JPS61140970A - Electrostatic stripping method - Google Patents

Abstract

PURPOSE:To stabilize the stripping of transfer paper by detecting the density of an original image near the front end of the image region and controlling the magnitude of the current to be passed to a charger for stripping the transfer paper. CONSTITUTION:The reflected light irradiated from a light source 20 to an original 21 is detected by an original density sensor 22 by which the original density is detected. The output from an original density sensor 22 is supplied to a variable resistor 11 as well as to a DC bias setting circuit 12. The circuit 12 takes the density output of the sensor 22 therein at a timing T1 and generates the DC voltage corresponding to the density output thereof. Said voltage is outputted to a high AC voltage generating circuit 13. The circuit 13 superposes the DC voltage to the specified high AC voltage and supplies the superposed voltage to a stripping charger 5. The circuit 13 is driven at the specific timing T2 to start the charger 5. The continuous and sure stripping of the transfer paper is thus made possible even with the original of any density from the original white over the entire surface up to the original black over the entire surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electrostatic peeling method in which transfer paper after toner image transfer is electrostatically peeled off from a photoreceptor by AC corona discharge from a charger.

<Prior art and its drawbacks> In the electrostatic peeling method, the ability to peel off the transfer paper that is in close contact with the photoreceptor changes depending on the relative relationship between the corona current and the potential distribution of the photoreceptor. The ability changes depending on the amount of toner adhering to the image forming area on the photoconductor, and is different for completely black originals (toner adheres to the entire image forming area) and for completely white originals (toner does not adhere to the entire image forming area). The difference in ability is the largest between the two cases. Therefore, if the magnitude of the current applied to the peeling charger is not appropriate, the transfer paper may not be able to be peeled off when the amount of toner adhesion is very large or very small.

By reducing the potential difference between the image area and the non-image area in the image forming area, the appropriate range of the current flowing to the peeling charger (peeling current) can be widened (and the amount of toner adhering to the image forming area can be large or small). This also ensures stable separation of the transfer paper.

However, the above method requires a full-surface light irradiation section to reduce the potential difference between the image area and the non-image area, and even if the entire surface is irradiated with light, the irradiation is performed from above the toner, which reduces the potential of the image area. There was a drawback that the potential could not be brought sufficiently close to the potential of the non-image area.

<Object of the Invention> The object of the invention is to provide a method that does not require a light irradiation means to reduce the potential difference between the image area and the non-image area, and can stably peel off the transfer paper even if the potential difference is large. An object of the present invention is to provide an electrostatic peeling method.

<Configuration and Effects of the Invention> The present invention detects the density near the leading edge of the image area of the original when scanning the original using an original density sensor, and in accordance with the detected density, controls the current flow to the charger for separating the transfer paper after the toner image has been transferred. It is characterized by controlling the size of.

With the above configuration, according to the present invention, the amount of toner adhering near the leading edge of the image forming area is proportional to the density near the leading edge of the image area of the document, so that optimum peeling can be performed according to the amount of toner adhering near the leading edge. The current can be set, and the transfer paper can be reliably peeled off regardless of the potential difference between the image area and the non-image area. Further, since the light irradiation means is not required, there is an advantage that the copying process is simplified and the size can be reduced by the fact that the light irradiation means is not required.

<Embodiment> FIG. 1 is a schematic diagram of the main parts of a copying machine in which the method of the present invention is implemented. In the figure, 1 is a main charger that uniformly charges the photoreceptor 8a formed on the surface of the photoreceptor drum 8, 2 is image light obtained by irradiating an original (not shown), 3 is a developing layer, 4 is a transfer charger for transferring the developed image onto the transfer paper 9; 5 is a peeling charger for peeling the transfer paper 9 from the photoreceptor drum 8; 6 is a static elimination charger for removing static from the surface of the photoreceptor drum after peeling; 7 is a charger for removing static electricity This is a static elimination lamp that cancels the residual charge after static elimination. It should be noted that a DC high voltage is applied to the main charger 1 and the transfer charger 4, and an AC high voltage is applied during static elimination charging 6. Further, a voltage obtained by adding a DC bias voltage to an AC high voltage is applied to the peeling charger 5. As will be described later, this DC bias voltage is set to an appropriate value depending on the density near the leading edge of the image forming area of the document. That is,
The effective value of the peeling current can be varied depending on the density of the original near the tip of the image forming box area of the original.

FIG. 2 is a diagram showing the configuration of a control section that controls the magnitude of the peeling current. The reflected light irradiated onto the original 21 from the light source 20 is received by an original density sensor 22 made of CDS, so that the density of the original can be detected. In this embodiment, the average density of the original 21 is detected by M-scanning, and the set value of the variable resistor 1) that determines the developing bias current is changed in accordance with the detected value. The output of the document density sensor 22 is further supplied to the DC bias setting circuit 12 as well as the variable resistor 1). The DC bias setting circuit I2 takes in the density output of the document density sensor 22 at timing T1, generates a DC voltage according to the density output, and outputs it to the AC high voltage generation circuit 13. Timing T1 is set to the timing at which the document density sensor 22 detects the density near the leading edge of the image area of the document 21 during the copying cycle.
The C voltage is supplied to the peeling charger 5 in a weighted manner. In addition,
The AC high voltage generating circuit 13 is driven at a specific timing T2 to start the peeling charger 5.

10 is a power source for supplying a developing current.

In the above configuration, when the copy start button is operated, the document density is detected by preliminary scanning, and the copy cycle begins, and the photoconductor drum 8 begins to rotate clockwise, the main charger 1 is started and the photoconductor 8a is activated. Uniform charging is performed. At this time, the original density sensor 22 detects the density near the leading edge of the image forming area of the original 21, and the DC bias setting circuit 12 is driven at the timing TI to generate a DC voltage according to the density output. Next, image light 2 from the original
When exposed, an electrostatic latent image with a potential difference between the image area and the non-image area is formed. Next, when the image forming area on which the electrostatic latent image is formed reaches the developing section, it is developed by the magnetic brush 3a. The AC high voltage generation circuit L3 is the above DC
The DC bias voltage generated by the bias setting circuit 12 is weighed with a constant AC high voltage, and the weighed voltage is applied to the peeling charger 5 at timing T2. On the other hand, in synchronization with the rotation of the photosensitive drum 8, the transfer paper 9 is also fed from a paper feed section (not shown) to the transfer section, and the transfer charger 4 is also supplied with a constant DC high voltage from a DC high voltage generation section (not shown). is supplied, the image developed in the developer tank 3 is transferred to the transfer paper 9 at the transfer section. At this time, the peeling charger 5 has already caused a corona discharge due to the voltage in which the AC high voltage and the DC bias voltage are combined from the AC high voltage generation circuit 13, so the peeling charger 5 peels off the peeling paper 9 after transfer from 8a and performs the next process. Send it to the engineering department. At this time, timing T1
If the density at the leading edge of the image forming area of the document detected in is low density, a peeling current suitable for the low density image flows. Further, if the density is high, a peeling current suitable for the high density image flows. Once the leading edge of the transfer paper 9 is peeled off from the drum 8, no problem will occur because the peeling has already been completed, regardless of the magnitude of the peeling current flowing from the peeling charger 5. Thereafter, the static eliminating charger 6 and the static eliminating lamp 7 are driven at appropriate timing, and one step of the copying process is completed.

Next, experimental results for the above example will be shown.

OPC (organic window photoconductor) was used as the photoreceptor 8a, and the potential of the image area at the stage of exposure to the image light 2 was set to 500 Å, and the potential of the non-image area was set to 100 Å. The frequency of the AC voltage of the ACC high voltage body part 13 is 300 Hz. In the case of an entirely black original under the above conditions, the best peeling efficiency is the DC peeling current flowing from the peeling charger 5 to the drum 8.
This is when the component is in the range of 1100 to 0 μA. The current value in this range is set by the DC bias setting circuit 12.
This is obtained when the bias voltage is between 180 and 650V. Further, in the case of an all-white original, the peeling efficiency is best when the DC component of the peeling current is in the range of 1100 to lOOμ. The DC bias voltage to obtain this current value is -80~
It is 1380V. FIG. 3 shows the relationship between this DC bias voltage and the DC current component of the peeling current. On the other hand, when the relationship between the surface potential of the photoreceptor and the concentration sensor output voltage was measured, the relationship shown in FIG. 4 was obtained.

Under the above conditions, the DC component of the peeling current was set to flow at 150 .mu.A for an all-black original, and 50 .mu.A for an all-white original.

In other words, if the DC bias voltage is set to 320■ for an entirely black original, and the DC bias voltage is set to 980■ for an entirely white original, then from the graphs in Figures 3 and 4, The relationship between the DC bias voltage and the concentration sensor output voltage shown in FIG. 5 could be obtained. That is, by setting the relationship shown in FIG. 5 in the DC bias setting circuit 12 using an analog circuit, it is possible to ensure that the transfer paper is continuously transferred regardless of the density of the original, from an all-white original to an all-black original. I was able to peel it off.

Note that under the above conditions, there is an overlap between the range of the C current component, which has good peeling efficiency in the case of an entirely black original, and the C current component, which has good peeling efficiency in the case of an entirely white original, in the range of 1100 to 0 μA. However, when a current value in this range was used fixedly, a stable peeling effect could not be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of a copying machine that implements the method of the present invention. FIG. 2 is a block diagram of a control section that controls the stripping current according to the magnitude of the developing current. 3 to 5 are graphs showing experimental results obtained with the apparatus shown in FIG. 2 under predetermined hole conditions. 5-@separate charger, 8-photoconductor drum, 8a-photoconductor, 9-transfer paper, 21-document, 22-document density sensor.

Claims (1)

[Claims] (1) When scanning a document, the density near the leading edge of the image area of the document is detected by a document density sensor, and the magnitude of the current applied to the charger for separating the transfer paper after the toner image is transferred is controlled according to the detected density. Characteristic electrostatic peeling method.