JP5445955B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus that employs a two-component developing device.

  Conventionally, in an image forming apparatus, in order to stabilize the image density, the toner adhesion amount of a toner pattern formed on an image carrier and the toner density of a developer are detected, and based on this, toner replenishment conditions and image formation are detected. Devices that perform process control to control conditions are known. In this apparatus, it is assumed that the toner density is controlled to a desired value. If the toner density cannot be controlled to a desired value, process control breaks down and an abnormal image is generated. Further, if the toner concentration is outside the appropriate range, unnecessary toner consumption, damage to other parts due to carrier adhesion to the photoreceptor, and the like may occur. For this reason, when the toner density falls outside the appropriate range, it is necessary to grasp this as an abnormality and take immediate measures.

  Therefore, when the toner density detection value of the toner density sensor for detecting the toner density exceeds a preset upper and lower limit value, it is determined that the toner density is abnormal. However, the toner density detection value by the toner density sensor exceeds the upper and lower limit values because the toner density actually becomes abnormal due to a failure of the toner replenishing means for replenishing the toner to the developing apparatus or the developer agitating means in the developing apparatus. It is not always the case. Due to the failure of the toner density sensor itself, there are cases where the toner density is actually detected erroneously even when the toner density is normal. For this reason, it is difficult to accurately determine whether or not an abnormality has actually occurred in the toner density depending on whether or not the toner density detection value of the toner density sensor exceeds the upper and lower limit values.

  Japanese Patent Application Laid-Open No. 2004-228688 compares the trend of fluctuation of the toner density detection value by the toner density sensor with the trend of fluctuation of the toner adhesion amount detection value by the toner adhesion amount sensor. An apparatus for determining that an abnormality has occurred in a detected value is described. Specifically, even if the toner density detection value of the toner density sensor is outside the range of the upper and lower limit values, the fluctuation tendency of the toner density detection value is compared with the fluctuation tendency of the toner adhesion amount detection value. Is determined to be normal, and image formation is continued. If there is a contradiction, it is determined that an abnormality has actually occurred in the toner density, and image formation is stopped. Even if the toner density detection value of the toner density sensor is within the set range, the fluctuation tendency of the toner density detection value is compared with the fluctuation tendency of the toner adhesion amount detection value. Image formation is stopped.

  When the toner density detection value by the toner density sensor exceeds the upper and lower limit values, and a failure of the toner density sensor, the toner replenishing means, the stirring means, or the like is considered, an appropriate action must be taken promptly by a service person. The service person needs to bring many replacement parts corresponding to all possible failures and analyze each possible failure one by one, which requires a lot of work and increases the downtime of the apparatus. On the other hand, if it is understood that the toner density sensor is faulty, the service person can deal with it simply by replacing the toner density sensor, so that the work is simple and the apparatus downtime is small. For this reason, it is desirable that if there is a failure in the toner concentration sensor, it can be easily identified. Furthermore, when the service person is called, if the failure is found in the toner concentration sensor, the service person does not need to bring many replacement parts corresponding to the failure of the toner replenishing means or the stirring means, and only the toner concentration sensor is installed. Bring it with you.

  Further, in the configuration in which the developing device is included in the process cartridge, the process cartridge is recycled and reused. However, if the analysis is troublesome without knowing where the failure is, it is discarded as it is. For this reason, even when the toner density sensor can be reused by replacing only the toner density sensor, it may be discarded. Also from this point, it is desirable that when the detected value of the toner density by the toner density sensor exceeds the upper and lower limit values, it is easily identified whether the cause is a failure of the toner density sensor itself.

  On the other hand, the apparatus of Patent Document 1 accurately determines the abnormality of the toner density detection value, determines whether the toner density is actually abnormal, and determines the subsequent image based on the determination result. It defines the forming operation and does not determine the failure of the toner density sensor itself.

  In addition, the apparatus of Patent Document 1 compares the fluctuation trend of the toner density detection value with the fluctuation trend of the toner adhesion amount detection value in order to judge the occurrence of the toner density abnormality, and judges the toner density abnormality. The image formation is continued for a while until it is done. On the other hand, the specific determination of the toner concentration sensor failure is much quicker and more reliable than the determination of the occurrence of an abnormal toner concentration, considering that the parts and measures taken by the service person will change based on the determination. Is required.

  The present invention has been made in view of the above background, and an object of the present invention is to provide toner replenishment conditions and image forming conditions based on the toner density detection value by the toner density detection means and the toner adhesion amount detection value by the toner adhesion amount detection means. In the image forming apparatus for controlling the toner, an image forming apparatus capable of quickly and accurately identifying the presence or absence of a failure in the toner density detecting means and taking appropriate measures in a short time is provided.

In order to achieve the above object, the invention of claim 1 is directed to a developing device for forming a toner image on an image carrier using a two-component developer comprising toner and carrier, and detecting the toner density in the developing device. Toner density detecting means for detecting toner adhesion amount detecting means for detecting the toner adhesion amount of the toner image formed on the image carrier, toner density detection value by the toner density detecting means, and toner adhesion amount detecting means In an image forming apparatus comprising a control unit for controlling a toner replenishing condition to the developing device and a toner image forming condition on the image carrier using a toner adhesion amount detection value, the control unit includes: Whether or not the toner density detection value detected by the toner density detection means is within a preset toner density appropriate range, and the adhesion amounts of a plurality of toner patterns having different adhesion amounts by the toner adhesion amount detection means It is determined whether or not the development gamma coefficient calculated from a plurality of detected toner adhesion amount detection values is within a preset development gamma coefficient appropriate range, and the respective determination results are compared to determine whether the toner density detection unit has failed. have a toner concentration detector failure determination mode for determining the presence or absence, the toner concentration detector failure determination mode, the toner density detection value by the toner concentration outside the adequate range, and, the development gamma coefficient development gamma coefficient appropriate range When it is determined that the toner density is within, it is determined that there is a failure in the toner density detecting means.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when it is determined that the toner concentration detecting unit has a failure in the toner concentration detecting unit failure determination mode, the toner concentration detection unit detects the toner concentration. The image formation is continued by determining the toner replenishment condition to the developing device and the toner image forming condition on the image carrier without using values.
The invention of claim 3 is the image forming apparatus according to claim 2, when it is determined that the failure of the toner concentration detecting means is above a toner concentration detector failure determination mode, the control means of the toner adhesion amount detection The toner supply condition is changed so as to be determined based on the value or the image area data.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first, second, and third aspects, the amount of adhesion differs between the control means and the toner adhesion amount detection means in the toner density detection means failure determination mode. The toner image forming conditions on the image carrier are determined using a plurality of toner adhesion amount detection values obtained by detecting the adhesion amounts of a plurality of toner patterns.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, and fourth aspects, when it is determined that the toner density detection unit has a failure in the toner density detection unit failure determination mode, The image forming apparatus includes a notification unit that notifies the outside that the toner density detection unit has failed.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, and fifth aspects, the image carrier, the developing device, and the toner density detecting unit are integrated. It is configured to be in the form of a process cartridge that is detachable from the main body of the image forming apparatus.
In the present invention, by providing a toner concentration detection unit failure determination mode for determining whether there is a failure in the toner concentration detection unit, it is possible to identify a failure in the toner concentration detection unit and take appropriate measures accordingly. Become. The toner density detection unit failure judgment mode is calculated from whether or not the toner density detection value is within a preset toner density appropriate range and a plurality of toner adhesion amount detection values obtained by detecting the adhesion amounts of a plurality of toner patterns having different adhesion amounts. It is determined whether or not the developed gamma coefficient is within a preset appropriate range of the developed gamma coefficient, and the respective determination results are compared to determine whether or not the toner density detecting means has failed. Specifically, for example, if the development gamma coefficient is within the appropriate range of the development gamma coefficient, each appropriate range is set in advance so that the actual toner density is always within the appropriate toner density range. With this setting, if the toner density is outside the proper range, the result that the development gamma coefficient is within the proper range cannot be obtained. Therefore, when the determination result that the toner density detection value is outside the proper range and the calculated development gamma coefficient is within the proper range is obtained, the toner detection value is different from the actual toner density, and the toner density detection means It can be determined that there is a failure.
Furthermore, the determination of the presence or absence of a failure of the toner concentration detection means in the toner concentration detection means failure determination mode can obtain high reliability for the following reason. Generally, a certain amount of error is included when the toner adhesion amount detecting means detects the toner adhesion amount of the toner pattern. In particular, if there is a local toner drop on the toner pattern, the toner adhesion amount detection value by the toner adhesion amount detection means is large and lacks accuracy. As described above, since the error is easily included in the toner adhesion amount detection value, if the determination is performed using the toner adhesion amount detection value itself, the accuracy may be lost. Therefore, by using a development gamma coefficient calculated from a plurality of toner adhesion amount detection values, even if there is an error in each toner adhesion amount detection value, the influence can be mitigated. In addition, since a plurality of toner patterns are created and detected at the same time, quickness can be obtained as compared with a case where image formation is continued and fluctuation trends are compared.

  According to the present invention, in the image forming apparatus that controls the toner replenishment condition and the image forming condition based on the toner density detection value by the toner density detection means and the toner adhesion amount detection value by the toner adhesion amount detection means, the toner density detection means Therefore, it is possible to quickly and accurately identify the failure and take an appropriate countermeasure in a short time.

1 is a schematic configuration diagram of a copier according to an embodiment. FIG. 2 is a schematic configuration diagram of an image forming unit. The block diagram in connection with an electric potential control apparatus. 4 is a flowchart of the operation of the control means, (a) is a flowchart of the potential control device, and (b) is a flowchart of toner concentration sensor (T sensor) failure determination. FIG. 3 is a block diagram related to a toner supply control device. 6 is a flowchart of the operation of the toner supply control device. FIG. 6 is an explanatory diagram of a toner pattern created in a toner density sensor failure determination mode. A graph for calculating a development gamma coefficient as development ability. The block diagram in connection with the electric potential control apparatus after the failure of a toner density sensor is specified. FIG. 3 is a block diagram related to a toner supply control device after a toner density sensor failure has been identified.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of a tandem type color laser copying machine (hereinafter simply referred to as “copying machine”) in which a plurality of photoconductors are arranged in parallel will be described.
FIG. 1 is a schematic configuration diagram of a copying machine according to the present embodiment. The copying machine includes a printer unit 100, a paper feeding device 200 on which the printer unit 100 is mounted, a scanner 300 fixed on the printer unit 100, and the like. An automatic document feeder (ADF) 400 fixed on the scanner 300 is also provided.

  The printer unit 100 is provided with an intermediate transfer belt 10 formed of an endless belt at the center thereof. The intermediate transfer belt 10 is stretched around support rollers 14, 15, and 16 as three support rotating bodies, and rotates and moves in the clockwise direction in the figure using the third support roller 16 as a drive roller. Further, among the three support rollers, the belt portion stretched between the first support roller 14 and the second support roller 15 has yellow (Y) along the belt moving direction as shown in FIG. ), Magenta (M), cyan (C), and black (K) four image forming units 18Y, 18M, 18C, and 18K that are arranged side by side are tandem image forming units 20 that are arranged to face each other. . An exposure device (optical writing unit) 21 is provided above the tandem image forming unit 20.

  The image forming units 18Y, 18M, 18C, and 18K have drum-shaped photoconductors 40Y, 40M, 40C, and 40K as image carriers. Each of the photoreceptors 40Y, 40M, 40C, and 40K has a charging device, a developing device, a cleaning unit, a static eliminator, and the like, which will be described later.

  The four primary transfer bias rollers 62Y, 62M, 62C, and 62K are arranged on the inner side of the intermediate transfer belt 10 facing the image forming portions 18Y, 18M, 18C, and 18K so as to contact the intermediate transfer belt 110, respectively. It is installed. The primary transfer bias rollers 62Y, 62M, 62C, and 62K are applied with a primary transfer bias from a power source (not shown). The primary transfer bias rollers 62Y, 62M, 62C, and 62K sequentially transfer the toner images formed by the image forming units 18Y, 18M, 18C, and 18K onto the intermediate transfer belt 10, and then onto the intermediate transfer belt 10. A four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed as a multiple toner image.

  A secondary transfer device 22 as a second transfer unit is provided on the opposite side of the tandem image forming unit 20 with the intermediate transfer belt 10 interposed therebetween. In the secondary transfer device 22, a secondary transfer belt 24, which is an endless belt as a transfer sheet conveying member, is stretched between two rollers 231 and 232. The secondary transfer belt 24 is provided so as to be pressed against the third support roller 16 via the intermediate transfer belt 10. The secondary transfer device 22 transfers the toner image on the intermediate transfer belt 10 to a transfer sheet S that is a transfer material.

  Further, on the left side of the second support roller 15 in the drawing, which is downstream of the secondary transfer device 22 in the moving direction of the intermediate transfer belt 10, an intermediate for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided. A transfer belt cleaning device 17 is provided.

Further, the toner adhesion amount for detecting the toner adhesion amount of the toner image on the intermediate transfer belt 10 downstream from the transfer position by the primary transfer bias rollers 62Y, 62M, 62C, and 62K and upstream from the secondary transfer device 22. A toner image detection sensor (P sensor) 310 is provided as detection means. A toner image sensor facing roller 311 is provided at a position facing the toner image detection sensor (P sensor) 310 with the intermediate transfer belt 10 interposed therebetween. In this embodiment, the intermediate transfer belt 10 having a volume resistance of 10 ¹⁰ [Ωcm ³ ] is used. If the volume resistance value is too low, for example, the bias leaks, causing an abnormal image. On the other hand, if it is too high, an appropriate value exists in order to generate an abnormal image due to a decrease in image density or discharge at a low image area.

  A fixing device 25 for fixing the toner image transferred onto the transfer sheet S is provided on the left side of the secondary transfer device 22 in the drawing. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 that is a heated endless belt. The secondary transfer device 22 described above also has a sheet conveyance function for conveying the transfer sheet S after transferring the toner image from the intermediate transfer belt 10 to the transfer sheet S to the fixing device 25. Of course, as the secondary transfer device 22, a transfer roller or a non-contact transfer charger may be used. In such a case, it is difficult to provide this sheet conveying function together. In the present embodiment, the transfer sheet S is inverted under such a secondary transfer device 22 and the fixing device 25 so as to record images on both sides of the transfer sheet S in parallel with the tandem image forming unit 20 described above. A sheet reversing device 28 is also provided.

  When making a copy using the copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is conveyed and moved onto the contact glass 32.

  On the other hand, when an original is set on the contact glass 32, the scanner 300 is immediately driven. Next, the first traveling body 33 and the second traveling body 34 are caused to travel. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.

  In parallel with this document reading, the drive roller 16 is rotated by a drive motor which is a drive source (not shown). As a result, the intermediate transfer belt 10 moves in the clockwise direction in the figure, and the remaining two support rollers (driven rollers) 14 and 15 rotate along with the movement.

  At the same time, the drum-shaped photoreceptors 40Y, 40M, 40C, and 40K as image carriers are rotated in the individual image forming units 18Y, 18M, 18C, and 18K, and the photoreceptors 40Y, 40M, 40C, and 40K are rotated. On top of this, exposure and development are performed using color-specific information for yellow, magenta, cyan, and black to form a single-color toner image (developed image). Then, the toner images on the respective photoconductors 40Y, 40M, 40C, and 40K are sequentially transferred onto the intermediate transfer belt 10 so as to overlap each other, thereby forming a four-color toner image on the intermediate transfer belt 10.

  In parallel with such image formation, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, the transfer sheet S is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages, and the separation roller The sheet is separated one by one at 45 and put into the sheet feeding path 46, conveyed by the conveying roller 47, guided to the sheet feeding path in the printer unit 100, and abutted against the registration roller 49 and stopped. Alternatively, the sheet feeding roller 50 is rotated to feed the transfer sheet S on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual sheet feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the four-color toner image on the intermediate transfer belt 10, and the transfer sheet S is sent between the intermediate transfer belt 10 and the secondary transfer device 22. The color toner image is transferred onto the transfer sheet S by transfer.

  After transfer of the toner image, the transfer sheet S is conveyed by the secondary transfer belt 24 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to the transfer toner image by the fixing belt 26 and the pressure roller 27. Is fixed by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.

  The intermediate transfer belt 10 after the toner image transfer is removed by an intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after the toner image is transferred, and the tandem image forming unit 20 forms an image again. Prepare. Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.

  When a thick paper is selected and copied, a half speed mode in which the driving speed of the photosensitive member, the intermediate transfer belt, or the like is halved may be performed. In the half speed mode, the order of driving is the same, but only the driving speed is half speed.

Next, the image forming units 18Y, 18M, 18C, and 18K of the tandem image forming unit 20 described above will be described in detail. The four image forming units 18Y, 18M, 18C, and 18K have substantially the same configuration except that each of the handled toner colors is different. explain.
FIG. 2 is a schematic configuration diagram of the image forming unit 18. The image forming unit 18 includes a charging device 60, a potential sensor 70, a developing device 61, a photoconductor cleaning device 63, a static elimination device (not shown), and the like around the drum-shaped photoconductor 40. In the present embodiment, the image forming unit 18 is in the form of a process cartridge in which these are integrally formed, and is detachable from the tandem image forming unit 20.

  At the time of image formation, the photoreceptor 40 is rotationally driven in the direction of arrow A by a drive motor (not shown). Then, after the surface of the photosensitive member 40 is uniformly charged by the charging device 60, the image data of the above-described original document or the like from the exposure device 21 is exposed by the writing exposure L to form an electrostatic latent image. The A color image signal based on the image data from the scanner 300 is subjected to image processing such as color conversion processing by an image processing unit (not shown), and is output to the exposure device 21 as image signals of each color of Y, M, C, and K. . The exposure device 21 converts an image signal from the image processing unit into an optical signal, and forms an electrostatic latent image by scanning and exposing the surface of the uniformly charged photoreceptor 40 based on the optical signal. To do.

  The developing device 61 includes a developing roller 61a as a developer carrying member that carries on its surface a two-component developer composed of a carrier and a toner housed therein and conveys it to a portion facing the photoreceptor 40. A developing bias is applied to the developing roller 61a from a power source (not shown), and a developing potential that is a potential difference is formed between the electrostatic latent image on the photoreceptor 40 and the developing roller 61a. Due to this development potential, the toner from the developer on the developing roller 61a is transferred to the electrostatic latent image on the photoreceptor 40, whereby the electrostatic latent image is developed and a toner image is formed. Further, a developer transport member 61b that stirs and transports the developer accommodated in the developing device 61 is provided. Further, a toner concentration sensor (T sensor) 312 as a toner concentration detecting means is disposed on the bottom surface of the developer conveying screw 61b, and the toner concentration can be detected at any time.

  In addition, a toner replenishing unit 61c that replenishes toner as the toner is consumed due to image formation is provided. The toner replenishing means 61c includes a toner cartridge that can be detachably replaced by a user and a sub hopper that serves as a buffer for temporarily storing toner, and supplies toner from the toner cartridge to the sub hopper and from the sub hopper to the developing device 61. To do. By providing the sub hopper, it is possible to continue image formation without lowering the toner density for a while even when the toner cartridge is empty.

  The toner image formed on the photoreceptor 40 by the developing device 61 is primarily transferred onto the intermediate transfer belt 10 as described above. After the toner image is transferred, the photoconductor 40 is cleaned of residual toner by the photoconductor cleaning device 63 and is discharged by a charge removal device (not shown) to prepare for the next image formation.

  In this way, the respective color image forming portions 18Y, 18M, 18C, and 18K form toner images of Y, M, C, and K on the respective color photoreceptors 40Y, 40M, 40C, and 40K. The image is primary-transferred superimposed on the top.

  The copying machine of this embodiment has a full color mode in which all the photoreceptors 40Y, 40M, 40C, and 40K are in contact with the surface of the intermediate transfer member 10 when the color of an image to be formed is full color, and K color when the color is black. And a monochrome mode in which the other photoreceptors 40Y, 40M, and 40C are separated from the surface of the intermediate transfer member 10. The copying machine of the present embodiment also has an auto color change mode that detects whether the original image read by the scanner is a monochrome image or a color image and automatically switches between the monochrome mode and the full color mode.

  In the monochrome mode, the first monochrome mode in which the photoconductors 40Y, 40M, and 40C other than the K-color photoconductor 40K are relatively spaced from the intermediate transfer belt to form an image, and the developing devices 61Y, 61M, There are two types of the second monochrome mode for stopping the operation of 61C. The second monochrome mode is a mode that is executed when the auto color change mode is selected. To switch between the monochrome mode, the full color mode, and the auto color change mode, an input unit is provided on an operation panel (not shown) serving as a manual operation unit so that the user can determine and input the mode.

  Since the mode can be selected by the user, there are the following advantages. For example, the original image is a color image, but when the user wants to make a monochrome image, the user can operate the operation panel to select the monochrome mode, and a monochrome image as desired by the user can be obtained. In addition, when the user selects the monochrome mode, the Y, M, and C photoconductors are always separated from the intermediate transfer belt 10, so that the deterioration of the Y, M, and C photoconductors can be suppressed. When the color mode is selected by the user, the monochrome mode is not switched in the case of a monochrome image as in the auto color change mode.

  Therefore, the printing speed when continuously printing a plurality of originals in which color originals and monochrome originals are mixed is faster than in the automatic color change mode. As a result, when the user selects the color mode, the user can quickly obtain print images of a plurality of originals in which color and monochrome are mixed.

Next, process control performed in the copying machine of this embodiment will be described.
Conventionally, in a developing device using a two-component developer, the developing ability varies depending on the toner concentration of the developer, the toner charge amount, and the like, and the image density varies. Therefore, a predetermined toner pattern is formed on the image carrier such as the photoreceptor 40 or the intermediate transfer belt 10, and the toner adhesion amount of the toner pattern is detected by a toner image detection sensor (P sensor) 310 which is an optical sensor. Further, the toner density of the developer at that time is detected by a toner density sensor (T sensor) 312, and image forming conditions, toner replenishing conditions, and the like are determined based on these detection results. As a result, even when the developing ability fluctuates, the fluctuation of the image density is suppressed by optimizing the control parameters of the image forming condition and the toner replenishment condition. In the copying machine of the present embodiment, as one of image density control means, a potential control device 401 that performs potential control for adjusting an image forming potential at a timing other than image formation, and a condition of a toner replenishment amount during printing are controlled. A toner supply control device 403 that performs toner supply control is provided.

  The toner concentration sensor (T sensor) 312 is a sensor that detects the toner concentration, which is the ratio of the carrier to the toner in the developer, by detecting the magnetic permeability. Since sensing is possible at any time regardless of the printing operation, the detection interval is set short. The detection timing is generally one that detects the toner density for each print. The value detected by the toner density sensor (T sensor) 312 is mainly used for controlling the toner replenishment amount. The toner image detection sensor (P sensor) 310 is a sensor that optically detects the adhesion amount of the toner pattern formed on the intermediate transfer belt 10. Since detection is performed by forming a predetermined pattern, it cannot be performed during the printing operation, and toner is also consumed. Therefore, the detection by the toner image detection sensor (P sensor) 310 is generally less frequent than the detection by the toner density sensor (T sensor) 312. Using the detection values of these sensors, the potential control is executed when a print job is not received or when a certain amount of time is taken at the end of the job. Further, when the non-image portion during printing is used (because the paper interval is short), the toner image detection sensor (P sensor) 310 of a predetermined pattern 1 patch is detected, and the control target value for toner supply control is corrected. There is also. In addition, a temperature / humidity sensor (not shown), which is an environmental sensor, is provided.

<Example 1>
FIG. 3 is a block diagram related to the potential control device. In the potential control device 401, the toner adhesion amount detected by the toner image detection sensor (P sensor) 310, the toner concentration detected by the toner concentration sensor 312, and the temperature and humidity detected by the temperature and humidity sensor (not shown). The toner density, the surface potential after exposure of the photosensitive member detected by the potential sensor 70, and the developing bias are input. The potential control device 401 outputs an optimum charging bias, developing bias, exposure light amount to the charging device 60, the developing device 61, and the exposure device 21, and an optimum toner density control target value to the toner replenishment control device 403. To do. A stable image density is provided by controlling each bias and toner supply in accordance with the optimum image forming conditions.

  Image density control by the potential control device 401 is executed exclusively and periodically with the printing operation, such as when the power is turned on or after printing a predetermined number of sheets (for example, 250 sheets). The reason why it is executed exclusively with the printing operation is that it is necessary to create a plurality of images having different densities.

  FIG. 4A is a flowchart of the operation of the potential control device 401. The operation of the potential control device 401 will be described in detail based on FIG. Prior to image density control, preprocessing such as adjustment of the LED light amount of the toner image detection sensor (P sensor) 310 is executed (STEP 1). Next, five patches having different densities are formed (STEP 2). FIG. 7 shows the gradation pattern of each patch created at this time. The latent image potential of each patch is detected by the potential sensor 70, and the toner adhesion amount of each patch is detected by the toner image detection sensor (P sensor) 310 (STEP 3). The development potential (the difference between the development bias Vb and the latent image potential Vl) is obtained from the output of the potential sensor 70. Further, the toner adhesion amount is obtained from the toner image detection sensor (P sensor) 310 (STEP 4). Then, a development gamma coefficient (development potential on the horizontal axis and the inclination when the toner adhesion amount is plotted on the vertical axis) shown in FIG. 8 is obtained from the relationship between the two (STEP 5). After determining whether or not the calculated value of the developing gamma coefficient as the developing capability is within the appropriate range (STEP 6), a developing potential is calculated from the developing gamma so that a predetermined target toner adhesion amount is obtained. Thereby, image forming conditions such as a developing bias, a charging bias, and an exposure light amount are determined (STEP 7). In parallel with this operation, the temperature and humidity at this time are detected by a temperature / humidity sensor (not shown), and the toner density is detected by a toner density sensor (T sensor) 312 (STEP 8). It is determined whether the toner density detection value detected by the toner density sensor (T sensor) 312 is within an appropriate range (STEP 9). When the toner density detection value is within the appropriate range, the temperature and humidity detected by the temperature and humidity sensor (not shown) and the toner density detection value detected by the toner density sensor (T sensor) 312 A suitable toner density is calculated to determine (or correct) a toner density control target value (STEP 7). Note that in a copying machine in which the potential sensor 70 is not installed, exposure is performed so that the latent image potential is constant, and patches having different densities may be formed while obtaining the development potential by changing the development bias. .

  In the series of potential control flows as described above, although not shown, an appropriate range is determined in advance for all the detected values, and an abnormal stop means for stopping as a detected value abnormality is provided if it is outside the appropriate range. Further, in the case of a detected value abnormality, the abnormality can be notified by the notification means. The detection value abnormality determination of the toner concentration sensor (T sensor) 312 will be described in detail below.

  There are various causes for the abnormality in the detection value by the toner concentration sensor (T sensor) 312. An abnormal detection value due to a decrease in toner concentration when the toner supply means 61c for supplying toner to the developing device 61 becomes unable to supply toner, and conversely, an abnormal detection value due to excessive toner concentration when the toner supply cannot be stopped can be considered. . In addition, there may be a case where the detection value becomes abnormal due to the state of the developer in the developing device 61 or a circulation problem, or a failure of the toner concentration sensor (T sensor) 312 itself. Even if the detected value of the same toner concentration sensor (T sensor) 312 is abnormal, there are various causes, and countermeasures and members to be replaced are different. Therefore, it is very important to specify the cause when considering maintainability.

  FIG. 4B is a flowchart for determining a failure of the toner density sensor (T sensor) 312. If the toner density detection value detected by the toner density sensor (T sensor) 312 is outside the preset appropriate range in (STEP 9) in the flowchart of the operation of the potential control device 401 in FIG. The failure determination of 4 (b) is performed (STEP 10). First, waiting for the completion of the calculation of the development gamma coefficient (the inclination when the horizontal axis represents the development potential and the vertical axis represents the toner adhesion amount) as the development capability in the flowchart (STEP 5) of FIG. 4A (STEP 11). ). It is determined whether or not the development gamma coefficient as the calculated development ability is within a preset appropriate range (STEP 12). If the development gamma coefficient is within the appropriate range, it is determined that the toner density sensor (T sensor) 312 is alone, and the notification means notifies the outside (STEP 13). If the development gamma coefficient is out of the appropriate range, the process ends abnormally by the sequence (STEP 6) in the flowchart of FIG.

  As described above, the failure determination of the toner density sensor (T sensor) 312 is performed by detecting whether or not the toner density detection value is within a preset toner density appropriate range and detecting a plurality of adhesion amounts of a plurality of toner patterns having different adhesion amounts. It is determined whether or not the development gamma coefficient calculated from the detected toner adhesion amount is within a predetermined development gamma coefficient appropriate range, and the respective determination results are compared to determine whether the toner density sensor (T sensor) 312 has failed. Judgment is made. Here, if the toner image detection sensor (P sensor) 310 detects a toner pattern on the intermediate transfer belt 10, if the development gamma coefficient as the development capability is within an appropriate range, the charging device 60, the development device 61, the primary transfer roller 62 is functioning normally. That is, if the development gamma coefficient is within the proper range of the development gamma coefficient, the appropriate range is set in advance so that the actual toner density is always within the proper toner density range. With this setting, if the toner density is outside the proper range, the result that the development gamma coefficient is within the proper range cannot be obtained. Therefore, when the determination result that the toner density detection value is outside the appropriate range and the calculated development gamma coefficient is within the appropriate range is obtained, the toner detection value is different from the actual toner density, and the toner density sensor (T It can be determined that there is a failure 312).

  Further, the failure determination of the toner density sensor (T sensor) 312 can obtain high reliability for the following reason. In general, when the toner image detection sensor (P sensor) 310 detects the toner adhesion amount of the toner pattern, a certain amount of error is included. In particular, when there is a local toner drop on the toner pattern, the toner adhesion amount detection value by the toner image detection sensor (P sensor) 310 is large and lacks accuracy. As described above, since the error is easily included in the toner adhesion amount detection value, if the determination is performed using the toner adhesion amount detection value itself, the accuracy may be lost. Therefore, by using a development gamma coefficient as a developing ability calculated from a plurality of toner adhesion amount detection values, even if there is an error in each toner adhesion amount detection value, the influence can be mitigated. . In addition, since a plurality of toner patterns are created and detected at the same time, quickness can be obtained as compared with a case where image formation is continued and fluctuation trends are compared.

Further, when there is an abnormality related to the toner replenishing means 61c on the developing device 61 side, a developer state, or a circulation problem, the toner pattern detected by the toner image detection sensor (P sensor) 310 is hardly formed. On the contrary, it may become a dark patch that exceeds the tolerance. In that case, the development gamma coefficient as the development capability is outside the appropriate range, and the image forming apparatus can be determined to be abnormal. If the output value of the toner density sensor (T sensor) 312 is outside the proper range even though the development gamma coefficient as the development capability is determined to be normal within the proper range, the toner density sensor ( T sensor) 312 alone can be identified as a failure. The installation position of the toner image detection sensor (P sensor) 310 may be anywhere as long as the toner pattern after development can be detected, and may be on the photoreceptor 40 immediately after development or on the paper conveyance belt. . The appropriate range of the development gamma coefficient as the developing ability is 0.5 to 2.0 (mg / cm ² / −kV), and the appropriate range of the toner concentration is 4 to 9 (wt%). It goes without saying that these appropriate ranges are values that are appropriately set by the image forming apparatus.

  Further, in the case of a failure of the toner density sensor (T sensor) 312 alone, printing can be performed without stopping the operation of the image forming apparatus. When the toner concentration sensor (T sensor) 312 is out of order, the input / output relationship of the potential control device 401 is changed as shown in FIG. 9, and the output and temperature / humidity of the toner concentration sensor (T sensor) 312 are changed. It is assumed that the toner density control target value calculated from the sensor is not updated. It should be noted that the output of the toner concentration sensor (T sensor) 312 is always acquired even if it is determined that the toner concentration sensor (T sensor) 312 alone has failed before the potential control device 401 executes the potential control. To do.

Next, for toner replenishment control during the printing operation, the control is changed as follows depending on whether the toner density sensor (T sensor) 312 is normal or malfunctioning.
FIG. 5 is a block diagram related to the toner supply control device. When the toner density sensor (T sensor) 312 is normal, as shown in FIG. 5, the toner replenishment control device 403 causes the toner density sensor 312 to detect the toner density, the image area, the toner density control target value, and the toner image detection. The toner adhesion amount detected by the sensor (P sensor) 310 and the target toner adhesion amount are input. The toner supply control device 403 calculates a toner supply amount and a toner density control target value based on the input data. By controlling toner supply in accordance with the toner supply conditions, a stable toner density and image density are provided.

  FIG. 6 is a flowchart of the operation of the toner supply control device 403. The operation of the toner supply control device 403 will be described in detail based on FIG. First, the image area is calculated according to the exposure time of the exposure means, and the toner consumption calculated theoretically is calculated (STEP 1). Based on the difference between the toner density sensor output and the toner density control target value at this time, it is determined whether the current toner density is darker or lighter than the target value (STEP 2). Based on the determination result of the toner consumption amount and the toner density, the toner replenishment amount is calculated (STEP 3). For example, if it is determined that the toner is lighter than the target value, a value that is 1.05 times the toner consumption calculated from the image area is set as the toner replenishment amount. When it is determined that the toner density is high, the toner replenishment amount is 0.95 times the toner consumption amount calculated from the image area. The toner supply amount calculated in this way is calculated and toner supply is executed (STEP 4).

In the copying machine of this embodiment, a toner patch for measuring image density is formed on a non-image portion between the image portion being printed. The image formation is performed at a timing of 10 times for each color, and when the image formation timing overlaps for each color, the patch of the color with the longest generation interval is formed. The K patch is a halftone patch with an image area of 50%, and the C, M, and Y patches are solid patches with an image area of 100%. This image density measurement patch is detected by a toner image detection sensor (P sensor) 310 to obtain a toner adhesion amount detection value. The toner density control target value is corrected from the toner adhesion amount detection value detected by the toner image detection sensor (P sensor) 310. The toner adhesion amount detection value detected by the toner image detection sensor (P sensor) 310 is compared with the target toner adhesion amount, and the correction of the toner density control target value is executed according to the result. Specifically, the difference between the toner adhesion amount detection value and the target toner adhesion amount is taken. When the toner adhesion amount within the difference of ± 0.012 [mg / cm ² ] is appropriate, the toner density control target value is set as the toner density value detected this time. When the difference is +0.012 [mg / cm ² ] or more and the toner adhesion amount detection value is high, the toner density control target value is corrected by −0.05%. On the other hand, when the difference is −0.012 [mg / cm ² ] or less and the toner adhesion amount detection value is low, the toner density control target value is corrected by + 0.05%. As described above, the control for correcting the toner concentration control target value according to the toner adhesion amount detection value that is the output of the toner image detection sensor (P sensor) 310 and correcting the toner replenishment amount based on the corrected value is performed. Is going. The corrected toner density control target value has been subjected to upper and lower limit processing in the range of 4.5 to 8.5% to prevent the toner density from running away. Also, the correction amount of the toner density control target value, the range of the toner density upper and lower limit processing, and the determination threshold value of the adhesion amount depend on the toner, the configuration of the developing device, the image formation interval of the toner patch between prints, etc. Appropriate values are appropriately determined for each image forming apparatus.

  On the other hand, when a failure of the toner density sensor (T sensor) 312 is specified, toner supply based on the image area is executed without using the toner density detection value output from the toner density sensor (T sensor) 312. To do. Correction of the toner density control target value is not executed. As a control for replenishing toner as much as the toner is consumed in this way, the function of keeping the image density stable is realized only by the image density control by the above-described potential control device. As a result, although it does not reach the original control, printing can be continued without causing downtime. When the toner density sensor (T sensor) 312 becomes abnormal value continuously five times during printing, the potential control is executed by interruption to execute the cause identification flow of the toner density sensor output abnormality.

<Example 2>
The second embodiment is substantially the same as the first embodiment, but the toner replenishment control when a failure of the toner density sensor (T sensor) 312 is specified is different. Of the components of the image forming apparatus according to the second embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here. To do.

FIG. 10 is a block diagram relating to the toner replenishment control device after the failure of the toner density sensor (T sensor) 312 is identified. When the toner density sensor (T sensor) 312 fails, as shown in FIG. 10, the toner replenishment control device 403 has the image area, the toner adhesion amount detected by the toner image detection sensor (P sensor) 310, and the target toner. Enter the amount of adhesion. The toner replenishment control device 403 calculates a toner replenishment amount based on the input data. Specifically, the image area is calculated according to the exposure time of the exposure device 21, and the toner consumption calculated theoretically is calculated. Next, the toner adhesion amount detected by the toner image detection sensor (P sensor) 310 is compared with the target toner adhesion amount, and the toner replenishment amount is corrected according to the result. Specifically, the difference between the detected toner adhesion amount and the target toner adhesion amount is taken, and when this difference is an appropriate toner adhesion amount within ± 0.012 [mg / cm ² ], (toner replenishment amount) = (Toner consumption). When the difference is +0.012 [mg / cm ² ] or more and the toner adhesion amount detection value is high, (toner replenishment amount) = (toner consumption amount) × 0.98. On the contrary, when the difference is −0.012 [mg / cm ² ] or less and the toner adhesion amount detection value is low, (toner replenishment amount) = (toner consumption amount) × 1.02. In this manner, control is performed to correct the toner replenishment amount in accordance with the toner adhesion amount detection value that is the output of the toner image detection sensor (P sensor) 310.

  In this case, since the absolute value of the toner density cannot be grasped and the toner density may run out of control, the above-described potential control execution interval is set shorter from every 250 sheets to every 100 sheets. As a result, the interval at which the toner density can be estimated by the development gamma coefficient as the developing ability is shortened, so that the runaway of the toner density can be prevented.

As described above, according to the present embodiment, the developing device 61 that forms a toner image using the two-component developer composed of toner and carrier, and the toner concentration sensor as the toner concentration detecting means that detects the toner concentration in the developing device 61. (T sensor) 312 and a toner image detection sensor (P sensor) 310 as toner adhesion amount detection means for detecting the toner adhesion amount of the toner image on the intermediate transfer belt 10. Using the toner density detection value by the toner density sensor (T sensor) 312 and the toner adhesion amount detection value by the toner image detection sensor (P sensor) 310, the toner supply condition to the developing device 61 by the toner supply control device 403 is set. Then, potential control as a toner image forming condition is performed by the potential control device 401, and process control for stabilizing the image density is performed. In such an image forming apparatus, whether or not the toner density detection value by the toner density sensor (T sensor) 312 is within a preset appropriate toner density range, and a plurality of toner adhesions detected by the toner image detection sensor (P sensor) 310. It is determined whether or not the development gamma coefficient as the development capability calculated from the detected amount is within a predetermined development gamma coefficient appropriate range, and the respective determination results are compared to determine whether the toner density sensor (T sensor) 312 has failed. A toner density detection unit failure determination mode for determination is provided.
Further, according to the present embodiment, when the detected toner density value is outside the proper toner density range and the calculated development gamma coefficient is within the proper development gamma coefficient range, the toner density sensor (T sensor) 312 Judge as a failure. According to this configuration, when the toner density detection value is outside the proper range, the development gamma coefficient is within the proper range, and the development capability is considered normal, the toner density sensor (T sensor) 312 malfunctions due to these contradictions. Judge. Here, when the toner density detection value is within the proper range and the development gamma coefficient is outside the proper range, and the determination results contradict each other, the toner density sensor (T sensor) ) It is dangerous that 312 determines that a failure has occurred and the response of the service person changes. In this embodiment, since the purpose is for a service person to take a quick and appropriate action, the possibility of erroneous determination can be avoided by limiting the toner density detection value to a value outside the appropriate range.
Further, according to the present embodiment, when it is determined that the toner concentration sensor (T sensor) 312 has failed in the toner concentration detection unit failure determination mode, the toner concentration detection value by the toner concentration sensor (T sensor) 312 is not used. The toner replenishment control device 403 controls toner replenishment conditions for the developing device 61, and the potential control device 401 performs potential control as toner image forming conditions, and continues image formation. As a result, even when the toner density sensor (T sensor) 312 fails, printing can be continued without causing downtime, although it does not reach the original image density stabilization control.
Further, according to the present embodiment, when it is determined that the toner concentration sensor (T sensor) 312 has failed in the toner concentration detection unit failure determination mode, the toner replenishment control device 403 displays the toner adhesion amount detection value or the image area data. Based on this, the toner supply condition is changed. As a result, even when the toner density sensor (T sensor) 312 fails, the printing can be continued without causing the toner density control to run away, although it does not reach the original toner density control.
Further, according to the present embodiment, a plurality of toner adhesion amount detection values obtained by detecting the adhesion amounts of a plurality of toner patterns having different adhesion amounts by the toner image detection sensor (P sensor) 310 in the toner density detection unit failure determination mode are used. Thus, the potential control is performed by the potential control device 401 to perform process control for stabilizing the image density at the time of printing. As described above, since the process control for stabilizing the image density at the time of printing is performed using the toner adhesion amount detection values of a plurality of toner patterns in the toner density detection unit failure determination mode, the toner patterns are separately created and detected. Compared to the case, it is possible to reduce toner consumption and to perform efficient and quick control.
Further, according to the present embodiment, when it is determined that the toner concentration sensor (T sensor) 312 has failed in the toner concentration detection unit failure determination mode, notification that the toner concentration sensor (T sensor) 312 has failed is notified to the outside. Means. By the notification means, the service person can recognize the occurrence of the failure of the toner concentration sensor (T sensor) 312 and can easily determine what to bring as a replacement part, so that the maintainability is improved and the downtime is also reduced.
In addition, according to the present embodiment, the photosensitive member 40, the developing device 61, and the toner density sensor (T sensor) 312 are integrally configured to be in the form of a process cartridge that can be attached to and detached from the main body of the image forming apparatus. As a result, when the process cartridge is collected, it has already been clarified that the single sensor has failed. Therefore, the time for analyzing the cause of the failure can be shortened and the maintainability can be improved. Also, it is possible to prevent the entire process cartridge from being discarded due to an unknown cause of failure.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 18 Image formation part 20 Tandem image formation part 21 Exposure apparatus 22 Secondary transfer apparatus 40 Photoconductor 60 Charging apparatus 61 Developing apparatus 61a Developing roller 61c Toner replenishing means 62 Primary transfer roller 63 Photoconductor cleaning apparatus 70 Potential sensor 100 Printer 310 Toner Image Detection Sensor (P Sensor)
312 Toner density sensor (T sensor)
401 Potential control device 403 Toner supply control device

JP 2002-108087 A JP 2002-278182 A

Claims (6)

A developing device that forms a toner image on an image carrier using a two-component developer composed of toner and a carrier, a toner density detecting means that detects a toner density in the developing device, and a toner density detector that is formed on the image carrier. A toner adhesion amount detection means for detecting the toner adhesion amount of the toner image, a toner density detection value by the toner density detection means, and a toner adhesion amount detection value by the toner adhesion amount detection means. In an image forming apparatus comprising a replenishment condition and a control means for controlling a toner image forming condition on the image carrier.
The control means determines whether or not the toner density detection value detected by the toner density detection means is within a preset appropriate toner density range, and determines the adhesion amounts of a plurality of toner patterns having different adhesion amounts by the toner adhesion amount detection means. It is determined whether or not the development gamma coefficient calculated from a plurality of detected toner adhesion amount detection values is within a preset development gamma coefficient appropriate range, and the respective determination results are compared to determine whether the toner density detection unit has failed. have a toner concentration detector failure determination mode for determining the presence or absence,
In the toner density detection unit failure determination mode, when it is determined that the toner density detection value is outside the proper toner density range and the development gamma coefficient is within the proper development gamma coefficient range, the failure of the toner density detection unit is detected. An image forming apparatus characterized in that it is determined to be present . The image forming apparatus 請 Motomeko 1, if in the toner concentration detector failure determination mode is the toner concentration detecting means determines that a failure is present, the developing device without the toner density detection value of the toner concentration detection means An image forming apparatus comprising: determining a toner replenishing condition for the toner and a condition for forming a toner image on the image carrier, and continuing image formation. 3. The image forming apparatus according to claim 2 , wherein when it is determined that there is a failure in the toner concentration detection means in the toner concentration detection means failure determination mode, the control means is based on the toner adhesion amount detection value or image area data. And changing the toner replenishment condition to determine the toner replenishment condition. The image forming apparatus according to claim 1, 2 or 3, wherein said control means, detects the deposition amount of different toner patterns adhesion amount by the toner concentration detection means failure judgment mode in the toner adhering amount detecting means An image forming apparatus for determining a toner image forming condition on the image carrier using a plurality of detected toner adhesion amounts. The image forming apparatus according to claim 1, 2, 3 or 4, when it is determined that the failure of the toner concentration detecting means is above a toner concentration detector failure determination mode, that toner concentration detection means has failed An image forming apparatus comprising notification means for notifying outside. The image forming apparatus according to claim 1, 2, 3, 4 or 5, and the image carrier, and the developing device, constructed integrally with the above-described toner density detection unit, detachable to the image forming apparatus main body An image forming apparatus characterized in that the process cartridge is in the form of a process cartridge.

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