JPS6248232B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in electrophotographic methods. Conventionally, in the electrophotographic method, a constant amount of light from a lamp is used to remove unnecessary electrostatic latent images on the photoreceptor drum, i.e., areas outside the image forming area, depending on the copy size, from the charging position to the developing position. A method of erasing is known from Utility Model Application Publication No. 52-155553. However, with this method, unnecessary electrostatic latent images on the photoreceptor drum are erased using a fixed amount of light.
The surface potential of the latent image erased portion is a constant potential, and when the developing bias voltage is changed manually or automatically according to the original image, the difference between the surface potential of the latent image erased portion and the developing bias voltage is As a result, side effects such as slight toner adhesion or carrier adhesion occur in the area where the latent image has been erased. An object of the present invention is to provide an electrophotographic method that can eliminate the above-mentioned side effects by changing the amount of light for erasing an electrostatic latent image in accordance with the developing bias voltage. Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a photosensitive drum 1 is rotationally driven by a driving motor, is uniformly charged by a charging device 2, and an original image is exposed by an exposure device to form an electrostatic latent image. This electrostatic latent image is developed by a developing device 3 and transferred to transfer paper from a paper feeding device.
Transcribed by. This transfer paper undergoes image fixation by a fixing device and is discharged as a copy outside the machine, and the photosensitive drum 1 is removed by a static eliminator 5, cleaned by a cleaning device 6, and reused. In the developing device 3, a developing bias voltage is applied from a power supply circuit 7 to a developing electrode, for example, a developing sleeve, and a bias is applied to the developing area. For example, it is changed stepwise depending on the concentration. This is an operation for obtaining a good copy image without background stains by always setting the developing bias voltage slightly higher than the background potential of the latent image formed by the original. Further, a latent image erasing lamp 8 is disposed between the charging device 2 and the developing device 3, and blinks in response to an output signal from the power supply circuit 9 to erase an unnecessary electrostatic latent image on the photosensitive drum 1. This prevents toner from adhering to unnecessary portions on the image forming apparatus 1. As shown in FIG. 2, the latent image erasing lamp 8 is made up of a plurality of lamps ₈₁ to ₈₇ separated from each other by a light shielding frame ₈₀ and arranged in the width direction of the photosensitive drum 1. In the traveling direction, all the lamps 8 ₁ to 8 ₇ are blinked in time by the power supply circuit 9, and in the width direction of the photosensitive drum 1, the lamps 8 ₁ , 8 ₇ or 8 _{1 are} blinked by the power supply circuit 9 according to the copy size. , 8 ₂ , 8 ₆ , 8 ₇ or 8 ₁ to _{8 3} , 8 ₅ to 8 ₇ are selectively turned on to erase unnecessary electrostatic latent images. Conventionally, the amount of light from each of the lamps 8 ₁ to 8 ₇ is always constant, and therefore the surface potential of the portion of the photosensitive drum 1 where the latent image is erased is also always constant. For example, the developing bias voltage can be set to 150, 300,
The lamp is switchable in three stages of 450V, and the surface potential of the area where the latent image is erased on the photoreceptor drum 1 is set to 100V, where almost no development occurs in the area where the latent image is erased even at the lowest developing bias voltage. A light amount of 8 ₁ to 8 ₇ is selected. However, in this case, if development is performed with a development bias voltage of 450V, carrier may adhere to the erased portion of the latent image in some cases. This is because a large potential difference of 350V occurs between the development bias voltage and the surface potential of the latent image erased area.To prevent this, if the surface potential of the latent image erased area is set higher, the development bias voltage of 150V is generated. If development is carried out, toner will adhere to the areas where the latent image has been erased. In this example, the intensity of the lamp 8 is also changed at the same time as the development bias voltage is changed, and the development bias voltage is set high and the light intensity of the lamp 8 is reduced, so that the axis between the surface potential of the latent image erased area and the development bias voltage is always small. This setting is made to prevent the carrier and toner from adhering to each other. In the power supply circuits 7 and 9, as shown in FIG.
A predetermined voltage is generated by each of 1 to 17.
The output voltages of the voltage sources 11 to 13 are set to each developing bias voltage, and the output voltages of the voltage sources 15 to 17 are set to each power supply voltage of the lamp 8. Normally, when the operation switches 18 and 19 are off, the logic circuit 20 turns off the relays 1K and 2K, and the output voltage of the voltage source 11 is the normally closed contacts 1K2 and 2K of the relays 1K and 2K.
1 and is applied to the developing device 3 from the output terminal 21 as a developing bias voltage. At the same time voltage source 15
The output voltage of relay 1K, 2K normally closed contact 1K
4,2K3 to the power supply terminal 22, and the voltage of this power supply terminal 22 is selectively applied to the lamps ₈₁ to ₈₇ at appropriate timings by a control circuit as in the conventional case. When the background density of the original is higher than the normal density and the operator turns on the operating switch 18, the logic circuit 20 turns on the relay 1K. Therefore, the output voltage of the voltage source 12 is supplied to the output terminal 21 via the normally open contact 1K1 of the relay 1K and the normally closed contact 2K1 of the relay 2K, and the output voltage of the voltage source 16 is supplied to the power supply terminal 22 via the normally open contact 1K1 of the relay 1K and the normally closed contact 2K1 of the relay 2K. It is supplied through the normally open contact 1K3 of the relay 2K and the normally closed contact 2K3 of the relay 2K. Further, when the original image has a lower density than usual and the operator turns on the operation switch 19, the logic circuit 20 turns on the relay 2K. Therefore, the output voltage of the voltage source 13 is supplied to the output terminal 21 via the normally open contact 2K2 of the relay 2K, and the output voltage of the voltage source 17 is supplied to the power supply terminal 22 via the normally closed contact 2K4 of the relay 2K. Supplied. Each output voltage V ₁ to _{V 3} of the voltage sources 11 to 13 is V ₃ <
There is a relationship of V ₁ < V ₂ , but voltage sources 15 to 17
The respective output voltages V ₄ to _{V 6} are set to have a relationship of V ₅ <V ₄ <V ₆ . Now, set the developing bias voltage V ₁ to _{V 3} to
When set to 150V, 300V, and 450V, the surface potentials V ₄ to V ₆ of the latent image erased portion on the photosensitive drum 1 are suitably about 100V, 200V, and 350V at each developing bias voltage V ₁ to _{V 3} . Therefore, when using a photosensitive drum with characteristics as shown in FIG.
It is necessary to set it to about 20, 12, 8 μWsec/cm ² for V ₄ to V ₆ . 12 when lamp 8 has a power supply voltage of 100V
When set to emit light with a light intensity of μWsec/cm ² , the light intensity of the lamp 8 is 33% lower and 67% higher at the above potentials V ₅ and V ₆ . Therefore, from the characteristics of the lamp 8 in FIG. 5, the power supply voltage V ₅ of the lamp 8,
You can see that V ₆ should be selected to 90V or 115V. In other words, the output voltage of voltage sources 11 to 13, 15 to 17
_V1 to _V6 are

You can make the relationship as shown in [Table]. The above example is an example in which the operator switches the developing bias voltage, but in other cases, for example, the amount of reflected light from the original or the latent image potential on the photoconductor generated by the original is detected and the developing bias voltage is adjusted accordingly. The present invention is equally applicable to a so-called auto-bias type electrophotographic method in which a voltage is applied to a developing device. In this case, of course, as shown in FIG. 6 or 7, the developing bias voltage may be changed in accordance with the above-mentioned light amount or the detected value of the latent image potential, and the light amount of the lamp 8 may be similarly changed. In addition to changing the input voltage of the lamp 8, various known techniques may be used to change the amount of light from the lamp 8, such as providing a slit and changing this. In addition, in the auto-bias type electrophotographic method, if the variable range of the developing bias voltage is set to 150 to 450 V as in the above example, the power supply voltage of the lamp 8 is changed to 115 V as shown in Fig. 8.
You can vary it to ~90V. As described above, in the electrophotographic method according to the present invention, the amount of light irradiated to erase unnecessary electrostatic latent images on the photoreceptor is changed according to the developing bias voltage, so that the surface potential of the portion where the latent image is erased is There is no large difference between the voltage and the developing bias voltage, and toner and carrier adhesion to the erased portion of the latent image is prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view showing an electrophotographic copying device according to an embodiment of the present invention, FIG. 2 is a perspective view showing a latent image erasing lamp of the same device, and FIG. 3 is a partial view of the same device. The block diagrams shown in FIGS. 4 to 8 are characteristic diagrams for explaining the present invention. 1... Photosensitive drum, 3... Developing device, 7...
Power supply circuit, 8... Lamp for latent image erasing, 9... Power supply circuit.

Claims (1)

[Claims] 1. In an electrophotographic method in which the developing bias voltage is adjusted manually or automatically according to the density of the original, and unnecessary electrostatic latent images on the photoreceptor are erased by light irradiation according to the copy size, An electrophotographic method characterized in that the amount of light irradiated is changed in accordance with the developing bias voltage so that it decreases as the voltage increases.