JPS62159165A - Separating device for electrostatic copying machine - Google Patents

Abstract

PURPOSE:To obtain an inexpensive separating device which has good separation performance by employing DC corona discharge which corresponds to image density as a means which separates transfer paper which is attracted to a photosensitive body from the photosensitive body. CONSTITUTION:Ions having the opposite polarity from the charge of the transfer paper 13 are supplied from a separation corona discharger 5 to neutralize the charge of the transfer paper 13, which separates from the photosensitive body 1 by its own weight and rigidity. The detection signal of the density of an original 10 placed on platen glass 9 is supplied from an original density sensor 19 to a high-voltage power source 17 for separation corona through a controller 20 to control the output of the high-voltage power source 17 according to the detection signal. When the image density is high and the separation performance is not good, a high output voltage is selected and corona discharge suitable to the image density is caused from the separation corona discharger 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a transfer paper separating device in an electrophotographic apparatus such as a copying machine, a printer, or a facsimile.

[Prior art] As a method for separating transfer paper that is electrostatically attracted to a photoreceptor, a corona discharge of alternating current with superimposed direct current is applied from the back of the transfer paper to neutralize and separate the electric charge on the back of the transfer paper. method is known. This is an attempt to obtain stable separation performance by utilizing the self-control property of AC corona discharge in which the potential of the transfer paper converges to the potential corresponding to a single superimposed DC current. In order to prevent the generation of striped patterns due to excessive static removal on the transfer paper, an inverter is used to generate an AC high voltage with a frequency of about 5008Z.

However, when such alternating current is used, reactive currents that do not contribute to corona discharge flow in the wiring from the power supply to the corona discharger and in the distributed capacitance of the wire electrodes and shield electrodes of the corona discharger, so it is difficult to use a large capacity inverter. Further, at a frequency of about 5001 (Z), a step-up transformer used in the inverter must have an iron core made of a silicon steel plate, which has the disadvantage of making the inverter larger and more expensive.

[Purpose] The present invention aims to provide a separation device that is inexpensive and has good separation performance by using DC corona discharge corresponding to the image density as a means for separating the transfer paper adsorbed onto the photoreceptor from the photoreceptor. It is something to do.

[Configuration] The present invention achieves stable separation performance with a small power source by controlling the output voltage or output current of a DC high voltage power source for corona discharge for separation in accordance with the image density of the copy document. Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the drum-shaped photoreceptor I is surrounded by a charging corona discharger 2, a developing device 3, a transfer corona discharger 4, a separation corona discharger 5, and a pre-cleaning static neutralization corona discharger. 6. A cleaning device 7 and a light source 8 for static elimination are provided, and reflected light 11 from an original document 10 placed on a platen glass 9 and illuminated by an exposure lamp (not shown) is charged via a lens system. A latent image of the original image is formed by being projected onto the photoconductor 1, which is visualized by the developing device 3, and transferred to the transfer paper 13 via the registration roller 12 by the corona discharger 4 for transfer. The toner image is transferred thereto, the transfer paper 13 is separated from the photoreceptor 1 by a separating corona discharger 5, and the separated transfer paper 13 is sent to a fixing device by a transport heald 14.

Further, the toner remaining on the photoconductor l is neutralized by a pre-cleaning static elimination corona discharger 6, the photoconductor 1 is cleaned by a static elimination cleaning device 7, and the static elimination light source 8
After being optically neutralized by the charging corona discharger 2, the copying process is continued. In addition, codes|symbols 15-18 are high voltage power supplies of each corona discharger.

The present invention provides such a copying apparatus with a document density sensor 19, and controls the output of the high-capacity power source 17 for the separated corona in accordance with the output of the document density sensor 19.

That is, to explain further, the density of the original 10 placed on the platen glass 9 is detected by the original density sensor 19 provided near the exposure lamp (not shown). ! High voltage power supply 17 for isolated corona through 20
is supplied to.

Since the process from charging to development in such an apparatus is a well-known electrophotographic process, the explanation will be omitted. However, the transfer paper 13 sent from the registration roller 12 is superimposed on the toner image on the photoreceptor drum l, and the transfer paper When the transfer corona discharger 4 applies ten ions from the back side of the transfer paper (3), the transfer paper (3) becomes ten-charged. As a result, the negatively charged toner is transferred to the transfer paper 13, but the transfer paper 13 is moved due to the electrostatic attraction with the one charge induced on the substrate side of the photoreceptor drum l corresponding to the ten charges on the transfer paper. It is adsorbed onto the photoreceptor drum l. Next, transfer paper 13
In order to separate the transfer paper from the photoreceptor drum, a separation corona discharger 5 applies an ion having an electric charge and a reverse characteristic to the transfer paper, and the transfer paper 13
When the charges are neutralized, the transfer paper 13 is separated from the photoreceptor due to its own weight and rigidity, and is transported to the next process by the transport belt 14. However, if the charge on the transfer paper 13 is completely neutralized, the electrostatic attraction between the transfer paper 13 and the toner will be reduced, and the toner will be retransferred to the photoreceptor, resulting in an abnormal image. For this reason, the output of the high-voltage power supply 17 for one-separation corona is set to a value that makes transfer and separation compatible.

Furthermore, it is known that the separability varies depending on the presence or absence of a toner layer on the photoreceptor 1. This is because the distance between the photoreceptor 1 and the transfer paper 13 changes depending on the presence or absence of a toner layer, and therefore the electrostatic attraction between the two also differs.

Therefore, in this embodiment, in order to perform the transfer and separation more reliably, the image density of the document related to the presence or absence or thickness of a toner layer is detected, and the output of the high-voltage power supply 17 for separating corona is adjusted according to this detection signal. It's in control.

An image density sensor 19 (not shown) provided near a document exposure light source detects the reflected light of the N document. The image density of the document is detected based on the intensity of this reflected light, and the control device 20 generates an output control signal corresponding to the image density and sends it to the high voltage power supply 17. As a result, the separated corona discharge device 5 performs an optimum corona discharge according to the degree of image source.

FIG. 2 shows the high voltage power supply 17 used in this example.
(a) is a block diagram of the high-voltage power supply 17, and (b) is a correspondence diagram of the output control signal from the control device 20 and the output voltage. In the figure (a), the high-voltage power supply 17 is an inverter having a well-known step-up transformer, and rectifies the high-voltage AC output of the inverter and supplies it to the corona discharger 5 for separation.

D,, D2 are output control terminals, and these terminals are connected to the power supply VP.
By connecting to one side of f', the state of 1'' is shown in the correspondence table in figure (b). To explain each mode in figure (b), No., L beam is 8, D Hong is "0". ", that is, it is in a float state, and the output of the high voltage power supply 17 is stopped and becomes OV. NO12 has Dl connected to the - of the power supply VPP, D2 is a float, and the voltage of -5.0 kv is the separated corona. It is added to the discharger 5. Below, in NO, 3, -563kv, NO
, 4 outputs -5,6kv.

With this configuration, if the image density of the yX draft is high, N
No. 0,2 is selected, and conversely, when the image density is low and the separation is not good, No. 094, which has a higher output voltage than No. 2, is selected.

The transfer paper that has undergone the separation process as described above is transported to the fixing device by the transport belt 14 as described above. next.

After the separation process, the photoreceptor is in an electrostatically disordered state, including -charged residual toner, photosensitive areas to which paper dust and separated corona were directly applied, and a photosensitive layer in the charged toner image area. It becomes.

In order to return such a photoreceptor to its initial state and use it repeatedly, the photoreceptor undergoes a cleaning and neutralization process. Prior to cleaning, the toner that is electrostatically adsorbed on the photoreceptor is neutralized and discharged, weakening the adsorption force and improving cleaning performance. That is, in order to neutralize the portion of the photosensitive layer that is uniformly charged when the separated corona is directly applied, +biased alternating current corona having the opposite polarity to these charges is applied by a pre-cleaning corona discharger 6. Next, a cleaning device is used. At step 7, the residual toner on the photoreceptor is removed by a fur brush and a blade, and ten charges on the photoreceptor layer are removed by the charge removal light source 8, and the photoreceptor returns to its initial state.

It is used repeatedly as above.

[Effect] As a means of separating the transfer paper from the photoreceptor, a DC corona discharge with a polarity opposite to that of the toner image is generated from the back side of the transfer paper, and the voltage or current of the DC corona discharge is controlled according to the image density of the original. By doing so, it is possible to obtain stable separation performance that is not affected by the original. Furthermore, by using DC corona discharge, the power source that generates high voltage can be made smaller and cheaper.

[Brief explanation of drawings]

FIG. 1 is a side view showing the configuration of an electrostatic copying machine embodying the present invention, and FIG. 2 is a diagram showing the operation of configuration 1 of the high-voltage power supply in FIG. ) is a control correspondence diagram. ■...Photoreceptor, 5...Corona discharger for separation. 9...Platen glass, lO...Original, 13...
Transfer paper, 17...High voltage power supply for isolated corona, 19
...Original density sensor, 20...Control device, VPP
...Power supply, D,, D2...Output control terminal.

Claims (2)

[Claims] (1) A separating device for an electrostatic copying machine, characterized in that the output voltage or output current of a DC high voltage power supply for separating corona discharge is controlled in accordance with the image density of a copy original. (2) In a separation device that performs transfer corona charging of the toner image formed on the photoconductor from the back side of the transfer paper with the polarity opposite to that of the toner image, and then performs separation charging with the same polarity as the toner image, An image density detection device for the copied original is provided, and depending on the output from this device, the high voltage power output of the transfer corona discharger is lowered below a predetermined value when the image density of the original is high, and conversely when the image density is low. 2. A separating device for an electrostatic copying machine according to claim 1, wherein the separating device is configured to control the output of the high-voltage power source to be higher than a predetermined value.