JP2008122539A - Image forming apparatus and facsimile device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide constitution particularly suitable for such control that the small change of toner concentration is repeated in a two-component developing type image forming apparatus. <P>SOLUTION: The image forming apparatus is equipped with a control part which controls input control voltage given to a magnetic permeability detection type toner concentration sensor, and compares output voltage from the sensor with prescribed reference voltage V<SB>std</SB>to control a supply screw for supplying toner on the basis of a result of detection. The control part changes the input control voltage (arrow A) when the target concentration of the toner in developer is changed to the prescribed amount or more. Meanwhile, the control part does not change the input control voltage but changes the reference voltage V<SB>std</SB>(arrow B) when the change amount of the target concentration is under the prescribed amount. <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.

Japanese Patent Application Laid-Open No. 2004-228561 discloses an image forming apparatus that controls toner density using a magnetic permeability detection type toner density sensor. The image forming apparatus disclosed in Patent Document 1 corrects an input control voltage applied to a toner density sensor when correcting the toner density sensor in accordance with changes in environmental factors, and then reduces the intensity of the input control voltage correction. The output voltage is corrected.
JP 2002-287441 A

  In the image forming apparatus as described above, it is generally preferable to use a toner density sensor whose output voltage changes greatly with respect to a change in toner density from the viewpoint of stabilization of toner density control. Yes.

  However, in the toner density sensor as described above, the toner density greatly fluctuates only by changing the input control voltage small. Therefore, it cannot be said that the control as disclosed in Patent Document 1 is necessarily suitable when the toner density is finely changed with a small pitch. Further, since the toner density greatly fluctuates due to a small shift of the input control voltage, there remains room for improvement from the viewpoint of more appropriate control of the toner density.

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 the first 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, based on a toner concentration sensor that detects the toner concentration of a two-component developer by a magnetic permeability detection method, a toner replenishing means that is driven to replenish toner to the developer, and an output of the toner concentration sensor And a controller for controlling the driving of the toner replenishing means. The control unit controls an input control voltage applied to the toner density sensor, compares the output value of the toner density sensor with a predetermined output reference value, and drives the toner replenishing unit based on the comparison result. Configure to control. The control unit changes the input control voltage when the target concentration of the toner of the two-component developer is changed to a predetermined amount or more, and changes the input control voltage when the target concentration is changed to be smaller than the predetermined amount. The output reference value is changed without changing the input control voltage.

  With this configuration, when the amount of change in the target density is small, the change in the target density can be accurately realized by changing the output reference value side to be compared without changing the input control voltage. Even if there is an error in the output reference value, the influence is not as great as the influence of the error in the input control voltage, so that the toner density can be accurately controlled to the intended density. Therefore, the present invention is particularly suitable for the control that repeatedly changes the target density. On the other hand, when the change amount of the target density is large, the change of the target density can be appropriately realized by changing the input control voltage.

  The image forming apparatus is preferably configured as follows. That is, a drive time acquisition unit is provided for acquiring a cumulative drive time from the start of use of the developing device. The target density of the toner of the two-component developer is determined based on the cumulative driving time.

  With this configuration, when the change in the target density due to the cumulative driving time is small, the change can be realized particularly accurately.

  The image forming apparatus is preferably configured as follows. That is, an environment acquisition unit that acquires environment values is provided. The target density of the toner of the two-component developer is determined based on the environment detection value acquired by the environment acquisition unit.

  With this configuration, even when the change in the target density due to the environment detection value is small, the change can be realized accurately.

  According to the second 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, based on a toner concentration sensor that detects the toner concentration of a two-component developer by a magnetic permeability detection method, a toner replenishing means that is driven to replenish toner to the developer, and an output of the toner concentration sensor A controller that controls the driving of the toner replenishing unit; a driving time acquiring unit that acquires a cumulative driving time from the start of use of the developing device; and an environment acquiring unit that acquires an environmental value. The control unit controls an input control voltage applied to the toner density sensor, compares the output value of the toner density sensor with a predetermined output reference value, and drives the toner replenishing unit based on the comparison result. Configure to control. When either one of the environment detection value acquired by the environment acquisition unit and the accumulated drive time acquired by the drive time acquisition unit is changed, the control unit changes the input control voltage to change the two components. When the target density of the toner of the system developer is changed and the other is changed, the target density is changed by changing the output reference value without changing the input control voltage.

  According to this configuration, the input control voltage is changed when one of the environment detection value and the cumulative drive time is changed, and the input reference voltage is not changed when the other is changed. Control to change the value side is performed. Thus, for example, when the target density of toner fluctuates greatly when the environmental detection value changes and fluctuates slightly when the accumulated driving time changes, the toner target density corresponds to the change in the accumulated driving time. This is advantageous in that the concentration can be finely and accurately controlled.

  In the image forming apparatus, the environmental value is preferably absolute humidity.

  As described above, when the input control voltage and the reference voltage are changed based on the absolute humidity that has a large influence on the detection value of the toner density sensor, the toner density can be controlled more appropriately.

  According to another aspect of the present invention, a facsimile machine 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 disposed inside the developer container 35, and the photosensitive drum 12. A developing roller 33 as a developer carrying member that is disposed in close proximity while forming a slight gap, and a regulating blade 34 that is disposed in proximity to the surface of the developing roller 33; It has.

  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 is used so as to use a region where the output voltage changes greatly and favorably following the change in the toner density (for example, a region where the output voltage is around the reference voltage V _std ). The input control voltage applied to the density 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.

  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 calculation unit 61 is input to the control unit 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.

  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 and the like are configured.

The storage unit 63 stores in advance the relationship between the cumulative driving time of the developing device 15 and the toner density (target density) to be a control target 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 multi-function peripheral 91 of the present embodiment, as shown in FIG. 6, when the absolute humidity is high (16.0 g / m ³ ), control is performed by the toner concentration sensor 38. The (apparent) target density is set to be low, and when the absolute humidity is low (2.0 g / m ³ ), the (apparent) target density controlled by the toner density sensor 38 is set to be high. Yes. As a result, the deviation of the detection value of the toner density sensor 38 due to the change in absolute humidity can be absorbed by changing the target density, and the actual 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 increases, the developer carrier deteriorates as described above, and the developability of the toner increases and the image density increases. From this point of view, the relationship stored in the storage unit 63 is such that the target density controlled by 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. In addition, the relationship is defined. 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 driving time are applied to the relationship stored in the storage unit 63 (FIG. 6) to obtain the target density of toner (S103). Then, the difference between the obtained target density and the target density at the previous control is obtained, and it is determined whether this difference is large (is greater than a predetermined value) (S104).

If the target density difference is equal to or greater than the predetermined value, the target density change is realized by changing the input control voltage applied to the toner density sensor 38 (S105). In the process of S105, the reference voltage V _std is also changed as necessary with the change of the input control voltage. On the other hand, when the target density difference is less than the predetermined value, the input control voltage applied to the toner density sensor 38 is not changed, and only the reference voltage _Vstd is changed (S106).

Thereby, for example, when changing the target density due to a small change in absolute humidity, the reference voltage V _std side as the output voltage comparison target is changed without changing the input control voltage applied to the toner density sensor 38. (S106). As a result, a small change in the target density can be realized accurately. Even if there is a slight error when changing the reference voltage V _std , the toner density does not deviate more than intended.

On the other hand, for the change of the target density due to a large change in absolute humidity, the input control voltage to the toner density sensor 38 is changed (S105). As a result, a large change in the target density can be realized with certainty. In addition, by setting the input control voltage so that the reference voltage V _std becomes equal to the target density, the output voltage greatly and favorably changes with the change in toner density (the output voltage is the reference voltage in the graph of FIG. 4). Since the region near V _std can be used, the toner density can be quickly stabilized.

Next, the input control voltage is input to the toner concentration sensor 38 while driving the stirring screws 31 and 32 and the like to cause the developer to flow, and the output voltage _Vout at this time is acquired (S107). Then, the obtained output voltage _Vout is compared with the reference voltage _Vstd (S108). 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 replenishing motor 64 is driven by a predetermined amount, and the supply screw 47 is rotated to remove the toner from the developing device 15. (S109). Then return to S107, until the output voltage V _out of the toner density sensor 38 becomes equal to or lower than the reference voltage V _std, it repeats the processing of S107 to S109.

If the output voltage V _out of the toner density sensor 38 was below the reference voltage V _std in S108 the decision to start image formation by the image forming unit 11 (S110), and waits until the image formation is completed (S 111). At this time, the driving time acquisition unit 67 measures the time by the timer circuit 65 as needed, and updates the driving accumulated time of the developing device 15. After completion of image formation, after stopping control of each part (S112), the process returns to S101 and waits for an image formation command again.

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, A supply screw 47 that is driven to supply toner to the developing device 15 and a control unit 62 that controls the drive of the supply screw 47 based on the output of the toner density sensor 38 are provided. The control unit 62 controls the input control voltage applied to the toner density sensor 38, compares the output voltage of the toner density sensor 38 with a predetermined reference voltage _Vstd, and based on the comparison result, The driving of the supply screw 47 is controlled. The control unit 62 changes the input control voltage when the toner target density of the two-component developer is changed to a predetermined amount or more, and changes the input density when the target density is changed to be smaller than the predetermined amount. The reference voltage V _std is changed without changing the input control voltage.

Thereby, when the change amount of the target density is small, the small change of the target density can be accurately realized by changing the reference voltage V _std to be compared without changing the input control voltage. Even if there is an error in the reference voltage V _std , the influence on the toner density is not as great as that caused by the error in the input control voltage, so that the toner density can be accurately controlled to the intended density. Therefore, the present invention is particularly suitable for the control that repeatedly changes the target density. On the other hand, when the change amount of the target density is large, the change of the target density can be appropriately realized by changing the input control voltage.

  The multi-function device 91 of this embodiment includes a drive time acquisition unit 67 that acquires the cumulative drive time from the start of use of the developing device 15 and an absolute humidity acquisition unit 66 that acquires absolute humidity. As shown in FIG. 6, the above-described target density of toner is determined based on the cumulative driving time and absolute humidity.

  Thereby, when the change of the target density due to the cumulative driving time and the absolute humidity is small, the change can be realized particularly accurately.

In the above control, the absolute humidity is acquired from the absolute humidity acquisition unit 66 as an environmental factor, and the input control voltage or the reference voltage V _std of the toner concentration sensor 38 is determined based on the absolute humidity.

Thus, the input control voltage and the reference voltage V _std are determined based on the absolute humidity that has a large influence on the detection value of the toner density sensor 38, so that the toner density can be controlled more appropriately.

In place of the control (S104 to S106) for determining whether the input control voltage is changed or the reference voltage is changed according to the amount of change in the target concentration, for example, the change in the target concentration caused by the change in absolute humidity is performed. In this case, it is possible to change the input control voltage, and to change the reference voltage V _std when the target density is changed due to the change in the cumulative driving time. The above control is effective when the change in the cumulative driving time has a smaller influence on the target density than the change in the absolute humidity. Conversely, the input control voltage is changed when the target concentration is changed due to a change in the cumulative driving time, and the reference voltage V _std is changed when the target concentration is changed due to a change in absolute humidity. It can also be controlled.

  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 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 target concentration (input control voltage or reference voltage) is determined based on the absolute humidity. It is also possible to determine the target concentration (input control voltage or reference voltage) based solely on the above. Also, the target concentration (input control voltage or reference 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 between absolute humidity, the accumulation drive time, and target density which are memorize | stored in a memory | storage part. FIG. 6 is a flowchart of toner density control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 Developing device 38 Toner concentration sensor 47 Supply screw 62 Control part 66 Absolute humidity acquisition part (environment acquisition means)
67 Drive time acquisition unit (drive time acquisition means)
91 Copy Facsimile MFP (image forming device)

Claims (6)

In an image forming apparatus including a two-component developing type developing device,
A toner concentration sensor for detecting the toner concentration of a two-component developer by a magnetic permeability detection method;
Toner replenishing means driven to replenish toner to the developer;
A control unit for controlling the driving of the toner replenishing means based on the output of the toner density sensor;
With
The control unit controls an input control voltage applied to the toner density sensor, compares the output value of the toner density sensor with a predetermined output reference value, and drives the toner replenishing unit based on the comparison result. Configured to control,
The control unit changes the input control voltage when the target concentration of the toner of the two-component developer is changed to a predetermined amount or more, and changes the input control voltage when the target concentration is changed to be smaller than the predetermined amount. An image forming apparatus, wherein the output reference value is changed without changing an input control voltage. The image forming apparatus according to claim 1,
Drive time acquisition means for acquiring a cumulative drive time from the start of use of the developer,
An image forming apparatus, wherein a target density of toner of the two-component developer is determined based on the cumulative driving time. The image forming apparatus according to claim 1, wherein
It has an environment acquisition means for acquiring environment values,
An image forming apparatus, wherein the target concentration of toner of the two-component developer is determined based on an environment detection value acquired by the environment acquisition unit. In an image forming apparatus including a two-component developing type developing device,
A toner concentration sensor for detecting the toner concentration of a two-component developer by a magnetic permeability detection method;
Toner replenishing means driven to replenish toner to the developer;
A control unit for controlling the driving of the toner replenishing means based on the output of the toner density sensor;
Drive time acquisition means for acquiring a cumulative drive time from the start of use of the developer;
An environment acquisition means for acquiring environment values;
With
The control unit controls an input control voltage applied to the toner density sensor, compares the output value of the toner density sensor with a predetermined output reference value, and drives the toner replenishing unit based on the comparison result. Configured to control,
When either one of the environment detection value acquired by the environment acquisition unit and the cumulative drive time acquired by the drive time acquisition unit is changed, the control unit changes the input control voltage to change the two components. An image characterized in that when the target density of the toner of the system developer is changed and the other is changed, the target density is changed by changing the output reference value without changing the input control voltage. Forming equipment.   5. The image forming apparatus according to claim 3, wherein the environmental value is absolute humidity.   A facsimile apparatus as an image forming apparatus according to any one of claims 1 to 5.

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