JPH11184186A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus capable of efficiently and effectively rearranging a developed toner image and improving the quality of the toner image. SOLUTION: A toner image rearranging means 10 provided with a plurality of grid electrodes 11 to 15 is arranged downstream of an image forming process with respect to a developing device 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus using electrophotography, such as a printer, a copying machine, a facsimile, and the like.

[0002]

2. Description of the Related Art FIG. 4 shows an example of an image forming apparatus utilizing electrophotography. The image forming apparatus according to the present embodiment rotatably includes a drum-shaped electrophotographic photosensitive member 1 serving as an image carrier, and an electrophotographic process unit is arranged around the photosensitive drum 1. That is, the electrophotographic process means includes a charging means for putting a required uniform charge on the photosensitive drum 1, for example, a corona charger 2, and the uniformly charged photosensitive drum 1
Exposure means 3 such as a laser generator for irradiating a laser beam thereon according to image data to form an electrostatic latent image, and further for developing the electrostatic latent image formed on the photosensitive drum 1 It has a developing unit 4. Developing device 4 as developing means
Comprises a developing container 41 for storing a developer,
The developing sleeve 42 is disposed at a position facing the photosensitive drum 1 at the opening 1. The developing sleeve 42 carries the developer in the developing container 41 and transports the developing agent to a developing area facing the photosensitive drum 1. At this time, the developing sleeve 4
After the developer on 2 is regulated to a predetermined thickness by the developer thickness regulating member 43, it is transported to the developing area. A predetermined developing bias voltage is applied to the developing sleeve 42 from the developing voltage generating means 50, and the electrostatic latent image on the photosensitive drum 1 is developed into a visible image, that is, a toner image. This toner image is transferred to the recording material P at a transfer position where the transfer unit 6 such as a corona charger is disposed. The photosensitive drum 1 is subjected to the next image forming process after the remaining toner is wiped off by the cleaning unit 7.

In such an electrophotographic image forming apparatus, image data is formed on the photosensitive drum 1 as an electrostatic latent image as a pattern based on the distribution of charge density. Also, the developing process for visualizing the electrostatic latent image
This is performed by moving the toner particles holding the charges to the electrostatic latent image by the electrostatic force. The force with which the toner particles are developed is the charge density of the electrostatic latent image and the developing electric field formed by the developing bias.

Further, when an attempt is made to form a toner image having an area of a certain size in this image forming apparatus, the developing electric field formed by the latent image is reduced even if the surface charge density in the area where the toner is to adhere is the same. Depends on location. That is, when the toner image forming region has a certain area, the developing electric field formed at the end of the region is stronger than that near the center. This phenomenon is known as the edge effect. Due to the edge effect of the developing electric field, the toner is often developed more near the edge of the area.

From another aspect, developing an electrostatic latent image with toner can be said to be a process of filling holes of electrostatic potential generated by a charge density distribution pattern of the electrostatic latent image with toner charges. For this reason, in the toner image portion after development, the electrostatic potential is flattened to some extent.

For this purpose, as shown in FIG.
After the difference in charge density of the electrostatic latent image is filled with the developed toner charge, the counter electrode 8 is further disposed on the counter electrode 8.
The rearrangement of the developed toner is performed by applying the rearrangement bias voltage. As a result, the toner image is made uniform within the image area of the developed toner image.

[0007]

However, in the prior art, the bias voltage generating means 6 is
An alternating bias voltage is applied from 0. For this reason, the toner image is also subjected to a horizontal electric field once when the electrode enters and when the electrode is detached, but moves only in a direction perpendicular to the image plane in a range of an effective electric field strength for moving the toner. It is possible. This significantly limits the effect of the application of the rearrangement bias voltage, and hinders the high quality of the toner image.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus capable of efficiently and effectively rearranging a developed toner image and improving the quality of the toner image.

[0009]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus which forms an electrostatic latent image on an image carrier and converts the electrostatic latent image into a toner image in a developing device, a toner including a plurality of electrodes on the downstream side of the image forming process with respect to the developing device An image forming apparatus comprising an image rearranging unit.

According to one embodiment of the present invention, a voltage waveform characteristic of an image pattern is applied to each electrode of the toner image rearranging means at a characteristic timing for each electrode. Preferably, an AC bias voltage is applied to each of the electrodes of the toner image rearranging unit with a period shifted for each electrode, and each of the electrodes of the toner image rearranging unit is applied to an image having a high spatial frequency. Applies a high frequency AC bias voltage and applies a low frequency AC bias voltage to an image having a low spatial frequency.

According to one embodiment of the present invention, if the distance between each electrode of the toner image rearranging means and the image carrier is L and the distance between each electrode is D, then L <2D, and preferably L <2D. Is L <D.

According to a preferred embodiment of the present invention, the developing device uses a one-component developer and converts the electrostatic latent image on the image carrier into a toner image by non-contact development.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows an embodiment of the image forming apparatus of the present invention. The image forming apparatus of the present embodiment has the same configuration as the electrophotographic image forming apparatus described with reference to FIG. Therefore,
Although detailed description is omitted in the present embodiment, the image forming apparatus rotatably includes a drum-shaped electrophotographic photosensitive member 1 serving as an image carrier, and an electrophotographic process unit is arranged around the photosensitive drum 1. As a result, an electrostatic latent image is formed on the photosensitive drum 1.

That is, the photosensitive drum 1 is uniformly charged by charging means 2 such as, for example, a corona charger.
A laser beam is irradiated on the photosensitive drum 1 by exposure means 3 such as a laser generator according to image data, and an electrostatic latent image is formed by a charge density distribution by charges generated by a photoelectric effect. The developing device 4 serving as a developing unit conveys the toner charged by the developing sleeve 42 as a developer carrier to a developing area facing the photosensitive drum 1.
A developing bias voltage is applied to the developing sleeve 42 by the developing voltage generating means 50 to move the toner to the photosensitive drum 1 and develop the electrostatic latent image formed on the photosensitive drum 1 into a toner image. .

According to the present invention, the toner image rearranging means 10 is arranged downstream of the developing device 4 in the image forming process. The toner image rearrangement means 10 has a plurality of, in this embodiment, five grid electrodes 11, 12, 13, 14, and 15. Therefore, the toner image on the photosensitive drum 1 is transferred to the transfer means 6 by the grid electrodes 11 to 1.
5 will be passed. Grid electrodes 11-1
5 includes a rearrangement bias voltage generating means 60 for each electrode.
A rearrangement bias voltage is applied from FIG. The toner image on the photosensitive drum 1 is rearranged by the rearrangement bias voltage. Next, the rearranged toner image is transferred to the recording material P at a transfer position where the transfer unit 6 such as a corona charger is disposed. The photosensitive drum 1 is subjected to the next image forming process after the remaining toner is wiped off by the cleaning unit 7.

FIG. 2 is an enlarged view of the vicinity of the toner image rearranging means 10. The grid electrodes 11 to 15 are arranged at a predetermined distance L from the photosensitive drum 1 and at a predetermined distance D from each other. Usually, L = 200 to 1000 μm,
D = 500 to 5000 μm, and in this embodiment, L =
200 μm, D = 500 μm, and five grid electrodes 11, 12, 13, 14, and 15 were arranged in parallel in the axial direction of the photosensitive drum 1. Grid electrodes 11 to
15 is not limited to five, and is selected as appropriate. Each of the grid electrodes 11 to 15 usually has a cross-sectional diameter of
It is a wire having a diameter of 50 to 100 μm.
A wire made of a gold-plated tungsten wire of 0 μm was used.

In this embodiment, each of the grid electrodes 11 to 15
Are supplied from the rearrangement bias power supplies 61 to 65 constituting the rearrangement bias voltage generation means 60 to the DC voltage V for each electrode.
An AC bias voltage Vpp on which dc was superimposed was applied.

The bias voltage Vpp applied to each of the grid electrodes 11 to 15 varies depending on the distance L between the photosensitive drum 1 and the distance D between the adjacent electrodes and the size of the electrodes, but Vpp = 200 V to 500 V. I was able to find an appropriate value between. The DC voltage Vdc changes the center value of Vpp. In the present invention, the DC voltage Vdc serves to adjust the strength of rearrangement, that is, to adjust the amount of movement of the toner, and Vdc = −200 to −200. An appropriate value was found between 600V.

More specifically, in this embodiment, the image forming apparatus shown in FIG.
An electrostatic latent image of 700 V and a bright portion potential of −100 V is formed, and a one-component developer is used.
With pp = 1800 V and Vdc = −550 V, a toner image was formed by reverse development. Next, an AC voltage Vp is applied to this toner image from the rearrangement bias power supplies 61 to 65 for each electrode.
By applying a rearrangement bias voltage where p = 350 V and DC voltage Vdc = -300 V, a high-quality image could be obtained.

FIG. 3 shows five grid electrodes 11, 12,.
The waveforms and timings of the bias voltages applied to 13, 14, and 15 are shown. According to the present embodiment, each grid electrode 1
To 1 to 15, the trapezoidal alternating bias voltages were applied with the adjacent cycles shifted, whereby the developed toner images could be rearranged to a state closer to the original image.

It has been found that the rearrangement effect becomes weaker as the grid electrodes 11 to 15 are separated from the photosensitive drum 1 by L = 500 μm, 700 μm, and 1000 μm. At this time, even if the applied bias voltage Vpp was increased in proportion to the distance, the reduction in the rearrangement effect could not be suppressed.

Using a developing device using a non-magnetic one-component developer and a developing device using a non-magnetic two-component developer, the effect of the rearranged grid electrodes 11 to 15 was examined. A greater rearrangement effect was obtained for the toner image developed by the one-component developing device. More specifically, when developing a line-shaped image, excess toner is generally developed at the edge of the line, resulting in noise. The rearrangement effect has an effect of pushing the toner not faithful to the latent image into the latent image portion, and was able to reduce noise at the line edge portion.

Further, when an image having a high spatial frequency is rearranged at a low frequency, a slight noise is generated in a portion of the image having a high spatial frequency. Applying a high-frequency rearrangement bias to images with a high spatial frequency and applying a low-frequency rearrangement bias to images with a low spatial frequency maximize the effect of the rearrangement bias. It was possible to pull out. More specifically, since the spatial frequency is high in the above-described line edge portion, a high-frequency rearrangement bias is used. This is to reduce the amount of toner movement during rearrangement. In a halftone image having a low spatial frequency, the toner is averaged over a wider range. That is, the larger the amount of movement of the toner, the more the noise could be reduced. When the rearrangement bias is at a high frequency, high-frequency noise is reduced, and a substantial reduction in resolution is prevented. Also, at low frequencies, it was possible to improve uniformity and substantial gradation.

[0025]

As described above, in the image forming apparatus of the present invention, an electrostatic latent image is formed on an image carrier, and the electrostatic latent image is formed into a toner image by a developing device. ,
Since the developing device has a toner image rearranging unit having a plurality of electrodes on the downstream side of the image forming process with respect to the developing device,
The rearrangement of the developed toner image can be performed efficiently and effectively, and the quality of the toner image can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a toner image rearrangement unit.

FIG. 3 is a timing chart of a voltage applied to a grid electrode serving as a toner image rearrangement unit.

FIG. 4 is a schematic configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image carrier (photosensitive drum) 2 charging device 3 exposure device 4 developing device 10 toner image rearranging means 11 to 15 grid electrode 50 developing voltage generating means 60 rearranging bias voltage generating means 61 to 65 rearranging bias power supply

Claims (6)

[Claims] 1. An image forming apparatus which forms an electrostatic latent image on an image carrier and converts the electrostatic latent image into a toner image in a developing device. An image forming apparatus comprising: a toner image rearranging unit having an electrode. 2. Each of the electrodes of the toner image rearranging means includes:
2. A characteristic voltage waveform applied to an image pattern at a characteristic timing for each electrode.
Image forming apparatus. 3. An electrode of the toner image rearranging means,
3. The image forming apparatus according to claim 2, wherein an AC bias voltage is applied with a period shifted for each electrode. 4. An electrode of the toner image rearranging means,
4. An image forming apparatus according to claim 3, wherein a high frequency AC bias voltage is applied to an image having a high spatial frequency, and a low frequency AC bias voltage is applied to an image having a low spatial frequency. apparatus. 5. The image processing apparatus according to claim 1, wherein L <2D where L is a distance between each electrode of said toner image rearranging unit and said image carrier, and D is a distance between each electrode. 5. The image forming apparatus according to any one of items 4. 6. The image forming apparatus according to claim 1, wherein the developing device uses a one-component developer and converts the electrostatic latent image on the image carrier into a toner image by non-contact development. The image forming apparatus according to the item.