JPS6321659A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To selectively execute a normal standard copying mode, a contour image formation mode, and a reversal contour image formation mode by turning ON and OFF a scorotron charger as a 2nd electrifying means and also switching a grid voltage. CONSTITUTION:The scorotron charger 4 performs the 2nd electrification of the surface of a photosensitive drum 1 where an electrostatic latent image is formed by an exposing device 3, a power source 41 is connected to a charging wire, and a power source 43 is connected to a grid 42. Further, the charge wire is applied with an alternating voltage from the power source 41 and the grid 42 is applied with a voltage from the power source 43 which has the same polarity with the electrifying charger 2 and is lower than the surface of an electrostatic latent image part and higher than the surface potential of an electrostatic-latent-image absent part. Consequently, ON/OFF control over the charger 4 is carried out to form a standard image corresponding to an original image in 1:1 proportion and the grid voltage value is switched to form a standard image, a contour image, and a reversal contour image selectively.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic reproduction apparatus, and more particularly to an electrophotographic reproduction apparatus which selects a normal standard copying mode and a positive contour image forming mode as well as a negative inverted contour image forming mode. The present invention relates to an electrophotographic copying apparatus that can be switched and executed.

BACKGROUND OF THE INVENTION Conventional techniques and their problems In general, contour lines are a part of an image that contains a lot of information, and at the same time sufficiently express the characteristics of the image, and thus play an important role in the image. Furthermore, images that have been converted into binary figures by drawing contour lines are easier to identify than ordinary grayscale images.

Extremely easy to handle in various processes such as decision and communication,
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, if two copies are made,
It can also be used when preparing so-called coloring book-like patterns, such as repeatedly adding a colored outline around a black pattern to make it more noticeable, or painting one pattern in different colors to create patterns with different colors. Useful.

By the way, conventional methods for forming contour images of this type include:
The present applicant has already developed a method in which an electrostatic latent image is developed using a conductive toner, which has a potential intermediate between the maximum and minimum surface potentials of the member to be developed. death,
A contour line of the electrostatic latent image on the developing member is drawn by applying a DC 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 can only be obtained as a negative image. Usually, the required contour image is a 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.

Therefore, the present invention is capable of selectively executing the normal standard copy mode and the contour image forming mode in which the contour portion is formed as a positive image, and also selectively executes the inverted contour image forming mode in which the contour portion is formed as a negative image. An object of the present invention is to provide an electrophotographic copying apparatus capable of performing the following steps.

Means for Solving the Problems Therefore, an electrophotographic copying apparatus according to the present invention includes: (i) a first charging unit that applies a constant electric charge to the surface of an electrophotographic photoreceptor; (i) an exposure means for exposing an original image to the surface of the electrophotographic photoreceptor that has passed through the charging means; (iv) a second charging means for recharging while applying a voltage lower than the surface potential of the electrostatic latent image image area formed by the electrostatic latent image and higher than the surface potential of the electrostatic latent image non-image area; a developing means for developing the electrostatic latent image formed through the charging means with a charged toner having a polarity opposite to that of the first charging means while applying a developing bias having the same polarity as the first charging means; (v) means for controlling on/off of the scorotron charger; and (vi) means for varying/controlling the voltage value applied to the crid of the scorotron charger.

In an electrophotographic copying device that has a configuration that exceeds the function, the second
By activating the scorotron charger, which is the charging means, and controlling its grid voltage, a positive contour image or an inverted negative contour image corresponding to the original image is formed, and the scorotron charger is activated. If not, a normal standard image corresponding one-to-one to the original image is formed.

That is, in the contour image forming mode, after exposing a positive image to the surface of the electrophotographic photoreceptor that has been charged with a constant potential by the first charging means (see (a) in FIG. 4), the second A scorotron charger, which is the charging means to which an alternating voltage has been applied, applies to the grid a voltage that is sufficiently lower than the surface potential of the electrostatic latent image image area and slightly higher than the surface potential of the electrostatic latent image non-image area. At the same time, recharge the battery. As a result, the surface potential at the center of the image area decreases to approximately the grid voltage, leaving the area inside the contour line, and the surface potential of the non-image area increases slightly to approximately the grid voltage, leaving the area outside the contour line. [See (b) in Figure 4.

Next, when regular development is performed by the developing means, toner adheres to the high potential area and is completely developed as a positive contour image [4th
See (C) in the figure.

In addition, in the inverted contour image forming mode, the grid of the scorotron charger, which is the second charging means, has a surface potential slightly lower than the surface potential of the electrostatic latent image area and sufficiently higher than the surface potential of the electrostatic latent image area. Recharging is performed while applying a high voltage. As a result, the surface potential at the center of the image area decreases slightly to approximately the grid voltage, leaving the area inside the contour line, and the surface potential of the non-image area increases to approximately the grid voltage, leaving the area outside the contour line. [See (b) in Figure 5.

Next, when regular development is carried out by the developing means, toner adheres to the high-potential area, and a negative inverted contour image with "blank white" outside the contour line is developed [(c in Figure 5)] Reference.

On the other hand, if the second charging means cannot be allowed to operate, the electrostatic latent image formed through the first charging means and exposure means will be applied to the original image in a one-to-one manner by normal regular development in the developing means. It will be developed accordingly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electrophotographic copying apparatus according to the present invention will be described below along with its copying process.

FIG. 1 schematically shows an electrophotographic copying apparatus according to an embodiment, and the electrophotographic photosensitive drum (1) is a well-known type having a photoconductive layer on its outer peripheral surface, and is rotatable in the direction of arrow (a). The following members and devices are installed around it.

The electrification charger (2) is used to perform first electrification to apply a constant electric charge to the surface of the photoreceptor drum (1), and 'WLi (21) is connected to the charge wire.

The exposure device (3) is for forming an electrostatic latent image corresponding to the original image on the surface of the photoreceptor drum (1) using a well-known slit exposure method, and includes an exposure lamp (37).

It consists of mirrors, lenses, etc.

The scorotron charger (4) is connected to the exposure device (3).
) to perform a second charge on the surface of the photoreceptor drum (1) on which an electrostatic latent image has been formed.The charge wire is connected to the power supply (41), and the grid (42) is connected to the power supply. (43) is connected. 114 for charge wire
(41), an alternating voltage is applied to the grid (42) from a power supply (43), which has the same polarity as the charger (2), is lower than the surface potential of the electrostatic latent image image area, and is not an electrostatic latent image image. A voltage higher than the surface potential of the part is applied. In addition, when the scorotron charger (4) is turned on,
The voltage values that can be applied to the OFF and grid (42) can be switched and controlled as explained below.

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 for developing bias (<53) 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). A charger (2) is connected to the developing sleeve (51) from a power source (53).
A developing bias of the same polarity is applied.

The transfer charger (6) applies an electric field from the back side to the copy paper (10) being conveyed in the direction of arrow (b), and the developing device (5) applies an electric field to the surface of the photoreceptor drum (1). It is used to transfer the formed toner image onto the copy paper (10), and a voltage of opposite polarity to that of the insulating toner is applied to the charge wire from the power source (61).

The separation charger (7) applies an alternating current electric field to the copy paper immediately after transfer to remove static electricity from the copy paper (10) and separate it from the surface of the photoreceptor drum (1). The wire has AC ta from Xl (71):
is applied.

The cleaning device (8) uses a blade method to remove toner remaining on the surface of the photoreceptor drum (1).

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.

FIG. 2 shows the operation panel (100) of the present copying apparatus.
101) is the print key, (102) is the numeric keypad, (1
03) 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 image density, and <107) is a display section thereof consisting of an LED. (108) is the list copy mode selection key, (109) its display lamp, (11
0) is a contour image formation mode selection key, (111) is its display lamp, (112) is an inverted contour image formation mode selection key, and (113) is its display lamp.

Control is by a microcomputer (120) shown in the first blade.
Each mode selection key (108)
The operations (110) and (112) are input to the terminals (1) to (2) of the microcomputer (120) as on/off signals for the changeover switch (121). Also, the terminal ■
is the electric current R (41') of the scorotron charger (4).

It was read by the correspondent! (41) is controlled to turn on and off.

Terminals ■ and ■ are Scorotron charger (4) Tsukrid electric! (43), and the terminal ■ is connected to the power supply (43).
The terminal (2) controls the output voltage value of the power supply (43).

Here, the operation of the changeover switch (121) corresponding to each copy mode in this embodiment, the output number from the microcomputer (120), the polarity of each charger etc. that can be controlled by it, and the applied chamber pressure are shown below. .

Note that all of these polarities may be reversed,
Of course, the voltage value is only an example.

The image forming method using the copying apparatus described above will be explained step by step for each mode.

(Standard copy mode) In this standard copy mode, normal copying is performed to form a copy image in one-to-one correspondence with the original image.
The operation can be completed by making the terminals ■ and ■ conductive. At this time, the power supplies (41>, (43) are turned off so that the scorotron charger (4) does not operate. At the same time, the indicator lamp (109) is turned on.

(i> First charging step The charger (2) applies a constant electric 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.

(i) Exposure step The original image is exposed to slit light on the surface of the photoreceptor drum (1) fully charged to a potential of +600V to form an electrostatic latent image. In this case, regarding the positive original image, as shown in (a) in Figure 4, the charges in the parts corresponding to the image areas (A) and (B) remain as a potential of +600V, which corresponds to the non-image area. The electric charge of the exposed portion decreases to about +100 μ upon irradiation with light.

(i) Second charging step Both power supplies (41) and (43) are turned off, the scorotron charger (4) does not operate, and this step is omitted. Therefore, the positive electrostatic latent image formed in the exposure process reaches the next development process as it is.

(iv) Developing process The positive latent image formed in the exposure process is transferred to the developing device (5
). At this time, a developing bias of +300 cm is completely applied to the developing sleeve (51). As a result, the negatively charged insulating toner adheres to the image areas (A) and (B) shown in (a) in Figure 4, and a normal toner image corresponding one-to-one to the original image is formed. Formed by regular development.

This toner image is then transferred onto the copy paper (10) by positive discharge from the transfer charger (6), and is completed as a copy image via a fixing device (not shown).

(Contour Image Formation Mode) In this contour image formation mode, only the contour part of a positive original image is formed as a positive copy image, and can be switched by operating the selection key (110). )
This is executed when the terminals ■ and ■ become conductive. At this time, the power supplies (41) and (43) are turned on so that the scorotron charger (4) operates, and the terminal (2) is set to "L" to supply +200 (200) to the grid power source (43). At the same time, the display lamp (10) is turned on.

(i) First charging step This is the same as in the standard copy mode.

(i) Exposure process A positive original image is slit-exposed on the surface of the photosensitive drum (1), which has been fully charged to a potential of 1,500 V, to form a positive electrostatic latent image. In this case, as shown in (a) in Figure 4,
The charge of the parts corresponding to image areas (A) and (B) is +60
The potential remains at 0V, and the charge in the portion corresponding to the non-image area decreases to about +100V by light irradiation.

(i) Second charging step The surface of the photosensitive drum (1) on which the positive electrostatic latent image is formed is charged by ±6. It is recharged by a scorotron charger (4) to which an alternating voltage of OkV is applied.

At this time, there is electricity on the grid (42)! From (43), +
The voltage of 2001 is applied. Guri/:ζ(42)
The voltage applied is sufficiently lower than the surface potential (+600 V) of the electrostatic latent image image area (A), (a) and slightly higher than the surface potential (+100 V) of the latent image non-image area.

Electric lines of force shown by arrows in FIG. 3 are formed between the surface of the photosensitive drum (1) and the grid (42).

The negative and positive ions generated from the charge wire are subjected to a withdrawal force along the lines of electric force. In this case, the lines of electric force that direct negative ions toward the surface of the photoreceptor drum (1) near the grid (42) are
It occurs only in the part (center part) other than the inner part (A') of the contour line. Therefore, the negative ions reach only the central portion of the surface image area (A) as indicated by the arrow pass, eliminate the charge in the area they reach, and lower the potential to approximately the same as the grid voltage (Vg). In addition, as shown by arrows →, positive ions are generated in areas outside the contour lines (A") and (
The voltage reaches only the non-image area except for the area B"), and the potential of the area it reaches is slightly increased to a potential approximately equal to the grid voltage (Vg).

That is, when explaining the surface potential of the photoreceptor drum (1), as shown in FIG. 4 (b), the image areas (A), (B)
The inner parts (A') and (B') of the contour line are left as high potential parts with a constant width and the initial surface potential of approximately +600V, while the outer parts (A'') and (B'') of the contour line are left as high potential parts. It remains as a low potential part of approximately +100V, and the outside part of the outline (
The non-image area excluding A") and (B") slightly rises to around the grid voltage (Vg: +200V), and the central part of the surface image area (A) almost reaches the grid voltage (Vg: +2
00V). Note that although the surface potential of the line image portion (B) hardly decreases, the width of the charge is slightly narrowed as the inner portion of the contour line (B′).

In other words, in this second charging step, the image area (A),
This means that the contour shown in (B) is formed as a positive electrostatic latent image.

(iv) Developing step The electrostatic latent image formed as a positive image of the outline in the second charging step is developed by a developing device (5). At this time, a developing bias of +300 cm is applied to the developing sleeve (51). This developing bias voltage (Vb) is
In order to prevent toner from adhering to the central part of the surface image area (A) where the surface potential has decreased in the second charging process (of course also in the non-image area), the central part of the surface image area (A) is It is slightly higher than the partial surface potential (+200V) and has the same polarity as the first charging step.

In this way, the negatively charged insulating toner is applied to the high potential area of the photoreceptor drum (1), that is, the outline of the image areas (A) and (B) as shown in FIG. Inner part (A').

(B), and a positive toner image of the so-called "inner edger" is formed by regular development.

By the way, the reason why the grid voltage (Vg) is made sufficiently lower than the surface potential (+600V) of the electrostatic latent image area is that the surface potential of the central part of this surface image area (A) is changed from the original value in the second charging step. This is to sufficiently reduce the surface potential of the non-image area, and to prevent the surface potential of the non-image area from increasing too much.

(Reversed contour image forming mode) In this reverse contour image forming mode, only the outline of a positive original image is reversed to form a negative copy image. ) is executed when the terminals ■ and ■ become conductive. At this time, the electric currents m (41) and (43) are turned on so that the scorotron charger (4) operates, and the terminal ■ is set to "H" so that the grid 'E! +5 to (43)
Supply 00■. At the same time, the display lamp (103) is turned on.

(i) First charging step This is the same as in the above two modes.

(i) W light process This is the same as in the above two modes. At this time, the electrostatic latent image formed on the surface of the photoreceptor drum (1) is also shown in FIG.
As shown in (a), it is the same as (a) in FIG.

(i) Second charging step The surface of the photoreceptor drum (1) on which the positive electrostatic latent image has been formed is charged with a scorotron charger () to which an alternating voltage of ±6.0 kV is applied from the electric current R (41). 4) Recharge. At this time, a voltage of +500 cm is applied to the grid (42) from the power source (43).The voltage that can be applied to the grid (42) is the surface potential ( 600 V) and sufficiently higher than the surface potential of the non-image area of the electrostatic latent image (100 V).

As in the contour image forming mode, electric lines of force indicated by arrows in FIG. 3 are formed between the surface of the photosensitive drum (1) and the grid (42). Therefore, the negative ions generated from the charge wire to which the alternating voltage has been applied reach only the central part of the surface image area (A) as shown by the arrow →, and remove the charge in the area where they reach the grid voltage (V
The potential is lowered slightly to approximately the same potential as g). In addition, positive ions are shown in the image area (A), (B
) reaches only the non-image area excluding the outside parts (A") and (B") of the contour line, and the potential of the reached part is set as the grid voltage (Vg)
The voltage is raised to approximately the same potential as .

That is, when explaining the surface potential of the photoreceptor drum (1), as shown in FIG. 5 (b), the image areas (A), (B)
The inner parts of the contour line (A゛) and (B'') are left as the highest part with a constant width of approximately +600V, which is the initial surface potential, and the outer parts of the contour line (A") and (B") are Parts are left as low potential parts of approximately +100V, and the non-image parts except for the contour outside parts (A") and (B") rise to approximately the grid voltage (vg: +5oov>), and the plane image part ( The center part of A) is almost the grid voltage (Vg: +500
It decreases slightly to around V).

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

(N) Developing Step In the second charging step, the electrostatic latent image formed as a negative image of the contour portion is developed by a developing device (5). At this time, a developing bias of +300V is applied to the developing sleeve (51) as in the above two modes, but this voltage (vb) is Particularly, in the second charging process, the surface potential is lower than the central part of the surface image area (A>) where the surface potential has slightly decreased and the non-image area where the surface potential has increased and is left as a low potential area outside the contour line (A"
), higher than (B“).

Therefore, the negatively charged insulating toner is applied to the high potential portions of the photoreceptor drum (1), that is, the outer contour line portions (A″) and (B
A negative toner image with a so-called "outer edge" is formed by regular development.

In this embodiment described above, the photoreceptor drum (1)
The distance (dg) between the surface of the grid (42) and the grid (42) (see FIG. 3) is 1.5 mm. This value is larger than the setting of the scorotron charger that has conventionally been used in this type of electrophotographic copying apparatus. This is to increase the extent to which the lines of electric force are directed toward the surface of the photoreceptor in the edge portion (contour) of the plane image portion (A) and the line image portion (B), thereby obtaining a good contour image. The state of this electric line of force is the distance 1! (dg). That is, the distance (d
By changing g), 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.

Further, in the above embodiment, a case was explained in which a non-magnetic toner was used as the insulating toner, but it may also have magnetism. A developing bias having a voltage slightly lower than the surface potential of the latent image area may be applied to reduce the density decreased in the second charging step.

Furthermore, it is also possible to apply a developing bias in which cross-ft pressures are superimposed.

As is clear from the above description, according to the present invention, as the second charging means, the surface of the electrophotographic photoreceptor on which the electrostatic latent image has been formed by the exposure means is charged with a scorotron charger. Since the grid is recharged by applying a voltage lower than the surface potential of the electrostatic latent image image area and higher than the surface potential of the electrostatic latent image non-image area to the grid, and the grid voltage value is varied and controlled, On the surface of the electrophotographic photoreceptor, a contour image in which the contour portion of the original image remains as a high potential portion or an inverted contour image in which the contour portion remains as a low potential portion is formed.Furthermore, in a developing process, these static areas are converted into a first latent image. Since regular development is performed with a charged toner having a polarity opposite to that of the charging process, toner adheres to the high potential portion of the electrostatic latent image during regular development, resulting in a positive contour image or a negative reversed contour image. Can be done. Furthermore, since a means for controlling on/off of the scorotron charger is provided, it is also possible to form a standard image that corresponds one-to-one to the original image. That is, the present invention turns on the scorotron charger, which is the second charging means.

It is possible to selectively form a standard image, a contour image, and an inverted contour image by simply turning off or switching the grid voltage value.

[Brief explanation of the drawing]

The drawings show an embodiment of the electrophotographic copying apparatus according to the present invention, FIG. 1 is a schematic configuration diagram of the electrophotographic copying apparatus, FIG. 2 is a plan view of the operation panel, and FIG. 3 is a diagram showing the outline image forming mode. A schematic diagram of the lines of electric force in the second charging process, FIG. 4 is a graph showing the potential of the electrostatic latent image in each process in the same mode,
FIG. 5 is a graph showing the potential of the electrostatic latent image in each step in the reverse contour image forming mode. (1>... Electrophotographic photosensitive drum, (2)... Charger, (3)... Exposure device, (4)... Scorotron charger, (41)... Power supply, (42 )
...Grid, (43)...Power source, (5)...Developing device, (51)...Developing sleeve, (108),
(110), (112)...Copy mode selection key,
(120)...microcomputer, (121)...
...Selector switch.

Claims (1)

[Scope of Claims] 1. A first charging device that applies a constant electric charge to the surface of the electrophotographic photoreceptor; and an exposure device that exposes a document image to the surface of the electrophotographic photoreceptor that has passed through the first charging device. and a scorotron charger to which an alternating voltage is applied to the surface of the electrophotographic photoreceptor that has passed through the exposure means, which is lower than the surface potential of the electrostatic latent image image area formed by the exposure means on the grid and which has no electrostatic latent image. a second charging means for recharging while applying a voltage higher than the surface potential of the image area; and an electrostatic latent image formed through the second charging means with a polarity opposite to that of the first charging means. a developing means for developing the charged toner while applying a developing bias of the same polarity as the first charging means; means for controlling on/off of the scorotron charger; and a voltage applied to the grid of the scorotron charger. An electrophotographic copying apparatus comprising: means for varying and controlling a value;