JPS6248236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a static eliminating and separating device used in an electrophotographic dry copying machine.

Some electrophotographic dry copying machines use a static eliminator to separate the transfer paper from the photoreceptor. FIG. 1 shows an example of such an electrophotographic dry type copying machine. In the image forming process, the photoreceptor drum 1 is driven to rotate in the direction of the arrow shown in the figure, and is first charged by a charging device 2 to have a uniform surface potential distribution over the entire surface. is given. Next, the photoreceptor drum 1 is irradiated with an optical image corresponding to the original document by an exposure device to form an electrostatic latent image, and the developing device 3 receives toner adhering to the image in accordance with the image to make it visible. Next, the transfer paper 4 fed from the paper feeder in synchronization with the photoreceptor drum 1 receives corona discharge from the non-image surface of the toner and the opposite polarity through the transfer device 5, and is brought into close contact with the photoreceptor drum 1 and exposed to light. A toner image is transferred from the body drum 1. The transfer paper 4 is then subjected to charge removal from the non-image surface by the charge removal/separation device 6 by corona discharge, the electrostatic attraction between the transfer paper 4 and the photoreceptor drum 1 is reduced, and the transfer paper 4 is separated from the photoreceptor drum 1 . When the separated transfer paper 4 passes through the fixing section 7, it receives heat from a heater to fuse the toner and is discharged as a copy.

FIG. 2 shows a charge model of the photosensitive drum 1 and the transfer paper 4 during transfer in the dry type copying machine. When corona discharge is applied by the transfer device 5 from the non-image surface of the transfer paper 4 in order to transfer the toner from the photoconductor drum 1 onto the transfer paper 4 during the transfer process, the photoconductor drum 1
is made up of a conductive support 8 and a photoreceptor 9, so the contact area between the transfer paper 4 and the support 8 becomes a capacitor.
Charges are accumulated there due to corona discharge, and the transfer paper 4 and the support 8 are electrostatically attracted to each other. In the separation process, it is necessary to weaken the attractive force using the static eliminator and separation device 6 to such an extent that the transfer paper 4 starts to separate due to its own stiffness. For this reason, the static eliminating/separating device 6 was configured to erase the accumulated charge by applying alternating current corona discharge to the transfer paper 4.

FIG. 3 is for experimentally confirming the static elimination effect of such a static elimination/separation device, and FIG. 4 is an attenuation curve of the photoreceptor surface potential in that case. After a uniform surface potential distribution is applied to the surface of the photoconductor by the charging device 2 while rotating the drum 1, an AC corona is applied by a static elimination separation device consisting of a corona discharger 10 and an AC power source 11 to change the surface potential to the surface potential. Total 1
2, the surface potential changed over time as shown in FIG. That is, the surface potential begins to attenuate from the moment the AC corona is applied to the photoreceptor surface and reaches a certain saturation potential, and the time constant of the attenuation curve is smaller when the voltage of the AC power source 11 is high, and the saturation potential is It did not depend on the initial potential and usually took a negative value. The reason is corona discharger 10
This is because the average corona current takes a negative value due to the difference in discharge characteristics between positive and negative. In actual measurements, the negative discharge current at the same voltage is about twice the positive discharge current. Therefore, the saturation potential takes a certain value that balances the static elimination effect due to the AC component and the charging current due to the DC component.

By the way, in order to separate the transfer paper, it is desirable to quickly erase the accumulated charges appearing between the transfer paper 4 and the support 8. In this sense, AC power supply 11
Increasing the AC voltage value is a preferable direction for the static elimination effect, but as described above, it causes the surface potential to be biased, that is, to produce a certain saturation potential. As a result, the transfer paper 4 and the support body 8 generate an attraction force due to their deviation, and when this force overcomes the stiffness of the transfer paper 4, a separation failure occurs.

Therefore, as shown in FIG. 5, an apparatus has been proposed in which a DC bias power supply 13 is inserted in series with an AC power supply 11 to apply a DC bias and remove the bias. However, with this device, corona discharge changes due to environmental factors such as temperature, humidity, and atmospheric pressure, and deterioration of the corona wire in the corona discharger, so it is not always possible to obtain the minimum deviation with a constant DC bias, and separation failure may occur. This may occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a static elimination/separation device that eliminates the above-mentioned drawbacks and can perform separation reliably.

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

This embodiment focuses on the fact that the DC component of corona discharge has the strongest effect on separation, and detects the DC component of corona discharge current and changes the DC bias voltage to constantly detect the DC component of corona discharge current. This is to keep it at a constant value near zero. That is,
As shown in FIG. 6, the corona discharger 10 includes a corona wire 14 and a shield frame 15, and the shield frame 15 is grounded together with the support 8 of the photosensitive drum 1 in the electrophotographic dry copying machine described above.
An AC power supply 1 is connected between the corona wire 14 and the ground point.
1. A DC bias power supply 19 and a parallel circuit of a resistor 16 and a capacitor 17 are connected in series. The corona wire 14 is supplied with the AC voltage from the AC power supply 11 and the DC bias voltage from the DC bias power supply 19 in a superimposed manner, and performs corona discharge on the transfer paper 4 on the photoreceptor drum 1 to remove static electricity from the photoreceptor drum 1.
Separate from. At this time, the alternating current component of the corona current bypasses the capacitor 17, and the voltage appearing across the resistor 16 due to the direct current component of the corona current is detected by the detection circuit 18. This detection circuit 18 is connected to a DC bias power supply 19 according to the voltage across the resistor 16.
is controlled to keep the DC component of the corona current at a constant value. Therefore, the suction force between the transfer paper 4 and the photosensitive drum 1 is always weakened to an extent that is weaker than the stiffness of the transfer paper 4, and the transfer paper 4 is reliably separated.

Note that the parallel circuit of the resistor 16 and the capacitor 17 operates in the same way even if it is inserted between the photosensitive drum 1 and the ground point as shown in FIG. Furthermore, various means can be used as the means for detecting the DC component of the corona current and the means for controlling the DC bias voltage based on the output thereof.

As described above, according to the static elimination/separation device of the present invention, the non-image surface of the transfer paper is charged, the transfer paper is brought into close contact with the photoreceptor, and the toner image on the photoreceptor is transferred to the transfer paper. , an electrophotographic copying machine that separates a transfer paper from a photoreceptor, comprising a corona discharger that removes static electricity from the transfer paper by corona discharge and separates it from the photoreceptor, and an AC power source that supplies an AC voltage to the corona discharger. a DC bias power supply connected in series to the AC power supply; a means for detecting the DC component of the corona discharge current; Since a control means is provided to maintain a predetermined value that ensures separation of the transfer paper, changes in corona discharge due to environmental factors, deterioration of the corona wire, etc. are eliminated.
Separation can be performed reliably.

[Brief explanation of the drawing]

Fig. 1 is a schematic front view of an example of a dry copying machine, Fig. 2 is a diagram showing a model of the charge on the photosensitive drum and transfer paper during transfer in the same dry copying machine, and Fig. 3 is a conventional static eliminator for removing static electricity. Figure 4 is a front view showing the device used to test the effect, Figure 4 is a characteristic curve diagram showing the surface potential attenuation characteristics obtained with the same device, Figure 5 is a wiring diagram showing a conventional static elimination separation device, Figures 6 and 4 are FIG. 7 is a wiring diagram showing one embodiment of the present invention. 1... Photosensitive drum, 10... Corona discharger,
11...AC power supply, 13...DC bias power supply,
16...Resistor, 17...Capacitor, 18...Detection circuit.

Claims (1)

[Claims] 1 An electrophotographic method in which the non-image surface of the transfer paper is charged to bring the transfer paper into close contact with the photoreceptor, the toner image on the photoreceptor is transferred to the transfer paper, and then the transfer paper is separated from the photoreceptor. In the copying machine, a corona discharger removes static electricity from the transfer paper by corona discharge and separates it from the photoreceptor, an AC power supply that supplies an AC voltage to the corona discharger, and a DC power supply connected in series to the AC power supply. a bias power supply, a means for detecting the DC component of the corona discharge current, and an output signal of the means to set the DC bias voltage of the DC bias power supply to a predetermined value that ensures that the DC component of the corona discharge current separates the transfer paper. What is claimed is: 1. A static eliminator and separator comprising: means for controlling so that