JP2008020696A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where, even in the cast toner is relatively largely consumed at a time, the risk that toner supply to a developing device is not in time can be reduced. <P>SOLUTION: The image forming apparatus is equipped with: a developing device 25 where toner stored in a toner storage chamber R is fed to a photoreceptor drum, thus an electrostatic latent image formed at the photoreceptor drum is developed, so as to form a toner image; a secondary transferring roller 275 for transferring the toner image to recording paper P; a conveyance mechanism 50 for conveying the recording paper P to the secondary transferring roller 275; and an interpaper setting part 61 for increasing interpaper time T as a spacing between recording paper P conveyed to the secondary transferring roller 275 by the conveyance mechanism 50 and the following recording paper P in accordance with the increase of the printing ratio in image data, and reducing the same in accordance with the reduction of the printing ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic method, such as a copying machine, a printer, a facsimile, or the like.

  In recent years, as the speed of image forming apparatuses has increased, a tandem that forms a color image in synchronism with the feeding of a transfer member and superimposes colors on the transfer member using a plurality of photoconductors corresponding to toner colors. The method is drawing attention.

  In such an image forming apparatus, as a developer used for developing an electrostatic latent image, a two-component developer composed of a magnetic carrier and a toner is widely used, and the two-component developer is placed on a magnetic brush roll. By holding and mixing the toner, the toner is charged, and only the toner is uniformly formed into a thin layer on the developing roll, and the electrostatic latent image formed on the drum surface is developed.

  In the developing device as described above, an agitation feed member such as a paddle for agitating the developer or a spiral for conveying the developer while agitating the developer is contained in a container for accommodating a two-component developer composed of a carrier and toner. Accordingly, uniform mixing of the toner and the carrier and frictional charging of the toner are sufficiently performed.

  By the way, at present, a compact image forming apparatus is desired. Therefore, a more compact developing apparatus is desired, and the capacity of the storage chamber for storing the developer is decreasing. When the capacity of the storage chamber decreases, it is necessary to replenish the toner frequently in order to compensate for the toner consumption accompanying the image output, and the toner density fluctuation due to the toner replenishment in the storage container also increases. In addition, when outputting an image with a high printing rate, the amount of toner consumed for image output becomes extremely large, and there is a possibility that toner replenishment may not be in time.

For this reason, the toner density in the storage chamber is measured and toner is replenished based on the measured value of the toner density (see, for example, Patent Document 1), or the difference between the toner replenishment amount and the toner consumption amount. In addition, there has been proposed an apparatus that ensures a constant toner density by extending the image formation time (see, for example, Patent Document 2).
JP-A-6-301287 JP 2005-1115050 A

  However, when the toner density in the storage chamber is measured and the toner is replenished based on the measured value of the toner density, a sensor that measures the position of the developing roll that supplies the toner to the photoconductor in the developing device and the toner density Due to the deviation from the position of the toner, there is a time lag from when the toner density decreases until this is detected, and toner replenishment is delayed, or the replenished toner is conveyed while being agitated by a paddle or spiral. The toner replenishment may be delayed due to the agitation and conveyance time, which may cause a decrease in image density due to a decrease in toner density.

  In addition, a motor that rotates a toner conveying member such as a spiral in order to detect a toner replenishment amount, in order to ensure a constant toner density by extending the image formation time from the difference between the toner replenishment amount and the toner consumption amount. Therefore, it takes a long time to detect the toner replenishment amount. As a result, the toner replenishment is delayed, and there is a possibility that the image density is lowered due to the decrease in the toner density.

  The present invention has been made in view of the above-described circumstances, and an image forming apparatus capable of reducing a possibility that toner supply to the developing device may not be in time even when a relatively large amount of toner is consumed at one time. The purpose is to provide.

  An image forming apparatus according to the present invention includes an image data acquisition unit that acquires image data representing an image, a paper storage unit that stores recording paper, a toner storage chamber that stores toner, and a toner concentration in the toner storage chamber. Based on the image data acquired by the image data acquisition unit by supplying the first toner replenishment control unit that adjusts to a preset density and supplying the toner stored in the toner storage chamber to the photosensitive drum. A developing unit that develops an electrostatic latent image formed on the photosensitive drum and forms a toner image, a transfer unit that transfers the toner image to a recording paper, and a recording paper stored in the paper storage unit The image acquired by the image data acquisition unit is a conveyance mechanism that conveys the transfer unit to the transfer unit, and an interval between the recording sheet conveyed to the transfer unit by the conveyance mechanism and the next recording sheet. Increase with respect to increase the direction of change in the printing rate in chromatography data, and a sheet interval setting unit to reduce relative decrease direction of change of the printing rate.

  According to this configuration, the image data to be printed is acquired by the image data acquisition unit. Further, the first toner replenishment control unit adjusts the toner density in the toner storage chamber to a preset density. Then, the toner stored in the toner storage chamber is supplied to the photosensitive drum, and the electrostatic latent image formed on the photosensitive drum is developed based on the image data acquired by the image data acquisition unit, and the toner An image is formed. Further, the toner image is transferred by the transfer unit to the recording paper conveyed by the conveyance mechanism from the paper storage unit, and image formation is performed. Further, the paper interval setting unit increases the paper interval time, which is the interval between the recording paper conveyed to the transfer unit and the next recording paper, in accordance with the increase in the printing rate of the image data acquired by the image data acquisition unit. And is decreased according to the decrease in the printing rate. In this case, when the printing rate increases, the toner consumption increases, and the toner density in the toner storage chamber decreases, the time between sheets increases, and the first toner supply control unit replenishes the toner storage chamber with toner. Since the time for adjusting the density is increased, it is possible to reduce the possibility that the toner supply to the toner storage chamber will not be in time. Further, when the printing rate is reduced and the toner consumption is reduced, and the first toner replenishment control unit does not need to increase the toner replenishment amount into the toner storage chamber, the time between sheets is reduced, A reduction in the number of images formed per unit time is reduced.

  The paper gap setting unit determines that the printing rate has increased when the printing rate exceeds a preset first printing rate, and when the printing rate has not reached the first printing rate, the printing rate. It is preferable to determine that has decreased. In this case, since the paper interval setting unit can set the paper interval time based on the comparison result between the printing rate and the first printing rate, the processing can be simplified.

  Further, the paper gap setting unit is configured such that when a toner image based on the image data in a state where the printing rate is reduced is transferred to the recording paper by the transfer unit for a preset number of sheets, the paper gap setting unit It is preferable to reduce the time. According to this configuration, after the time that the toner image based on the image data with the reduced printing rate is transferred to the recording sheet by the transfer unit for a preset number of sheets has elapsed, the sheet interval setting unit Since the time is reduced, it becomes easy to secure the adjustment time of the toner concentration performed by the first toner replenishment control unit in response to the decrease in the printing rate and the decrease in the toner consumption.

  Further, it is preferable that the paper interval setting unit sets an initial paper interval time longer than the shortest paper interval time preset as the shortest paper interval time as the initial value of the paper interval time. In this case, when forming the first image whose printing rate is unknown, the paper interval time is set to the initial paper interval time longer than the shortest paper interval time, so the first toner replenishment control unit puts toner into the toner storage chamber. The time required for replenishing and adjusting the toner density is increased as compared with the case where the paper interval time is set to the shortest paper interval time, thereby reducing the possibility that the toner supply to the toner storage chamber will not be in time. it can.

  In addition, the paper gap setting unit, when the paper gap time is the initial paper gap time as the initial value, when the printing rate decreases, the paper gap setting unit does not wait for the set number of sheets to be transferred. It is preferred to reduce the time between. In this case, when the printing rate decreases, the paper interval time set as the initial value at the initial paper interval time longer than the shortest paper interval time can be reduced without waiting for the set number of sheets to be transferred. It is possible to reduce the number of images formed per unit time by increasing the time between sheets as necessary.

  And a toner density measuring unit that measures the toner density of the toner in the toner storage chamber, and when the toner density measured by the toner density measuring unit reaches a near-end determination threshold for detecting a near-end, the development is stopped and the toner is stopped. A second toner replenishment control unit that replenishes the toner storage chamber, and the near-end determination threshold value is changed in a direction in which the density is decreased in accordance with the increase in the printing rate, and in a direction in which the density is increased in accordance with the decrease in the printing rate. It is preferable to further include a near-end determination threshold value setting unit that changes the threshold value.

  According to this configuration, the toner concentration of the toner in the toner storage chamber is measured by the toner concentration measuring unit. Then, when the toner density measured by the toner density measuring unit reaches the near-end determination threshold for detecting the near end by the second toner supply control unit, the development is stopped and the toner is supplied to the toner storage chamber. Further, the near-end determination threshold value setting unit changes the near-end determination threshold value in the direction where the density is low in accordance with the increase in the printing rate, and the density is changed in the direction in which the density is high in accordance with the decrease in the printing rate. When the toner consumption increases and the toner concentration in the toner containing chamber temporarily decreases and may reach the near-end determination threshold, the near-end determination threshold setting unit changes the near-end determination threshold in the direction of decreasing density. As a result, the possibility that the second toner replenishment controller erroneously stops the development and the toner replenishment operation to the toner storage chamber is reduced.

  The near-end determination threshold value setting unit determines that the printing rate has increased when the printing rate exceeds a preset second printing rate, and if the printing rate is less than the second printing rate, the printing is performed. It is preferable to judge that the rate has decreased. According to this configuration, the near-end determination threshold value setting unit can set the near-end determination threshold value based on the comparison result between the printing rate and the second printing rate, so that the processing can be simplified.

  In the image forming apparatus having such a configuration, when the printing rate increases, the toner consumption increases, and the toner concentration in the toner storage chamber decreases, the time between sheets is increased, and the first toner supply control unit is in the toner storage chamber. Since the time for replenishing the toner and adjusting the toner density is increased, it is possible to reduce the possibility that the replenishment of the toner into the toner storage chamber will not be in time. Further, when the printing rate is reduced and the toner consumption is reduced, and the first toner replenishment control unit does not need to increase the toner replenishment amount into the toner storage chamber, the time between sheets is reduced, A reduction in the number of images formed per unit time is reduced.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  The developing apparatus according to the present invention can be applied to an electrophotographic image forming apparatus such as a copying apparatus, a printer apparatus, and a facsimile apparatus. As an example, a case where the developing apparatus is applied to a color printer apparatus will be described below.

  First, a color printer apparatus that is an example of an image forming apparatus will be described. FIG. 1 is a diagram showing a schematic configuration of a color printer apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of the electrical configuration of the color printer apparatus shown in FIG. In FIG. 1, a color printer CP includes a paper storage unit 10 (paper storage unit), an image forming unit 20, a fixing unit 30, a paper discharge unit 40, a transport mechanism 50, a control unit 60, and a communication interface. A sheet storage unit 10, an image forming unit 20, a fixing unit 30, a transport mechanism 50, a control unit 60, and a communication interface circuit 70 are housed in the substantially box-shaped apparatus main body 1, and the paper discharge unit 40. Is provided at the top of the apparatus body 1.

  The paper storage unit 10 stores recording paper P as an example of a transfer material to be used for printing processing, and feeds out the recording paper P under the control of the control unit 60. A predetermined number (one in this embodiment) of paper cassettes 11 is provided in the paper storage unit 10 so as to be detachable from the apparatus main body 1.

  At the upstream end of the paper cassette 11 (upper left of the paper cassette 11 in the example shown in FIG. 1), a pickup roller 12 that feeds the recording paper P from the paper bundle one by one is provided. The recording paper P fed out from the paper cassette 11 by driving the pickup roller 12 is fed to the transport mechanism 50. Further, the transport mechanism 50 is provided with a pair of registration rollers 51 that adjust the timing for supplying the recording paper P to the image forming unit 20.

  Under the control of the control unit 60, the image forming unit 20 applies the recording paper P that is fed out from the sheet bundle stored in the paper storage unit 10 based on the image signal received by the communication interface circuit 70 from a computer or the like. On the other hand, an image transfer process is performed.

  The communication interface circuit 70 is an example of an image data acquisition unit, and is connected to an external device such as a computer via a LAN (Local Area Network) 71 or the like and transmits / receives various signals to / from the external device. For example, a network interface (10 / 100Base-TX) or the like is used. The image forming unit 20 includes an image forming unit 21 that forms a toner image and a transfer device 27 that transfers the toner image formed by the image forming unit 21 onto a recording paper P.

  The image data acquisition unit is not limited to the communication interface circuit 70. For example, in an image forming apparatus such as a copying machine or a facsimile, the image data acquisition unit may be a scanner device that acquires a document image.

  The image forming unit 21 includes a yellow unit 21Y, a magenta unit 21M, a cyan unit 21C, and a black unit that are sequentially arranged in a substantially horizontal direction from the upstream side (the right side of the paper surface in FIG. 1) to the downstream side. 21K and an exposure unit 24 disposed at the lower position of each unit. Each of these units 21Y, 21M, 21C, and 21K has the same configuration, and is positioned and attached to each device in the apparatus main body 1 with a predetermined relative positional relationship. In the present specification, when referring generically, it is indicated by a reference symbol without a suffix, and when referring to an individual configuration, it is indicated by a reference symbol with a suffix.

  Each of these units 21Y, 21M, 21C, and 21K includes a photosensitive drum 22, a charger 23, a developing device 25 (developing unit), and a cleaning device 26. The photosensitive drum 22 is arranged in the front-rear direction ( Rotation of the photosensitive drum 22 is performed from a position directly below the photosensitive drum 22 along the peripheral surface of the photosensitive drum 22 so as to be rotatable about a drum axis extending in a direction orthogonal to the paper surface of FIG. The charger 23, the developing device 25, and the cleaning device 26 are disposed in the counterclockwise direction.

  The photosensitive drum 22 is for forming an electrostatic latent image and a toner image (visible image) according to the electrostatic latent image on the peripheral surface. The charger 23 forms a uniform charge on the peripheral surface of the photosensitive drum 22 rotating counterclockwise around the drum axis. For example, the peripheral surface abuts on the peripheral surface of the photosensitive drum 22. However, it is configured to include a charging roller that applies electric charges to the photosensitive drum 22 while being driven to rotate. The developing device 25 supplies toner to the peripheral surface of the photosensitive drum 22 to attach the toner to the portion where the electrostatic latent image is formed on the peripheral surface, and thereby the toner image is formed on the peripheral surface of the photosensitive drum 22. To form. In the present embodiment, in order to cope with color, yellow (Y) toner is stored in the developing device 25Y of the yellow unit 21Y, and magenta (M) toner is stored in the developing device 25M of the magenta unit 21M. The cyan (C) toner is stored in the developing device 25C of the cyan unit 21C, and the black (K) toner is stored in the black developing device 25K of the black unit 21K. . The developing device 25 will be described in detail later. The cleaning device 26 is for removing the toner remaining on the peripheral surface of the photosensitive drum 22 after the transfer process and cleaning it. The peripheral surface of the photosensitive drum 22 cleaned by the cleaning device 26 is again directed to the charger 23 for the next image forming process.

  The exposure unit 24 irradiates the peripheral surface of the rotating photosensitive drum 22 with a laser beam to which intensity is applied based on the image data between the charger 23 and the developing device 25, so that the circumference of the photosensitive drum 22 is irradiated. An electrostatic latent image is formed on the surface. The exposure unit 24 applies the laser beams corresponding to the colors yellow, magenta, cyan, and black to the photosensitive drums 22Y, 22M, 22C, and 22K in the units 21Y, 21M, 21C, and 21K in order to correspond to the colors. It is configured to irradiate. When the peripheral surface of the charged photoconductive drum 22 is irradiated with laser light, the charge of the irradiated portion is erased according to the intensity of the laser light, whereby an electrostatic latent image is formed on the peripheral surface of the photoconductive drum 22. It is formed. The image data includes yellow, magenta, cyan, and black development colors generated by the control unit 60 by performing a process such as a known color correction process on an image signal from an external device such as a computer received by the communication interface circuit 70. These image data.

  The transfer device 27 is a device for transferring the toner image formed on the peripheral surface of the photosensitive drum 22 onto the recording paper P, and includes an intermediate transfer belt 271, a primary transfer roller 272, a driving roller 273, a driven roller 274, and the like. A secondary transfer roller 275 (transfer section) is provided. The intermediate transfer belt 271 is endless, and is stretched to a position immediately above the units 21Y, 21M, 21C, and 21K by the primary transfer roller 272, the drive roller 273, and the driven roller 274, and the rotational driving force of the drive roller 273 Can be rotated clockwise. The primary transfer roller 272 is provided so as to correspond to the photosensitive drums 22Y, 22M, 22C, and 22K of the units 21Y, 21M, 21C, and 21K, and holds the intermediate transfer belt 271 from the photosensitive drum 22 to the intermediate transfer belt 271. Is arranged to prevent the floating. The secondary transfer roller 275 is disposed at a position facing the drive roller 273 on the outer peripheral surface of the intermediate transfer belt 271.

  The drive roller 273 is grounded. The primary transfer roller 272 is configured to apply a voltage having a polarity opposite to that of the toner as a primary transfer bias while the toner image in the image area is primarily transferred from the photosensitive drum 22 to the intermediate transfer belt 271. . The secondary transfer roller 275 is configured to apply a voltage having a polarity opposite to that of the toner as a secondary transfer bias while the toner image on the intermediate transfer belt 271 is secondarily transferred to the recording paper P. ing. As described above, the printer device CP according to the present embodiment employs the indirect transfer method.

  An intermediate transfer belt cleaning device 276 is provided on the right side of the driven roller 274 on the paper surface, and the toner remaining on the surface of the intermediate transfer belt 271 after the toner image is transferred to the recording paper P is removed. The intermediate transfer belt 271 removed by the intermediate transfer belt cleaning device 276 and cleaned thereby is supplied to the photosensitive drum 22.

  The fixing unit 30 performs a fixing process by heating on the toner image of the recording paper P that has been subjected to the transfer process by the image forming unit 20 under the control of the control unit 60. A heat roller 31 and a pressure roller 32 are provided so as to face the heat roller 31 and face each other. Then, the recording paper P after the transfer process includes a heat roller 31 that is driven to rotate clockwise around the roller axis, and a pressure roller 32 that is driven to rotate counterclockwise around the roller axis. By passing through the nip between the two, the heat from the heat roller 31 is obtained and the fixing process is performed. The recording paper P subjected to the fixing process is discharged to the paper discharge unit 40 by the transport mechanism 50.

  The paper discharge unit 40 discharges the recording paper P on which the fixing process has been performed by the fixing unit 30 and stores the discharged recording paper P. The paper discharge unit 40 is formed by recessing the top of the apparatus main body 1, and a paper discharge tray 41 for receiving the recording paper P discharged is formed at the bottom of the recess.

  The transport mechanism 50 transports the recording paper P fed from the paper storage unit 10 to the paper discharge unit 40 via the image forming unit 20 and the fixing unit 30 under the control of the control unit 60.

  The control unit 60 is connected to the sheet storage unit 10, the image forming unit 20, the fixing unit 30, the transport mechanism 50, the communication interface circuit 70, and the like, and controls these in accordance with the functions to thereby control each unit of the color printer CP. It governs control. The control unit 60 is, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores various programs executed by the CPU, data necessary for the execution in advance, and a so-called working memory of the CPU. A RAM (Random Access Memory) and its peripheral circuits are provided.

  The control unit 60 functions as a paper gap setting unit 61, a toner supply control unit 62, and a near-end determination threshold setting unit 63 by executing a program stored in the ROM, for example.

  The paper interval setting unit 61 starts from the end of the recording paper P on which the image has been transferred by the secondary transfer roller 275 passing through the secondary transfer roller 275 until the leading edge of the next recording paper P reaches the secondary transfer roller 275. The paper interval time T, which is the time interval, increases as the printing rate of the image data received by the communication interface circuit 70 increases, and decreases as the printing rate decreases.

  The toner replenishment control unit 62 includes a first toner replenishment control unit that adjusts the toner density in the developing device 25 to a preset density, and a near-end determination threshold value Nth for detecting near-end in the toner concentration in the developing device 25. Then, it functions as a second toner supply control unit that performs toner supply control for stopping development and supplying toner to the developing device 25.

  The near-end determination threshold value setting unit 63 changes the near-end determination threshold value Nth in a direction in which the density is light according to an increase in the printing rate of the image data, and changes in a direction in which the density is dark according to a decrease in the printing rate.

  Further, for example, an expansion time table TB shown in FIG. 4 is stored in the ROM. The expansion time table TB will be described later.

  The image forming operation in the color printer CP having such a configuration will be described. First, the charging drum 23 charges the photosensitive drum 22, and then the exposure unit 24 performs exposure so that the electrostatic latent image is exposed to light. It is formed on the surface of the body drum 22. The electrostatic latent image is converted into a toner image by the developing device 25, and the toner image formed on the surface of the photosensitive drum 22 is transferred onto the intermediate transfer belt 271 by the transfer bias applied to the primary transfer roller 272. The Then, the residual toner remaining on the photosensitive drum 22 without being transferred to the intermediate transfer belt 271 is cleaned by the cleaning device 26 and stored in a collection bottle (not shown). Such exposure, development, and transfer operations are sequentially performed on the development colors of yellow, magenta, cyan, and black, and the toner images of the respective colors are superimposed on the surface of the intermediate transfer belt 271 so that the intermediate transfer belt. A full-color toner image is formed on 271.

  When the full-color toner image is formed on the intermediate transfer belt 271, the secondary transfer roller 275 is brought into contact with the intermediate transfer belt 271, and the recording paper P conveyed by the conveyance mechanism 50 from the paper storage unit 10 is registered with the registration roller 51. The full-color toner image formed on the intermediate transfer belt 271 is transferred onto the recording paper P by the secondary transfer bias applied to the secondary transfer roller 275. The full-color toner image transferred to the recording paper P is fixed to the recording paper P by heating and pressurization by the fixing unit 30, and the recording paper P is discharged to the paper discharge unit 40. The toner remaining on the intermediate transfer belt 271 is cleaned by bringing the intermediate transfer belt cleaning device 276 of the intermediate transfer belt 271 into contact with the intermediate transfer belt 271 after the secondary transfer, and is stored in a collection bottle (not shown). Is done.

  Next, the developing device 25 provided in each of the units 21Y, 21M, 21C, and 21K will be further described. FIG. 3 is a diagram for explaining the configuration of the developing device according to the embodiment. 3A is a side cross-sectional view of the developing device taken along line AA in FIG. 3B, and FIG. 3B is a plan cross-sectional view showing the configuration of the developing device. In FIG. 3B, the magnet roller is omitted for the sake of convenience in order to facilitate understanding of the configuration of the storage chamber and the stirrer.

  In FIG. 3, the developing device 25 includes a developing roller 251, a magnet roller 252, a doctor blade 253, a stirrer 254, and a toner concentration sensor 255 (toner concentration measuring unit). The developing roller 251, magnet roller 252, doctor blade 253, stirrer 254, and toner density sensor 255 have a developing device housing having a storage chamber R (toner storage chamber) for storing toner and carrier as a two-component developer at the bottom. It is housed in the body 250.

  The storage chamber R includes first and second storage chambers R1 and R2 that are partitioned and juxtaposed by a partition wall W1 extending in the longitudinal direction, and the first and second storage chambers at both ends of the partition wall W1. R1 and R2 are connected. A toner supply opening 256 for supplying toner from the toner hopper (not shown) for storing toner to the storage chamber R is opened above one end of the storage chamber R, as indicated by a two-dot chain line. In the storage chamber R shown in FIG. 3, in order to separate the toner replenished from the toner hopper from the toner stirred by the first and second stirrers 2541 and 2542, a portion immediately below the toner supply opening 256 in the second storage chamber. A partition wall W2 that separates the other portions from each other is further provided in the second storage chamber R2.

  Further, between the toner supply opening 256 and the toner hopper, a toner transfer roller (not shown) for transferring toner from the toner hopper to the toner supply opening 256 is disposed. The toner transport roller is rotationally driven by a toner motor (not shown) controlled by the control unit 60. By the rotation of the toner conveying roller, the toner is conveyed from the toner hopper to the toner replenishing opening 256, and the toner amount per unit time (toner replenishing speed) conveyed from the toner hopper to the toner replenishing opening 256 is adjusted by the rotation speed of the toner conveying roller. The

  The agitator 254 conveys the toner replenished from the toner hopper to the magnet roller 252 while agitating, and the first and second agitators 2541 disposed in the first and second storage chambers R1 and R2, respectively. 2542. Each of the first and second stirrers 2541 and 2542 is configured to include a rotation shaft in which spiral (spiral) blades are formed in substantially the entire region in the axial direction.

  The toner concentration sensor 255 measures the toner concentration in the storage chamber R, and outputs a measurement value (toner level) of the measurement result to the control unit 60. The toner concentration sensor 255 is disposed at the bottom of the first storage chamber R1 that is a predetermined distance away from the toner supply opening 256. The toner concentration sensor 255 includes a magnetic permeability sensor that measures the magnetic permeability, for example, and measures the toner concentration by measuring the magnetic permeability that changes in accordance with the toner concentration. When the toner is a non-magnetic material, the toner level of the toner concentration sensor 255 increases as the toner concentration decreases, and conversely decreases as the toner concentration increases. Further, the toner level of the toner density sensor 255 is expressed by 10 bits, for example, and is indicated by a value from 0 to 1023.

  The magnet roller 252 pumps toner from the storage chamber R by magnetic force, and transports and supplies the pumped toner to the peripheral surface of the developing roller 251 while adhering the pumped toner to the outer peripheral surface. The magnet roller 252 is disposed above the second stirrer 2542 (above the second storage chamber R2) so as to be spaced apart from the second stirrer 2542 in the direction of the rotation axis of the second stirrer 2542. Has been. The magnet roller 252 is, for example, a cylindrical magnet roller body in which a required number of permanent magnets are embedded and fixed without rotating with respect to the movable bearing, and a circumferentially fitted surface of the magnet roller body. And a cylindrical sleeve made of a nonmagnetic metal material.

  The doctor blade 253 is a blade-like member that regulates the thickness of the toner layer formed on the peripheral surface of the magnet roller 252. The doctor blade 253 is disposed opposite the circumferential surface of the magnet roller 252 with a predetermined distance.

  The developing roller 251 receives toner from the magnet roller 252 to form a toner layer on the outer peripheral surface thereof, and develops the electrostatic latent image formed on the peripheral surface of the photosensitive drum 22 with the toner in the toner layer. Is. The developing roller 251 is disposed opposite the circumferential surface of the magnet roller 252 with a predetermined distance.

  The developing device 25 having such a configuration is arranged such that the developing roller 251 is opposed to the peripheral surface of the photosensitive drum 22 with a predetermined distance therebetween. In the developing device 25, the toner replenished from the toner replenishing opening 256 is conveyed from one end of the first storage chamber R1 to the other end while being agitated by the first agitator 2541. The toner conveyed to the other end by the first stirrer 2541 passes through the first gap CR1 that communicates the first storage chamber R1 and the second storage chamber R2 on the other end side to the second storage chamber R2. be introduced. The toner introduced into the second storage chamber is conveyed from the other end of the second storage chamber R2 to the one end while being agitated by the second stirrer 2542, and a part of the toner is supplied to the magnet roller 252 and the rest. Is returned to the first storage chamber R1 through the second gap CR2 that communicates the second storage chamber R2 and the first storage chamber R1 on one end side. Thus, the toner supplied from the toner hopper to the storage chamber R is circulated through the first and second storage chambers R1 and R2 by the first and second stirrers 2541 and 2542, mixed with the carrier by stirring, and triboelectrically charged. Part of the toner is pumped up by the magnet roller 252 and consumed. Then, the toner concentration is measured by the toner concentration sensor 255 during the conveyance by the first stirrer 2541, and the toner level is output to the control unit 60. As will be described later, the controller 60 is replenished from the toner hopper so that the toner concentration of the toner in the first and second storage chambers R1 and R2 becomes a target value based on the toner level measured by the toner concentration sensor 255. The toner density is controlled by adjusting the toner amount.

  Here, from the viewpoint of more accurately measuring the toner concentration of the residual toner that is consumed during the conveyance in the second storage chamber R2 and returned to the first storage chamber R1, the toner concentration sensor 255 is configured to store the residual toner in the first storage chamber R2. 2 It is desirable to be disposed at a location returning from the storage chamber R2 to the first storage chamber R1, but if it is disposed at such a location, the toner replenished to the toner replenishment opening 256 too close to the toner replenishment opening 256 The toner density may be measured directly. Therefore, the toner concentration sensor 255 is a first distance away from the toner supply opening 256 by a predetermined distance in consideration of such a trade-off factor in order to measure the toner concentration of the toner in the storage chamber R with higher accuracy. Arranged at the bottom of the storage chamber R1.

  Next, the operation of the printer apparatus CP according to the present embodiment will be described. First, the toner supply operation of the printer apparatus CP according to the present embodiment will be described. FIG. 5 is an explanatory diagram for explaining a toner supply operation according to the embodiment. The horizontal axis in FIG. 5 is a time axis indicating the passage of time, and the vertical axis is the toner level.

  In FIG. 5, when the color printer device CP is activated, the toner replenishment control unit 62 ignores the output from the toner density sensor 255 for a predetermined time to prevent malfunction, and then can continue development. A first toner replenishing step (normal replenishment mode) for replenishing toner to the storage chamber R so as to maintain the toner concentration of the toner in the storage chamber R is executed. More specifically, in this normal replenishment mode, the toner replenishment control unit 62 monitors the output of the toner density sensor 255 and when the toner level from the toner density sensor 255 becomes equal to or higher than the toner replenishment level during image formation. Then, the toner is replenished from the toner hopper while continuing the image forming operation.

  The controller 60 stores a replenishment duty table in which the toner level from the toner density sensor 255 and the ON time in PWM (Pulse Width Modulation) control of the toner motor are associated with each other. When the toner is replenished, by referring to this replenishment duty table, the toner motor is PWM-controlled during the on-time corresponding to the toner level from the toner concentration sensor 255, and according to the toner level from the toner concentration sensor 255. The toner is supplied from the toner hopper to the storage chamber R through the toner supply opening 256 at the toner supply speed.

  Thus, the toner replenishment level is a target value for maintaining the toner concentration of the toner in the storage chamber R so that the development can be continued with the image quality required by the specifications of the color printer device CP.

  On the other hand, when the toner supply cannot follow the toner consumption, or when an image that consumes a relatively large amount of toner, such as high-density printing, is formed, as shown in FIG. In addition, the toner level from the toner density sensor 255 further exceeds the toner supply level and exceeds the near-end determination threshold value Nth. When the state where the toner level exceeds the near-end determination threshold Nth continues for a predetermined time (empty level continuous detection time), the toner replenishment control unit 62 shifts from the normal replenishment mode to the treatment mode and performs a treatment.

  In this treatment mode, the toner replenishment control unit 62 first stops the developing operation and replenishes toner from the toner hopper while operating the agitators 2541 and 2542 (AP replenishment). When the toner level becomes equal to or lower than the treatment off level due to the replenishment of the toner, the operation of replenishing the toner from the toner hopper is stopped, and only the agitator is operated for a predetermined time (aging after AP replenishment).

  Further, in order to prevent erroneous determination of the transition to the treatment mode, the state in which the toner level exceeds the near-end determination threshold value Nth as described above is configured to shift to the treatment mode after continuing for a predetermined time.

  The near-end determination threshold Nth is a toner level corresponding to the toner density when the toner in the storage chamber R is near-end. The near end is a state where there is no toner or a state where there is almost no toner (toner density that cannot be developed with an image quality of a level required by the specifications of the color printer CP).

  Here, the toner replenishment control unit 62 changes the near-end determination threshold value Nth from the near-end determination threshold value Nth1 to the near-end determination threshold value Nth2 in the direction of decreasing density as the printing rate increases, and near-end determination as the printing rate decreases. The density is changed from the threshold value Nth2 to the near-end determination threshold value Nth1 in a higher direction. This is because, for example, when an image that consumes a relatively large amount of toner at a time, such as high-density printing, is formed, the toner level of the toner concentration sensor 255 may suddenly rise (the detected density drastically decreases) In some cases, the toner density in the storage chamber R of the developing device 25 is determined to be near end even though it is not near end, and an aging operation is performed. For this reason, for example, when an image that consumes a relatively large amount of toner at a time, such as high-density printing with a high printing rate, is formed, the near-end determination threshold Nth is increased from the near-end determination threshold Nth1 to the near-end determination threshold Nth2. Such a malfunction is prevented by changing in the low density direction.

  In this treatment mode, as shown in FIG. 5, the toner supply control unit 62 first executes an AP supply operation. More specifically, in this AP replenishment operation, the toner replenishment control unit 62 stops development and replenishes toner from the toner hopper while operating the first and second agitators 2541 and 2542.

  Next, the toner replenishment control unit 62 determines whether the toner level from the toner density sensor 255 is equal to or lower than the treatment off level. The treatment off level is set between the toner supply level and the near-end determination threshold value Nth1. As a result of this determination, when the toner level from the toner density sensor 255 becomes equal to or lower than the treatment off level, the control unit 60 executes non-replenishing aging after AP replenishment described later.

  Accordingly, the toner replenishment control unit 62 continues the AP replenishment operation until the toner concentration of the toner in the storage chamber R is equal to or lower than the treatment off level, and supplies toner to the storage chamber R while stopping development and stirring. The second toner replenishing step is executed.

  Then, when the toner level from the toner density sensor 255 decreases due to the toner supply by the AP supply operation, and the toner level from the toner density sensor 255 becomes equal to or lower than the treatment off level, the control unit 60 stops the development. The first toner stirring step (staging without replenishment after AP replenishment) is performed for a first predetermined time. More specifically, in the non-replenishing aging after the AP replenishment, the control unit 60 stops the operation of replenishing the toner from the toner hopper (that is, stops driving the toner motor), and the first and second agitation. Only the machines 2541 and 2542 are operated for a first predetermined time. The first predetermined time is set to, for example, a time that is half or more of a one-round time in which the toner circulates through the storage chamber R and makes one round.

  When the first predetermined time has elapsed, the toner replenishment control unit 62 then stops the development and performs the second agitation process for replenishing toner to the storage chamber R while performing agitation (aging with replenishment after AP replenishment). A second predetermined time is executed. More specifically, in the aging with replenishment after AP replenishment, the toner replenishment control unit 62 replenishes toner from the toner hopper at a toner replenishment speed corresponding to the toner level from the toner density sensor 255 (that is, toner motor). The first and second stirrers 2541 and 2542 are operated for a second predetermined time. The second predetermined time is set to, for example, one or more rounds in which the toner circulates through the storage chamber R and makes one round.

  When the second predetermined time has elapsed, the toner replenishment control unit 62 then executes a first toner agitation step (aging without replenishment after AP replenishment) for a first predetermined time, in which development is stopped and agitation is performed. . In this way, the first toner stirring step and the second toner stirring step are executed alternately.

  When the first predetermined time elapses, the toner replenishment control unit 62 ends the treatment mode, restarts the image forming operation, and replenishes toner in the normal replenishment mode. In the above-described embodiment, the toner is a non-magnetic material, but may be a magnetic material.

  Next, an image forming operation of the printer device CP according to the present embodiment will be described. The toner supply operation shown in FIG. 5 is performed in parallel with the image forming operation. FIG. 6 is a flowchart showing an example of an image forming operation of the printer apparatus CP shown in FIG.

  First, image data representing an image of a document to be printed is acquired from an external device such as a computer by the communication interface circuit 70 via the LAN 71 (step S1). Next, the paper interval setting unit 61 sets the enlargement time Te to 500 msec, and sets a variable n for counting the set number of sheets to 4, for example (step S2).

  The paper interval time T is obtained by adding the enlargement time Te to the shortest paper interval time Ts preset as the shortest paper interval time. The shortest paper interval time Ts is set according to the image forming speed of the image forming unit 20, for example, and is set to 100 msec, for example. That is, when the enlargement time Te is set to 500 msec, the paper interval time T is set to 600 msec (initial paper interval time) longer than the shortest paper interval time Ts.

  Next, the near end determination threshold value setting unit 63 sets the near end determination threshold value Nth to, for example, 600, which is the near end determination threshold value Nth1 (step S3).

  Next, in response to a control signal from the control unit 60, the recording paper P stored in the paper storage unit 10 is conveyed to the image forming unit 20. Then, in the image forming unit 20, the toner image for one page formed on the intermediate transfer belt 271 based on the image data received by the communication interface circuit 70 is transferred to the recording paper P by the secondary transfer roller 275, The image is fixed by the fixing unit 30 and discharged to the paper discharge tray 41. Then, the sheet is set such that the time from when the end of the recording sheet P passes through the secondary transfer roller 275 to when the leading end of the next recording sheet P reaches the secondary transfer roller 275 is the sheet interval time T. The next recording paper P stored in the storage unit 10 is transported by the transport mechanism 50, and the timing is adjusted by the registration rollers 51 (step S4).

  In this case, since the paper interval time T is set to 600 msec (initial paper interval time) longer than the shortest paper interval time Ts in the initial state, the printing rate is high from the first image data and the toner consumption is high. Even so, since the paper interval time T is set to 600 msec (initial paper interval time) longer than the shortest paper interval time Ts, the next image formation is performed after the first image formation of the first sheet is executed. As a result of increasing the time until execution, a time for performing the toner replenishment processing by the toner replenishment control unit 62 is secured, and the possibility that the toner replenishment to the developing device may not be in time can be reduced.

  Next, the sheet spacing setting unit 61 calculates the ratio of the number of dots on which toner is placed among all the dots in the image data for one page used for image formation in step S4 as the printing rate (step S4). S5).

  Next, the paper spacing setting unit 61 confirms whether or not the printing rate is 20% or more. If the printing rate is 20% or more (YES in step S6), it is determined that the printing rate is high and the paper spacing is high. The process proceeds to step S7 in order to increase the time T. On the other hand, if the printing rate is not less than 20% (NO in step S6), it is determined that the printing rate is low and it is determined whether to reduce the paper interval time T. The process proceeds to S13. In this case, 20% corresponds to an example of the first and second printing rates in the claims.

  The first printing rate is set in advance, for example, so that a relatively large amount of toner is consumed, and the toner supply of the toner supply control unit 62 operating in parallel with the image forming operation may not be in time. . The second printing rate is a printing rate that causes a relatively large amount of toner to be consumed, the toner level of the toner density sensor 255 is rapidly increased, and the toner supply control unit 62 may erroneously determine the near end. Are preset. In this case, the first and second printing rates are both set to 20%, but the first printing rate and the second printing rate may be set to different printing rates.

  Next, in step S7, the variable n is set to 0 by the sheet interval setting unit 61. Next, the paper interval setting unit 61 sets the expansion time Te corresponding to the printing rate based on the expansion time table TB shown in FIG. 4 (step S8).

  In the enlarged time table TB shown in FIG. 4, the printing performance is 3 of 20 sheets capable of printing 20 sheets per minute, 25 sheets capable of printing 25 sheets per minute, and 32 sheets capable of printing 32 sheets per minute. For each model, the printing rate, the enlargement time Te, and the printing speed are stored in association with each other. In the enlargement time table TB shown in FIG. 4, for example, the enlargement time Te becomes longer as the model has a higher printing speed. Note that the expansion time table TB does not need to correspond to a plurality of types of printing performance, and does not need to include a printing speed corresponding to the printing rate. For example, a 20-sheet printer having the corresponding printing performance may be included. It is only necessary that the print rate and the enlargement time Te in the printer apparatus CP are stored in association with each other.

  In addition, since the enlargement time table TB associates the print rate with the enlargement time Te so that the enlargement time Te increases in accordance with the increase in the print rate step by step in increments of 10%. The paper interval setting unit 61 sets the enlargement time Te corresponding to the print rate based on the enlargement time table TB, thereby increasing the paper interval time T in accordance with the increase in the print rate of the image data. It will decrease according to the decrease.

  In step S8, the expansion time Te may be set to a preset time, for example, 1000 msec, without using the expansion time table TB. This eliminates the need for selecting the enlargement time Te with reference to the enlargement time table TB, and sets the enlargement time Te based on the determination result in step S6 as to whether the printing rate is 20% or more. Therefore, the process of step S8 can be simplified.

  Next, the near-end determination threshold value setting unit 63 increases the near-end determination threshold value Nth and sets it to 650, which is a near-end determination threshold value Nth2 (step S9). Thereby, in step S6, when the printing rate becomes 20% (second printing rate) or more and there is a possibility that a relatively large amount of toner is consumed and the toner replenishment control unit 62 erroneously determines near end, The near-end determination threshold value setting unit 63 increases the near-end determination threshold value Nth and increases it from 600 (near-end determination threshold value Nth1) to 650 (near-end determination threshold value Nth2), thereby reducing the erroneous transition to the treatment mode. The

  Next, the paper gap setting unit 61 checks whether or not the image data acquired by the communication interface circuit 70 includes the image data of the next page (step S10), and if there is no next page (step S10). If the next page remains (YES in step S10), the enlargement time Te is added to the shortest paper interval time Ts to calculate and set the paper interval time T (step NO). S11), the process again proceeds to step S4, and after the end of the recording paper P on which the previous page has been imaged passes through the secondary transfer roller 275, the leading edge of the next recording paper P reaches the secondary transfer roller 275. The next recording paper P stored in the paper storage unit 10 is transported by the transport mechanism 50 so that the time until it reaches the newly set paper interval time T, and the registration roller Timing adjustment is performed at 1 (step S4).

  In this case, as the printing rate is higher and the toner consumption is increased, the paper interval time T is increased, and the time until the next image formation is executed after the image formation for one page is executed is increased. As a result, the time for performing the toner replenishment process by the toner replenishment control unit 62 is increased, and the possibility that the toner replenishment to the developing device may not be in time can be reduced. In addition, the inter-paper time T is adjusted according to the increase / decrease of the printing rate, that is, the increase / decrease of the toner consumption for one page, and the time for performing the toner replenishment process is increased / decreased. Is reduced.

  Next, in step S6, when the printing rate is less than 20% (NO in step S6), the paper interval setting unit 61 checks whether or not the enlargement time Te is zero (step S13), and the enlargement time Te. Is zero (YES in step S13), the enlargement time Te cannot be reduced any further, so the process proceeds to step S14 without changing the enlargement time Te, and if the enlargement time Te is not zero (in step S13). NO), the process proceeds to step S15 in order to confirm the number of images formed with the printing rate less than 20%, that is, the number of toner images transferred to the recording paper P by the secondary transfer roller 275.

  Next, in step S14, the near end determination threshold value setting unit 63 sets the near end determination threshold value Nth to 600 (near end determination threshold value Nth1) (step S14), and the process proceeds to step S10. Thus, even if the near-end determination threshold Nth is increased and set to 650 (near-end determination threshold Nth2) in order to avoid erroneous near-end detection due to a temporary increase in toner consumption, the printing rate Decreases to less than 20% (second printing rate), the near-end determination threshold value Nth is decreased to 600. Therefore, the near-end determination threshold value Nth remains increased during toner consumption at a normal image density. Thus, it is possible to reduce the delay in the near-end detection.

  In step S13, if the enlargement time Te is not zero (NO in step S13), 1 is added to the variable n by the paper interval setting unit 61 in step S15, and the image data in a state where the printing rate is reduced to less than 20%. The number of images formed on the basis of the number is counted. Next, the paper spacing setting unit 61 compares the variables n and 4 (step S16), and four or more sheets of images are continuously formed with the variable n being larger than 4 and thus the printing rate being less than 20%. If YES (YES in step S16), the enlargement time Te is set to zero, the paper interval time T is reduced (step S17), the near-end determination threshold Nth is further reduced to 600 (step S14), and the process proceeds to step S10. To do. Since the operation after step S10 is as described above, its description is omitted.

  On the other hand, in step S16, if the variable n is 4 or less, and therefore the image rate is less than 20% and four or more images are not continuously formed (YES in step S16), the enlargement time Te is changed. Without proceeding to step S18.

  As a result, for example, when the printing rate becomes less than 20% (NO in step S6), the toner replenishment is performed by immediately increasing the toner consumption by setting the enlargement time Te to zero without performing the processing of steps S15 and S16. The control of the toner density in the storage chamber R by the control unit 62 may not be in time, and the toner density may decrease. However, in the printer CP, even when the printing rate is less than 20% (NO in step S6), four or more sheets are continuously printed in a state where the printing rate is less than 20% by the processing in steps S15 and S16. Since the enlargement time Te is set to zero after waiting for the image formation, the toner concentration adjustment time in the storage chamber R by the toner replenishment control unit 62 can be secured.

  Further, when the printing rate is in the range of 20% or more (YES in step S6), the toner concentration in the storage chamber R is less affected by reducing the enlargement time Te. Therefore, in step S8, the enlargement time table TB is followed. When the enlargement time Te is reduced, the enlargement time Te is reduced without waiting for continuous image formation for a set number of sheets or more, and the printing speed is improved.

  For the first sheet on which image formation has started, 4 is substituted for the variable n as an initial value in step S2, so if the printing rate is less than 20% (NO in step S6). In step S15, 1 is added and n becomes 5. In step S16, it is determined that n is larger than 4 (YES in step S16), and the enlargement time Te is set to zero without waiting for the set number of images to be formed. The interval time T is set to the shortest sheet interval time Ts. As a result, when the sheet interval time T is increased as an initial value in step S2 on the first sheet on which image formation has started, waiting for image formation for a set number of sheets when the printing rate is less than 20%. Since the inter-paper time T can be immediately set to the shortest inter-paper time Ts without any increase, the decrease in the printing speed by unnecessarily increasing the inter-paper time T is reduced.

  Although the case where the set number of sheets is four is shown, the set number of sheets may be set as appropriate so that the toner replenishment control unit 62 can secure the toner concentration adjustment time in the storage chamber R.

  Next, in step S18, since the enlargement time Te is not set to zero and the sheet interval time T is increased, the near-end determination threshold value setting unit 63 maintains the near-end determination threshold value Nth at 650. The process proceeds to S10. Since the operation after step S10 is as described above, its description is omitted.

1 is a diagram illustrating a schematic configuration of a color printer apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of an electrical configuration of the color printer apparatus illustrated in FIG. 1. It is a figure for demonstrating the structure of the image development apparatus shown in FIG. It is a figure for demonstrating an example of an expansion time table. FIG. 4 is a diagram for explaining an operation of a toner supply control unit shown in FIG. 3. 3 is a flowchart illustrating an example of an image forming operation of the printer device illustrated in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus main body 20 Image forming part 21 Image forming unit 21C Cyan unit 21K Black unit 21M Magenta unit 21Y Yellow unit 22 Photosensitive drum 23 Charger 24 Exposure unit 25 Developing unit 25C Developing unit 25K Developing unit 25M Developing unit 25Y Developing device 27 Transfer device 30 Fixing unit 40 Paper discharge unit 50 Transport mechanism 60 Control unit 61 Paper gap setting unit 62 Toner replenishment control unit 63 Near-end determination threshold value setting unit 70 Communication interface circuit 275 Secondary transfer roller CP Printer device P Recording paper R , R1, R2 storage room T paper interval TB expansion time table Te expansion time

Claims (7)

An image data acquisition unit for acquiring image data representing an image;
A paper container for storing recording paper;
A toner storage chamber for storing toner;
A first toner replenishment control unit that adjusts the toner concentration in the toner storage chamber to a preset concentration;
By supplying the toner stored in the toner storage chamber to the photosensitive drum, the electrostatic latent image formed on the photosensitive drum is developed based on the image data acquired by the image data acquisition unit, A developing unit for forming a toner image;
A transfer portion for transferring the toner image to a recording paper;
A transport mechanism for transporting the recording paper stored in the paper storage unit to the transfer unit;
The inter-sheet time, which is the interval between the recording sheet conveyed to the transfer unit by the conveyance mechanism and the next recording sheet, with respect to the change in the increasing direction of the printing rate in the image data acquired by the image data acquisition unit An image forming apparatus, comprising: a paper gap setting unit that increases and decreases a change in the printing rate in a decreasing direction. The paper gap setting unit determines that the printing rate has increased when the printing rate exceeds a preset first printing rate, and the printing rate decreases when the printing rate is less than the first printing rate. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined to have performed. The paper gap setting unit sets the paper gap time when a toner image based on the image data in a state where the printing rate is reduced is transferred to the recording paper by the transfer unit for a preset number of sheets. The image forming apparatus according to claim 1, wherein the image forming apparatus decreases. The paper interval setting unit sets an initial paper interval time longer than the shortest paper interval time preset as the shortest paper interval time as an initial value of the paper interval time. The image forming apparatus according to claim 1. In the case where the sheet interval time is the initial sheet interval time as the initial value, the sheet interval setting unit, when the printing rate decreases, does not wait for the set number of sheets to be transferred without waiting for the sheet interval time. The image forming apparatus according to claim 4, wherein A toner concentration measuring unit for measuring the toner concentration of the toner in the toner storage chamber;
A second toner replenishment control unit configured to stop the development and replenish toner to the toner storage chamber when the toner concentration measured by the toner concentration measurement unit becomes a near-end determination threshold for detecting near-end;
A near-end determination threshold value setting unit that changes the near-end determination threshold value in a direction in which the density decreases in accordance with an increase in the printing rate and changes in a direction in which the density increases in response to a decrease in the printing rate. The image forming apparatus according to claim 1. The near-end determination threshold value setting unit determines that the printing rate has increased when the printing rate exceeds a preset second printing rate, and when the printing rate is less than the second printing rate, the printing rate is The image forming apparatus according to claim 6, wherein the image forming apparatus is determined to have decreased.

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