JP2015022063A - Image forming apparatus and abnormal image detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce frequency of execution of operation to determine presence or absence of a developer on a non-image area so as to suppress deterioration of components.SOLUTION: An image forming apparatus includes latent image carriers 2 that each carry a latent image on the surface, charging means 3 each for charging the surface of the latent image carrier 2, latent image forming means 6 each for forming a latent image on the surface of the latent image carrier 2 charged by the charging means 3, and developing means 4 each for attaching a developer to a latent image part on the latent image carrier 2 using a potential difference between the latent image part and the developing means 4 to develop the latent image into a visible image. The image forming apparatus includes a first determination mode to determine whether or not a developing start point where the adhesion amount of a developer is 0 is within a predetermined developing potential range, the developing start point obtained from the relationship between a developing potential, which is a potential difference between the latent image part and developing means 4, and the adhesion amount of a developer to the latent image part; and a second determination mode to determine whether or not the developer is present on a non-image area in which no image is carried when the developing start point is determined not to be within the predetermined developing potential range in the first determination mode.

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, or a multifunction machine of these, and an abnormal image detection method in the image forming apparatus.

  In an electrophotographic image forming apparatus such as a printer, a copier, a facsimile, or a composite machine of these, the image forming ability changes greatly due to changes in the surrounding environment such as temperature and deterioration over time of toner and developing rollers. May end up. Sometimes, an image (abnormal image) that is different from the information that should be printed is output due to a charging failure of the photoconductor due to a failure of the charging means, a cleaning failure of the intermediate transfer belt due to a failure of the cleaning means, or other abnormalities. Sometimes it ends up. Therefore, an image forming apparatus capable of detecting such an abnormal image is desired.

  For example, Patent Document 1 proposes a method for detecting the presence or absence of toner on a non-image area of a transfer body in a paper interval and an end sequence during continuous image formation in order to detect abnormal images easily at low cost. Yes.

  However, in the method proposed in Patent Document 1, since the presence / absence of toner is detected at every sheet interval, the usage frequency (driving time) of the detection means increases, and the components such as sensors constituting the detection means are increased. There is concern about the promotion of deterioration.

  Therefore, in view of such circumstances, the present invention provides an image forming apparatus and an abnormal image detection method capable of reducing the frequency of execution of the operation for determining the presence or absence of a developer on a non-image area and suppressing deterioration of components. It is something to try.

  In order to solve the above problems, the present invention provides a latent image carrier that carries a latent image on a surface, a charging unit that charges the surface of the latent image carrier, and the latent image carrier that is charged by the charging unit. A latent image forming unit that forms a latent image on the surface of the latent image, and a developing unit that attaches a developer to the latent image unit by a potential difference between the latent image unit on the latent image carrier and visualizes the latent image unit. In the image forming apparatus, the development start point at which the developer adhesion amount becomes 0 is determined from the relationship between the development potential, which is a potential difference between the latent image portion and the developing unit, and the developer adhesion amount to the latent image portion. When the development start point is determined not to be within the predetermined development potential range by the first determination mode for determining whether or not it is within the predetermined development potential range and the first determination mode. Develop on non-image areas where no image is carried And having a second determination mode determines whether there is.

  According to the present invention, the second determination mode is performed when it is determined by the first determination mode that the development start point is not within the predetermined development potential range. The execution frequency of the presence / absence determination of the developer on the region (second determination mode) can be reduced. That is, since it is not necessary to perform the second determination mode until it is determined that there is a possibility of occurrence of an abnormal image in the first determination mode, the execution frequency of the determination operation in the second determination mode is reduced. Can do. As a result, the use frequency (drive time) of the detection means used for the presence / absence determination (second determination mode) of the developer on the non-image area can be reduced, so that deterioration of the components of the detection means is suppressed. In addition, it is possible to extend the life and maintain the abnormal image determination performance.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus to which the present invention is applied. It is a figure which shows the optical sensor which detects the pattern image transferred on the intermediate transfer belt, and the pattern image. It is a figure which shows the structure of an optical sensor. It is a figure which shows the whole flow of abnormal image detection control and toner density control. It is a block diagram of the control system regarding the 1st judgment mode. It is a figure which shows the relationship between development potential and toner adhesion amount. It is a block diagram of the control system regarding a 2nd determination mode. FIG. 4 is a diagram illustrating an effective image area and a non-image area on an intermediate transfer belt. It is a figure which shows the case where a non-image area | region exists in an effective image area | region. It is a figure which shows the kind of abnormal image. It is a figure which shows the flow of 2nd determination mode. It is a figure which shows the graph of the output change of each optical sensor when performing 1st determination mode and performing 2nd determination mode. 1 is a schematic configuration diagram of a direct transfer type image forming apparatus.

  Hereinafter, the present invention will be described with reference to the accompanying drawings. In the drawings for explaining the present invention, components such as members and components having the same function or shape are denoted by the same reference numerals as much as possible, and once described, the description will be given. Omitted.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus to which the present invention is applied. First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus shown in FIG. 1 includes four process units 1Y, 1M, 1C, and 1Bk as image forming units that can be attached to and detached from the apparatus main body (image forming apparatus main body) 100. Each process unit 1Y, 1C, 1M, 1Bk contains developers of different colors of yellow (Y), cyan (C), magenta (M), and black (Bk) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the process units 1Y, 1C, 1M, and 1Bk includes a photosensitive member 2 as a latent image carrier, a charging roller 3 as a charging unit that charges the surface of the photosensitive member 2, and a latent image on the photosensitive member 2. The image forming apparatus includes a developing device 4 as a developing unit that visualizes an image and a cleaning blade 5 as a cleaning unit that cleans the surface of the photoreceptor 2. Further, an LED head array 6 is provided to face each photoconductor 2 as a latent image forming means for exposing the surface of each photoconductor 2 to form a latent image (electrostatic latent image).

  In addition, the image forming apparatus includes a transfer device 7 that transfers an image to a sheet as a recording medium, a paper feeding device 8 that supplies the sheet, a fixing device 9 that fixes the image transferred to the sheet, and a sheet outside the apparatus. And a paper discharge device 10 for discharging the paper.

  The transfer device 7 includes an intermediate transfer belt 11 as an intermediate transfer member, a primary transfer roller 12 as a primary transfer unit, a secondary transfer roller 13 as a secondary transfer unit, and the like. The intermediate transfer belt 11 is an endless belt, and is stretched by a driving roller 14, a driven roller 15, and a plurality of primary transfer rollers 12. As the driving roller 14 rotates counterclockwise in the figure, the intermediate transfer belt 11 rotates.

  Each primary transfer roller 12 is disposed at a position facing each photoconductor 2 and is in contact with the inner peripheral surface of the intermediate transfer belt 11 at each position. As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other to form a primary transfer nip. Each primary transfer roller 12 is connected to a power source (not shown) so that a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied.

  The secondary transfer roller 13 is disposed at a position facing the driving roller 14 and is in contact with the outer peripheral surface of the intermediate transfer belt 11 at that position. Thereby, a secondary transfer nip is formed at a contact portion between the secondary transfer roller 13 and the intermediate transfer belt 11. Similarly to the primary transfer roller 12, the secondary transfer roller 13 is connected to a power source (not shown) so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied. .

  Further, on the outer periphery of the intermediate transfer belt 11, a belt cleaning device 16 that cleans the surface of the intermediate transfer belt 11, a waste toner collection container 17 that collects waste toner removed by the belt cleaning device 16, and the intermediate transfer belt 11 And a detecting means 18 for detecting the toner density (toner adhesion amount).

  The paper feeding device 8 includes a paper feeding cassette 19 that stores paper P and a paper feeding roller 20 that feeds the paper P stored in the paper feeding cassette 19. In addition, a pair of registration rollers 21 are provided on the downstream side of the paper feeding direction with respect to the paper feeding roller 20 as timing rollers for feeding the paper to the secondary transfer nip at the timing of conveyance. The paper P includes cardboard, postcard, envelope, plain paper, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like. Further, an OHP sheet, an OHP film, or the like can be used as a recording medium other than paper.

  The fixing device 9 includes a fixing roller 22 as a fixing member and a pressure roller 23 as a pressure member. The fixing roller 22 is heated by a heating source such as a heater (not shown). The pressure roller 23 is pressed toward the fixing roller 22 and comes into contact with the fixing roller 22, and a fixing nip is formed at the contact portion.

  The paper discharge device 10 includes a pair of paper discharge rollers 24. In addition, the apparatus main body 100 is provided with a paper discharge tray (not shown) on which sheets discharged outside the apparatus are stacked.

Next, an image forming operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the photoreceptors 2 of the process units 1Y, 1C, 1M, and 1Bk are rotated counterclockwise in the drawing, and the surface of each photoreceptor 2 is made to have a predetermined polarity by the charging roller 3. It is charged like this. An electrostatic latent image is formed on the charging surface of each photoreceptor 2 by exposure from the LED head array 6 based on image information from a reading device or a computer (not shown). At this time, the image information to be exposed on each photoconductor 2 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. As the electrostatic latent image formed on the photosensitive member 2 is supplied with toner by each developing device 4, the electrostatic latent image is visualized (visualized) as a toner image.

  Specifically, the developing device 4 includes a developing roller 25 as a developer carrying member for carrying a developer on the surface, and by applying a predetermined developing bias to the developing roller 25, the photoreceptor 2 and the developing roller 25. A potential difference is generated between In accordance with the developing electric field formed by this potential difference, the toner on the developing roller 25 moves to the surface of the photoreceptor 2, and the toner adheres to the latent image portion on the photoreceptor 2 and development is performed.

  When the image forming operation is started, the drive roller 14 that stretches the intermediate transfer belt 11 is driven to rotate, whereby the rotation of the intermediate transfer belt 11 is started. The primary transfer roller 12 is applied with a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current, whereby the primary transfer nip between each primary transfer roller 12 and each photoreceptor 2 is applied. A transfer electric field is formed.

  Thereafter, when each color toner image on the photoconductor 2 reaches the primary transfer nip as the photoconductor 2 rotates, the toner image on each photoconductor 2 is formed by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 11. Thus, a full-color toner image is carried on the surface of the intermediate transfer belt 11. Further, the toner on each photoreceptor 2 that could not be transferred to the intermediate transfer belt 11 is removed by the cleaning blade 5.

  When the image forming operation is started, the paper feed roller 20 starts to rotate and the paper P is sent out from the paper feed cassette 19. The fed paper P is temporarily stopped by the registration roller 21. Thereafter, rotation of the registration roller 21 is started at a predetermined timing, and the paper P is conveyed to the secondary transfer nip in accordance with the timing when the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip.

  At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 11 is applied to the secondary transfer roller 13, thereby forming a transfer electric field in the secondary transfer nip. . Then, the toner image on the intermediate transfer belt 11 is collectively transferred onto the paper P by this transfer electric field. Further, the residual toner on the intermediate transfer belt 11 that could not be transferred onto the paper P is removed by the belt cleaning device 16 and collected in a waste toner collecting container 17.

  Thereafter, the sheet P on which the toner image is transferred is conveyed to the fixing device 9 and is heated and pressed by passing through the fixing nip between the fixing roller 22 and the pressure roller 23, so The toner image is fixed. Then, the paper P is discharged out of the apparatus by the paper discharge roller 24 and stocked on a paper discharge tray (not shown).

  The above description is an image forming operation when a full-color image is formed on a sheet. A single-color image is formed using any one of the four process units 1Y, 1C, 1M, and 1Bk, or two Alternatively, it is possible to form two-color or three-color images using three process units.

2 and 3 show the configuration of the detection means for detecting the toner density (toner adhesion amount) on the intermediate transfer belt.
As shown in FIG. 2, in the present embodiment, the detection unit 18 includes three optical sensors (density sensors) 30 arranged side by side in the width direction of the intermediate transfer belt 11. Each optical sensor 30 is supported in a state of being separated from the intermediate transfer belt 11 by a support member (not shown).

  As shown in FIG. 3, each optical sensor 30 includes one light emitting element 31 that projects light on the intermediate transfer belt 11 that is a detection target, and two light receiving elements 32 and 33 that receive reflected light from the intermediate transfer belt 11. A casing 34 that houses the light emitting element 31 and the light receiving elements 32 and 33. Of the two light receiving elements 32 and 33, one light receiving element 32 is a light receiving element for detecting regular reflection light, and the other light receiving element 33 is a light receiving element for detecting diffuse reflection light. Here, an infrared LED is used as the light emitting element 31, but a laser light emitting element or the like may be used instead. Further, as each of the light receiving elements 32 and 33, a phototransistor is used, but an element composed of a photodiode, an amplifier circuit, or the like may be used. Further, the number of optical sensors 30 may be one.

  Since the surface of the intermediate transfer belt 11 has a high glossiness, the reflected light is mainly specularly reflected, but the specularly reflected light is reduced at locations where black toner is attached. The light receiving element 32 for detecting regular reflection light has a mechanism capable of detecting the black toner density by detecting the decrease in the amount of regular reflection light. On the other hand, the diffused light detection light receiving element 33 can detect the color toner density by detecting the diffuse reflected light reflected from the color toner other than black.

  Using the optical sensor 30 configured as described above, the image forming apparatus of the present embodiment executes a process control operation for adjusting the image density to an appropriate density. Specifically, first, a pattern image (tone pattern) for image density detection is formed on the surface of each photoconductor 2 in the same process as the above image forming operation, and the pattern image is formed on the intermediate transfer belt 11. Transcript. As shown in FIG. 2, when the pattern image 35 on the intermediate transfer belt 11 is conveyed to a position facing the optical sensor 30 as the intermediate transfer belt 11 travels, the pattern image 35 is transferred by the optical sensor 30. The toner density is detected.

  Then, the image forming conditions are adjusted so that the detected toner density becomes the target value. The image forming conditions are adjusted by controlling, for example, the charging bias of the charging roller 3, the developing bias of the developing device 4, the exposure amount of the LED head array 6, and the like. By controlling the developing bias, the thickness of the toner layer of the toner image can be adjusted, and by controlling the charging bias or the exposure amount, the dot size (tone reproducibility) of the toner image is adjusted. It is possible. In this way, the density of the toner image transferred to the recording paper is maintained at an appropriate density so that a high quality image can be obtained.

  However, an abnormal image may be generated due to various other factors such as a failure of the charging roller or the cleaning blade, a change in the surrounding environment, a deterioration with time of the toner or the developing roller, or the like. Therefore, in this embodiment, the occurrence of an abnormal image is detected as follows.

FIG. 4 is a diagram showing an overall flow of abnormal image detection control and toner density control.
The abnormal image detection and toner density control operations are performed when a predetermined start instruction is issued. The predetermined start instruction is issued every time the cumulative number of printed sheets reaches a predetermined number such as 200 sheets or 300 sheets. First, when there is a predetermined start instruction, a mode reset is performed between a first determination mode and a second determination mode for determining the presence or absence of an abnormal image, which will be described later. Thereafter, the calibration operation of the optical sensor 30 is performed, and the light emission amount is adjusted so that the detection voltage value of the optical sensor 30 with respect to the surface of the intermediate transfer belt becomes a predetermined value.

  As a result, when the calibration of the optical sensor 30 is successful, the development bias is continuously controlled. On the other hand, if the calibration of the optical sensor 30 is not successful, the control operation is terminated. If the development bias is controlled and the control is successful, the first determination mode is performed. On the other hand, if the development bias control is not successful, a predetermined error process is performed and the control operation is terminated.

  In the first determination mode, it is determined whether or not an abnormal image is likely to occur. The specific processing in the first determination mode will be described later. As a result of performing the first determination mode, when it is determined that there is no possibility of occurrence of an abnormal image, the charging voltage environment is subsequently controlled. As a result, when the control of the charging voltage environment is successful, normal termination processing is performed and the control operation is terminated. On the other hand, if the control of the charging voltage environment is not successful, the control operation is terminated after performing a predetermined error process.

  Further, when it is determined that there is a possibility that an abnormal image is generated as a result of performing the first determination mode, the second determination mode is performed. In the second determination mode, it is determined whether there is toner on the non-image area of the intermediate transfer belt 11. Note that specific processing in the second determination mode will be described later. And after performing this 2nd determination mode to a predetermined timing, control operation is complete | finished.

  Hereinafter, the first determination mode and the second determination mode will be described in detail.

First, the first determination mode will be described.
FIG. 5 shows a block diagram of a control system related to the first determination mode.
As shown in FIG. 5, the control system related to the first determination mode is based on the detection result of the toner adhesion amount detection means 41 that detects the toner adhesion amount (developer adhesion amount) of the pattern image and the toner adhesion amount detection means 41. Based on the relationship estimation means 42 for estimating the relationship between the development potential and the toner adhesion amount based on the relationship between the development potential and the toner adhesion amount estimated by the relationship estimation means 42, the development start point is within a predetermined development potential range. Development start point abnormality determination means 43 for determining whether or not.

  In the present embodiment, the optical sensor 30 is used as the toner adhesion amount detection means 41. A pattern image (solid image) formed on the photosensitive member 2 is transferred onto the intermediate transfer belt 11 at each timing when the abnormal image detection control is started, that is, every time when the cumulative number of printed sheets reaches a predetermined number. Is detected by the optical sensor 30. At this time, the pattern images formed on the photoconductor 2 are a plurality of pattern images formed with different development potentials.

  The developing potential here indicates a potential difference between the latent image portion on the photosensitive member 2 and the developing roller 25. The larger the developing potential, the more toner on the developing roller 25 is on the photosensitive member 2. The force to move to the latent image portion is increased. Therefore, the larger the development potential, the more the toner adhesion amount of the pattern image tends to increase. That is, in the first determination mode, first, the optical sensor 30 detects a plurality of pattern images having different toner adhesion amounts.

  The relationship estimation means 42 obtains (estimates) the relationship between the development potential and the toner adhesion amount to the latent image portion based on the toner adhesion amounts of the plurality of pattern images detected by the optical sensor 30. For example, as shown in FIG. 6, the relationship between the development potential and the toner adhesion amount is created by plotting the toner adhesion amount detection data with the development potential as the horizontal axis and the toner adhesion amount as the vertical axis. Can be obtained. A parameter indicating the slope of this graph is called development γ, and represents the relationship between the development potential and the pattern image, that is, development characteristics. The development characteristics are not always constant and vary depending on various factors such as the usage environment of the apparatus and the degree of deterioration of the toner or the developing roller. In FIG. 6, three examples of development characteristics indicated by symbols x, y, and z are displayed.

  Further, the intersections Ex, Ey, Ez of the development characteristic graph shown in FIG. 6 and the horizontal axis, that is, the value of the development potential at which the toner adhesion amount becomes 0 is called the development start point, and the development start point abnormality determination means. 43 determines whether the development start point is within a predetermined development potential range J. The predetermined development potential range J is a range for determining whether or not an abnormal image has occurred. If the image forming operation is normally performed, as shown by the development characteristics x and y in FIG. The start points Ex and Ey are included in a predetermined development potential range J. However, if the development characteristics change greatly as shown by the symbol z in FIG. 6 due to the factors described above and the development start point Ez is out of the predetermined development potential range J, the non-latent image on the photosensitive member 2 is obtained. There is a possibility that an abnormal image such as so-called scumming occurs where toner adheres to the non-image area of the intermediate transfer belt 11. In the example shown in FIG. 6, the predetermined development potential range is set to a range of −50 to 50. However, the range is not limited to this range, and may be set as appropriate according to the standard of the apparatus. Good.

  As described above, as a result of determining whether or not the development start point is within the predetermined development potential range by the development start point abnormality determination means 43, it is determined that the development start point is within the predetermined development potential range. If so, the second determination mode is not performed. Thereafter, the first determination mode is not performed until the cumulative number of printed sheets reaches the predetermined number again, and the first determination mode is performed when the cumulative number of printed sheets reaches the predetermined number of sheets again. On the other hand, when it is determined that the development start point is not within the predetermined development potential range, the second determination mode is performed.

Next, the second determination mode will be described.
FIG. 7 shows a block diagram of a control system related to the second determination mode.
As shown in FIG. 7, the control system relating to the second determination mode includes a non-image area determination unit 51, a surface detection unit 52, a developer presence / absence determination unit 53, a reference value storage unit 54, and an abnormality determination unit 55. And warning means 56, image data storage means 57, operation stop means 58, and stop release means 59.

  The non-image area determination unit 51 is a unit that determines a non-image area on the intermediate transfer belt 11. The non-image area determining means 51 is an area B other than each effective image area A to which the image G for one page on the intermediate transfer belt 11 shown in FIG. A region corresponding to between the recording media) and a region behind the last effective image region A are determined as non-image regions. Further, as shown in FIG. 9, depending on the image to be formed, there may be a certain extent of a region C where the image G is not transferred, even within the effective image region A. The area C in which the image G in the effective image area A is not transferred may be determined as a non-image area.

  The image area for one page formed on the photoreceptor 2 is determined by transmitting a preset image area signal. Specifically, a frame gate signal that defines an effective image area in the sub-scanning direction, which is an image conveyance direction, and a line gate signal that defines an effective image area in the main scanning direction orthogonal to the sub-scanning direction are preset. While these signals are transmitted, an electrostatic latent image is formed on the surface of the photoreceptor 2 based on the image data. Further, when the signal is not transmitted, an electrostatic latent image is not formed on the surface of the photoreceptor 2. In this embodiment, the non-image area on the intermediate transfer belt 11 is determined based on the timing at which the transmission of the frame gate signal that defines the effective image area in the sub-scanning direction is stopped. As described above, the method of determining the non-image area based on the transmission timing of the frame signal has an advantage that the determination can be easily performed.

  The surface detection means 52 is a means for detecting the surface of the intermediate transfer belt 11 in the non-image area. In the present embodiment, the optical sensor 30 is used as the surface detecting unit 52, and the reflected light of the non-image area of the intermediate transfer belt 11 is detected by the optical sensor 30.

  The developer presence / absence judging means 53 is a means for judging the presence / absence of toner (developer) in the non-image area on the intermediate transfer belt 11 based on the detection result of the optical sensor 30. There is a clear difference in the toner density detected by the optical sensor 30 between the presence and absence of toner in the non-image area. Assuming that the toner density is detected in increments of 0% to 100%, the toner density detected when no toner is present shows a value near 0%, and the toner density detected when toner is present is 100. The value near% is shown. Here, the toner density of 50% is set as a reference density (reference value). When the detected toner density exceeds 50%, it is determined that “toner is present”, and when it is less than 50%, it is determined that “toner is absent”. I have to. As described above, when the reference density is a fixed value, it is possible to simplify the determination process of the presence / absence of toner and reduce the information processing burden. The reference density is not limited to 50%. If it is not a value near 0% or a value near 100%, a value between them can be selected as appropriate and set as a reference density. The preset reference density is stored in the reference value storage means 54.

  The abnormality determination means 55 is a means for determining the type of abnormality according to the number of optical sensors 30 determined as “toner present”. In the present embodiment, three optical sensors 30 are used, but the number of optical sensors 30 is not limited to this. One optical sensor 30 having a plurality of detection regions may be used.

  As the types of abnormalities, for example, there are those shown in FIG. In FIG. 10, (a) is an abnormal image formed by the weakly charged toner falling from the process unit, (b) is an abnormal image formed in a vertical belt shape due to the charging roller being dirty, (c) ) Is an all-solid abnormal image formed by the charging failure of the photosensitive member 2.

  In the present embodiment, when any one of the two optical sensors 30 detects toner (toner density capable of confirming the presence of toner) in the non-image area, there is a possibility of an abnormality due to partial toner adhesion. Therefore, the abnormality is determined as shown in FIG. 10 (a) or (b). On the other hand, when all the optical sensors 30 detect toner in the non-image area (toner density capable of confirming the presence of toner), it is determined that the image is a solid image shown in FIG.

  The warning means 56 is a means for issuing a warning when it is determined that there is an abnormality. As a warning method by the warning means 56, a visual warning such as blinking of a lamp, an audible warning such as output of a warning sound or a voice message, or a warning method using a combination thereof can be selected as appropriate.

  The image data storage unit 57 is a unit that stores image data when it is determined that there is an abnormality. In the present embodiment, when the presence of toner is confirmed in the non-image area on the intermediate transfer belt 11 and is determined to be abnormal, the image data storage unit 57 performs an effective image area (or a predetermined image) immediately before the non-image area. Image data in the area) is saved.

  The operation stop unit 58 is a unit that automatically stops the image forming operation of the image forming apparatus when it is determined that there is an abnormality. Further, the stop by the operation stopping means 58 can be canceled by the stop releasing means 59. The stop cancellation unit 59 is configured to be operable by, for example, a touch panel or a switch provided in the image forming apparatus.

Hereinafter, the operation in the second determination mode will be described with reference to the flowchart of FIG.
First, when the second determination mode is started, the non-image area determination unit 51 determines the non-image area B on the intermediate transfer belt 11 based on the timing of stopping transmission of the frame gate signal. In the present embodiment, the non-image region B is determined based on the timing of stopping transmission of the frame gate signal for forming a black image.

  When the non-image area B reaches the detection position of each optical sensor 30, the surface of the non-image area B is detected by each optical sensor 30 (surface detection means 52) to calculate the toner density D (FIG. 11). S2). The toner density D is calculated by a ratio (V / Vsg) between the detection voltage value V of the optical sensor 30 in the non-image area B and the detection voltage value Vsg detected on the surface (background surface) of the intermediate transfer belt 11 in advance. ) Is converted into toner density using a calculation table or function. The timing of detecting the surface of the intermediate transfer belt 11 in advance is performed during a process control operation for adjusting the image density to an appropriate density, an initialization operation performed when the power is turned on, or when returning from the energy saving mode.

  Thereafter, the detected density D in the non-image area B and the reference density Dth stored in the reference value storage means 54 are compared by the developer presence / absence judgment means 53 to determine the presence / absence of toner (S3 in FIG. 11). ). When the detected density D is less than the reference density Dth, it is determined that there is no toner in the non-image area B. That is, in this case, it is determined that there is no abnormality. Thereafter, it is confirmed whether there is a subsequent print request (S13 in FIG. 11), and if there is a print request, printing is continued.

  On the other hand, when the detected density D exceeds the reference density Dth, it is determined that “toner is present” in the non-image area B. In this case, whether or not all the optical sensors 30 are determined to be “toner present” is confirmed by the abnormality determination means 55, and the type of abnormality is determined based on the result (S4 in FIG. 11). If all the optical sensors 30 determine that “toner is present”, it is determined that all solid images are abnormal as shown in FIG. Further, when it is determined that “toner is present” in any one of the three optical sensors 30 in the non-image area, a portion as shown in FIG. It is determined that the toner is abnormal due to the adhesion of toner.

  When it is determined that all the solid images are abnormal, the image forming operation is automatically stopped by the operation stopping means 58 in order to prevent the occurrence of the abnormal image thereafter (S5 in FIG. 11). Thereafter, the execution of the image forming operation is prohibited until the cause of the abnormality is removed by, for example, repair by a service person or replacement of the process unit. Further, since there is a possibility that an abnormality has occurred in the image in the effective image area A immediately before the non-image area B determined to be abnormal, the image data in the effective image area A immediately before that is saved for backup. (S6 in FIG. 11). The image data is stored by the image data storage means 57. If there is subsequent image data, it is stored by the image data storage means 57 so that the image data is not lost. Further, in this case, a warning is issued by the warning means 56 in order to notify the user or the like of the abnormality (S7 in FIG. 11). Note that the storage of the image data is temporary. After the abnormality of the image forming apparatus is removed, printing is resumed. If the image is normally printed based on the stored image data, the image data is erased.

  On the other hand, if it is determined that there is an abnormality due to the adhesion of partial toner other than the solid image, the image forming operation is stopped by the operation stopping means 58 (see FIG. 11), as in the case of the all solid image abnormality. S8), image data storage by the image data storage means 57 (S9 in FIG. 11), and abnormality notification by the warning means 56 (S10 in FIG. 11). However, in this case, unlike when all solid images are abnormal, after the image forming operation is automatically stopped, the user is confirmed whether or not to stop using the image forming apparatus (S11 in FIG. 11). . Specifically, an instruction item (soft key) capable of selecting whether to stop using is displayed on a touch panel or the like provided in the image forming apparatus. For example, when the user looks at the printed image and determines that the abnormal level is acceptable, the stop canceling unit 59 cancels the stop of the image forming operation by instructing that the use is not stopped on the touch panel or the like. (S12 in FIG. 11). Then, after the stop of the image forming operation is canceled, it is confirmed whether or not there is a subsequent print request (S13 in FIG. 11), and if there is a print request, printing is continued. Further, when the stop of the image forming operation is released, it is not necessary to print again the image first confirmed by the user, and the image data once stored is deleted. On the other hand, if the user decides that it is better to stop the image forming operation, instruct the user to stop using the touch panel, etc., and prohibit the image forming operation from being executed until the cause of the abnormality is removed by a service person etc. To do. In this case, if there is subsequent image data, the image data is stored by the image data storage means 57 so that the image data is not lost.

  Thereafter, the determination of the presence or absence of an abnormal image in the same second determination mode is repeated for each non-image area. When the cumulative number of printed sheets reaches a predetermined number during execution of the second determination mode, a mode reset is performed (see FIG. 4), and the control shifts to the control for performing the first determination mode. In the first determination mode, if it is determined that the development start point is within the predetermined development potential range, that is, there is no possibility of occurrence of an abnormal image, the second determination mode is not performed.

  As described above, according to the present invention, it is determined whether or not an abnormal image is generated in the first determination mode, and only when it is determined that there is a possibility of occurrence of an abnormal image, the second determination mode. Therefore, the execution frequency of the presence / absence determination of the developer on the non-image area (second determination mode) can be reduced as compared with the conventional control. As a result, the use frequency (drive time) of the detection means used for the presence / absence determination (second determination mode) of the developer on the non-image area can be reduced, so that deterioration of the components of the detection means is suppressed. Longer life can be achieved.

  In particular, when an optical sensor is used as a means for detecting the presence or absence of toner, the output of the optical sensor tends to change due to a temperature rise due to self-heating of the optical sensor when the accumulated light emission time becomes longer. Therefore, as in the past, whether or not there is a possibility of occurrence of an abnormal image, always determining the presence or absence of the developer on the non-image area, the accumulated light emission time of the optical sensor becomes longer, the output fluctuation Increases and the detection accuracy decreases.

  On the other hand, in the embodiment of the present invention, the presence / absence determination of the developer on the non-image area (second determination mode) is performed only when there is a possibility of occurrence of an abnormal image. That is, since it is not necessary to perform the second determination mode until it is determined that there is a possibility of occurrence of an abnormal image in the first determination mode, the light emission time of the optical sensor in the second determination mode is shortened, It is possible to suppress a decrease in detection accuracy.

FIG. 12 is a diagram illustrating a graph of the output change of each optical sensor when the first determination mode is performed and when the second determination mode is performed.
As shown by the solid line graph in FIG. 12, when the second determination mode is continuously performed, since the non-image area is detected for each sheet interval, the output of the optical sensor greatly decreases as the number of printed sheets increases. . On the other hand, as shown by the dotted line graph in FIG. 12, the first determination mode is performed only by detecting the pattern image by the optical sensor for every predetermined cumulative number of printed sheets (for example, 200 sheets or 300 sheets). Therefore, compared with the second determination mode, the light emission time of the optical sensor is much shorter, and as a result, the output reduction is also small. Thus, even if it continues in 1st determination mode, the output fall of an optical sensor is small and it can maintain detection accuracy.

  Note that the light emission timing of the optical sensor in the first determination mode and the light emission timing of the optical sensor in the second determination mode are not limited to the timings described in the above embodiment, and can be changed as appropriate. However, the light emission time of the optical sensor per unit image formation time when performing the first determination mode is shorter than the light emission time of the optical sensor per unit image formation time when performing the second determination mode. It is desirable to set the light emission timing in each mode.

Further, the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.
In the above-described embodiment, the present invention is applied to an indirect transfer type image forming apparatus that indirectly transfers images on a plurality of photoreceptors 2 to a sheet via an intermediate transfer belt 11 as shown in FIG. Although the case has been described as an example, the present invention directly transfers a plurality of images on the photosensitive member 2 onto a sheet conveyed by a conveying belt (conveying member) 60 as shown in FIG. The present invention can also be applied to other image forming apparatuses. In other words, the first determination mode and the second determination mode may be performed using the conveyance belt 60 instead of the intermediate transfer belt in the above embodiment.

  In addition, if possible, an optical sensor may be arranged to face the photoconductor 2, and a non-image area or a pattern image on the photoconductor may be detected by the optical sensor. Therefore, the present invention can be applied not only to a tandem color image forming apparatus including four process units but also to a four-cycle color image forming apparatus and a monochrome image forming apparatus. Further, the image forming apparatus to which the present invention can be applied includes a printer, a copier, a facsimile, or a complex machine thereof. The developing method may be a one-component developing method using a one-component developer composed of toner, or a two-component developing method using a two-component developer composed of toner and carrier.

2 Photoconductor (latent image carrier)
3 Charging roller (charging means)
4 Developing device (Developing means)
6 LED head array (latent image forming means)
30 Optical sensor (detection means)
35 Pattern image A Effective image area B Non-image area C Non-image area Ex, Ey, Ez Development start point J Development potential range

JP 2011-28160 A

Claims (8)

A latent image carrier that carries a latent image on the surface;
Charging means for charging the surface of the latent image carrier;
Latent image forming means for forming a latent image on the surface of the latent image carrier charged by the charging means;
In an image forming apparatus comprising: a developing unit that attaches a developer to the latent image portion by a potential difference with the latent image portion on the latent image carrier and visualizes the latent image portion.
From the relationship between the development potential, which is a potential difference between the latent image portion and the developing means, and the developer adhesion amount to the latent image portion, the development start point at which the developer adhesion amount becomes 0 is a predetermined development potential. A first determination mode for determining whether or not it is within a range;
A second determination that determines whether or not there is a developer on a non-image area where no image is carried when the first determination mode determines that the development start point is not within the predetermined development potential range; And an image forming apparatus.   The image forming apparatus according to claim 1, wherein the relationship between the development potential and the developer adhesion amount is obtained by detecting the developer adhesion amounts of a plurality of pattern images formed at different development potentials.   The image forming apparatus according to claim 1, wherein an optical sensor is used as a detection unit that detects the presence or absence of the developer on the non-image area in the second determination mode. Detection of the pattern image in the first determination mode is performed by an optical sensor,
The light emission time of the optical sensor per unit image formation time when performing the first determination mode is shorter than the light emission time of the optical sensor per unit image formation time when performing the second determination mode. The image forming apparatus according to claim 3, wherein the light emission timing of the optical sensor in each mode is set.   5. The image forming apparatus according to claim 3, wherein the presence or absence of the developer is detected at least for each non-image area corresponding to between the recording media by the optical sensor.   6. The image forming apparatus according to claim 5, wherein in the second determination mode, an area between effective image areas determined by transmission of a preset image area signal is determined as the non-image area. .   The image forming apparatus according to claim 6, wherein in the effective image area, when there is an area where no image is formed based on image data, the area is determined as the non-image area. A latent image carrier that carries a latent image on the surface;
Charging means for charging the surface of the latent image carrier;
Latent image forming means for forming a latent image on the surface of the latent image carrier charged by the charging means;
An abnormal image detection method in an image forming apparatus, comprising: a developing unit that attaches a developer to the latent image portion by a potential difference with the latent image portion on the latent image carrier and visualizes the image,
From the relationship between the development potential, which is a potential difference between the latent image portion and the developing means, and the developer adhesion amount to the latent image portion, the development start point at which the developer adhesion amount becomes 0 is a predetermined development potential. Perform a first determination mode for determining whether or not the current position is within the range;
A second determination that determines whether or not there is a developer on a non-image area where no image is carried when the first determination mode determines that the development start point is not within the predetermined development potential range; An abnormal image detection method characterized by performing the determination mode.

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