JP2010085591A - Developing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that minimizes the effect of a toner layer during leak detection and is able to apply leak voltages to both an image part and a white part without wasting toner and to provide an image forming apparatus that has a developing device. <P>SOLUTION: A first bias circuit 30 for applying Vslv (DS) and Vslv(AC) is connected to a developing roller 23. A second bias circuit 31 for applying a Vmag (DC) and Vmag (AC) is connected to a magnetic roller 22. A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31. A leak detector 35 is connected to the first bias circuit 30. In order to detect occurrence of leak, the Vmag (DC) is equally applied to the Vslv (DC) or applied in the direction in which toner moves from the developing roller 23 to the magnetic roller 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 including the developing device, and in particular, uses a two-component developer composed of a magnetic carrier and a 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 a charged toner on the body.

  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. The development gap and the resistance value of the developing roller differ for each development due to wear of the spacers and the like. In addition, since the ease of occurrence of a leak varies depending on the use environment of the apparatus, when the same AC voltage is selected uniformly, a leak may occur or image density unevenness may occur.

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 method of Patent Document 1, a toner layer is formed on the toner carrier even when a leak occurs and is detected. However, if a leak is detected in a state where the toner layer is formed on the toner carrier, the leak generation voltage is likely to vary due to a change in the thickness of the toner layer, a change in the toner charge amount, and the like, resulting in poor measurement accuracy. For this reason, it is necessary to determine an optimum AC voltage in consideration of variations in leakage occurrence voltage.

  Further, in the case of reversal development using positively charged toner, as shown in FIG. 5, the leakage of the white background portion (unexposed portion) is the negative peak of the white background portion potential V0 of the photosensitive member and the AC voltage applied to the toner carrier. The image portion (exposure portion) leak occurs due to the potential difference A from the value (−Vpp), and the potential difference between the image portion potential VL of the photosensitive member and the positive peak value (+ Vpp) of the AC voltage applied to the toner carrier. Generated by B.

  Here, the white background portion potential V0 changes according to environmental conditions, durability conditions (elapsed time), and the like, but the image portion potential VL is maintained substantially constant. For example, when the white background portion potential V0 is lowered, the potential difference A is also reduced, so that leakage at the white background portion is difficult to occur. As a result, the control works in the direction of increasing the peak-to-peak value (Vpp) of the AC voltage. However, since the image portion potential VL does not change, if the peak-to-peak value is increased, the potential difference B is increased, and leakage tends to occur in the image portion.

  In other words, since the occurrence of leaks is different between the image area and the white background area, the method of detecting only the leak of the white background area is not sufficient.In order to improve the leak detection performance, not only on the white background area side but also on the image area side. It is necessary to detect the occurrence of leaks. However, in the conventional technology, when the leak is detected in the image portion, the toner on the toner carrier adheres to the image portion and consumes the toner. Only detection was possible. Therefore, there has been a demand for the development of a leak detection method that is less susceptible to the change in V0 and less susceptible to the toner layer.

  In view of the above problems, the present invention includes a developing device capable of reducing the influence of a toner layer at the time of detecting a leak as much as possible and detecting the occurrence of a leak in both an image portion and a white background portion without consuming toner. Another object of the present invention is to provide an image forming apparatus.

  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 unit that applies a DC voltage or a DC voltage and an AC voltage to the toner supply member, and applies a DC voltage and an AC voltage to the toner carrier. Leak generating means for changing the applied AC voltage to generate a leak between the image carrier and the toner carrier, and a leak detecting means for detecting the leak generated by the leak generator. And the leak generating means has a DC voltage applied to the toner supply member equal to or equal to a DC voltage applied to the toner carrier, or from the toner carrier. It is characterized by causing a leak in a state where the toner supply member is a toner is applied in the direction of movement.

Further, the present invention is a reversal development method in which the developing device having the above-described configuration is developed by causing toner to fly to the exposed portion of the image carrier, and the exposed portion potential on the surface of the image carrier is VL, When the applied DC voltage is Vslv (DC), VL and Vslv (DC) when the leak is generated by the leak generating means satisfy the following conditional expression (1).
| VL | ≧ | Vslv (DC) | (1)

Further, the present invention is a forward rotation developing method in which in the developing device having the above-described configuration, the toner is ejected and developed on an unexposed portion of the image carrier, and the potential of the unexposed portion on the surface of the image carrier is set to V0. When the direct-current voltage applied to the carrier is Vslv (DC), V0 and Vslv (DC) when the leak is generated by the leak generating means satisfy the following conditional expression (2).
| V0 | ≦ | Vslv (DC) | (2)

  According to the present invention, in the developing device configured as described above, the leak generating unit generates a leak by stepwise changing a DC voltage applied to the toner carrier, and the leak detecting unit generates a leak each time. And a DC voltage that maximizes the AC voltage applied to the toner carrier when leak is detected is set as a DC voltage applied during development.

  The present invention also provides an image forming apparatus equipped with the developing device having the above-described configuration.

  According to the first configuration of the present invention, leakage can be generated and detected in a state where there is almost no toner thin layer on the toner carrier, and the leak point is stably detected without being affected by the toner thin layer. As a result, the variation in leakage generation voltage is suppressed, and the measurement accuracy is increased. In addition, since the formation of the toner layer on the toner carrier is suppressed as much as possible, even if leak detection is performed in the image portion (exposure portion), toner consumption hardly occurs. Therefore, it is possible to detect both of the white background and the image portion on the image carrier and detect the leak at a time, and it is possible to perform more reliable leak detection as compared with the case where the leak detection is performed only on the white background. it can.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, in the case of the reversal development method, the exposure unit potential VL on the surface of the image carrier when the leak occurs and the toner carrier are applied. When the direct current voltage Vslv (DC) satisfies the conditional expression | VL | ≧ | Vslv (DC) |, the potential difference between the exposed portion (image portion) of the image carrier and the toner carrier does not move the toner. Alternatively, since the toner moves in the direction from the exposure unit side to the toner carrier, the toner adhesion to the exposure unit can be more effectively suppressed.

  Further, according to the third configuration of the present invention, in the developing device having the first configuration, in the case of the forward developing method, the potential of the unexposed portion V0 on the surface of the image carrier when the leak occurs and the toner carrier When the applied DC voltage Vslv (DC) satisfies the conditional expression | V0 | ≦ | Vslv (DC) |, the potential difference between the unexposed part (image part) of the image carrier and the toner carrier Does not move, or moves in the direction from the unexposed portion to the toner carrier, so that toner adhesion to the unexposed portion can be more effectively suppressed.

  According to the fourth configuration of the present invention, in the developing device of the first configuration, the DC voltage applied to the toner carrier is changed stepwise to generate a leak, and when the leak is detected, the toner carrier By setting the DC voltage at which the AC voltage applied to the maximum is set as the DC voltage applied during development, Vslv (DC) is set to be the strongest against leakage, and the AC voltage is set to the maximum voltage within the range where leakage does not occur. Can be set to

  Further, according to the fifth configuration of the present invention, by mounting the developing device having any one of the first to fourth configurations, leakage and image density unevenness can be detected based on the accurately detected leak generation voltage. Since an optimal AC voltage that does not occur can be selected, an image forming apparatus that can simultaneously solve the occurrence of noise due to current leakage and the occurrence of uneven image density is obtained.

  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.

  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 the first and second are passed through developer passages (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 1 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. After the layer thickness of the magnetic brush on the magnetic roller 22 is regulated by the ear cutting blade 25, the magnetic brush 22 is conveyed to the opposite portion between the magnetic roller 22 and the developing roller 23, and Vmag (DC) applied to the magnetic roller 22 and the developing roller 23. A toner thin layer is formed on the developing roller 23 by a potential difference ΔV with respect to Vslv (DC) applied to the toner 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. Further, the magnetic roller 22 has a second combined waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a rectangular wave Vmag (AC) having a phase different from 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 facing portion between the photosensitive drum 1 a and the 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 voltage variable device 33 changes the Vslv (AC) applied to the developing roller 23 to generate a leak between the DSs. Then, based on the potential difference between the DSs when the leak is detected by the leak detection device 35 (hereinafter referred to as leak generation voltage), the peak-to-peak value of the AC voltage applied between the DSs (hereinafter referred to as inter-DS Vpp). ) Is set to a range where no leak occurs.

  In the present invention, when leakage is detected and detected, Vmag (DC) applied to the magnetic roller 22 is equal to Vslv (DC) applied to the developing roller 23 or toner is supplied from the developing roller 23 side. It is applied in the direction of moving toward the magnetic roller 22 side. For example, when using a positively charged toner whose charging direction is positive (plus side), Vslv (DC) ≧ Vmag (DC), and when using a negatively charged toner whose charging direction is negative (minus side), Vslv (DC) ≦ Vmag (DC).

  As a result, leakage can be generated and detected in a state where there is almost no toner thin layer on the developing roller 23, and the leak point can be stably detected without being affected by the toner thin layer. The measurement accuracy is increased by suppressing the variation of. Accordingly, the setting accuracy of the inter-DS Vpp is also improved.

  Further, since the formation of the toner layer on the developing roller 23 is suppressed as much as possible, almost no toner is consumed even if leak detection is performed in the image portion (exposure portion). For this reason, it is possible to detect both the white background portion and the image portion on the photosensitive drum 1a and detect leaks at a time, and to perform more reliable leak detection than when leak detection is performed only on the white background portion. Can do.

  Further, if the potential difference between the image portion on the surface of the photosensitive member and the developing roller 23 is set to 0 or a voltage is applied in a direction in which the toner moves from the image portion to the developing roller 23 side, the toner image on the photosensitive member is transferred. Since the formation is suppressed, toner consumption can be further reduced.

For example, in the case of the reversal development method in which toner is allowed to fly to the exposed portion on the surface of the photoreceptor, conditional expression (1) may be satisfied when the potential of the exposed portion on the surface of the photoreceptor is VL.
| VL | ≧ | Vslv (DC) | (1)
According to the conditional expression (1), the potential difference between the exposure unit and the developing roller is the direction in which the toner does not move or moves from the exposure unit to the developing roller 23 side. Can be suppressed.

On the other hand, in the case of the forward development method in which the toner is allowed to fly to the unexposed portion on the surface of the photoreceptor, conditional expression (2) may be satisfied when the potential of the unexposed portion on the surface of the photoreceptor is V0.
| V0 | ≦ | Vslv (DC) | (2)
According to the conditional expression (2), the potential difference between the unexposed portion and the developing roller is the direction in which the toner does not move or moves from the unexposed portion to the developing roller 23 side. It can be effectively suppressed.

  Further, due to the change in Vslv (DC), the leak occurrence site is also switched between the image portion and the white background portion. Then, the leak occurrence voltage becomes maximum when the leak occurrence portion is switched between the image portion and the white background portion. Therefore, if Vslv (DC) is changed stepwise and the occurrence and location of leakage are detected each time, Vslv (DC) at which the leakage occurrence voltage becomes maximum can be easily determined. By setting (DC) as a DC voltage to be applied during development, the setting is such that leakage hardly occurs.

  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, the developing device using positively charged toner whose charging direction is positive (plus side) is described as an example. However, the developing device using negatively charged toner whose charging direction is negative (minus side). The same applies to the above. In this case, since the toner moves from the low potential side (high on the negative side) to the high side (low on the negative side), the potential difference between the developing roller 23 and the photosensitive drums 1a to 1d is the same as the case where positively charged toner is used. On the contrary, the effect when the relations of the conditional expressions (1) and (2) are satisfied is the same as when the positively charged toner is used.

  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 test machine as shown in FIG. 1 in which the developing device of the present invention shown in FIG. 2 is mounted, leakage is generated and detected by changing Vslv (DC) and Vmag (DC). The variation and toner adhesion to the image area were compared. 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 300 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 is used. The mixing ratio (T / C) was 12% by weight.

  The voltage application conditions to the developing roller were Vslv (DC) = 50 V, Vslv (AC) frequency was 4.5 kHz, and Duty = 45%. The voltage application conditions between the MSs were Vmag (AC) −Vslv (AC) = 1800 V, frequency = 4.5 kHz, Duty = 75%.

  As an evaluation method, when Vslv (DC) applied to the developing roller and Vmag (DC) applied to the magnetic roller are both 75 V (Invention 1), Vslv (DC) is 75 V, and Vmag (DC) is 0 V. (Invention 2), Vslv (DC) and Vmag (DC) are both 0 V (Invention 3), Vslv (DC) is 75 V, and Vmag (DC) is 275 V (Comparative Example 1) For each, a leak was generated 10 times by changing Vslv (AC), and the average voltage and the deviation at the time of the leak were determined. Further, the toner adhesion was evaluated by measuring the ID (image density) of the image area. The evaluation results are shown in Table 1.

  As is apparent from Table 1, in Comparative Example 1 in which leakage occurred under normal development conditions in which Vslv (DC) was 75 V and Vmag (DC) was 275 V, the leakage generation voltage was 1541 V, and the deviation of the measured value Was 30. The ID of the image portion was as high as 1.42. The cause of this is that a voltage is applied in the direction in which the toner moves from the magnetic roller to the developing roller, and since a toner layer is formed on the developing roller, the leakage generation voltage tends to vary, and the toner on the developing roller is exposed to light. This is considered to be because it adheres to the image part of the body drum.

  On the other hand, in the first aspect of the present invention in which Vslv (DC) and Vmag (DC) are both 75 V, since the potential difference ΔV between the MSs is 0 V, toner movement from the magnetic roller to the developing roller does not occur, and in the image portion The ID was as low as 0.29. Further, the deviation of the leak generation voltage was as small as 16. Further, in the second aspect of the present invention in which Vmag (DC) is set to 0 V, the voltage is applied in the direction in which the toner moves from the developing roller to the magnetic roller. The ID in the image area was 0.2, which was lower than that of the first invention.

  The leakage voltages measured in the present inventions 1 and 2 were both about 1500 V, which was about 40 V lower than that of Comparative Example 1. This is because the leak generation voltage can be measured without being influenced by the toner layer in the present inventions 1 and 2, and therefore the original leak generation voltage is lower than that of Comparative Example 1 in which the leak generation voltage has increased due to the toner layer. Is considered to be measurable.

  In the first aspect of the present invention in which Vslv (DC) and Vmag (DC) are both 0 V, there is a condition that prevents toner movement from the developing roller to the photosensitive drum, and the ID in the image portion is 0.11. It was even lower than 2. In the third aspect of the present invention, the leak generation voltage is reduced to 1350. This is because the potential difference B shown in FIG. 5 is reduced and the potential difference A is increased by reducing Vslv (DC) to 0V. Therefore, this is a result of the leak occurrence location moving from the image portion to the white background portion. Therefore, when Vslv (DC) is set to 75V, the leak occurrence location moves again from the white background portion to the image portion, and the leak occurrence voltage also becomes 1500V.

  From the above results, by setting Vslv (DC) and Vmag (DC) so that toner movement from the magnetic roller to the developing roller does not occur when a leak occurs, it is possible to reduce the variation in the measurement of the leak occurrence voltage and to reduce the image. It was confirmed that toner consumption due to toner adhesion to the area can also be suppressed. 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.

  Using the same testing machine as in Example 1, the leakage generation voltage and the leakage occurrence location when Vslv (DC) was changed were investigated. The conditions of the testing machine are the same as in Example 1, and while maintaining Vslv (DC) and Vmag (DC) at the same voltage, a leak is generated by gradually changing from 90 V to 20 V by 10 V, and the voltage at the time of leak detection And the leak detection site was investigated. The results are shown in Table 2.

  As a test image pattern for generating a leak, a vertical band pattern as shown in FIG. 4 was used. The length L of each vertical belt R is set longer than the circumferential length of the developing roller. Focusing on the fact that the toner layer on the developing roller is likely to cause a leak, this creates a situation where the toner layer on the developing roller becomes thinner by consuming the toner, and the leak under that situation is posted. It is to do. In this embodiment, since Vslv (DC) and Vmag (DC) are set to the same voltage, in actuality, toner hardly adheres to the image portion (vertical band). When leak detection is simultaneously performed in the image forming units Pa to Pd, a test image pattern that forms a vertical band R of each color of cyan, magenta, yellow, and black may be used.

  As is apparent from Table 2, when Vslv (DC) is lowered, the leak occurrence portion changes from the image portion to the white background portion, and the leak occurrence voltage becomes maximum at this switching portion. Therefore, by setting Vslv (DC) (70 V in this case) at which the leak occurrence site is switched, Vslv (DC) is the strongest setting against leakage, and the peak-to-peak value of Vslv (AC), that is, the inter-DS Vpp, It was confirmed that the maximum value can be set in a range where no leak occurs.

  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.

  INDUSTRIAL APPLICABILITY The present invention is applicable to a developing device that develops an electrostatic latent image on an image carrier by holding only the charged toner on the toner carrier using a toner supply member, and the toner carrier by a voltage application unit. A leak generating means for generating a leak between the image carrier and the toner carrier by changing an AC voltage applied to the toner carrier, and a leak detecting means for detecting a leak generated by the leak generator. The leak generating means leaks in a state where the DC voltage applied to the toner supply member is equal to the DC voltage applied to the toner carrier, or in a state where the toner is applied in the direction in which the toner moves from the toner carrier to the toner supply member. Is generated.

  As a result, the leak point can be detected stably without being affected by the toner thin layer, and thus a developing device with high leak measurement accuracy can be provided. In addition, since the formation of the toner layer on the toner carrier is suppressed as much as possible, it is possible to detect leaks at a time by forming both the white background portion and the image portion on the image carrier without consuming toner. Thus, it is possible to perform more reliable leak detection than when leak detection is performed only on the white background.

  In the reversal development method, the exposure portion potential VL on the surface of the image carrier when a leak occurs and the direct-current voltage Vslv (DC) applied to the toner carrier satisfy | VL | ≧ | Vslv (DC) | In order to satisfy this, in the forward rotation developing method, the unexposed portion potential V0 on the surface of the image carrier when a leak occurs and the DC voltage Vslv (DC) applied to the toner carrier are | V0 | ≦ | Vslv ( If DC) | is satisfied, the developing device can more effectively suppress toner consumption.

  In addition, the DC voltage applied to the toner carrier is changed stepwise to generate a leak, and the DC voltage that maximizes the AC voltage applied to the toner carrier when leak is detected is set as the DC voltage applied during development. As a result, the developing device can set the AC voltage to the maximum voltage within a range where leakage does 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 figures which show the test image pattern used in Example 2. FIG. FIG. 4 is a diagram showing a relationship between an AC voltage Vpp and a DC voltage Vdc applied to the developing roller, a leak occurrence location on the surface of the photoreceptor, and a leak occurrence voltage.

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)
100 Image forming apparatus Pa to Pd Image forming unit

Claims (5)

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;
A developing device having a voltage applying means for applying a DC voltage or a DC voltage and an AC voltage to the toner supply member and applying a DC voltage and an AC voltage to the toner carrier;
Leak generating means for changing the AC voltage applied to the toner carrier by the voltage application means to generate a leak between the image carrier and the toner carrier;
Leak detection means for detecting a leak generated by the leak generation means,
The leak generating means is applied with a DC voltage applied to the toner supply member equal to a DC voltage applied to the toner carrier, or applied in a direction in which the toner moves from the toner carrier to the toner supply member. A developing device that generates a leak in a state. This is a reversal development method in which toner is blown to the exposed portion of the image carrier for development, where the exposure portion potential on the surface of the image carrier is VL, and the DC voltage applied to the toner carrier is Vslv (DC). 2. The developing device according to claim 1, wherein VL and Vslv (DC) when the leak is generated by the leak generating unit satisfy the following conditional expression (1):
| VL | ≧ | Vslv (DC) | (1) This is a forward rotation developing method in which toner is ejected and developed on an unexposed portion of the image carrier, and the unexposed portion potential on the surface of the image carrier is V0, and the DC voltage applied to the toner carrier is Vslv (DC The developing device according to claim 1, wherein V0 and Vslv (DC) when the leak is generated by the leak generating unit satisfy the following conditional expression (2).
| V0 | ≦ | Vslv (DC) | (2)   The leak generating means changes the DC voltage applied to the toner carrier in a stepwise manner to generate a leak. The leak detector detects the occurrence of the leak each time, and at the time of detecting the leak, the toner carrier The developing device according to claim 1, wherein a DC voltage that maximizes the AC voltage applied to is set as a DC voltage applied during development.   An image forming apparatus on which the developing device according to claim 1 is mounted.

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