JP2010217327A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the inside of the machine from becoming dirty due to remaining toner adhered to a sealing member provided in a cleaning device. <P>SOLUTION: This image forming device includes a preliminary charging member 26 for charging the remaining toner by transfer bias voltage to be applied on a transfer roll 20 and preliminary bias voltage having reversed polarity to that of the transfer bias voltage, an inferring means for inferring amount of charging of the remaining toner based on values of transfer current flowing into a photosensitive drum 12 from the transfer roll 20, and a charging current increasing and decreasing means for increasing or decreasing a value of charging current of the preliminary charging member 26 to let it reach the predetermined scope. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In a general electrophotographic image forming apparatus represented by a copying machine or a laser printer, a toner image formed on an image carrier is usually directly transferred to a recording medium or via an intermediate transfer medium. Transferred to a recording medium. Residual toner remaining on the surface of the image carrier without being transferred to the recording medium or intermediate transfer medium is collected by a cleaning device.

  In the cleaning device, generally, a sealing member is used to seal a space between the collection container and the surface of the image holding member so that the collected residual toner does not leak out of the collection container.

  On the other hand, in the image forming apparatus disclosed in Patent Document 1, the secondary transfer residual toner remaining on the intermediate transfer belt is charged to a positive polarity by a toner charging roller, and the secondary transfer residual toner is charged to a negative polarity. The photosensitive drum is electrostatically attracted again to be removed together with the residual toner on the photosensitive drum by a photosensitive drum cleaner (cleaning device).

  Here, the charge amount of the residual toner varies depending on the temperature and humidity. However, in the image forming apparatus disclosed in Patent Document 1, a toner charging auxiliary roller is provided on the upstream side of the toner charging roller, and the secondary transfer is performed prior to the toner charging roller. The remaining toner is positively charged. The nip portion between the toner charging roller and the intermediate transfer belt is adjusted by adjusting the charge applied to the residual toner from the toner charging auxiliary roll according to the temperature and humidity in the image forming apparatus detected by the temperature / humidity sensor. The secondary transfer residual toner splashing generated in the vicinity is suppressed.

JP 2004-117892 A

  It is an object of the present invention to suppress in-machine contamination due to residual toner adhering to a seal member provided in a cleaning device.

  The image forming apparatus according to claim 1, an image holding member, a charging device to which a charging bias voltage is applied and charging the surface of the image holding member, and a surface of the image holding member charged by the charging device. An exposure device that exposes and forms an electrostatic latent image on the surface; a developing device that develops the electrostatic latent image with a developer to form a toner image on the surface of the image carrier; and the charging bias voltage; A transfer device that applies a transfer bias voltage having a reverse polarity to transfer the toner image to a transfer medium, and a pre-bias voltage that is reverse to the transfer bias voltage is applied to the image without being transferred to the transfer medium. The pre-charging device according to any one of claims 1 to 4, wherein the residual toner remaining on the surface of the holding body is charged (please modify. The same applies to the scope of claims), and an opening provided on the surface of the image carrier. From the opening A collecting container for collecting the residual toner, a cleaning member provided in the collecting container for scraping the residual toner from the surface of the image carrier to the opening, and the opening on the upstream side in the transport direction of the residual toner. A cleaning device provided at an edge of the portion and having a seal member that closes a gap between the edge and the image carrier.

  According to a second aspect of the present invention, in the preliminary charging device according to the first aspect, the development transfer condition is a transfer current value of the transfer device.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the developer is a two-component developer including a carrier and a toner, and the development transfer condition is that of the two-component developer. This is the toner density detected by the detecting means for detecting the toner density.

  According to a fourth aspect of the present invention, in the preliminary charging device according to the second aspect, the development transfer condition is an increase / decrease rate of the transfer current value.

  According to the first aspect of the present invention, in-machine contamination due to residual toner adhering to the seal member can be reduced and the life of the image forming apparatus can be extended, compared with the case where the present configuration is not provided. .

  According to the second aspect of the present invention, in-machine contamination due to residual toner adhering to the seal member due to fluctuations in transfer conditions can be reduced as compared with the case where this configuration is not provided.

  According to the third aspect of the present invention, in-machine contamination due to residual toner adhering to the seal member due to fluctuations in toner concentration can be reduced as compared with the case where the present configuration is not provided.

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

1 is a diagram schematically illustrating a main part of an image forming apparatus according to a first embodiment of the present invention. 6 is a graph schematically showing the relationship between temperature and humidity and the charging potential of toner. 6 is a graph showing a relationship between an output transfer current value and an output charging current value in residual toner charge amount control according to the first embodiment of the present invention. 6 is a graph showing a relationship between an output charging current value of residual toner charge amount control and a residual toner charge amount according to the first embodiment of the present invention; 3 is a flowchart showing a flow of transfer current control and residual toner charge amount control according to the first embodiment of the present invention. 4 is a graph showing a relationship between a process speed and an output transfer current value in transfer current control according to the first embodiment of the present invention. It is a figure which shows typically the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. 4 is a graph schematically showing a relationship between toner density and toner charging potential. 6 is a graph showing a relationship between a toner concentration for each temperature and humidity and a charge amount of the toner. 6 is a graph showing a relationship between a toner density and an output charging current value in residual toner charge amount control according to a second embodiment of the present invention. 6 is a flowchart showing a flow of residual toner charge amount control according to a second embodiment of the present invention. (A) is a schematic diagram showing the control range of the charging potential of the residual toner by the conventional preliminary charging member, and (B) is the charging potential of the residual toner by the preliminary charging member according to the first embodiment of the present invention. It is a schematic diagram which shows the control range.

  First, the image forming apparatus 10 according to the first embodiment of the present invention will be described. FIG. 1 is a diagram schematically illustrating a main part of the image forming apparatus 10.

  The image forming apparatus 10 includes a photosensitive drum 12 (image holding member) having a photosensitive layer (not shown) formed on the surface thereof and rotating in the direction of arrow K. The photosensitive drum 12 is charged to a predetermined charging potential (in this embodiment, −700 v) by a charging device 14 to which a charging bias voltage is applied from a charging bias voltage power source (not shown). The charging bias voltage may be only a direct current voltage (DC), or may be a so-called AC + DC superimposed voltage obtained by superimposing an alternating current voltage on a direct current voltage. The photosensitive drum 12 is grounded.

  An exposure device 16 is provided on the downstream side of the charging device 14 in the rotation direction of the photosensitive drum 12. The exposure device 16 is composed of an LED array and exposes the surface of the charged photosensitive drum 12 in accordance with the output image, and forms an electrostatic latent image by attenuating the surface potential of the exposed portion to a predetermined post-exposure potential. To do.

  The electrostatic latent image is developed by a developing device 18 provided on the downstream side of the rotation direction of the photosensitive drum 12 of the exposure device 16, and a toner image is formed on the surface of the photosensitive drum 12. The developing device 18 includes a developing roll 17, to which a developing bias voltage is applied from a developing bias voltage power source (not shown), and the toner (toner in the developer G) accommodated in the developing device 18. ) Is held. The developing device 18 causes the toner held on the developing roll 17 to adhere to the surface of the photosensitive drum 12 to develop the electrostatic latent image, and forms a toner image on the surface of the photosensitive drum 12. As the developer G, a two-component developer containing at least a toner and a carrier is used, but a one-component developer containing no carrier may be used.

  The toner image formed on the surface of the photosensitive drum 12 is transferred onto the printing paper P (recording medium) with a predetermined transfer bias voltage by a transfer roll 20 provided on the downstream side of the developing device 18 in the rotation direction of the photosensitive drum 12. Transcribed. A transfer bias voltage power source 22 is connected to the transfer roll 20, and a transfer bias voltage having a reverse polarity (positive polarity in this embodiment) to the above-described charging bias voltage is applied. The transfer bias voltage power supply 22 is connected to a control unit 44 described later, and the transfer current of the transfer roll 20 is controlled.

  The printing paper P to which the toner image has been transferred is conveyed to a fixing device (not shown) having a heat source, and the toner image is fixed to the printing paper P.

  On the other hand, the residual toner remaining on the surface of the photosensitive drum 12 without being transferred to the printing paper P is set to a predetermined charging potential by the preliminary charging member 26 provided on the downstream side of the photosensitive drum 12 in the rotation direction of the transfer roll 20. Is charged. A charging bias voltage power source 36 is connected to the preliminary charging member 26, and a charging bias voltage having a polarity opposite to that of the transfer roll 20 (negative polarity in this embodiment) is applied. The charging bias voltage power source 36 is connected to a control unit 44 described later, and the charging current value of the preliminary charging member 26 is controlled. These preliminary charging members 26 and the control unit 44 constitute a preliminary charging device. In this embodiment, a charger using corona discharge such as corotron or scorotron is used as the preliminary charging member 26, but a conductive roll or the like may be used.

  Residual toner charged to a predetermined charging potential by the preliminary charging member 26 is removed by a cleaning device 28 provided on the downstream side in the rotation direction of the photosensitive drum 12. The cleaning device 28 includes a housing 30 (collection container) that collects residual toner, and a cleaning blade 32 (cleaning member) provided in the housing 30, and an opening of the housing 30 is formed in the photosensitive drum 12. It is arranged toward the surface. The cleaning blade 32 is formed in a plate shape made of an elastic body such as rubber, and the cleaning blade 32 is brought into contact with the surface of the photosensitive drum 12 to clean (scrap off) residual toner. The cleaned residual toner is once accommodated (collected) in the housing 30 and discharged to the outside of the housing 30 through a discharge hole (not shown).

  In addition, the housing 30 is provided with a seal member 34 that prevents residual toner cleaned by the cleaning blade 32 from splashing and leaking outside the housing 30. The seal member 34 is formed in a film shape (thin plate shape), one end of which is fixed to the edge (inner wall) of the opening of the housing 30 with an adhesive or the like, and the other end is in contact with the surface of the photosensitive drum 12. It is provided so as to close a gap between the edge of the opening and the photosensitive drum 12. In FIG. 1, the thickness of the sealing member 34 is exaggerated for easy understanding. The material, shape, etc. of the seal 34 can be changed as appropriate.

  A neutralization device 40 is provided on the downstream side of the cleaning device 28 in the rotation direction of the photosensitive drum 12. The static eliminator 40 is composed of an erase lamp, and discharges the surface of the photosensitive drum 12 by exposing the surface of the photosensitive drum 12. The charged photosensitive drum 12 is charged again by the charging device 14.

  Next, transfer current control will be described.

  The charge amount of the toner image (toner forming the toner image) formed on the surface of the photosensitive drum 12 varies depending on the temperature and humidity inside and outside the image forming apparatus 10. Therefore, the transfer current control is performed in the control unit 44.

  A temperature / humidity sensor 42 for detecting the temperature and humidity in the image forming apparatus 10 is connected to the control unit 44, and transfer applied to the transfer roll 20 according to the temperature and humidity detected by the temperature / humidity sensor 42. The bias voltage is increased or decreased, and the transfer current discharged from the transfer roll 20 to the photosensitive drum 12 is controlled to be a predetermined value.

The control unit 44 includes an output transfer current table storage unit 46 including a nonvolatile memory. The output transfer current table storage unit 46 stores in advance an output transfer current value that flows from the transfer roll 20 to the photosensitive drum 12 for each temperature and humidity in the image forming apparatus 10. The temperature and humidity and the output transfer current value are obtained from experiments, and are set as follows, for example.
Environment 1 (high temperature and high humidity): Temperature 28 ° C., humidity 85% Output transfer current value: 28.6 uA
Environment 2 (normal temperature and humidity): Temperature 22 ° C., Humidity 55% Output transfer current value: 26.0 uA
Environment 3 (low temperature and low humidity): Temperature 10 ° C., humidity 15% Output transfer current value: 23.4 uA
Note that the above data was obtained from experiments to be described later.

  The control unit 44 reads out the output transfer current value corresponding to the temperature and humidity detected by the temperature / humidity sensor 42 from the output transfer current table storage unit 46 and transfers the transfer bias voltage value corresponding to the output transfer current value to the transfer bias. By setting the voltage power supply 22, the transfer current value of the transfer roll 20 is controlled. The controller 44 stores resistance values of the transfer roll 20 and various wirings and circuits obtained from experiments, and the transfer bias set in the transfer bias voltage power source 22 from the resistance value and the output transfer current value. The voltage value is calculated.

  In this embodiment, the temperature / humidity sensor 42 is installed in the image forming apparatus 10 and the temperature and humidity in the image forming apparatus 10 are detected as an example. However, the temperature / humidity sensor 42 is used as the image forming apparatus 10. It may be installed outside and the transfer current control may be performed based on the temperature and humidity outside the image forming apparatus 10.

  Next, residual toner charge amount control will be described.

  The charge amount of the residual toner remaining on the surface of the photosensitive drum 12 varies depending on the output transfer current value output from the transfer roll 20 to the photosensitive drum 12. For this reason, the control unit 44 performs residual toner charge amount control.

  2A to 2C, as comparative examples, in the image forming apparatus 10 to which the residual toner charge amount control according to the present embodiment is not applied, three environments (environment 1) having different temperatures and humidity are shown. (High temperature and high humidity): 28 ° C., 85%, Environment 2 (normal temperature and normal humidity): 22 ° C., 55%, Environment 3 (low temperature and low humidity): 10 ° C., 15%) are schematically shown. ing. 2A shows the charging potential of the toner (toner image) before being transferred to the printing paper P by the transfer roll 20, and FIG. 2B shows the surface of the photosensitive drum 12 without being transferred to the printing paper P. FIG. 2C shows the charging potential of the residual toner charged by the preliminary charging member 26. Note that reference numerals 50, 52, and 54 in the figure correspond to the environments 1, 2, and 3, respectively. The vertical axis represents the number of toners (number of particles) per unit area of the image formable region of the photosensitive drum 12, and the horizontal axis represents the charging potential of the toner. FIG. 4 shows a correlation between a general transfer current value and the charge amount of the residual toner.

  As shown in FIG. 2A, the charged potential of the toner image (toner) formed on the surface of the photosensitive drum 12 differs depending on the environments 1 to 3. Therefore, the transfer current value for transferring the toner image onto the printing paper P is increased or decreased according to the environment 1 to the environment 3 by the transfer current control described above. By increasing or decreasing the transfer current value, the charged potential of the residual toner remaining on the surface of the photosensitive drum 12 without being transferred to the printing paper P is increased or decreased (see FIG. 2B). As described above, when a constant charge (charging current) is applied from the preliminary charging member 26 to the residual toner whose charging potential varies depending on each of the environments 1 to 3, the charging potential of the residual toner is low in the environment 1 where the charging potential is low. Run short. Thereby, for example, the residual toner is scraped off by the seal member 34 provided at the edge of the opening of the cleaning blade 32 on the upstream side in the rotation direction of the photosensitive drum 12 (upstream side in the residual toner conveyance direction). 10 (especially, the preliminary charging member 26) may be contaminated. (If the charging potential is insufficient, the electrostatic adhesion between the residual toner and the photosensitive member is reduced, so that the seal member scrapes off.) On the other hand, in the environment 3 where the charging potential is high, the charging potential of the residual toner is excessive. It becomes. If the charged potential of the residual toner becomes excessive, the electrostatic adhesion between the residual toner and the photosensitive member increases, and the cleaning performance by the cleaning blade decreases. Therefore, it is desirable to control the charging potential (charge amount) of the residual toner to a value within a predetermined range.

  FIG. 12A schematically shows a control range of the charging potential of the residual toner by the conventional preliminary charging member, and FIG. 12B shows the preliminary charging member 26 of the present embodiment. A control range of the charging potential of the residual toner is schematically shown.

  The conventional preliminary charging member reduces the charge amount of the residual toner, and corrects the surface potential unevenness of the photosensitive drum 12 after the transfer. When the charge amount of the residual toner is reduced, the electrostatic adhesion between the residual toner and the photosensitive drum 12 is weakened, so that the cleaning property is improved. Further, the surface potential of the photosensitive drum 12 after the transfer may be uneven due to an image difference (toner amount) or the like, and the unevenness may remain at the time of charging in the next process. Is going. Conventionally, if the amount of charge of the residual toner after passing through the preliminary charging member is set within the range indicated by reference numeral 80 shown in FIG. 12A, cleaning properties can be secured (actually, for potential unevenness correction). Since there is a necessary charging output, it was used on the negative charging side as indicated by reference numeral 82).

  However, recently, the lubricant is applied to the surface of the photosensitive drum 12 in order to extend the life of the photosensitive drum 12, and the toner has a more spherical shape in order to improve the image quality. The non-electrostatic adhesion force between the residual toner after passing through the preliminary charging member 26 and the photosensitive drum 12 is reduced. For this reason, when the charge amount of the residual toner after passing through the preliminary charging member 26 becomes close to 0 (see reference numeral 84 in FIG. 12B), the seal member 34 scrapes off, or the upper limit value of the toner charge amount becomes small. ing. Therefore, it is necessary to set the charging range of the residual toner after passing through the preliminary charging member 26 as indicated by reference numeral 86 shown in FIG. 12B (in fact, there is a charging output necessary for correcting the potential unevenness, so that it is indicated by reference numeral 88. It will be used on the negative charging side).

  Here, in the residual toner charge amount control according to the present embodiment, the charge amount of the residual toner is estimated from the transfer current value (development transfer condition) of the transfer roll 20, and the preliminary charge is performed based on the estimated charge amount of the residual toner. The charging current value discharged from the member 26 to the photosensitive drum 12 (flowing into the photosensitive drum 12) is increased or decreased to control the residual toner charge amount to be within a predetermined range. For example, when the transfer current value is large, the charging potential of the residual toner charged to the positive polarity becomes high, and the charge necessary to charge the residual toner to the reverse polarity (negative polarity) becomes large. It needs to be bigger. On the other hand, when the transfer current value is small, the charging potential of the residual toner becomes low, and the charge necessary to charge the residual toner to the reverse polarity becomes small. Therefore, it is necessary to reduce the charging current value. The charge applied to the residual toner, that is, the charging current value is determined using the correlation between the transfer current value and the charging current value.

  Specifically, the control unit 44 includes an output charging current table storage unit 48 (estimating means) made of a nonvolatile memory or the like. The output charging current table storage unit 48 stores an output charging current value flowing from the preliminary charging member 26 to the photosensitive drum 12 for each transfer current value (output transfer current value) flowing from the transfer roll 20 to the photosensitive drum 12. Is stored in advance. The output transfer current value and the output charging current value are obtained from experiments, and as an example, the correlation between the output transfer current value and the output charging current value as shown in FIG. 3 is stored. FIG. 3 is obtained from the experimental results described later.

  The control unit 44 reads out the output charging current value corresponding to the output transfer current value from the output charging current table storage unit 48 and sets the preliminary charging bias voltage value corresponding to the output charging current value in the charging bias voltage power source 36. Thus, the charging current value flowing from the preliminary charging member 26 into the photosensitive drum 12 is controlled to the output charging current value. The controller 44 stores resistance values of the preliminary charging member 26 and various wirings and circuits obtained from the experiment, and the preliminary value set in the charging bias voltage power source 36 from the resistance value and the output charging current value. The charging bias voltage value is calculated.

  Next, the flow of transfer current control and residual toner charge amount control will be described with reference to the flowchart shown in FIG.

  After the development process by the developing device 18 is completed, the temperature and humidity in the image forming apparatus 10 is detected by the temperature and humidity sensor 42 in step 100 and output to the control unit 44. Next, in step 102, the output transfer current value corresponding to the temperature and humidity detected by the temperature / humidity sensor 42 is read from the output transfer current table storage unit 46. Next, in step 104, a transfer bias voltage value corresponding to the output transfer current value read from the output transfer current table storage unit 46 is set in the transfer bias voltage power supply 22. As a result, the transfer current value of the transfer roll 20 becomes the output transfer current value, and the toner image is transferred to the printing paper P. Next, in step 106, the transfer process by the transfer roll 20 is completed.

  After the transfer process by the transfer roll 20 is completed, in step 108, the output charging current value corresponding to the output transfer current value is read from the output charging current table storage unit 48. Next, in step 110, a preliminary charging bias voltage value corresponding to the output charging current value read from the output charging current table storage unit 48 is set in the charging bias voltage power source 36. As a result, the charging current value of the preliminary charging member 26 becomes the output charging current value, and the residual toner is charged to a predetermined charging potential. Next, in step 112, the preliminary charging process by the preliminary charging member 26 ends.

  Next, an example of the experimental result is shown.

  First, in the above environment 1 to environment 3, the output transfer current value output to the transfer roll 20 was changed, and it was confirmed that the residual toner scraped off by the seal member 34 occurred. This experiment is performed in the order of environment 2, environment 1, and environment 3 to form a toner image in 5% of the image formable area on the surface of the photosensitive drum 12, and 30,000 sheets of printing paper in each environment 1 to environment 3. Appropriate output was made. FIG. 4 is an experimental result showing the charge amount of the residual toner after being charged by the preliminary charging member 26.

<Experimental conditions>
Recording paper size: A4LEF (Long Edge Feed)
Process speed (peripheral speed of the photosensitive drum 12): 220 mm / s
Maximum image density (Dmax): 1.65
・ Developer (two-component developer)
Toner: Made of polyester resin (manufactured by emulsion polymerization method), average particle size of 5.8 um, additives (titanium compound, silica, cerium oxide, etc.), additive particle size of 20 nm to 150 nm
Carrier: magnetic powder coated with methacrylic resin (average particle size 35 μm), resistance 12.0 logΩ (development bias voltage −600 V)
Seal member: made of thermoplastic polyurethane, thickness 0.2 mm, free length 6.0 mm, contact angle 20 degrees with respect to the surface of the photoconductor drum 12 Output current value output to the photoconductor drum Environment 2 (normal temperature and humidity) ): 26.0 uA (reference output transfer current value)
Environment 1 (high temperature and high humidity): 28.6 uA (110% of the reference output transfer current value)
Environment 3 (low temperature and low humidity): 23.4uA (90% of the standard output transfer current value)
-Output charging current value output to the photosensitive drum Environment 2 (room temperature and humidity): -300 uA
Environment 1 (high temperature and high humidity): -300uA
Environment 3 (low temperature and low humidity): -300uA

  Next, residual toner charge amount control is performed, and the output charging current value output from the preliminary charging member 26 to the photosensitive drum 12 is increased or decreased in accordance with the output transfer current value output from the transfer roll 20 to the photosensitive drum 12. It was confirmed that the residual toner was not scraped off by the seal member 34. Note that the same experimental conditions as in the above experiment are omitted as appropriate.

<Experimental conditions>
-Output transfer current value output to the photosensitive drum Environment 2 (room temperature and humidity): 26.0 uA (reference output transfer current value)
Environment 1 (high temperature and high humidity): 28.6 uA (110% of the reference output transfer current value)
Environment 3 (low temperature and low humidity): 23.4uA (90% of the standard output transfer current value)
-Output charging current value output to the photosensitive drum Environment 2 (room temperature and humidity): -300uA (reference output charging current value)
Environment 1 (high temperature and high humidity): -330uA (110% of reference output transfer current value)
Environment 3 (low temperature and low humidity): -270 uA (90% of the standard output transfer current value)

  As can be seen from the above experimental results, when the output transfer current value and the output charging current value in environment 2 (room temperature and humidity) are set as the reference output transfer current value and the reference output charging current value, respectively, the environment relative to the reference output transfer current value The increase / decrease rate of the output transfer current value of 1 and environment 3 and the increase / decrease rate of the output charge current value of environment 1 and environment 3 with respect to the reference output charging current value match. Therefore, in the residual toner charge amount control, by calculating the increase / decrease rate of the output transfer current with respect to the predetermined reference transfer current value set in advance, and by increasing / decreasing the predetermined reference charge current value set in advance by this increase / decrease rate, An output charging current value corresponding to each environment 1 to environment 3 is obtained.

  In the transfer current control described above, the transfer current value output to the transfer roll 20 is controlled based on the temperature and humidity detected by the temperature / humidity sensor 42, but the transfer current value is controlled based on the process speed. Also good. The process speed means the speed of a series of image forming processes from the charging device 14 to the charge eliminating device 40, and specifically the peripheral speed of the photosensitive drum 12.

  FIG. 6 shows the relationship between the process speed and the output transfer current value. For example, the process speed is increased or decreased according to the thickness (for example, postcard printing) of the printing paper P that is the printing medium. When the process speed is increased, the charging time by the transfer roll 20 is shortened, so that the charging current necessary for the transfer is increased. Conversely, when the process speed is decreased, the transfer time is increased, and the charging current necessary for the transfer is increased. Becomes smaller. The charge amount of the residual toner may be estimated from the correlation between the process speed and the output transfer current value, and the output charging current value by the preliminary charging member 26 may be controlled.

  Next, the image forming apparatus 60 according to the second embodiment will be described. Note that the same components as those in the first embodiment are denoted by the same reference numerals and will be appropriately omitted.

  The charge amount of the toner image (toner) formed on the surface of the photosensitive drum 12 also varies depending on the toner concentration of the developer G. Therefore, in the image forming apparatus 60, residual toner charge amount control based on the toner density is performed.

  As shown in FIG. 7, the developing device 18 includes a toner concentration sensor 62 (detecting means) that measures the toner concentration of the developer G stored in the developing device 18 (the ratio of the toner in the afterimage agent G). Yes. The toner concentration sensor 62 is an ATC (Automatic Threshold Control) sensor that detects the toner concentration by detecting the magnetic permeability of the developer G accommodated in the developing device 18, and outputs the detected toner concentration to the control unit 44. To do. The controller 44 controls the charging current value of the preliminary charging member 26 to the output charging current value by setting the preliminary charging bias voltage value corresponding to the toner density detected by the toner density sensor 62 in the charging bias voltage power source 36. To do.

  8A to 8C show, as a comparative example, two developers (developers) having different toner concentrations in the image forming apparatus 10 to which the residual toner charging control according to the present embodiment is not applied. 1 (low density): 6.5%, developer 2 (high density): 7.5%) is schematically shown. 8A shows the charging potential of the toner (toner image) before being transferred to the printing paper P by the transfer roll 20, and FIG. 8B shows the surface of the photosensitive drum 12 without being transferred to the printing paper P. FIG. 8C shows the charging potential of the residual toner charged by the preliminary charging member 26. Reference numerals 66 and 68 in the figure correspond to the developers 1 and 2, respectively. The vertical axis represents the number of toners (number of particles) per unit area of the toner image formable region of the photosensitive drum 12, and the horizontal axis represents the charging potential of the toner.

  As shown in FIG. 8B, the charged potential of the residual toner after transfer varies depending on the toner density of the developer G. Further, as shown in FIG. 9, the charged potential of the remaining toner also varies depending on the environment 1 to the environment 3. In this way, when a constant charge (charging current) is applied from the preliminary charging member 26 to the residual toner having a different charging potential depending on the toner density and the environments 1 to 3, the charging potential of the residual toner is low in the developer 1 having a low charging potential. Is insufficient and is scraped off by contact with the seal member 34, for example, and the preliminary charging member 26 becomes dirty or the image forming apparatus 10 is contaminated. (If the charging potential is insufficient, the electrostatic adhesion between the residual toner and the photosensitive member is reduced, so that the seal member scrapes off.) On the other hand, in the developer 2 having a high charging potential, the charging potential of the residual toner is high. It becomes excessive. If the charged potential of the residual toner becomes excessive, the electrostatic adhesion between the residual toner and the photosensitive member increases, and the cleaning performance by the cleaning blade decreases. Therefore, it is desirable to control the charging potential (charge amount) of the residual toner to a value within a predetermined range.

  Here, in the residual toner charge amount control according to the present embodiment, the residual toner is determined based on the temperature and humidity (development transfer condition) detected by the temperature / humidity sensor 42 and the toner concentration (development transfer condition) detected by the toner density sensor 62. The charge amount of the toner is estimated, and the charging current value of the preliminary charging member 26 is increased or decreased based on the estimated charge amount of the residual toner, and control is performed so that the charge amount of the residual toner becomes a value within a predetermined range. For example, when the toner concentration is low in a low temperature and low humidity environment, the charge potential of the residual toner charged to the positive polarity becomes high, and the charge necessary to charge the residual toner to the reverse polarity (negative polarity) is large. Therefore, it is necessary to increase the charging current value. Conversely, when the toner concentration is high in a high temperature and high humidity environment, the charging potential of the residual toner is lowered, and the charge necessary to charge the residual toner to the opposite polarity is reduced, so the charging current value is reduced. There is a need. Using such a correlation between the transfer current and the charging current, a charging current value for charging the residual toner is determined.

  Specifically, the control unit 44 includes an output charging current table storage unit 72 (estimating unit) that includes a nonvolatile memory or the like. The output charging current table storage unit 72 stores in advance the output charging current value of the preliminary charging member 26 for each toner concentration in each environment (for example, environment 1 to environment 3). The toner concentration and the output charging current value are obtained from experiments, and as an example, the correlation between the toner concentration and the output charging current value shown in FIG. 10 is stored. FIG. 10 is obtained from the experimental results described later.

  The control unit 44 reads out the output charging current value corresponding to the temperature and humidity detected by the temperature / humidity sensor 42 and the toner concentration detected by the toner concentration sensor 62 from the output charging current table storage unit 72 and outputs the output charging current. A preliminary charging bias voltage value corresponding to the current value is set in the charging bias voltage power source 36. Thus, the charging current value flowing from the preliminary charging member 26 into the photosensitive drum 12 is controlled to the output charging current value. The controller 44 stores resistance values of the preliminary charging member 26 and various wirings and circuits obtained from the experiment, and the preliminary value set in the charging bias voltage power source 36 from the resistance value and the output charging current value. The charging bias voltage value is calculated.

  Next, the flow of residual toner charge amount control will be described with reference to the flowchart shown in FIG.

  After the transfer process by the transfer roll 20 is completed, the temperature and humidity in the image forming apparatus 10 are detected by the temperature / humidity sensor 42 in step 120 and output to the control unit 44. Next, in step 122, the toner concentration of the developer G is detected by the toner concentration sensor 62 and output to the control unit 44. Next, in step 124, the output charging current value corresponding to the temperature and humidity detected by the temperature / humidity sensor 42 and the toner concentration detected by the toner concentration sensor 62 is read from the output charging current table storage unit 72. Next, in step 126, a preliminary charging bias voltage value corresponding to the output charging current value read from the output charging current table storage unit 72 is set in the charging bias voltage power source 36. As a result, the charging current value of the preliminary charging member 26 is controlled to the output charging current value, and the residual toner is charged to a predetermined charging potential. Next, at step 128, the preliminary charging process by the preliminary charging member 26 ends.

  Next, an example of the experimental result is shown.

  First, in the above-described environments 1 and 3, the charging current value of the preliminary charging device 26 was changed according to the toner concentration of the developer G, and it was confirmed that the residual toner was not scraped off by the seal member 34. Note that the same experimental conditions as the experiment shown in the first embodiment are omitted as appropriate.

<Experimental conditions>
・ Setting value of toner density of developer G in each environment 1 and 3 Environment 1 (high temperature and high humidity): 6%, 6.5%, 7.0% (reference toner density 6.5%)
Environment 3 (low temperature and low humidity): 7%, 7.5%, 8.0% (reference toner density 7.5%)
-Output charging current value output to the photosensitive drum: -300uA (reference output charging current value)

As shown in the above experimental results and FIG. 10, when the reference toner concentrations of the environments 1 and 3 are set to 6.5% and 7.5%, respectively, the output charging current value I ₁ is obtained by the equation (1). be able to.
I ₁ = I ₀ + (TC ₀ −TC) × 200 (1)
Here, I ₀ : reference output charging current value, TC ₀ : reference toner density in each environment, TC: measured value of toner density (corresponding to the set value of toner density in this experiment).

  In the present embodiment, the output charging current value is estimated from the temperature and humidity detected by the temperature / humidity sensor 42 and the toner concentration detected by the toner concentration sensor 62, but the toner concentration detected by the toner concentration sensor 62 is used. The output charging current value may be estimated using only.

  In this embodiment, an ATC sensor is used as the toner concentration sensor 62, but the present invention is not limited to this. For example, a patch image for toner density detection may be formed on the surface of the photosensitive drum 12, and the density of this patch image may be detected by a density sensor provided on the side of the photosensitive drum 12.

  In the first and second embodiments, the toner image is transferred onto the printing paper P by the transfer roll 20 as an example. However, instead of the printing paper P, the toner image is transferred to an intermediate transfer belt or the like. May be.

  Moreover, the experimental result shown above is an example to the last, and does not limit the structure of this invention at all. Each set value used in the experiment can be appropriately changed according to the configuration of the image forming apparatus and the environment in which the image forming apparatus is placed.

  The first and second embodiments of the present invention have been described above. However, the present invention is not limited to such embodiments, and the first and second embodiments may be used in combination. Of course, various embodiments can be implemented without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photosensitive drum (Image holding body)
14 Charging Device 16 Exposure Device 17 Developing Roll (Developing Device)
18 Developing device 20 Transfer roll (transfer device)
26 Pre-charging member (pre-charging device)
28 Cleaning device 30 Housing (collection container)
32 Cleaning blade (cleaning member)
34 Sealing member 44 Control unit (charging current increasing / decreasing means)
48 Output charging current table storage (assuming means)
60 Image forming apparatus 62 Toner density sensor (detection means)
72 Output charging current table storage section (assuming means)

Claims (4)

An image carrier,
A charging device to which a charging bias voltage is applied to charge the surface of the image carrier;
An exposure device that exposes the surface of the image carrier charged by the charging device and forms an electrostatic latent image on the surface;
A developing device that develops the electrostatic latent image with a developer and forms a toner image on a surface of the image carrier;
A transfer device that applies a transfer bias voltage having a polarity opposite to that of the charging bias voltage and transfers the toner image to a transfer medium;
5. The correction according to claim 1, wherein a preliminary bias voltage having a polarity opposite to the transfer bias voltage is applied to charge residual toner remaining on the surface of the image carrier without being transferred to the transfer medium. ) And a preliminary charging device described in
The opening is directed to the surface of the image carrier, a collection container for collecting the residual toner from the opening, and the residual toner provided in the collection container for scraping the residual toner from the surface of the image carrier to the opening. A cleaning device comprising: a cleaning member to be dropped; and a seal member provided at an edge of the opening on the upstream side in the transport direction of the residual toner and closing a gap between the edge and the image carrier;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the development transfer condition is a transfer current value of the transfer device. The developer is a two-component developer containing a carrier and a toner;
The image forming apparatus according to claim 1, wherein the development transfer condition is a toner concentration detected by a detection unit that detects a toner concentration of the two-component developer.   The image forming apparatus according to claim 2, wherein the development transfer condition is an increase / decrease rate of the transfer current value.

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