JP2005316170A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing image quality defects due to the insufficient supply of developer, and also, capable of avoiding the damage of a photoreceptor and a fixing unit without installing a plurality of sensors in every developing unit. <P>SOLUTION: A patch image is formed at every image formation cycle, and the patch image is read by a density sensor (100), and when the density of the patch image is lower than a prescribed density level (Th_level), the developer is supplied (102 and 104), then, a patch image is formed again and the density of the patch image is detected (106), and when the density of the patch image is lower than the prescribed density level (Th_level) again, the contrast is reduced, and the image forming operation is continued (108 and 110), and also, a warning that the concentration of the developer is reduced is given (112). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus provided with a two-component developing type developing apparatus.

  In recent years, image forming apparatuses such as copying machines, printers, and facsimiles have been downsized, and the developing devices in the apparatus have also been downsized. When the developing unit is downsized, the developing roll in the developing unit is also downsized, and the developer adsorbed on the surface of the developing roll by the magnetic force also receives a stronger centrifugal force than before, so that it becomes easy to fly. When a two-component developer composed of a carrier and a toner is used, the carrier in the developer flying to the photoreceptor causes image quality defects such as color loss and damage to the photoreceptor and the fixing device (hereinafter referred to as BCO). ). Therefore, it is necessary to consider that the toner density in the developing device is not lowered too much and the development contrast is not increased too much.

  Further, the downsizing of the developing device causes a decrease in the amount of supplied toner, and in continuous printing of high-density images, an excessive amount of consumption with respect to the supply causes a decrease in toner density in the developing device.

  On the other hand, there has been proposed a technique that avoids problems due to lack of toner or out of toner. For example, in the technique described in Patent Document 1, a sensor for detecting the remaining amount of toner is provided, and when the remaining amount of toner becomes a predetermined value or less, the development width is reduced to reduce the image density. Yes. This avoids problems due to lack of toner or out of toner.

In recent years, the number of sensors has been decreasing due to cost reduction, and an apparatus has been proposed in which a toner density sensor (hereinafter referred to as a TC sensor) in the developing unit and an empty toner detection sensor in the toner cartridge are omitted. ing. In this case, the patch image is formed, and the reflection density of the formed patch image is read to detect the toner density in the developing device and the toner cartridge empty.
Patent No. 2505226

  However, in the technique described in Patent Document 1, a sensor for detecting the remaining amount of toner is required in the developing device, and in the color image forming apparatus, a sensor is required for each developing device of each color, resulting in high cost. There is a problem.

  The present invention has been made in consideration of the above facts, and can suppress image quality defects due to insufficient supply of developer and the like without providing a plurality of sensors for each developing device, and also to a photoreceptor and a fixing device. An object of the present invention is to provide an image forming apparatus capable of avoiding the damage.

  In order to achieve the above object, the invention described in claim 1 is directed to a developing device that develops a latent image formed on a photoreceptor using a developer, and a latent image of a patch image having a predetermined density. Detecting means for detecting the density of the patch image formed on the developing device and when the density of the patch image detected by the detecting means falls below a predetermined density; Contrast adjusting means for adjusting the development contrast to be equal to or lower than a predetermined contrast.

  According to the first aspect of the present invention, in the developing device, the latent image formed on the photoreceptor is developed with the developer. For example, the latent image is developed using a two-component developer or the like. Further, the detection means forms a latent image of a patch image having a predetermined density on the photosensitive member, and detects the density of the patch image developed by the developing device.

  Then, the contrast adjustment unit performs adjustment so that the development contrast at the time of image formation is equal to or less than the predetermined contrast when the density of the patch image detected by the detection unit falls below a predetermined density. That is, the contrast is adjusted according to the density detected by a single detection means without requiring a plurality of sensors. As a result, even if the image density is lowered due to a shortage of developer or the like, the image is formed by reducing the contrast, so that an image having a low density can be formed, but image quality defects can be suppressed.

  Further, since the image is formed with the contrast lowered, damage to the photosensitive member and the fixing device due to the flying of the carrier can be avoided even if a two-component developer is used.

  Therefore, it is possible to suppress image quality defects due to a shortage of developer or the like without providing a plurality of sensors for each developing device, and it is possible to avoid damage to the photoreceptor and the fixing device.

  The invention according to claim 2 is predicted by a developing device that develops the latent image formed on the photoreceptor using a developer, a predicting unit that predicts a developer concentration of the developing device, and the predicting unit. Contrast adjustment means for adjusting the development contrast during image formation to a predetermined contrast or less when the predicted value falls below a predetermined developer concentration.

  According to the second aspect of the present invention, in the developing device, the latent image formed on the photoconductor is developed with the developer. For example, the latent image is developed using two-component development or the like. Further, the predicting means predicts the developer concentration of the developing device. For example, the predicting unit can obtain image density information by detecting light emitted from an exposure apparatus that forms a latent image, and can predict the developer concentration from the integrated value of the image density information. It becomes possible. Alternatively, image density information can be obtained by analyzing image data for image formation, and the developer concentration can be predicted from the integrated value of the image density information.

  Then, the contrast adjustment unit performs adjustment so that the development contrast at the time of image formation is equal to or less than the predetermined contrast when the predicted value predicted by the prediction unit is lower than the other developer concentration. That is, the contrast is adjusted according to the predicted value predicted by the prediction means without requiring any sensor. As a result, even if the image density is lowered due to a shortage of developer or the like, the image is formed by reducing the contrast, so that an image having a low density can be formed, but image quality defects can be suppressed.

  Further, since the image is formed with the contrast lowered, damage to the photosensitive member and the fixing device due to the flying of the carrier can be avoided even if the two-component developer is used.

  Accordingly, without providing a plurality of sensors for each developing device, it is possible to suppress image quality defects due to lack of developer or the like, and it is possible to avoid damage to the photoreceptor and the fixing device.

  The contrast adjusting means of claim 1 and claim 2, for example, adjusts the exposure amount of an exposure apparatus that forms a latent image by irradiating light to a photoconductor as in the invention of claim 3. At least one of an exposure amount adjusting unit and a developing bias adjusting unit that adjusts a developing bias in the developing device may be applied, or an image for adjusting a target image density as in the invention of claim 4. You may make it apply a density adjustment means.

  As described above, according to the present invention, it is possible to suppress image quality defects due to lack of developer or the like without providing a plurality of sensors for each developing device, and to avoid damage to the photoreceptor and the fixing device. There is an effect that can be.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a four-cycle full-color printer.

  FIG. 1 is a diagram showing a schematic configuration of a four-cycle full-color printer as an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, a photosensitive drum 2 is rotatably disposed in the full color printer main body 1 at an upper right portion slightly from the center. As this photosensitive drum 2, for example, a drum made of a conductive cylinder having a diameter of about 47 mm whose surface is coated with a photosensitive layer made of OPC or the like is used. It is rotationally driven at a process speed of about 150 mm / sec. The surface of the photosensitive drum 2 is charged to a predetermined potential by a charging roll 3 disposed almost directly below the photosensitive drum 2, and then ROS 4 disposed at a position just below the photosensitive drum 2. Image exposure with a laser beam (LB) is performed by (Raster Output Scanner), and an electrostatic latent image corresponding to image information is formed. The electrostatic latent image formed on the photosensitive drum 2 passes through the developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) in the circumferential direction. The toner is developed by a rotary developing device 5 arranged along the toner image to form a toner image of a predetermined color.

  At this time, charging, exposure and development processes are repeated a predetermined number of times on the surface of the photosensitive drum 2 in accordance with the color of the image to be formed. In the rotary developing device 5, the corresponding color developing devices 5 </ b> Y, 5 </ b> M, 5 </ b> C, and 5 </ b> K move to a developing position facing the photosensitive drum 2. For example, when a full-color image is formed, the charging, exposure, and development processes are performed on the surface of the photosensitive drum 2 in yellow (Y), magenta (M), cyan (C), and black (K) colors. The toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially formed on the surface of the photosensitive drum 2. . The number of rotations of the photosensitive drum 2 when the toner image is formed varies depending on the size of the image. For example, in the case of A4 size, one image can be obtained by rotating the photosensitive drum 2 three times. It is formed. That is, a toner image corresponding to each color of yellow (Y), magenta (N / 1), cyan (C), and black (K) is displayed on the surface of the photosensitive drum 2 every time the photosensitive drum 2 rotates three times. Is formed. Hereinafter, this cycle for forming one image (for example, for one page) is referred to as an image forming cycle.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drum 2 are intermediately provided on the outer periphery of the photosensitive drum 2 as an intermediate transfer member. At the primary transfer position around which the transfer belt 6 is wound, the primary transfer is performed by the primary transfer roll 7 while being superimposed on the intermediate transfer belt 6. The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred in multiple onto the intermediate transfer belt 6 are recorded on the recording paper 9 fed at a predetermined timing. Secondary transfer is collectively performed by the secondary transfer roll 8. The recording paper 9 is fed from a paper feed cassette 10 disposed at the bottom of the full-color printer main body 1 by a pick-up roll 11 and is fed in a state where it is rolled one by one by a feed roll 12 and a retard roll 13. The roller 14 is conveyed to the secondary transfer position of the intermediate transfer belt 6 in synchronization with the toner image transferred onto the intermediate transfer belt 6.

  The intermediate transfer belt 6 is stretched by a plurality of rolls, and is driven as the photosensitive drum 2 rotates, for example, so as to circulate at a predetermined process speed (about 150 mm / sec). The intermediate transfer belt 6 intermediately transfers a wrap-in roll 15 that specifies the wrap position of the intermediate transfer belt 6 on the upstream side in the rotational direction of the photosensitive drum 2 and a toner image formed on the photosensitive drum 2. The primary transfer roll 7 to be transferred onto the belt 6, the wrap-out roll 16 for specifying the wrap position of the intermediate transfer belt 6 on the downstream side of the wrap position, and the secondary transfer roll 8 are in contact with each other via the intermediate transfer belt 6. The backup roll 17, the first cleaning backup roll 19 facing the cleaning device 18 of the intermediate transfer belt 6, and the second cleaning backup roll 20 are stretched with a predetermined tension.

  The full-color printer according to the embodiment of the present invention is miniaturized as much as possible as a whole, but the rotary developing device 5 occupies a large space of the full-color printer main body 1. Therefore, the full-color printer main body 1 is designed to improve the maintainability of the intermediate transfer belt 6 and the rotary developing device 5 while achieving downsizing of the device. Specifically, the intermediate transfer belt 6 includes an image forming unit 21 including the photosensitive drum 2 and the charging roll 3, and an upper cover 22 as a replacement cover for the full-color printer main body 1. By opening, the entire image forming unit 21 is configured to be detachable from the full-color printer main body 1. A position sensor 23 composed of a reflective photosensor for detecting a toner patch formed on the intermediate transfer belt 6 is disposed above the intermediate transfer belt 6, and the intermediate transfer of the photosensitive drum 2 is performed. A density sensor 64 that detects the toner density of the patch formed on the intermediate transfer belt 6 is provided on the downstream side in the conveyance direction of the belt 6.

  More specifically, the image forming unit 21 includes the photosensitive drum 2, the charging roll 3, the intermediate transfer belt 6, and a plurality of rolls 7, 15 to 17, 19, 20 that stretch the intermediate transfer belt 6. The cleaning device 18 for the intermediate transfer belt 6 and the cleaning device 34 for the photosensitive drum 2 are integrally mounted. The image forming unit 21 can be taken out from the printer body 1 by holding and holding a handle (not shown) provided on the upper portion of the image forming unit 21 by hand.

  On the other hand, the recording paper 9 onto which the toner image has been transferred from the intermediate transfer belt 6 is conveyed to a fixing device 27, and the toner image is fixed on the recording paper 9 by heat and pressure by the fixing device 27. In this case, the paper is discharged as it is onto a discharge tray 29 provided at the top of the printer main body 1 by the discharge roll 28.

  As shown in FIG. 2, the rotary developing device 5 of the full-color printer according to this embodiment includes yellow (Y), magenta (M), cyan (C), and black (K) along the counterclockwise direction. The five developing devices 5Y, 5M, 5C and 5K are mounted along the circumferential direction, and yellow (Y), magenta (M), Five developer cartridges 45Y, 45M, 45C, and 45K of cyan (C) and black (K) are mounted along the circumferential direction.

  Inside each of the developing devices 5Y, 5M, 5C, and 5K, a part of the developing devices 5Y, 5M, 5C, and 5K is disposed so as to be exposed to the outer periphery, and is perpendicular to the paper surface. Developing rolls 48Y, 48M, 48C, and 48K that are long in the direction, and two spiral augers 49 and 50 that extend in parallel to the developing rolls 48Y, 48M, 48C, and 48K are arranged. In the developing units 5Y, 5M, 5C, and 5K, when the developing rolls 48Y, 48M, 48C, and 48K rotate, one auger 49 uses the developer contained in the developing units 5Y, 5M, 5C, and 5K as the paper surface. Transport while stirring in one vertical direction. On the other hand, the other auger 50 conveys the developer in a direction opposite to the conveying direction of the auger 50 while stirring the developer, and supplies the developer evenly to the developing rolls 48Y, 48M, 48C, and 48K. .

More specifically, each developer cartridge 45Y, 45M, 45C, 45K is provided with a spiral agitator 51 (see FIG. 2) that is rotatably arranged. The developer is supplied to the auger 49 by conveying the developer in the agent cartridges 45Y, 45M, 45C, and 45K to the auger 49 while stirring. Then, the augers 49 and 50 are conveyed while stirring to supply the developer evenly to the developing rolls 48Y, 48M, 48C and 48K.
[First Embodiment]
Next, the configuration of the control system of the full color printer according to the first embodiment of the present invention will be described.

  FIG. 3 is a block diagram showing the configuration of the control system of the full-color printer according to the first embodiment of the present invention.

  The control unit 60 of the full-color printer according to the present embodiment forms a patch image having a predetermined density for each image formation at a predetermined interval, detects the density of the patch image, and sets the detection density in advance. When the density is lower than the set density (Th_level), the developer of the corresponding developing devices 5Y, 5M, 5C, and 5K of the developing device 5 is supplied, the patch image is formed again, and the density of the patch image is detected again. When the detected density is lower than a predetermined density (Th_level), each function is controlled so as to perform image formation with a low contrast at the time of image formation.

  That is, the control unit 60 includes the ROS 4, the developing device (each developing device 5Y, 5M, 5C, and 5K) 5, the photosensitive drum 2, the intermediate transfer belt drive system 68, and the recording paper transport system 66 for transporting the recording paper. , And the density sensor 64 are connected, and each mechanism connected to the control unit 60 is controlled by the control unit 60.

  Further, the control unit 60 stores patch data (patch data having a predetermined density) for forming a predetermined patch image to be formed every time the image is formed. When the patch data is output from the control unit 60 to the ROS 4, the photosensitive drum 2 is irradiated with laser light based on the patch data.

  When image data to be image-formed is input to the control unit 60 and an image formation instruction is given, the control unit 60 outputs predetermined patch data to the ROS 4, as well as the developing device 5 and the photosensitive drum 2. The patch image is formed on the intermediate transfer belt 6 by controlling each mechanism so as to perform the patch image formation based on the patch data by controlling the intermediate transfer belt driving system 68. Here, the density of the patch image formed on the intermediate transfer belt 6 is detected by the density sensor 64, and the detection result is input to the control unit 60.

  Based on the detection result, the control unit 60 controls the supply of the developer to the developing devices 5Y, 5M, 5C, and 5K of the developing device 5 and the contrast adjustment at the time of image formation. When supplying the developer, the developer is supplied by rotating the agitator 51 and the augers 49 and 50 by controlling the drive motors 62 of the developing units 5Y, 5M, 5C, and 5K. The contrast adjustment by the control unit 60 may be performed by controlling the ROS 4 to adjust the exposure amount to control the contrast, or adjusting the developing bias of the developing device 5 to control the contrast. Alternatively, other means may be applied so that the target image density is a predetermined density or less, or a combination of these may be used.

  Subsequently, after the developer supply or contrast control is performed, the control unit 60 controls each mechanism to perform an image forming operation. That is, the ROS 4 is controlled based on the image data input to the control unit 60, the driving and charging of the photosensitive drum 2 are controlled, and a latent image is formed on the photosensitive drum 2, and the photosensitive member. After the latent image on the drum 2 is developed and a toner image is formed, the toner image is formed on the intermediate transfer belt 6 by controlling the intermediate transfer belt drive system 68, the recording paper transport system 66, and the like. Transferred onto recording paper. Specifically, the latent image formed on the photosensitive drum 2 is developed by the developing devices 5Y, 5M, 5C, and 5K, and a four-color toner image (full color toner image) is formed on the photosensitive drum 2. Thereafter, a full-color toner image is formed on the intermediate transfer belt 6 and transferred to a recording sheet.

  Here, an example of processing performed by the control unit 60 of the full-color printer according to the first embodiment of the present invention will be described.

  FIG. 4 is a flowchart showing an example of the flow of processing performed by the control unit 60 of the full-color printer according to the first embodiment of the present invention. Note that the flowchart of FIG. 4 will be described as processing performed for each image forming cycle.

  When an image formation instruction is given, first, in step 100, the control unit 60 performs patch image formation and patch density reading processing (first patch image). That is, patch data of a predetermined density stored in the control unit 60 is output to the ROS 4, and the developing device 5, the photosensitive drum 2, and the intermediate transfer belt drive system 68 are controlled, and a patch image based on the patch data is transferred to the intermediate transfer. The patch image formed on the belt 6 is read by the density sensor 64 and input to the controller 60.

  Next, in step 102, it is determined whether or not the patch image input to the control unit 60 is lower than a predetermined patch density (Th_level). If the determination is negative, the processing is terminated and the image is displayed. Transition to forming operation.

  If the determination in step 102 is affirmed, the process proceeds to step 104, where developer supply processing is performed. That is, the control unit 60 controls the driving motors 62 of the developing devices 5Y, 5M, 5C, and 5K, and the agitator 51 and the augers 49 and 50 are rotationally driven to supply the developer. It should be noted that a patch image is formed for each color and the density is detected, and when the density is lowered in any color, the developer of the corresponding developing device may be supplied. When the density of the color is lowered, the developer may be supplied to all the developing devices.

  In step 106, patch image formation and patch density reading processing are performed again (second patch image). That is, patch data of a predetermined density stored in the control unit 60 is output to the ROS 4, and the developing device 5, the photosensitive drum 2, and the intermediate transfer belt drive system 68 are controlled, and a patch image based on the patch data is transferred to the intermediate transfer. The second patch image formed on the belt 6 is read by the density sensor 64 and input to the control unit 60.

  Subsequently, in step 108, it is determined again whether the patch image input to the control unit 60 is lower than a predetermined patch density (Th_level). If the determination is negative, the process ends and the image is displayed. Transition to forming operation.

  If the determination at step 108 is affirmative, the routine proceeds to step 110 where contrast reduction processing is performed. That is, control is performed so as to reduce the contrast (for example, below a predetermined contrast) by adjusting the exposure amount of the ROS 4 at the time of image formation. As a result, it is possible to perform image formation with reduced image quality defects although the contrast is reduced. Note that as the contrast adjustment at this time, as described above, the exposure amount of the ROS 4 may be controlled (for example, the exposure amount may be controlled to be a predetermined value or less), or the development of the developing device 5 may be performed. Contrast adjustment may be performed by controlling the bias (for example, controlling the developing bias to be equal to or lower than a predetermined value), or in addition, means for making the target image density equal to or lower than the predetermined density is applied. You may make it carry out, and you may make it combine these.

  Next, in step 112, a warning for lowering the developer concentration is given, and a series of processing is terminated and the process proceeds to an image forming operation. The processing applies, for example, notification means such as a display means for displaying a message indicating that the developer concentration is reduced to the user, or a speaker for generating a sound or the like indicating that the developer concentration is decreasing. be able to.

  As described above, in the present embodiment, the developer is supplied when the density of the first patch image is lower than the predetermined value, and the second patch image after the supply of the developer is lower than the predetermined value. In this case, the image is formed at a low density by lowering the contrast, but the image formation can be continued while suppressing the image quality defect by forming the image while suppressing the consumption of the developer. .

  Further, by forming an image with a reduced contrast, damage to the photosensitive drum 2 and the fixing device 27 due to the flying of the carrier can be avoided.

That is, in the present embodiment, since the sensor can be implemented by including only the single density sensor 64, a plurality of sensors for detecting the developer remaining amount for each of the developing devices 5Y, 5M, C, and K are provided. By providing a single sensor without providing it, image quality defects can be suppressed and damage to the photoreceptor and the fixing device can be avoided.
[Second Embodiment]
Subsequently, the configuration of the control system of the full-color printer according to the second embodiment of the present invention will be described.

  FIG. 5 is a block diagram showing the configuration of the control system of the full-color printer according to the second embodiment of the present invention.

  In the first embodiment, the example in which the density control of the developer is controlled by forming the patch image and detecting the patch density at every predetermined image formation is described. However, the full color printer according to the present embodiment is described. The control unit 61 controls the contrast using the integrated value of the image density information as a predicted value of the developer density instead of detecting the patch density.

  That is, as in the first embodiment, the controller 61 is connected to the ROS 4, the developing device (each developing device 5Y, 5M, 5C, 5K) 5, the photosensitive drum 2, and the intermediate transfer belt drive system 68. Instead of the density sensor 64, a light amount monitor 70 constituted by a photodiode or the like for monitoring the light amount of the laser light irradiated from the ROS 4 to the photosensitive drum 2 at the time of image formation is connected.

  In this embodiment, the light emission of the ROS 4 is monitored by the light amount monitor 70 as the image density information, and the image density information is acquired by accumulating the light amount. However, the image density information is calculated from the image data input to the control unit 61. You may do it.

  Specifically, the control unit 61 detects the light quantity of each image forming cycle with the light quantity monitor 70 and integrates it, thereby acquiring the integrated value of the light quantity as the image density information and setting it as the predicted value of the developer density.

  Further, the control unit 61 stores an image density threshold value (light amount integrated value) for performing contrast control. When the integrated value of the light amount detected by the light amount monitor 70 reaches the threshold value, At the end of the image forming cycle, the image forming operation is stopped and the developer is forcibly supplied or the image forming operation is continued with the contrast lowered. Note that whether to supply the developer forcibly or continue the image forming operation with the contrast lowered can be performed by the user interface 72 or the like connected to the control unit 61.

  As in the first embodiment, the contrast adjustment by the control unit 61 may be performed by controlling the ROS 4 to adjust the exposure amount to control the contrast, or adjusting the developing bias of the developing device 5. Alternatively, the contrast may be controlled, or a means for making the target image density equal to or lower than a predetermined density may be applied, or these may be combined.

  Next, an example of processing performed by the control unit 61 of the full-color printer according to the second embodiment of the present invention will be described.

  FIG. 6 is a flowchart illustrating an example of a flow of processing performed by the control unit 61 of the full-color printer according to the second embodiment of the present invention.

  When an image formation instruction is performed, first, the control unit 61 inputs image data to the ROS 4 so that the ROS 4 irradiates the photosensitive drum 2 with laser light based on the image data. When the image density information in one page (image forming cycle) is detected by the light amount monitor 70, the image density information is input to the control unit 61.

  In step 202, image density information is integrated (Total image = integrated value of each page image density information), and the process proceeds to step 204.

  In step 204, it is determined whether or not a contrast reduction processing flag, which will be described later, is set. If the determination is affirmative, image formation with reduced contrast is continued, and the process returns to step 200 again to perform the above processing. Repeated. At this time, as in the first embodiment, a patch image is further formed and the density of the patch image is detected. If the density is less than the predetermined density, the developer is forcibly supplied. Also good.

  If the determination in step 204 is negative, the process proceeds to step 206 to determine whether or not the integrated value of the image density information (Total image) exceeds the threshold value (Th_level) stored in the control unit 61. The That is, it is determined whether or not the developer density is lower than a predetermined density based on the predicted value (the integrated value of the image density information). If the determination is negative, the process returns to step 200 to return to the above-described case. The process is repeated.

  If the determination in step 206 is affirmative, that is, if the developer concentration falls below a predetermined concentration, the routine proceeds to step 208, where it is determined whether forced developer replenishment setting has been made. This determination is made by determining whether or not the forced developer replenishment setting has been made in advance by the user interface 72 by the user. If the determination is negative, the process proceeds to step 210 and the contrast reduction process is performed. In step 212, a flag for performing the contrast reduction process is set, and the process returns to step 200 to repeat the above-described process. That is, the image forming cycle of the remaining job is continued by controlling the exposure amount of the ROS 4 at the time of image formation to reduce the contrast. As a result, it is possible to perform image formation with reduced image quality defects although the contrast is reduced. In addition, as the contrast adjustment at this time, as described above, the contrast adjustment may be performed by controlling the transfer bias of the developing device 5, or the target image density is set to a predetermined density or less. Means for achieving the above may be applied, or these may be combined.

  On the other hand, if the determination in step 208 is affirmed, the process proceeds to step 214, and the image forming operation is interrupted when the current image forming cycle ends.

  In step 216, forced developer replenishment is performed. That is, the driving motor 62 of each of the developing devices 5Y, 5M, C, and 5K is driven and controlled by the control unit 61, whereby the agitator 51 and the augers 49 and 50 are rotated and the developer is replenished. Migrate to

  In step 218, the integrated value of the image density (Total image) is reset, and the series of processes is terminated. At this time, as in the first embodiment, a patch image may be further formed, and the density of the patch image may be detected. If the density is less than the predetermined density, further developer replenishment may be performed.

  As described above, in the present embodiment, when the integrated value (Total image) of the image density information exceeds a preset threshold value (Th_level), that is, the predicted value of the developer density falls below a predetermined density. In this case, it is possible to set whether to interrupt the continuous image formation and forcibly replenish the developer, or to continue the continuous image formation with a lower development contrast. In the case of continuing, as in the first embodiment, although the density for image formation is low, the image formation can be continued while suppressing image quality defects by suppressing the consumption of the developer to form an image. In addition, damage to the photosensitive drum 2 and the fixing device 27 can be avoided. Further, when the developer is forcibly replenished, it is possible to maintain the same image quality as in a normal image forming operation, and naturally, damage to the photosensitive drum 2 and the fixing device 27 is avoided. can do.

  In addition, in this embodiment, since it is possible to reduce the image formation contrast without forming a patch image, it is possible to avoid image quality defects and device damage even when continuously printing high image density images. Become.

  In the second embodiment, when the continuous image formation is continued with the contrast lowered, the image forming operation is continued with the single threshold reduction width using the single threshold value. For example, a plurality of threshold values and a plurality of contrast reduction widths corresponding to the threshold values are stored in the control unit 61 in advance, and the contrast is gradually decreased by the contrast reduction width corresponding to the threshold values. May be.

  In the second embodiment, when the integrated value of the image density information (Total image) greatly exceeds the threshold (Th_level), regardless of the setting of whether to perform forced developer replenishment or contrast reduction processing. The developer may be forcibly replenished.

  Further, in the second embodiment, the total image density information is integrated. However, the present invention is not limited to this, and the image density information corresponding to each color is individually integrated to forcibly supply the developer. When doing so, the developer may be replenished only to the corresponding developing device.

1 is a diagram showing a schematic configuration of a four-cycle full-color printer as an image forming apparatus according to an embodiment of the present invention. It is a figure which shows schematic structure of a rotary developing device. 1 is a block diagram illustrating a configuration of a control system of a full-color printer according to a first embodiment of the present invention. 3 is a flowchart illustrating an example of a flow of processing performed by a control unit of the full-color printer according to the first embodiment of the present invention. It is a block diagram which shows the structure of the control system of the full color printer concerning 2nd Embodiment of this invention. It is a flowchart which shows an example of the flow of the process performed in the control part of the full-color printer concerning 2nd Embodiment of this invention.

Explanation of symbols

2 Photosensitive drum 4 ROS
5 Developing Device 27 Intermediate Transfer Belt 60, 61 Control Unit 64 Density Sensor 70 Light Level Monitor

Claims (4)

A developing device for developing the latent image formed on the photoreceptor using a developer;
Detecting means for forming a latent image of a patch image having a predetermined density on a photoreceptor and detecting the density of the patch image developed by the developing device;
Contrast adjustment means for adjusting the development contrast at the time of image formation to a predetermined contrast or less when the density of the patch image detected by the detection means falls below a predetermined density;
An image forming apparatus. A developing device for developing the latent image formed on the photoreceptor using a developer;
Predicting means for predicting the developer concentration of the developing device;
Contrast adjustment means for adjusting the development contrast at the time of image formation to be equal to or lower than a predetermined contrast when the predicted value predicted by the prediction means falls below a predetermined developer concentration;
An image forming apparatus.   The contrast adjusting means is at least one of an exposure amount adjusting means for adjusting an exposure amount of an exposure apparatus that irradiates light to the photosensitive member to form a latent image, and a developing bias adjusting means for adjusting a developing bias in the developing apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   4. The image forming apparatus according to claim 1, wherein the contrast adjusting unit includes an image density adjusting unit that adjusts a target image density.

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