JPS5834828B2 - Genzo Denkiyoku Henobia Inkahouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of applying a bias to a developing electrode of a developing device that develops an electrostatic latent image formed on a photoreceptor in an electronic copying machine.

The effect of a developing electrode in liquid developing an electrostatic latent image formed on a photoreceptor is well known.

In order to use such a developing electrode, a conductive electrode plate is placed close to and facing the electrostatic latent image, a developer is filled in the gap between the electrode plate and the photoreceptor, and the electrode plate is electrically connected to the electrostatic latent image. In recent years, a method has been proposed and is being put into practice that utilizes the potential induced in the electrode plate by the potential of the electrostatic latent image when it is placed in a floating state.

The potential induced in the developing electrode has the same polarity as the potential of the electrostatic latent image, and its absolute value is slightly smaller than the average potential of the area of the electrostatic latent image facing the electrode plate.

Here, the average potential means the spatial average of the potential of the background portion and the potential of the image portion in the electrostatic latent image.

Therefore, if the potential of the developing electrode is made to be slightly higher than the average potential of the electrostatic latent image by further applying a slight potential to the developing electrode, the image area of the toner in the developing solution can be applied during development. Since adhesion to the background can be prevented without interfering with adhesion to the surface, a high-contrast copy image without background stains can be obtained.

As described above, in order to make the potential of the developing electrode slightly higher than the average potential of the electrostatic latent image, the present inventors first forcibly charged the developing electrode with a charge of the same polarity as the electrostatic latent image. inject into
We proposed a method in which a minute current is passed from the developing electrode to the photoreceptor through the developer.

(Patent Application No. 50-41589).

This method is ideal as long as the density of the background part of the copy document is uniform, because the potential of the developing electrode follows the fluctuation of the average potential while maintaining a constant minute potential difference with the average potential of the electrostatic latent image. However, if there is a sudden change in the density of the background part of the copy original in the direction corresponding to the direction of the progress of the electrostatic latent image, and the specific resistance of the developer is low,
Staining may occur in this area of the copied image.

A specific example of a sudden change in the density of the background area of a copied original is when the background area of the original is color-coded into two tones, and such originals cannot be copied using current electronic copying machines. It's not a rare thing.

Such stains can be prevented by extremely increasing the resistivity of the developer, but preventing the stains in this way imposes strict conditions on the selection of the developer. , it is not a practical idea.

As described above, an object of the present invention is to provide a bias application method to a developing electrode that does not cause the above-mentioned stains on the copied image even if there is a sudden change in the density of the background portion of the copied original. That's true.

The present invention will be described below with reference to the drawings.

First, with reference to FIG. 1, it will be explained how the above-mentioned stain occurs.

In FIG. 1, the symbol O indicates an original.

It is assumed that the background part of document O is divided into two tones, part A and part B, and part A has a darker background color than part B.

The direction of the arrow indicates the direction in which the document is optically scanned.

Now, if we assume that the average potential at image parts A and B of the electrostatic latent image is as shown in graph 1-1 in Figure 1,
The potential induced in the developing electrode by the average potential of the electrostatic latent image, the potential added by forced charge injection into the developing electrode, and the potential sum of the induced potential are, respectively, graph 1- 2 and 1-3.

Then, near the boundary between the portion A and the partial amount, a region is created in which the sum of the potentials of the developing electrodes is lower than the potential of the background portion in the portion A, and background stains occur in the portion corresponding to the area of the copied image. .

To make the explanation easier to understand, this background stain is shown by diagonal lines on the original O, assuming that the original O is a copy.

As is clear from the above explanation, the problem of background staining can be prevented not only in the portion A but also in the portion B if the bias potential VA+ΔV with respect to the portion A can be maintained.

The present invention is characterized by using an impedance conversion circuit with a simple configuration to apply a bias potential of the developing electrode, which is determined according to the average potential near the leading end of the electrostatic latent image, to the trailing end of the electrostatic latent image. The purpose is to prevent the above-mentioned background staining by applying a bias so as to maintain a constant value throughout.

FIG. 2 schematically shows only the essential parts of an example of a device for carrying out the present invention.

That is, in FIG. 2, 1 is a photoreceptor, 2 is a developing electrode, 3 is a charger, 4 is an impedance conversion circuit, Sw 1 and Sw 2 are switches, and SL 2 S2 and Ss t S4t are contacts. , symbol R indicates a resistor, symbol C indicates a capacitor, and symbol E indicates a DC voltage power source.

The photoreceptor 1 is formed into a drum shape and is rotatable in the direction of the arrow, and after its surface is charged by corona discharge from the corona discharge electrode 31 of the charger 3, an optical image is formed by an exposure optical system (not shown). to form an electrostatic latent image on the surface.

The electrostatic latent image formed in this way is moved by the rotation of the photoreceptor 10 and is developed in the developing section, that is, in the vicinity of the developing electrode 2 to the photoreceptor 1. The placement conditions of the document are adjusted so that there is an electrostatic latent image portion corresponding to the portion A of the document O shown in FIG. 1 at the leading end of the direction.

That is, the average potential of the tip is made higher than the average potential of the electrostatic latent image portion that follows it.

The developing electrode 2 also serves as a developing plate, is integrally formed, and is electrically connected to the corona discharge electrode 31 of the charger 3.
and a charge collection plate 3 disposed between the shield member 32 and the shield member 32.
3, so that when the corona discharge electrode 31 discharges, the charge collected on the charge collection plate 33 is forcibly injected.

As shown in FIG. 3, the impedance conversion circuit 4 has M
O8 type field effect transistor F, resistor R1 for protecting transistor F, and transistor Tr1
, Tr2, resistance R2゜R3, R4, R for stabilizing operation
5, and operates using a DC voltage power source E as a power source.

The operation of the impedance converter 4 is as follows.

That is, contact P on the input side. When an arbitrary potential V is applied to
The current from the DC voltage power source E flows through the transistor Trl.
and flows through transistor F1 and resistor R5, and first, due to the action of transistor F, contact P.

The potential at point P becomes equal to the potential at point P, and the transistor Tr2 operates at the next point L, and the potential at point 11 becomes equal to the potential at point 12. Thus, depending on the fluctuation of the human potential, approximately This means that an equal L potential is obtained at the contact P3 on the output side.

Now, the implementation of the present invention using the apparatus shown in FIG. 2 is as follows.

That is, during development, first the switch Sw1 is connected to the contact SI side, and the switch Sw2 is connected to the contact S3 side.
3, this connects the developing electrode 2 to the input terminal of the impedance conversion circuit 40, and connects the memory circuit consisting of the resistor R and the capacitor C to the output side.

By the way, the switch Sw1 closes the contact SI after a predetermined period of time after the photoreceptor 1 starts rotating for the copying process.
82 automatically by a known method.

The predetermined time is determined as the time after the photoreceptor 10 starts rotating, when the formed electrostatic latent image reaches a predetermined portion near the tip of the electrostatic latent image, which is determined to be about 50 to 100 mm from the tip.

Now, when the photoconductor 1 starts rotating and the leading end of the formed electrostatic latent image reaches the developing part, the developing electrode 2 is exposed to the electrostatic latent image opposite to it, as described above. A potential corresponding to the average potential of the image area is induced, and this induced potential and the charge collection plate 3
3 is applied to the input side of the impedance conversion circuit 40, and -
According to the above, a potential equal to the above potential sum is obtained at the output side of the impedance conversion circuit 4.

The potential obtained on the output side of the impedance conversion circuit 4 is
By charging the capacitor C while changing the average potential at the tip of the electrostatic latent image, the capacitor C and the resistor R
The data is input into a memory circuit consisting of:

Then, when the switch Sw1 switches from contact S1 to S2 after a predetermined period of time, the potential is slightly higher in absolute value than the average potential near the tip of the electrostatic latent body, in accordance with FIG. 1, VA+△■ The potential is stored in the memory circuit.

For this purpose, the time constant for charging the memory circuit is chosen to be appropriately small.

Now, after switch Sw 1 is switched as above,
- In order, the switch Sw2 is switched from the contact S3 to the contact S4 using any known method.

Then, by switching the switches Sw 1 and Sw 2, the potential stored in the memory circuit, that is, the potential VA+△■ in the example of FIG. 1, is applied to the impedance conversion circuit 40, and the impedance conversion A potential equal to this potential obtained at the output side of the circuit 4 is now applied to the developing electrode 2.
is applied to

Thereafter, since the input to the impedance conversion circuit 4 becomes a constant potential, the potential of the developing electrode 2 also continues to maintain the potential stored in the memory circuit.

That is, if we refer to FIG. 1 again, the switch Sw
1 and Sw 2 until the end of development, the developing electrode continues to maintain a constant potential of VA+Δ■, thus making it possible to prevent the above-mentioned problem of background staining.

Of course, the switches Sw 1 and Sw 2 return to the contacts S, , S3, respectively, after the development is completed.

Further, as shown in FIG.
When the switch 1b is divided into two parts, the number of connection contacts for the switch Sw2 can be reduced by one by connecting as shown in the figure.

However, in FIG. 4, the reference numeral S5 indicates a contact point for opening the switch Sw2, and in the case of the apparatus shown in FIG.
Since it can be used as if it were a detection electrode, the switching timing of the switch Sw ISw 2 can be increased.

As described above, according to the present invention, when there is a sudden change in the density of the background part of a document, the developing electrode can completely prevent the background stain that tends to occur in the copied image at a position corresponding to the vicinity of the density change part. It is possible to provide a method for applying a bias to.

It should be noted that the present invention provides scales and chopsticks that achieve the same developing effect as conventional methods when developing copies of originals with uniform background density.
It's no good.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the occurrence of skin stains that are intended to be rain-proofed by the present invention, FIG. 2 is a diagram showing only the essential parts of an example of an apparatus for carrying out the present invention, and FIG. The figure shows the second
FIG. 4 is a circuit diagram showing a specific configuration of an impedance conversion circuit indicated by reference numeral 4 in the figure. FIG. 4 is a diagram schematically showing only the main parts of another example of an apparatus for implementing the present invention. O...- Original, 1... Photoreceptor, 2...-
...Development electrode, 4...-impedance conversion circuit.

Claims (1)

[Claims] 1. While moving the surface of the photoconductor, when supplying a developer to the electrostatic latent image formed on the surface to perform development, the average surface potential of the corresponding electrostatic latent image is applied to the developing electrode. In addition to the potential induced accordingly, a charge of the same polarity as the electrostatic latent image is forcibly injected, and a minute current is passed from the developing electrode to the photoreceptor side, so that the supply value of the potential of the developing electrode is raised to the above value. In the bias application method in which the average surface potential is slightly larger than the supply value, a potential induced in the developing electrode according to the average potential near the leading edge of the electrostatic latent image;
The potential sum of the potential added to the developing electrode due to the forced injection of charges is applied to the input section of the impedance conversion circuit, a potential approximately equal to the above potential sum is obtained at the output section, and this is stored in the memory circuit. After that, the stored constant potential is applied to the input section of the impedance conversion circuit, and then the application of the potential sum to the input section is released from 1 to 1, and a constant potential approximately equal to the constant potential obtained at the output section is applied. A method for applying a bias to a developing electrode, characterized in that a potential is applied to the developing electrode.