JP5255972B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus provided with the same, and more particularly to a developing roller using a two-component developer composed of a magnetic carrier and toner The present invention relates to a drive control method for a developing device that develops an electrostatic latent image on an image carrier while holding only the charged toner.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects.

  Further, in the case of color printing in which color superposition is performed, since the toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, full-color image forming apparatuses often employ a two-component development system that charges and conveys only toner that does not contain a carrier component. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one means for solving these problems, a magnetic roller (toner supply member) is used to transfer the developer onto a developing roller (toner carrier) installed in a non-contact manner with respect to the image carrier (photoconductor). In this case, a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and an electrostatic latent image on the image carrier (photoconductor) is formed by an AC electric field. A developing method for adhering toner has been proposed.

  In this developing system, noise and image density unevenness due to current leakage between the developing roller and the photosensitive member have been problems. This is because if the AC component of the developing bias applied to the developing roller in the developing region is too high, the potential difference between the surface potential of the photoconductor and the peak value of the AC voltage increases, causing a leak between the photoconductor and the developing roller. If the AC component is too low, the potential difference between the surface potential of the photoconductor and the peak value of the AC voltage becomes small, and the toner does not fly sufficiently from the developing roller onto the photoconductor, resulting in uneven image density. This is because it occurs.

  For this reason, it is necessary to select an AC voltage for the developing bias so that the above-mentioned problems do not occur. In practice, however, the forming accuracy and mounting accuracy of the developing roller and the gap (developing gap) between the photosensitive member and the developing roller are determined. Since the development gap and the resistance value of the developing roller change due to the wear of the spacers, etc., the likelihood of occurrence of leakage varies with time even for each developing device or even with the same developing device. Further, since the ease of occurrence of the leak varies depending on the use environment of the apparatus, if the same AC voltage is selected uniformly, there may be a case where a leak occurs or image density unevenness occurs.

Therefore, Patent Document 1 discloses a leak generating means for generating a leak between an image carrier (photosensitive member) and a toner carrier (developing roller), and a current flowing between the image carrier and the toner carrier. And a developing device capable of selecting an optimum AC voltage that does not cause leakage or unevenness of image density based on a leakage generation voltage when the leakage is intentionally generated. It is disclosed.
Japanese Patent Laid-Open No. 2003-287942

  In the developing device described above, density calibration (density adjustment) is performed to adjust the thickness of the toner layer on the toner carrier. As an example of density calibration, a DC image and an AC voltage applied to the developing roller are fixed, and a reference image is formed while changing the DC voltage among the DC and AC voltages applied to the magnetic roller. Then, the density of the reference image is read on the photosensitive member or the intermediate transfer member.

  The greater the potential difference of the DC component between the magnetic roller and the developing roller, the thicker the toner layer formed on the developing roller and the higher the image density. Therefore, the density of the reference image increases with changes in the DC voltage applied to the magnetic roller. Change. Therefore, a toner layer thickness that provides a predetermined image density, that is, a DC voltage applied to the magnetic roller is selected, and the value is set as a calibration result.

  When performing the density calibration as described above, if a leak occurs between the photosensitive member and the developing roller, an accurate reference image cannot be formed. This is related to the occurrence of leakage and the toner layer thickness. When the toner layer on the developing roller is thin, leakage is likely to occur between the photoconductor and the developing roller. Conversely, when the toner layer is thick, the leakage occurs. It is difficult to do.

  Therefore, when the DC voltage applied to the magnetic roller is changed, a low DC voltage is applied even if no leakage occurs when a high DC voltage is applied and a thick toner layer is actually used. When a thin toner layer is formed, a leak occurs, and the density of the reference image at that voltage becomes extremely low. In some cases, the output of the voltage is stopped and a subsequent reference image cannot be formed. There was a problem that density calibration could not be executed with high accuracy.

  According to the method of Patent Document 1, it is possible to set the optimum AC voltage to be applied to the developing roller by detecting the occurrence of leakage between the photoconductor and the developing roller. However, no consideration has been given to the occurrence of leaks during density calibration as described above.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a developing device capable of performing calibration with high accuracy by suppressing the occurrence of leak during density calibration for adjusting the toner layer thickness, and an image forming apparatus including the developing device. The purpose is to do.

  In order to achieve the above object, the present invention provides a toner carrier that is disposed so as to face the image carrier in a non-contact manner, a toner supply member that forms a toner thin layer on the toner carrier using a magnetic brush, And a voltage applying means for applying a DC voltage and an AC voltage to the toner carrying member, and changing the AC voltage applied to the toner carrying body by the voltage applying means to change the image carrying Leak generating means for generating a leak between a body and the toner carrying body, a leak detecting means for detecting a leak generated by the leak generating means, and the image carrier based on a detection result of the leak detecting means -A control means for setting a peak-to-peak value DS Vpp of the AC voltage applied between the toner carriers, the control means for setting the set DS-to-DS Vpp. There perform concentration adjustment, the toner supply member on the basis of the density adjustment result - is characterized by setting at least one of the Duty of the potential difference between the AC component of the DC component of the voltage applied between the toner carrying member.

  According to the present invention, in the developing device configured as described above, the density adjustment is performed by changing at least one of a DC voltage applied to the toner supply member and an AC voltage Duty.

  The present invention further includes a developing device having the above-described configuration and a density detecting unit that detects the density of the toner image developed by the developing device, and the inter-DS Vpp set based on the detection result of the leak detecting unit. And at least one of the potential difference of the DC component of the voltage applied between the toner supply member and the toner carrier and the duty of the AC component are changed stepwise to form a reference image, and the density detection The image forming apparatus sets at least one of the potential difference of the DC component and the duty of the AC component so that the density becomes a target value based on the density detection result of the reference image by the means.

  According to the first configuration of the present invention, since the DS Vpp between which the leak does not occur between the image carrier and the toner carrier is preset, the leak does not occur even during the density adjustment. Accordingly, the density adjustment can be performed with high accuracy, and at least one of the potential difference of the DC component of the voltage applied between the toner supply member and the toner carrier and the duty of the AC component can be set to an appropriate value.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, the density adjustment is performed by changing at least one of the DC voltage applied to the toner supply member and the duty of the AC voltage. Thus, it is not necessary to adjust the voltage applied to the toner carrier so that the Vpp between DSs is kept constant, and the voltage control becomes simpler.

  According to the third configuration of the present invention, the development device having the first or second configuration described above and a density detection unit that detects the density of the toner image developed by the development device are provided. The Vpp between DS set based on the detection result is fixed, and at least one of the potential difference of the DC component of the voltage applied between the toner supply member and the toner carrying member and the duty of the AC component are changed stepwise. By forming an image, it is possible to form a reference image having an appropriate density according to a voltage change between the toner supply member and the toner carrier. Accordingly, it is possible to set at least one of the potential difference of the direct current component and the duty of the alternating current component to an optimum state where the image density becomes the target value based on the density detection result of the reference image by the density detection means. Thus, the image forming apparatus is free from the occurrence of a decrease in image quality.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 moving adjacent to each image forming unit, and then the secondary transfer roller 9. In this case, the toner image is transferred onto the transfer paper P at once, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transcribed above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 7 is distributed to the paper transport path 18 by the branching unit 14, and the secondary transfer roller 9 with the image surface reversed. Re-conveyed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  A density detection sensor 40 is disposed on the downstream side of the image forming unit Pd and the upstream side of the secondary transfer roller 9. The density detection sensor 40 irradiates the reference image formed on the intermediate transfer belt 8 in the image forming units Pa to Pd with measurement light, and detects the amount of reflected light from each reference image. A detection result is transmitted to the control part 37 mentioned later as a light reception output signal. As the density detection sensor 40, an optical sensor including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is generally used. When measuring the density of the reference image, when the measurement light is sequentially irradiated from the light emitting element to each reference image on the intermediate transfer belt 8, the measurement light is received as light reflected by the toner and light reflected by the belt surface. Incident on the element.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amount of the light receiving element is reduced. On the other hand, when the adhesion amount of toner is small, conversely, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element. Therefore, the toner adhesion amount (image density) of the reference image of each color is detected based on the output value of the received light signal based on the received reflected light amount, and the exposure value and the development bias characteristic value are compared with a predetermined reference density. By adjusting, density correction is performed for each color.

  Since the density detection sensor 40 needs to strictly define the distance to the measurement object, as shown in FIG. 1, it opposes the driving roller 11 with a small distance variation to the surface of the intermediate transfer belt 8. The intermediate transfer belt 8 is positioned in the width direction according to the density correction pattern formation position on the intermediate transfer belt 8.

  The density detection sensor 40 may be disposed at another position where the reference image on the intermediate transfer belt 8 can be detected. For example, when the density detection sensor 40 is disposed on the downstream side of the secondary transfer roller 9, the image forming units Pa to. There is a possibility that the time from when the reference image is formed by Pd to when the density detection is performed becomes longer, and when the reference image comes into contact with the secondary transfer roller 9, the surface state of the reference image may change. Therefore, as shown in FIG. 1, it is preferable to dispose on the downstream side of the image forming unit Pd and the upstream side of the contact position of the secondary transfer roller 9.

  FIG. 2 is a side sectional view showing a configuration of a developing device used in the image forming apparatus of the present invention. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and is supplied to the first and second via a developer passage (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  Note that a toner concentration sensor (not shown) is disposed in the developing container 20 so as to face the first stirring screw 21a, and the toner supply port 20d is supplied from the supply device according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 20 via

  The magnetic roller 22 includes a nonmagnetic rotating sleeve 22a and a fixed magnet roller body 22b having a plurality of magnetic poles (here, five poles) contained in the rotating sleeve. The developing roller 23 is composed of a non-magnetic developing sleeve, and the magnetic roller 22 and the developing roller 23 are opposed to each other at a facing position (opposing position) with a predetermined gap.

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Then, a magnetic brush (not shown) is formed on the magnetic roller 22, and the thickness of the magnetic brush on the magnetic roller 22 is regulated by the earbrushing blade 25, and then the opposite portion between the magnetic roller 22 and the developing roller 23. A thin toner layer is formed on the developing roller 23 by the potential difference ΔV between Vmag (DC) conveyed and applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23 and a magnetic field.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. The magnetic roller 22 has a second composite waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a Vmag (AC) of a rectangular wave having a phase different from that of Vslv (AC). Applied from the bias circuit 31.

  Accordingly, the voltage applied between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as MS) is a composite waveform Vmag-Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a portion facing the photosensitive drum 1 a developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  The remaining toner that is not used for development is conveyed again to the opposite portion between the developing roller 23 and the magnetic roller 22 and collected by the magnetic brush on the magnetic roller 22. Then, the magnetic brush is peeled off from the magnetic roller 22 at the same polarity portion of the fixed magnet roller body 22b, and then formed again on the magnetic roller 22 as a two-component developer uniformly charged with an appropriate toner concentration. And conveyed to the ear cutting blade 25.

  Further, a voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC), Vslv (AC) applied to the developing roller 23 and Vmag applied to the magnetic roller 22. (DC) and Vmag (AC) can be varied. Further, a leak detection device 35 is connected to the first bias circuit 30. When a leak occurs between the photosensitive drum 1a and the developing roller 23 (hereinafter referred to as DS), the current flowing through the first bias circuit 30 increases rapidly, so the current flowing through the first bias circuit 30 is monitored. By doing so, it is possible to detect the occurrence of a leak.

  The control unit 37 transmits a control signal to the voltage variable device 33 and is applied from the first bias circuit 30 and the second bias circuit 31 to Vslv (DC), Vslv (AC), Vmag (DC), and Vmag (AC). To control. Further, a leak is generated between the DSs by changing Vslv (AC), and applied between the DSs based on the potential difference between the DSs when the leak is detected by the leak detection device 35 (hereinafter referred to as a leak generation voltage). The peak-to-peak value of the alternating voltage (hereinafter referred to as the inter-DS Vpp) is set in a range where no leakage occurs.

  The storage unit 39 is composed of, for example, a readable / writable RAM (Random Access Memory). In addition to the control program used by the control unit 37, the Vpp between DSs set based on the detection result of the leak detection device 35 and the density calibration are used. Necessary for control such as a potential difference Vmag (DC) -Vslv (DC) (hereinafter referred to as ΔV between MSs) of a DC voltage applied between a magnetic roller and a developing roller used in a calibration (hereinafter simply referred to as calibration) Is stored. Note that the control unit 37 and the storage unit 39 may be combined with the control unit and the storage unit of the entire image forming apparatus 100, or may be arranged independently to control the developing devices 3a to 3d.

  The present invention is characterized in that, when performing calibration, the inter-DS Vpp is set based on the leak detection result between the DSs, and the calibration is executed while fixing the conditions of the set inter-DS Vpp. . Specifically, prior to calibration, leak generation and detection are performed between DSs using the voltage variable device 33 and the leak detection device 35, and the leak generation voltage is measured. Then, the inter-DS Vpp is set within a range not exceeding the measured leakage generation voltage.

  Next, the set Vpp between DSs is fixed, and Vmag (DC) is changed stepwise to form a plurality of reference images on the photosensitive drums 1a to 1d. The formed reference image is transferred onto the intermediate transfer belt 8 and then the density is detected by the density detection sensor 40. Then, Vmag (DC) is set based on the detection result so that the density of the reference image becomes the target value (reference value).

  Thereby, since the Vpp between DSs in which no leak occurs between DSs is set in advance, no leak occurs even during calibration in which Vmag (DC) is changed stepwise. Therefore, calibration can be executed with high accuracy.

  Note that, here, ΔV between MSs is changed by changing Vmag (DC) stepwise, but Vslv (DC) may be changed stepwise instead of Vmag (DC). In this case, Vslv (AC) is adjusted according to the change in Vslv (DC) so that the inter-DS Vpp is maintained constant.

  Further, the thickness of the toner layer on the developing roller 23 can be adjusted by changing the duty of the AC voltage applied between the MSs instead of changing the ΔV between the MSs. Also in this case, the duty of Vmag (AC) may be changed, or the duty of Vslv (AC) may be changed. When the duty of Vslv (AC) is changed, the peak-to-peak value of Vslv (AC) and Vslv (DC) are adjusted so that the Vpp between DSs is maintained constant. Further, the toner layer thickness on the developing roller 23 can be adjusted by changing both the ΔV between the MSs and the duty of the AC voltage applied between the MSs.

  FIG. 4 is a flowchart showing a calibration setting procedure in the image forming apparatus provided with the developing device of the present invention. The setting of Vmag (DC) will be described in accordance with the steps in FIG. 4 while referring to FIGS. 1 and 2 as necessary. First, when the apparatus is started up or when calibration is started by a user operation (step S1), Vslv (AC) is varied by the voltage variable apparatus 33 (step S2). Then, leak detection between the DSs is performed by the leak detection device 35 (step S3), and when a leak is detected, a leak occurrence voltage is measured. Then, the inter-DS Vpp value is set within a range not exceeding the measured leak occurrence voltage (step S4), and Vslv (DC) and Vslv (AC) corresponding to the inter-DS Vpp value are set.

  Next, Vmag (DC) is changed stepwise while Vslv (DC) and Vslv (AC) are fixed, and a reference image is formed on the photosensitive drums 1a to 1d (step S5). Then, the density of the reference image transferred onto the intermediate transfer belt 8 is measured by the density detection sensor 40 (step S6), and Vmag (DC) as a target density is set (step S7). Finally, the reference image on the intermediate transfer belt 8 is removed by the belt cleaner 19 to complete the calibration (step S8).

  According to the control of FIG. 4, since the Vpp between DSs in which no leakage occurs between DSs is set prior to calibration, when Vmag (DC) is subsequently changed and calibration is performed, a low Vmag (DC ) No longer leaks when applied. Therefore, there is no possibility that the density of the reference image formed during the calibration is suddenly lowered, and it is possible to set the appropriate Vmag (DC) by executing the calibration with high accuracy.

  Note that FIG. 4 illustrates an example in which calibration is performed by changing Vmag (DC) in stages, but Vslv (DC) is changed in stages instead of Vmag (DC), or Vmag (AC ) Or Vslv (AC) duty can be changed by the same procedure as in FIG.

  Further, here, the density of the reference image transferred onto the intermediate transfer belt 8 by the density detection sensor 40 is measured. However, the density detection sensor is disposed in the vicinity of each of the photosensitive drums 1a to 1d, and the density of the reference image is measured. May be measured on the photosensitive drums 1a to 1d.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the embodiments described above, a reversal development method in which positively charged toner having a positive charging direction (positive side) is used and the toner is allowed to fly to an exposed portion on the surface of the photoreceptor has been described as an example. The present invention can be applied in exactly the same manner to a developing device that uses negatively charged toner having negative (minus side) and a forward developing type developing device that causes toner to fly to an unexposed portion on the surface of the photoreceptor.

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and includes a developing device such as a digital or analog type monochrome copying machine, a monochrome printer, a rotary developing type color printer, a color copying machine, a facsimile, or the like. The present invention can be applied to various image forming apparatuses. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  Using the testing machine as shown in FIG. 1 equipped with the developing device of the present invention shown in FIG. 2, the influence of the occurrence of leak between DSs on the calibration accuracy was investigated. The test was performed in a cyan image forming portion Pa including the photosensitive drum 1a and the developing device 3a.

The test machine conditions were a printing speed of 40 sheets / minute, a photosensitive drum peripheral speed of 200 mm / sec, and a drum surface potential of 230 V for the white background potential (V0) and 20 V for the image portion potential (VL). Further, the developing roller is alumite-treated, the developing roller has a peripheral speed ratio of 1: 3 (forward rotation) with respect to the photoreceptor, and the magnetic roller has a peripheral speed ratio of 1: 5 with respect to the developing roller. (Counter rotation). The DS gap was 0.12 mm, and the MS gap was 0.3 mm. As the developer, a two-component developer comprising a positively charged toner having an average particle diameter of 6.8 μm, a volume resistivity of 10 ¹⁰ Ω, a saturation magnetization of 65 emu / g, and a coated ferrite carrier having an average particle diameter of 45 μm (mixing of toner with carrier) The ratio T / C = 12% by weight) was used.

  The voltage application conditions to the developing roller were Vslv (DC) = 50 V, the frequency of Vslv (AC) was 3.85 kHz, and Duty = 45%. The voltage application conditions between the MSs were Vmag (AC) −Vslv (AC) = 1800 V, frequency = 3.85 kHz, and Duty = 70%.

  As a test method, leak generation and detection are performed prior to calibration, and calibration is performed when the inter-DS Vpp is set (the present invention) and when the inter-DS Vpp is not set (comparative example). This was executed and the ID (image density) of the reference image when Vmag (DC) was changed was measured. The results are shown in FIG.

  As is apparent from FIG. 5, in the present invention in which the inter-DS Vpp is set based on the leak detection result (shown by a solid line in FIG. 5), the ID of the reference image increases in proportion to the ΔV between the MSs. ΔV between MS to achieve the target value (0.48) of (0.48) was 175V (intersection with the dashed line in the figure). On the other hand, in the comparative example in which the Vpp between DSs was not set (indicated by a broken line in FIG. 5), a leak occurred between the DSs when the ΔV between MSs was 100V and 150V, and the density of the reference image was extremely lowered. As a result, the ΔV between MSs for achieving the target ID value (0.48) was 195V. When the MS-to-MS ΔV was set to 195 V, the actual image density was higher than the target value, and the characters were crushed and the resolution was reduced.

  Using the same testing machine as in Example 1, the effect of the occurrence of leakage between the DSs on the calibration accuracy when the calibration was performed by changing the duty of the AC voltage applied between the MSs was investigated. Here, the ratio of the positive waveform to one cycle of the AC waveform is Duty. When positively charged toner is used, the toner movement time from the magnetic roller to the developing roller becomes longer as the Duty becomes larger. Further, the conditions of the tester and the test method were the same as those in Example 1. The results are shown in FIG.

  As apparent from FIG. 6, in the present invention in which the Vpp between DSs is set based on the leak detection result (indicated by a solid line in FIG. 6), the ID of the reference image is the duty of the AC voltage applied between the MSs. The AC voltage Duty (intersection with the alternate long and short dash line in the figure) for achieving the target ID value (0.48) was 68%. On the other hand, in the comparative example in which the Vpp between DSs was not set (indicated by a broken line in FIG. 6), when the duty of the AC voltage applied between the MSs was 60% and 65%, a leak occurred between the DSs. The image density is extremely low. As a result, the duty of the AC voltage for achieving the target ID value (0.48) was 70%. When the duty of the AC voltage applied between the MSs was set to 70%, the actual image density became higher than the target value, and the characters were crushed and the resolution was reduced.

  Based on the above results, leaks are generated and detected prior to calibration, and by setting the Vpp between DSs based on the detection results, the occurrence of leaks between DSs is effectively prevented and calibration is performed accurately. It was confirmed that it can be executed well. Here, the test was performed in the cyan image forming portion Pa, but it has been confirmed that similar results can be obtained in the magenta, yellow, and black image forming portions Pb to Pd.

  The above embodiment is merely an example of the present invention, and the drum surface potential, conditions for applying voltage to the developing roller and the magnetic roller, and the like can be appropriately set according to the specifications of the apparatus and the usage environment.

  The present invention can be applied to a developing device that uses a toner supply member to hold only a charged toner on a toner carrying member and develop an electrostatic latent image on the image carrying member. The inter-DS Vpp is set based on the density, the density adjustment is performed using the set inter-DS Vpp, and the potential difference between the DC component of the voltage applied between the toner supply member and the toner carrier based on the density adjustment result and the AC At least one of the component duties is set.

  As a result, the density adjustment is accurately performed under the condition that no leakage occurs, and at least one of the potential difference of the DC component of the voltage applied between the toner supply member and the toner carrier is set to an appropriate value. A configurable developing device can be provided.

  In addition, when density adjustment is performed, if at least one of the DC voltage applied to the toner supply member and the duty of the AC voltage is changed, it is applied to the toner carrier so that the Vpp between DSs is maintained constant. Therefore, it is not necessary to adjust the voltage to be developed, and the developing device is simpler in voltage control.

  In addition, since the image forming apparatus includes the developing device of the present invention and the density detecting unit that detects the density of the toner image developed by the developing device, the density adjustment can be accurately performed using a reference image having an appropriate density. It can be executed well. Therefore, it is possible to provide an image forming apparatus in which image defects such as character collapse and resolution reduction do not occur.

FIG. 1 is a schematic diagram showing an overall configuration of an image forming apparatus equipped with a developing device of the present invention. These are side surface sectional views which show the structure of the developing device of this invention. These are figures which show an example of the bias waveform applied to a developing roller and a magnetic roller. These are flowcharts showing a calibration execution procedure in an image forming apparatus provided with the developing device of the present invention. These are the graphs which show the relationship between (DELTA) V between MS in Example 1, and ID of a reference | standard image. These are the graphs which show the relationship between Duty of the alternating voltage applied between MS in Example 2, and ID of a reference | standard image.

Explanation of symbols

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller (toner supply member)
23 Developing roller (toner carrier)
25 Bone cutting blade 30 First bias circuit (voltage application means)
31 Second bias circuit (voltage applying means)
33 Voltage variable device (leak generating means)
35 Leak detection device (leak detection means)
37 Control part (control means)
39 Storage 40 Density detection sensor (density detection means)
100 Image forming apparatus Pa to Pd Image forming unit

Claims (2)

A toner carrier that is disposed to face the image carrier in a non-contact manner;
A toner supply member that forms a toner thin layer on the toner carrier using a magnetic brush;
Voltage application means for applying a DC voltage and an AC voltage to the toner supply member and the toner carrier;
Leak generating means for changing the alternating voltage applied to the toner carrier by the voltage application means to generate a leak between the image carrier and the toner carrier;
Leak detecting means for detecting a leak generated by the leak generating means;
A developing device for chromatic and control means for setting the peak-to-peak value DS between Vpp of the AC voltage applied between the toner carrying member, and - the leakage the image bearing member based on the detection result detecting means
Density detecting means for detecting the image density of the toner image developed on the image carrier by the developing device,
The control means is configured to fix the Vpp between DS set based on the detection result of the leak detection means, and between the potential difference MS of the DC component of the voltage applied between the toner supply member and the toner carrier. And at least one of the AC component Duty is changed stepwise by changing only the voltage applied to the toner supply member to form a reference image on the image carrier, and by the density detection means. Based on the detected change in the image density of the reference image, at least one of the ΔV between MSs and the duty of the AC component where the image density becomes a target value is estimated, and the estimated ΔV between MSs or the duty of the AC component is set as a set value. An image forming apparatus. " The image forming apparatus according to claim 1, wherein the reference image is formed by changing at least one of a DC voltage and a duty of an AC voltage applied to the toner supply member.

Images