JPH01154175A - Image forming device - Google Patents

Abstract

PURPOSE:To accomplish a small-sized, simple, and economical image forming device by uniformly electrifying the surface of an image carrier whereby an electrifying member on which an overlap voltage consisting of both DC and AC voltages is impressed is brought into contact with the surface of the image carrier, and varying the DC voltage used in the process of forming an image and that used after forming an image. CONSTITUTION:Without depending on a corona electrifying device, the uniform electrification on the surface of the image carrier 1 is created by contact (direct) electrification where the electrifying member 20 on which the voltage is impressed abuts on the surface of the image carrier 1. Said voltage impressed on the electrifying member 20 is the overlap voltage consisting of both DC and AC voltages. While the image carrier 1 makes a later rotation or turn during one rotation after forming the image, the DC voltage for the electrifying member 20 which abuts on the surface of the image carrier 1 is turned into a second DC voltage which is lower than a first voltage impressed at the time of forming an image. The destaticizing operation for the image carrier 1 necessary to form an image satisfactorily is performed by the electrifying device 20 of the image carrier 1. Thus, the image forming device is small-sized, simplified, and economized as much as possible.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to image bearing devices such as drum-type photoconductors and endless belt-type photoconductors that are rotated or rotationally driven, such as in transfer-type electrophotographic copying machines. The present invention relates to an image forming apparatus in which image formation is performed by applying an image forming process including a step of uniformly charging the surface of the image carrier, and the image carrier is used repeatedly.

[Conventional technology]

FIG. 2 shows a schematic configuration of a general transfer type electronic copying machine using a drum-type photoreceptor.

In the figure, reference numeral 1 denotes a drum-type photoreceptor as an image carrier, which is rotated at a predetermined circumferential speed in the direction of the arrow around an axis 1a. During the rotation process, the photoreceptor L is uniformly charged with a predetermined positive or negative potential on its peripheral surface by the charging device 2, and then subjected to light image exposure L (slit exposure, (laser beam scanning exposure, etc.). As a result, electrostatic latent images corresponding to the exposed images are sequentially formed on the circumferential surface of the photoreceptor.

The electrostatic latent image is then developed with toner in a developing device 4, and the toner developed image is transferred from a paper feed section (not shown) to the photoreceptor 1 and the transfer device 5 by a transfer device 5, which is synchronized with the rotation of the photoreceptor 1. The images are sequentially transferred onto the surface of the transfer material P that is fed by -C.

The transfer material P that has undergone the image transfer is separated from the photoreceptor surface and introduced into the image fixing device 8, where the image is fixed and printed out outside the machine as a copy.

After the image has been transferred, the surface of the photoreceptor is cleaned by a cleaning device 6 to remove residual toner and is repeatedly used for image formation.

As the uniform charging device 2 for the photoreceptor 1, a corona charging device is generally widely used. A contact charging method has also been proposed in which a contact member is provided on the photoreceptor 1 and a voltage is applied to the contact member to charge the photoreceptor.

[Problems to be Solved by the Invention] These charging devices require a so-called pre-exposure step in which the photoreceptor 1 is exposed to light over the entire surface to remove static electricity before the charging step, and a pre-exposure step is performed for the photoreceptor 1 that is used repeatedly. Afterwards, a full-surface exposure step was required in which the photoreceptor was exposed to light to remove any remaining potential.

That is, in order to use the photoreceptor l repeatedly, it is necessary to once eliminate the potential contrast of the electrostatic latent image remaining on one surface of the photoreceptor from the previous image formation before the charging process for the next image formation. There is. This is because in the conventional corona charging device 2, if the potential contrast of the electrostatic latent image from the previous image formation remains and the surface of the photoreceptor is charged for the next image formation, the entire surface of the photoreceptor is charged uniformly. This is because charging cannot be carried out, and the potential contrast caused by the previous electrostatic latent image remains, which appears as a ghost in the next formed image.

Furthermore, even after image formation is completed, it is necessary to attenuate the potential on all surfaces of the photoreceptors 1 and 2 before bringing them to a halt state. This is because if the photoreceptor (1i) is left charged, the characteristics such as sensitivity of the photoreceptor tend to change.

In FIG. 2, reference numeral 7 denotes a photoconductor full-surface exposure device (eraser) disposed at an open position between the charging device 2 and the cleaning device 6 to remove the charge from the photoconductor l. In each repeated image forming cycle, the photoreceptor 1 is uniformly charged by the charging device 2 by being fully exposed to light by the exposure device 7 and subjected to charge removal processing before being charged by the charging device 2 in each repeated image forming cycle. Further, after image formation is completed, the charging device 2 is turned off, and the photosensitive weight is rotated by at least one circumferential surface (post-rotation).
During this time, the entire surface of the photoreceptor is exposed by the exposure device 7 to attenuate the potential on the entire circumferential surface of the photoreceptor, and then the rotation of the photoreceptor is stopped and put on standby.

The present invention eliminates the need for providing a full-surface exposure device 7, etc. for the above-mentioned charge removal process of the photoreceptor by making the charging device also serve as a charge removal device for the photoreceptor, which is an image bearing member, thereby increasing the efficiency of the image forming apparatus. The aim is to make the system more compact, simpler, and lower in cost.

[Means for solving problems]

In the present invention, an image forming process is performed by applying an image forming process including a step of uniformly charging the surface of an image bearing member, in which the rotating acid is rotationally driven, and the image bearing member is used repeatedly to form an image. In the apparatus, the surface of the image carrier is uniformly charged by bringing a conductive member to which a superimposed voltage of a DC voltage and an AC voltage is applied to the surface of the image carrier into contact with the surface of the image carrier; The DC voltage is set to a DC voltage, and the DC voltage is set to a second DC voltage at a level lower than the first DC voltage during post-rotation of at least one circumferential surface of the image carrier after image formation, or during the post-rotation period. The gist of the present invention is an image forming apparatus characterized by:

[Function] (a) Uniform charging of the image carrier surface is performed by contact (direct) charging, which is performed by bringing a voltage-applied conductive member into contact with the image carrier surface, without using a corona charging device; By setting the voltage applied to the conductive member to be a superimposed voltage of the first DC voltage and AC voltage, the potential contrast of the electrostatic latent image from the previous image forming process remains on the surface of the image carrier. Even if the image bearing member surface is charged uniformly in each part without the potential contrast of the previous electrostatic latent image remaining, ghost images due to the residual potential contrast of the previous electrostatic latent image do not actually appear in the output image.

Therefore, there is no need to provide a pre-discharging (exposure) device for once discharging the image carrier surface before the charging process during the pre-rotation or pre-movement period of the image carrier or in each repeated image forming cycle.

Note that, of course, if uniform charging of the image bearing surface is performed using a corona charging device, or if the voltage applied to the conductive member is only DC voltage even in contact charging, it is necessary to install a device that performs static neutralization before the charging process. If not provided, a ghost image will appear or will likely appear due to the residual potential contrast of the previous image formation.

(b) Post-rotational formation for at least one circumferential surface of the image bearing member after image formation is performed is such that during the post-rotation period, the DC voltage applied to the conductive member that is in contact with the surface of the image bearing member is changed to the first rotation voltage at the time of image formation. By setting the second DC voltage to a level lower than the DC voltage, the potential can be uniformly and neatly attenuated in each part of the image bearing surface.

Therefore, the potential remaining on the image carrier after image formation can be attenuated by lowering the level of DC voltage applied to it using a conductive member as a charging device. There is no need to set it up.

〔Example〕

FIG. 1 shows a schematic configuration of an embodiment of the apparatus, and constituent members common to those of the apparatus shown in the example of FIG.

The photoreceptor 1 in this example is an OPC (organic photoconductor) photoreceptor, and the photoreceptor is charged not by a corona charging device as shown in FIG. 2, but by a contact (direct) type charging device.

Reference numeral 20 denotes a conductive member of a contact type charging device that is brought into contact with the photoreceptor 1, and in this example, it is a roller made of conductive rubber (hereinafter referred to as a charging roller). The charging roller 20 has at least a conductive surface and has a resistance of 102 to 1.
08 Ω is appropriate, and in this example, a 105 Ω conductive urethane gum acid roller was used. The charging roller 20 applies a predetermined pressure (for example, a linear pressure of 0.01 to 0.0
．． 2kg/cm) and is kept in constant pressure contact.
In this example, the rotation is driven by the rotation of the photoreceptor 1. The charging roller 20 may be actively driven by a drive source to rotate at a predetermined circumferential speed in the forward or reverse direction of the rotation of the photoreceptor 1, or may be driven non-rotatably with respect to the rotating photoreceptor 1. Pressure contact may also be applied.

Reference numeral 21 denotes a voltage application power supply unit for the charging roller 20, which includes a DC power supply 22 and an AC power supply 23.

Reference numeral 30 denotes a reciprocating type document table glass, and the document O is placed and set on this glass 301- with the image surface facing downward.
The downward image surface of the document O is sequentially illuminated and scanned from one end to the other end by the exposure lamp 31 during the forward or backward movement of the glass, and the reflected light from the document image surface is reflected onto the mirror 32.
33 → imaging lens 34 → mirror 35 → 36 to the exposure unit 3 for the photoreceptor 1, where the light image of the document image is slit-exposed on the surface of the photoreceptor 1.

During the pre-rotation period of the photoreceptor l and each image forming cycle of reversal, the charging roller 20 is supplied with the first D by the DC power supply 22.
A superimposed voltage vDc+vAc of the C voltage vDC and the AC voltage VAC from the AC power supply 23 is applied. In this example, the first DCC voltage oc is -700V, the peak-to-peak voltage V pp is 1500V, and the frequency is 1000H2 (
7) A superimposed voltage with a sinusoidal AC voltage VAC was applied.

As a result, each part of the photoreceptor was uniformly charged to a surface potential of approximately 1,700V.

In this configuration, when the photoreceptor l was repeatedly used to form images, the electrostatic latent image formed by the previous image formation was removed because there was no pre-exposure on the photoreceptor surface immediately before the charging roller 20, which was conventionally required. Although a potential contrast remains, each part of the photoreceptor surface immediately after passing through the charging roller 20 is uniformly charged to -700V over the entire surface of the photoreceptor. Therefore, even without the conventional pre-exposure, ghosts due to previous electrostatic latent images do not occur in the image. Uniform charging property is achieved by contact charging using the roller 20.
This is done by applying a voltage that is a combination of a DC voltage and an AC voltage. By the way, when the photoconductor was charged with only DC voltage, the photoconductor surface potential was charged to about -700V by applying a DC voltage of -1200V to -1300V, but the uniformity of charging was quite poor, and the photoconductor When 1 was used repeatedly, the potential contrast of the previous electrostatic latent image remained and appeared as a ghost in the image. The reason why uniform charging is achieved by superimposing an AC voltage is not clearly understood, but it is thought that the charging mechanism is due to a discharge phenomenon that occurs at or near the contact area between the roller 20 and the photoreceptor 1. It is thought that the uniformity of charging is improved because reverse discharge occurs from the photoreceptor 1 to the charging roller 20.

In this way, the photoreceptor 1 is repeatedly used to form an image, and when the image formation is completed, the electric potential remaining on the photoreceptor 1 is attenuated and supplied to the charging roller 20 in order to enter the standby state. The level of the DC voltage of the voltage is lowered from the first DC voltage -700V to the second DC voltage -100V. That is, at least one of the photoconductors l after image formation is completed.
In the post-rotation period for the circumferential surface, -toov (7) Second DC voltage DCM, voltage vI)c, and peak-to-peak voltage V $
1-P='1500V, frequency 1000H2 (7) A voltage superimposed on the sine wave AC voltage VAC is applied to the charging roller 20.

As a result, the surface potential on the photoreceptor l is approximately -10
The voltage is attenuated to 0V, which is the same potential as that obtained by exposing the entire surface of the photoreceptor to substantially eliminate the charge.

Thereafter, all voltages are turned off to stop the rotation of the photoreceptor 1 and enter a standby state. Therefore, even if the photoreceptor is left as it is, there will be no change in the characteristics of the photoreceptor.

In the above embodiment, the second DC voltage after image formation was set to -100V, but this value is set to a potential value that does not cause any change in the characteristics of the photoreceptor used even if it is left as it is. Just set it.

More preferably, the potential of the photoreceptor is set to be lower than the potential at which static electricity is substantially removed by strong vibration light.For various ordinary photoreceptors, there is no problem if the second DC voltage is set to 50V or less. Probably.

〔Effect of the invention〕

As described above, according to the present invention, image formation is performed by applying an image forming process including a step of uniformly charging the surface of an image carrier that is rotated or rotationally driven, and the image carrier is For image forming apparatuses that are used repeatedly, the charging device of the image bearing member can perform the static electricity removal process required for good image formation. There is no need to provide (exposure) equipment and post-static elimination (exposure) equipment, and this type of image forming apparatus can be made as compact, simple, and cost-effective as possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the apparatus, and FIG. 2 is a diagram of an example of the conventional apparatus. 1 is a rotating drum type photoreceptor, 2 is a charging device, 3 is a photo-image exposure section, 4 is a developing device, 5 is a transfer device, 6 is a cleaning device, 7 is a full-surface exposure device for static elimination, 8 is a fixing device, 2
1 is a power supply section, 22 is a DC power supply, and 23 is an AC power supply. Procedural amendment (practical) 1. Display of the case 1986 Patent Application No. 313905 2, Name of the invention Image forming device 3, Person making the amendment Relationship to the case Patent applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (100)
) Canon Co., Ltd. Representative Ryuzo Kaku
Part 4, Agent's residence: 3-30-25 Shimomaruko, Ota-ku, Tokyo 146, Japan Description subject to amendment 6, Contents of amendment (1) The scope of claims is amended as shown in the attached sheet. (2) On page 8, line 14 of the specification, "after J for charging device"
Insert the charging member barrel. Claim 11 Rotational formation is an image forming process in which an image forming process is applied to the surface of a rotatably driven image carrier, including a step of uniformly charging the surface of the image carrier, and the image carrier is used to form images that can be used repeatedly. In the forming apparatus, the surface of the image carrier is uniformly charged by bringing a charging member to which a superimposed voltage of a DC voltage and an AC voltage is applied to the surface of the image carrier into contact with the surface of the image carrier; The DC voltage is set to a DC voltage, and the DC voltage is set to a second DC voltage at a level lower than the first DC voltage during a post-rotation of at least one circumferential surface of the image carrier after image formation, or during a post-mouthing period. An image forming apparatus characterized by:

Claims (1)

[Claims] 1. Image formation is performed by applying an image forming process that includes a step of uniformly charging the surface of the image carrier to be rotated or rotationally driven, and the image carrier is repeatedly charged. In the image forming apparatus used, the surface of the image carrier is uniformly charged by contacting the conductive member to which a superimposed voltage of DC voltage and AC voltage is applied, and the DC voltage is applied during the image forming process. is set to a first DC voltage, and the DC voltage is set to a first DC voltage lower than the first DC voltage during post-rotation of at least one peripheral surface of the image bearing member after image formation, or during the post-rotation period. An image forming apparatus characterized in that the DC voltage is set to 2. 2. The image forming apparatus according to claim 1, wherein the second DC voltage is set to a voltage lower than a potential at which static electricity is substantially removed from the photoreceptor by intense exposure.