JPH05181348A - Charging device - Google Patents

Abstract

PURPOSE:To satisfy both the charging characteristic and discharge efficiency to a photoreceptor or the like. CONSTITUTION:A charge corotron (charging device) is formed of a slender shield case 55 having a band opening part in a determined direction, first and second discharge wire 58, 59 arranged in parallel to each other in the shield case 55, and a grid plate 63 arranged to cover the discharge wires 58, 59 and having an opening part for releasing charges the opening ratio of which is changed in the direction orthogonal to the longitudinal direction of the discharge wires. In this example, the opening ratio of the grid plate part just under the first discharge wire 58 is set to 90%, and the opening ratio of the grid plate part just under the second discharge wire to 65%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an image recording device such as an electrophotographic copying machine or a laser printer, and more particularly to a charging device having a grid.

[0002]

2. Description of the Related Art Most of image recording apparatuses such as electrophotographic copying machines and laser printers are adapted to form an electrostatic latent image on a photosensitive member and develop the electrostatic latent image with toner to record the image. .. In such an apparatus, various charging devices are arranged around the photoconductor to perform various processes such as charging and transfer of toner to paper.

FIG. 10 shows a main part of a laser printer capable of recording an image with two colors. Around the photosensitive drum 11 of this laser printer, the first
There are two developing devices, a first developing device 12 that develops with the recording color of No. 2 and a second developing device 13 that develops with the second recording color. In this figure, the photosensitive drum 11 is indicated by the arrow 1.
It shall rotate in four directions (counterclockwise). A charge corotron 15 for initially uniformly charging the surface of the photosensitive drum 11 is arranged upstream of the first developing device 12. A first laser beam scanning mechanism 16 scans a space between the charge corotron 15 and the first developing device 12 with a first laser beam 17. Further, the second laser beam scanning mechanism 1 is provided between the first developing device 12 and the second developing device 13.
The second laser beam 19 is scanned by means of 8. The first developing device 12 develops the first electrostatic latent image formed by the scanning of the first laser beam 17 with, for example, black toner to form a black toner image on the surface of the photosensitive drum 11. The second developing device 13 develops the second electrostatic latent image formed by the scanning of the second laser beam 19 with toner having a polarity opposite to that of the toner used in the first developing device 12, and the photosensitive drum For example, a red toner image is added to the surface of 11. In this way, two color toner images are created on the drum surface.

A pre-transfer corotron 21 and a transfer corotron 2 are provided downstream of the second developing device 13.
2 are arranged in this order. The pre-transfer corotron 21 plays the role of aligning the polarities of the toner during transfer. After that, the transfer corotron 22 transfers the toner image onto the sheet 25 conveyed in the direction of arrow 24. After the transfer, the photosensitive drum 11 is cleaned of unnecessary toner by the cleaning blade 26, and is then irradiated by the static elimination lamp 27 to remove unnecessary charges.

By the way, in such an image recording apparatus as a laser printer or an electrophotographic copying machine, an organic photoconductor is often used for a photoconductor drum, a photoconductor belt or the like. In an organic photoconductor, a charge corotron is generally used to charge negative charges. However, it is difficult to uniformly charge the surface of the photoconductor with such negative charging as compared with positive charging.

FIG. 11 shows a general tendency of the discharge state of the discharge wire in the negative charging device. When a negative DC high voltage of, for example, about -4 KV (kilovolt) to about -7 KV is applied to the discharge wire 31 to cause discharge on the photoconductor 32 that is separated from the discharge wire 31 by a predetermined distance,
Bright spots 33 are generated on the discharge wire 31 at predetermined intervals. Then, a dense discharge 34 is generated in a predetermined range around these bright spots 33. The photoconductor 32 is the discharge wire 3
If it moves in a direction 35 orthogonal to 1 at a constant speed, as a result, uneven charging occurs in the photoconductor 32 in the form of a strip.

FIG. 12 is an exaggerated representation of the lightness and darkness of an image when charged by a charging device having such a discharge characteristic for a document having a uniform density over the entire surface. Although different depending on the developing method, according to the normal developing method, the image is dark on the recording paper 36 at the strip-shaped portion 37 where the discharge is well performed, and the image is light on the other portion 38. In an extreme case, "white spots" may occur in the thin part of the image, and characters and the like in that part may be lost.

In order to solve such a problem of the negative charging device, two methods have been conventionally adopted. In the first method, the discharge wire is made as thin as possible to ensure the uniformity of discharge. However, according to this method, the diameter of the discharge wire is, for example, about 30 μm or less, so that there is a problem that the wire is easily cut when cleaning or when a paper jam occurs. Further, in a large-sized device, the length of the discharge wire becomes long, so that there is a problem that a wire having a too small diameter cannot be used in order to maintain its strength. Therefore, conventionally, a charging device called a scorotron has been widely used.

FIG. 13 is for explaining the principle of the scorotron. In the scorotron, for example, the aperture ratio between the discharge wire 41 of -5 KV and the photoconductor 42 is 60% to 9%.
A conductive grid 43 set to a predetermined value between about 0% is arranged, and a negative voltage of, for example, about -800V is applied to this. In this scorotron,
Since most of the discharge is generated between the discharge wire 41 and the grid 43, it is necessary to apply a voltage having a larger absolute value to the discharge wire 41 than before. As a result of this, FIG.
Since the dense charge portion 34 shown by 1 is thickened, the discharge unevenness can be greatly reduced by this effect and the effect of mitigating the ripple component by the grid 43.

[0010]

However, when such a scorotron is used, since the discharge efficiency is poor, the grid 43 is used when the scorotron is used in an image recording apparatus for recording at high speed.
There has been a problem that sufficient charging cannot be performed unless the aperture ratio is increased from 80% to 90%. Of course, in this case, there is a problem that the charging characteristics in the longitudinal direction of the discharge wire 41 must be sacrificed to some extent. Therefore, a charging device in which a plurality of discharge wires are arranged to supplement the charge amount has been realized, but a device satisfying both charging characteristics and charging efficiency has not been realized yet.

Therefore, an object of the present invention is to provide a charging device which can satisfy both charging characteristics and discharge efficiency.

[0012]

According to a first aspect of the present invention, an elongated shield case having a strip-shaped opening in a predetermined direction, a plurality of discharge wires arranged in parallel with each other in the shield case, and The charging device is provided with a grid plate which is arranged so as to cover the plurality of discharge wires and in which the aperture ratio of the opening portion for discharging the charges is changed depending on the location.

That is, according to the first aspect of the invention, the aperture ratios of the grid plates of the plurality of discharge wires are made different,
The above-mentioned object is achieved by avoiding unnecessary reduction of the aperture ratio.

According to a second aspect of the present invention, there is provided an elongated shield case having a strip-shaped opening in a predetermined direction, and a plurality of discharge wires arranged in the shield case at intervals in the longitudinal direction thereof. A first high voltage applying means for applying a high voltage of direct current to a part of the plurality of discharge wires, and a second high voltage applying means for applying a high voltage of superposed direct current and alternating current to the rest of the plurality of discharge wires. The charging device is equipped with it.

That is, according to the second aspect of the invention, a high DC voltage is applied to some of the plurality of discharge wires arranged in the shield case, and a high voltage in which DC and AC are superposed on the other wires. Is applied and two types of discharge characteristics are used together to make the charging uniform. Depending on the charging device, a grid plate may be used together therewith.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 2 shows a main part of a laser printer using the charging device according to one embodiment of the present invention. Figure 1
The same parts as 0 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In this laser printer, as the charge corotron 51, a scorotron as a charging device containing two discharge wires is used. The charge corotron 51 is connected to a high voltage circuit 52 that generates a high DC voltage.

FIG. 1 shows the main part of this charge corotron. In the charge corotron 51, insulator blocks 56 and 57 are arranged at both ends of an elongated aluminum shield case 55 having a U-shaped cross section, and first and second discharge wires 58 and 59 are provided at predetermined intervals therebetween. It is placed and stretched in parallel. One end of each of these discharge wires has a corresponding high voltage application plug 61, 6
Connected to 2. A grid plate 63 made of a metal plate is attached to an opening side of the shield case 55 which is not shielded, with an insulator (not shown) interposed therebetween. The grid plate 63 is electrically connected to the plug 64. The shield case 55 is designed to be grounded via its fixture when the charge corotron 51 is attached to the laser printer.

FIG. 3 shows an open state of the grid plate. The grid plate 63 has a first discharge wire 58.
The elliptical opening patterns 65 and 66 are arranged so that the areas corresponding to and the areas corresponding to the second discharge wire 59 have different opening ratios. These opening patterns 6
The portions 5 and 66 are openings by a method such as etching, and the electric charges pass through this and are discharged toward the photoconductor drum 11 shown in FIG.

The pattern of the first opening pattern 65 is set so that the opening ratio of the grid plate 63 to the first discharge wire 58 (hereinafter referred to as the first opening ratio) is 80% to 95%. ing. Second opening pattern 66
Indicates that the aperture ratio of the grid plate 63 to the second discharge wire 59 (hereinafter referred to as the second aperture ratio) is 60% to 80%.
The pattern is set so that As a result, the first discharge wire 58 performs efficient charging while allowing some uneven charging, and the second discharge wire 59 equalizes the charge amount so that a substantially desired charge potential is realized. .. In the charge corotron 51 of this example, the first aperture ratio was set to 90% and the second aperture ratio was set to 65%.

For comparison with the charge corotron of this embodiment, FIG. 4 shows a charge corotron (hereinafter referred to as a reference charge corotron) in which a grid plate having a constant aperture ratio is arranged on the laser printer of this embodiment. 2) represents the distribution of the surface potential of the photosensitive drum when (4) is used. The horizontal axis represents each measurement position (1) to (10) in the axial direction of the photosensitive drum. The vertical axis represents the surface potential measured at these measurement positions (1) to (10).

In order to compare the charge corotron 51 of this embodiment and the reference charge corotron as accurately as possible, the reference charge corotron also uses a scorotron using two discharge wires as shown in FIG. And In addition, a DC voltage of 5.9 KV (kilovolt) is applied to the two discharge wires, and -700 V is applied to the grid plate.
Was applied. In this figure, the polygonal line 71 is the case where the aperture ratio of the grid plate is 83.2%, and the other polygonal line 72
Shows the case where the aperture ratio is 64%. In the former case, since the aperture ratio is high, the charges efficiently reach the photoconductor drum, but the uneven charging as described above occurs.
In the latter case, charging is carried out uniformly, but the aperture ratio is low, so sufficient charging is not carried out.

FIG. 5 simply shows the principle of measuring the potential at each measurement position. After the photoconductor drum 11 is charged by the charge corotron 51 (FIG. 2), the operation of the laser printer is stopped, and the measurement by the electrometer is performed at each measurement position (1) to (10).

FIG. 6 shows the distribution of the surface potential by the charge corotron of this embodiment by the same measuring method. Also in this embodiment, two discharge wires 58, 5 are used.
A DC voltage of 5.9 KV (kilovolt) was applied to 9 (FIG. 1), and a voltage of −700 V was applied to grid plate 63 (FIG. 1). As can be seen from the characteristic indicated by the broken line 73, the charging is performed substantially uniformly by the two-stage discharge in which the aperture ratio of the grid plate 63 is different, and the charging amount is sufficiently increased as compared with FIG. ..

Modification

FIG. 7 shows a charging device according to a modification of the present invention. A partition plate 83 made of a metal such as aluminum is arranged at a central position of a shield case 82 having a U-shaped cross section. Discharge wires 84 and 85 are stretched in parallel with each other in each of the two elongated spaces divided by the partition plate 83. Each discharge wire 84, 85
One end of is connected to the corresponding high-voltage applying plugs 61 and 62. In this figure, the charging device 81 is arranged so that the discharge direction is the opposite of that in FIG. No grid plate is arranged in the charging device 81 shown in FIG.

In the charging device 81 of this modification, the first
A high DC voltage is applied to the discharge wire 84, and a high voltage in which AC and DC are superposed is applied to the second discharge wire 85. Of these, the voltage applied to the first discharge wire 84 is -5.7 KV. Second discharge wire 85
The voltage applied to is an AC of 2 KV and a DC of -700 V in effective value.

8 and 9 are for explaining the charging characteristics of the charging device of this modification. The measurement of the electric potential at each measurement position (1) to (10) is performed by the method shown in FIG. In FIG. 8, only voltage application to the first discharge wire 84 is performed. As indicated by the polygonal line 91, the photosensitive drum 11 (FIG. 5) has uneven charging in the axial direction due to the discharge due to the high DC voltage of −5.7 KV.

On the other hand, FIG. 9 shows two discharge wires 8
4 and 85 show a state in which a specified voltage is applied to each of them. As shown by the polygonal line 92, it can be seen that the charging characteristics are made uniform by the effect of the discharge due to the alternating current. It goes without saying that if a grid plate is added to the charging device 81 of this modified example, the charging characteristics can be further improved even when the aperture ratio is considerably high. Further, in this case, it is possible to change the aperture ratio for each region corresponding to the two discharge wires 84 and 85, or to dispose the grid plate only on one side.

In the above-described embodiments and modified examples, an elliptical set is used as an opening pattern for adjusting the aperture ratio of the grid plate, but it goes without saying that any other pattern may be used. Is. Further, the pattern to be formed may have a finer grain.
Further, the pattern may be changed depending on the location corresponding to the bright spot 33 and the location other than that as described in FIG. 11, or the aperture ratio may be periodically changed in the axial direction of the photoconductor drum 11 accordingly. Is also effective.

Although two discharge wires are used in the embodiment and the modification, three or more discharge wires may be used.

[0033]

As described above, according to the charging device of the first aspect, the aperture ratio of the grid plate arranged on the outlet side of the shield case accommodating a plurality of discharge wires is set in the longitudinal direction of the discharge wires. Since it is changed to, the charging efficiency can be maximized and a charging device with less uneven charging can be created, and a high-speed and high-quality image recording device can be created.

According to the second aspect of the present invention, the plurality of discharge wires arranged in the shield case are divided into two groups, one of which is applied with a high-voltage DC voltage and the other of which is connected to DC. Since the high voltage on which the alternating current is superimposed is applied, the charging can be made uniform without the grid plate, and the charging can be efficiently performed. Further, when the grid plate is not required, there is an advantage that a voltage generating circuit for applying the grid plate is not required.

[Brief description of drawings]

FIG. 1 is a perspective view showing a charge corotron as a charging device in an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a main part of a laser printer using the charge corotron of this embodiment.

FIG. 3 is a plan view of a grid plate of this embodiment.

FIG. 4 is a characteristic diagram showing charging characteristics of a scorotron for comparison with the charging characteristics of the charge corotron of the present embodiment.

FIG. 5 is an explanatory diagram showing respective measurement positions of charging of a photosensitive drum.

FIG. 6 is a characteristic diagram showing charging characteristics of the charge corotron of the present embodiment.

FIG. 7 is a perspective view of a charging device according to a modified example.

FIG. 8 is a characteristic diagram showing a charging characteristic when a voltage is applied only to a first discharge wire in the charging device of this modified example.

FIG. 9 is a characteristic diagram showing charging characteristics when a voltage is applied to two discharge wires in the charging device of this modification.

FIG. 10 is a schematic configuration diagram showing an outline of a laser printer using a conventional charging device.

FIG. 11 is an explanatory diagram showing a general tendency of a discharge state of a discharge wire in a negative charging device.

FIG. 12 is an explanatory diagram showing the shade of an image when charged by the conventional charging device shown in FIG. 11.

FIG. 13 is an explanatory diagram for explaining the principle of the scorotron.

[Explanation of symbols]

51 ... Charge corotron (charging device), 55 ... Shield case, 58 ... First discharge wire, 59 ... Second discharge wire, 63 ... Grid plate, 65, 66 ... Opening pattern, 81 ... Charging device, 83 ... Partition board.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneya Kajiura 3-7-1, Iwatsuki City, Saitama Prefecture Fuji-Zerox Co., Ltd. Iwatsuki Plant (72) Inventor Yoshifumi Ozaki 3--7 Prefecture, Iwatsuki City, Saitama Prefecture No. 1 Fuji Xerox Co., Ltd. Iwatsuki Office

Claims (2)

[Claims] 1. An elongated shield case having a strip-shaped opening in a predetermined direction, a plurality of discharge wires arranged in parallel with each other in the shield case, and an electric charge arranged so as to cover the plurality of discharge wires. And a grid plate in which an aperture ratio of an opening portion for discharging the discharge is changed in a direction orthogonal to a length direction of the discharge wire. 2. An elongated shield case having a strip-shaped opening in a predetermined direction, a plurality of discharge wires arranged in the shield case at intervals in the longitudinal direction, and a part of the plurality of discharge wires. And a second high voltage applying means for applying a high voltage in which a direct current and an alternating current are superposed on the rest of the plurality of discharge wires. Charging device.