherein the plurality of image forming units include image forming units that form images of cyan, magenta, yellow, and black, and the predetermined one color is black. apparatus. An image forming apparatus that includes a plurality of image forming units that form images of different colors, and that can form a color image by multiple-transferring each color image formed by each image forming unit to a transfer unit or a transfer material. ,
Detecting means for detecting a color shift of a color image caused by a shift of any transfer position of the image forming means;
Correction means for correcting the color misregistration based on the detection result by the detection means,
Determining means for determining whether the original image is monochrome or color based on predetermined determination conditions,
When the color shift detected by the detection unit is uncorrectable, a control unit that changes a determination condition of the determination unit so as to be easily determined to be monochrome,
An image forming apparatus comprising: 6. The method according to claim 5, wherein when the color shift detected by the detection unit is not correctable, the control unit prohibits the formation of a color image in addition to the change of the determination condition of the determination unit. The image forming apparatus according to any one of the preceding claims.

Images