JP2010175879A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing leakage between an image carrier and a toner carrier, and simultaneously preventing the density unevenness of a half image due to the change of DS interval (distance between a developing roller and a photoreceptor). <P>SOLUTION: If the DS interval is long, a Duty ratio is decreased and Vmax is increased, thereby making Vmax-VL greater. The Vmax decreases by decreasing the Duty ratio. However, Vmin also acts in an increasing direction, that is, in the direction in which a potential difference V0-Vmin (indicated by a hatched arrow in the drawing) by which toner is pulled back to a developing roller from the surface of a photoreceptor decreases. Accordingly, even if the DS interval is long, developability on the photoreceptor improves and a half image can be uniformly reproduced. Alternatively, if the DS interval is short, the Duty ratio is increased and the Vmax is decreased, thereby making the Vmax-VL smaller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly, to drive a developing device that holds only a charged toner on a toner carrier and develops an electrostatic latent image on the image carrier in a non-contact manner. It relates to a control method.

  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, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed. 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 development method, unlike the charging by friction between the regulating blade and the toner, it is necessary to fly the toner sufficiently charged by the stirring of the toner and the carrier to the surface of the photosensitive member. The design of the surface property of the developing roller becomes important. In addition, with the recent demand for higher image quality, the toner has become smaller in particle size. However, as the toner particle size becomes smaller, the van der Waals force of the toner increases, making it difficult to fly smoothly onto the surface of the photoreceptor. I have to. For this reason, the distance between the developing roller and the photosensitive member (hereinafter referred to as the DS distance) tends to be narrowed so that the developing conditions make it easier for the toner to move.

  However, if the distance between the DSs is narrowed, the generation of noise due to current leakage between the developing roller and the photosensitive member becomes a problem, so that it is necessary to reduce the amplitude of the AC component. On the other hand, if the amplitude 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. appear.

  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. Patent Document 2 discloses an image forming apparatus in which information on the size of the gap between the toner carrier and the image carrier is stored, and the amplitude of the developing bias is set based on the information. Yes.

Japanese Patent Laid-Open No. 2003-287942 JP 2003-255678 A

  FIG. 9 is a diagram showing the relationship between the developing bias and the photoreceptor surface potential when the peak-to-peak value (hereinafter also referred to as Vpp) of the developing bias is changed. When positively charged toner is used, the likelihood of leakage is determined by the potential difference Vmax−VL (black arrow) between the positive peak value Vmax of the AC component of the developing bias and the exposed portion (image portion) potential VL of the photoreceptor. That is, in order to avoid the occurrence of leak, Vmax−VL may be reduced to a range where no leak occurs. However, in this case, it is necessary to ensure developability that does not cause unevenness in the half image even if Vmax is lowered to some extent. For this purpose, it is necessary to improve the surface properties of the developing roller or to consider the external additive formulation of the toner, but the description is omitted here. Since it is difficult to increase the exposure portion potential VL, it is necessary to adjust Vmax−VL by decreasing Vmax.

  On the other hand, as the potential difference V0−Vmin (hatching arrow) between the unexposed portion (white background) potential V0 of the photoreceptor and the negative peak value Vmin of the AC component of the developing bias increases, the toner is pulled back from the photoreceptor surface to the developing roller. The potential difference increases. If this potential difference becomes too large, toner movement to the photosensitive member is hindered, causing a density unevenness of the half image.

  When the distance between the DSs is narrow, the leak-proof voltage decreases and leaks easily occur. Therefore, when Vmax is decreased and Vmax−VL is decreased as shown in FIG. 9A, Vmin increases and V0−Vmin is decreased. The half image tends to be uniform. On the other hand, when the distance between the DSs is large, leakage hardly occurs, but developability deteriorates. Therefore, when Vmax is increased as shown in FIG. 9B in order to improve developability, V0−Vmin increases. There was a problem that unevenness of the half image occurred. Therefore, in the methods of Patent Documents 1 and 2 in which Vpp is changed, it is difficult to simultaneously suppress the occurrence of leakage and the density unevenness of the half image when the inter-DS distance varies.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of simultaneously suppressing the occurrence of a leak between an image carrier and a toner carrier and the density unevenness of a half image due to a change in the distance between DSs. To do.

  In order to achieve the above object, the present invention provides an image carrier, a toner carrier that is disposed so as to face the image carrier in a non-contact manner, and a voltage applying unit that applies a DC voltage and an AC voltage to the toner carrier. And a developing device that develops an electrostatic latent image formed on the surface of the image carrier, wherein the toner is based on a distance between the image carrier and the toner carrier. The duty ratio of the AC voltage applied to the carrier is adjusted.

  According to the present invention, in the image forming apparatus configured as described above, the image calculated using position information of the toner carrier in the developing device and position information of the image carrier in a unit including the image carrier. The duty ratio of the AC voltage applied to the toner carrier is adjusted based on the closest distance of the distance between the carrier and the toner carrier.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, pulleys are provided at both ends of the toner carrier so as to regulate a distance between the toner carrier and the contact point between the pulley and the image carrier. When the plane passing through is a reference plane, the position information of the toner carrier is distance data from the toner carrier surface to the reference plane measured at a plurality of locations in the longitudinal direction of the toner carrier, and the image The position information of the carrier is characterized by protrusion amount data from the reference surface of the surface of the image carrier measured at a location corresponding to the measurement location of the distance data of the toner carrier.

  According to the present invention, in the image forming apparatus configured as described above, the first storage unit storing the position information of the toner carrier is mounted on the developing device, and the second storage stores the position information of the image carrier. Means is mounted on the unit, and reading means for reading information stored in the first and second storage means is provided.

  According to the first configuration of the present invention, since Vmax that affects the occurrence of leakage is set by adjusting the duty ratio, Vmin increases when Vmax is lowered, and toner is pulled back from the surface of the photosensitive member to the developing roller. It acts in the direction of decreasing the potential difference. Accordingly, the uniformity of the half image can be ensured even when the distance between the DSs is long. In addition, the cost is lower than when Vpp is changed.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the position information of the toner carrier in the developing device and the position information of the image carrier in the unit including the image carrier are obtained. By adjusting the duty ratio based on the closest distance among the distances between the image carrier and the toner carrier calculated by using the positional information of the toner carrier and the image carrier before assembly of the developing device and the unit. Can be measured separately, the closest distance between the DSs used to adjust the duty ratio can be easily determined.

  Further, according to the third configuration of the present invention, in the image forming apparatus having the second configuration, the surface information of the toner carrier measured at a plurality of positions in the longitudinal direction of the toner carrier. The distance information from the reference surface to the reference surface, and the position information of the image carrier is the protrusion amount data from the reference surface of the image carrier surface measured at the location corresponding to the measurement location of the distance data of the toner carrier. The closest distance between the DSs can be calculated more accurately.

  According to the fourth configuration of the present invention, in the image forming apparatus having the second or third configuration, the first storage unit storing the position information of the toner carrier is mounted on the developing device, and the image carrier is provided. When the developing device or the unit is replaced by mounting the second storage means storing the body position information on the unit and providing the reading means for reading the information stored in the first and second storage means In addition, the data in the storage means can be read by the reading means, and the duty ratio of the AC voltage according to the closest distance between the DSs can be set each time.

1 is a schematic diagram showing the overall configuration of an image forming apparatus of the present invention. Side surface sectional view showing a configuration of a developing device mounted in the image forming apparatus of the present invention The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller The figure which shows the change of the bias waveform applied between the photoconductive drum and the developing roller when the duty ratio of the alternating voltage is changed. The figure which shows a mode that the developing apparatus is attached to a dummy photoconductor and the distance data of the developing roller from the reference surface in P1 to P3 is measured. The figure which shows the method of measuring the maximum protrusion amount from the reference plane in P1-P3 of a photoconductive drum. Block diagram explaining the read control path of the RFID memory The graph which shows the leak-proof voltage measured in the Example, and Vmax actually set The figure which shows the change of the bias waveform applied between a photoconductive drum and a developing roller when changing Vpp of alternating voltage.

  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 (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to 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 magenta, cyan, 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, magenta, cyan, 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 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. 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 the potential difference ΔV from Vslv (DC) applied to the magnetic field and the magnetic field between the fixed magnet roller body 22b.

  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 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.

  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, based on the distance between the DSs, the AC voltage applied between the DSs 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, data necessary for control, such as a Vmax setting table that associates the distance between DS and Vmax, is stored. Remembered. The control unit 37 and the storage unit 39 may be combined with the CPU 45 and the main storage unit 47 (see FIG. 7) that control the entire image forming apparatus 100, or are independent for controlling the developing devices 3a to 3d. May be arranged.

  In the present invention, as shown in FIG. 4, the duty ratio of Vslv (AC) is changed based on the measurement result of the distance between DSs, and Vmax is set to a range where no leak occurs. The duty ratio here refers to the ratio of the time of the plus-side waveform to one cycle of the AC waveform.

  Further, when changing the duty ratio, it is assumed that the duty ratio is changed while Vpp and the area center voltage (= Vslv (DC)) are kept constant. For example, in an AC voltage with a duty ratio of 50%, the area center voltage is ½ the height of the waveform. When the duty ratio of this AC voltage is lowered to 30%, the plus-side waveform increases, and the ratio of the portion exceeding the area center voltage becomes 70% of the entire waveform. That is, the electric field (development voltage component) that contributes to toner movement onto the photosensitive drum increases in inverse proportion to the duty ratio.

  Specifically, when the distance between the DSs is long, as shown in FIG. 4A, Vmax−VL is further increased by lowering the duty ratio and increasing Vmax. Here, when the duty ratio is decreased, Vmax increases, but Vmin also increases (absolute value decreases), that is, the potential difference V0−Vmin (hatching arrow in the figure) decreases in the direction in which the toner is pulled back from the photosensitive member surface to the developing roller. Therefore, even when the distance between the DSs is long, the developability to the photosensitive member is improved and the half image can be reproduced uniformly.

  On the other hand, when the distance between the DSs is short, as shown in FIG. 4B, the Vmax−VL is made smaller by increasing the duty ratio and decreasing Vmax. At this time, Vmin also decreases (absolute value increases), so V0-Vmin (hatching arrow in the figure) increases, but the half image becomes uniform because the DS distance is close. Note that if V0−Vmin becomes too large, the toner movement to the photosensitive member is hindered, causing non-uniformity in the half image. Therefore, it is necessary to set the duty ratio appropriately according to the distance between the DSs.

  In actual control, the distance between DSs in an actual machine is measured at three points, and the closest distance is detected. The distance between DS can be measured by using a thickness gauge or by taking a photo with a CCD camera while rotating the developing roller and photoconductor, but measuring with a laser micrometer Most preferable in terms of accuracy. However, in order to use a laser micrometer, it is necessary to arrange the light emitting unit and the light receiving unit at predetermined positions, so it is difficult to measure the distance between DSs with each unit mounted on an actual image forming apparatus. It is. Therefore, before assembling the image forming apparatus, the maximum protruding amounts of the developing roller and the photosensitive drum are measured in advance with the developing device 3a and the drum unit including the photosensitive drum 1a, and the maximum protruding amount data of each unit is used as a basis. It is practical to calculate the closest distance between DSs.

  As shown in FIG. 5, pulleys 40 that contact the outer peripheral surface of the photosensitive drum 1a are attached to both ends of the developing roller 23, and the distance between the DSs is set by defining the outer diameter of the pulley 40. Yes. Therefore, the developing device 3a is installed on the dummy photosensitive member 41 with a very small outer diameter using a jig, and the developing roller 23 is rotated in a state where the pulley 40 is in contact with the dummy photosensitive member 41. The distance from the surface (reference surface) of the photoreceptor 41 is measured at three locations in the longitudinal direction of the developing roller 23. Here, since the fluctuation of the outer diameter of the dummy photoconductor 41 is extremely small, the fluctuation of the distance from the reference surface is synonymous with the fluctuation of the protruding amount of the developing roller 23. In FIG. 5, the distance between the DSs is measured over the entire circumferential direction of the developing roller 23 at three positions, ie, both ends P1, P3 of the developing region and the central portion P2 that is equidistant (95 mm) from P1 and P3. The shortest distances a, b, and c from the reference plane are calculated.

  As for the drum unit having the photosensitive drum 1a, as shown in FIG. 6, two locations P0 and P4 where the pulley 40 of the developing device 3a contacts, and three of P1 to P3 where the protruding amount of the developing roller 23 is measured. The outer diameter of the photosensitive drum 1a at a position facing the location is measured. Specifically, the contacts P0 and P4 of the pulley 40 are connected by a straight line, and the amount of protrusion of the photosensitive drum 1a (the amount of swelling toward the developing roller) from the surface (reference surface) passing through the straight line is stored in P1 to P3. Measurements are made over the entire circumferential direction of the photosensitive drum 1a at corresponding positions, and the maximum protrusion amounts α, β, and γ from the reference surface at each location are calculated.

  Then, the shortest distances a, b, c of the developing roller 23 from the reference surface and the maximum protrusion amounts α, β, γ of the photosensitive drum 1 a are abutted to obtain the DS distances a-α, b-β, c-γ. Calculate and determine the closest DS distance. Here, the measurement of the distance between the developing roller 23 of the developing device 3a and the photosensitive drum 1a has been described, but the developing devices 3b to 3d and the photosensitive drums 1b to 1d can be similarly performed.

  At this time, the leak is predicted to occur at the lowest Vmax at the determined closest DS distance. Next, when the leak occurrence voltage (leakage resistance voltage) is derived based on the determined DS distance and the Vmax setting table, a voltage (here, a margin) that is lower than the leak occurrence voltage by a predetermined voltage to avoid the leak. Therefore, it is necessary to set the actual Vmax to Vmax, so that the duty ratio of Vslv (AC) is changed so as to be Vmax.

  Thereby, Vmax corresponding to the closest distance between the DSs is set, so that the occurrence of a leak between the DSs is suppressed. Further, when Vmax is increased by changing the duty ratio, Vmin is also increased, so that the uniformity of the half image can be ensured even when the distance between the DSs is long. Furthermore, in terms of the design of the high-voltage substrate, changing the duty ratio is less expensive than changing Vpp.

  The setting of Vmax as described above may be performed when the developing device and the drum unit are actually attached to the image forming apparatus. However, if the developing device or the drum unit is replaced during use, it is necessary to reset Vmax again. Therefore, each unit is equipped with a wireless tag such as an RFID [Radio Frequency Identification] memory in which the shortest distances a, b, c and the maximum protrusions α, β, γ are stored as data, and the data in the wireless tag is stored. If a reading device is mounted on the apparatus main body side, it is possible to read data in the wireless tag and set Vmax every time when the image forming apparatus is powered on.

  FIG. 7 is a block diagram for explaining a control path of the image forming apparatus of the present invention. A circuit for reading data from the RFID memory 43 mounted in the developing devices 3a to 3d shown in FIG. 1 will be described. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, in FIG. 7, description of circuits that are not involved in reading with respect to the RFID memory 43 is omitted.

  A developing device detection sensor 49 for detecting the presence or absence of the developing devices 3a to 3d is connected to an internal bus 47 to which a CPU (Central Processing Unit) 45 for controlling the entire image forming apparatus 100 is connected. The main storage unit 50 stores a control program and control data for controlling each unit of the image forming apparatus 100. The display unit 51 displays the state of each part of the image forming apparatus 100, the image forming status, and the number of copies, and can be used as a touch panel to perform various settings such as functions such as double-sided printing and black-and-white reversal, magnification setting, and density setting. Yes. The RFID memory control circuit 53 reads distance data (shortest distances a, b, c) stored in the RFID memory 43 via the antennas 55 and 57. The read result is transmitted to the CPU 45.

  Although not shown here, the RFID memory 43 is also mounted on the drum unit including the photosensitive drums 1a to 1d, and the protruding amount data (maximum protruding amounts α, β, γ) of the photosensitive drum is stored. The RFID memory control circuit 53 reads the maximum protrusion amounts α, β, γ in the RFID memory 43 mounted on the drum unit, and transmits the result to the CPU 45. The CPU 45 calculates the DS distances a−α, b−β, and c−γ, and determines the closest DS distance.

  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 addition, the present invention is not limited to the developing device including the magnetic roller 22 and the developing roller 23 as shown in FIG. 2, and may be configured to include a developing roller that is disposed in a non-contact manner and opposed to the image carrier. For example, the present invention can be applied to various developing apparatuses using a magnetic one-component developer or a two-component developer composed of a toner component and a magnetic carrier.

  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.

  When Vmax is set by changing the duty ratio of Vslv (AC) according to the distance between DS using a testing machine (FS-C5030 modified by Kyocera Mita Co., Ltd.) as shown in FIG. 1 (invention), and About the case where Vmax of Vslv (AC) was changed and Vmax was set (comparative example), the occurrence state of half image unevenness 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 such that the drum surface potential was 300 V for the white background potential (V0) and 20 V for the image portion potential (VL). The developing roller used was alumite-treated, and Vslv (DC) = 40V. The circumferential speed of the developing roller is 1.6 times the circumferential speed ratio with respect to the photoreceptor (forward rotation on the facing surface), and the circumferential speed of the magnetic roller is 1.5 times the circumferential speed ratio with respect to the developing roller (counter rotation on the facing surface). did. 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.

(Measurement of distance between DS)
A combination of four types of developing devices (No. 1 to 4) and drum units (No. 1 to 4) is prepared, and a laser micrometer is used to connect the developing roller 23 and the dummy photosensitive member 41 as shown in FIG. The distance was measured, and the closest distances a, b, and c at three locations P1 to P3 were calculated. Further, the outer diameter data of the positions corresponding to P1 to P3 of the photosensitive drum shown in FIG. 6 was measured using a laser micrometer, and the maximum values α, β and γ were calculated. Then, DS distances a-α, b-β, and c-γ were calculated, and the closest DS distance was determined for each combination. The results are shown in Tables 1 to 4.

  As shown in Table 1, in the combination of the developing device 1 and the drum unit 1, the closest distance between the DSs was 114 μm. Similarly, from Tables 2 to 4, the combination of the developing device 2 and the drum unit 2 was 105 μm, the combination of the developing device 3 and the drum unit 3 was 94 μm, and the combination of the developing device 4 and the drum unit 4 was 86 μm.

(Vmax setting)
With respect to the above combinations 1 to 4, the voltage at which leakage occurs was measured by gradually increasing the Vpp of Vslv (AC) applied to the developing roller 23 from the reference value. Then, as shown in FIG. 8, a voltage (indicated by ● in the figure) obtained by lowering the measured leakage resistance voltage (indicated by ▲ in the figure) by 100 V was set as Vmax. Table 5 shows the measurement result and the set value of Vmax.

(Evaluation of uniformity of half image)
As a method of adjusting to Vmax set in Table 5, when Vpp of Vslv (AC) is fixed to 1390V and the duty ratio is changed, the duty ratio of Vslv (AC) is fixed to 35%, In the case of adjusting by changing Vpp, a half image (25%) was actually printed, and the uniformity was visually evaluated. Table 6 shows the evaluation results when the duty ratio is changed, and Table 7 shows the evaluation results when Vpp is changed. The uniformity of the half image was evaluated as “◯” when the pitch unevenness of the developing roller or the photosensitive drum was not recognized, “Δ” when the pitch unevenness was slightly recognized, and “x” when the pitch unevenness was remarkably recognized.

  As is apparent from Tables 6 and 7, in the comparative example in which Vmax was changed by changing Vpp, pitch unevenness occurred in the half image when the distance between DS was 105 μm or more, but Vmax was changed by changing the duty ratio. In the adjusted present invention, the half image was printed uniformly regardless of the distance between the DSs. This is because Vmax needs to be set high when the distance between the DSs is long, but when Vpp is changed, Vmin also decreases at the same time, so that the toner is pulled back from the photoconductor to the developing roller, and the half image is uneven. It is thought to become.

  On the other hand, when the duty ratio is changed, Vmin increases when the distance between DSs is long and Vmax is increased. Therefore, the potential difference V0-Vmin for pulling toner from the photosensitive member to the developing roller is reduced, and half images are printed uniformly. It is considered possible. For example, when the distance between the DSs is 114 μm, Vmin is −466 V when Vpp is changed to 1446 V, and V0−Vmin is 766 V because the white background potential V0 of the photosensitive member is 300 V. On the other hand, when the duty ratio is changed to 32%, Vmin is −410V, and V0−Vmin is 710V, which is smaller than the change in Vpp.

  From the above results, the present invention in which the Vmax is adjusted by changing the duty ratio has an effect on the developability as compared with the comparative example in which the Vmax is adjusted by changing the Vpp, and the occurrence of leak is prevented and half It was confirmed that the uniformity of the image can be secured. 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.

  INDUSTRIAL APPLICABILITY The present invention is applicable to an image forming apparatus including a developing device that develops an electrostatic latent image on an image carrier by holding only a charged toner on the toner carrier using a toner supply member. The duty ratio of the AC voltage applied to the toner carrier is adjusted based on the distance between the carrier and the toner carrier.

  Accordingly, it is possible to provide an image forming apparatus that can suppress the occurrence of leakage between the image carrier and the toner carrier and can ensure the uniformity of the half image even when the distance between the DSs is long.

  Further, the position information of the toner carrier in the developing device and the position information of the image carrier in the unit including the image carrier are separately measured before the assembly of the developing device and the unit, and the position information is used. By selecting the closest distance among the calculated distances between DSs, the closest distance between the DSs can be easily determined. Specifically, the image carrier measured at a location corresponding to the measurement location of the distance data of the toner carrier from the shortest distance from the toner carrier surface to the reference surface measured at a plurality of locations in the longitudinal direction of the toner carrier. The value obtained by subtracting the maximum protrusion from the reference surface of the body surface is obtained for each measurement point, and the nearest value between the DSs can be accurately calculated by taking the minimum value among them as the closest distance between the DSs. Become.

  In addition, the developing device and the unit are equipped with a storage unit such as an RFID memory that stores the position information of the toner carrier or the image carrier, and the information stored in each storage unit is read by the reading unit. Even when is replaced, the image forming apparatus can set the duty ratio of the AC voltage corresponding to the closest distance between the DSs each time.

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 22 Magnetic roller 23 Developing roller (toner carrier)
30 First bias circuit (voltage applying means)
31 Second bias circuit 33 Voltage variable device 37 (developing device) control unit 39 (developing device) storage unit 40 pulley 43 RFID memory (storage unit)
45 CPU
53 RFID memory control circuit (reading means)
100 Image forming apparatus Pa to Pd Image forming unit

Claims (4)

An image carrier;
An electrostatic image formed on the surface of the image carrier, comprising: a toner carrier that is disposed so as to face the image carrier in a non-contact manner; and a voltage applying unit that applies a DC voltage and an AC voltage to the toner carrier. A developing device for developing the latent image;
In an image forming apparatus comprising:
An image forming apparatus, wherein a duty ratio of an AC voltage applied to the toner carrier is adjusted based on a distance between the image carrier and the toner carrier.   Of the distance between the image carrier and the toner carrier calculated using the position information of the toner carrier in the developing device and the position information of the image carrier in the unit including the image carrier, The image forming apparatus according to claim 1, wherein a duty ratio of an AC voltage applied to the toner carrier is adjusted based on a closest distance.   Pulleys for regulating the distance from the image carrier are attached to both ends of the toner carrier, and when the plane passing through the contact point between the pulley and the image carrier is used as a reference plane, the toner carrier Is the distance data from the toner carrier surface to the reference plane measured at a plurality of locations in the longitudinal direction of the toner carrier, and the position information of the image carrier is the distance of the toner carrier. The image forming apparatus according to claim 2, wherein the image forming apparatus is protrusion amount data from a reference surface of the surface of the image carrier measured at a location corresponding to a data measurement location.   The first storage unit storing the position information of the toner carrier is mounted on the developing device, the second storage unit storing the position information of the image carrier is mounted on the unit, and the first and 4. The image forming apparatus according to claim 2, further comprising a reading unit that reads information stored in the second storage unit.

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