JP2010072341A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses excessive supply of toner to a developing part. <P>SOLUTION: After double-sided printing is continued by a predetermined number of sheets or more, a patch image is formed by a developing device 64 and density of the patch image is detected by a density sensor 224. When the density of the patch image detected by the density sensor 224 is thinner than target toner density stored in a target toner density memory 122, and a value of difference between them is equal to or above a predetermined value V1, a toner supply stop flag stored in a toner supply stop flag memory 124 is updated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an image forming unit having a charged image carrier and a developing unit that develops an electrostatic latent image formed on the surface of the image carrier using a two-component developer including a toner and a carrier is provided. As an image forming apparatus, an image forming apparatus capable of duplex printing is known. At the time of double-sided printing, first, in the image forming unit, the toner image developed on the surface of the image carrier by the developing unit is transferred to one side of the printing paper. Next, after the toner image is heated and fixed on one side of the printing paper by the fixing unit, the front and back sides of the printing paper are reversed and conveyed again to the image forming unit. In the image forming unit, the toner image developed on the surface of the image carrier by the developing unit is transferred to the other side of the printing paper, and the toner image is heated and fixed on the other side of the printing paper in the fixing unit.

  Here, at the time of double-sided printing, since the printing paper heated in the fixing unit and brought into a high temperature state is re-conveyed to the image forming unit, the temperature of the developing unit rises. In particular, when double-sided printing is continuously performed, the temperature in the developing unit rises remarkably, and the density of the toner image developed in the developing unit decreases.

By the way, as a technique for suppressing the temperature rise around the developing unit due to double-sided printing, for example, in Patent Document 1, when the temperature around the developing unit rises, the number of image formations per unit time is reduced. Further, in Patent Document 2, after the toner image is heated and fixed on one side of the printing paper, the printing paper is cooled at a predetermined interval and then conveyed again to the image forming unit, thereby increasing the temperature of the developing unit. Suppressed.
JP 2003-122192 A JP 2004-333930 A

  An object of the present invention is to obtain an image forming apparatus that suppresses excessive supply of toner to a developing unit.

  2. The image forming apparatus according to claim 1, wherein the latent image formed on the surface of the charged image carrier is developed with a two-component developer containing a carrier and toner, and a toner image is formed on the surface of the image carrier. An image forming unit that forms the toner image on a recording medium; a fixing unit that heat-fixes the toner image formed on the recording medium to the recording medium; and Reversing the front and back of the recording medium on which the toner image is fixed by the fixing unit, and re-conveying the recording medium to the image forming unit, and detecting the density of the density adjustment image formed by the developing unit And a density detection unit that is stored in the storage container according to a difference between the density of the image for density adjustment detected by the density detection unit and a target toner density that serves as a reference for the toner density of the two-component developer. Toner When the difference between the density of the density adjustment image detected by the density detection means and the target toner density after the toner supply means for supplying to the image portion and the double-sided printing continues for a predetermined number of sheets or more is a predetermined value or more, Toner supply control means for stopping toner supply by the toner supply means.

  The image forming apparatus according to claim 2, wherein the toner supply control unit stops the toner supply based on a density of a toner image formed on the surface of the image carrier when the toner supply by the toner supply unit is stopped. Toner is supplied to the developing unit by a supply means.

  The image forming apparatus according to claim 3, wherein when the toner supply control unit stops the toner supply by the toner supply unit, the temperature increase prevention control unit that activates the temperature increase prevention unit that prevents the temperature increase of the developing unit. It has.

  The image forming apparatus according to claim 4, wherein a plurality of the image forming units are provided along a conveyance direction of the recording medium, and the density detection unit is provided on the most downstream side in the conveyance direction of the recording medium. The density of the density adjustment image formed by the most downstream developing unit in the image forming unit is detected, and the toner supply control means detects that the difference between the density adjustment image density and the target toner density is a predetermined value or more. At this time, the toner supply to the most downstream developing unit by the toner supply means is stopped.

  The image forming apparatus according to claim 5, further comprising: a toner remaining amount calculating unit that calculates a remaining amount of toner in the storage container and the developing unit based on a density of a toner image formed on a surface of the image carrier. The toner supply control unit has a difference between the density of the density adjustment image detected by the density detection unit and the target toner density after the double-sided printing is continued for a predetermined number or more and a toner remaining amount. When the remaining amount of toner calculated by the amount calculation unit is equal to or greater than a predetermined value, the toner supply to the developing unit by the toner supply unit is stopped.

  The image forming apparatus according to claim 6, further comprising a temperature sensor that detects an environmental temperature, wherein the toner supply control unit detects the density adjustment image detected by the density detection unit after duplex printing has continued for a predetermined number of sheets or more. When the difference between the density of toner and the target toner density is equal to or greater than a predetermined value and the environmental temperature detected by the temperature sensor is equal to or greater than the predetermined value, the toner supply means stops supplying toner to the developing unit Let

  The image forming apparatus according to claim 7, wherein the temperature rise prevention means decelerates the image forming speed in the image forming unit.

  The image forming apparatus according to claim 8, wherein the temperature rise prevention unit decelerates the developing speed in the developing unit.

  The image forming apparatus according to claim 9, wherein the temperature rise prevention unit prohibits double-sided printing by the image forming unit.

  The image forming apparatus according to claim 10, wherein the temperature rise prevention unit prohibits image formation by the image forming unit.

  The image forming apparatus according to claim 11, wherein after the temperature rise prevention unit is activated, a difference between the density of the density adjustment image detected by the density detection unit and the target toner density becomes a predetermined value or more. The image forming operation stopping means for stopping the image forming operation is provided.

  The image forming apparatus according to claim 12, wherein after the temperature rise prevention unit operates, the number of printed sheets in the image forming unit exceeds a predetermined number, and the density adjustment image detected by the density detection unit is detected. An image forming operation stop unit is provided to stop the image forming operation when the difference between the density and the target toner density exceeds a predetermined value.

  According to the first aspect of the present invention, it is possible to suppress the excessive supply of toner to the developing unit as compared with the case where the present configuration is not provided.

  According to the second aspect of the present invention, it is possible to suppress a decrease in the toner concentration of the two-component developer as compared with the case where this configuration is not provided.

  According to the third aspect of the present invention, the temperature of the developing portion can be lowered early as compared with the case where the present configuration is not provided.

  According to the fourth aspect of the present invention, toner supply control to the developing unit can be simplified as compared with the case where the present configuration is not provided.

  According to the fifth aspect of the present invention, the influence of the remaining amount of toner on the determination accuracy of the toner supply stop determination unit can be suppressed as compared with the case where this configuration is not provided.

  According to the sixth aspect of the present invention, the temperature of the developing portion can be lowered as compared with the case where this configuration is not provided.

  According to the seventh aspect of the present invention, the temperature of the developing portion can be lowered compared to the case where the present configuration is not provided.

  According to the eighth aspect of the present invention, the temperature of the developing portion can be lowered as compared with the case where this configuration is not provided.

  According to the ninth aspect of the present invention, the temperature of the developing portion can be lowered as compared with the case where this configuration is not provided.

  According to the tenth aspect of the present invention, the temperature of the developing portion can be lowered as compared with the case where this configuration is not provided.

  According to the eleventh aspect of the present invention, it is possible to prevent a failure of the developing unit due to an abnormality as compared with the case where the present configuration is not provided.

  According to the twelfth aspect of the present invention, it is possible to prevent failure of the developing unit due to abnormality as compared with the case where the present configuration is not provided.

  FIG. 1 shows an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes an image forming apparatus main body 12, and a paper feed tray 14 in which print sheets P (recording media) are stacked and stored in a bundle is disposed below the image forming apparatus main body 12. Has been.

  A pickup roll 16 is disposed immediately above the front end side (right end side in FIG. 1) of the paper feed tray 14 to send out the print paper P from the paper feed tray 14 in pressure contact with the front end side of the upper surface of the print paper P. .

  On the downstream side of the pickup roll 16, a plurality of (for example, two) transport roll pairs 24 that sandwich and transport the printing paper P, and a registration roll pair 25 for skew correction of the printing paper P are arranged. Between the transport roll pair 24 and the registration roll pair 25, a first transport path 22 is formed that extends from the nip portion of the transport roll pair 24, gently curves upward, and extends to the nip portion of the registration roll pair 25.

  The printing paper P transported from the paper feed tray 14 is guided upward by the first transport path 22, temporarily stopped by the registration roll pair 25, and then between a photosensitive drum 30 and a transfer device 38 described later at a predetermined timing. It is conveyed between.

  The image forming apparatus main body 12 is provided with a conveyor belt 26 in the vertical direction. The conveyor belt 26 is stretched between a tension roller 27 disposed above and a tension roller 29 disposed below, and the tension belt 27 or the tension roller 29 is rotationally driven, whereby the conveyor belt 26 is rotated. 26 rotates (circulation drive) in a predetermined direction (arrow A direction). On the upstream side of the conveyance belt 26 in the sheet conveyance direction, a charging roll 31 that charges the surface of the conveyance belt 26 and presses the printing sheet P electrostatically attracted to the conveyance belt 26 against the conveyance belt 26 is provided on the conveyance belt 26. It is provided adjacent to.

  A plurality of process cartridges 28Y, 28M, 28C, and 28K corresponding to the respective colors of yellow, magenta, cyan, and black are vertically arranged in the vertical direction facing the conveyance belt 26. Each process cartridge 28Y, 28M, 28C, 28K includes a photoreceptor unit 35 and a developing device 64 (developing unit).

  The photoreceptor unit 35 includes a photoreceptor drum 30 (image carrier) that is rotationally driven, a charging roller 32, and a cleaning device 39. The charging roller 32 uniformly charges the surface of the photosensitive drum 30, and the cleaning device 39 removes the toner remaining on the photosensitive drum 30.

  An exposure device 34 is arranged in the vertical direction on the side of each process cartridge 28Y, 28M, 28C, 28K. The exposure device 34 irradiates the photosensitive drum 30 uniformly charged by the charging roller 32 with a laser to form an electrostatic latent image on the photosensitive drum 30.

  As shown in FIGS. 1 and 2, the developing device 64 opposes the photosensitive drum 30 and converts the electrostatic latent image on the photosensitive drum 30 into a visible image with a two-component developer G composed of toner and a magnetic carrier. And a toner supply unit 70 (storage container) for supplying toner to the developing unit 68.

  The developing unit 68 includes a housing 80, and a developer storage chamber 84 is formed in the housing 80. The developer storage chamber 84 is filled with a two-component developer G corresponding to each color of yellow (Y), magenta (M), black (K), and cyan (C). As the developer, a two-component developer including a toner and a carrier is used. The toner contains at least a binder resin and a colorant, and an external additive is added depending on the purpose. As the carrier, magnetic powder such as iron is applied, and the surface of the magnetic powder may have a resin coating layer.

  Further, in the developer storage chamber 84, a developing roller 86 as a developer carrying member, an auger 88 for agitating and conveying the two-component developer G, an auger 89, and the amount of the two-component developer G on the developing roller 86 A developer regulating roll 50 that regulates the above is provided.

  The developing roller 86 is disposed to face the photosensitive drum 30. The developing roller 86 includes a cylindrical sleeve 86A made of a nonmagnetic conductive material and a magnet roll 86B disposed in the hollow of the sleeve 86A, and is rotatably supported by the housing 80. The magnet roll 86B is fixedly supported, and the sleeve 86A is configured to rotate around the magnet roll 86B in a fixed direction (arrow B direction) by a driving source (not shown). A predetermined developing bias VB (for example, a voltage in which alternating current is superimposed on direct current) is applied to the sleeve 86A from a developing bias power source (not shown). Further, a developing electric field is formed between the developing roller 86 and the photosensitive drum 30 by the developing bias VB applied to the sleeve 86A.

  The auger 88 and the auger 89 are disposed below the developing roller 86. The auger 88 and the auger 89 are rotatably supported on the peripheral wall of the housing 80 and convey the two-component developer G to the developing roller 86 while stirring. As a result, each toner in the two-component developer G is frictionally charged to a predetermined polarity. The conveyed two-component developer G is supplied to the developing roller 86 and is carried in a state where a magnetic brush is formed on the surface of the developing roller 86.

  A developer regulating roll 50 is disposed at a position facing the developing roller 86. A predetermined gap is provided between the developer regulating roll 50 and the developing roller 86, and the developer regulating roll 50 allows a magnetic brush made of the two-component developer G carried on the surface of the developing roller 86 to have a predetermined gap. It is regulated to be thick. When the magnetic brush regulated to a predetermined thickness by the developer regulating roll 50 reaches a position facing the surface of the photosensitive drum 30, only the toner contained in the two-component developer G is developed by the developing electric field. It adheres to the electrostatic latent image portion formed above, is visualized as a toner image, and is developed.

  The toner supply unit 70 provided adjacent to the developing unit 68 includes a toner storage chamber 150, and a replenishment toner T is stored in the toner storage chamber 150. In addition, a toner agitating and conveying member 152 that agitates and conveys the replenishment toner T is provided inside the toner storage chamber 150.

  The toner storage chamber 150 and the developer storage chamber 84 are partitioned by a wall portion 154, and a dispense chamber 158 is formed below the wall portion 154. The toner storage chamber 150 and the developer storage chamber 84 communicate with each other through an opening 162 and a toner supply port 164 formed on the side wall of the dispense chamber 158. In addition, a dispense auger 160 (toner supply means) is provided inside the dispense chamber 158. The dispense auger 160 is configured to be rotationally driven by a motor (not shown), and the replenishing toner T accommodated in the toner accommodating chamber 150 is caused to rotate in the dispensing chamber 158 by rotationally driving the dispensing auger 160. Then, the toner is supplied from the toner supply port 164 to the developer storage chamber 84.

  As shown in FIG. 1, a transfer device 38 that transfers toner images formed on the photosensitive drum 30 to the printing paper P on the inner peripheral side of the conveying belt 26 in the lateral direction facing the photosensitive drum 30. Is provided.

  Further, a density sensor 224 (density detection means) is disposed on the side of the conveyor belt 26 so that its detection surface faces the circumferential surface of the conveyor belt 26. The density sensor 224 is a reflective sensor, and irradiates light from a light emitting element such as an LED onto a patch image (density adjustment image) formed at a detection position on the surface of the conveyor belt 26, and the reflected light. Is detected by a light receiving element such as a photodiode, and an electric signal corresponding to the density value of the patch image is output to the main controller 202 described later.

  The image forming unit 36 according to the present embodiment includes the above-described photosensitive drum 30, the charging roller 32, the exposure device 34, the developing device 64, and the transfer device 38.

  A second transport path 23 is formed on the downstream side of the transport belt 26 in the paper transport direction to guide the print paper P sent from the transport belt 26 to the discharge tray 20. In the second transport path 23, a fixing device 40 that fixes the transferred toner image onto the printing paper P, a transport roll pair 42 that sandwiches and transports the printing paper P, and a discharge roll that discharges the printing paper P to the discharge tray 20. The pair 44 (re-conveying means) is arranged in this order. The fixing device 40 has a heat source, and fixes the toner image on the printing paper P by pressurizing and heating the sheet on which the toner image is transferred.

  In addition, a third conveyance path 46 (re-conveying means) for returning the printing paper P switched back by the discharge roll pair 44 back to the registration roll pair 25 is formed at a position facing the conveyance belt 26. In this third transport path 46, a plurality (for example, two) of transport roll pairs 48 (re-transport means) for holding and transporting the printing paper P downward are arranged, and an image is formed on one side during duplex printing. The printed paper P is switched back by the discharge roll pair 44 and guided to the third conveyance path 46, conveyed downward by the plurality of conveyance roll pairs 48, and niped to the registration roll pair 25 by the reverse roller 49 (reconveying means). To be conveyed.

  Next, an image forming operation for forming an image in the image forming apparatus according to the present embodiment will be described.

  In the image forming apparatus according to the present embodiment, when an image is formed on the printing paper P, first, the printing paper P taken out from the paper feed tray 14 is conveyed to the registration roll pair 25 by the plurality of conveyance roll pairs 24, and Skew correction is performed by the registration roll pair 25, and the sheet is fed to the conveyance belt 26 disposed in the image forming apparatus main body 12. The printing paper P sent to the conveyor belt 26 is pressed against the conveyor belt 26 by the charging roll 31 and is electrostatically attracted to the electrified conveyor belt 26 and conveyed upward, and yellow, magenta, cyan, and black are printed. Sequentially sent to a predetermined transfer position corresponding to each color.

  On the printing paper P sent to a predetermined transfer position, the toner images of the respective colors formed on the photosensitive drum 30 are transferred by the transfer device 38 to form a full color image. Further, the toner image conveyed and transferred to the fixing device 40 is fixed by the fixing device 40.

  When an image is formed only on one side of the printing paper P (during single-sided printing), after the toner image is fixed, the printing paper P is discharged to the discharge tray 20 by the discharge roll pair 44. On the other hand, when an image is formed on both sides of the printing paper P (during double-sided printing), after the image is formed on one side, the printing paper P is switched back by the discharge roll pair 44 and reversed to the third transport path. It is sent to 46. Further, the sheet is fed again from the third conveyance path 46 to the registration roll pair 25, an image is formed on the opposite surface where no image is recorded, and an image is formed on both sides of the printing paper P.

  Next, a schematic configuration of the control system in the image forming apparatus according to the present embodiment will be described.

  FIG. 3 is a block diagram showing the main part of the control system for the image forming operation. The main power management unit 200 is connected to a commercial power source (not shown), generates low voltage power and high voltage power, and supplies driving power to each unit via a power supply line.

  A user interface 220 is connected to the main controller 202 (toner supply control means, temperature rise prevention means, temperature rise prevention control means, image forming operation stop means, toner remaining amount calculation means) and relates to image formation and the like by user operation. An instruction is given, and information such as when an image is formed is notified to the user.

  The main controller 202 is connected to a network line with an external host computer and scanner (not shown) so that image data can be input.

  When the image data is input, the main controller 202 analyzes the print instruction information included in the image data and the image data, converts the print data into a format suitable for the image forming unit 36 (for example, bitmap data), and the image data. Image data is sent to the formation processing control unit 206.

  The image formation processing control unit 206 synchronizes each of the optical scanning system control unit 208, the drive system control unit 210, the charger control unit 212, the developing device control unit 214, and the fixing control unit 216 based on the input image data. Control and execute image formation.

  The main controller 202 is connected to a temperature sensor 222 for detecting the environment. The temperature sensor 222 detects the environmental temperature outside the image forming apparatus main body 12 and outputs the detected temperature to the main controller 202.

  Further, a density sensor 224 that detects the density of the patch image is connected to the main controller 202. The patch image is a toner image formed for toner density adjustment, and is used for adjusting the density of the toner image formed on the printing paper P.

  FIG. 4 is a block diagram functionally showing a control system related to toner density control in the main controller 202. This block diagram functionally divides the processing necessary for the control relating to the toner density adjustment, and does not limit the hardware configuration.

  The main controller 202 includes a CPU, a ROM, a RAM, and the like. The main controller 202 exchanges various data and signals, and controls the entire image forming apparatus 10 by executing various programs stored in the ROM. . In addition, the predetermined area of the RAM stores the number of duplex prints and the density value of the patch image detected by the density sensor 224 for each duplex print instruction from the user.

  The main controller 202 includes a toner supply amount calculation unit 110 (toner supply control unit), a motor drive control unit 112 (toner supply control unit), a toner supply stop determination unit 114 (toner supply control unit), and a temperature rise elimination unit control unit 116. (Temperature rise prevention control means), a toner supply stop cancellation determination unit 118 (toner supply control means), an abnormality detection unit 120 (image forming operation stop means), a target toner concentration memory 122, and a toner supply stop flag memory 124. Yes.

  Here, the main controller 202 performs toner concentration control for setting the toner concentration of the two-component developer G (ratio of toner in the two-component developer G) to an appropriate value. In the toner density control, a toner consumption amount is estimated from the density of the toner image formed on the surface of the photoconductive drum 30, and a toner amount corresponding to the estimated consumption amount is replenished. This is performed in combination with a method of estimating the excess or deficiency of the toner amount from the difference value between the detection result and the target toner density and replenishing the toner so that the excess or deficiency is eliminated.

  The toner supply amount calculation unit 110 calculates the supply amount of toner supplied to the developer storage chamber 84 (see FIG. 2) of the development unit 68. A difference value between the toner supply amount R 1 based on the density of the toner image formed on the surface of the photosensitive drum 30, and the target toner density stored in the target toner density memory 122 and the density of the patch image detected by the density sensor 224. The toner supply amount R2 is calculated from the toner supply amount R2, and the toner supply amount R calculated based on the toner supply amounts R1 and R2 is transmitted to the motor drive control unit 112. The toner image density is the number of pixels (pixels) of the toner image, which is counted when image data for forming the toner image is generated, and is temporarily stored in the RAM of the main controller 202. In addition, the toner supply amount calculation unit 110 calculates the toner supply amount R2 only when a toner supply stop flag stored in a toner supply stop flag memory 124 described later is 0 (initial value). The target toner density memory 122 stores predetermined values V1, V2, V3, and V4, which will be described later, in addition to the target toner density.

  The motor drive control unit 112 increases or decreases the rotation time of a motor (not shown) that drives the dispense auger 160 (see FIG. 2), and supplies toner corresponding to the toner supply amount R to the developing unit 68. In the image forming apparatus 10 according to the present embodiment, the rotation speed of the dispense auger 160 is constant, and the toner supply amount is adjusted by increasing / decreasing only the rotation time. Therefore, the toner supply amount R is calculated as the toner replenishment time (the rotation time of the dispense auger 160).

  The toner supply stop determination unit 114 determines that the density of the patch image detected by the density sensor 224 after the duplex printing is continued for a predetermined number of sheets or more is lower than the target toner density stored in the target toner density memory 122, and the difference between them is predetermined. When the value is equal to or greater than V1, the toner supply stop flag (initial value: 0) stored in the toner supply stop flag memory 124 is updated (stopped: 1). As a result, the toner supply amount calculation unit 110 calculates only the toner supply amount R1 based on the density of the toner image (the toner supply amount R2 based on the density of the patch image is not calculated).

  When the toner supply stop flag stored in the toner supply stop flag memory 124 is 1 (stopped), the temperature rise canceling means control unit 116 controls the main controller 202 not to accept a double-sided print instruction from the user. To temporarily stop the duplex printing function. As a result, the heated printing paper P is not conveyed again to the image forming unit 36, and the temperature rise in the developing device 64 is suppressed.

  The temperature rise canceling means control unit 116 transmits a control signal to the main controller 202 so as not to accept not only a double-sided printing instruction but also a single-sided printing instruction from the user, and temporarily stops the image forming operation itself. Alternatively, the number of images formed per unit time may be temporarily reduced. Further, the rotational speed of the developing roller 86 may be reduced within a range that does not deteriorate the image quality. By reducing the rotation speed of the developing roller 86, the frictional heat between the sleeve 86A and the two-component developer G is suppressed, and the temperature rise of the developing device 64 is suppressed.

  In the toner supply stop cancellation determination unit 118, the toner density based on a predetermined condition, for example, the number of single-sided printing performed after stopping the toner density control based on the density of the patch image exceeds the predetermined number, or the toner density based on the density of the patch image. When the elapsed time after stopping the control exceeds a predetermined time, the toner supply stop flag stored in the toner supply stop flag memory 124 is updated assuming that the temperature rise of the developing device 64 has been canceled ( During stop: 1 → Initial value: 0). As a result, the toner supply amount calculation unit 110 calculates the toner supply amount R1 based on the density of the toner image and the toner supply amount R2 based on the density of the patch image.

  The abnormality detection unit 120 determines that the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122 and the difference is equal to or greater than the predetermined value V3. The image forming operation in is stopped. This is a function for removing an adverse effect caused by the fact that the density sensor 224 cannot detect the correct toner density when the toner density of the two-component developer G decreases or increases due to some cause. When such an abnormality is detected, the abnormality detection unit 120 transmits a stop control signal for stopping the image forming operation to the main controller 202. The main controller 202 that has received the stop control signal transmits a control signal to the image forming process control unit 206 to stop the image forming operation, and outputs a message to the user interface 220 that the image forming operation has been stopped to To inform.

  Next, the operation of toner density control will be described.

  The toner density control is performed by the main controller 202 executing various processes for each image forming operation. In the present embodiment, toner density control is performed only for the developing device 64 arranged on the most downstream side in the conveyance direction of the printing paper P. This is because the developing device 64 is closest to the fixing device 40 having a heat source and is more susceptible to temperature rise than the other developing devices 64.

  The toner supply amount supplied to the developing device 64 is calculated according to the flowchart shown in FIG. First, in step 250, the density of the toner image stored in the RAM of the main controller 202 is read. In step 252, the toner supply amount R1 based on the density is calculated as the toner replenishment time (the rotation time of the dispense auger 160).

  Upon receiving the toner supply amount R, the motor drive control unit 112 increases or decreases the rotation time of a motor (not shown) that drives the dispense auger 160 (see FIG. 2) in accordance with the toner supply amount R, and sends it to the developing unit 68. Supply toner T is supplied.

  Next, in step 254, the toner supply stop flag stored in the toner supply stop flag memory 124 is read, and it is determined whether or not the toner supply stop flag is 1 (stopped). In 256, the toner supply amount R1 is substituted for the toner supply amount R, the toner supply amount R is transmitted to the motor drive control unit 112, and the process is terminated.

  If the determination in step 254 is negative, a control signal for creating a patch image is transmitted to the image formation processing control unit 206 in step 258. Upon receiving the control signal, the image forming process control unit 206 controls the developing device control unit 214 to form a patch image on the transport belt 26. The density of the patch image detected by the density sensor 224 is output to the main controller 202.

  In step 260, the patch image density is read from the RAM of the main controller 202 and the target toner density is read from the target toner density memory 122. Next, in step 262, the toner supply amount R2 is calculated according to the difference between the density sensor 224 and the target toner density, and in step 264, the toner supply amounts R1 and R2 are substituted into the toner supply amount R (= R1 + R2). Then, the toner supply amount R is transmitted to the motor drive control unit 112, and the process ends.

  Next, the flow of toner supply stop determination based on the density of the patch image will be described with reference to the flowchart shown in FIG.

  First, in step 270, the continuous duplex printing number stored in the RAM of the main controller 202 is read. Next, in step 272, it is determined whether or not the number of continuous double-sided printed sheets is a predetermined number (300 sheets in the present embodiment) or more. If the determination is negative, the process ends.

  If the determination in step 272 is affirmative, a control signal for creating a patch image is transmitted to the image forming process control unit 206 in step 274. Upon receiving the control signal, the image forming process control unit 206 controls the developing device control unit 214 to form a patch image on the transport belt 26. The density of the patch image detected by the density sensor 224 is output to the main controller 202.

  Next, in step 276, the density of the patch image stored in the RAM of the main controller 202 is read, and the target toner density is read from the target toner density memory 122. Next, in step 278, the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122, and the difference value is a predetermined value V1 (0 in this embodiment). .2V) or more is determined, and if the determination is negative, the process ends.

  If the determination in step 278 is affirmative, in step 280, the toner supply stop flag stored in the toner supply stop flag memory 124 is updated to 1 (stopped), and the stop update signal is sent to the temperature rise canceling means control unit 116. Send and finish the process.

  Receiving the stop update signal, the temperature rise canceling means control unit 116 transmits a stop control signal to the main controller 202 so as not to accept a double-sided printing instruction from the user, and temporarily stops the double-sided printing function. Receiving the stop control signal, the main controller 202 outputs a message to the user interface 220 indicating that the duplex printing function has been stopped, and notifies the user. As a result, the heated printing paper P is not conveyed again to the image forming unit 36, and the temperature rise in the developing device 64 is suppressed. Further, the main controller 202 counts the number of single-sided printed sheets after receiving the stop control signal, and accumulates and stores the single-sided printed sheet count value in a predetermined area of the RAM. Further, the main controller 202 stores the stop start time when the stop control signal is received in a predetermined area of the RAM.

  Note that when the temperature rise canceling means control unit 116 temporarily reduces the number of images formed per unit time or reduces the rotation speed of the developing roller 86 within a range that does not deteriorate the image quality, A corresponding control signal is transmitted to the image forming process control unit 206. Upon receiving the control signal, the image formation processing control unit 206 transmits the control signal to the drive system control unit 210 or the fixing control unit 216, and controls the number of images formed per unit time and the rotation speed of the developing roller 86.

  Next, the flow of toner supply start determination based on the density of the patch image will be described with reference to the flowchart shown in FIG.

  First, at step 290, the toner supply stop flag stored in the toner supply stop flag memory 124 is read out, and it is determined whether or not the toner supply stop flag is 1 (stopped). And the toner supply stop control based on the density of the patch image is continued.

  If the determination in step 290 is affirmative, in step 292, the single-sided printing sheet count value is read from the RAM of the main controller 202, and whether or not the single-sided printing sheet count value is equal to or greater than a predetermined number (100 sheets in this embodiment). Determine. If the determination is affirmative, it is considered that the temperature increase of the developing device 64 has been eliminated, and in step 294, the toner supply stop flag stored in the toner supply stop flag memory 124 is updated to 0 (initial value). The start update signal is transmitted to the temperature rise canceling means control unit 116, and the process is terminated. Receiving the start update signal, the temperature rise canceling means control unit 116 transmits a start control signal that enables reception of a double-sided printing instruction from the user to the main controller 202 to cancel the suspension of the double-sided printing function.

  If the determination in step 292 is negative, in step 296, the stop start time is read from the RAM of the main controller 202, the stop start time is compared with the machine time (current time), and a predetermined time (this time) is determined from the stop start time. In the embodiment, it is determined whether or not 5 minutes have elapsed, and if the determination is affirmative, it is considered that the temperature increase of the developing device 64 has been eliminated, and the process of step 294 is performed.

  If the determination in step 296 is negative, a control signal for creating a patch image is transmitted to the image forming process control unit 206 in step 298. Upon receiving the control signal, the image forming process control unit 206 controls the developing device control unit 214 to form a patch image on the transport belt 26. The density of the patch image detected by the density sensor 224 is output to the main controller 202.

  Next, in step 300, the density of the patch image stored in the RAM of the main controller 202 is read and the target toner density is read from the target toner density memory 122. Next, in step 302, the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122, and the difference is a predetermined value V2 (in this embodiment, 0. 0). 1V) is determined. If the determination is affirmative, it is assumed that the temperature rise of the developing device 64 has been eliminated, and the process of step 294 is performed. If the determination is negative, the process ends and toner supply based on the density of the patch image is performed. Continue the stop control.

  Next, the flow of toner density abnormality detection will be described with reference to the flowchart shown in FIG.

  First, at step 310, a control signal for creating a patch image is transmitted to the image forming process control unit 206. At step 312, the density of the patch image stored in the RAM of the main controller 202 is read and the target toner density memory 122 is read. The target toner density is read out from.

  Next, in step 314, the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122, and the difference value is a predetermined value V3 (in this embodiment, 0). .3V) or higher is determined. If the determination is affirmative, in step 316, a control signal for stopping the image forming operation is transmitted to the main controller 202, and the process ends. The main controller 202 that has received the control signal controls the image forming process control unit 206 to stop all image forming processes and outputs a message to the user interface 220 that the image forming operation has been stopped. As a result, it is assumed that an abnormality has occurred in the developing device 64 due to factors other than the temperature rise of the developing device 64 due to double-sided printing, and the image forming operation is stopped.

  If the determination in step 314 is negative, in step 318, the single-sided printed sheet count value is read from the RAM of the main controller 202, and whether or not the single-sided printed sheet count value has exceeded a predetermined number (50 sheets in this embodiment). If the determination is negative and the determination is negative, the process ends.

  If the determination in step 318 is affirmative, in step 320, a control signal for creating a patch image is transmitted to the image formation processing control unit 206, and in step 322, the density of the patch image output from the density sensor 224, and the target The target toner density is read from the toner density memory.

  Next, in step 324, the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122, and the difference value is a predetermined value V4 (in this embodiment, 0). .25V) or more is determined, and if the determination is affirmative, the process of step 316 is performed. Thus, even if the determination in step 314 is negative, the toner density of the patch image is detected again after the number of single-sided printed sheets after the toner supply stop exceeds a predetermined number (50 sheets in this embodiment). If the toner density is not improved (increased) to a predetermined value V4 set in advance, it is assumed that an abnormality has occurred in the developing device 64 due to factors other than a temperature rise of the developing device 64 due to double-sided printing. Then, the image forming operation is stopped. If the determination in step 324 is negative, the process ends.

  In the present embodiment, toner density control as described above is performed. In the present embodiment, the toner density control is performed only for the developing device 64 arranged on the most downstream side in the conveyance direction of the printing paper P. However, the present invention is not limited to this, and all the developing devices 64 are controlled. In this case, it is possible to determine whether to stop supplying toner to each developing device 64 based on the density of the patch image formed by each developing device 64, or to develop the toner. The toner supply stop determination may be performed based only on the density of the patch image formed by the device 64, and the other developing device 64 may be controlled according to the determination result.

  Further, in the toner supply stop determination based on the density of the patch image (see FIG. 6), the determination accuracy is improved by considering the installation environment of the image forming apparatus 10 and the toner remaining amount in the developing device 64. That is, when the temperature of the environment in which the image forming apparatus 10 is installed reaches, for example, about 30 degrees, the density of the toner image formed on the surface of the photosensitive drum 30 tends to be high. Further, when the remaining amount of toner in the developing device 64 decreases, the density of the toner image naturally decreases. By eliminating the decrease in the density of the toner image due to factors other than double-sided printing, the determination accuracy is improved.

  Specifically, as shown in the flowchart of FIG. 9, first, in step 330, the continuous duplex printing number stored in the RAM of the main controller 202 is read. Next, in step 332, it is determined whether or not the number of continuous duplex prints is equal to or greater than a predetermined number (300 in this embodiment). If the determination is negative, the process ends.

  If the determination in step 332 is affirmed, whether or not the detected temperature (temperature outside the image forming apparatus main body 12) detected by the temperature sensor 222 in step 314 is equal to or higher than a predetermined temperature (28 degrees in the present embodiment). If the determination is negative and the determination is negative, the process ends.

  If the determination in step 334 is affirmative, the remaining amount of toner in the developing device 64 is calculated in step 336. The remaining amount of toner is calculated by estimating the toner consumption from the cumulative value of the density of the toner image formed on the surface of the photosensitive drum 30. The remaining amount of toner is a ratio of the remaining amount of toner to the amount of toner when not used, and is calculated as a percentage. Next, in step 338, it is determined whether or not the remaining amount of toner in the developing device 64 is greater than or equal to a predetermined amount (in this embodiment, 20 percent). If the determination is negative, the process ends.

  Next, if the determination in step 338 is affirmative, in step 340, a control signal for creating a patch image is transmitted to the image formation processing control unit 206, and in step 342, the density of the patch image output from the density sensor 224 is transmitted. , And the target toner density is read from the target toner density memory. Next, in step 344, the density of the patch image detected by the density sensor 224 is lighter than the target toner density stored in the target toner density memory 122, and the difference value is a predetermined value V1 (0 in this embodiment). .2V) or more is determined, and if the determination is negative, the process ends.

  If the determination in step 344 is affirmative, in step 346, the toner supply stop flag stored in the toner supply stop flag memory 124 is updated to 1 (stopped), and the stop update signal is updated to the temperature rise canceling means control unit 116. To finish the process.

  In this embodiment, the developing unit 68 and the toner supply unit 70 are integrally formed. However, as shown in FIG. 10, the developing unit 68 and the toner supply unit 130 (storage container) are separated from each other. The toner supply unit 130 may be configured to be replaceable.

  A supply pipe 132 is provided in the toner supply unit 130 in which the replenishment toner T is stored. By connecting the supply pipe 132 to the developing unit 68, the replenishment toner T can be supplied from the toner storage chamber 150 of the toner supply unit 130 to the developer storage chamber 84 of the development unit 68. A dispense auger 134 (toner supply means) is rotatably provided inside the supply pipe 132. The dispense auger 134 is provided with a spiral projection, and the replenishing toner T accommodated in the toner accommodating chamber 150 is routed through the supply pipe 132 by rotating the dispense auger 134 by a motor (not shown). Then, the developer is supplied to the developer storage chamber 84. In other words, the toner concentration of the two-component developer G is adjusted by controlling the motor connected to the dispense auger 134 and increasing / decreasing the rotation time of the dispense auger 134.

  Further, the density sensor 224 is not limited to the one that detects the density of the patch image formed on the conveyance belt 26, and may be the one that detects the density of the patch image formed on the surface of the photosensitive drum 30.

  Further, the processing shown in FIGS. 5 to 9 may be performed not when each image forming operation is performed but when the number of printed sheets reaches a predetermined specified value or more.

  Further, the toner density control processing (see FIGS. 5 to 9) described in the above embodiment is an example, and unnecessary steps are deleted or new steps are performed without departing from the gist of the present invention. Needless to say, they can be added or the processing order can be changed.

  In the present embodiment, various parameters (for example, the number of continuous duplex prints, the predetermined value V1 to the predetermined value V4, etc.) in toner density control are based on experiments using actual machines, computer simulations based on actual machine design specifications, and the like. However, the design may be changed as appropriate according to the installation environment of the image forming apparatus 10, and the present invention is not limited to the above-described embodiment.

  The present invention is not limited to the present embodiment, and various modifications, changes, and improvements can be made without departing from the gist of the present invention.

1 is a schematic configuration diagram illustrating an entire image forming apparatus according to an exemplary embodiment. FIG. 2 is a schematic enlarged cross-sectional view of a developing device according to the present embodiment. FIG. 3 is a control block diagram illustrating a schematic configuration of a control system for image formation in an image forming unit of the image forming apparatus according to the embodiment. FIG. 4 is a block diagram functionally showing toner density control in the main controller according to the present embodiment. 6 is a flowchart showing a flow of toner supply amount calculation processing according to the present embodiment. 6 is a flowchart showing a flow of processing for determining whether to stop supplying toner based on the density of a patch image according to the present embodiment. 6 is a flowchart showing a flow of processing for determining toner supply start based on the density of a patch image according to the present embodiment. 6 is a flowchart showing a flow of processing for detecting an abnormality in toner density according to the present embodiment. 10 is a flowchart showing a flow of processing of a modified example of toner supply stop determination based on the density of a patch image according to the present embodiment. It is a general | schematic expanded sectional view of the modification of the developing device which concerns on this embodiment.

Explanation of symbols

10 Image forming apparatus 30 Photosensitive drum (image carrier)
36 Image forming unit 40 Fixing device (fixing unit)
44 discharge roll pair 46 transport path (re-transport means)
48 Transport roll pair (re-transport means)
49 Reverse roller (re-carrying means)
64 Developing device (developing part)
70 Toner supply unit (storage container)
112 Motor drive control unit (toner supply control means)
114 Toner supply stop determination unit (toner supply control means)
116 Temperature rise elimination means control unit (temperature rise prevention means)
120 Abnormality detection unit (image forming operation stop means)
130 Toner supply unit (storage container)
134 Dispense Auger (Toner Supply Unit)
160 Dispensing Auger (Toner Supply Unit)
202 Main controller (toner supply control means, temperature rise prevention means, toner remaining amount detection means, image forming operation stop means)
222 Temperature sensor 224 Concentration sensor (Concentration detection means)
G Two-component developer P Printing paper (recording medium)

Claims (12)

A latent image formed on the surface of the charged image carrier is developed with a two-component developer containing a carrier and a toner, and a developing unit for forming a toner image on the surface of the image carrier is provided on a recording medium. An image forming unit for forming the toner image;
A fixing unit that heat-fixes the toner image formed on the recording medium to the recording medium;
A re-conveying unit that reverses the front and back of the recording medium on which the toner image is fixed by the fixing unit during double-sided printing, and re-conveys the recording medium to the image forming unit;
Density detecting means for detecting the density of the density adjusting image formed in the developing unit;
In accordance with the difference between the density of the image for density adjustment detected by the density detection means and the target toner density that is a reference of the toner density of the two-component developer, the toner stored in the storage container is transferred to the developing unit. Toner supply means for supplying;
The toner supply by the toner supply unit is stopped when the difference between the density of the density adjustment image detected by the density detection unit and the target toner density is equal to or greater than a predetermined value after the duplex printing is continued for a predetermined number of sheets or more. Toner supply control means;
An image forming apparatus comprising:   The toner supply control unit causes the toner supply unit to supply toner to the developing unit based on the density of the toner image formed on the surface of the image carrier when the toner supply by the toner supply unit is stopped. The image forming apparatus according to claim 1.   3. The temperature increase prevention control unit that activates a temperature increase prevention unit that prevents a temperature increase of the developing unit when the toner supply control unit stops toner supply by the toner supply unit. Image forming apparatus. A plurality of the image forming units are provided along the conveyance direction of the recording medium,
The density detection means detects the density of the density adjustment image formed by the most downstream developing section in the image forming section provided on the most downstream side in the conveyance direction of the recording medium, and the toner supply control means The toner supply to the most downstream developing unit by the toner supply unit is stopped when the difference between the density of the density adjustment image and the target toner density is a predetermined value or more. 2. The image forming apparatus according to item 1. A toner remaining amount calculating means for calculating a toner remaining amount of the storage container and the developing unit based on a density of a toner image formed on the surface of the image carrier,
The toner supply control unit has a difference between the density of the density adjustment image detected by the density detection unit and the target toner density after the double-sided printing is continued for a predetermined number or more and a toner remaining amount. The image forming apparatus according to claim 1, wherein when the remaining amount of toner calculated by the amount calculation unit is equal to or greater than a predetermined value, the toner supply to the developing unit by the toner supply unit is stopped. It has a temperature sensor that detects the ambient temperature,
The toner supply control means has a difference between the density of the density adjustment image detected by the density detection means and the target toner density after the double-sided printing is continued for a predetermined number of sheets or more, and the temperature The image forming apparatus according to claim 1, wherein when the environmental temperature detected by the sensor is equal to or higher than a predetermined value, the toner supply to the developing unit by the toner supply unit is stopped.   The image forming apparatus according to claim 3, wherein the temperature rise prevention unit reduces the image forming speed in the image forming unit.   The image forming apparatus according to claim 3, wherein the temperature rise prevention unit decelerates a developing speed in the developing unit.   The image forming apparatus according to claim 3, wherein the temperature rise prevention unit prohibits double-sided printing by the image forming unit.   The image forming apparatus according to claim 3, wherein the temperature rise prevention unit prohibits image formation by the image forming unit.   After the temperature rise prevention unit is activated, when the difference between the density adjustment image density detected by the density detection unit and the target toner density exceeds a predetermined value, the image forming operation is stopped. The image forming apparatus according to claim 3, further comprising a unit.   After the temperature rise prevention unit is activated, the number of printed sheets in the image forming unit exceeds a predetermined number, and the difference between the density of the density adjustment image detected by the density detection unit and the target toner density is predetermined. The image forming apparatus according to claim 3, further comprising an image forming operation stop unit that stops the image forming operation when the value is equal to or greater than the value.

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