JP2008116757A - Image forming apparatus and facsimile machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent unstabilization of image density in the case of restarting the drive of an image forming apparatus which is left to be in a non-active state for a long time, regarding the image forming apparatus equipped with a two-component developing system developing unit. <P>SOLUTION: The image forming apparatus includes: a toner concentration sensor for detecting toner concentration of two-component developer by a permeability detection system; a control part capable of changing an input control voltage to be imparted to the toner concentration sensor; an agitating screw and an agitating paddle for making the developer flow in the developing unit; a stop time counting part for counting the stop time when the agitating screw and the agitating paddle are in the non-active state. The control part 62 offsets the input control voltage when the stop time is equal to or exceeding a prescribed time during an image forming period (S104 and S105), and the control part 62 controls the offset amount of the input control voltage to be zero after an operation of forming the prescribed amount (TH 2 sheets) of images is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a facsimile apparatus. More specifically, the present invention relates to a configuration for appropriately controlling image density using a magnetic permeability detection type toner density sensor in an image forming apparatus including a two-component development type developer.

Patent Document 1 points out that in a conventional image forming apparatus, the image density increases immediately after the start of operation due to a short-term change in the toner charge amount caused by leaving the developing unit in a stopped state for a long time. In order to do this, the following configuration is proposed. In other words, the image forming apparatus disclosed in Patent Document 1 includes a developing unit that uses a two-component developer, a machine stop timer that counts the elapsed time from the stop of the operation of the developing unit, and an elapsed time from the start of the operation of the developing unit. A printing operation timer that counts time and a correction unit that substantially corrects the output value of the toner density sensor used for control by the control unit based on the time measured by these two timers are provided.
JP 2004-85707 A

  The configuration of Patent Document 1 is useful in that it can improve the increase in image density after the operation is started after being left for a long time, but the above correction is canceled when a certain period of time elapses thereafter. Will be. On the other hand, after the operation of the image forming apparatus is started, the image forming operation is not necessarily performed at a constant pace. Therefore, in the configuration of Patent Document 1, the correction of the output value of the toner density sensor becomes excessive or vice versa. However, there is a risk that the image density may become unstable due to insufficient correction.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to an aspect of the present invention, the following configuration of an image forming apparatus including a two-component developing type developing device is provided. That is, a toner concentration sensor that detects the toner concentration of a two-component developer by a magnetic permeability detection method, a sensor control unit that can change an input control voltage applied to the toner concentration sensor, and a developer in the developer And a stop time acquisition means for acquiring a stop time when the flow means is in a stopped state. The sensor control means offsets the input control voltage when the stop time is equal to or longer than a predetermined time during image formation. After the input control voltage is offset, after a predetermined amount of image formation is performed, control is performed to make the input control voltage offset amount zero.

  With this configuration, when the driving is resumed after being left for a long time in a state where the image forming apparatus is stopped, the toner carrier is unstable due to a temporary decrease in the charge retention amount of the carrier of the developer. Can be prevented by offsetting the input control voltage. In addition, when a predetermined amount of image formation is performed and the developer is sufficiently stirred in the developing unit, the offset amount of the input control voltage becomes zero, so control corresponding to the recovery of the charge retention amount of the carrier is performed. It can be carried out.

  In the image forming apparatus, it is preferable that the offset amount gradually approaches zero immediately after the input control voltage is offset until the predetermined amount of image formation is performed.

  With this configuration, the offset amount is gradually reduced to zero as the charge retention amount of the carrier of the developer gradually recovers as the image formation proceeds, so that the toner density can be further stabilized.

  In the image forming apparatus, when the image formation is completed without the image formation amount being less than the predetermined amount, the driving of the flow unit is continued even after the completion, and the amount corresponding to the predetermined amount is It is preferable to stop after rotating the flow means.

  With this configuration, even if the image formation amount is small, it is not necessary to correct the input control voltage from the next image formation, and the toner density can be immediately stabilized to form an image. Therefore, the usability of the multifunction machine can be further improved.

  According to another aspect of the present invention, a facsimile apparatus as the image forming apparatus is provided.

  Next, the image forming apparatus of this embodiment will be described with reference to the drawings. 1 is an external perspective view of a copy facsimile multifunction peripheral according to an embodiment of the present invention, FIG. 2 is a front sectional view showing the inside of the main body of the multifunction peripheral, and FIG. 3 is a front sectional view showing the state of an image forming unit in detail. It is an enlarged view. 4 is a graph showing the relationship between the toner density and the output voltage of the toner density sensor, and FIG. 5 is a block diagram relating to toner density control. FIG. 6 is a graph showing the relationship between absolute humidity, cumulative drive time, and input control voltage stored in the storage unit. FIG. 7 is a flowchart of toner density control.

  As shown in the external perspective view of FIG. 1, a copy facsimile multifunction peripheral 91 as an image forming apparatus instructs an image reading unit 92 that functions as a flatbed scanner and an auto document feed scanner, and the number of copies, a facsimile transmission destination, and the like. An operation panel 93, a main body 94 incorporating an image forming unit for forming an image on a sheet as a recording medium, and a sheet feeding cassette 95 for sequentially supplying the sheet.

  The copy facsimile multifunction peripheral 91 includes a front cover 97 on the front side of the main body 94 (the side on which the operation panel 93 is provided) and a jam access cover 98 on one side surface. The front cover 97 and the jam access cover 98 are provided so as to be freely opened and closed. For example, when performing maintenance work, the inside of the main body 94 can be accessed by opening the covers 97 and 98.

  FIG. 2 shows the inside of the main body 94. As shown in FIG. 2, a paper feed cassette 95 that supplies paper 100 is provided at the bottom of the main body 94. The paper feed cassette 95 is configured to be able to be pulled out to the front side of the apparatus (the front side of the paper in FIG. 2). An image forming unit 11 is disposed above the paper feed cassette 95, and a fixing unit 81 and a paper discharge tray 96 are further provided above the image forming unit 11.

  Inside the main body 94, a transport path 85 for transporting the paper 100 from the paper feed cassette 95 to the paper discharge tray 96 is formed. The transport path 85 extends upward from one end side of the paper feed cassette 95 to reach the image forming unit 11, extends further upward, passes through the fixing unit 81, and then curves in the horizontal direction to discharge the paper discharge tray 96. It is configured to reach the top. Although not shown in FIG. 2, the image reading unit 92 and the operation panel 93 are disposed above the paper discharge tray 96.

  The paper feed cassette 95 is formed so as to be open upward, and a plate-like flapper 86 is rotatably provided at the bottom thereof. A plurality of sheets of paper 100 are stacked on the flapper 86. A temperature sensor 28 capable of detecting the temperature inside the main body 94 and a humidity sensor 29 capable of detecting humidity (relative humidity) are disposed at appropriate positions of the paper feed cassette 95.

  A paper feed roller 21 is disposed above the flapper 86. Then, the paper feed roller 21 is driven while pushing up the flapper 86 upward by a biasing spring (not shown), whereby the uppermost paper 100 is separated and picked up and sent out toward the transport path 85. .

  A separation roller 22 is disposed immediately downstream of the paper feed roller 21 in the transport path 85. The separation roller 22 is driven while the paper 100 is nipped between the rollers arranged opposite to the roller, and separates the paper 100 one by one. A registration roller 23 is disposed on the downstream side of the separation roller 22. The registration roller 23 is driven while the paper 100 is nipped between the registration roller 23 and a roller disposed opposite to the registration roller 23, thereby conveying the paper 100 to the downstream image forming unit 11 while correcting the skew of the paper 100.

  As shown in FIG. 2 and FIG. 3, which is an enlarged view of a main part thereof, the image forming unit 11 includes a charger 13, an LED head 14, a developing device 15, a transfer roller 16, around the photosensitive drum 12. The cleaner 17 is arranged.

  The photosensitive drum 12 is configured such that a photoconductive film made of an organic photoreceptor is formed on the surface and is rotated by an electric motor (not shown). The charger 13 is configured as a non-contact corona charging type so-called scorotron charger, and the surface of the photosensitive drum 12 is uniformly charged, for example, negatively by the charger 13.

  The LED head 14 as an exposure device is disposed downstream of the charger 13 (refers to the downstream side in the rotation direction of the photosensitive drum 12. Hereinafter, the same applies to the description of the developing device 15, the transfer roller 16, and the cleaner 17). In this configuration, a large number of light emitting diodes (LEDs) are arranged in the paper width direction. The LED head 14 selectively emits light corresponding to the image data of the facsimile document received via the telephone line or the image data read by the image reading unit 92. As a result, the surface of the photosensitive drum 12 is selectively exposed, and the electrostatic energy is formed by losing the charge energy of the exposed portion.

  The developing device 15 is disposed on the downstream side of the LED head 14. The developing device 15 is configured in a two-component developing system using toner (pigment powder) and carrier (magnetic powder) as developers. Specifically, the developing device 15 includes a developer container 35 made of a synthetic resin, two stirring screws 31 and 32 and a stirring paddle 37 (flow means) disposed inside the developer container 35, and the photosensitive member. A developing roller 33 serving as a developer carrying member supported by the developer container 35 while being arranged close to the drum 12 while forming a slight gap, and a restriction placed close to the surface of the developing roller 33 Blade 34.

  The stirring screws 31 and 32 are driven to rotate, thereby circulating the two-component developer in the developer container 35. Further, the agitation paddle 37 is also rotationally driven so that the toner and the carrier are frictionally charged and adsorbed to each other by electrostatic force.

  The developing roller 33 is formed in a cylindrical shape from a non-magnetic material, and is rotatably fitted to the outside of a cylindrical magnetic body 36. The internal magnetic body 36 attracts the carrier to the surface of the developing roller 33 by the magnetism, and rotates the developing roller 33 in this state, so that the toner and the carrier are held on the surface of the developing roller 33 and the photosensitive drum. 12 side. Note that the thickness of the developer on the surface of the developing roller 33 is regulated to be uniform by the regulating blade 34.

  Thereafter, in the vicinity of the photosensitive drum 12 and the developing roller 33, only the portion of the two-component developer on the surface of the developing roller 33 where the toner corresponds to the exposed portion by the LED head 14 moves to the surface of the photosensitive drum 12. Move selectively. As a result, a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 12. The remaining toner that has not moved to the carrier and the photosensitive drum 12 side of the developer is collected in the developer container 35.

  A toner concentration sensor 38 is disposed at an appropriate position in the developer container 35. As the toner concentration sensor 38, a magnetic permeability detection method using an inductance component of a coil is employed in the present embodiment. The space in the developer container 35 is connected to the toner cartridge 8 via a toner supply pipe 39 as a toner supply path.

  The transfer roller 16 is disposed on the downstream side of the developing device 15 and is disposed on the opposite side of the photosensitive drum 12 with the conveyance path 85 interposed therebetween. A predetermined voltage from a power source is applied to the transfer roller 16. Accordingly, the toner image formed on the surface of the photosensitive drum 12 moves so as to approach the transfer roller 16 side by the rotation of the photosensitive drum 12, and is transferred to the paper 100 by the electric field attraction force.

  The cleaner 17 is disposed on the downstream side of the transfer roller 16 and is configured to scrape residual toner that has not been transferred to the paper 100 at the transfer roller 16 portion from the surface of the photosensitive drum 12. The collected residual toner is sent to the toner cartridge 8 via a return path (not shown) by a conveying member such as a paddle 25 and a screw 26 and stored in a waste toner storage chamber 43 described later.

  Of the configuration of the image forming unit 11, at least the photosensitive drum 12, the charger 13, the developing device 15 (including the developing roller 33), and the cleaner 17 are integrated as a process cartridge (process unit) 5. Composed. The process cartridge 5 is detachably attached to the image forming unit 11. For example, when the life of the developer or the photosensitive drum 12 is reached, the process cartridge 5 can be removed from the copy facsimile multifunction peripheral 91 and replaced with a new one. It has become. The sheet 100 on which the toner image is transferred in the image forming unit 11 is sent to the fixing unit 81 on the downstream side of the conveyance path 85 by the rotation of the photosensitive drum 12.

  As shown in FIGS. 2 and 3, the fixing unit 81 includes a heat roller 82 that incorporates a heating source (such as a halogen lamp) and is driven to rotate, and a press roller 83 that is disposed to face the heat roller 82. It is equipped with. The press roller 83 is pressed against the heat roller 82 by a biasing spring (not shown). With this configuration, when the paper 100 passes between the heat roller 82 and the press roller 83, the toner of the toner image is melted and fixed to the paper 100 by the heat of the high-temperature heat roller 82 and the pressure by the press roller 83. The fixing unit 81 is provided with a separation claw 84 for preventing the paper 100 from being wrapped around the heat roller 82 while being stuck.

  As shown in FIG. 2, a conveyance roller 87 is provided on the downstream side of the fixing unit 81, and a paper discharge roller 88 is provided on the further downstream side. With this configuration, the sheet 100 sent from the fixing unit 81 is nipped between the transport roller 87 and the driven roller disposed opposite thereto, and is sent downstream. Further, the sheet 100 is nipped between the sheet discharge roller 88 and a driven roller disposed opposite thereto, and is discharged onto the sheet discharge tray 96.

  Next, a configuration for supplying toner to the developing device 15 will be described. As shown in FIG. 3, the main body 94 includes a toner cartridge 8 that is detachable. The toner cartridge 8 includes a synthetic resin toner container 40, and a toner storage chamber 41, a toner buffer unit 42, and a waste toner storage chamber 43 are formed in the toner container 40.

  A predetermined amount of toner is sealed in the toner storage chamber 41, and a paddle 45 is installed therein. The paddle 45 is rotated to agitate the toner. Further, a screw 46 is disposed in a chamber adjacent to the toner storage chamber 41 so that the toner in the toner storage chamber 41 is transferred to the toner buffer unit 42.

  Further, the toner supply pipe 39 is connected to the toner buffer section 42, and a supply screw (toner replenishing means) 47 is disposed inside the toner supply pipe 39. With this configuration, when the toner density sensor 38 detects that the toner density of the developer in the developing device 15 has decreased, the supply screw 47 is driven to supply new toner in the toner buffer section 42 to the developer container. It is comprised so that it may supply to the inside of 35.

  A toner detection sensor 48 is installed inside the toner buffer unit 42. As the toner detection sensor 48, for example, it is conceivable to use a piezoelectric vibration type sensor that detects powder by vibrating the vibration surface. The toner detection sensor 48 is disposed at a predetermined height in the toner buffer unit 42, and when the toner in the toner buffer unit 42 exceeds a predetermined amount, the toner detection sensor 48 detects the toner and outputs a predetermined signal. Configured to send.

Next, the output voltage characteristics of the toner density sensor 38 will be described with reference to FIG. In the graph shown in FIG. 4, the horizontal axis indicates the toner density, and the vertical axis indicates the output voltage of the toner density sensor 38. As shown in this graph, the toner density sensor 38 has a characteristic that the relationship between the toner density and the output voltage is changed in accordance with a control voltage (hereinafter, input control voltage) input to the sensor (FIG. 4 shows the case where the input control voltages are 6V, 7V, and 8V, respectively). Therefore, for example, when the toner density is controlled so that the output voltage of the toner density sensor 38 becomes the predetermined reference voltage V _std , the corresponding developing device 15 depends on whether the input control voltage is 6V, 7V, or 8V. The toner density is different between D ₁ , D ₂ , and D ₃ .

In view of this characteristic, in general, the toner density is used so that an area in which the output voltage changes favorably following the change in the toner density (for example, an area in which the output voltage is around the reference voltage V _std ) is used. The input control voltage applied to the sensor 38 is set to a predetermined value and used. For example, when it is desired to keep the actual toner density in the developing device 15 in the vicinity of D ₂ , the input voltage of 7 V is applied to the toner density sensor 38 and development is performed so that the output voltage is in the vicinity of the reference voltage V _std. It is only necessary to control the supply of toner to the agent.

  However, the toner density sensor 38 has a characteristic that the detection value changes depending on an environmental factor (specifically, absolute humidity) in which the image forming unit 11 is installed. For example, even when the toner concentration of the developer is the same, when the absolute humidity is low, the charge retention amount of the carrier of the developer increases, so the repulsive force between the carriers also increases and the magnetic permeability per unit volume decreases. The toner concentration sensor 38 regards this decrease in magnetic permeability as a decrease in carrier (increase in toner) and detects the toner concentration higher than the actual one, so this needs to be corrected. On the other hand, when the absolute humidity is high, the charge retention amount of the carriers decreases, so the repulsive force between the carriers also decreases and the magnetic permeability per unit volume increases. The toner concentration sensor 38 regards this increase in magnetic permeability as an increase in carrier (a decrease in toner) and detects the toner concentration lower than the actual one, so it is necessary to correct this.

  Further, the carrier of the two-component developer generally deteriorates gradually as the cumulative driving time (cumulative usage amount) from the start of use of the developing device 15 increases, and the charging ability of the toner generally decreases. . As causes of this deterioration, it has been pointed out that the charge imparting ability is reduced due to adhesion of the toner component to the carrier surface, and the resistance is reduced due to wear of the coating film of the carrier. When the toner is insufficiently charged due to the deterioration of the carrier, the developability of the toner is increased, so that the image density is increased. Therefore, in order to stabilize the formed image, it is necessary to control the toner concentration of the developer in consideration of the above-described viewpoint of carrier deterioration.

  Furthermore, when the two-component developer in the developing device 15 is not stirred for a long time and the flow stop state continues, the charge retention amount of the carrier is temporarily reduced, as in the case where the above absolute humidity is high. The toner density sensor 38 detects the toner density lower than the actual density. Therefore, in order to stabilize the toner density and the formed image density, it is necessary to consider a temporary decrease in the charge retention amount of the carrier.

  Next, an electrical configuration for controlling the toner density will be described with reference to FIG. As shown in the block diagram of FIG. 5, the outputs of the temperature sensor 28 and the humidity sensor 29 are input to an absolute humidity calculator 61, where the absolute humidity (environmental value) is calculated by a known equation. The temperature sensor 28, the humidity sensor 29, the absolute humidity calculation unit 61, and the like constitute an absolute humidity acquisition unit 66 for acquiring absolute humidity. The absolute humidity calculated by the absolute humidity calculating unit 61 is input to the control unit (sensor control means) 62.

  In addition, a timer circuit 65 is connected to the control unit 62 so that the cumulative driving time of the developing device 15 from the time when the developing device 15 is first used can be acquired. The timer circuit 65 and an appropriate storage unit (not shown) for storing the cumulative drive time constitute a drive time acquisition unit 67 for acquiring the cumulative drive time. Information on the drive time acquired by the drive time acquisition unit 67 is input to the control unit 62.

  The controller 62 is connected to the toner density sensor 38 and is configured to control an input control voltage applied to the toner density sensor 38. Further, the output of the toner density sensor 38 is input to the control unit 62. In addition, a storage unit 63 that stores information for various controls is connected to the control unit 62.

  A timer circuit 71 is connected to the controller 62, and the stop time of the developing device 15 since the last use of the developing device (specifically, the stirring screws 31, 32 and the stirring paddle 37 are stopped). Accumulated time) can be obtained. The timer circuit 71 and an appropriate storage unit (not shown) for storing the stop time constitute a stop time acquisition unit 72 for acquiring the developer flow stop time. Information on the stop time acquired by the stop time acquisition unit 72 is input to the control unit 62.

  Further, a toner replenishing motor 64 for driving the supply screw 47 and the like is connected to the control unit 62, and its driving / stopping can be controlled by the control unit 62.

  In the present embodiment, the absolute humidity calculation unit 61, the control unit 62, the storage unit 63, and the like are configured as a microcomputer and include a CPU, a ROM, a RAM, and the like (not shown). That is, the hardware described above is combined with the control software stored in the ROM or the like, and the above-mentioned absolute humidity calculation unit 61, control unit 62, storage unit 63, absolute humidity acquisition unit 66, drive is added to the multi-function device 91. A time acquisition unit 67, a stop time acquisition unit 72, and the like are configured.

The storage unit 63 stores in advance the relationship between the cumulative drive time of the developing device 15 and the input control voltage for a plurality of absolute humidity. In the graph of FIG. 6, the absolute humidity is ^{2.0g / m 3, 6.0g / m} 3, are illustrated the three cases of 16.0 g / m ^3, which is example one in order to simplify the description The above relationship is actually stored for many absolute humidity cases. Various changes can be made to the absolute humidity for storing the relationship in the storage unit 63.

Here, as described above, the toner concentration sensor 38 tends to detect the toner concentration lower than the actual when the absolute humidity is high, and detects the toner concentration higher than the actual when the absolute humidity is low. In view of this point, in the relationship stored in the storage unit 63 in the multifunction peripheral 91 of the present embodiment, as shown in FIG. 6, when the absolute humidity is high (16.0 g / m ³ ), the input control voltage is low. Similarly, when the absolute humidity is low (2.0 g / m ³ ), the input control voltage is set to be high. Thereby, the deviation of the detection value of the toner density sensor 38 due to the change in absolute humidity is absorbed by the change of the input control voltage, and the toner density of the developer can be accurately controlled.

Further, as the multi-function device 91 is continuously used and the cumulative driving time of the developing device 15 is increased, the carrier of the developer is deteriorated as described above, the developability of the toner is increased, and the image density is increased. From this point of view, the relationship stored in the storage unit 63 is such that the input control voltage of the toner density sensor 38 decreases as the cumulative driving time of the developing device 15 increases from zero for any of the curves shown in FIG. , The relationship is defined. When the input control voltage is lowered, the toner density corresponding to the reference voltage V _std is lowered. Therefore, the above relationship is controlled so that the toner density of the developer is lowered as the cumulative driving time is increased (development is increased). Means that. As a result, the density of the formed image can be kept constant, and deterioration in image quality such as fogging can be prevented.

  Next, the toner density control described with reference to FIG. 5 will be described in more detail with reference to the flowchart of FIG. When this control is started, first, it waits until an image formation command based on reception of a facsimile, copy operation, or the like is received (S101). When the image formation command is received, the absolute humidity and the cumulative driving time are acquired (S102). Specifically, the temperature sensor 28 detects the temperature, the humidity sensor 29 detects the humidity, the absolute humidity calculation unit 61 calculates the absolute humidity from both detection values, and the cumulative driving time of the developing device 15 is calculated based on the driving time. Obtained from the time obtaining unit 67.

  Next, the obtained absolute humidity and accumulated drive time are applied to the relationship stored in the storage unit 63 (FIG. 6) to obtain an input control voltage to be applied to the toner density sensor 38 (S103).

  Next, it is checked whether or not the stop time of the developing device 15 obtained from the stop time acquisition unit 72 is a predetermined time or more (S104). If the stop time is equal to or longer than the predetermined time, the correction amount ΔV for correcting the input control voltage is set to a predetermined value (≠ 0) (S105).

  That is, when the image forming command is not input to the multi-function device 91 for a long time and the stirring screws 31 and 32 and the stirring paddle 37 in the developing device 15 are not driven for a long time, the developer is left unstirred and left as a carrier. The charge retention amount decreases, the repulsive force between carriers weakens, the carrier density increases, and the magnetic permeability per unit volume increases. The toner concentration sensor 38 regards this increase in magnetic permeability as an increase in carrier (decrease in toner), and detects the toner concentration lower than actual.

  Therefore, in this embodiment, in order to prevent the above situation by controlling the actual toner density to be low, a value that is determined in advance by experiments or the like is set as the correction amount ΔV. Specifically, the correction amount ΔV is a negative value so that the input control voltage is lowered to absorb the deviation of the detected value. When it is determined in S104 that the stop time is less than the predetermined time, the correction amount ΔV of the input control voltage is set to zero.

Next, driving of the image forming unit 11 including the developing device 15 is started (S106), and toner is supplied to the developing device 15 as necessary (S107). The process of S107 will be specifically described. The above input control voltage is input to the toner density sensor 38, the output voltage _Vout is obtained, and this is compared with the reference voltage _Vstd . At this time, the toner control sensor 38 is supplied with the input control voltage corrected by the correction amount ΔV. When the output voltage V _out is higher than the reference voltage V _std, it means that the toner density is lower than the target. Therefore, the toner supply motor 64 is output until the output voltage V _out of the toner density sensor 38 becomes equal to or lower than the reference voltage V _std. And the toner is supplied to the developing device 15 by the supply screw 47. Further, in order to uniformly stir the developer in the developing device 15, the stirring screws 31 and 32 and the stirring paddle 37 are appropriately driven.

  Next, it is checked whether or not the input control voltage correction amount ΔV is zero (S108). If zero, the process proceeds to the image forming step of S113.

  If the correction amount ΔV is not zero, it is checked whether the count value (that is, the number of printed sheets) counted up every time one image is formed (that is, one page) exceeds a predetermined value TH1. (S109). If it is equal to or smaller than the predetermined value TH1, the process proceeds to the image forming step of S113.

  If the number of printed sheets exceeds a predetermined value TH1, it is checked whether or not the number of printed sheets exceeds a predetermined value TH2 (TH2> TH1) (S110). If the value is less than the predetermined value TH2, the correction amount ΔV of the input control voltage is reset to a value closer to zero than the value set in S105 (S111). On the other hand, if it exceeds the predetermined value TH2, the correction amount ΔV is set to zero (S112). In either case, the process proceeds to the image forming step of S113.

  In the image forming step, image formation is actually performed in the process of S113. Note that the processing described in S107 to S113 is repeated until the number of image formations is completed for all pages. At this time, the drive time acquisition unit 67 measures the time as needed by the timer circuit 65 and updates the drive accumulated time of the developing unit 15.

  After completion of image formation, stop control of each part is performed (S114). At this time, a process of resetting the stop time stored in the stop time acquisition unit 72 to zero is also performed. Thereafter, the process returns to S101 and again waits for an image formation command.

  With the above control, when the stop time of the developing device 15 (stop time of the stirring screws 31, 32, etc.) so far during image formation is longer than a predetermined time, it is corrected when the number of printed sheets is less than TH1. When the amount of printing is greater than TH1 and less than TH2 with the amount ΔV, the input control voltage of the toner density sensor 38 is offset corrected and the image is formed with the correction amount ΔV reset to a value close to zero. It is composed. When the number of printed sheets exceeds TH2, the correction amount ΔV is set to zero, and the image is formed with a normal input control voltage. As a result, it is possible to control to compensate for a temporary decrease in the charge retention amount of the carrier after being left for a long time without driving the developing device 15, and appropriately cope with the recovery of the charge retention amount accompanying the progress of image formation. The toner density can be stabilized.

  As described above, the copy facsimile multifunction peripheral 91 according to the present embodiment includes the two-component developing type developing device 15, the toner concentration sensor 38 that detects the toner concentration of the two-component developer by the magnetic permeability detection method, The control unit 62 capable of changing the input control voltage applied to the toner concentration sensor 38, the stirring screws 31, 32 and the stirring paddle 37 for causing the developer of the developing device 15 to flow, the stirring screws 31, 32, and the stirring A stop time acquisition unit 72 that acquires a stop time when the paddle 37 is in a stop state. The controller 62 offsets the input control voltage by the correction amount ΔV when the stop time is equal to or longer than a predetermined time during image formation (S104, S105). After the input control voltage is offset, after TH2 images are formed, control is performed to make the input control voltage correction amount ΔV zero (S110, S112).

  As a result, when the drive is restarted after being left for a long time in a stopped state, the toner carrier destabilization caused by the temporary decrease in the charge retention amount of the carrier of the developer is input controlled. This can be prevented by voltage offset. Further, when the image formation of TH2 sheets is performed and the developer is sufficiently agitated in the developing device 15, the input control voltage correction amount ΔV automatically becomes zero, which is suitable for recovery of the carrier charge retention amount. It can correspond to.

  Further, in the present embodiment, when the TH1 image is formed immediately after the input control voltage is offset (corrected) and the TH2 image is formed, the correction amount ΔV is gradually reduced to zero. (S109 to S111).

  As a result, the correction amount ΔV gradually approaches zero as the charge retention amount of the carrier gradually recovers as the image is formed, so that the toner density can be further stabilized.

  Note that the number of printed sheets in one image formation varies depending on the number of copies, the number of copies, the number of received pages of the facsimile, and the like, and the number of printed sheets is smaller than the number of printed sheets (TH2 sheets) that sets the correction amount ΔV to zero. It is also conceivable that the formation ends. In this embodiment, in this case, the drive of the stirring screw 31 and the stirring paddle 37 is continued even after the image formation is completed, and the stirring screw 31 and the stirring paddle 37 are rotated by an amount corresponding to the predetermined amount (for two TH). Control to stop after that.

  This eliminates the need for correction of the input control voltage from the next image formation, so that the image can be formed immediately with good toner density stabilization. Therefore, the usability of the multifunction device 91 can be further improved.

  Although the preferred embodiment of the present invention and the modification thereof have been described above, the above-described configuration can be changed as follows, for example.

  The method for measuring the amount of image formation after the start of image formation is not limited to the number of pages (number of sheets), and for example, the rotation count value of the developing roller can be used.

  The correction amount (offset amount) ΔV of the input control voltage is not limited to being changed in two steps as in the above-described embodiment, and can be changed in three or more steps.

  The relationship between the cumulative drive time of the developing device 15 and the input control voltage of the toner density sensor 38 can be stored in, for example, a lookup table format instead of being stored in the storage unit 63 in the form of a function.

  For example, the accumulated rotation count value of the developing roller 33 can be used as the accumulated use value of the developing unit 15 representing the deterioration of the carrier, instead of acquiring the accumulated driving time from the start of use of the developing unit 15.

  In the above embodiment, the absolute humidity is calculated from the detection values of the temperature sensor 28 and the humidity sensor 29, and the input control voltage to the toner concentration sensor 38 is determined based on the absolute humidity. However, for example, only the detection value of the temperature sensor 28 is determined. The input control voltage can also be determined based on In this case, the storage unit 63 stores the relationship between the cumulative drive time and the input control voltage for a plurality of temperatures. Also, the input control voltage can be determined based only on the detection value of the humidity sensor.

  The configuration of the present invention can be applied to, for example, a printer, a copier, a facsimile machine, and the like instead of the copy facsimile multifunction machine 91.

1 is an external perspective view of a copy facsimile multifunction peripheral according to an embodiment of the present invention. Front sectional drawing which shows the mode inside a main body. The front cross-sectional enlarged view which shows the mode of an image formation part in detail. The graph which shows the relationship between a toner density and the output voltage of a toner density sensor. FIG. 6 is a block diagram relating to toner density control. The graph which shows the relationship of absolute humidity, the accumulation drive time, and input control voltage which are memorize | stored in a memory | storage part. FIG. 6 is a flowchart of toner density control.

Explanation of symbols

15 Developing unit 31, 32 Stir screw (flow means)
37 Stir paddle (fluid means)
38 Toner concentration sensor 62 Control unit (sensor control means)
71 Stop time acquisition unit ΔV Input control voltage correction amount (offset amount)

Claims (4)

In an image forming apparatus provided with a two-component development type developer,
A toner concentration sensor for detecting the toner concentration of a two-component developer by a magnetic permeability detection method;
Sensor control means capable of changing the input control voltage applied to the toner density sensor;
A flow means for flowing the developer of the developing unit;
Stop time acquisition means for acquiring the stop time when the flow means was in a stopped state;
With
The sensor control means offsets the input control voltage when the stop time is a predetermined time or more during image formation,
An image forming apparatus, wherein after the input control voltage is offset, after a predetermined amount of image formation is performed, the input control voltage is offset to zero.   The image forming apparatus according to claim 1, wherein the offset amount is gradually approached to zero immediately after the input control voltage is offset until the predetermined amount of image formation is performed. An image forming apparatus.   3. The image forming apparatus according to claim 1, wherein when the image formation is completed when the image formation amount does not reach the predetermined amount, the flow unit is continuously driven even after the completion. An image forming apparatus, wherein the flow unit is rotated after being rotated by an amount corresponding to a fixed amount and then stopped.   A facsimile apparatus as an image forming apparatus according to any one of claims 1 to 3.

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