JP6245956B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine that forms an image on a sheet.

  In an image forming apparatus, a periodic abnormal image such as density unevenness may occur in an output image. As a cause thereof, there is an abnormality of a roller-shaped part.

  In order to prevent the occurrence of this periodic abnormal image, for example, a technique described in Patent Document 1 has been proposed. Specifically, image data having a uniform density is printed on recording paper by an image forming apparatus, the image on the printed recording paper is read by an image reading apparatus, and the density data of the read image is subjected to frequency analysis such as Fourier transform. To calculate the generation period of the abnormal image. Then, the component causing the abnormal image is specified by comparing the calculated generation cycle of the abnormal image with the circumference of each roller-shaped component in the image forming apparatus.

JP 2006-106556 A

  However, in the technique described in Patent Document 1, when there are a plurality of roller-shaped parts having the same circumferential length in the image forming apparatus, it is difficult to identify the part that causes the abnormal image.

  In this case, in order to identify which part is causing the abnormal image, it is necessary to test whether the abnormal image can be resolved by actually replacing the part that may be abnormal. It took time to identify the part that caused the abnormal image.

  Therefore, an object of the present invention is to provide an image forming apparatus that can quickly and accurately identify a component that causes an abnormal image when a periodic abnormal image occurs in the output image. .

  In order to achieve the above object, an image forming apparatus according to the present invention includes a first rotating component and a second rotating component, and an image forming unit that forms a test image on a sheet; An abnormality occurs in either the first rotating component or the second rotating component in accordance with the reading unit that reads the test image formed on the image and the period of density unevenness of the test image read by the reading unit. If the abnormal part cannot be specified by the specifying means and the specifying means, the density unevenness period caused by the rotation of the first rotating part and the rotation of the second rotating part Control means for changing the driving speed of at least one of the first rotating component and the second rotating component to form a test image again on the sheet so as to make the period of density unevenness to be different. Characterized in that it has a.

  According to the present invention, when a periodic abnormal image occurs in an output image, it is possible to quickly and accurately identify a component that is the cause of the abnormal image.

2 is a cross-sectional view of an image forming apparatus 300. FIG. 3 is a block diagram of a control unit of the image forming apparatus 300. FIG. FIG. 3 is a diagram for explaining a configuration of an operation unit 205. It is a figure explaining the display content of the operation part 205 at the time of abnormal component analysis. It is a flowchart which shows the abnormal component specific process in 1st Embodiment. It is a figure explaining the analysis method of density nonuniformity. It is a flowchart which shows the abnormal component specific process in 2nd Embodiment.

[First Embodiment]
FIG. 1 is a cross-sectional view of the image forming apparatus 300. The image forming apparatus 300 includes a document feeder 500, an image reader 400, and a printer 119. The document feeder 500 conveys the document set on the sheet feed tray from left to right on the platen glass through a curved path one by one from the first page, and then discharges it to the sheet discharge tray. Make paper. At this time, the image on the document passing through the platen glass is read by the image sensor 207 in the image reader 400 serving as reading means.

  The document image read by the image sensor 207 is subjected to image processing and is sent to the exposure control units 103y to 103k for each of Y (yellow), M (magenta), C (cyan), and K (black) colors. Sent. The toner replenishing units 101y to 101k supply toner to the developing units 102y to 102k.

  The laser beams output from the exposure control units 103y to 103k are applied to the photosensitive drums 10y to 10k, and electrostatic latent images are formed on the photosensitive drums 10y to 10k whose surfaces are uniformly charged by the charging rollers 130y to 130k. Is done. The electrostatic latent images on the photosensitive drums 10y to 10k are developed with toner by the developing units 102y to 102k. Then, the toner images on the photosensitive drums 10y to 10k are transferred to the intermediate transfer belt 104 in a superimposed manner by the primary transfer rollers 105y to 105k.

  Thereafter, the toner image on the intermediate transfer belt 104 is transferred by the secondary transfer roller 106 to a sheet fed from any one of the cassettes 109 and 110, the manual sheet feeding unit 111, and the duplex conveyance path 112. The sheet onto which the toner image has been transferred is conveyed to a fixing device 170, and is subjected to toner fixing processing by receiving heat and pressure from fixing rollers 113 and 114.

  The sheet that has passed through the fixing device 170 is once guided to the path 122 by the switching member 121, and after the trailing end of the sheet has passed through the switching member 121, the sheet is switched back and guided to the discharge roller 118 by the switching member 121. As a result, the toner transfer surface is discharged from the image forming apparatus 300 by the discharge roller 118 in a state where the surface to which the toner is transferred faces downward (face down).

  When performing duplex printing, the sheet that has passed through the fixing unit 170 is once guided to the path 122 by the switching member 121. Then, the sheet is switched back after the trailing edge of the sheet passes through the switching member 123, and the sheet is guided to the duplex conveyance path 112 by the switching member 123. Accordingly, it is possible to perform a paper refeeding operation so as to perform image formation on the second side.

  FIG. 2 is a block diagram of the control unit of the image forming apparatus 300. The CPU 201 is a processing circuit that controls the image forming apparatus. The ROM 202 stores a control program executed by the CPU 201 and the like. The RAM 203 is used as a work area necessary for the CPU 201 to control the image forming apparatus 300. The RAM 203 stores a digital image obtained when the image reader 400 reads a document, a digital image transmitted from the outside of the image forming apparatus 300 via the external I / F 204, and the like. The RAM 203 is also used as a work area for performing image processing on digital images obtained from the image reader 400 and the external I / F 204 during image processing.

  The user sets a copy job to be executed by the image forming apparatus 300 using the operation unit 205. In addition to the operation unit 205, a print job can be executed via the external I / F 204.

  An image that has been digitized by reading a document by the image reader 400 is subjected to image processing based on settings from the operation unit 205 and the like, and then stored in the RAM 203. The external I / F 204 is connected to a network such as TCP / IP, and receives a print job execution instruction from a computer connected to the network or notifies the computer of information in the image forming apparatus 300. Can do.

  When conveying a sheet, the CPU 201 controls the motor group 330 to drive each conveyance roller, and detects the conveyed sheet using the sensor group 320 such as the sensors 160 and 171 on the sheet conveyance path. Detect paper jams.

  The image output unit 208 includes the exposure control unit 103, the toner replenishing unit 101, the developing unit 102, the charging roller 130, the photosensitive drum 10, the primary transfer roller 105, the intermediate transfer belt 104, the secondary transfer roller 106, the fixing device 170, and the like. including. The image output unit 208 is controlled by the CPU 201 to form a print image or a test image.

  FIG. 3 is a diagram illustrating the configuration of the operation unit 205. A touch panel 301 is provided on the operation unit 205, and soft keys are displayed on the screen. With the soft keys displayed on the operation unit 205, it is possible to select a sheet and set modes such as single-sided / double-sided printing and color / monochrome printing. When the user presses the start key 302, the image forming apparatus 300 starts an image forming operation.

  FIG. 4 is a diagram for explaining the display contents of the operation unit 205 at the time of abnormal part analysis. These display data are stored in the ROM 202, and the CPU 201 reads out this data and displays it on the touch panel 301.

  FIG. 5 is a flowchart showing the abnormal part specifying process in the first embodiment. A program for executing this flowchart is stored in the ROM 202 and is executed by being read by the CPU 201. Note that the processing according to this flowchart is executed in response to an instruction from the operation unit 205 by the user.

  First, the CPU 201 sets the drive speed during normal image formation for each component (photosensitive drum 10, charging roller 130, primary transfer roller 105, secondary transfer roller 106, etc.) of the image output unit 208 (S501). . Then, the CPU 201 displays the operation start screen shown in FIG. 4A on the touch panel 301 (S502), and waits until the user presses the OK key (S503).

  When the user presses the OK key, the CPU 201 operates each component of the image output unit 208 at the set drive speed, and the test image (halftone image) having a uniform density shown in FIG. 6 is displayed on the sheet. (S504). The sheet on which the test image is formed is referred to as a test chart.

  When the test chart printing is completed, the CPU 201 displays a test chart setting instruction screen shown in FIG. 4B on the touch panel 301 (S505), and waits until the user presses the OK key (S506).

  When the user presses the OK key, the CPU 201 causes the image sensor 207 in the image reader 400 to read the test chart image set on the document table, and stores the read image data in the RAM 203 (S507). ).

  Thereafter, the CPU 201 analyzes density unevenness in the read image data (S508), and identifies an abnormal part based on the result of density unevenness analysis (S509). Details of these processes will be described later.

  Next, the CPU 201 determines whether there is an abnormal part (S510). When there is no abnormal part, the CPU 201 displays on the touch panel 301 that there is no abnormal part as shown in FIG. 4C (S511). On the other hand, when there is an abnormal part, the CPU 201 determines whether or not one abnormal part can be specified from among a plurality of parts constituting the image output unit 208 (S512).

  When one abnormal component can be specified, the CPU 201 displays information on the abnormal component on the touch panel 301 as shown in FIG. 4D, and notifies the user of the abnormal component (S513). FIG. 4D shows an example where the secondary transfer roller 106 has an abnormality.

  On the other hand, when one abnormal component cannot be specified, the CPU 201 changes the drive speed of the component that is a candidate for the abnormal component (S514). Details of the drive speed change will be described later. After that, the CPU 201 returns to the process of S502, prints a test image on the sheet again, and reads the test image again to identify the abnormal part again.

<Density unevenness analysis method>
Next, the density unevenness analysis method described in S508 of FIG. 5 will be described. FIG. 6A is a diagram illustrating a test image printed in S504. The test image on the test chart is a halftone image of A3 size (297 mm × 420 mm), the main scanning is 7015 (dot), and the sub-scanning is 9921 (dot). Since the test chart is uniformly formed on the entire sheet in halftone, periodic density unevenness occurs when there is an abnormality in the roller-shaped parts. Calculate by the method.

  FIG. 6B shows the luminance data in the sheet conveyance direction by averaging the two-dimensional luminance data obtained by reading the test chart in the main scanning direction orthogonal to the sheet conveyance direction (sub-scanning direction). It is a thing. That is, it is data obtained by averaging luminance data of 7015 (dots) in the main scanning direction with respect to 9921 (dots) in the sub-scanning direction. The brightness data in the sheet conveyance direction created here is stored in the RAM 203.

  FIG. 6C is a graph obtained by performing fast Fourier transform (FFT) on the luminance data of FIG. 6B. When the CPU 201 performs fast Fourier transform on the luminance data of the test chart, it can be expressed as intensity for each frequency, and it is possible to analyze what period is included in the density unevenness.

  After the luminance value data is converted into the intensity for each frequency, the CPU 201 emphasizes the intensity of the characteristic frequency. Specifically, the CPU 201 extracts the intensity peak value in FIG. 6C and performs a filter process for multiplying the intensity peak value by 10. By performing inverse Fourier transform after performing this filter processing, it is possible to emphasize the period of density unevenness due to the roller-shaped parts.

  FIG. 6D is a graph of the luminance value of the test chart in which the feature of density unevenness is emphasized by the above inverse Fourier transform. Based on the waveform of this graph, the CPU 201 calculates a density unevenness period L and stores it in the RAM 203. The period L corresponds to the peak-to-peak interval in the graph of FIG.

  In this example, the filtering process for multiplying the intensity peak value by 10 is performed. However, a plurality of points (for example, 10 points) are extracted in descending order of the intensity, and the filtering process for multiplying the intensity of these 10 points by 10 is performed. It doesn't matter.

<Identification method of abnormal parts>
Next, the method for identifying an abnormal part described in S509 of FIG. 5 will be described. Table 1 below is a table showing data such as the circumference of each part of the image output unit 208, and is stored in the ROM 202.

  For the density unevenness period L obtained by the density unevenness analysis in S508, the CPU 201 determines whether there is a component whose peripheral length is included in the range of L-1.5 mm to L + 1.5 mm. Parts whose perimeter is within this range are abnormal parts that cause density unevenness. For example, when the density unevenness period L is 50.1 mm, the CPU 201 determines that the secondary transfer roller 106 is an abnormal component by referring to Table 1 stored in the ROM 202.

  However, for example, when the density unevenness period L is 62.8 mm, there are two abnormal parts that cause density unevenness, the developing sleeve and the primary transfer roller 105, and the abnormal part cannot be specified as one. This is because the circumferential length of the developing sleeve and the circumferential length of the primary transfer roller are substantially the same. In such a case, the drive speed described below is changed.

<How to change the driving speed of rotating parts>
Next, the driving speed changing method described in S514 of FIG. 5 will be described. As described above, when one abnormal part cannot be specified, the CPU 201 changes the driving speed of the abnormal candidate part to a speed different from that during normal image formation for re-specification.

  As shown in Table 1, since the circumferential lengths of the developing sleeve and the primary transfer roller are the same, it is impossible to specify whether the developing sleeve is abnormal or the primary transfer roller is abnormal. In such a case, the cycle of density unevenness caused by the rotation of the developing sleeve is made half the circumference (≈31.41 mm) by doubling the driving speed of the developing sleeve. As a result, the CPU 201 can distinguish whether the developing sleeve is abnormal or the primary transfer roller is abnormal.

  Table 2 shows data after changing the developing sleeve drive speed, and is stored in the ROM 202. The CPU 201 identifies an abnormal part by comparing the density unevenness period L obtained by the density unevenness analysis in S <b> 508 with the density unevenness period for each part described in Table 2 stored in the ROM 202.

  As is apparent from this table, there is no component other than the developing sleeve that generates density unevenness with a period as high as 31.41 mm. Therefore, the driving speed of the developing sleeve is set to twice the normal speed, and the test chart is printed. Accordingly, if the density unevenness period L is in the range of 62.83 ± 1.5 mm, the primary transfer roller is abnormal, and if the period L is in the range of 31.41 ± 1.5 mm, the developing sleeve is abnormal. Can be specified.

  Note that the change in the driving speed is not limited to twice, and may be any number as long as there are no other parts that cause density unevenness in the same period.

  As described above, according to the present embodiment, when a periodic abnormal image occurs in the output image, it is possible to quickly and accurately identify the component that is the cause of the abnormal image.

[Second Embodiment]
In the first embodiment, when one abnormal component cannot be specified, control is performed to change the drive speed of the abnormal component candidate. On the other hand, in the second embodiment, the drive speed is changed in advance, and a test chart is printed in a state where there is no part that generates density unevenness in the same cycle, so that an abnormal part can be identified by one analysis. I have to.

  FIG. 7 is a flowchart showing the abnormal part specifying process in the second embodiment. A program for executing this flowchart is stored in the ROM 202 and is executed by being read by the CPU 201. Note that the processing according to this flowchart is executed in response to an instruction from the operation unit 205 by the user.

  First, the CPU 201 sets a driving speed for a test chart for each component (the photosensitive drum 10, the charging roller 130, the primary transfer roller 105, the secondary transfer roller 106, and the like) of the image output unit 208 (S701). Specifically, as shown in Table 2, the developing sleeve drive speed is doubled, and the period of density unevenness caused by the rotation of the developing sleeve is made half the circumference (≈31.41 mm). On the other hand, except for the developing sleeve, the same speed as that during normal image formation is set. The processing of S702 to S710 is the same as the processing of S502 to S510 in FIG.

  When there is no abnormal part in S710, the CPU 201 displays on the touch panel 301 that there is no abnormal part as shown in FIG. 4C (S711). On the other hand, when there is an abnormal part, unlike the first embodiment, one abnormal part can always be specified, so the CPU 201 displays information on the abnormal part on the touch panel as shown in FIG. 301, and notifies the user of abnormal parts (S712).

  As described above, according to the second embodiment, as in the first embodiment, when a periodic abnormal image occurs in the output image, the component causing the abnormal image is accurately detected. And can be quickly identified.

10 Photosensitive drum (rotating parts)
105 Primary transfer roller (rotating parts)
106 Secondary transfer roller (Rotating parts)
130 Charging roller (rotating parts)
201 CPU (specifying means)
202 ROM
203 RAM
205 Operation unit 207 Image sensor (reading means)
208 Image output unit (image forming means)
300 Image forming apparatus

Claims (7)

An image forming means including a first rotating component and a second rotating component, and forming a test image on the sheet;
Reading means for reading a test image formed on a sheet by the image forming means;
A specifying unit for specifying which of the first rotating component and the second rotating component is abnormal in accordance with a period of density unevenness of the test image read by the reading unit;
When the abnormal part cannot be specified by the specifying means, the period of density unevenness caused by the rotation of the first rotating part is different from the period of density unevenness caused by the rotation of the second rotating part. And a control means for changing the driving speed of at least one of the first rotating component and the second rotating component to form a test image on the sheet again.
An image forming apparatus comprising: The test image is an image forming apparatus according to claim 1, characterized in that the uniform density of the halftone image. The specifying unit converts the reading data of the halftone image by the reading unit into luminance data in the sheet conveyance direction, and calculates the intensity at each frequency of density unevenness by fast Fourier transforming the converted luminance data. The density unevenness period is calculated from a waveform obtained by performing an inverse Fourier transform after emphasizing the peak value of the intensity with respect to the calculated intensity of each density unevenness for each frequency. 2. The image forming apparatus according to 2 . The specifying unit compares the calculated density unevenness period with a density unevenness period caused by rotation of the first rotating component and a density unevenness period caused by rotation of the second rotating component. 4. The image forming apparatus according to claim 3 , wherein one of the first rotating component and the second rotating component is identified as abnormal. 5. The first rotating component and the second rotating component are respectively a photosensitive drum on which an electrostatic latent image is formed, a charging roller for charging the surface of the photosensitive drum, and developing the electrostatic latent image with toner. A developing sleeve, a primary transfer roller for transferring a toner image developed by the developing sleeve, and a secondary transfer roller for transferring a toner image transferred by the primary transfer roller onto a sheet. The image forming apparatus according to claim 1 . When said first rotary component and abnormal in any of the second rotating parts is not generated, according to claim 1, characterized by further comprising display means for displaying that a faulty part is not Image forming apparatus. The If you can identify an abnormal part by identifying means, the image forming apparatus according to claim 1, characterized by further comprising display means for displaying the identified faulty part.

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