JPS6161187A - Electrophotographic recording device - Google Patents

Abstract

PURPOSE:To obtain a stable copying density, and to obtain a copy of high quality by controlling its transfer efficiency in a relation to the number of sheets of copying or a drop of the surface potential of an image carrying body, etc. CONSTITUTION:A transfer device consists of a body part consisting of a shielding case 11, etc., and a control device 20 containing a control lattice of the body part as a part of its constituting element. In this state, when an external signal S related to the number of sheets of copying is applied to a selecting circuit 13, first of all, a resistance S1 is selected, copying is executed in a state that a control lattice 15X has been connected to the resistance S1, and in this state, for instance, when copying of the third sheet is ended, the selecting circuit 13 selects a diode S2 instead of the resistance S1 based on the external signal S, and copying is executed in a state that the control lattice 15X has been connected to this S2. When the diode S2 is selected, a corona of the same polarity as a toner in a transfer area X is leaked to its earth and the efficiency of the transfer rises, and lowering in density is compensated.

Description

[Detailed Description of the Invention] Technical Field> The present invention utilizes a so-called retention method in which a large number of copies are obtained by repeatedly developing and transferring a single electrostatic latent image formed on an image carrier. The present invention relates to an electrophotographic recording apparatus such as a copying machine, and is designed to compensate for a decrease in density especially when copying a large number of copies to obtain high quality copies.

<Prior Art> Conventionally, a retention method has been proposed in which a plurality of copies are obtained by repeatedly developing and transferring a latent charge image formed once. This method has the great advantage that when making multiple copies from the same original, it is possible to make copies without repeating the entire copying process. It is desirable that the density remains constant throughout the repetition, but in reality, the copy density decreases over time due to leakage through the developer tank during development or dark decay observed in ordinary two-layer photoreceptors. There is a problem in that stable copying quality cannot be obtained due to the decrease in quality.

<Purpose> The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to improve the transfer of the transfer device in relation to the number of copies or the decrease in the surface potential of the image carrier. It is an object of the present invention to provide an electrophotographic recording apparatus that can obtain stable copy density by controlling efficiency and thereby obtain high-quality copies.

<Example> The present invention will be explained in detail below based on the drawings.

FIG. 1 is a schematic diagram of an electrophotographic recording apparatus according to the present invention. In the figure, ``■'' is a photosensitive drum, and the drum is supported by a shaft 9 so as to rotate in the direction of the arrow in the figure. The photosensitive drum 1 is uniformly charged by a corona charger 2, and then an optical image L of the document (or a laser beam modulated by a recording signal, etc.) is exposed by an exposure device (not shown) to form a static image on the drum 1. A latent image is formed.

Next, the latent image formed on the photosensitive drum 1 is transferred to a developing section 3.
The drum is developed with colored toner particles to form a toner image on the drum. The photosensitive drum 1 further rotates, and a toner image transfer device 4 feeds paper from a paper feed center (not shown) or the like, and transfers a transfer paper (not shown) from direction A to direction B in the figure. come into contact with

In the transfer device 4, a charger effectively performs a corona discharge having a polarity opposite to that of toner charging at a transfer portion having a structure as described later from the back side of the transfer paper, and the toner image is transferred to the transfer paper.

The transfer paper onto which the toner image has been transferred is conveyed to a fixing device 6 via a peeling device 5, and a first copy is obtained. Photoreceptor-1
The latent image of - continues to rotate and is developed again through the inactive static eliminating section 7, cleaning section 8, pre-charging section 2, and exposure section, until the number of sheets possible or required is developed.・Transfer is repeated and ends.

FIG. 2 is a block diagram of the transfer device 4, and a more detailed explanation will now be given based on this diagram. Transfer device is shield case 1
1, and a control device 20 which includes the control grid of the main body part as part of its components.

The shield case 11 is made of stainless steel or alumina, and a wire electrode (tungsten) 10 connected to an AC high voltage power source 12 is installed inside the shield case 11 . The AC high-voltage power supply 12 is configured to output a waveform that has undergone waveform conversion, and is configured to apply a voltage biased in the direction opposite to the polarity of the toner with respect to zero potential. For example, the frequency is about 300H, the voltage peak is about ±7 KV, and it is configured so that a width of 1 to ZKV (components on the same polarity side as the toner) can be cut from the waveform peak. Note that a configuration may be adopted in which a DC bias voltage is applied and the voltage is biased to the opposite polarity side to the toner and applied to the wire electrode 10.

A wire made of metal such as stainless steel or tungsten is stretched through the opening of the shield case 11 to form a control grid 15.
X, 15Y are formed, and the transfer region X and the charge removal region Y are constituted by these control grids. The control grid 15Y in the static elimination area Y is to prevent discharge contamination on the second and subsequent copies (copy contamination), and must be grounded directly or through a resistor at all times except for the final copy of a multi-copy process.

The control grid 15X of the transfer area X is connected to the selection circuit 13 constituting the above-mentioned control device 20, and is grounded via the resistor S1 or diode S2 under the control of this selection circuit.

In response to an external signal S such as a signal related to the number of copies, the selection circuit 13 strengthens the transfer electric field to compensate for the decrease in density caused by the potential attenuation of the latent image, which increases with the number of copies. The connection relationship between the control grid 15X, the resistor Sl, and the diode S2 is selected.

Next, the operation will be explained using the case of copying five sheets as an example.

Now, when an external signal S related to the number of copies is applied to the selection circuit 13, the circuit first selects the resistor S1, and copies are performed with the control grid 15X connected to the resistor S1. When the third copy is completed in this state, the selection circuit 13 selects the diode S2 instead of the resistor S1 based on the external signal S, and connects the control grid 1.5X to the diode S2. 4~ with connected
The fifth copy is made. When diode S2 is selected, corona of the same polarity as the toner in transfer area X leaks to ground, thereby increasing the efficiency of transfer and compensating for density loss. Therefore, the fourth and fifth copies are made with this compensated density. This situation is as shown in FIG. 3. In particular, the timing of selecting the diode S2 in place of the resistor S1 is of course determined in relation to the copy density, but in this embodiment, the number of copies is determined. When a predetermined number of sheets is reached, the selection is automatically switched.

In the above embodiment, a so-called binary selection of the resistor S1 and the diode S2 has been described, but the configuration is such that a plurality of resistors having different resistance values are provided and these are sequentially selected to gradually increase the transfer efficiency. You may.

As for the external signal S, in addition to the signal related to the number of copies as in the embodiment, it is also possible to use a state detection signal of the surface potential of the photoreceptor, but the point is to detect the density drop to the number of copies to be made. Any signal that is emitted at a timing that relaxes the situation may be used.

FIG. 5 and FIG. 6 are diagrams showing other embodiments.

FIG. 5 shows an example in which the above-mentioned control device 20 is connected to the control grid 15Y, and in particular, the latent image is re-formed every time two copies are made, and a large number of copies are made.
When transferring the first sheet, the resistor S3 side is selected (or directly grounded), and when transferring the second sheet, the diode S4 side is selected. According to such a configuration,
There is an advantage that discharge contamination that may occur when the diode S4 side is selected can be prevented.

Fig. 6 shows the one shown in Fig. 2 with a charger 14 added to expand the charge removal area Y, and the control grid 15Y is always grounded or connected through a resistor except for the final number of copies to be made using the same latent image. and grounded. Further, the control contents of the control device 20 are basically the same as described above.

In each of the embodiments described above, one block of control grid is controlled, but the control grid may be divided into a plurality of blocks and each block may be controlled.

<Effects> As explained in detail above, the electrophotographic recording apparatus of the present invention can achieve the following effects by controlling the transfer efficiency of the transfer device in relation to the number of copies or the potential image of the surface potential of the image carrier.
Since the density reduction caused by copying a large number of copies is compensated for, high-quality copies can be obtained very easily.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of the apparatus of the present invention, Figure 2 is a detailed diagram of the same transfer apparatus, Figure 3 is a diagram showing the relationship between the number of copies and density by the apparatus of the present invention, and Figure 4 is the number of copies by the conventional apparatus. FIGS. 5 and 6 are diagrams showing other examples. 1 is a photosensitive drum, 3 is a developing section, 4 is a transfer device, 10 is a wire electrode, 11 is a shield case, 12 is an AC high voltage power supply, 13 is a selection circuit, 15X, 15Y are control grids, 20
is the control device, S is the external signal, Sl is the resistor, and S2 is the diode agent Patent attorney Aihiko Fukushi (and 2 others) No. 11 No. 311 fl (yriy,)' No. 21 No. 4 w1 ~

Claims (1)

[Claims] 1. In an electrophotographic recording device that obtains a large number of copies by repeatedly developing and transferring a single electrostatic latent image formed on an image carrier, An electrophotographic recording apparatus characterized by comprising a control means for controlling transfer efficiency of a transfer device in relation to the number of sheets or a decrease in surface potential of an image carrier. 2. The electrophotographic recording apparatus according to claim 1, wherein the control means includes a control grid of the transfer device as a part of its constituent elements. 3. The control means includes a control grid of the transfer device as a part of its components, and controls the transfer efficiency of the transfer device by switching the grounding mode of the control grid. An electrophotographic recording device according to claim 1. 4. The transfer device comprises a corona charger, an AC high-voltage power source connected to the charger, and a control grid provided in the opening of the charger. The electrophotographic recording device according to item 1.