JP5200808B2 - Image forming apparatus, latent image carrier unit, and developing unit - Google Patents

Description

  The present invention relates to an image forming apparatus, a latent image carrier unit, and a developing unit.

  In the image forming process, the developing device develops the latent image formed on the photoreceptor as a toner image. The developing device forms a magnetic brush when developing the latent image as a toner image, and brings the tip of the formed magnetic brush into contact with the photosensitive member.

Here, due to the contact of the magnetic brush or the like, a toner image with poor graininess that is pinched on the photoreceptor is developed. Specifically, a sweep-like toner image is developed, and is particularly noticeable in a halftone halftone image or the like.
It has been confirmed that sweeping occurs not only in the two-component development method for forming a magnetic brush but also in the one-component development method.

A developing device is disclosed in which an electrode is provided on the downstream side in the rotation direction of the photosensitive member relative to the developing unit in order to remove the sweep, and the toner reciprocates between the photosensitive member and the electrode (see Patent Document 1).
According to the technique of Japanese Patent Laid-Open No. 2004-228688, the toner causing reciprocation from the toner image once developed on the photoreceptor is rearranged by the reciprocating movement of the toner between the photoreceptor and the electrode, and the scavenging is removed. Can be removed.
JP-A-4-372964

  However, although the developing device of Patent Document 1 has a sweep removal effect, it cannot improve the local excess or deficiency of the toner amount. Specifically, in the moving direction of the toner image, the toner cannot be rearranged when the toner is disposed in excess or insufficient than the appropriate amount at the leading or trailing edge of the toner image.

  An object of the present invention is to remove the sweep and to rearrange the toner at an appropriate position so that the amount of toner is appropriate at the leading edge or the trailing edge of the toner image.

According to the present invention,
In an image forming apparatus including a toner rearrangement unit that rearranges toner in the toner image by applying an electric field to the toner image developed on the moving latent image carrier.
The toner rearrangement means includes
A plurality of strip-shaped electrodes arranged facing the surface of the latent image carrier at a predetermined interval in the moving direction of the toner image and extending along a direction orthogonal to the moving direction of the toner image; ,
Voltage application means for applying an alternating voltage of three or more phases to the strip electrode;
An image forming apparatus is provided.

According to the present invention, even when the degree of granularity is poor and a sweep-like toner image is developed on the photoreceptor, the toner can be rearranged at an appropriate position. Further, even when the toner is excessive or insufficient at the leading or trailing edge of the toner image, the toner can be rearranged at an appropriate position.

  Hereinafter, optimal configurations and operations of the image forming apparatus, the latent image carrier unit, and the developing unit in the present embodiment will be described in detail with reference to the drawings.

First, the configuration will be described.
FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100.
The image forming apparatus 100 includes a reading unit 1, an image forming unit 2, a paper feeding unit 3, a transport unit 4, and the like.

The reading unit 1 includes an optical system such as a contact glass, a platen glass, a light source, a mirror, a condenser lens, and a CCD.
The reading unit 1 converts the image of the document F placed on the reading tray by the optical system into an electric signal, and outputs the converted electric signal to the image forming unit 2.

The image forming unit 2 includes a charging device 2b, an exposure device 2c, a developing device 2d, a toner rearrangement electrode 2e, a transfer roller 2f, a cleaning device 2g, and the like around a photoconductor 2a having a drum shape. The
The image forming unit 2 forms a toner image on the photoreceptor 2a using each of the above devices, and transfers the formed toner image onto the paper DP. The operation performed by the toner rearrangement electrode 2e will be described later.

  Although FIG. 1 shows the image forming unit 2 capable of forming only a monochrome image, the image forming unit 2 is not necessarily limited thereto, and may be an image forming unit capable of forming a color image.

FIG. 2 shows an image forming unit 20 capable of forming a color image.
The image forming unit 20 includes a yellow image forming unit Y, a magenta image forming unit M, a cyan image forming unit C, and a black image forming unit K. Each of the image forming portions Y, M, C, and K is provided along the moving direction of the intermediate transfer body 20A.

  The yellow image forming unit Y includes a photoreceptor 21Y, a charging device 22Y, an exposure device 23Y, a developing device 24Y, a toner rearrangement electrode 25Y, a transfer roller 26Y, a cleaning device 27Y, and the like.

  The yellow image forming portion Y forms a toner image on the photoreceptor 21Y, and transfers the formed toner image to the intermediate transfer member 20A. The operation performed by the toner rearrangement electrode 25Y is the same as that of the toner rearrangement electrode 2e shown in FIG. 1, and will be described later using the toner rearrangement electrode 2e as an example. The magenta image forming unit M, the cyan image forming unit C, and the black image forming unit K perform the same configuration and operation as the yellow image forming unit Y, and thus the description thereof is omitted here.

  Returning to FIG. 1, the paper feed unit 3 includes a paper feed tray 3a, a manual feed tray 3b, a paper feed roller 3c, and the like. The paper feed tray 3 a and the manual feed tray 3 b accommodate a plurality of paper DP, and the paper feed roller 3 c supplies the paper DP to the image forming unit 2 via the transport unit 4.

  The transport unit 4 includes a transport path 4a, a switching claw 4b, a reverse roller 4c, and the like. The transport path 4a transports the paper DP to the image forming processing unit 21 and transports the paper DP to the outside together with the operation of the switching claw 4b or the reverse roller 4c.

FIG. 3A shows a schematic cross-sectional view of the toner rearrangement unit.
The toner rearrangement unit 201e includes a photoreceptor 2a and a toner rearrangement electrode 2e in one casing constituting the image forming apparatus 100. The toner rearrangement unit 202e configured to include the developing device 2d and the toner rearrangement electrode 2e may be used, and the toner rearrangement units 201e and 202e are configured to include at least the toner rearrangement electrode 2e.

The toner rearrangement electrode 2e is disposed downstream of the developing device 2d in the rotation direction of the photosensitive member 2a, and is disposed opposite to the photosensitive member 2a.
Further, as shown in FIG. 3B, the shape of the surface of the toner rearrangement electrode 2e facing the photosensitive member 2a may be a flat surface, or as shown in FIG. 3C, it is equidistant from the surface of the photosensitive member 2a. Such a curved surface may be used.

FIG. 4A shows a surface view of the toner rearrangement electrode 2e. FIG. 4B shows a cross-sectional view of the toner rearrangement electrode 2e.
As shown in FIGS. 4A and 4B, the toner rearrangement electrode 2e is configured to include a plurality of electrodes 20e with a minute interval in the toner image moving direction.
The length of the toner rearrangement electrode 2e in the toner image moving direction is 15 [mm], and the thickness S of the surface protective layer is 15 [μm]. The length of each electrode 20e in the longitudinal direction is 300 [mm], the length L in the toner image moving direction is 40 [μm], and the repetition pitch P in the toner image moving direction is 80 [μm].

Here, [the length L of the electrode 20e in the moving direction of the toner image] / [the repetition pitch P of the moving direction of the electrode 20e in the toner image] is preferably 0.3 <L / P <0.7.
When L / P is 0.3 or less, the surface area of the electrode 20e becomes too small, and the ability to reciprocate the toner in the toner image facing direction is poor. If the ability to reciprocate is inferior, the toner repositioning effect is diminished, and the graininess cannot be sufficiently improved. When L / P is 0.7 or more, the electric lines of force near the center of the toner rearrangement electrode 2e are substantially vertical, and the ability to move the toner in the toner image moving direction is poor. Therefore, the toner amount cannot be made sufficiently uniform.

Further, it is desirable that the repetition pitch P in the orthogonal direction of the electrodes 20e is 50 [μm] <P <200 [μm].
When the repetition pitch P is 50 [μm] or less, the speed at which the toner is moved in the toner image moving direction is too slow. If the moving speed is too slow, the toner rearrangement effect is diminished and the toner amount cannot be made sufficiently uniform. Further, when the repetition pitch P is 200 [μm] or more, the speed of moving the toner in the toner image moving direction is too high. If the moving speed is too fast, the toner rearrangement effect is reduced as in the case where the moving speed is too slow, so that the toner amount cannot be made sufficiently uniform.

The distance D between the toner rearrangement electrode 2e and the photoreceptor 2a is 100 [μm].
Here, the [repeat pitch P of the electrode 20e in the moving direction of the toner image] / [distance D] is preferably 0.5 <P / D <1.2.
When P / D is 0.5 or less, the electric field in the vicinity of the photoreceptor 2a is too weak, and the speed at which the toner moves in the toner image moving direction becomes slow. Therefore, the toner rearrangement effect is weakened and the toner amount cannot be made sufficiently uniform. Further, when P / D is 1.2 or more, the electric field in the toner image moving direction in the vicinity of the photosensitive member 2a becomes relatively strong, and the ability to reciprocate the toner in the opposite direction is inferior. Therefore, the graininess cannot be improved sufficiently.

FIG. 5 shows a functional block diagram of the toner rearrangement device.
As shown in FIG. 5, the toner rearrangement device 21e includes a toner rearrangement electrode 2e and a voltage application device 200e.

  The toner rearrangement electrode 2e includes a plurality of electrodes 20e and an insulator portion. The shape of the electrode 20e is not necessarily limited to the shape shown in FIG. For example, the longitudinal direction of the electrode 20e may be substantially the same as the direction orthogonal to the toner image moving direction, and a plurality of electrodes 20e may be arranged in the toner image moving direction.

The voltage applying device 200e is connected to each electrode 20e. Specifically, the DC power supply DS is connected to the multiphase AC power supply ES, and the multiphase AC power supply ES is connected to each electrode 20e.
The control unit 5 controls the operations of the DC power supply DS and the multiphase AC power supply ES to apply a four-phase alternating voltage to the toner rearrangement electrode 2e.

By applying a four-phase alternating voltage to the toner rearrangement electrode 2e, the toner rearrangement electrode 2e forms a traveling wave electric field in the vicinity of the surface of the electrode 20e.
Here, the direction of the traveling wave electric field to be formed differs depending on the developing method of the toner image.
When the developing method of the toner image is reverse development, the toner amount is insufficient at the front end in the toner image moving direction (image missing), and the toner amount is excessive at the rear end (sweeping up). In this case, the toner rearrangement electrode 2e needs to form a traveling wave electric field in the toner image moving direction.
On the other hand, when the developing method of the toner image is normal rotation development, sweeping occurs at the front end in the moving direction of the toner image, and image missing occurs at the rear end. In this case, the toner rearrangement electrode 2e needs to form a traveling wave electric field in the direction opposite to the toner image moving direction.

FIG. 6 shows an example of an alternating voltage waveform.
An alternating voltage having a different phase is applied to each of the electrodes 1 to 4. Therefore, the electrodes 1 to 4 form a traveling wave electric field in the vicinity of the electrode surface. The waveform of the alternating voltage shown in FIG. 6 is a rectangular wave, but is not limited thereto, and may be a half wave, for example.

Hereinafter, the performance evaluation result will be described.
In order to evaluate the performance of the image forming apparatus 100, (1) the shape of the electrode 20e, (2) the development direction, (3) presence / absence of traveling wave electric field, and (4) traveling wave traveling direction are changed. A performance evaluation test was conducted.

  In addition, the graininess rank, sweep / image missing rank, and overall evaluation of the image formed on the paper DP by changing each of the elements (1) to (4) were used as the performance evaluation results. The image to be formed was a halftone dot image.

The graininess rank and the sweeping / image missing rank were visually evaluated in five levels, and the overall evaluation was OK when the rank of all items was 4 or more, and NG when the rank of one item was 3 or less. The granularity ranks 4 and 3 were determined based on whether the portion where the graininess was poor and the sweep occurred was partial or overall. The sweeping / image missing ranks 4 and 3 are determined based on whether or not the location where the sweeping / image missing occurs over the entire length of the leading edge or the trailing edge of the image.
The contents of the performance evaluation test and the performance evaluation results are shown in Table 1.

According to the performance evaluation results shown in Table 1, in the case of the image forming apparatus 100 including the toner rearrangement electrode 2e composed of a plurality of electrodes 20e, the granularity is good, and there is no sweeping and no sweeping / image loss. Good images were formed (Examples 1 to 4).
In particular, when the surface shape of the electrode 20e is a curved surface that is equidistant from the photoreceptor 2a, a sufficient toner rearrangement effect can be obtained (Examples 2 and 4).

Comparative example

  In the case of an image forming apparatus provided with a toner rearrangement electrode composed of one electrode 20e, a traveling wave electric field is not formed, so that the toner does not move in the toner image moving direction but reciprocates only in the opposite direction. Therefore, although the graininess is improved and the sweep removal effect is obtained, the sweeping / image defect is not improved, and an image having the sweep / image defect is formed over the entire length of the leading edge or the trailing edge (Comparative Example). 1-4).

  In the case of an image forming apparatus that does not include a toner rearrangement electrode, the toner does not move in the toner image moving direction and the opposite direction. Therefore, images with remarkable sweeping and sweeping / image loss were formed (Comparative Examples 5 to 6).

  As described above, according to the present embodiment, the traveling-wave electric field can be formed in the toner image moving direction by the toner rearrangement device 21e. Therefore, the toner can be conveyed not only in the facing direction but also in the direction of the traveling wave electric field, and the toner rearrangement effect can be improved. Specifically, it is possible to form a toner image that is faithful to the latent image with improved sweeping / image defect while removing the sweep.

  Also, the phase of the alternating voltage applied to the electrode 20e is controlled so that a traveling wave electric field is formed in the toner image moving direction when the toner image development method is reverse development, and the toner image development method is normal rotation development. Can form a traveling wave electric field in the direction opposite to the toner image moving direction. Therefore, sweeping / image loss can be improved appropriately.

1 is an overall configuration diagram of an image forming apparatus. FIG. 3 is a configuration diagram illustrating a color image forming unit. FIG. 3 is a schematic cross-sectional view illustrating a toner rearrangement unit. FIG. 3 is a schematic cross-sectional view illustrating a toner rearrangement unit. FIG. 3 is a schematic cross-sectional view illustrating a toner rearrangement unit. It is a surface view of a toner rearrangement electrode. FIG. 3 is a schematic cross-sectional view of a toner rearrangement electrode. 3 is a functional block diagram of a toner rearrangement device. FIG. It is a figure which shows an example of the waveform of an alternating voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 1 Reading part 2 Image forming part 2a Photoconductor 2e Toner rearrangement electrode 20e Electrode 21e Toner rearrangement apparatus 3 Paper feed part 4 Conveying part 200e Voltage application apparatus

Claims (10)

In an image forming apparatus including a toner rearrangement unit that rearranges toner in the toner image by applying an electric field to the toner image developed on the moving latent image carrier.
The toner rearrangement means includes
A plurality of strip-shaped electrodes arranged facing the surface of the latent image carrier at a predetermined interval in the moving direction of the toner image and extending along a direction orthogonal to the moving direction of the toner image; ,
Voltage application means for applying an alternating voltage of three or more phases to the strip electrode;
An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein each of the plurality of strip-like electrodes has a longitudinal direction substantially the same as a direction orthogonal to a moving direction of the toner image.   The image forming apparatus according to claim 1, wherein the voltage applying unit forms a traveling wave electric field along a moving direction of the toner image.   The image forming apparatus according to claim 3, wherein the voltage application unit forms a traveling wave electric field that travels in a moving direction of the toner image when the toner image is developed by reverse development.   5. The image forming apparatus according to claim 3, wherein the voltage application unit forms a traveling wave electric field that travels in a direction opposite to a moving direction of the toner image when the toner image is developed by forward rotation development.   The image forming apparatus according to claim 1, wherein the voltage application unit includes a power source that generates an alternating voltage and a control unit that controls a phase of the alternating voltage generated from the power source. The latent image carrier for carrying the toner image and the electrode group for rearranging the toner of the toner image are housed in the same casing,
The electrode group faces the surface of the latent image carrier and is disposed at a predetermined interval in the moving direction of the surface of the latent image carrier, and along a direction perpendicular to the moving direction of the toner image. have a plurality of strip-shaped electrodes extending Te,
Voltage applying means for forming a traveling wave electric field along the moving direction of the toner image by applying an alternating voltage of three or more phases to the strip electrode;
A latent image carrier unit.   The latent image carrier unit according to claim 7, wherein each of the plurality of strip electrodes has a longitudinal direction substantially the same as a direction orthogonal to a moving direction of the toner image. A developing device for developing a toner image on a moving latent image carrier and an electrode group for rearranging the toner of the toner image are housed in the same casing,
The electrode group is disposed at a position facing the surface of the latent image carrier on the downstream side in the movement direction of the toner image with respect to the developing device at a predetermined interval in the movement direction of the surface of the latent image carrier. And a plurality of strip electrodes extending along a direction perpendicular to the moving direction of the toner image,
Voltage applying means for forming a traveling wave electric field along the moving direction of the toner image by applying an alternating voltage of three or more phases to the strip electrode;
Development unit equipped with. The developing unit according to claim 9, wherein each of the plurality of strip-shaped electrodes has a longitudinal direction substantially the same as a direction orthogonal to a moving direction of the toner image.

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