JP2008122537A - Image forming apparatus and facsimile device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration in image quality due to sudden change of toner concentration in an image forming apparatus equipped with a two-component developing type developing device. <P>SOLUTION: The image forming apparatus is equipped with: a toner concentration sensor 38 for detecting the toner concentration of two-component type developer by a magnetic permeability detection system; a supply screw driven by a toner replenishment motor 64 in order to replenish the developing device 15 with toner; and a control part 62 controlling the drive of the supply screw on the basis of output from the toner concentration sensor 38. The control part 62 corrects output from the toner concentration sensor 38 so as to achieve prescribed toner concentration at which fogging is not caused on an image whatever value absolute humidity acquired by an absolute humidity acquiring part 66 shows. Developing bias to the developing device 15 is corrected to a side where image density is increased in the range of the absolute humidity where the image density of the formed image is lowered at the prescribed toner concentration. <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. In the configuration disclosed in the second embodiment of Patent Document 1, the toner density is controlled not only based on the toner density detected by the toner density sensor but also based on the humidity detected by the humidity sensor. Thus, Patent Document 1 assumes that it is possible to obtain an image quality with a stable toner density by performing correction in consideration of the environment.
JP 2001-290361 A

  However, in the configuration of Patent Document 1 described above, for example, when the humidity increases, the toner concentration is controlled to be low so as to avoid image fogging. In order to thicken the toner, the toner is replenished rapidly, resulting in poor charging of the toner due to poor stirring, which may cause image fogging. Therefore, there remains room for improvement from the viewpoint of more appropriate control of the toner concentration with respect to changes in factors such as humidity.

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 A control unit that controls driving of the toner replenishing unit; and an environment acquisition unit that acquires an environmental value. The controller is configured to be able to correct the output of the toner density sensor and to be able to change the developing bias applied to the developing device. The control unit corrects the output of the toner concentration sensor so as to realize a predetermined toner concentration that does not cause fogging in the image regardless of the environment detection value that can be acquired by the environment acquisition unit. Control is performed so that the developing bias is corrected toward the side where the image density is increased in the range of the environmental detection value where the image density is decreased at a predetermined toner density.

  With this configuration, the output correction of the toner density can be used to correct (only) the detection of the toner density sensor higher / lower than the actual toner density due to the change of the environmental value. That is, fogging due to an increase in toner developability based on environmental changes is automatically prevented by setting the toner density, while a decrease in image density caused by a decrease in toner developability is prevented by correcting the development bias. . As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Therefore, for example, rapid toner replenishment can be avoided and the toner density can be quickly stabilized, so that image fogging due to toner charging failure can be prevented.

  The image forming apparatus is preferably configured as follows. That is, a scorotron charger for charging the photoconductor is provided, and the control unit is configured to change the grid bias of the scorotron charger. The control unit performs control so that the developing bias and the grid bias are corrected toward the side where the image density is increased in the range of the environmental detection value where the image density is decreased at the predetermined toner density.

  With this configuration, the low toner developability (decrease in image density) due to environmental changes is dealt with by correcting the development bias and grid bias, so that the reduction in image density can be prevented more reliably.

  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 control unit that controls driving of the toner replenishing unit; and an environment acquisition unit that acquires an environmental value. The controller is configured to be able to correct the output of the toner density sensor and to be able to change the developing bias applied to the developing device. The control unit corrects the output of the toner density sensor so as to realize a predetermined toner density that makes the image density equal to or higher than a predetermined density regardless of the environment detection value that can be acquired by the environment acquisition unit. At the same time, control is performed so that the developing bias is corrected to a side where the image density becomes lighter in the range of the environmental detection value where the image is fogged at the predetermined toner density.

  With this configuration, the output correction of the toner density can be used to correct (only) the detection of the toner density sensor higher / lower than the actual toner density due to the change of the environmental value. That is, a decrease in image density due to a decrease in toner developability due to environmental changes is automatically prevented by setting the toner density, while fogging due to an increase in toner developability is prevented by correcting the development bias. . As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Therefore, for example, rapid toner replenishment can be avoided and the toner density can be quickly stabilized, so that image fogging due to toner charging failure can be prevented.

  The image forming apparatus is preferably configured as follows. That is, a scorotron charger for charging the photoconductor is provided, and the control unit is configured to change the grid bias of the scorotron charger. The control unit controls the developing bias and the grid bias so that the image density is reduced in a range of the environmental detection value where the image is fogged at the predetermined toner density.

  With this configuration, an increase in toner developability (image fogging) due to environmental changes is dealt with by correcting the development bias and grid bias, so that image fogging can be prevented more reliably.

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

  With this configuration, the output of the toner concentration sensor and the development bias are controlled based on the absolute humidity that has a large influence on the detection value of the toner density sensor and also has a large influence on the level of developability, so that the toner density can be controlled appropriately. At the same time, the formed image density can be stabilized well.

  According to a third 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 control unit that controls driving of the toner replenishing unit; and a driving time acquisition unit that acquires a cumulative driving time from the start of use of the developing device. The controller is configured to be able to correct the output of the toner density sensor and to be able to change the developing bias applied to the developing device. The control unit corrects the output of the toner density sensor so as to realize a predetermined toner density at which no fog occurs in the image regardless of the cumulative driving time, and the image density becomes low at the predetermined toner density. In the range of the cumulative driving time, the developing bias is controlled so as to be corrected toward the side where the image density is increased.

  With this configuration, output correction of the toner density can be used to (only) correct the detection of the toner density sensor higher / lower than the actual toner density due to the change in the cumulative driving time. That is, fogging due to an increase in toner developability when the cumulative drive time is long is automatically prevented by setting the toner density, while image density caused by a decrease in toner developability when the cumulative drive time is short. The decrease is prevented by correcting the developing bias. As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Therefore, for example, rapid toner replenishment can be avoided and the toner density can be quickly stabilized, so that image fogging due to toner charging failure can be prevented.

  The image forming apparatus is preferably configured as follows. That is, a scorotron charger for charging the photoconductor is provided, and the control unit is configured to change the grid bias of the scorotron charger. The control unit performs control so that the developing bias and the grid bias are corrected toward the side where the image density is increased in the range of the cumulative driving time in which the image density is decreased at the predetermined toner density.

  With this configuration, the low toner developability (decrease in image density) when the cumulative driving time is short is dealt with by correcting the development bias and the grid bias, so that the reduction in image density can be prevented more reliably.

  According to a fourth 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 control unit that controls driving of the toner replenishing unit; and a driving time acquisition unit that acquires a cumulative driving time from the start of use of the developing device. The controller is configured to be able to correct the output of the toner density sensor and to be able to change the developing bias applied to the developing device. The control unit corrects the output of the toner density sensor so as to achieve a predetermined toner density at which the image density is equal to or higher than a predetermined density regardless of the cumulative driving time, and at the predetermined toner density, the control unit covers the image. In the range of the cumulative drive time in which the above occurs, the developing bias is controlled so as to be corrected toward the side where the image density is reduced.

  With this configuration, output correction of the toner density can be used to (only) correct the detection of the toner density sensor higher / lower than the actual toner density due to the change in the cumulative driving time. That is, a decrease in image density due to a decrease in toner developability when the cumulative driving time is short is automatically prevented by setting the toner density, while an increase in toner developability when the cumulative driving time is long. Fog is prevented by correcting the development bias. As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Therefore, for example, rapid toner replenishment can be avoided and the toner density can be quickly stabilized, so that image fogging due to toner charging failure can be prevented.

  The image forming apparatus is preferably configured as follows. That is, a scorotron charger for charging the photoconductor is provided, and the control unit is configured to change the grid bias of the scorotron charger. The control unit controls the developing bias and the grid bias so that the image density is reduced in a range of the cumulative driving time in which the image is fogged at the predetermined toner density.

  With this configuration, the increase in toner developability (image fogging) when the cumulative driving time is long is dealt with by correcting the development bias and the grid bias, so that image fogging can be prevented more reliably.

  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 diagram illustrating an example of table contents 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 (photosensitive member) 12 has a photoconductive film formed of an organic photosensitive member formed on the surface thereof, and is configured to be rotationally driven 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 charger 13 has a grid electrode between the corona wire and the member to be charged, and the grid bias can be controlled by a voltage applied to the grid electrode.

  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. A predetermined developing bias is applied to the developing roller 33.

  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. The above setting (initial setting) of the input control voltage can be performed when the developing device 15 is used for the first time, for example.

  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. As causes of this deterioration, adhesion of toner components to the carrier surface, resistance reduction due to wear of the carrier coating film, etc. have been pointed out. Since the carrier retention amount of the deteriorated carrier decreases, the toner density sensor 38 detects the toner density lower than the actual density (as in the case where the absolute humidity is high), and it is necessary to correct this. .

  Further, even if the toner concentration is the same, if the absolute humidity is low or the carrier is close to a new one, the attracting force between the toner and the carrier becomes strong, so that the developability of the toner is lowered and the image becomes thin. On the other hand, if the absolute humidity is high or the carrier is deteriorated, the toner and carrier attracting force is weakened, so that the developability of the toner is increased and the image becomes dark. Therefore, in order to stabilize the density of the formed image, control in consideration of the above viewpoint is necessary.

  Next, an electrical configuration for controlling toner density and image 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 control unit 62 is connected to the toner concentration sensor 38 and is configured to be able to apply the input control voltage to the toner concentration 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.

  The control unit 62 is connected to the charger 13 and the developing device 15 respectively, and can change the grid bias of the charger 13 and the developing bias of the developing device 15. Further, a toner replenishing motor 64 for driving the supply screw 47 and the like is connected to the control unit 62, and the driving / driving stop thereof 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.

  As shown in the upper side of FIG. 6, the storage unit 63 divides the possible values of the absolute humidity acquired by the absolute humidity calculation unit 61 into a plurality of ranges, and outputs correction of the toner density sensor 38 for each range. The correction value of the developing bias applied to the developing device 15 and the correction value of the grid bias applied to the grid electrode of the charger 13 are stored in a table system. Further, as shown in the lower side of FIG. 6, the storage unit 63 divides the value that can be taken by the driving time acquisition unit 67 into a plurality of ranges, and the toner density sensor for each range. The output correction value 38, the development bias correction value applied to the developing device 15, and the grid bias correction value applied to the grid electrode of the charger 13 are stored in a table format.

  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 device 91 of the present embodiment, the output of the toner concentration sensor 38 is increased in the direction in which the toner concentration is increased in the range where the absolute humidity is high compared to the low range. It is determined to correct (Y1 to Y6 in FIG. 6).

  Further, as the cumulative driving time of the developing device 15 becomes longer, the carrier of the developer deteriorates and its charge retention capability decreases, so that the toner concentration sensor 38 sets the toner concentration higher than the actual one as in the case where the absolute humidity is high. There is a tendency to detect low. In view of this point, in the relationship stored in the storage unit 63 in the MFP of the present embodiment, the output of the toner concentration sensor 38 is increased in a direction in which the toner concentration is increased in a range where the cumulative driving time is large compared to a small range. It is determined to correct (W1 to W6 in FIG. 6).

  The output voltage of the toner density sensor 38 is appropriately corrected by the correction related to the absolute humidity and the cumulative driving time, and the determination of the driving / stopping of the toner replenishing motor 64 is performed based on the corrected output voltage. As a result, the toner concentration of the developer in the developer container 35 is controlled to be constant.

  The constant toner density to be controlled is formed regardless of the absolute humidity and the cumulative driving time if the copy facsimile multifunction peripheral 91 is used under normal use conditions and is a normal development bias and grid bias. It is determined in advance based on theoretical values, experiments, and the like so that the toner density does not cause fog in the image. That is, if the humidity is high, or the accumulated driving time is long and the carrier is deteriorated, even if the actual toner density is the same, the developability tends to be high and the image density tends to be high. In this respect, in the present embodiment, a toner density that does not cause fogging in the formed image is set in advance even when the image density becomes high, and the toner density of the developer is controlled so as to be the toner density. To do. Therefore, as long as the output of the toner density sensor 38 is corrected according to the correction values Y1 to Y6 and W1 to W6 in FIG. It can be prevented.

  On the other hand, when the humidity is low, or the cumulative driving time is short and the carrier is close to a new one, the developability is low and the image density tends to be thin even if the actual toner density is the same. In this respect, in the present embodiment, in a range where the absolute humidity is low and the cumulative driving time is short, the developing bias applied to the developing device 15 and the grid bias of the charging device 13 are corrected to the side where the image density is increased. The relationship stored in the storage unit 63 is defined (a1 to a6, b1 to b6, c1 to c6, d1 to d6 in FIG. 6). Thereby, it is possible to appropriately prevent a decrease in image density.

  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 temperature sensor 28 detects the temperature, the humidity sensor 29 detects the humidity, and the absolute humidity calculation unit 61 calculates the absolute humidity from both detection values (S102). Further, the cumulative driving time of the developing device 15 is acquired from the driving time acquisition unit 67 (S103).

  Next, the obtained absolute humidity and accumulated drive time are applied to the relationship stored in the storage unit 63 (FIG. 6) to correct the development bias and the grid bias (S104).

Next, a predetermined input control voltage is input to the toner concentration sensor 38 while the agitating screws 31 and 32 are driven to flow the developer, and the output voltage at this time is acquired. Further, the correction amount is obtained by applying the absolute humidity and the cumulative driving time to the relationship recorded in the storage unit 63 (FIG. 6), and the output is corrected by applying this correction amount to the output voltage. Output voltage _Vout is obtained (S105). Then, the obtained output voltage _Vout is compared with the reference voltage _Vstd (S106). 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. (S107). Then return to S105, until the output voltage V _out after the correction of the toner density sensor 38 becomes equal to or lower than the reference voltage V _std, it repeats the processing of S105 to S107.

If the output voltage V _out of the toner density sensor 38 is equal to or lower than the reference voltage V _{std in} the determination of S106, image formation by the image forming unit 11 is started (S108) and waits until the image formation is completed (S109). At the time of image formation, the development bias and the grid bias corrected in step S104 are used. 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, after stopping control of each part (S110), the process returns to S101 and waits for an image formation command again.

  As described above, the copy facsimile multifunction peripheral 91 according to this embodiment including the two-component developing type developing device 15 includes 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 replenish toner to the developing device 15, a control unit 62 that controls the drive of the supply screw 47 based on the output of the toner density sensor 38, and an absolute humidity acquisition that acquires absolute humidity Unit 66. The control unit 62 is configured to be able to correct the output of the toner density sensor 38 and to be able to change the developing bias applied to the developing device 15. Further, the control unit 62 outputs the output of the toner concentration sensor 38 so as to realize a predetermined toner concentration that does not cause the image to be fogged regardless of the absolute humidity that can be acquired by the absolute humidity acquisition unit 66. In addition to correction, control is performed so that the developing bias is corrected to the side where the image density becomes deeper in the absolute humidity range and the cumulative drive time range where the image density becomes lighter at the predetermined toner density.

  In this configuration, the output correction of the toner density can be used to (only) correct the detection of the toner density sensor 38 higher / lower than the actual toner density due to the change in absolute humidity. In other words, fog due to increase in developability at high humidity is automatically prevented by setting the toner density, while decrease in image density due to decrease in developability at low humidity is prevented by correcting the development bias. The As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Accordingly, it is possible to quickly stabilize the toner concentration in the developer container 35 while avoiding sudden toner replenishment, and thus it is possible to prevent image fogging due to toner charging failure.

  In this embodiment, the scorotron charger 13 for charging the photosensitive drum 12 is provided, and the controller 62 is configured to change the grid bias of the charger 13. Then, the control unit 62 performs control so as to correct the grid bias to the side where the image density increases in addition to the developing bias in the range of the absolute humidity where the image density decreases at the predetermined toner density.

  As a result, a decrease in developability (decrease in image density) caused by low humidity is dealt with by correcting the development bias and the grid bias, so that a decrease in image density can be prevented more reliably.

  In this embodiment, the absolute humidity is acquired from the absolute humidity acquisition unit 66 as an environmental factor to be detected, and the output voltage of the toner concentration sensor 38 is corrected based on this absolute humidity.

  As a result, the output voltage of the toner concentration sensor 38, the developing bias of the developing device 15, the charging device, and the charging device are greatly influenced on the detected value of the toner concentration sensor 38, and on the absolute humidity which has a large effect on the magnitude of developability. Since the 13 grid biases are corrected, the toner density can be controlled more appropriately.

  Further, the copy facsimile multifunction peripheral 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. Then, the control unit 62 corrects the output of the toner density sensor 38 so as to realize a predetermined toner density at which no fog occurs in the image regardless of the cumulative driving time, and the image density decreases at the predetermined toner density. In the range of the cumulative driving time, the developing bias is controlled to be corrected to the side where the image density increases.

  In this configuration, fog due to increase in developability when the developing device 15 is used for a long period of time (deterioration of carrier) is automatically prevented by setting the toner concentration, while developing performance when the carrier is close to a new one. A decrease in image density due to lowness is prevented by correcting the developing bias. As a result, the necessary width of the output correction of the toner density sensor (which leads to the actual toner density change control) is reduced, so that the required change amount of the toner density can be reduced. Accordingly, it is possible to quickly stabilize the toner concentration in the developer container 35 while avoiding sudden toner replenishment, and thus it is possible to prevent image fogging due to toner charging failure.

  In this embodiment, the scorotron charger 13 for charging the photosensitive drum 12 is provided, and the controller 62 is configured to change the grid bias of the charger 13. Then, the control unit 62 performs control so as to correct the grid bias to the side where the image density increases in addition to the development bias in the range of the cumulative driving time in which the image density decreases at the predetermined toner density.

  As a result, since the low developability (decrease in image density) when the carrier is nearly new is dealt with by correcting the development bias and grid bias, it is possible to more reliably prevent the image density from being lowered.

  Although the preferred embodiment of the present invention has been described above, the above configuration can be changed as follows, for example.

  In the above embodiment, the development bias and the grid bias are corrected as necessary. However, for example, a configuration in which only the development bias is corrected can be changed.

  Instead of setting the toner control density to a toner density that does not cause fogging at any absolute humidity and cumulative drive time (in the normal use range), the image density is above the predetermined density at any absolute humidity and cumulative drive time. Toner density can be set. In this case, the developing bias and the grid bias are corrected so that the image becomes light in the range of the absolute humidity and the cumulative driving time in which the image is fogged.

As a method of correcting the output of the toner density sensor 38, instead of simply correcting the output voltage, the output voltage of the toner density sensor 38 is substantially changed by changing the input control voltage input to the toner density sensor 38. A correction method can be employed. Further, by correcting the reference voltage V _std that is an object to be compared with the output voltage, substantially the same effect as that obtained by correcting the output voltage can be obtained.

  The relationship stored in the storage unit 63 is not limited to the table format as shown in FIG.

  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 correction amount of the output value of the toner density sensor 38 is determined based on the absolute humidity. It can also be determined based on the value alone. It can also 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 figure which shows an example of the table content memorize | stored in a memory | storage part. FIG. 6 is a flowchart of toner density control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 Charging device 15 Developing device 38 Toner density sensor 47 Supply screw (toner supply means)
62 Control Unit 63 Storage Unit (Storage Unit)
64 Toner supply motor 66 Absolute humidity acquisition unit (environment acquisition means)
67 Drive time acquisition unit (drive time acquisition means)
91 Copy Facsimile MFP (image forming device)

Claims (10)

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;
An environment acquisition means for acquiring environment values;
With
The control unit is configured to be able to correct the output of the toner density sensor, and to be able to change a developing bias applied to the developing device,
The control unit corrects the output of the toner concentration sensor so as to realize a predetermined toner concentration that does not cause fogging in the image regardless of the environment detection value that can be acquired by the environment acquisition unit. An image forming apparatus, wherein the developing bias is controlled to be corrected toward a higher image density in a range of the environmental detection value where the image density becomes lower at a predetermined toner density. The image forming apparatus according to claim 1,
A scorotron charger for charging the photoconductor, and the control unit is configured to change the grid bias of the scorotron charger,
The control unit performs control so as to correct the developing bias and the grid bias toward a higher image density in the range of the environmental detection value where the image density becomes lighter at the predetermined toner density. Forming equipment. 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;
An environment acquisition means for acquiring environment values;
With
The control unit is configured to be able to correct the output of the toner density sensor, and to be able to change a developing bias applied to the developing device,
The control unit corrects the output of the toner density sensor so as to realize a predetermined toner density that makes the image density equal to or higher than a predetermined density regardless of the environment detection value that can be acquired by the environment acquisition unit. In addition, the image forming apparatus is configured to control the developing bias so as to reduce the image density in a range of the environmental detection value in which the image is fogged at the predetermined toner density. The image forming apparatus according to claim 1,
A scorotron charger for charging the photoconductor, and the control unit is configured to change the grid bias of the scorotron charger,
The control unit performs control so as to correct the developing bias and the grid bias toward a side where the image density is reduced in a range of the environment detection value in which the image is fogged at the predetermined toner density. Forming equipment.   5. The image forming apparatus according to claim 1, wherein the environmental value is absolute humidity. 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;
Drive time acquisition means for acquiring a cumulative drive time from the start of use of the developer;
With
The control unit is configured to be able to correct the output of the toner density sensor, and to be able to change a developing bias applied to the developing device,
The control unit corrects the output of the toner density sensor so as to realize a predetermined toner density at which no fog occurs in the image regardless of the cumulative driving time, and the image density becomes low at the predetermined toner density. An image forming apparatus, wherein the developing bias is controlled to be corrected toward a higher image density within a range of cumulative driving time. The image forming apparatus according to claim 6,
A scorotron charger for charging the photoconductor, and the control unit is configured to change the grid bias of the scorotron charger,
The control unit performs control so that the developing bias and the grid bias are corrected to a side where the image density is increased in a range of the cumulative driving time in which the image density is decreased at the predetermined toner density. Forming equipment. 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;
With
The control unit is configured to be able to correct the output of the toner density sensor, and to be able to change a developing bias applied to the developing device,
The control unit corrects the output of the toner density sensor so as to achieve a predetermined toner density at which the image density is equal to or higher than a predetermined density regardless of the cumulative driving time, and at the predetermined toner density, the control unit covers the image. An image forming apparatus, wherein the developing bias is controlled to be corrected to a side where the image density is reduced in a range of the cumulative driving time in which the image is generated. The image forming apparatus according to claim 8, wherein
A scorotron charger for charging the photoconductor, and the control unit is configured to change the grid bias of the scorotron charger,
The control unit controls the developing bias and the grid bias so as to correct the image density to be thinner in a range of the cumulative driving time in which the image is fogged at the predetermined toner density. Forming equipment.   A facsimile apparatus as an image forming apparatus according to any one of claims 1 to 9.

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