JP2004341232A - Image forming apparatus and image density control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize exact detection of an abnormal state of an apparatus without increasing processing time, with respect to a technology for controlling image density based upon patch image density detection results. <P>SOLUTION: Among patch images Ip(1) to Ip(6) formed by altering and setting a development bias Vb that is a density control factor, the two patch images Ip (1) and Ip(6) formed with the minimum development bias Vb (1) and the maximum development bias Vb(6), respectively, are used as "patch images for determining an abnormal state". Density differences ΔDv are calculated from the density detection result of them. In the case that the value does not reach a predetermined reference value, it is determined as an error. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention forms a patch image at each stage while changing and setting the density control factor in multiple stages, detects the image density of each patch image, and adjusts the density control factor based on the detection result. The present invention relates to an image forming apparatus for controlling density and an image density control method.
[0002]
[Prior art]
2. Description of the Related Art An electrophotographic image forming apparatus such as a printer, a copying machine, and a facsimile machine includes a density sensor for detecting an image density of a toner image to be formed. As the density sensor, an optical method that irradiates light toward the surface of an image carrier that carries a toner image and detects light emitted from the surface is generally used. In an image forming apparatus having such a density sensor, a test small image (patch image) having a predetermined image pattern is formed as necessary, and the image density is detected by the density sensor. By adjusting various image forming conditions based on the results, a predetermined image density can be stably obtained.
[0003]
For example, in the image forming apparatus described in Patent Document 1 filed by the present applicant, the development bias as a density control factor affecting the image density is optimized as described below. That is, a patch image is formed while the developing bias is changed and set within the variable range, and the optimum value of the developing bias at which the image density becomes the target density is found from the density detection results of those patch images. Then, in order to accurately obtain the optimum value, two processing modes having different developing bias variable ranges are prepared, and one of them is selectively executed according to the operation state of the apparatus.
[0004]
[Patent Document 1]
JP 2001-75319 A (FIG. 5)
[0005]
[Problems to be solved by the invention]
In this type of image forming apparatus, a change in the density control factor may not be correctly reflected in the density detection result of the patch image due to an abnormality of the apparatus. For example, if the toner adheres to the density sensor and becomes dirty, a part of the light emitted from the density sensor and a part of the light incident on the density sensor are blocked or scattered, and the light amount cannot be detected correctly. As a result, the detection accuracy of the image density decreases.
[0006]
As described above, in a state where the change of the density control factor is not correctly reflected in the density detection result, it is not possible to accurately adjust the image forming condition based on the detection result. However, in the above-described related art, such a phenomenon is not considered, and therefore, if density detection is performed while the detection accuracy is lowered, the image forming condition may be set to an unfavorable condition.
[0007]
On the other hand, in order to solve this problem, it is expected to perform an operation check of the apparatus including the density sensor before performing the density detection, but a certain effect can be expected. In this case, the processing time for controlling the image density is reduced. , The waiting time of the user increases, the throughput of image formation decreases, and the like, which hinders an increase in the speed of the apparatus.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of a technique for controlling an image density based on a detection result of a patch image density to accurately detect an abnormality of an apparatus without increasing a processing time. I do.
[0009]
[Means for Solving the Problems]
An image forming apparatus and an image density control method according to the present invention achieve a patch image at each stage while changing and setting a density control factor affecting image density to N stages (an integer of N ≧ 2). And controlling the image density by detecting the image densities of the N patch images, and adjusting the density control factor based on the detection results. The number of patch images (an integer of 2 ≦ M ≦ N) is defined as an abnormality determination patch image, and the presence or absence of an abnormality in the apparatus is determined based on the image density detection result of the abnormality determination patch image. .
[0010]
In the invention configured as described above, an image is actually formed, and the presence or absence of an abnormality in the apparatus is determined based on the density detection result. Therefore, it is possible to take appropriate measures when the image density indicates an abnormal value. As a result, it is avoided that the image forming conditions are set to unfavorable conditions. Further, since a patch image formed for performing density control is used as an image for abnormality determination, it is not necessary to separately form an image for abnormality determination or check the operation of the apparatus in advance. Therefore, the image density control can be performed in a short time without increasing the processing time.
[0011]
Note that the “density detection result” here refers to a value obtained as an image density of the patch image as a result of performing density detection on the formed patch image, and therefore, necessarily a true value of the patch image. It does not refer to image density. That is, in the abnormality determination of the present invention performed based on the image density detection result, either the case where the image density itself of the patch image is abnormal or the case where an abnormal detection result is obtained due to the abnormality in the density detection process. Can also be detected.
[0012]
Here, two or more patch images formed with different setting values of the density control factors are used as the patch images for abnormality determination. As described above, the reliability of determination can be improved by using the density detection results of a plurality of patch images. In this case, a predetermined calculation may be performed on the density detection results of a plurality of patch images, and the result may be used to determine the presence or absence of an abnormality. For example, the determination can be performed using an average value of the density detection results of a plurality of patch images, a relative magnitude relationship between the density detection results, and the like.
[0013]
For example, the number M of the patch images for abnormality determination is set to 2, and the presence or absence of an abnormality of the apparatus can be determined based on the ratio or difference of the image densities detected for each of the two patch images. More specifically, when the ratio or difference of the image densities is not within a predetermined appropriate range, it can be determined that there is an abnormality in the apparatus.
[0014]
That is, for two patch images formed under two different image forming conditions, it is expected that the difference between the conditions is reflected in the image density. Therefore, if the density detection results of these two patch images are not in a relatively appropriate relationship, it can be determined that there is some abnormality in the apparatus.
[0015]
As a method of selecting such two abnormality determination patch images, for example, a patch image having the highest detected image density among the plurality of patch images is set as one of the two abnormality determination patch images. The detected patch image with the lowest image density can be used as the other of the abnormality determination patch images. Further, as another selection method, among the plurality of patch images, the patch image when the density control factor is set such that the image density is the highest in the relationship between the density control factor and the image density is set as the patch image. A patch image when the density control factor is set so that the image density becomes the lowest density in the relationship between the density control factor and the image density while being one of the two abnormality determination patch images. It can be the other of the patch images.
[0016]
Among the two selection methods exemplified here, in the former, the patch image having the highest measured image density value and the lowest image density value among the patch images are determined as the patch images for abnormality determination. On the other hand, in the latter case, a patch image that would have the highest density and a patch image that would have the lowest density if there is no abnormality in the apparatus are not the measured values but the patch images for abnormality determination. In any case, among the plurality of patch images, the two patch images are most remarkably different in density from each other. As described above, by performing an abnormality determination on an image having a remarkable difference in density between two patch images as an abnormality determination patch image, it is possible to more reliably detect an abnormality in the apparatus.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Two embodiments of the image forming apparatus according to the present invention will be described below. However, between these two embodiments, the device configuration and the basic operation are the same, and only a part of the operation is different. . Thus, here, the device configuration and operation common to the two embodiments will be described first, and then the characteristic operation of each of the two embodiments will be sequentially described.
[0018]
(Device configuration)
FIG. 1 is a diagram showing an apparatus configuration of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus 1 forms a full-color image by superimposing toners (developers) of four colors of yellow (Y), cyan (C), magenta (M), and black (K), or forms a black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In the image forming apparatus 1, when an image signal is provided from an external device such as a host computer to the main controller 11, the engine controller 10 controls each unit of the engine unit EG in accordance with a command from the main controller 11 to generate a predetermined image. A forming operation is performed to form an image corresponding to the image signal on the sheet S.
[0019]
In the engine section EG, the photoreceptor 22 is provided rotatably in the direction of arrow D1 in FIG. A charging unit 23, a rotary developing unit 4, and a cleaning unit 25 are arranged around the photoconductor 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes toner remaining on the surface of the photoconductor 22 after the primary transfer, and collects the toner in a waste toner tank provided inside. The photoconductor 22, the charging unit 23, and the cleaning unit 25 integrally constitute a photoconductor cartridge 2, and the photoconductor cartridge 2 is integrally detachable from the main body of the apparatus 1.
[0020]
Then, the light beam L is emitted from the exposure unit 6 toward the outer peripheral surface of the photoconductor 22 charged by the charging unit 23. The exposure unit 6 forms an electrostatic latent image corresponding to the image signal by exposing the light beam L onto the photoreceptor 22 in accordance with an image signal provided from an external device.
[0021]
The electrostatic latent image thus formed is developed by the developing unit 4 with toner. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 provided rotatably about a rotation axis orthogonal to the paper surface of FIG. A yellow developing device 4Y containing a toner, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Then, based on a control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoconductor 22 or a predetermined gap is formed. When the developing device is positioned at a predetermined developing position facing away from the developing device, toner is applied to the surface of the photoconductor 22 from a developing roller provided in the developing device and carrying a toner of a selected color. As a result, the electrostatic latent image on the photoconductor 22 is visualized with the selected toner color.
[0022]
The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer area TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched over a plurality of rollers 72 to 75, and a driving unit (not shown) that rotates the roller 73 to rotate the intermediate transfer belt 71 in a predetermined rotation direction D2. It has. When the color image is to be transferred to the sheet S, the toner images of each color formed on the photoreceptor 22 are superimposed on the intermediate transfer belt 71 to form a color image, and are taken out of the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed along the conveyance path F to the secondary transfer area TR2.
[0023]
At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing for feeding the sheet S to the secondary transfer area TR2 is controlled. Specifically, a gate roller 81 is provided on the transport path F in front of the secondary transfer region TR2, and the sheet is rotated by the gate roller 81 in accordance with the timing of the orbital movement of the intermediate transfer belt 71. S is sent to the secondary transfer area TR2 at a predetermined timing.
[0024]
Further, the sheet S on which the color image has been formed is conveyed to the discharge tray 89 provided on the upper surface of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. In the case where images are formed on both sides of the sheet S, when the rear end of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is transported along the reverse transport path FR in the direction of arrow D3. Then, the sheet is again put on the transport path F before the gate roller 81. At this time, in the secondary transfer area TR2, the surface of the sheet S on which the image is transferred by contact with the intermediate transfer belt 71 is transferred first. It is the opposite side of the surface. Thus, an image can be formed on both sides of the sheet S.
[0025]
In addition, the device 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11, as shown in FIG. The display unit 12 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, provides an operation guide to the user, a progress status of an image forming operation, and further indicates occurrence of an abnormality in the apparatus and replacement time of any unit. A predetermined message for notification is displayed.
[0026]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image provided from an external device such as a host computer via the interface 112. Reference numeral 106 denotes a ROM for storing an operation program executed by the CPU 101 and control data for controlling the engine unit EG, and reference numeral 107 denotes a RAM for temporarily storing the operation results and other data in the CPU 101. is there.
[0027]
A cleaner 76 is arranged near the roller 75. The cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, while moving to the roller 75 side, the blade of the cleaner 76 contacts the surface of the intermediate transfer belt 71 wrapped around the roller 75, and the toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Is removed. As described above, by bringing the cleaner 76 into contact with the area around the roller 75 in the surface area of the intermediate transfer belt 71, the cleaner 76 is not affected by the fluttering caused by the rotation of the belt 71, and thus has a constant effect. With this pressure, the cleaner 76 can be brought into contact with the intermediate transfer belt 71, so that an excellent toner removing effect can be obtained.
[0028]
Further, a density sensor 60 is disposed near the roller 75. The density sensor 60 is provided to face the surface of the intermediate transfer belt 71, and measures the image density of a toner image formed on the outer peripheral surface of the intermediate transfer belt 71 as necessary. As this type of density sensor, a known technique, for example, a sensor that irradiates a toner image with light and detects the amount of reflected light can be used.
[0029]
Based on the measurement results, the apparatus 1 adjusts operating conditions of each section of the apparatus that affect image quality, for example, development bias applied to each developing unit and intensity of the exposure beam L. , The approaches differ from each other in the two embodiments. Also, the presence or absence of an abnormality in the apparatus is determined using the same measurement result.
[0030]
(1st Embodiment)
FIG. 3 is a flowchart showing a first embodiment of the developing bias adjustment in the image forming apparatus. FIG. 4 is a diagram showing a patch image formed in this embodiment. In this embodiment, a patch image is formed while changing and setting the developing bias Vb, and the optimum developing bias Vbopt for setting the image density to the target density Dtgt is calculated based on the density detection result.
[0031]
First, a patch image of a predetermined pattern (for example, a solid image) is formed at each bias value while changing the developing bias Vb from the minimum value Vb (1) to the maximum value Vb (6) in the variable range in six steps, one step at a time. Then, the image is transferred to the intermediate transfer belt 71 (Step S101). Thus, as shown in FIG. 4A, on the surface of the intermediate transfer belt 71, six patch images Ip (1) to Ip (6) formed with different developing biases along the moving direction D2. Will be lined up.
[0032]
Next, the image density of each of these patch images Ip (1) to Ip (6) is detected by the density sensor 60 (step S102). Here, the density detection results D of the patch images Ip (1) to Ip (6) are represented by Dv (1) to Dv (6), respectively. The subscript “v” indicates that the developing bias Vb is to be controlled.
[0033]
In this image forming apparatus, if there is no abnormality in the apparatus, the image density increases as the developing bias Vb increases. Therefore, plotting the relationship between the developing bias Vb and the density detection result D of the patch image should be, for example, a white circle shown in FIG. 4B. Therefore, the density detection result Dv (6) of the patch image Ip (6) formed by setting the developing bias Vb to the maximum value Vb (6) is obtained by setting the developing bias Vb to the minimum value Vb (1). The density detection result Dv (1) of the formed patch image Ip (1) should be a sufficiently large value.
[0034]
However, if there is an abnormality in the device, a result different from the above may be obtained. For example, if the density sensor 60 is contaminated due to adhesion of toner or the like, part of the emitted light emitted from the density sensor 60 toward the patch image and part of the incident light reflected on the patch image and incident on the density sensor 60 are blocked.・ It is scattered. In this case, the density detection results Dv (1) to Dv (6) of the patch images Ip (1) to Ip (6) are different from the actual image densities of the patch images. Further, for example, contamination on the surface of the intermediate transfer belt 71 serving as a base of the patch image may affect the density detection result. On the other hand, if the developing bias Vb actually applied to the developing device does not change correctly according to the setting due to an abnormality in the electric circuit, the density change of each of the patch images Ip (1) to Ip (6) does not appear. .
[0035]
As described above, an abnormality appearing in the process of bias adjustment, that is, an abnormality in which the image density of each patch image cannot be correctly detected or the density itself of the patch image does not show an original change, is referred to as the two patch images Ip described above. It can be detected by comparing the density detection results of (1) and Ip (6). That is, in this embodiment, the patch image Ip (6) formed by setting the developing bias Vb to the maximum value Vb (6) and the patch image Ip formed by setting the developing bias Vb to the minimum value Vb (1). By comparing the density detection results Dv (6) and Dv (1) with (1) as an “abnormality determination patch image”, the presence or absence of this type of abnormality can be determined.
[0036]
Specifically, as shown in FIG. 3, the difference ΔDv between the density detection results Dv (6) and Dv (1) of the two abnormality determination patch images is obtained (step S103), and the density difference ΔDv is set in advance. When the density difference ΔDv is equal to or more than the reference value, it is determined that the density difference is appropriate. On the other hand, when the density difference is less than the reference value, it is determined that there is some abnormality (step S104).
[0037]
The reference value is a value determined based on a variable range of the developing bias Vb and a corresponding change in image density in design. That is, the variable range of the developing bias Vb is set so as to secure a necessary and sufficient density adjustment range, but the density adjustment range may be narrowed due to an abnormality in the apparatus. Therefore, in order to secure the minimum density adjustment range, an allowable lower limit value of the density difference ΔDv is set as the reference value, and when the density difference ΔDv is less than the reference value, it is determined that there is an abnormality. This makes it possible to accurately determine the presence or absence of such an abnormality.
[0038]
When the density difference ΔDv is appropriate, the optimum developing bias Vbopt is calculated based on the density detection results of the patch images Ip (1) to Ip (6) (step S105). In the example of FIG. 4B, the target value Dtgt of the image density D is determined by the density detection result Dv (4) of the patch image Ip (4) formed with the developing bias Vb (4) and the developing bias Vb (5). It is located between the density detection result Dv (5) of the formed patch image Ip (5). Accordingly, the white circle shown in FIG. 4B corresponds to the intersection of the straight line (dotted line) connecting the two points corresponding to these two types of developing bias and the straight line (dotted line) corresponding to the target density Dtgt. As the value of the developing bias Vb, the optimum developing bias Vbopt can be obtained.
[0039]
Then, in the subsequent image forming operation, by forming a toner image while setting the developing bias Vb to the optimum value Vbopt, it is possible to form an image with a desired image density.
[0040]
On the other hand, if the density difference ΔDv is not appropriate, the reliability of the density detection results Dv (1) to Dv (6) is low and there is a high possibility that an abnormality has occurred in the apparatus. In this case, a predetermined error process is executed instead (step S106). Although the content of the error processing is arbitrary, for example, a message for notifying the user of the occurrence of the abnormality can be displayed on the display unit 12. In particular, as described above, since such an error often occurs due to the contamination of the density sensor 60, it is effective to display a message urging the user to clean the density sensor 60. By performing the cleaning work in this way, the abnormality is eliminated, and after that, if the bias adjustment operation of FIG. 3 is re-executed, the bias adjustment can be completed correctly without an error in many cases. Then, the user may be caused to perform such a cleaning operation.
[0041]
However, since there is a possibility that a serious abnormality has occurred in the apparatus, if the abnormality is clearly recognized, for example, there is no difference between the density detection results of the two abnormality determination patch images, or the magnitude relationship is reversed. In such a case, or in a case where improvement is not seen even when the bias adjustment is performed again, a message may be displayed on the display unit 12 to urge the dedicated service person to request an inspection.
[0042]
As described above, in this embodiment, the image density is controlled to a desired value by adjusting the developing bias Vb, which is one of the density control factors affecting the image density. Then, two of the patch images Ip (1) to Ip (6) formed for that purpose are also used as patch images for abnormality determination. If the density difference ΔDv is not an appropriate value, an error is generated. The decision is made. Therefore, it is possible to determine the presence or absence of an abnormality in the apparatus together with adjusting the concentration control factor without performing an operation check in advance.
[0043]
In this embodiment, the increment of the developing bias Vb is set in six steps, but the increment, that is, the numerical value N in the present invention is not limited to this numerical value. By increasing the number of steps, the developing bias Vb can be more finely adjusted. However, since the number of patch images formed increases, the consumption of toner and the processing time increase. Therefore, it is desirable to determine the interval according to the specifications of the apparatus such as the width of the variable range of the developing bias Vb and the required image quality.
[0044]
Then, the presence or absence of an abnormality in the apparatus is determined from the relative relationship of the density detection results for some of the plurality of patch images formed in this manner. Any number may be used.
[0045]
In addition, for the other density control factors, for example, the intensity (exposure power) of the light beam L irradiated from the exposure unit 6 to the photoconductor 22, the optimum value is obtained in the same manner as described above, and the detected value is changed due to an abnormality in the apparatus. If it is not appropriate, it is determined that an error has occurred, and error processing can be appropriately performed. In this case, the number N of steps of the density control factor, the number M of patch images for abnormality determination, the image pattern of the patch image to be formed, and the like may be different from the above as necessary.
[0046]
(2nd Embodiment)
FIG. 5 is a flowchart showing a second embodiment of the developing bias adjustment in the image forming apparatus. In the developing bias adjustment (1) of the first embodiment, two patch images Ip (6) and Ip (1) corresponding to the maximum value Vb (6) and the minimum value Vb (1) of the developing bias Vb as a density control factor. Was previously selected as the patch image for abnormality determination. On the other hand, in the developing bias adjustment (2) of the second embodiment, the patch image for abnormality determination is not determined in advance, but the actual measured value of the detected image density is determined based on the highest and lowest values. The difference is that two patch images are used as patch images for abnormality determination.
[0047]
That is, as shown in FIG. 5, in the developing bias adjustment (2) of the second embodiment, the maximum value Dmax and the minimum value Dmax (Dv (1) to Dv (6)) are selected from the density detection results Dv (1) to Dv (6) of the six patch images. Dmin is selected (step S203), and the difference between the two is set as the density difference ΔDv (step S204), which is different from the first embodiment (FIG. 3), but the other processes are the same.
[0048]
As described above, in the developing bias adjustment of the two embodiments, the method of selecting the two patch images as the patch images for abnormality determination is different, but the abnormality determination of the apparatus is similarly performed by any method. Is possible. In particular, when the abnormality of the apparatus is relatively minor, such as contamination of the density sensor 60 or the intermediate transfer belt 71, it is selected as an abnormality determination image in the developing bias adjustment (2) of the second embodiment. As a result, there is a high possibility that the two abnormality determination patch images will be the same two images Ip (1) and Ip (6) as the abnormality determination patch image in the first embodiment.
[0049]
In the developing bias adjustment (2) of the second embodiment, for example, when only the density detection result of a specific patch image shows an abnormal value due to mixing of electric noise or local contamination of the intermediate transfer belt 71, for example. Can also be determined as an error. In some cases, such a situation cannot be dealt with only by the development bias adjustment (1) of the first embodiment, but the control is simpler because the process of extracting the maximum value and the minimum value is unnecessary.
[0050]
(Other)
Note that the present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in each of the above-described embodiments, the difference ΔDv between the density detection results of the two patch images as the patch images for abnormality determination is obtained, and the presence or absence of an abnormality in the apparatus is determined based on whether the density difference ΔDv is within an appropriate range. Has been determined. However, the present invention is not limited to this. For example, the presence or absence of an abnormality may be determined based on the density ratio of two patch images, the average density value of two or more patch images, and the like.
[0051]
Further, for example, in the above embodiment, the developing bias Vb is changed and set so as to be sequentially increased from the minimum value in the variable range. However, the setting order is not limited to this, and the setting order is not limited to this. It may be set so as to decrease, or may be in another order. The same applies to other concentration control factors.
[0052]
In each of the above embodiments, an error is determined when the density difference ΔDv between the two patch images for abnormality determination is less than a predetermined reference value. This is to determine the lower limit of the density change amount that can be determined to be appropriate in order to detect an abnormality in which the density change of the patch image due to the development bias change is smaller than expected. Conversely, when an abnormality such as a density change that is larger than expected can occur, an appropriate upper limit value of the density change amount may be determined in order to cope with this. That is, if the detected density difference ΔDv is between the upper limit value and the lower limit value, it may be determined to be appropriate.
[0053]
Further, in each of the above embodiments, the image density of the patch image transferred onto the intermediate transfer belt 71 is detected by the density sensor 60. In addition, for example, a density sensor is disposed to face the photoconductor 22. Alternatively, the image density of the patch image visualized on the photoconductor 22 may be detected.
[0054]
In each of the above embodiments, the present invention is applied to an apparatus that forms an image using four color toners of yellow, magenta, cyan, and black. However, the type and number of toner colors are limited to the above. It is not what is done. For example, the present invention can be applied to an apparatus capable of forming only a black-and-white monochrome image. In addition to the rotary developing system of the present invention, a so-called tandem type image forming apparatus in which developing units corresponding to respective toner colors are arranged so as to be arranged in a line in the sheet conveying direction. The present invention is also applicable. Further, the present invention is not limited to the electrophotographic apparatus as in the above embodiment, but is applicable to all image forming apparatuses.
[Brief description of the drawings]
FIG. 1 is a diagram showing an apparatus configuration of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus of FIG. 1;
FIG. 3 is a flowchart illustrating a first embodiment of developing bias adjustment in the image forming apparatus.
FIG. 4 is a diagram showing a patch image formed in this embodiment.
FIG. 5 is a flowchart illustrating a second embodiment of the developing bias adjustment in the image forming apparatus.
[Explanation of symbols]
Reference numeral 60: density sensor, 71: intermediate transfer belt, Ip (1) to Ip (6): patch image, Ip (1), Ip (6): patch image for abnormality determination, Vb: developing bias (density control factor)

Claims (6)

A patch image is formed at each stage while changing and setting the density control factor affecting the image density to N stages (N ≧ 2 integers), and the image densities of the N patch images are respectively detected. In an image forming apparatus that controls image density by adjusting the density control factor based on a result,
Of the N patch images, M patch images (an integer of 2 ≦ M ≦ N) are used as abnormality determination patch images, and based on the image density detection result of the abnormality determination patch images, an abnormality of the apparatus is determined. An image forming apparatus for determining the presence or absence. 2. The image forming apparatus according to claim 1, wherein the number M of the abnormality determination patch images is 2, and the presence or absence of an abnormality in the apparatus is determined based on a ratio or a difference between image densities detected for each of the two patch images. 3. The image forming apparatus according to claim 2, wherein when the ratio or the difference between the image densities is not within a predetermined appropriate range, it is determined that the apparatus is abnormal. The patch image having the highest detected image density among the plurality of patch images is regarded as one of the two patch images for abnormality determination, and the patch image having the lowest detected image density is defined as the patch image for abnormality determination. The image forming apparatus according to claim 2, wherein the other is the other of the above. Among the plurality of patch images, a patch image when the density control factor is set so that the image density is the highest in the relationship between the density control factor and the image density is a patch image of the two abnormality determination patch images. A patch image when the density control factor is set such that the image density is the lowest in the relationship between the density control factor and the image density, and the other patch image for the abnormality determination. 4. The image forming apparatus according to 2 or 3. A patch image is formed at each stage while changing and setting the density control factor affecting the image density to N stages (N ≧ 2 integers), and the image densities of the N patch images are respectively detected. The image density is controlled by adjusting the density control factor based on the result.
Of the N patch images, M patch images (an integer of 2 ≦ M ≦ N) are used as abnormality determination patch images, and based on the image density detection result of the abnormality determination patch images, an abnormality of the apparatus is determined. An image density control method characterized by determining the presence or absence.

Images