JP2021089362A - Image forming apparatus and method for selecting image defect repairing operation - Google Patents

Abstract

To reduce the time required for selection of a repairing operation when an image defect occurs in an image forming apparatus of an electrophotographic system to prevent a reduction in productivity.SOLUTION: According to an image forming apparatus, a control unit forms, on a photoreceptor drum, pattern images in which the image density changes in multiple steps in a sub scanning direction. The control unit acquires development current characteristics for the image density on the basis of a result of detection, which is performed by a development current detection unit, of the value of a development current while the pattern images are formed. The control unit selects an image defect repairing operation when an image defect occurs on the basis of the acquired development current characteristics.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus and a method for selecting an operation for repairing an image defect.

Conventionally, in an electrophotographic image forming apparatus, a developing current detecting unit for detecting a measured value of a developing current flowing between an image carrier and a developer carrier is provided, and the developing current calculated based on image forming conditions is provided. A technique has been proposed for determining whether or not an image defect has occurred by comparing the estimated value with the measured value of the developing current (see, for example, Patent Document 1).

JP-A-2018-0633364

With the technique described in Patent Document 1, it is possible to determine whether or not an image defect has occurred, but it is not possible to identify the cause of the image defect. Therefore, it takes time for the operator to select and repair the repair operation according to the cause, and the downtime (stop time of the image formation time) required for this work reduces the productivity.

An object of the present invention is to make it possible to shorten the time required for selecting a repair operation when an image defect occurs in an electrophotographic image forming apparatus, and to suppress a decrease in productivity.

In order to solve the above problems, the invention according to claim 1 is
Image carrier and
A charging device that charges the surface of the image carrier,
An exposure apparatus that scans and exposes the charged image carrier to form a latent image.
A developing device that forms an image by supplying toner to the image carrier on which the latent image is formed by a developer carrier.
A developing current detection unit that detects the value of the developing current flowing between the image carrier and the developer carrier, and a developing current detector.
An image forming apparatus equipped with
A pattern image whose image density changes in multiple steps in the sub-scanning direction is formed on the image carrier, and based on the detection result of the development current value by the development current detection unit during the formation of the pattern image, the image carrier is formed. A control unit that acquires the development current characteristics with respect to the image density and selects the repair operation of the image defects when an image defect occurs based on the acquired development current characteristics.
To be equipped.

The invention according to claim 2 is the invention according to claim 1.
The control unit compares the inclinations of the development current characteristics in each of the highlight unit, the halftone unit, and the shadow unit, and selects the image defect repair operation based on the comparison result.

The invention according to claim 3 is the invention according to claim 2.
The control unit compares the inclinations of the development current characteristics in each of the highlight unit, the halftone unit, and the shadow unit, identifies the cause of the image defect based on the comparison result, and responds to the identified cause. Select a repair action.

The invention according to claim 4 is the invention according to any one of claims 1 to 3.
The control unit automatically executes the selected repair operation.

The invention according to claim 5 is the invention according to any one of claims 1 to 3.
The control unit notifies the user of the selected repair operation by means of the notification means.

The invention according to claim 6 is the invention according to any one of claims 1 to 5.
The control unit forms the pattern image on the image carrier a plurality of times under the same conditions, causes the developing current detection unit to detect the value of the developing current a plurality of times, and based on the detection results of the plurality of times, the control unit detects the value of the developing current. The repair operation for the image defect is selected.

The invention according to claim 7 is the invention according to any one of claims 1 to 6.
The image defect repairing operation is one or more of the charging device repairing operation, the developing device repairing operation, the image carrier repairing operation, and the exposure device repairing operation.

The invention according to claim 8 is the invention according to any one of claims 1 to 7.
After executing the repair operation, the control unit again forms the pattern image on the image carrier under the same conditions, causes the development current detection unit to detect the value of the development current, and determines the detection result. Based on this, it is determined whether or not the image defect has been resolved.

The invention according to claim 9 is the invention according to any one of claims 1 to 8.
The pattern image is an image in which a plurality of gradation patterns whose image densities change stepwise in the sub-scanning direction are arranged so as not to overlap with each other in the longitudinal direction of the image carrier.
The control unit identifies the position in the longitudinal direction of the image carrier on which image defects occur, based on the development current characteristics acquired while forming each of the gradation patterns in the pattern image. ..

The invention according to claim 10 is the invention according to any one of claims 1 to 8.
The pattern image is a pattern image in which a plurality of diagonal band-shaped patterns having different image densities are arranged side by side in the sub-scanning direction.
Based on the time change of the value of the developing current detected while the diagonal band-shaped pattern is formed on the image carrier, the control unit is the length of the image carrier on which image defects occur. Identify the position of the direction.

The invention according to claim 11
Image carrier and
A charging device that charges the surface of the image carrier,
An exposure apparatus that scans and exposes the charged image carrier to form a latent image.
A developing device that forms an image by supplying toner to the image carrier on which the latent image is formed by a developer carrier.
A developing current detection unit that detects the value of the developing current flowing between the image carrier and the developer carrier, and a developing current detector.
This is a method for selecting an operation for repairing an image defect in an image forming apparatus including the above.
A step of forming a pattern image in which the image density changes in multiple steps in the sub-scanning direction on the image carrier, and
Based on the detection result of the development current value by the development current detection unit while forming the pattern image, the development current characteristic with respect to the image density is acquired, and the image defect is caused based on the acquired development current characteristic. The process of selecting the repair operation for the image defect when it occurs, the degree, and
including.

According to the present invention, it is possible to shorten the time required for selecting the repair operation when an image defect occurs in the electrophotographic image forming apparatus, so that it is possible to suppress a decrease in productivity.

It is a figure which shows the schematic structure of the image forming apparatus. It is a block diagram which shows the main functional composition of an image forming apparatus. It is a flowchart which shows the image defect detection process executed by the control part of FIG. It is a figure which shows an example of a pattern image. It is a figure which shows the development current characteristic profile when there is no image defect. It is a figure which shows the development current characteristic profile at the time of the image defect caused by the charging device. It is a figure which shows the development current characteristic profile at the time of the image defect caused by the developing apparatus. It is a figure which shows the development current characteristic profile at the time of the occurrence of an image defect caused by a photoconductor drum or an exposure apparatus. It is a figure which shows typically the image defect caused by the charging device. It is a figure which shows typically the image defect caused by the developing apparatus. It is a figure which shows typically the image defect caused by the photoconductor drum or the exposure apparatus. It is a figure which shows an example of the pattern image which has a diagonal band pattern. It is a figure which shows another example of the pattern image which has a diagonal band pattern. It is a graph which shows the time change of the development current value when the diagonal band-shaped pattern of 100% image density shown in FIG. 7A is formed. It is a graph which shows the time change of the development current value when an image defect occurs when the diagonal band pattern of 100% image density shown in FIG. 7A is formed. It is a figure for demonstrating the method of specifying the occurrence position of the image defect in the pattern image which has an oblique band-shaped pattern.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

(Structure of image forming apparatus 1)
FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a main functional configuration of the image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 shown in FIGS. 1 and 2 is a color image forming apparatus using an electrophotographic process technique. That is, the image forming apparatus 1 transfers (primary transfer) the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photoconductor drum 413 to the intermediate transfer belt 421. ), And after superimposing the toner images of four colors on the intermediate transfer belt 421, the image is formed by transferring (secondary transfer) to the paper S.

The image forming apparatus 1 employs a tandem method in which the photoconductor drums 413 corresponding to the four colors of YMCK are arranged in series in the traveling direction of the intermediate transfer belt 421, and the toner images of each color are sequentially transferred to the intermediate transfer belt 421. ..

As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, a storage unit 70, and a communication unit 80. It includes a developing current detection unit 90 and a control unit 100.

The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program according to the processing content from the ROM 102, develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 shown in FIG. 2 in cooperation with the expanded program.

The image reading unit 10 includes an automatic document feeding device 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.
The automatic document feeding device 11 conveys the document D placed on the document tray by the conveying mechanism and sends it out to the document image scanning device 12. The automatic document feeding device 11 can continuously read a large number of images (including both sides) of the documents D placed on the document tray at once.

The document image scanning device 12 optically scans the document conveyed on the contact glass from the automatic document feeding device 11 or the document placed on the contact glass, and the reflected light from the document is a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and the original image is read. The image scanning unit 10 generates input image data based on the scanning result by the document image scanning device 12. The image processing unit 30 performs predetermined image processing on the input image data.

The operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like according to a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

The image processing unit 30 includes a circuit or the like that performs digital image processing according to initial settings or user settings on the input image data. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression processing, and the like, in addition to gradation correction, on the image data. The image data subjected to these processes is input to the image forming unit 40.

The image forming unit 40 is an image forming unit 41Y, 41M, 41C, 41K, intermediate transfer for forming an image with each colored toner of Y component, M component, C component, and K component based on the input image data. It includes a unit 42 and the like.

The image forming units 41Y, 41M, 41C, 41K for the Y component, the M component, the C component, and the K component have the same configuration. For convenience of illustration and description, common components are indicated by the same reference numerals, and when distinguishing them, they are indicated by adding Y, M, C, or K to the reference numerals. In FIG. 1, reference numerals are given only to the components of the image forming unit 41Y for the Y component, and the reference numerals are omitted for the other components of the image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photoconductor drum (corresponding to the “image carrier” of the present invention) 413, a charging device 414, a drum cleaning device 415, and the like. Each device (including the photoconductor drum 413) constituting the image forming unit 41 has the x direction shown in FIG. 1 as the longitudinal direction (axial direction).

The photoconductor drum 413 has, for example, an undercoat layer (UCL: Under Coat Layer) and a charge generation layer (CGL: Charge) on the peripheral surface of a conductive cylinder (aluminum element tube) made of aluminum having a drum diameter of 80 [mm]. It is a negatively charged organic photo-conductor (OPC) in which a generation layer (Generation Layer) and a charge transport layer (CTL) are sequentially laminated.

The control unit 100 rotates the photoconductor drum 413 at a constant peripheral speed by controlling the drive current supplied to the drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 uniformly charges the surface of the photoconductor drum 413 having photoconductivity to a negative electrode property.
The exposure apparatus 411 is composed of, for example, a semiconductor laser, and scans and exposes a charged photoconductor drum 413 to form a latent image.

The developing device 412 is a developing device of a two-component developing method, and a toner image of each color component is visualized by adhering toner of each color component to the surface of the photoconductor drum 413 to form a toner image. The developing roller 412A (corresponding to the "developer carrier" of the present invention) included in the developing apparatus 412 supports the developing agent while rotating, and supplies the toner contained in the developing agent to the photoconductor drum 413 to provide the photoconductor. A toner image is formed on the surface of the drum 413.

The drum cleaning device 415 is attached to the photoconductor drum 413 for the purpose of improving the releasability of the drum cleaning blade, the photoconductor drum 413, and the toner that are in sliding contact with the surface of the photoconductor drum 413 and suppressing the wear of the photoconductor film thickness. It has a lubricant application brush 415A or the like to which a lubricant (lubricant) is applied, and removes transfer residual toner remaining on the surface of the photoconductor drum 413 after the primary transfer.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

The intermediate transfer belt 421 is composed of an endless belt, and is stretched in a loop on a plurality of support rollers 423. At least one of the plurality of support rollers 423 is composed of a driving roller, and the other is composed of a driven roller. For example, it is preferable that the roller 423A arranged on the downstream side in the belt traveling direction with respect to the primary transfer roller 422 for the K component is the drive roller. This makes it easier to keep the running speed of the belt in the primary transfer unit constant. As the drive roller 423A rotates, the intermediate transfer belt 421 travels at a constant speed in the direction of arrow A.

The primary transfer roller 422 is arranged on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photoconductor drum 413 of each color component. By pressing the primary transfer roller 422 against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched between them, a primary transfer nip for transferring the toner image from the photoconductor drum 413 to the intermediate transfer belt 421 is formed.

The secondary transfer roller 424 is arranged on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the roller 423B (hereinafter referred to as “backup roller 423B”) arranged on the downstream side of the drive roller 423A in the belt traveling direction. By pressing the secondary transfer roller 424 against the backup roller 423B with the intermediate transfer belt 421 sandwiched between them, a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S is formed.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed on the intermediate transfer belt 421 and the primary transfer is performed. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and a charge having a polarity opposite to that of the toner is applied to the back surface side (the side that contacts the primary transfer roller 422) of the intermediate transfer belt 421 to obtain a toner image. It is electrostatically transferred to the intermediate transfer belt 421.

After that, when the paper S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the paper S. Specifically, a secondary transfer bias is applied to the secondary transfer roller 424, and a charge having a polarity opposite to that of the toner is applied to the back surface side of the paper S (the side that comes into contact with the secondary transfer roller 424) to obtain a toner image. Is electrostatically transferred to the paper S. The paper S on which the toner image is transferred is conveyed toward the fixing portion 60.

The belt cleaning device 426 has a belt cleaning blade or the like that is in sliding contact with the surface of the intermediate transfer belt 421, and removes the transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration in which the secondary transfer belt is stretched in a loop on a plurality of support rollers including the secondary transfer roller (so-called belt-type secondary transfer unit) is adopted. Is also good.

The fixing unit 60 fixes the toner image on the paper S by secondarily transferring the toner image and heating and pressurizing the conveyed paper S with the fixing nip.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. The three paper feed tray units 51a to 51c constituting the paper feed unit 51 accommodate the paper S (standard paper, special paper) identified based on the basis weight, size, etc. for each preset type. .. The transport path portion 53 has a plurality of transport roller pairs such as a resist roller pair 53a.

The paper S housed in the paper feed tray units 51a to 51c is sent out one by one from the uppermost portion, and is conveyed to the image forming unit 40 by the transfer path unit 53. At this time, the resist roller portion in which the resist roller pair 53a is arranged corrects the inclination of the fed paper S and adjusts the transfer timing. Then, in the image forming unit 40, the toner image of the intermediate transfer belt 421 is collectively secondarily transferred to one surface of the paper S, and the fixing step is performed in the fixing unit 60. The image-formed paper S is discharged to the outside of the machine by the paper ejection unit 52 provided with the paper ejection roller 52a.

The paper S may be long paper or roll paper. In this case, the paper S is housed in a paper feeding device (not shown) connected to the image forming apparatus 1, and the paper S held by the paper feeding device is connected to the paper feeding port 54 from the paper feeding device. It is supplied to the image forming apparatus 1 via the image forming apparatus 1 and sent out to the transport path portion 53.

The storage unit 70 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory), a hard disk drive, or the like. The storage unit 70 stores various data including various setting information related to the image forming apparatus 1.

For example, the storage unit 70 stores pattern image information 701. The pattern image information 701 is information for forming a pattern image (see FIGS. 4, 7A, 7B) used for identifying the cause of the image defect in the image defect detection process described later, and is at least the photoconductor drum 413. Elapsed time t from the start of image formation of the pattern image to, and the position in the longitudinal direction of the photoconductor drum 413 on which the pattern (the image portion on which the toner of the pattern image is placed) is formed and the image of the formed pattern. Contains information indicating the correspondence of concentrations.

The communication unit 80 is composed of a communication control card such as a LAN (Local Area Network) card, and is connected to an external device (for example, a personal computer) connected to a communication network such as a LAN or WAN (Wide Area Network). Send and receive various data.

The developing current detection unit 90 is arranged in each image forming unit 41, and detects an actually measured value of the developing current flowing between the photoconductor drum 413 and the developing roller 412A. The development current detection unit 90 detects the measured value of the development current by applying the development bias to the development roller 412A by the development bias application unit (not shown), and outputs the measured value to the control unit 100.

(Operation of image forming apparatus 1)
Next, the operation of the image forming apparatus 1 will be described.
The control unit 100 of the image forming apparatus 1 executes the image defect detection process at a predetermined timing such as the timing when a predetermined number of images are formed by the job.
FIG. 3 is a flowchart showing the flow of image defect detection processing. The image defect detection process is executed in cooperation with the program stored in the control unit 100 and the storage unit 70.

Here, as shown in FIG. 1, the exposure device 411, the developing device 412, and the charging device 414 are arranged around the photoconductor drum 413 in parallel with the photoconductor drum 413, and are placed on the photoconductor drum 413 as described above. On the other hand, processing such as charging, exposure, and development is performed. Therefore, in any of the photoconductor drum 413, the exposure device 411, the developing device 412, and the charging device 414, there is an abnormality at a certain position in the longitudinal direction (for example, stains on the exposure device 411 and the charging device 414, and ears of the developing device 412. If there is clogging, uneven coating of the lubricant on the photoconductor drum 413, etc.), the portion corresponding to the abnormal portion of the toner image formed on the photoconductor drum 413 is mainly in the rotation direction (secondary scanning direction, longitudinal direction) of the photoconductor drum 413. Image defects such as streaks (vertical streaks) extending in the direction orthogonal to the direction appear. The image defect detection process is a process of detecting an image defect such as a vertical streak, identifying the cause, and repairing the image defect.
Hereinafter, the image defect detection process will be described with reference to FIG.

First, the control unit 100 starts forming a pattern image in each of the image forming units 41Y, 41M, 41C, and 41K (step S1).
In step S1, the control unit 100 causes each image forming unit 41 to start image forming of the pattern image. The pattern image is an image used for identifying the cause of image defects, and is an image having a pattern in which the image density changes in multiple steps in the sub-scanning direction (direction orthogonal to the longitudinal direction of the photoconductor drum 413). In the pattern image, the width and area of each image density are constant.

FIG. 4 shows an example of a pattern image. In the pattern image shown in FIG. 4, a plurality of gradation patterns whose image densities change stepwise from the highlight portion to the halftone portion to the shadow portion are arranged so as not to overlap in the longitudinal direction of the photoconductor drum 413 (preferably). Is an image (arranged so as to cover the entire longitudinal direction).
For example, when a pattern image consisting of one gradation pattern over the entire longitudinal direction of the photoconductor drum 413 is formed, the ratio (difference) of the change in the developing current value caused by the image defect becomes smaller than the normal developing current value, so that the image Although it is difficult to detect defects, the ratio of changes in the development current value due to image defects to the normal development current value by reducing the development current value detected per scanning line by dividing the longitudinal direction in this way. Is preferable because the accuracy of detecting image defects can be improved.
Further, the development current value at the time of forming each gradation pattern is detected and the processes shown in steps S5 to S6 described later are executed to acquire the development current characteristic with respect to the image density at the time of forming each gradation pattern to form each gradation pattern. By determining whether or not an image defect has occurred at that time, when there is a gradation pattern in which an image defect has occurred, the gradation pattern forms the position in the longitudinal direction of the photoconductor drum 413 at the location where the image defect has occurred. It is preferable because it can be specified within the specified range.

Here, the image density can be changed, for example, by changing the line width or dot diameter of the screen while keeping the exposure amount output from the exposure apparatus 411 per dot constant, or the line width or dot diameter of the screen. It can also be changed by changing the amount of exposure output per dot while keeping the value constant. In the present embodiment, a case where the image density is changed by changing the line width and the dot diameter of the screen (changing the halftone dot area ratio (%)) while keeping the exposure amount output per dot constant will be described as an example. However, the image density may be changed by changing the exposure amount output per dot.

When the control unit 100 starts image formation of the pattern image, the control unit 100 acquires the development current value from the development current detection unit 90 (step S2), and obtains the acquired development current value from the image formation start time t0 on the photoconductor drum 413. It is stored in the RAM in association with the elapsed time t (step S3).
For example, the control unit 100 causes the development current detection unit 90 to detect the development current value every time a toner image for one scanning line is formed on the photoconductor drum 413.

Next, the control unit 100 determines whether or not the image formation of the pattern image is completed (step S4).
When it is determined that the image formation of the pattern image is not completed (step S4; NO), the control unit 100 returns to step S2 and repeatedly executes steps S2 to S4.

When it is determined that the image formation of the pattern image is completed (step S4; YES), the control unit 100 generates a profile (hereinafter, referred to as a development current characteristic profile) representing the characteristics of the development current value with respect to the image density (step). S5).
In the development current characteristic profile, the integrated value of the development current value detected by the development current detection unit 90 while forming a pattern with the image density is calculated for each image density, and the horizontal axis is the image density and the vertical axis is the vertical axis. It can be generated by plotting on a graph with the axis as the developing current value (integrated value). In step S5, a developing current characteristic profile is generated for each gradation pattern formed on the photoconductor drum 413.

5A-5D are diagrams showing an example of the development current characteristic profile formed in step S5. In step S5, as shown in FIGS. 5A to 5D, a profile is generated in which the horizontal axis is the image density and the vertical axis is the developing current value. Here, the 0-A section on the horizontal axis in FIGS. 5A to 5D is a highlight section, the AB section is a halftone section, and the BC section is a shadow section. In the present embodiment, for example, the highlight portion is defined as having an image density of 0 to less than 30%, the halftone portion is defined as having an image density of 30% to less than 70%, and the shadow portion is defined as having an image density of 70% to 100%.
In the following description, the highlight portion inclination refers to the inclination of a straight line connecting 0 (origin) and the intersection of the developing current characteristic profile and the A line. The halftone slope refers to the slope of a straight line connecting the intersection of the developing current characteristic profile and the A line and the intersection of the developing current characteristic profile and the B line. The shadow portion inclination refers to the inclination of a straight line connecting the intersection of the developing current characteristic profile and the B line and the intersection of the developing current characteristic profile and the C line.

FIG. 5A is a diagram showing a development current characteristic profile when no image defect has occurred. Here, when the toner moves from the developing roller 412A to the photoconductor drum 413, a developing current corresponding to the amount of the transferred toner flows between the developing roller 412A and the photoconductor drum 413. That is, as the image density increases (proportionally), the developing current value increases. Therefore, as shown in FIG. 5A, the development current characteristic with respect to the image density when a normal pattern image without image defects is formed becomes a straight line rising to the right.
Comparing the tilt of the highlight portion, the tilt of the halftone portion, and the tilt of the shadow portion of the development current characteristic profile when there is no image defect (normal), the relationship is as follows.
"Highlight part tilt = Midtone part tilt = Shadow part tilt"

FIG. 5B is a diagram showing a developing current characteristic profile when an image defect occurs due to the charging device 414. In FIG. 5B, the solid line shows the developing current characteristic profile when an image defect occurs due to the charging device 414, and the dotted line shows the normal developing current characteristic profile for comparison.
Examples of cases where image defects occur due to the charging device 414 include the case where the charging grid becomes dirty and excessive discharge occurs, and the photoconductor drum 413 at the location corresponding to the portion where the grid is dirty includes. The surface potential V0 (unexposed potential) becomes locally high. In this case, since the exposure amount is large in the shadow portion, the potential also drops completely and the image is not defective. However, in the highlight portion, a potential abnormality (potential does not easily drop) occurs and the development amount decreases, as shown in FIG. 6A. In addition, image defects (vertical streaks) occur in the highlight area. Therefore, when an image defect occurs due to the charging device 414, as shown in FIG. 5B, the development current value is smaller than normal in the highlight portion, and the streaks are eliminated toward the shadow portion, so that the development current The value is equivalent to normal.
Comparing the tilt of the highlight portion, the tilt of the halftone portion, and the tilt of the shadow portion of the development current characteristic profile when an image defect occurs due to the charging device 414, the relationship is as follows.
"Highlight part tilt <Shadow part tilt <Midtone part tilt"

FIG. 5C is a diagram showing a developing current characteristic profile when an image defect occurs due to the developing device 412. In FIG. 5C, the solid line shows the development current characteristic profile when an image defect occurs due to the developing device 412, and the dotted line shows the normal development current characteristic profile for comparison.
Examples of cases where image defects occur due to the developing apparatus 412 include cases where ear clogging occurs on the developing roller 412A, which causes defective transfer of the developer. In this case, as shown in FIG. 6B, no image defect occurs in the highlight portion and the halftone portion, but an image defect (vertical streak) occurs in the shadow portion. This is because in the highlight area where the amount of development is small, even if the amount of developer transported is slightly reduced due to clogging of the ears, image failure does not occur, but in the shadow area where a large amount of development is required, the developability becomes insufficient. This is because it leads to image defects. Therefore, when an image defect occurs due to the developing device 412, as shown in FIG. 5C, the developing current value does not change from normal in the highlight part and the halftone part, but the developing current value in the shadow part becomes. It will be lower than normal.
Comparing the inclination of the highlight portion, the inclination of the halftone portion, and the inclination of the shadow portion of the development current characteristic profile when a streak caused by the developing device 412 occurs, the relationship is as follows.
"Shadow part tilt <Midtone part tilt, Highlight part tilt"

FIG. 5D is a diagram showing a development current characteristic profile when an image defect occurs due to the exposure apparatus 411 or the photoconductor drum 413. In FIG. 5D, the solid line shows the development current characteristic profile when an image defect occurs due to the exposure apparatus 411 or the photoconductor drum 413, and the dotted line shows the normal development current characteristic profile for comparison. ing.
Examples of cases where image defects occur due to the exposure apparatus 411 include a decrease in the exposure amount due to stains on the exposure window and the like. In this case, since the exposure is insufficient as a whole, as shown in FIG. 6C, image defects (vertical streaks) occur in the entire region from the highlight portion to the shadow portion. As shown in FIG. 5D, the developing current value is smaller than normal in all of the highlight portion, the halftone portion, and the shadow portion.
Further, examples of cases where image defects occur due to the photoconductor drum 413 include scratches on the photoconductor and uneven application of lubricant to the surface of the photoconductor. In this case, since potential unevenness occurs in the entire region from the highlight portion to the shadow portion, image defects (vertical streaks) occur in the entire region from the highlight portion to the shadow portion, as shown in FIG. 6C. As shown in FIG. 5D, the developing current value is smaller than normal in all of the highlight portion, the halftone portion, and the shadow portion.
Comparing the tilt of the highlight portion, the tilt of the halftone portion, and the tilt of the shadow portion of the development current characteristic profile when an image defect occurs due to the exposure device 411 or the photoconductor drum 413, the relationship is as follows. ..
"Highlight part tilt <Midtone part tilt, Shadow part tilt"

Next, the control unit 100 determines whether or not an image defect has occurred based on the generated development current characteristic profile (step S6).
The control unit 100 calculates the highlight portion inclination, the halftone portion inclination, and the shadow portion inclination of the generated development current characteristic profile, and as shown in FIG. 5A, the highlight portion inclination and the halftone portion of the development current characteristic profile. If the tilt and the tilt of the shadow portion are the same, it is determined that no image defect has occurred, and in other cases, it is determined that an image defect has occurred. In step S6, if the highlight portion inclination, the halftone portion inclination, and the shadow portion inclination are equal in the development current characteristic profile for all the gradation patterns, it is determined that no image defect has occurred, and even one of them is equal. If there is no development current characteristic profile, it is judged that an image defect has occurred.

When it is determined that no image defect has occurred (step S6; NO), the control unit 100 ends the image defect detection process.

On the other hand, when it is determined that an image defect has occurred (step S6; YES), the control unit 100 compares the tilt of the highlight portion, the tilt of the halftone portion, and the tilt of the shadow portion of the development current characteristic profile to obtain an image defect. Identify the cause (step S7).
Specifically, in the case of "highlight portion inclination <shadow portion inclination <halftone portion inclination", it is specified that the charging device 414 is the cause. In the case of "shadow portion tilt <halftone portion tilt, highlight portion tilt", it is identified that the cause is the developing device 412. In the case of "highlight portion tilt <halftone portion tilt, shadow portion tilt", it is identified that the cause is the exposure apparatus 411 or the photoconductor drum 413.

Next, the control unit 100 selects a repair operation according to the identified cause (step S8). When there are a plurality of identified causes, the control unit 100 selects a plurality of repair operations.
When it is determined that the charging device 414 is the cause, the control unit 100 selects the repair operation of the charging device.
When it is determined that the developing device 412 is the cause, the control unit 100 selects the repair operation of the developing device.
When it is determined that the cause is the photoconductor drum 413 or the exposure device 411, the control unit 100 selects the repair operation of the photoconductor as the first repair operation and the repair operation of the exposure device as the second repair operation. To do.

Next, the control unit 100 executes the selected repair operation (step S9).

As a cause of the image defect in the charging device 414, it is considered that the grid of the band electrode is contaminated with toner or the like and excessive discharge is caused as described above. Therefore, when the repair operation of the charging device is selected in step S8, the control unit 100 executes, for example, an operation of automatically cleaning the grid of the band electrode by the band electrode automatic cleaning mechanism as the repairing operation of the charging device.

As a cause of image defects in the developing apparatus 412, it is assumed that the developing agent is poorly conveyed (clogging of ears) on the developing roller 412A. Therefore, when the repair operation of the developing device is selected in step S8, the control unit 100 develops, for example, a large amount of toner (for example, equivalent to 10 A3 solid images) in order to expel foreign matter that is a cause of ear clogging. The operation (hereinafter referred to as a toner refresh operation) is executed as a repair operation of the developing device.
Further, the repair operation of the developing device is not a toner refreshing operation, but a foreign matter is formed by rotating the developing roller 412A in the reverse direction (for example, rotating the developing roller in the reverse direction by 3 mm) at the time of non-image formation (when the power is turned on or when the JOB is finished). It may be an action of spitting out.

As a cause of image defects in the photoconductor drum 413, it is assumed that uneven coating of the lubricant is generated on the surface of the photoconductor drum 413. Therefore, when the photoconductor repair operation is selected in step S8, for example, the control unit 100 increases the rotation speed of the lubricant application brush 415A to twice the normal rotation speed and rotates it for a predetermined time to cause uneven lubricant application. The operation of uniformly applying the lubricant (hereinafter, this operation is referred to as a photoconductor refreshing operation) is performed as a photoconductor repairing operation.

It is conceivable that the cause of the image defect in the exposure apparatus 411 is that the exposure window is contaminated with toner or the like and the exposure is defective. Therefore, when the repair operation of the exposure device is selected in step S8, the control unit 100 executes, for example, an automatic exposure window cleaning operation by the exposure window cleaning mechanism as the repair operation of the exposure device.

When the first repair operation and the second repair operation are selected, first, the first repair operation is executed, and then steps S1 to S6 are executed again to develop the pattern image at the time of formation. A current characteristic profile is generated to determine whether or not the image defect has been resolved. If it is determined that the image defect has been resolved, the repair operation is terminated, but if it is determined that the image defect has not been resolved, the second repair operation is executed.

Further, the control unit 100 determines the position in the longitudinal direction of the photoconductor drum 413 in which the gradation pattern in which the image defect is detected based on the development current characteristic profile in step S6 is formed among the plurality of gradation patterns included in the pattern image. It is also possible to specify the position where the image defect has occurred and execute the selected repair operation for that position. As a result, the time required for the repair operation can be shortened.

Next, the control unit 100 executes a repair confirmation operation (step S10), and determines whether or not the image defect has been resolved (step S11).
Specifically, steps S1 to S6 are executed again to generate the development current characteristic profile at the time of forming the pattern image, and it is determined whether or not the image defect has been resolved.

When it is determined that the image defect has not been resolved (step S11; YES), the control unit 100 displays on the display unit 21 that the repair operation has been performed but the image defect has not been resolved (step S12), and the image defect is detected. End the process.
When it is determined that the image defect has been resolved (step S11; YES), the control unit 100 ends the image defect detection process.

In the above description, a development current characteristic profile is created for each gradation pattern, and the presence or absence of an image defect, the identification of the cause when an image defect occurs, and the selection of a repair operation are selected. However, the same image in a plurality of gradation patterns is used. One development current characteristic profile is created by integrating the development current values detected during the formation of the density portion and plotting them on a graph, and the presence or absence of image defects, the identification of the cause when image defects occur, and the selection of repair operations are selected. You may do it.

Further, when the toner image is formed on the photoconductor drum 413, if the developing roller 412A and the photoconductor drum 413 are shaken, the developing current detected by the developing current detection unit 90 changes, which affects the detection of image defects. In some cases. Therefore, in order to avoid this, the control unit 100 forms the pattern image a plurality of times under the same conditions, and causes the development current detection unit 90 to detect the time change of the development current value a plurality of times, and the detection result is a plurality of times. It is preferable to select the repair operation for image defects based on the above. This makes it possible to accurately identify the position where the image defect has occurred.

Further, in the image defect detection process shown in FIG. 3, the control unit 100 selects the repair operation in step S8 and then automatically executes the repair. However, the information of the selected repair operation is displayed on the display unit 21. It may be displayed on the screen to notify the user and prompt the user to execute the repair operation. In this case, if an operation mode (for example, a toner refresh mode) corresponding to the selected repair operation is prepared in advance, the user instructs the operation unit 22 to shift to the operation mode and performs the repair operation. Can be executed. In addition, for example, when an operation mode corresponding to the selected repair operation is not prepared (for example, when an automatic cleaning mechanism for an exposure window or a grid of band electrodes is not provided), the user manually performs the operation. A repair operation (for example, wiping the exposure window) may be performed. Further, when a plurality of gradation patterns are formed so as not to overlap in the longitudinal direction of the photoconductor drum 413, the control unit 100 images the position in the longitudinal direction of the photoconductor drum 413 in which the gradation pattern in which the image defect is detected is formed. It is also possible to specify the position where the defect has occurred and display the specified position on the display unit 21 together. As a result, for example, when the user performs the repair operation, the repair operation can be performed efficiently, and the time required for the repair operation can be shortened.
The notification means for notifying the user is not limited to the display, and may be notified by another method such as voice.

Further, in the above description, the case where the pattern image used in the image defect detection process is a pattern image in which a plurality of gradation patterns are arranged has been described as an example, but the present invention is not limited to this, and for example, FIGS. 7A and 7B. As shown, a pattern image in which a plurality of diagonal band-shaped patterns having different image densities are arranged side by side in the sub-scanning direction may be used. 7A to 7B show, as an example, an image in which a plurality of diagonal band-shaped patterns are formed in 10% increments between an image density of 100% and an image density of 10%. The plurality of diagonal strip-shaped patterns may not be continuous as shown in FIG. 7A, or may be continuous (may be connected) as shown in FIG. 7B. The width of each band pattern and the time formed on the photoconductor drum 413 (t0 to t1, t2 to t3, t4 to t5, t6 to t7, t8 to t9 shown in FIG. 7A) are the same.

FIG. 8A is a graph showing the time change of the developing current value when the diagonal band-shaped pattern having an image density of 100% shown in FIG. 7A is formed. As shown in FIG. 8A, the developing current value when a diagonal band-shaped pattern having a single image density is formed is substantially constant from the image formation start time t0 to the image formation end time t1 except for the rising and falling periods (excluding the rising and falling periods). Id1). FIG. 8B is a graph showing the time change of the developing current value when an image defect (vertical streak) occurs when the band pattern having an image density of 100% shown in FIG. 7A is formed. As shown in FIG. 8B, when an image defect occurs, the developing current value during that period (tA to tB) becomes lower than that of the surroundings.
Therefore, the image defect is based on the elapsed time tA from the start of image formation when the developing current value starts to be lower than the surroundings and the elapsed time tB from the start of image formation when the developing current value returns to the same level as the surroundings. The position in the longitudinal direction of the photoconductor drum 413 in which the above is generated can be specified. Specifically, when the band-shaped pattern is a pattern extending from the upper left to the lower right, as shown in FIG. 9, the pattern is formed at the position tA (x) where the image defect occurs at the time tA. It is the rightmost position at the designated position (having a width of length L). Further, the position tB (x) at which the image defect occurs at the time tB is the leftmost position at the position where the pattern is formed (having a width of the length L) at the time tB. Therefore, the area between tA (x) and tB (x) can be specified as the position in the longitudinal direction of the photoconductor drum 413 in which the image defect occurs. When the band-shaped pattern is a pattern extending from the upper right to the lower left, the position tA (x) where the image defect occurs at the time tA is the position (having a width of length L) where the pattern is formed at the time tA. This is the leftmost position. Further, the position tB (x) at which the image defect occurs at the time tB is the rightmost position at the position where the pattern is formed (having the width of the length L) at the time tB. Therefore, the area between tA (x) and tB (x) can be specified as the position in the longitudinal direction of the photoconductor drum 413 in which the image defect occurs.

When the pattern images shown in FIGS. 7A to 7B are used, the development current values from immediately after the rise to just before the fall of the development current values at the time of forming the diagonal band pattern of each image density are integrated and the horizontal axis is the image density. The developing current characteristic profile can be obtained by plotting on a graph in which the vertical axis is the developing current value. Then, as described above, the presence or absence of image defects and the repair operation of image defects are selected based on the comparison of the inclinations of the highlight portion, the halftone portion, and the shadow portion of the acquired development current characteristic profile. Can be done.

(Verification experiment)
A verification experiment was conducted to verify the effect of the above embodiment.
In the embodiment, steps S1 to S6 of the above-mentioned image defect detection process are executed every time 5000 sheets are printed by the image forming apparatus having the above configuration, and if there is no image defect, the process returns to printing and an image defect is detected. In this case, steps S7 to S9 were performed to repair the defective image, and the process of returning to printing was repeated to print 100,000 sheets. Then, the time when printing was stopped (the time when the cause of the image defect was identified and the repair operation was performed) was measured.
Also, as a comparative example, when the operator notices an image defect and stops printing while printing 100,000 sheets, the print stop time (the operator identifies the cause of the image defect and responds to the cause. The time required to complete the repair work) was measured.

［表Ｉ］に示すように、比較例では、１８２分かかったのに対し、実施例では、２３分であった。
以上より、本実施形態の画像不良検出処理を実行することにより、画像不良の原因に応じた修復動作の選択及び修復によるプリント停止時間を大幅に短縮することができ、生産性の低下を大幅に抑制することができることが確認できた。 [Table I] shows the experimental results of the verification experiment.

As shown in [Table I], it took 182 minutes in the comparative example, whereas it took 23 minutes in the example.
From the above, by executing the image defect detection process of the present embodiment, it is possible to significantly shorten the print stop time due to the selection of the restoration operation according to the cause of the image defect and the restoration, and the productivity is significantly reduced. It was confirmed that it can be suppressed.

As described above, according to the image forming apparatus 1, the control unit 100 causes the photoconductor drum 413 to form a pattern image whose image density changes in multiple steps in the sub-scanning direction, and while forming the pattern image. Based on the detection result of the development current value by the development current detection unit 90 of the above, the development current characteristic with respect to the image density is acquired, and based on the acquired development current characteristic, the image defect is repaired when the image defect occurs. Select an action.
Therefore, it is possible to shorten the time required for selecting the repair operation when an image defect occurs, and thus it is possible to suppress a decrease in productivity.

For example, it is possible to compare the slopes of the development current characteristics of each of the highlight portion, the halftone portion, and the shadow portion, and select the image defect repair operation based on the comparison result.

Further, by notifying the user of the selected repair operation by the notification means, it is not necessary for the user to inspect the inside of the image forming apparatus to specify which repair operation should be performed, so that the decrease in productivity is suppressed. It becomes possible.

Further, by automatically executing the selected repair operation, the time required for the repair operation can be significantly shortened, and the decrease in productivity can be suppressed.

Further, after the repair operation is executed, a pattern image is formed again on the photoconductor drum 413 under the same conditions, and the developing current detection unit 90 is made to detect the value of the developing current, and based on the detection result, an image defect is generated. By determining whether or not the image has been resolved, it is possible to confirm whether or not the image defect has been correctly repaired.

Further, as the pattern image, by using an image in which a plurality of gradation patterns whose image densities change stepwise in the sub-scanning direction are arranged so as not to overlap with each other in the longitudinal direction of the photoconductor drum 413, the photoconductor drum 413 is formed. Since it is possible to specify the position where the image defect occurs in the longitudinal direction, it is possible to efficiently perform the repair operation.

Further, the control unit 100 uses a pattern image in which a plurality of diagonal band-shaped patterns having different image densities are arranged side by side in the sub-scanning direction as the pattern image, so that an image defect occurs in the longitudinal direction of the photoconductor drum 413. Since the position can be specified, the repair operation can be performed efficiently.

The description content in the above-described embodiment is a preferable example of the present invention, and is not limited thereto.
For example, in the above-described embodiment, a color image forming apparatus for primary transfer of an image formed on a photoconductor drum to an intermediate transfer belt and transfer of the image from the intermediate transfer belt to paper by a secondary transfer roller has been described as an example. However, the present invention is also applicable to a monochrome image forming apparatus that transfers an image directly from a photoconductor drum to paper by a transfer roller.

Further, in the above embodiment, the image defect detection process has been described as being executed every time a predetermined number of sheets are printed, but the present invention is not limited to this, and for example, the image defect detection process may be automatically executed when the power is turned on. , It may be executed when an environmental change (change in temperature, humidity, etc.) exceeding a predetermined threshold value occurs.

In addition, the number of stages of the multi-step image density pattern included in the pattern image (image density step), the order of the image density, the orientation of the diagonal band pattern (upper left to lower right, upper right to lower left), etc. are shown in the figure. Not limited to.

Further, in the above description, an example in which a non-volatile memory, a hard disk, or the like is used as a computer-readable medium for the program according to the present invention has been disclosed, but the present invention is not limited to this example. As another computer-readable medium, a portable recording medium such as a CD-ROM can be applied. A carrier wave is also applied as a medium for providing data of the program according to the present invention via a communication line.

In addition, the detailed configuration and detailed operation of the image forming apparatus can be appropriately changed without departing from the spirit of the present invention.

1 Image forming device 100 Control unit 10 Image reading unit 20 Operation display unit 30 Image processing unit 40 Image forming unit 411 Exposure device 412 Developing device 412A Developing roller 413 Photoreceptor drum 414 Charging device 50 Paper transport unit 60 Fixing unit 70 Storage unit 701 Pattern image information 80 Communication unit 90 Development current detector

Claims (11)

Image carrier and
A charging device that charges the surface of the image carrier,
An exposure apparatus that scans and exposes the charged image carrier to form a latent image.
A developing device that forms an image by supplying toner to the image carrier on which the latent image is formed by a developer carrier.
A developing current detection unit that detects the value of the developing current flowing between the image carrier and the developer carrier, and a developing current detector.
An image forming apparatus equipped with
A pattern image whose image density changes in multiple steps in the sub-scanning direction is formed on the image carrier, and based on the detection result of the development current value by the development current detection unit during the formation of the pattern image, the image carrier is formed. A control unit that acquires the development current characteristics with respect to the image density and selects the repair operation of the image defects when an image defect occurs based on the acquired development current characteristics.
An image forming apparatus comprising. The first aspect of claim 1, wherein the control unit compares the inclinations of the development current characteristics in each of the highlight unit, the halftone unit, and the shadow unit, and selects the image defect repair operation based on the comparison result. Image forming device. The control unit compares the inclinations of the development current characteristics in each of the highlight unit, the halftone unit, and the shadow unit, identifies the cause of the image defect based on the comparison result, and responds to the identified cause. The image forming apparatus according to claim 2, wherein the restoration operation is selected. The image forming apparatus according to any one of claims 1 to 3, wherein the control unit automatically executes the selected repair operation. The image forming apparatus according to any one of claims 1 to 3, wherein the control unit notifies the user of the selected repair operation by means of a notification means. The control unit forms the pattern image on the image carrier a plurality of times under the same conditions, causes the developing current detection unit to detect the value of the developing current a plurality of times, and based on the detection results of the plurality of times, the control unit detects the value of the developing current. The image forming apparatus according to any one of claims 1 to 5, which selects the repair operation of the image defect. The repair operation of the image defect is one or more of one or more of the repair operation of the charging device, the repair operation of the developing device, the repairing operation of the image carrier, and the repairing operation of the exposure device. The image forming apparatus according to any one of the above. After executing the repair operation, the control unit again forms the pattern image on the image carrier under the same conditions, causes the development current detection unit to detect the value of the development current, and determines the detection result. The image forming apparatus according to any one of claims 1 to 7, which determines whether or not the image defect has been resolved based on the above. The pattern image is an image in which a plurality of gradation patterns whose image densities change stepwise in the sub-scanning direction are arranged so as not to overlap with each other in the longitudinal direction of the image carrier.
A claim that the control unit identifies a position where an image defect occurs in a position in the longitudinal direction of the image carrier based on the development current characteristic acquired while forming each of the gradation patterns in the pattern image. Item 2. The image forming apparatus according to any one of Items 1 to 8. The pattern image is a pattern image in which a plurality of diagonal band-shaped patterns having different image densities are arranged side by side in the sub-scanning direction.
Based on the time change of the value of the developing current detected while the diagonal band-shaped pattern is formed on the image carrier, the control unit causes an image defect at a position in the longitudinal direction of the image carrier. The image forming apparatus according to any one of claims 1 to 8, wherein the generation position is specified. Image carrier and
A charging device that charges the surface of the image carrier,
An exposure apparatus that scans and exposes the charged image carrier to form a latent image.
A developing device that forms an image by supplying toner to the image carrier on which the latent image is formed by a developer carrier.
A developing current detection unit that detects the value of the developing current flowing between the image carrier and the developer carrier, and a developing current detector.
This is a method for selecting an operation for repairing an image defect in an image forming apparatus including the above.
A step of forming a pattern image in which the image density changes in multiple steps in the sub-scanning direction on the image carrier, and
Based on the detection result of the development current value by the development current detection unit while forming the pattern image, the development current characteristic with respect to the image density is acquired, and the image defect is caused based on the acquired development current characteristic. The process of selecting the repair operation for the image defect when it occurs, and
How to select the repair operation for defective images including.

Images