JPS62262877A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To form a positive electrostatic latent image on which a contour part of an original image has been left, by setting a voltage applied to a grid, to a voltage value having the same polarity as a voltage applied to the first electrifying device, and lower than the surface potential of an image part of the electrostatic latent image and higher than the surface potential of a non-image part. CONSTITUTION:A voltage whose polarity is opposite to that of a voltage applied to an electrifying charger 2 from an electrode 41 is applied to a charge wire, and a voltage which has the same polarity as that of a voltage applied to the electrostatic charger 2 from a power source 43 and is lower the surface potential of an electrostatic latent image part and higher than the surface potential of a non-image part is applied to a grid 42. A developer consists of a mixture of a magnetic carrier and an insulating toner, and they are electrostatically charged to the opposite polarity to each other by triboelectrification, and the insulating toner is electrostatically charged to the polarity opposite to the polarity of the electrifying charger 2. In this state, when the insulating toner has no magnetism, a developing bias slightly higher than a grid voltage and having the same polarity as the electrostatic charger 2 is applied to a developing sleeve 51 from a power source 51, and when said toner has magnetism, a developing bias which is lower than the grid voltage, and also, to which an AC voltage has been superposed is applied.

Description

[Detailed description of the invention] Industrial advantage y′? The present invention relates to an electrophotographic copying apparatus, and particularly to an electrophotographic copying apparatus capable of selectively executing a normal standard copying mode and a contour image forming mode using electrophotography.

Problems with Jubeieda Sojinjo In general, contour lines in an image contain a lot of information, and at the same time fully express the characteristics of the image, and play an important role in the image. Furthermore, an image that has been converted into a binary figure by drawing outlines is easier to identify than a normal grayscale image.

It is extremely easy to handle in determining and processing various transmission lines.
Converting an image into a binary figure by drawing a contour line is extremely effective in terms of image pattern recognition, image correction and emphasis, bandwidth compression, and the like. Also, for example, by repeating two copies and adding a colored outline around a black pattern to make it more noticeable, or by painting two patterns in different colors to create patterns with different colors, so-called coloring books can be used. It is also useful when preparing a specific pattern.

By the way, conventional methods for forming contour images of this type include:
The present applicant has already developed a one-component toner developing method in which an electrostatic latent image is developed using a conductive tosser, which has an intermediate potential between the maximum and minimum surface potentials of the member to be developed, and It is characterized by extracting the outline of the electrostatic latent image on the developing member by applying a direct current 7 bias having a polarity opposite to that of the electrostatic latent image charge between the developing member and the conductive toner carrier. proposed a method (see Japanese Unexamined Patent Publication No. 134635/1983).

However, in this method, the contour formed as an electrostatic latent image is a negative image, and the conductive toner adheres to areas with a large potential difference based on the potential difference on the surface of the electrostatic latent image carrier, that is, areas other than the contour line. Therefore, the developed image is obtained only as a negative image. Normally, the required contour image is a positive image (black image), so the problem is that in order to make a positive image, the negative contour image obtained by this method must be copied again using reversal development. have.

SUMMARY OF THE INVENTION Therefore, the present invention provides an electrophotographic copying apparatus that can selectively execute a normal standard copying mode and a contour image forming mode that forms a contour image as a positive image, and can also form a contour image with sufficient density. The purpose is to.

13 = Problem 1 a first charging device; a second image exposure device with a grid;
(b) the voltage applied to the second charging device is an alternating voltage or a direct current having a polarity opposite to that of the voltage applied to the first charging device; voltage, and the voltage applied to the grid has the same polarity as the voltage applied to the first charging device and is lower than the surface potential of the image area of the electrostatic latent image formed by the image exposure device, and is not an image. (c) a developer containing a charged toner having a polarity opposite to that of the electrostatic latent image is stored in the developing device to perform regular development; (d) a voltage value higher than the surface potential of the second The present invention is characterized in that it is possible to select between a contour image forming mode in which the charging device is operated and a standard copying mode in which it is not operated.

In the electrophotographic copying apparatus having the structure shown in FIG. A normal standard image is formed.

That is, in the contour image forming mode, after a positive image is exposed on the surface of the electrophotographic photoreceptor to which a constant electric charge is applied by the first charging device (see (a) in FIG. 5), the second charging device For example, a DC voltage having the opposite polarity to the voltage applied to the first charging device is applied to the charging device, and a DC voltage having the same polarity as the voltage applied to the first charging device is applied to the grid, and the image exposure device Recharging is performed while applying a voltage that is lower than the surface potential of the image area of the electrostatic latent image formed in the process and higher than the surface potential of the non-image area. As a result, the surface potential of the electrostatic latent image area is reduced to approximately the grid voltage, leaving the contour area (see (b) in FIG. 5).

Next, the electrostatic latent image formed through the second charging device is regularly developed using charged toner having a polarity opposite to that of the electrostatic latent image. As a result, the charged toner adheres to the contour of the electrostatic latent image portion that remains at a high potential, and the contour image is developed as a positive image (see (c) in FIG. 5).

On the other hand, this electrophotographic copying apparatus uses a regular development method that converts a positive electrostatic latent image into a positive toner image.
Copying in the standard copying mode is possible unless the second charging device is operated.

That is, the positive electrostatic latent image formed through the image exposure device is not affected by the second charging device, and is processed into a positive image corresponding one-to-one to the original image by the developing device as normal regular development. It is developed as

[First Embodiment] FIG. 1 schematically shows an electrophotographic copying apparatus according to a first embodiment of the present invention, in which the electrophotographic photoreceptor drum (1) is a well-known type having a photoconductive layer on the outer peripheral surface. It can be rotated in the direction of arrow (8), and the following members and devices are installed around it.

The charging charge-v(2) functions as a first charging device that applies a constant electric charge to the surface of the photoreceptor drum (1), and a power source (21) is connected to the charge wire.

The image exposure device 3) applies light to the document placed on the document platen glass (34) and uses a well-known slit exposure method to form an electrostatic latent image on the surface of the photoreceptor drum (1) corresponding to the document image. It is used to form an image and is composed of an exposure lamp (31), a mirror (not shown), a lens (33), etc., and a power source (32) is connected to the exposure lamp (31).

The scorotron charger (4) is connected to the exposure device (3).
) functions as a second charging device for recharging the surface of the photoreceptor drum (1) on which an electrostatic latent image is formed, and a power source (41) is connected to the wire. A power source (43) is connected to the grid (42). A voltage having a polarity opposite to that applied to the charger (2) is applied from the power source (41) to the charge wire A'. In addition, the grid (42) also has a power source (
A voltage having the same polarity as the voltage applied from 43) to the charger <2) is applied, which is lower than the surface potential of the electrostatic latent image image area and higher than the surface potential of the non-image area.

The developing device (5) is a well-known magnetic brush type device that includes a developing sleeve (51) that includes a built-in magnetic roller (52) with N and S poles magnetized around its periphery, and also functions as a developing electrode. A power source (53) for developing bias is connected to the developing sleeve (51). The developer is made of a mixture of a magnetic carrier and an insulating toner, which are charged to opposite polarities by frictional charging, and the insulating toner is charged to a polarity opposite to that of the charger (2). If the toner is not magnetic, the developing sleeve (
51), a voltage slightly higher than the grid voltage and having the same polarity as the charger (2>) is applied from the voltage 1 (53). On the other hand, when the insulating toner has magnetism, a developing bias lower than the grid voltage and on which an alternating current voltage is superimposed is applied to the developing sleeve (51). In this case, it is possible to use only insulating l-chi. Also,
It is not necessary to superimpose an alternating current voltage on the developing bias.

The transfer charger 6) applies an electric field to the copy paper (lO) conveyed in the direction of the arrow (b) from the back side thereof, and the developing device (5) applies an electric field to the copy paper (lO) conveyed in the direction of arrow (b). The charge wire is used to transfer the toner image formed on the copy paper (10), and a voltage having a polarity opposite to that of the insulating tosser is applied to the charge wire from the power source (61).

Separation charge V (7) applies an alternating current electric field to the copy paper immediately after transfer to remove electricity from the copy paper (10) and separate it from the surface of the photoreceptor (1). AC voltage is applied to the charge wire from a power source (71).

The cleaning device (8) is for removing toner remaining on the surface of the photoreceptor drum (1) using a blade method.

The eraser lamp (9) is used to remove charges remaining on the surface of the photoreceptor drum (1) by irradiating light in preparation for the next copying process.

Control of this copying apparatus is mainly performed by a microcomputer (CPU), and as shown in FIG.
i(32), (41), (43), (52) etc. on,
The microcomputer (CPtJ) also processes off control or voltage switching control of the power source (32), which will be described in detail below.

FIG. 2 shows an operation panel (100), in which (101) is a print key, (102) is a numeric keypad, (103) is a clear/stop key, and (104) is a display section for displaying the number of copies, etc. (105) and (106) are up/down keys for adjusting the image density, and (107) is the display section consisting of an LED.
This is done by controlling the amount of light in step 1). (108
) is the standard copy mode selection key, (105> is its display section, (110) is the contour image formation mode selection key, (111)
) are their display sections, and as shown in FIG. 3, they are each connected to a microcomputer (CPU).

Here, the polarity and voltage of each charge in this example are shown.

[I] When using non-magnetic insulating toner Charge charge ＼・[Power supply (21)] Positive polarity +5.5kV Exposure light amount corresponding to the non-image area of the document by the exposure lamp (31) (standard value) Contour image formation Mode: 2.21x-sec Standard copy mode: 1.71x, sec Scorotron Chihe-sha [Electricity m(4t)] Negative polarity -6
, 0kV Grid [Electric*(43)] Positive polarity +220■ Development bias [Power supply (53)] Positive polarity +250■ To transfer charge [Power supply (61)] Positive polarity +5.5kV Non-magnetic insulating toner Negative polarity [I [] When using magnetic insulating toner, charger [power supply (21)] Positive polarity +5.5kV Amount of exposure light corresponding to the non-image area of the document by the exposure lamp (31) (standard value) In contour image formation mode: 2 .21xSee standard copy mode: 1.71xSec Scorotron charger [Km (4t> ]) Negative polarity -6.O
k V lid [power supply (43)] Positive polarity +220v Developing bias [power supply (53)] Positive polarity (DC) + 170V (AC) 350Vrms, 1kHz Development start potential +250 ■Magnetic insulating toner Negative polarity Please note these polarities: may all be the opposite,
Of course, the voltage value, exposure light amount, etc. are merely examples.

The method for forming an image using the copying apparatus described above will be explained in order of steps.

(Contour image forming mode) This contour image forming mode is executed by turning on the selection key (110).

(1> First charging step A charger (2) applies a constant potential charge to the surface of the photoreceptor drum (1). As a result, in this example, the surface potential of the photoreceptor drum (1) is +600V. becomes.

(ii> Exposure step + The original image is exposed to slit light on the surface of the photoreceptor drum (1) charged to a potential of 600 V to form an electrostatic latent image. In this case, as shown in (a) in FIG. Image part (A)
, the charge of the part corresponding to (B) remains as a potential of +600■, and the charge of the part corresponding to the non-image part is 2.21x
・It decreases to about +90V at the exposure light amount of see.

Note that a positive original image is used.

(ij) Second charging process The surface of the photoreceptor drum (1) on which the electrostatic latent image has been formed is charged with a scorotron charge-v (4) to which a voltage of -6,000 kV has been applied from the power source (41). Recharge at .

At this time, the grid (42> is supplied with +2 from the power supply (43)).
A voltage of 20μ is applied. The voltage applied to the scorotron charger (4) is of opposite polarity to the voltage applied to the charger (2). Also, grid (42)
The voltage applied to the electrostatic latent image area (A>, (2) has the same polarity as the voltage applied to the charged charge (2)
The voltage value is lower than the surface potential (+600V) of B) and higher than the surface potential of the non-image area (+90V>).

Electric lines of force shown by arrows in FIG. 4 are formed between the surface of the photosensitive drum (1) and the grid (42).

The negative polarity ions generated from the wire are subjected to a transport force along the lines of electric force. In this case, the electric lines of force that direct negative ions toward the surface of the photoreceptor drum (1) near the grid (42) occur only in the central part of the saw, except for inside the contour of the surface image area (A). do not have. Therefore,
As shown by the arrow →, the negative ions reach only the central part of the surface image area (A), excluding the inside of the outline, and eliminate the charge in the area they reach, reaching a potential near the grid voltage (+220V). lower.

That is, to describe the surface potential of the photoreceptor drum (1), as shown in FIG. left behind,
The inside of the contour part of the surface image part (A) and the line image part (B) have a constant width and are a high potential part (approximately +600■ which is the initial surface potential).
Vo), C remains, and the central portion of the plane image portion (B) drops to approximately the grid voltage (Vg: +220V) (Vo'). Note that the line image area (B) has a surface potential (V
o) is hardly reduced, but the width of the charge is slightly narrowed.

In other words, in this second charging step, the image area (A),
This means that the outline in (B) is formed as an electrostatic latent image of the bong.

1ν) Developing step ``Second charging'': The electrostatic latent image formed as a positive image of the outline on the culm is developed in the developing device 5). If the insulating toner does not have magnetism, the developing sleeve (5
1), a developing bias of +250 cm is applied. This developing bias is applied to the charger in order to prevent toner from adhering to the central part of the electrostatic latent image area (of course in the non-image area) where the surface potential has decreased in the second charging process. (2) The central part of the surface image area (A) has the same polarity as the voltage applied to the grid voltage (Vg: 220V), is slightly higher than the grid voltage (Vg: 220V), and has decreased to a value approximately equal to the grid voltage (Vg). The voltage (Vb) is slightly higher than the potential (Vo') of .

On the other hand, if the insulating toner has magnetism, the developing sleeve (51) has AC350V, 1kHz and +17V.
0V (7) Developing bias is applied. This developing bias voltage JEf(Vb)It, the grid voltage (■g
= +22o■), and lower than the potential (Vo') at the center of the surface image area (A), which has dropped to a value approximately equal to the grid voltage (Vg). however,
When an insulating toner with magnetism is used, there is a threshold value due to magnetic binding force, so development is possible when the surface potential is 25
Start around 0V. For this reason, the electrostatic latent image reduced in the second charging process is applied to the central part of the image area (of course also to the non-image area).
There is no chance that toner will stick to it and cause it to fog.

In this way, the negatively charged insulating toner is transferred to the high potential area (Vo) of the photoreceptor drum (1), that is, the image area (A>).

A toner image attached to the outline of (B), that is, an "inner border" is formed by regular development.

=16- This l/chi image is then transferred to the copy paper (10)-, L by the negative polarity discharge 11L of the transfer charge (6), and is formed as a copy image via a fixing device (not shown). be done.

(Standard copy mode) This standard copy mode is executed by turning on the selection key (108), but it is also automatically selected in the initial setting of the control.

(1) First charging step m This is the same as in the contour image forming mode.

(i)? ! Light process In this case, the amount of exposure light is 1.71x-sec, which is lower than in the contour image forming mode, and the charge in the portion corresponding to non-image 1 is 150V. In this way, the amount of exposure light that lowers the non-image area potential (1) to 150V is an appropriate value for normal development in normal copying.

(iii>Second charging step electrification fi (41), (43) are both turned off, and Scoroto[1-n charge~(4) does not operate.
The positive electrostatic latent image formed in the exposure process reaches the next development process as it is.

ν) Development process The same as in the contour image forming mode. As a result, the negatively charged insulating I water is attached to the image areas (A) and (B) shown in (a) in Figure 5 [2. A toner image is formed by regular development.

Here, conditions for forming a good contour image will be explained.

Through experiments conducted by the present inventors, the factors that affect the state of the contour image, especially the density, are determined by the initial surface potential (Vo).
, non-image area surface potential (Vi), grid voltage (Vg
), and these relationships, especially (Vg) and (Vi
) was found to be important. That is, (V
When the potential difference between g) and (Vi) was set to a large value, a good contour image with sufficient density was formed. but,
When the potential difference between the two was set small, only a thin outline image with a slightly low density was formed.

This is thought to be due to the fact that the lines of electric force between the grid (42) and the photosensitive drum (1) differ based on the potential difference between (Vg) and (Vi). That is, (Vg)-
When the potential difference of (Vi) increases, the lines of electric force that go from the -edge part of the image area to the non-image area increase. A contour image is formed because ions of negative polarity do not reach this edge from the grid (42) side. As a result, a high potential is maintained, and a good contour image with sufficient density is formed.

Therefore, in the contour image forming mode, recharging is performed in contrast to the standard copy mode.
In addition to operating the charge~<4), in the first embodiment, the amount of exposure light of the exposure device (3) was increased, and as a result, the potential difference of (Vg) - (Vi) was increased. .

In the first embodiment, as described above, (Vg) (Vi)
Various copying experiments were conducted under the condition of -220-90=130V, and good contour images with sufficient density could be obtained in all cases.

However, in contour image formation mode, an image can be formed using the same light as in standard copy mode without increasing the amount of exposure light.
Temilt [(Vg)-(Vi)=220-150-70
V], only a thin outline image with a slightly low density could be obtained.

Generally speaking (in normal standard copying mode), increasing the exposure light amount is due to a decrease in the sensitivity of the electrophotographic photoreceptor, or when using an original with a colored background, which may cause toner fog. This is a case where there is a risk. In this case, the image e degree decreases. However, the increase in the exposure light amount in the first embodiment has nothing to do with toner fog removal, and (Vg)
The potential difference (Vi) increases, and conversely the density of the contour image increases.

Furthermore, in the first embodiment, the distance (dg) (see FIG. 4) between the surface of the photosensitive drum (1) and the grid (42) is 1.5 mm. This value is larger than the setting for the scorotron charge conventionally used in this type of electrophotographic copying apparatus.

This is to increase the degree to which the electric lines of force are directed toward the surface of the photoreceptor in the edge portion (contour) of the plane image portion (A) or the line image portion (B), and to obtain a good contour image. The state of the electric lines of force changes depending on the distance (dg). That is, by changing the distance (dg), it is possible to arbitrarily change the width of the contour line obtained as an image, and as the distance (dg) increases, the width tends to increase as well.

This point will be discussed in Section 2 below. The same applies to the third embodiment.

[Second Embodiment] In this second embodiment, the second charging device is operated in the contour image forming mode, and the initial charging potential (■0) by the first charging device is lowered than in the standard copying mode.

Specifically, as shown in FIGS. 6 and 7, a scorotron charger (2') is used as the first charging device,
The voltage control circuit (24') of the grid (23') is composed of varistors (VSI), (VS2) and a switch (3) connected to their connection point.
SW) is grounded. That is, in the standard copy mode, the switch (SW) is off and the grid (23
') is Ha IJ Suke (VSI), (VS2) (7)
A total voltage (+600V) is applied. At this time, the initial charging potential (Vo) on the surface of the photoreceptor drum (1) is +6
It is 00■.

On the other hand, in the contour image forming mode, the switch (SW) is turned on, and a voltage (+490V) only by the divided varistors (VSI) is applied to the grid (23').

At this time, the initial charging potential (V
o) decreases to 490■.

In the next exposure process, the exposure device (3) is used for both modes.
．． Image exposure is performed with an exposure light amount of 71xsec (standard value for non-image portions of the original). In this case, the image area potential (V
o') are the same as the initial charging potential (Vo), respectively.
The voltage is maintained at +600V in the standard copy mode and +490V in the contour image forming mode, and the non-image area potential (Vi) decreases to +150V and +110V, respectively. Hereinafter, similarly to the first embodiment, in the contour image forming mode, the scorotron charger (4) is turned on and the grid voltage (Vg
: Recharging is performed under the condition of +220V), and in the standard copy mode, the Scorotron chip (4) is turned off and recharging is not performed, and the voltage is +250V in both modes.
Regular development is performed while applying the development bias (2). It should be noted that the specific values in E-C are for the case where an insulating toner having no magnetism is used.

That is, in the second embodiment, the potential difference between (Vg) and (Vi) in the contour image forming mode is 110V (22(]-1
10), and a good contour image with sufficient density could be obtained.

On the other hand, when a contour image is formed by setting the initial charging potential (Vo) in the same manner as in the standard copying mode without lowering it, only a contour image with a slightly lower density can be obtained. This means that the potential difference between (Vg) and (Vi) is 70V.
(220-150), which is small.

In addition to controlling the grid voltage of the scorotron charger (2), methods for lowering the initial charging potential (Vo) include lowering the voltage applied to the charger (2) itself. It may be controlled.

- Generally (in normal standard copy mode), initial band = 23
- The reason for lowering the electric potential (Vo) is to increase the image density by 1. However, in the second embodiment, the initial charging potential (V
By lowering o), the potential difference between (Vg) and (Vi) increases and the image density of the contour image increases.

[Third Embodiment] In this third embodiment, the second charging device is operated in the contour image forming mode, and the developing bias voltage is raised higher than in the standard copying mode. The apparatus of the embodiment will be explained with reference to the apparatus shown in FIG.

Specifically, in both modes, +600 in the first charging process.
An initial charging potential of V is applied, and in the exposure process, the image area potential (Vo') is +600V, and the non-image area potential (Vi)
An electrostatic latent image of +150V is formed. Below, in the standard copy mode, turn off the scorotron charge (4), and in the contour image formation mode, turn off the scorotron charge (4).
-Turn on gee v(4) to increase the grid voltage (Vg: +
Recharging is carried out under the conditions of 270■〉. Next, regular development is performed while applying a developing bias of 250 .mu. in the standard copying mode and while applying a developing bias of 300 .mu. in the outline image forming mode. Note that the specific values and the like here are for the case where an insulating toner without magnetism is used.

In the third embodiment described below, the potential difference between (Vg) and (Vi) in the contour image forming mode is 120V (270-1
50), and a good contour image with sufficient density could be obtained.

On the other hand, when a contour image was formed by performing development while applying a development/swiss ratio of 250 .mu. as in the standard copying mode, only a contour image with a slightly low density could be obtained. This means that if development is carried out with a developing bias of 250 µ, it is necessary to set the grid voltage (Vg) in the second charging step to 220 µ, which is lower than the developing bias voltage (Vb). This is because the potential difference of Vi) becomes as small as 70V (220-150).

In general (in normal standard copying mode), increasing the developing bias voltage is due to a decrease in the sensitivity of the electrophotographic photoreceptor,
This is a case where there is a risk of toner fogging, such as when using an original with a colored background, which lowers the image density. However, the increase in the developing bias voltage in the third embodiment has nothing to do with toner fog removal;
The potential difference between Vi and Vi increases, and conversely, the density of the contour image increases.

[Other Embodiments] In each of the above embodiments, the first charging device (
2), (2') is shown in which a DC voltage of opposite polarity is applied, but an alternating voltage may also be applied.

In this case, in the second charging step, the surface potential of the electrostatic latent image area is reduced to approximately the grid voltage, leaving the contour area, and the surface potential of the non-image area is reduced to almost the grid voltage, leaving the area near the image area. The voltage will rise to around -.

Achievements of the Invention As is clear from the above description, according to the present invention, a second charging device having a grid is provided between the image exposure device and the developing device, and an electric current is applied to the second charging device. The voltage is an alternating voltage or a direct current voltage of opposite polarity to the voltage applied to the first charging device, and the voltage applied to the grid is a voltage of the same polarity as the voltage applied to the first charging device and image exposure. Because the voltage value was set lower than the surface potential of the image area of the electrostatic latent image formed by the device and higher than the surface potential of the non-image area, the outline of the original image remained as a high potential area on the surface of the electrophotographic photoreceptor. A positive electrostatic latent image is formed, and since regular development is carried out by storing a developer containing charged toner with a polarity opposite to that of the electrostatic latent image in the developing device, in this regular development, the electrostatic latent image is The toner adheres to the contour portion of the document image, which is the high potential portion of the latent image, and a positive contour image can be obtained. Moreover,
Since it is possible to select between a contour image forming mode in which the second charging device is operated and a standard copying mode in which it is not operated, the user can arbitrarily perform copying in either mode.
It's convenient. In addition, when in contour image formation mode,
By setting a large difference between the grid voltage of the second charging device and the surface potential of the non-image area of the electrostatic latent image, it is possible to obtain a high-density, high-quality contour image.

[Brief explanation of drawings]

1 to 5 show a first embodiment of the present invention.
2 is a schematic diagram of the copying device, FIG. 2 is a plan view of the operation panel, FIG. 3 is a block diagram of the control circuit, FIG. 4 is a schematic diagram of electric lines of force due to the second charging device, and FIG. 3 is a graph showing the potential of an electrostatic latent image in each image forming process. FIGS. 6 and 7 show a second embodiment of the present invention, with FIG. 6 being a schematic configuration diagram of a copying apparatus, and FIG. 7 being a grid voltage control circuit diagram of a first charging device. (1)... Electrophotographic photoreceptor drum, (2)... Charging chip, (2')... Scorotron charge 1, (23')... Grid, (24') ... Grid voltage control circuit, (3) ... Image exposure device, (3
1)...Exposure lamp, (32)...M, R1 (4)
... Scorotron charger, (42) ... Grid, (43) ... Power supply, (5) ... Development device,
<51>...Developing sleeve, (53)...Developing bias power supply.

Claims (1)

[Scope of Claims] 1. At least a first charging device, an image exposure device, a second charging device having a grid, and a developing device having a developing electrode are disposed along the moving direction of the electrophotographic photoreceptor, The voltage applied to the second charging device is an alternating voltage or a DC voltage of opposite polarity to the voltage applied to the first charging device, and the voltage applied to the grid is applied to the first charging device. The electrostatic latent image formed in the image exposure device has a voltage value of the same polarity as the voltage that is lower than the surface potential of the image area and higher than the surface potential of the non-image area of the electrostatic latent image formed in the image exposure device. A developer containing a charged toner having a polarity opposite to that of the image is stored to perform regular development, and a contour image forming mode in which the second charging device is operated and a standard copying mode in which it is not operated can be selected. An electrophotographic copying device characterized by: 2. The electrophotographic copying apparatus according to claim 1, wherein when in the contour image forming mode, the amount of exposure light of the image exposure device is increased compared to when in the standard mode. 3. The electrophotographic copying apparatus according to claim 1, wherein in the contour image forming mode, the charging potential of the surface of the electrophotographic photoreceptor by the first charging device is lowered than in the standard copying mode. 4. The electrophotographic copying apparatus according to claim 1, wherein in the contour image forming mode, the voltage value of the developing bias is higher than in the standard copying mode.