JP2010210958A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus capable of removing the toner on a developer carrier and of suppressing the generation of development history. <P>SOLUTION: An auxiliary electrode 11 is at a position which is opposite to a released position of a magnet roller 8, and at a predetermined interval from the surface of a developing sleeve 9, and an auxiliary voltage applying part 12 applies AC components with reversed phase with AC components of bias voltage, with respect to the auxiliary electrode 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus that develop an electrostatic latent image formed on an electrostatic latent image carrier with toner by applying an alternating voltage superimposed on a DC voltage as a developing bias.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed by charging the surface of an electrostatic latent image carrier (for example, a photoconductor) and exposing the charged area according to image information. A developing method for developing and visualizing (developing) the electrostatic latent image is employed.

  As a developing method, a two-component developer containing a magnetic carrier and a toner is used, and the toner is frictionally charged and attracted by the electrostatic force of the electrostatic latent image formed on the surface of the electrostatic latent image carrier. A developing method for developing the electrostatic latent image to form a toner image is used.

  This developing device has a cylindrical developing sleeve having a plurality of magnetic poles inside and rotatably supported on the outside. The developing carrier holds a magnetic carrier with toner attached thereto and transports it to the developing region. To develop. In such a configuration, toner triboelectric charge control is relatively easy and is used in many devices.

  In the developing device, in order to perform uniform development with no density unevenness and no development history, the developer on the developing sleeve that has once passed through the developing region is completely removed and new developer is supplied to the developing sleeve. is necessary. In this case, the developer refers to both the magnetic carrier and the toner.

  In the developing device described in Patent Document 1, a rotating roller is provided at a position opposite to the release position of the magnet roller, and a DC voltage is applied between the developing sleeve and the rotating roller. The DC voltage is applied in the direction in which the carrier on the developing sleeve moves toward the rotating roller, thereby electrically removing the carrier from the developing sleeve and suppressing the occurrence of ghost (development history).

  Further, the developing device described in Patent Document 2 includes a developing sleeve that performs development using an alternating electric field, and a rotating member for collecting toner that is provided downstream of the developing unit. Ghosts are removed by applying an alternating electric field between them.

JP-A-5-158353 Japanese Patent Laid-Open No. 4-297171

  In the developing device described in Patent Document 1, most of the toner adhering to the carrier moves to the rotating roller side together with the carrier, but with respect to a part of the toner adhering to the carrier near the developing sleeve surface and the toner adhering directly to the developing sleeve. Thus, since the electric field is applied in the direction in which the toner moves to the developing sleeve, it is not removed and the development history remains.

  In the developing device described in Patent Document 2, since an AC electric field is applied in an area where the carrier exists, the toner adhering to the carrier close to the surface of the developing sleeve and the toner adhering directly to the developing sleeve are not removed. The history remains.

  An object of the present invention is to provide a developing device and an image forming apparatus that can remove the toner on the developer carrying member and suppress the development history.

The present invention includes a developer carrier to which a bias voltage in which an AC component is superimposed on a DC component is applied, and an electrostatic latent image carrier on which an electrostatic latent image is formed. In a developing device for developing with toner,
The developer carrier has a magnet roller in which a plurality of magnetic pole members are arranged along the circumferential direction, and a developing sleeve that is externally fitted to the magnet roller and configured to be rotatable.
An auxiliary electrode disposed at a position facing the release position of the magnet roller and spaced from the developing sleeve surface by a predetermined distance;
A developing device comprising: an auxiliary voltage applying unit that applies an alternating current component whose phase is reversed to an alternating current component of the bias voltage to the auxiliary electrode.

  In the invention, it is preferable that the auxiliary voltage applying unit applies the same DC component as the DC component applied to the developer carrier to the auxiliary electrode.

  The auxiliary electrode is configured to be rotatable around an axis parallel to the rotation axis of the developing sleeve.

In the present invention, the peak voltage of the bias voltage applied in the direction in which the toner moves from the developer carrier to the electrostatic latent image carrier is V1, the image portion potential of the electrostatic latent image carrier is VL, The closest distance between the developer carrier and the electrostatic latent image carrier is d1, the closest distance between the developer carrier and the auxiliary electrode member is d2, and the peak applied to the developer carrier is When the two-peak voltage is VppB and the peak-to-peak voltage applied to the auxiliary electrode is VppM,
The following formula (1) is satisfied.
| V1-VL | / d1 <(VppB + VppM) / (2 × d2) (1)

In the present invention, the time during which a voltage is applied in the direction of moving the toner from the developer carrier to the electrostatic latent image carrier is T1, and the toner is transferred from the electrostatic latent image carrier to the developer carrier. The time during which the voltage is applied in the moving direction is T2, the duty ratio D of the bias voltage applied to the developer carrying member is T1 / (T1 + T2),
The peak voltage of the bias voltage applied in the direction in which the toner moves from the developer carrier to the electrostatic latent image carrier is V1, the image portion potential of the electrostatic latent image carrier is VL, and the developer carrier. D1 is the closest distance between the electrostatic latent image carrier and the electrostatic latent image carrier, d2 is the closest distance between the developer carrier and the auxiliary electrode member, and the peak-to-peak voltage applied to the developer carrier is When VppB and the peak-to-peak voltage applied to the auxiliary electrode is VppM,
The following formula (2) is satisfied.
| V1-VL | / d1 <(1-D) × (VppB + VppM) / d2 (2)
The present invention also provides an image forming apparatus including a developing device.

  According to the present invention, the auxiliary electrode is disposed at a position opposed to the release position of the magnet roller and at a predetermined distance from the surface of the developing sleeve, and the auxiliary voltage applying unit is disposed on the auxiliary electrode. Then, an AC component whose phase is inverted from that of the AC component of the bias voltage is applied.

  Since the developer on the developing sleeve is released and an alternating current component whose phase is reversed from the alternating current component of the bias voltage is applied to the position facing the portion where there is little developer, the development history caused by the toner on the developing sleeve is reduced. Can be suppressed.

  Further, compared to a blade that mechanically scrapes off the developer on the developing sleeve, stress on the developer does not occur. Furthermore, even when the developer remains at the release position, the developer can easily fly to the auxiliary electrode side, so that the development history can be suppressed.

  According to the invention, the auxiliary voltage applying unit applies the same DC component as the DC component applied to the developer carrying member to the auxiliary electrode.

  When the DC component is applied in the direction in which the toner adheres to the auxiliary electrode, the toner is accumulated on the auxiliary electrode, and it becomes difficult to apply an electric field, or the toner is clogged between the developing sleeve and the auxiliary electrode. . In addition, when a DC component having a polarity opposite to this is applied, the toner easily returns to the developing sleeve, and the effect of suppressing the development history is weakened.

  However, by applying the same DC component as the DC component applied to the developer carrier to the auxiliary electrode, the developer is less likely to adhere to the developing sleeve and the auxiliary electrode, so that the development history is suppressed. In addition, toner adhesion to the auxiliary electrode can be prevented.

  According to the invention, the auxiliary electrode is configured to be rotatable around an axis parallel to the rotation axis of the developing sleeve.

  Thereby, even if the fluidity | liquidity of a developer falls, the clogging of the developer between a developing sleeve and an auxiliary electrode can be prevented.

  Further, according to the present invention, by satisfying the formula (1), the electric field for separating the developer from the developing sleeve near the auxiliary electrode is stronger than the electric field for separating the developer from the developing sleeve in the developing region. Thus, the effect of suppressing the development history generated in the development area is further increased.

  Further, according to the present invention, by satisfying the formula (2), even when the duty ratio is not 50%, the development is performed near the auxiliary electrode rather than the electric field for separating the developer from the development sleeve in the development region. Since the electric field for separating the agent from the developing sleeve becomes strong, the effect of suppressing the development history generated in the developing region is further increased.

  Further, according to the present invention, it is possible to perform high-quality image formation with a development history suppressed.

1 is a schematic diagram illustrating a configuration of an image forming apparatus 100 according to a first embodiment of the present invention. 2 is a schematic diagram illustrating a configuration of a developing device 1 provided in an image forming station unit 50. FIG. It is a figure which shows the bias waveform applied in the image development apparatus 1 of 1st Embodiment. FIG. 6 is a diagram illustrating a voltage applied to the developing sleeve 9 and a potential of the photosensitive member 51 in a developing region. It is a figure which shows the bias waveform applied in the developing device 1 of 2nd Embodiment. 6 is a diagram illustrating a voltage applied to the developing sleeve 9 and a surface potential of the photosensitive member 51. FIG. It is a figure which shows the bias waveform applied in the developing device 1 of 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  First, the configuration of the first embodiment of the image forming apparatus according to the present invention will be described. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus 100 according to the first embodiment of the present invention. Note that FIG. 1 is an example that is simplified and described mainly with respect to main components of the image forming apparatus 100.

  The image forming apparatus 100 includes a plurality of photoconductors 51 serving as electrostatic latent image carriers. In this embodiment, the image forming apparatus 100 displays color images including four images for yellow image, magenta image, cyan image, and black image. This is a tandem color image forming apparatus that can be formed. The image forming apparatus 100 is based on image data transmitted from various terminal devices such as a PC (Personal Computer) connected via a network and image data read by a document reading device such as a scanner. The printer P has a printer function for forming a color image or a monochrome image on the paper P as a (recording medium).

  As shown in FIG. 1, the image forming apparatus 100 forms an image on the paper P by the image forming station unit 50 (50Y, 50M, 50C, 50B) having a function of forming a toner image on the paper P. A fixing device 40 having a function of fixing the toner image, and a transport unit 30 having a function of transporting the paper P from the supply tray 60 on which the paper P is placed to the image forming station unit 50 and the fixing device 40. .

  The image forming station unit 50 includes four image forming stations 50Y, 50M, 50C, and 50B for yellow image, magenta image, cyan image, and black image, respectively.

  Specifically, between the supply tray 60 and the fixing device 40, the yellow image forming station 50Y, the magenta image forming station 50M, the cyan image forming station 50C, and the black image forming station 50B are arranged in this order from the supply tray 60 side. Is arranged.

  The image forming stations 50Y, 50M, 50C, and 50B for each color have substantially the same configuration except for the type of toner, and yellow, magenta, and cyan are based on image data corresponding to each color. , And a black toner image are formed and transferred onto a paper P that finally becomes a recording medium.

  The image forming station unit 50 according to the present embodiment is configured to form images of four colors of yellow, magenta, cyan, and black. However, the image forming station unit 50 is not limited to these four colors, and for example, has the same hue as cyan and magenta. It may be configured to form a six-color toner image to which light cyan (LC) and light magenta (Lm) having lower densities are added.

  Note that the reference numerals of the component parts of the respective image forming stations in FIG. 1 are described with the image forming station 50Y for yellow images as a representative, and the reference numerals of the constituent parts of the other image forming station units 50M, 50C, 50B are as follows. Omitted.

  Each of the image forming stations 50Y, 50M, 50C, and 50B includes a photoconductor 51 serving as a latent image carrier on which an electrostatic latent image is formed, and a charging device 52 is provided around the photoconductor 51 in the circumferential direction. An exposure device 53, a developing device 1, a transfer roller 55, and a cleaning device 56 are disposed.

  The photosensitive member 51 has a substantially cylindrical drum shape having a photosensitive material such as OPC (Organic Photoconductor) on the surface, and is disposed below the exposure device 53. The photosensitive member 51 is predetermined by a driving unit and a control unit. It is controlled to be rotated in the direction (the direction of arrow F in the figure).

  The charging device 52 is a charging means for uniformly charging the surface of the photoconductor 51 to a predetermined potential, and is disposed above the photoconductor 51 and in the vicinity of the outer peripheral surface thereof. In this embodiment, a charging roller of a contact type is used, but a charging device such as a charger type, a brush type, or an ion emission charging type may be used.

  The exposure device 53 irradiates the surface of the photoconductor 51 charged by the charging device 52 with laser light based on the image data output from the image processing unit, thereby converting the image data onto the surface. It has a function of writing a corresponding electrostatic latent image. The exposure device 53 receives image data corresponding to yellow, magenta, cyan, or black according to each of the image forming stations 50Y, 50M, 50C, and 50B, so that the electrostatic latent image corresponding to the corresponding color is input. Each image is formed. As the exposure device 53, a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror, or a writing device (for example, a writing head) in which light emitting elements such as EL and LEDs are arranged in an array can be used. .

  The developing device 1 has a developing roller 3 serving as a developer carrying member for carrying the developer. The developing roller 3 is configured such that the developing roller 3 and the photosensitive member 51 are close to each other and the developer is conveyed to a developing region where the toner moves to the photosensitive member 51. In the present embodiment, the developing device 1 uses a two-component developer containing toner and carrier to develop the electrostatic latent image formed on the surface of the photoconductor 51 by the exposure device 53 to generate a toner image (possible Image).

  The developing device 1 accommodates yellow, magenta, cyan, or black developer according to the image formation of each of the image forming stations 50Y, 50M, 50C, and 50B. These developers include toner charged to the same polarity as the surface potential of the charged photoreceptor 51. The polarity of the surface potential of the photoconductor 51 and the charging polarity of the toner to be used may be positive or negative, but are negative in this embodiment.

  The transfer roller 55 transfers the toner image formed on the photosensitive member 51 onto the surface of the paper P conveyed by the conveyance belt 33. The transfer roller 55 has a polarity opposite to the charging polarity of the toner (in this embodiment, the normal polarity). A transfer roller to which a bias voltage of (plus) polarity) is applied.

  The cleaning device 56 removes and collects the toner remaining on the outer peripheral surface of the photoreceptor 51 after the toner image is transferred to the paper P. In the present embodiment, the photosensitive member 51 is disposed at a position substantially opposite to the developing device 1 with the photosensitive member 51 interposed therebetween, and on the side of the photosensitive member 51.

  The conveyance unit 30 includes a driving roller 31, a driven roller 32, and a conveyance belt 33, and conveys the paper P on which the toner images of each color are transferred at the image forming stations 50Y, 50M, 50C, and 50B. The transport unit 30 has a configuration in which an endless transport belt 33 is stretched between the driving roller 31 and the driven roller 32, and the paper P fed from the supply tray 60 is fed to each image forming station 50Y, Transport to 50M, 50C, 50B in order.

  The fixing device 40 includes a heating roller 41 and a pressure roller 42, and conveys the paper P to a fixing nip portion where the heating roller 41 and the pressure roller 42 abut, thereby fixing the toner image transferred onto the paper P by thermocompression bonding to the paper P. Let

  In the image forming apparatus 100 configured as described above, the sheet P conveyed by the conveying unit 30 is opposed to the image forming stations 50Y, 50M, 50C, and 50B when they pass through the positions facing the photoreceptor 51. At the position, the toner images on the respective photoreceptors 51 are sequentially transferred onto the paper P by the action of the transfer electric field by the transfer roller 55 disposed below via the transport belt 33. As a result, the toner images of the respective colors are transferred so as to overlap on the paper P, and a desired full-color toner image is formed on the paper P. The paper P onto which the toner image has been transferred in this manner is subjected to a toner image fixing process by the fixing device 40 and then sent to a paper discharge tray.

  Next, the configuration of the developing device 1 will be described. FIG. 2 is a schematic diagram showing a configuration of the developing device 1 provided in the image forming station unit 50 shown in FIG. FIG. 2 shows an example in which the main components of the developing device 1 are simplified and described.

  As shown in FIG. 2, in addition to the above-described developing roller 3, the developing device 1 includes a regulating blade 6 that serves as a regulating member that regulates the layer thickness of the developer on the developing roller 3, and the developer on the developing roller 3. A pair of agitating and conveying screws 4 and 5 serving as a conveying member and an agitating and agitating member for conveying and developing the developer, and a developing tank 2 for storing a two-component developer containing toner and a carrier are provided.

  In the developing tank 2, a pair of agitating and conveying screws 4 and 5 are arranged so that their rotational axes are substantially parallel. A partition wall 7 is provided between the agitating and conveying screws 4 and 5 to partition the inside of the developing tank 2 except for both end sides in the axial direction. By providing the partition wall 7 in the developing tank 2 in this way, an independent developer transport path is formed in the developing tank 2 with the partition wall 7 as a boundary. In the developing device 1, the toner in the developer accommodated in the developing tank 2 is agitated with the carrier by the agitating operation of the agitating and conveying screws 4 and 5 disposed in the developing tank 2 and is frictionally charged. It is like that.

  Further, a developing opening Q is provided at a position facing the photosensitive member 51 in the developing tank 2, and a developing gap (about 0.3 to 1.0 mm) is provided between the developing roller 3 and the photosensitive member 51. Is provided in the developing tank 2 so that a part is exposed from the opening Q of the developing tank 2.

  The developing roller 3 includes a magnet roller 8 including a plurality of magnetic pole members arranged in parallel along the circumferential direction, and is rotatably attached to the magnet roller 8 in a fixed direction (the arrow G direction in FIG. 2). And a non-magnetic developing sleeve 9 formed of a substantially cylindrical aluminum alloy and brass or the like, which is fitted in a predetermined direction (an arrow G in FIG. 2) by a control means and a driving means. Direction).

  The developer is a two-component developer containing toner and a magnetic carrier. The developer is attracted to the surface of the developing sleeve 9 by the magnetic force of the magnet, and is conveyed on the developing sleeve 9 along the rotation direction G of the developing sleeve 9. At this time, the carrier is attracted to the surface of the developing sleeve 9 by the magnetic force of the magnet roller 8 to form a magnetic brush, and the toner adheres to the carrier by Coulomb force by frictional charging.

  Further, on the upstream side in the rotation direction G of the developing sleeve 9 in the developing opening Q, the tip end portion of the regulating blade 6 is disposed so as to face the developing sleeve 9. In the present embodiment, the regulating blade 6 is configured to regulate the layer thickness of the developer formed on the surface of the developing roller 3.

  By configuring the developing device 1 in this embodiment in such a configuration, the developing device 1 supplies a certain amount of developer to a position facing the photoconductor 51, and among the developers supplied to the facing position, The toner is attracted to the photoconductor 51 by electrostatic force, and the electrostatic latent image formed on the photoconductor 51 is developed to form a toner image. Of the developer supplied to the opposite position, the carrier and the toner that has not been developed are returned to the developing tank 2 again by the rotation of the developing sleeve 9.

  The developing device 1 according to the present embodiment includes a bias voltage application unit 10 serving as a bias voltage applying unit that applies a vibration bias voltage to the developing sleeve 9 of the developing roller 3. The vibration bias voltage is applied so that the potential difference between the developing sleeve 9 and the photosensitive member 51 changes continuously and periodically.

  The applied vibration bias voltage includes a development-side potential that can exert a force in a direction from the developing sleeve 9 toward the photosensitive member 51 with respect to the charged toner, and the photosensitive member 51 to the developing sleeve 9 with respect to the charged toner. This is an alternating voltage at which the reverse development side potential that can exert a force in the direction of switching is alternately switched.

The developing device 1 of this embodiment further includes an auxiliary electrode 11.
The auxiliary electrode 11 is disposed in the vicinity of the outer surface of the developing sleeve 9, and is disposed at a position opposite to an intermediate position between two magnetic poles having the same magnetism among the magnetic poles of the magnet roller 8. The distance d2 between the auxiliary electrode 11 and the developing sleeve 9 is approximately the same as the closest distance d1 between the photosensitive member 51 and the developing sleeve 9. Specifically, it is appropriate to set d1 = d2 = about 0.5 mm.

  In the magnet roller 8, the middle position between two magnetic poles having the same polarity (for example, the N pole) is a so-called release position, in which the magnetic force from each magnetic pole repels and the carrier on the developing sleeve 9 moves away from the developing sleeve 9. Power is added to. Therefore, there is no carrier on the developing sleeve 9 near the auxiliary electrode 11.

  The auxiliary electrode 11 is made of a member that can rotate and has a conductive surface layer portion. As a material, a metal such as aluminum can be used. By making the auxiliary electrode 11 rotatable, it is possible to prevent the toner and the carrier from being clogged between the auxiliary electrode 11 and the developing sleeve 9 when the developer deteriorates and the fluidity is lowered.

  The developing device 1 includes an auxiliary voltage application unit 12 serving as auxiliary voltage application means for applying an auxiliary voltage to the auxiliary electrode 11. The applied auxiliary voltage is an AC voltage having the same waveform as the waveform of the vibration bias voltage applied to the developing sleeve 9 and having the phase inverted.

  FIG. 3 is a diagram illustrating a bias waveform applied in the developing device 1 of the first embodiment. 3A shows the waveform of the vibration bias voltage, FIG. 3B shows the waveform of the auxiliary voltage, and FIG. 3C shows the potential difference between the auxiliary electrode 11 and the developing sleeve 9. . In FIG. 3, the downward direction is positive (plus) in any waveform diagram.

  For example, as shown in FIG. 3 (a), the vibration bias voltage is a -450V DC component (VdcB), a peak-to-peak voltage (Vpp) of 1 kV, a frequency of 8 kHz, and a duty ratio of 50%. The component (VacB) is superimposed and applied to the developing sleeve 9. Since the direct current component (Vdc) is adjusted to keep the image density constant, -450 V is a standard value.

  As shown in FIG. 3B, for example, the auxiliary voltage is a -450V direct current component (VdcM), a peak-to-peak voltage (Vpp) of 1 kV, a frequency of 8 kHz, and a duty ratio of 50%. (VacM) is superimposed and applied to the auxiliary electrode 11.

  Compared with the waveform of the voltage applied to the developing sleeve, a waveform having an inverted phase is applied. The direct current component (VdcM) is set to −450 V, which is the same as the vibration bias voltage. Since the DC component (VdcB) of the vibration bias voltage applied to the developing sleeve 9 is adjusted to keep the density constant, the DC component (VdcM) applied to the auxiliary electrode 11 is also the same as VdcB. To be adjusted.

  FIG. 4 shows the voltage applied to the developing sleeve 9 and the potential of the photosensitive member 51 in the region of the developing opening Q (developing region) where the toner flies from the surface of the developing sleeve 9 to the photosensitive member 51 and development is performed. Assuming that the potential of the image portion of the photosensitive member 51 is VL and the potential of the non-image portion is V0, the developing-side potential in the direction in which the toner on the developing sleeve 9 is moved to the photosensitive member 51 is | V1-V0 | Thus, in the non-image portion, | V1-VL |. For this reason, the ratio of the toner leaving the developing sleeve 9 and the toner remaining in the developing sleeve 9 is different between the image portion and the non-image portion, and the development history remains in the developing sleeve 9.

  Specifically, if V0 = −600V and VL = −100V, V1 = −950V, so that | V1−V0 | = 850V in the image portion and | V1−VL | = 350V in the non-image portion. The difference causes the development history on the development sleeve 9.

  The potential difference between the auxiliary electrode 11 and the developing sleeve 9 is a voltage obtained by subtracting the voltage of FIG. 3A from the voltage of FIG. 3B as shown in FIG. Specifically, the AC component has a frequency of 8 kHz, a duty ratio of 50%, a peak-to-peak voltage (Vpp) of 2 kV, and the DC component is zero. Since the potential difference applied in the direction from the developing sleeve 9 toward the auxiliary electrode 11 is Vpp, it is 1 kV in this case.

  There is no carrier on the developing sleeve 9 facing the auxiliary electrode 11, and the toner adhering to the developing sleeve 9 remains. Since the distance between the auxiliary electrode 11 and the developing sleeve 9 is the same as the distance between the photoconductor 51 and the developing sleeve 9, the toner on the developing sleeve 9 in the region facing the auxiliary electrode 11 is more developed than the developing region. The force attracted to the auxiliary electrode 11 side is applied by the strong electric field force. Accordingly, since a force larger than the force due to the reverse development side potential applied in the direction of moving the toner on the developing sleeve 9 to the photosensitive member 51 is applied in the developing region, the development history in the developing region can be eliminated.

  With such a configuration, unlike the scraping of the toner on the developing sleeve 9 by a blade or the like, mechanical stress on the developing sleeve 9 does not occur.

  When the DC component is applied in the direction in which the toner adheres to the auxiliary electrode 11, the toner is accumulated in the auxiliary electrode 11, and it becomes difficult to apply an electric field, or the toner is clogged between the developing sleeve 9 and the auxiliary electrode 11. End up.

  Further, when the DC component is applied in the reverse direction, the toner easily returns onto the developing sleeve 9 and the effect of improving the development history is weakened. For this reason, the DC component applied to the developing sleeve 9 and the DC component applied to the auxiliary electrode 11 are made the same so that the toner does not easily return to the developing sleeve 9 and the auxiliary electrode 11.

  Further, when the developer fluidity is lowered due to the deterioration of the developer, the carrier detachment state due to the magnetic repulsion at the same pole portion of the magnet roller 8 may be lowered. Even when such a carrier remains slightly in the release position, the carrier and the toner fly together due to the alternating electric field between the developing sleeve 9 and the auxiliary electrode 11, so that the developer once leaves the developing sleeve 9. Thus, the development history is suppressed.

  When the distance d2 between the auxiliary electrode 11 and the developing sleeve 9 is different from the distance d1 between the photosensitive member 51 and the developing sleeve 9, the electric field acting on the toner on the developing sleeve 9 in the vicinity of the auxiliary electrode 11 causes the developing sleeve in the developing region. If the electric field acting on the toner on the toner 9 is larger than that, the development history can be suppressed. Since the electric field can be calculated by dividing the voltage by the distance, a condition that has a large effect of eliminating the development history is | V1-VL | / d1 <Vpp / d2.

Next, a second embodiment of the present invention will be described. In the first embodiment, the peak-to-peak voltage applied to the auxiliary electrode 11 is the same as the peak-to-peak voltage applied to the developing sleeve 9, but in this embodiment, the peak-to-peak voltage applied to the auxiliary electrode 11 is the same. The peak voltage (VppB) is different from the peak-to-peak voltage (VppM) applied to the developing sleeve 9.
The voltage applied to the developing sleeve 9 and the configuration of the auxiliary electrode 11 are the same as those in the first embodiment.

  FIG. 5 is a diagram illustrating a bias waveform applied in the developing device 1 of the second embodiment. 5A shows the waveform of the vibration bias voltage, FIG. 5B shows the waveform of the auxiliary voltage, and FIG. 5C shows the potential difference between the auxiliary electrode 11 and the developing sleeve 9. . In FIG. 5, the downward direction is positive (plus) in any waveform diagram.

  As shown in FIG. 5 (a), the vibration bias voltage is a -450V DC component (VdcB), a peak-to-peak voltage (Vpp) of 1 kV, a frequency of 8 kHz, and a duty ratio of 50%. (VacB) is superimposed and applied to the developing sleeve 9. As shown in FIG. 5B, the auxiliary voltage is applied to the auxiliary electrode 11 by superimposing a rectangular wave AC component (VacB) having a peak-to-peak voltage (Vpp) of 800 V, a frequency of 8 kHz, and a duty ratio of 50%. Applied.

  As shown in FIG. 5C, the potential difference between the auxiliary electrode 11 and the developing sleeve 9 is a voltage obtained by subtracting the voltage in FIG. 5A from the voltage in FIG. 5B. Specifically, the AC component has a frequency of 8 kHz, a duty ratio of 50%, a peak-to-peak voltage (Vpp) of 1.8 kV obtained by adding VppB and VppM, and the DC component is zero. Since the potential difference in the direction from the developing sleeve 9 toward the auxiliary electrode 11 is (VppB + VppM) / 2, in this case, it is 900V.

  Since the distance between the auxiliary electrode 11 and the developing sleeve 9 is the same as the distance between the photoconductor 51 and the developing sleeve 9, the toner on the developing sleeve 9 in the region facing the auxiliary electrode 11 is more developed than the developing region. The force attracted to the auxiliary electrode 11 side is applied by the strong electric field force. Accordingly, a force greater than the force due to the reverse development side potential applied in the direction in which the toner on the developing sleeve 9 is moved to the photosensitive member 51 in the developing region is applied, so that the development history in the developing region can be suppressed.

  Here, in a configuration in which the distance d2 between the auxiliary electrode 11 and the developing sleeve 9 is different from the distance d1 between the photosensitive member 51 and the developing sleeve 9, the electric field acting on the toner on the developing sleeve 9 near the auxiliary electrode 11 develops. If it is larger than the electric field acting on the toner on the developing sleeve 9 in the region, the development history can be suppressed. Since the electric field can be calculated by dividing the above voltage by the distance, the condition that has a great effect of suppressing the development history is | V1−VL | / d1 <(VppB + VppM) / (2 × d2).

  Next, a third embodiment will be described. In the first embodiment and the second embodiment, the vibration bias waveform applied to the developing sleeve 9 is a rectangular wave having a duty ratio of 50%. However, in the third embodiment, as a waveform applied to the developing sleeve 9, The duty ratio is not 50%.

  The duty ratio is defined as T1 / (T1 + T2), where T1 is the time during which the voltage is applied in the direction in which the toner is moved from the developing sleeve 9 to the photoconductor 51 and T2 is the time during which the voltage is applied in the reverse direction. .

A case where the duty ratio is smaller than 50% will be described.
By reducing the duty ratio of the vibration bias voltage, carrier adhesion and toner fog can be reduced.

  With respect to the non-image portion of the electrostatic latent image, carrier adhesion can be reduced by making the reverse development side potential smaller than the development side potential.

  The increase in fog can be suppressed by lengthening the application time of the reverse development side potential.

  FIG. 6 is a diagram showing the voltage applied to the developing sleeve 9 and the surface potential of the photoreceptor 51. The AC component has a frequency of 8 kHz, a duty ratio of 40%, a peak-to-peak voltage of 1 kV, and a DC component of −450 V. When the duty ratio is not 50%, the average value is DC. In this case, V1 = −1050V and V2 = −50V.

  When V0 = −600V and VL = −100V, | V1−V0 | = 950V in the image portion and | V1−VL | = 450V in the non-image portion, and this difference causes the development history due to the toner on the developing sleeve 9. It has become.

  FIG. 7 is a diagram illustrating a bias waveform applied in the developing device 1 of the third embodiment. 7A shows the waveform of the vibration bias voltage, FIG. 7B shows the waveform of the auxiliary voltage, and FIG. 7C shows the potential difference between the auxiliary electrode 11 and the developing sleeve 9. . In FIG. 7, the downward direction is positive (plus) in any waveform diagram.

  Since the potential difference in the direction from the developing sleeve 9 toward the auxiliary electrode 11 is (1−Duty) × (VppB + VppM), in this embodiment, it is 1080V. Since this voltage is larger than the voltage applied in the direction in which the toner on the developing sleeve 9 is moved to the photosensitive member 51 in the developing region, the distance d2 between the auxiliary electrode 11 and the developing sleeve 9 is the distance between the photosensitive member 51 and the developing sleeve 9. With the same configuration as the distance d1, the development history in the development area can be suppressed.

  Further, in the configuration in which the distance d2 between the auxiliary electrode 11 and the developing sleeve 9 is different from the distance d1 between the photosensitive member 51 and the developing sleeve 9, the electric field acting on the toner on the developing sleeve 9 near the auxiliary electrode 11 is generated in the developing region. If it is larger than the electric field acting on the toner on the developing sleeve 9, the development history can be suppressed. Since the electric field can be calculated by dividing the voltage by the distance, a condition that has a large effect of suppressing the development history is | V1−VL | / d1 <(1−Duty) × (VppB + VppM) / d2.

DESCRIPTION OF SYMBOLS 1 Developing apparatus 3 Developing roller 8 Magnet roller 9 Developing sleeve 10 Bias voltage application part 11 Auxiliary electrode 12 Auxiliary voltage application part

Claims (6)

A developer carrying member to which a bias voltage in which an alternating current component is superimposed on a direct current component is applied, and an electrostatic latent image carrying member on which an electrostatic latent image is formed are developed, and the formed electrostatic latent image is developed with toner. In the developing device,
The developer carrier has a magnet roller in which a plurality of magnetic pole members are arranged along the circumferential direction, and a developing sleeve that is externally fitted to the magnet roller and configured to be rotatable.
An auxiliary electrode disposed at a position facing the release position of the magnet roller and spaced from the developing sleeve surface by a predetermined distance;
A developing device, comprising: an auxiliary voltage application unit that applies an alternating current component whose phase is inverted to an alternating current component of the bias voltage to the auxiliary electrode.   The developing device according to claim 1, wherein the auxiliary voltage applying unit applies the same DC component as the DC component applied to the developer carrier to the auxiliary electrode.   The developing device according to claim 1, wherein the auxiliary electrode is configured to be rotatable around an axis parallel to a rotation axis of the developing sleeve. The peak voltage of the bias voltage applied in the direction in which the toner moves from the developer carrier to the electrostatic latent image carrier is V1, the image portion potential of the electrostatic latent image carrier is VL, and the developer carrier. D1 is the closest distance between the electrostatic latent image carrier and the electrostatic latent image carrier, d2 is the closest distance between the developer carrier and the auxiliary electrode member, and the peak-to-peak voltage applied to the developer carrier is When VppB and the peak-to-peak voltage applied to the auxiliary electrode is VppM,
The developing device according to claim 1, wherein the following expression (1) is satisfied.
| V1-VL | / d1 <(VppB + VppM) / (2 × d2) (1) The time during which the voltage is applied in the direction in which the toner is moved from the developer carrier to the electrostatic latent image carrier is T1, and the voltage in the direction in which the toner is moved from the electrostatic latent image carrier to the developer carrier. Is set to T2, the duty ratio D of the bias voltage applied to the developer carrier is T1 / (T1 + T2),
The peak voltage of the bias voltage applied in the direction in which the toner moves from the developer carrier to the electrostatic latent image carrier is V1, the image portion potential of the electrostatic latent image carrier is VL, and the developer carrier. D1 is the closest distance between the electrostatic latent image carrier and the electrostatic latent image carrier, d2 is the closest distance between the developer carrier and the auxiliary electrode member, and the peak-to-peak voltage applied to the developer carrier is When VppB and the peak-to-peak voltage applied to the auxiliary electrode is VppM,
The developing device according to claim 1, wherein the following expression (2) is satisfied.
| V1-VL | / d1 <(1-D) × (VppB + VppM) / d2 (2)   An image forming apparatus comprising the developing device according to claim 1.

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