JP4474958B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and in particular, develops an electrostatic latent image formed on an image carrier with toner, and transfers the developed toner image on the image carrier to a recording medium. The present invention relates to an image forming apparatus to be formed.

  Conventionally, image forming apparatuses such as laser printers, facsimile machines, and copiers are provided with a photosensitive drum as an image carrier, and the surface of the photosensitive drum is uniformly charged, and then a light beam based on image data is irradiated. In some cases, an electrostatic latent image is formed on a photosensitive drum, the electrostatic latent image is developed using toner, and the image developed on the photosensitive drum is transferred to a recording medium to form an image. It was.

  In this type of image forming apparatus, when the developed image on the photosensitive drum is transferred, all the toner cannot be transferred, and a slight amount of toner remains on the photosensitive drum after the transfer. . The residual toner is hereinafter referred to as transfer residual toner.

  There is also a so-called retransfer toner that is once transferred to a recording medium, but again adheres to the photosensitive drum. In the image forming apparatus corresponding to the formation of the color image, the color image is obtained by superimposing and transferring the images of different colors. Therefore, at the time of transfer, the other color toner already transferred is transferred to the photosensitive drum. May stick to the top.

  The toner adhering to the photosensitive drum after the transfer may adhere to a charger or an exposure device provided around the photosensitive drum or may be mixed into the developing device. This will prevent image formation.

  For this reason, a cleaner having a mechanism for collecting the toner on the photosensitive drum and a mechanism for discarding the collected toner is generally disposed around the photosensitive drum on the downstream side of the transfer position. It was.

  However, in recent years, with the widespread use of such image forming apparatuses, it has been desired to reduce the cost and size of the apparatus, and it has been proposed to simplify the above-described cleaner. Note that the configuration of the image forming apparatus in which the cleaner is simplified may be referred to as a “cleanerless system”.

  That is, the mechanism for discarding toner needs to secure a toner storage space and a space for disposal work. Therefore, by omitting the mechanism, the apparatus can be reduced in size efficiently. In an image forming apparatus corresponding to a color image by providing a plurality of photosensitive drums and transferring images with different toner colors by the respective photosensitive drums, the number of the cleaners is provided by the number of the photosensitive drums. Therefore, simplification of the cleaner is particularly effective for downsizing the apparatus.

  By the way, in an image forming apparatus that performs toner development by a two-component development method that performs development using a developer containing two components of toner and carrier as main components, including the cleanerless system as described above, toner is developed prior to development. In addition, it is necessary to charge the carrier, and as the charging method, a method of performing frictional charging by stirring the toner and the carrier is often employed.

  Conventionally, as a technique related to an image forming apparatus that performs development using toner charged by this type of triboelectric charging, toner concentration (relative to the total weight of carrier particles and toner particles), which is an important factor in stabilizing image quality, is known. For the purpose of controlling the toner particle weight ratio) to be constant, the apparent magnetic permeability of the developer in the developing device is detected, and the toner replenishing means is operated based on the detection result for development. There has been a technique for controlling the toner density in the container (for example, see Patent Document 1).

Also, when the reference patch density deviates greatly from the reference density for the purpose of eliminating the need for the developer toner density sensor and controlling the image density so that the use range of the toner density is not increased more than necessary. Determines whether the reference patch potential is normal, and if it is determined that the reference patch potential is not normal, measures the development potential contrast of the reference patch portion, and then determines the development potential contrast for each development potential contrast or development potential contrast difference. Each time, the toner supply amount is compared with a preset toner supply amount restriction condition, and according to the result, it is determined whether or not to limit the toner supply amount calculated based on the density comparison result between the reference patch density and the reference density. In some cases, there is a technique for performing the restriction (see, for example, Patent Document 2).
JP 2000-284560 A JP 7-271117 A

  By the way, in an image forming apparatus that performs toner development with toner charged by frictional charging by the two-component development method, the image occupancy rate (printing density) of the toner image developed by the developing device with respect to the recording medium (recording paper) is high. If image formation is continued in this state, the toner may not be sufficiently agitated with the carrier and may be conveyed to the development area with a low charge amount.

  That is, in this type of image forming apparatus, toner is replenished so that the amount of replenishment increases as the image occupancy increases during image formation. However, image formation with a high image occupancy is performed. As a result, the toner replenishment amount becomes excessive, and sufficient agitation cannot be performed.

  In this case, toner cloud (Toner Cloud) is likely to occur due to the low charge amount, or fog (a phenomenon in which the toner adheres to the non-image area that should originally become white by development and the density increases) It becomes easy to do. Note that the toner cloud is likely to be generated when the charge amount is low because the adhesion force between the toner and the carrier is weakened when the charge amount is low, and only the toner is detached by a slight impact or the like.

  In particular, in the above-described cleanerless system, the toner cloud easily adheres to the charger and the exposure apparatus, and as a result, image unevenness is likely to occur. Further, since the charging ability of the toner is lowered in a high humidity environment, the occurrence of this phenomenon is further accelerated. When a linear exposure device such as a light emitting diode is used as the exposure device, the image unevenness due to adhesion tends to occur even with a small amount of toner cloud.

  However, since the techniques described in Patent Document 1 and Patent Document 2 described above do not particularly take into consideration the occurrence of an excessive amount of toner replenishment according to the image occupancy rate, the reduction in the toner charge amount is not necessarily prevented. There was a problem that it cannot be said that it can be done.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus capable of effectively preventing a decrease in toner charge amount.

In order to achieve the above object, the image forming apparatus according to claim 1 develops the electrostatic latent image formed on the image carrier with toner by a developing means, and develops the developed toner image on the image carrier. An image forming apparatus that forms an image by transferring the toner onto a recording medium, the toner supplying unit supplying the developing unit with the toner, the humidity detecting unit detecting the relative humidity, and the print job while executing a print job. Image occupancy ratio deriving means for deriving an image occupancy ratio of the toner image developed by the developing means with respect to the recording medium, driving time detecting means for detecting the driving time of the developing means, and detected by the driving time detecting means until the driving time reaches the threshold, the combination of the image occupancy ratio derived at the detected relative humidity and the image occupancy deriving means by said humidity detecting means, said developing means smell A first combination of a relative humidity that is equal to or higher than a first relative humidity and an image occupancy that is equal to or higher than a first image occupancy that are predetermined as a combination that does not generate a toner cloud of the replenished toner, or the first A second relative humidity that is greater than or equal to a second relative humidity that is lower than the relative humidity and that is less than the first relative humidity and an image occupancy that is greater than or equal to the second image occupancy greater than the first image occupancy. A determination unit that determines whether or not the combination is two, and when the determination unit determines that the combination is not the first or second combination , the amount is increased in accordance with the increase in the image occupancy rate. wherein deriving the toner supply amount, to derive the toner supply amount so that the upper limit a predetermined amount of the case where it is determined that becomes the first or second combination by said determination means A toner supply amount deriving means, during execution of the print job, and a, and control means for controlling the toner supply means such that the toner supply amount and derived by the toner supply amount deriving means.

  According to the image forming apparatus of the first aspect, the electrostatic latent image formed on the image carrier is developed by the developing means with toner, and the developed toner image on the image carrier is transferred to the recording medium. As a result, an image is formed.

The image forming apparatus according to the present invention is configured such that the toner is replenished to the developing unit by a toner replenishing unit, the relative humidity is detected by the humidity detecting unit, and the print job is being executed. An image occupancy rate of the toner image developed by the developing unit with respect to the recording medium is derived by an image occupancy rate deriving unit. The humidity detection means includes a humidity sensor such as a polymer sensor, a metal oxide sensor, or an electrolyte sensor.

Here, in the present invention, whether or not the combination of the relative humidity and the image occupancy is a condition that the charge amount of the toner replenished to the developing unit by the toner replenishing unit is smaller than the target charge amount. or it is determined by the determine constant means, the toner supply amount deriving means, the toner supply amount as if it is determined not in the condition increases as the image occupancy ratio is high is derived by determine a constant means , if it is determined that becomes the condition by determine a constant means the toner supply amount such that the upper limit amount is derived, during execution of the print job, such that the derived toner supply amount The toner replenishing means is controlled by the control means.

That is, the toner charge amount greatly depends on the combination of the image occupation ratio of the toner image developed by the developing unit with respect to the recording medium and the relative humidity.

  FIG. 7 shows a graph showing the measurement result of the toner charge amount after image formation on 100 recording media when the image occupation ratio is changed in the range from 0% to 100%. Here, actual measurement results are shown when the relative humidity is 15%, 55%, and 85% as representative values of three levels of low humidity, normal humidity, and high humidity, respectively.

  As shown in the figure, the toner charge amount tends to decrease as the image occupancy increases, and tends to occur as the relative humidity increases. Here, the threshold value of the toner charge amount generated by the toner cloud varies depending on the configuration of the developing unit and the type of developer. In the actual measurement, it has been confirmed that toner cloud is generated when the toner charge amount is 20 μC / g or less. In this case, the replenishment amount corresponding to the amount of image occupancy exceeding 40% under high humidity. When toner is replenished, there is a high possibility that toner cloud is generated.

  Focusing on this point, in the present invention, the relative humidity and the image occupancy rate are limited to the toner replenishment amount limiting conditions that limit the upper limit amount of the toner replenishment amount (for example, a condition for generating a toner cloud or a condition for causing fogging). If it is determined that the toner replenishment amount restriction condition is not satisfied, the toner replenishment amount is derived so as to increase as the image occupancy increases, and the toner replenishment amount restriction condition is satisfied. Is determined, the toner replenishment amount is derived so as to reach a predetermined upper limit amount, thereby effectively preventing a decrease in toner charge amount.

As described above, according to the image forming apparatus of the first aspect, the combination of the relative humidity and the image occupation ratio of the toner image developed by the developing unit with respect to the recording medium is supplied to the developing unit by the toner supplying unit. the charge amount determines whether or not it is smaller becomes conditions than the charge amount of the target, the toner supply amount to be larger as the image occupancy ratio is high if it is determined not in the above conditions When it is determined that the above condition is satisfied, the toner replenishment amount is derived so that the predetermined upper limit amount is obtained, and control is performed so that the derived toner replenishment amount is obtained during execution of the print job. Therefore, the toner charge amount can be effectively prevented from decreasing.

In the present invention, as in the invention described in claim 2 , it is preferable to provide a plurality of the threshold values.
Further, according to the present invention, as in the third aspect of the present invention, when the toner replenishment amount deriving unit determines that the condition does not satisfy the condition, the previous toner replenishment amount is derived. When the toner replenishment amount is sometimes limited, it is preferable to derive the toner replenishment amount so that the toner replenishment amount is increased within a range not satisfying the above condition. Thereby, it is possible to suppress a decrease in the density of the formed image due to the restriction of the toner replenishment amount.

As described above, according to the present invention, the combination of the relative humidity and the image occupation ratio of the toner image developed by the developing unit with respect to the recording medium is the target charge amount of the toner supplied to the developing unit by the toner supplying unit. or has become smaller becomes conditions than the charge amount whether determined that, when it is determined that not in the condition to derive a toner supply amount to be larger as the image occupancy ratio is high, the condition If it is determined that the toner replenishment amount is determined, the toner replenishment amount is derived so that the predetermined upper limit amount is obtained, and the toner replenishment amount is controlled during execution of the print job. It is possible to obtain an excellent effect that it is possible to effectively prevent the decrease in the temperature.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a configuration of an image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 has an endless belt-like intermediate transfer belt 14 that is stretched around a plurality of winding rollers 12 and conveyed in the direction of arrow E by driving a motor (not shown). A plurality of image forming units 15 (details will be described later) are arranged along the longitudinal direction of the intermediate transfer belt 14.

  Note that the image forming apparatus 10 in the present embodiment also supports color image formation, and toners corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K). Image forming units 15Y, 15M, 15C, and 15K that form images are provided. Hereinafter, the members provided for each color are shown by adding alphabets (Y / M / C / K) indicating the respective colors at the end of the reference numerals. The description will be made by omitting the alphabet at the end of the code.

  The different color toner images formed by the image forming units 15 are transferred onto the intermediate transfer belt 14 so as to overlap each other on the belt surface of the intermediate transfer belt 14. As a result, a color toner image is formed on the intermediate transfer belt 14. In this embodiment, the toner image in which the four color toner images are transferred in a superimposed manner is referred to as a final toner image.

  On the downstream side of the four image forming units 15 in the conveying direction of the intermediate transfer belt 14, a transfer device 26 including two rollers 26A and 26B facing each other is disposed. The final toner image formed on the intermediate transfer body belt 14 is sent between the rollers 26A and 26B, taken out from the paper tray 29 provided at the bottom of the image forming apparatus 10, and is similarly supplied to the rollers 26A and 26B. It is transferred to the paper 28 that has been conveyed in between.

  In addition, a fixing device 30 including a pressure roller 30A and a heating roller 30B is disposed on the conveyance path of the paper 28 onto which the final toner image has been transferred. The paper 28 conveyed to the fixing device 30 is nipped and conveyed by the pressure roller 30A and the heating roller 30B, whereby the final toner image is melted and pressed against the paper 28 to be fixed. As a result, a desired image (color image) is formed on the paper 28. The paper 28 on which the image is formed is discharged out of the apparatus.

  On the other hand, a cleaner 32 that collects toner remaining on the intermediate transfer belt 14 without being transferred to the paper 28 by the transfer device 26 is disposed downstream of the transfer device 26 in the transport direction of the intermediate transfer belt 14. ing. The cleaner 32 is provided with a blade 34 so as to be in contact with the intermediate transfer belt 14, and collects residual toner by rubbing it.

  A sensor unit 36 for detecting the density of toner transferred to a predetermined position other than the image forming area on the intermediate transfer belt 14 is provided on the downstream side of the image forming unit 15 in the conveyance direction of the intermediate transfer belt 14. It has been.

  FIG. 2 shows the configuration of the image forming unit 15. Since the configuration of each image forming unit 15 is the same, the description is omitted here by omitting the last symbol indicating each color.

  As shown in the figure, the image forming unit 15 includes a photosensitive drum 16 that is disposed in contact with the intermediate transfer belt 14 and rotates at a predetermined speed in the arrow F direction.

  A charging roller 18 for charging the photosensitive drum 16 is disposed on the circumferential surface of each photosensitive drum 16. The charging roller 18 is a conductive roller, and its peripheral surface is in contact with the peripheral surface of the photosensitive drum 16, and is arranged so that the axial direction of the charging roller 18 coincides with the axial direction of the photosensitive drum 16. Has been.

  A predetermined voltage (in this embodiment, DC voltage −500 V) in which a DC (direct current) component and an AC (alternating current) component are superimposed is applied to the charging roller 18, and follows the rotation of the photosensitive drum 16. While rotating in this manner, the surface of the photosensitive drum 16 is uniformly charged to a predetermined potential (about −500 V in the present embodiment).

  Further, an exposure device 20 for forming an electrostatic latent image on the photosensitive drum 16 is provided on the circumferential surface on the downstream side of the charging roller 18 in the rotation direction (arrow F direction) of each photosensitive drum 16. It has been. The exposure device 20 includes an LED array in which a plurality of LEDs (light emitting diodes) are arranged, and light based on image data in the axial direction of the photosensitive drum 16 uniformly charged by the charging roller 18. Irradiate while scanning the beam. The potential of the region irradiated with the light beam by the exposure device 20 rises (in this embodiment, about −200 V), and an electrostatic latent image is formed on the photosensitive drum 16.

  Further, an electrostatic latent image formed on the photosensitive drum 16 is provided in a predetermined color (any one of yellow / magenta / cyan / black) around the exposure device 20 in the rotation direction of each photosensitive drum 16. A developing unit 22 is provided for developing with a single color toner to form a toner image. In the present embodiment, a developer including two components of a negative polarity toner and a positive polarity carrier is applied. In order to improve the development efficiency and the transfer efficiency described later, the toner particles are preferably spherical.

  As shown in the figure, the developing unit 22 includes a developing roller 38 and a blade 40 that are disposed close to the photosensitive drum 16. The developing roller 38 is charged to the same polarity as the surface of the photosensitive drum 16 (negative polarity in the present embodiment), and toner is attached to the peripheral surface by a positive polarity carrier loaded in the developing device 22. Further, the developing roller 38 is rotationally driven in the same direction as the rotation direction of the photosensitive drum 16 (in the direction of arrow G in the figure), and the toner adhering to the developing roller 38 is dropped by the blade 40 and is uniformly applied to the developing roller 38. To be attached to.

  As the developing roller rotates in the direction of arrow G, the toner attached to the developing roller 38 is conveyed to the surface of the photosensitive drum 16, and the surface of the photosensitive drum 16 and the toner are moved in the opposite directions. As a result, the toner is rubbed against the photosensitive drum 16, so that the electrostatic latent image formed on the photosensitive drum 16 is efficiently developed.

  When the surface potential Vh of the unexposed part of the photosensitive drum 16 is −500 V and the surface potential Vl of the exposed part is −200 V, a bias voltage is applied to the developing roller 38 to develop the surface potential Vdev of the developing roller 38. Is set to −400 V, the toner adhering to the developing roller 38 adheres to the exposed portion on the photosensitive drum 16. Therefore, the electrostatic latent image formed on the photosensitive drum 16 is reversely developed.

  On the other hand, the inside of the developing device 22 is partitioned into a first chamber 46A and a second chamber 46B by a partition wall 44. The developer stirring screw 42A is provided in the first chamber 46A, and the developer stirring is provided in the second chamber 46B. Screws 42B are respectively disposed.

  The developer agitating screw 42A agitates and conveys the developer in the first chamber 46A, and the developer agitating screw 42B is a toner replenished by the rotation of the conveying screw 48C from the toner discharge port 48B in the toner replenishing tank 48A of the toner replenishing unit 48. And the developer already present in the developing device 22 are agitated and conveyed.

  The partition wall 44 is formed with a developer passage (not shown) that allows the first chamber 46A and the second chamber 46B to communicate with each other at the front and back end portions in FIG. Due to the conveying force of the developer agitating screw 42B, the developer in the first chamber 46A in which the toner is consumed by the development moves from one passage into the second chamber 46B, and from the toner replenishing section 48 in the second chamber 46B. The developer replenished with toner moves from the other passage into the first chamber 46A.

  On the other hand, a transfer roller 25 for transferring the toner image on each photoconductive drum 16 to the intermediate transfer belt 14 is provided around the downstream side of the developing device 22 in the rotation direction of each photoconductive drum 16. The transfer roller 25 rotates in the direction of arrow H, conveys the intermediate transfer member belt 14 at a predetermined speed, and sequentially opposes the photosensitive drum 16. Further, the transfer roller 25 is positively charged and transfers the toner on the photosensitive drum 16 onto the intermediate transfer belt 14.

  Here, the transfer roller 25 cannot transfer all of the toner on the photosensitive drum 16 to the intermediate transfer belt 14, and the toner on the photosensitive drum 16 that has passed the position where the transfer roller 25 is disposed is not transferred. Slightly remains (transfer residual toner).

  There is also toner (retransfer toner) whose polarity is reversed to plus by the transfer roller 25 and reattached on the photosensitive drum 16. Note that when the other color toner image has already been transferred onto the intermediate transfer belt 14 when passing through the position where the transfer roller 25 is disposed, the retransfer toner includes the other color toner. .

  Therefore, a cleaning roll 24 that temporarily holds the transfer residual toner or the retransfer toner on the photosensitive drum 16 is disposed downstream of the transfer roller 25 on the peripheral surface of the photosensitive drum 16. The cleaning roll 24 has conductive brush hairs planted on the surface thereof, and is arranged so that the brush hairs come into contact with the photosensitive drum 16 so that the brush hairs are charged and rotated. It has become.

  The cleaning roll 24 is charged to a negative polarity (-500 V in the present embodiment) during the image formation period and is rotated in the same direction as the rotation direction of the photosensitive drum 16. As a result, the positive transfer toner adhering to the surface of the photosensitive drum 16 is attracted to the brush hair and collected.

  The cleaning roller 24 does not collect the negative transfer residual toner, and the photosensitive drum 16 is charged and exposed while remaining on the photosensitive drum 16, so that the transfer residual adhered to the non-image portion. The toner is collected in the developing device 22 by rubbing with the carrier and toner attached to the developing roller 38 of the developing device 22.

  The retransfer toner collected by the cleaning roll 24 is discharged onto the photosensitive drum 16 in a cleaning mode executed during non-image formation such as when a job is completed.

  In the cleaning mode, the cleaning roll 24 is charged to a positive polarity (in this embodiment, +500 V), and rotated so as to follow the rotation of the photosensitive drum 16 in a direction different from the rotation direction of the photosensitive drum 16. The As a result, the positive transfer toner held on the cleaning roll 24 is discharged onto the photosensitive drum 16.

  The retransfer toner discharged on the photosensitive drum 16 in this way is conveyed to the transfer position by the rotation of the photosensitive drum 16.

  In the cleaning mode, the transfer roller 25 is negatively charged, and the retransfer toner conveyed to the transfer position is transferred onto the intermediate transfer belt 14 by the transfer roller 25, and the intermediate transfer belt 14. To the cleaner 32 and scraped off by the blade 34 of the cleaner 32.

  By the way, in the image forming apparatus 10 according to the present embodiment, when the electrostatic latent image is developed by the developing unit 22, the toner replenishing unit 48 supplies an amount of toner corresponding to the image occupation ratio of the developed toner image to the paper 28. We are going to replenish sequentially.

  However, as described with reference to FIG. 7, a decrease in toner charge amount tends to occur as the image occupancy increases and as the relative humidity increases.

  For this reason, in the image forming apparatus 10 according to the present embodiment, the toner replenishment amount is not determined based only on the image occupancy rate, but the relative humidity is considered in addition to the image occupancy rate, and the image occupancy rate and When the relative humidity becomes a toner replenishment amount limiting condition that should limit the upper limit of the toner replenishment amount, the toner replenishment amount per unit time is forcibly limited.

  FIG. 3 is a block diagram illustrating a functional configuration related to toner replenishment control in the image forming apparatus 10.

  As shown in the figure, the image forming apparatus 10 includes a control unit 50 that controls the entire operation of the image forming apparatus 10. The intermediate transfer belt 14 and the image forming units 15 described above are included in the image forming apparatus 10. The operations of the photosensitive drum 16, the charging roller 18, the exposure device 20, the developing device 22, and the toner supply unit 48 are controlled by the control unit 50. In the drawing, only connection lines from the control unit 50 to the charging roller 18 and the toner supply unit 48 are shown in order to avoid complications.

  On the other hand, each image forming unit 15 is provided with a humidity sensor 52 for detecting the relative humidity. The humidity sensor 52 is electrically connected to the control unit 50, and the control unit 50 can always detect the relative humidity. The humidity sensor 52 may be installed at any position in the image forming apparatus 10, but is used for toner replenishment control in each image forming unit 15. It is installed near the developing device 22 in the forming unit 15.

  Each image forming unit 15 is provided with a timer 54 for measuring the continuous drive time of the developing device 22. The timer 54 is electrically connected to the control unit 50, and the control unit 50 can always grasp the continuous drive time of the developing device 22 of each image forming unit 15.

  Further, the image forming apparatus 10 includes a storage unit 56 for storing various programs, various table information, and the like in advance, and temporarily storing image data indicating an image to be formed. The storage unit 56 is also electrically connected to the control unit 50, and the control unit 50 can access the storage unit 56 at any time.

  Here, the storage unit 56 stores in advance a toner replenishment amount setting table for restricting the upper limit amount of toner replenishment amount per unit time when the image occupation ratio and the relative humidity become the toner replenishment amount restriction conditions. Has been.

  FIG. 4 schematically shows the toner supply amount setting table. As shown in the figure, the toner replenishment amount setting table according to the present embodiment includes stage information representing a plurality of division stages in each information of continuous drive time, image occupancy, and relative humidity of the developing device 22, A toner replenishment amount coefficient corresponding to the stage information is associated with each other.

  Specifically, the stage information of the continuous driving time of the developing device 22 includes three-stage information of 0 hour to less than 20 hours, 20 hours to less than 40 hours, and 40 hours or more. Further, as the stage information of the image occupancy rate, 0% or more and less than 40%, 40% or more and less than 55%, 55% or more and less than 70%, 70% or more and 85% for each stage information of the continuous driving time of the developing device 22. 5 levels of information of less than% and 85% or more are included. Further, as the relative humidity stage information, information of four stages of 40% or more and less than 55%, 55% or more and less than 70%, 70% or more and less than 85%, and 85% or more is included.

  On the other hand, the toner replenishment amount coefficient is such that, for example, the image occupancy is 0% or more and less than 85% when the continuous driving time of the developing device 22 is 0 hour or more and less than 20 hours as shown in FIG. “40” is a coefficient corresponding to the case where the relative humidity is within the range of 85% or more, and the image occupancy is within the range where the continuous driving time of the developing device 22 is 20 hours or more and less than 40 hours. Is stored as a coefficient corresponding to the case where the relative humidity is in the range of 40% or more and less than 70%.

  In the image forming apparatus 10 according to the present embodiment, the toner replenishment amount setting table is measured by using actual toners used in the image forming apparatus 10 as an example and various humidity conditions as shown in FIG. The toner corresponding to the combination of the conditions of the continuous driving time, the image occupancy rate, and the relative humidity of the developing device 22 which is a condition for generating the toner cloud based on the characteristics obtained by acquiring the toner charge amount change characteristic below The replenishment amount coefficient derived as the upper limit value of the image occupying ratio that can be used as a condition for preventing the occurrence of toner cloud is applied.

  By the way, in the image forming apparatus 10 according to the present embodiment, when the image forming process for one print job is executed, a process for controlling the toner supply from the toner supply unit 48 to the developing device 22 (hereinafter referred to as “toner”). "Supply control process").

  Next, the operation of the image forming apparatus 10 when executing the toner supply control process will be described with reference to FIG. FIG. 5 is a flowchart showing a flow of processing of a toner supply control processing program executed by the control unit 50 of the image forming apparatus 10 when the toner supply control process is executed. The program is stored in the storage unit 56. It is stored in advance in a predetermined area. Here, a case will be described in which image data indicating an image to be printed and information indicating the number of prints are stored in a predetermined area of the storage unit 56 by the control unit 50 for each print job. Furthermore, here, only control related to one image forming unit 15 will be described in order to avoid complications, but the control unit 50 executes similar processing for each image forming unit 15.

  First, in step 100 in the figure, the image data stored in the storage unit 56 and information indicating the number of prints are read in the print job (hereinafter referred to as “processing target print job”) being executed at this time, In the next step 102, based on the read image data and information, the image occupation ratio of the toner image developed by the developing device 22 in the processing target print job with respect to the paper 28 is calculated. Here, as the image occupancy, an average value of the image occupancy for each toner image developed by the developing device 22 in the processing target print job is calculated.

  In the next step 104, information indicating the continuous drive time of the developing device 22 is read from the timer 54, and in the next step 106, the relative humidity is detected based on the output signal from the humidity sensor 52.

  In the next step 108, it is determined whether or not the toner replenishment amount coefficient corresponding to the continuous drive time, image occupancy, and relative humidity of the developing device 22 obtained by the above processing is stored in the toner replenishment amount setting table. Thus, it is determined whether or not the toner replenishment amount coefficient is limited. If the determination is affirmative, the process proceeds to step 110.

  In step 110, the toner replenishment amount K per unit time is calculated by the following equation (1).

K = C × D (1)
Here, C is a value of 1/100 (1/100) of the toner replenishment amount coefficient corresponding to the continuous drive time, image occupancy, and relative humidity of the developing device 22 obtained by the above processing, and D is Each predetermined toner replenishment unit amount is represented. In the image forming apparatus 10 according to the present embodiment, the toner replenishment unit amount D is set in advance as a toner amount necessary for forming a toner image with the maximum density on the entire surface of one sheet 28. A value obtained by experiment or computer simulation based on the design specification of the image forming apparatus 10 is applied. In this embodiment, as a value when printing 20 sheets of A4 size paper per minute, 0.94 (mg / sec) is applied.

  In the next step 112, information indicating the difference between the image occupancy calculated in the processing in step 102 and the toner replenishment amount coefficient applied in the processing in step 110 is used. Information is stored in a predetermined area of the storage unit 56, and then the process proceeds to step 126. In the image forming apparatus 10 according to the present embodiment, 0 (zero) is stored in the predetermined area of the storage unit 56 as the initial setting of the toner supply shortage information. When a value other than 0 is already stored in the storage unit 56, information indicating a value obtained by adding the difference to the value is stored (overwritten) as toner replenishment insufficient information.

  On the other hand, if a negative determination is made in step 108, the process proceeds to step 114, and the toner replenishment amount K per unit time is calculated by the following equation (2).

K = S × D (2)
Here, S represents a value of 1/100 (1/100) of the image occupancy calculated in step 102.

  In the next step 116, the toner supply shortage information stored in the storage unit 56 is read. In the next step 118, it is determined whether or not the read toner supply shortage information exceeds 0 (zero). It is determined whether or not toner replenishment has been insufficient at the previous toner replenishment. If the determination is negative, the process proceeds to step 126. If the determination is affirmative, the process proceeds to step 120.

  In step 120, the amount of toner shortage indicated by the toner replenishment shortage information read out in step 116 is increased as much as possible with respect to the toner replenishment amount K calculated in step 114. The increase in the amount of toner shortage at this time is obtained when the toner replenishment amount coefficient corresponding to the continuous driving time and relative humidity of the developing device 22 obtained by the above processing is stored in the toner replenishment amount setting table. Then, the value obtained by multiplying the toner replenishment unit amount D by 1/100 (1/100) of the maximum value of the toner replenishment amount coefficient is increased as the upper limit amount, and the development obtained by the above processing is performed. When the toner replenishment amount coefficient corresponding to the continuous drive time and relative humidity of the device 22 is not stored in the toner replenishment amount setting table, the toner replenishment unit amount D is increased as the upper limit amount.

  In the next step 122, it is determined whether or not the toner supply shortage indicated by the toner supply shortage information read out by the processing of step 116 cannot be solved with the toner supply amount increased to the toner supply amount K by the processing of step 120. If the determination is negative, the process proceeds to step 123 to clear the toner supply shortage information to 0 (zero), and then the process proceeds to step 126. If the determination is affirmative, the process proceeds to step 124.

  In step 124, information indicating the amount of toner replenishment that could not be compensated for by the processing in step 120 is stored (overwritten) in a predetermined area of the storage unit 56 as toner replenishment insufficient information, and then the process proceeds to step 126.

  In step 126, the toner replenishing unit 48 is controlled so that the toner replenishing amount K per unit time obtained by the above processing is obtained, and then the toner replenishing control processing program is terminated.

  FIG. 6 shows an example of the transition of the toner replenishment amount and the transition of the toner density corresponding to the increase in the number of formed images (number of printed sheets) by executing the above toner replenishment control processing program. FIG. 4A shows the case where the toner replenishment amount coefficient is limited to 40% as the transition of the toner replenishment amount, and the vertical axis represents the case where the toner replenishment unit amount D is 100%. It is shown as a percentage of toner replenishment amount.

  As shown in the figure, in this case, when the number of printed sheets is in the range from 0 to 100, the toner is replenished by an amount corresponding to the image occupancy without being a toner replenishment amount restriction condition. The predetermined appropriate value (8% in the figure) is maintained.

  On the other hand, if the number of printed sheets is within the range of 100 to 200, the toner replenishment amount restriction condition is imposed, so that the upper limit amount of toner replenishment amount is forcibly limited, and the toner density within this range falls from an appropriate value. It will gradually decline.

  However, since the toner replenishment amount restriction condition is not satisfied when the number of printed sheets is in the range of 200 to 300 sheets, the toner replenishment amount is limited to the toner replenishment amount to compensate for the shortage of toner replenishment amount within the range of 100 to 200 sheets. The amount is increased within the range that does not meet the conditions. For this reason, the toner density gradually recovers toward the appropriate value within this range.

  Thereafter, the toner density changes in the same manner as described above. As a result, the influence on the toner density due to the limitation of the upper limit of the toner replenishment amount can be minimized.

  As described in detail above, according to the present embodiment, the toner replenishment amount restriction that the relative humidity and the image occupancy ratio of the toner image developed by the developing device 22 with respect to the paper 28 limit the upper limit amount of the toner replenishment amount. It is determined whether or not the condition is satisfied (corresponding to step 108 of the toner replenishment control processing program). If it is determined that the toner replenishment amount restriction condition is not satisfied, the image occupancy rate increases as the image occupation ratio increases. Then, the toner replenishment amount is derived (corresponding to step 114 of the toner replenishment control processing program), and if it is determined that the toner replenishment amount restriction condition is satisfied, the toner replenishment amount is set to a predetermined upper limit amount. Derived (corresponding to step 110 of the toner replenishment control processing program) and the toner replenishing unit 48 is controlled so as to obtain the derived toner replenishment amount. It is possible to prevent a decrease in toner charge quantity effectively.

  Further, according to the present embodiment, in addition to the relative humidity and the image occupancy rate, it is determined whether or not the continuous driving time of the developing device 22 is a toner supply amount restriction condition that restricts the upper limit amount of the toner supply amount. Since it is added as a parameter at the time of determination, it is possible to derive the toner replenishment amount with higher accuracy, and to more effectively prevent the toner charge amount from decreasing.

  Further, according to the present embodiment, when the toner supply amount restriction condition is not satisfied, and when the toner supply amount is restricted at the time of deriving the previous toner supply amount, the increase amount is within a range not satisfying the toner supply amount restriction condition. Thus, since the toner replenishment amount is derived, it is possible to suppress a decrease in density of the formed image due to the restriction of the toner replenishment amount.

  In the present embodiment, the case where the toner replenishment control process is executed every execution of one print job has been described. However, the present invention is not limited to this, and for example, a predetermined period when the print job is executed It can also be set to be executed every time. Also in this case, the same effects as in the present embodiment can be obtained.

  In addition, the configuration (see FIGS. 1 to 3) of the image forming apparatus 10 described in the present embodiment is also an example, and it is needless to say that the configuration can be appropriately changed without departing from the gist of the present invention.

  For example, in the present embodiment, the case where the continuous drive time of the developing device 22 is measured by the timer 54 provided separately from the control unit 50 has been described, but the present invention is not limited to this. For example, the function of the timer 54 may be provided in the control unit 50, and the continuous driving time may be measured by the control unit 50 itself.

  In this embodiment, the case where the present invention is applied to a so-called tandem type image forming apparatus having four image forming units 15 has been described. However, the present invention is not limited to this, and for example, The present invention may be applied to an image forming apparatus having only one image forming unit 15.

  In these cases, the same effects as in the present embodiment can be obtained.

  Furthermore, the processing flow (see FIG. 5) of the toner replenishment control processing program described in the present embodiment (see FIG. 5), the configuration of the toner replenishment amount setting table (see FIG. 4), various arithmetic expressions (formula (1), (See formula (2).) Is also an example, and it goes without saying that it can be changed as appropriate without departing from the gist of the present invention.

  For example, in the toner replenishment control processing program according to the present embodiment, when the previous toner replenishment amount is insufficient, the toner replenishment amount K can be calculated with respect to the toner replenishment amount K by calculating the formula (2). Although the case where the amount of toner shortage is increased as much as described has been described, the present invention is not limited to this, and for example, the amount of toner shortage is increased as much as possible by assigning the value of the image occupancy ratio to the expression (2). By applying it as a value that can be used, it is possible to increase the amount of toner shortage by the calculation according to equation (2). Also in this case, the same effects as in the present embodiment can be obtained.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 1 is a schematic configuration diagram of an image forming unit according to an embodiment. 3 is a block diagram illustrating a functional configuration related to toner replenishment control in the image forming apparatus according to the embodiment. FIG. FIG. 6 is a schematic diagram illustrating a configuration of a toner replenishment amount setting table according to the embodiment. 6 is a flowchart illustrating a processing flow of a toner supply control processing program according to the embodiment. 6 is a graph showing an example of a change in toner replenishment amount as a result of an increase in the number of image formations (number of printed sheets) by execution of a toner replenishment control processing program according to an embodiment and a change in toner density corresponding thereto. FIG. 10 is a diagram for explaining a state of reduction in toner charge amount, and is a graph showing actual measurement results of toner charge amount with respect to image occupancy under various humidity conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Intermediate transfer belt 15 Image forming unit 16 Photosensitive drum (image carrier)
22 Developer (Developer)
28 paper (recording medium)
48 Toner supply part (toner supply means)
50 control unit (image occupancy rate deriving unit, toner limit determining unit, toner replenishment amount deriving unit, control unit)
52 Humidity sensor (humidity detection means)
54 Timer (Driving time detection means)
56 storage unit

Claims (3)

An image forming apparatus that forms an image by developing an electrostatic latent image formed on an image carrier with toner by a developing unit and transferring the developed toner image on the image carrier to a recording medium,
Toner replenishing means for replenishing the developing means with the toner;
Humidity detecting means for detecting relative humidity;
Image occupancy rate deriving means for deriving an image occupancy rate of the toner image developed by the developing unit during execution of the print job with respect to the recording medium;
Driving time detecting means for detecting the driving time of the developing means;
The combination of the relative humidity detected by the humidity detection means and the image occupancy derived by the image occupancy derivation means until the drive time detected by the drive time detection means reaches a threshold is the development. A first combination of a relative humidity greater than or equal to a first relative humidity and an image occupancy greater than or equal to a first image occupancy predetermined as a combination that does not generate a toner cloud of toner replenished by the means; A second relative humidity lower than the first relative humidity, a relative humidity lower than the first relative humidity, and an image occupation ratio equal to or higher than the second image occupation ratio larger than the first image occupation ratio. Determining means for determining whether or not the second combination of
When the determination means determines that the first or second combination is not achieved, the toner replenishment amount is derived so as to increase as the image occupancy increases, and the determination means determines the first replenishment amount . Or a toner replenishment amount deriving means for deriving the toner replenishment amount so as to reach a predetermined upper limit when it is determined that the second combination is achieved;
Control means for controlling the toner replenishing means so that the toner replenishment amount derived by the toner replenishment amount deriving means during execution of the print job;
An image forming apparatus. The image forming apparatus according to claim 1, wherein the a plurality of the threshold. The toner replenishment amount deriving unit restricts the toner replenishment amount when the determination unit determines that one of the first and second combinations is not achieved and when the previous toner replenishment amount is derived. 3. The image forming apparatus according to claim 1 , wherein the toner replenishment amount is derived so as to increase within a range that does not satisfy the one combination.

Images