JPH0524516B2 - - Google Patents

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 1 is uniformly charged to 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 transferred transfer material P.

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 as a copy outside the machine.

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.

A corona charging device is generally widely used as the uniform charging device 2 for the photoreceptor 1. 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 entire surface of the photoreceptor 1 is exposed to light to remove static electricity before the charging step, and a step in which the image formation is completed. 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 repeatedly use the photoreceptor 1,
It is necessary to temporarily eliminate the potential contrast of the electrostatic latent image remaining on the surface of the photoreceptor from the previous image formation before the charging step for the next image formation. 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 due to the previous electrostatic latent image remains, which appears as a ghost in the next formed image.

Further, even after image formation is completed, it is necessary to eliminate the potential on all surfaces of the photoreceptor 1 before bringing it to a halt state. This is because if the photoreceptor is left charged, 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 between the charging device 2 and the cleaning device 6 in order to eliminate static electricity from the photoconductor 1.
shows. 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. After the image formation is completed, the charging device 2 is turned off and the photoreceptor 1 is rotated by at least one circumference (post-rotation). During this time, the entire surface of the photoreceptor is exposed by the exposure device 7 to increase the potential of the entire circumference of the photoreceptor. After attenuation, 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. Miniaturization/
The purpose is to simplify and reduce costs.

[Means for solving problems]

an image carrier, an image forming means for forming an image on the image carrier, and a contact member that contacts the image carrier;
Voltage applying means for applying voltage to the contact member;
In the image forming apparatus, the voltage applying means applies a first voltage including a first DC component and an AC component to the contact member when charging the image carrier; and a second applying means for applying a second voltage including a second DC component and an AC component to the contact member when static electricity is removed from the image carrier, and the second DC component is equal to or higher than the first DC component. It is characterized by being smaller than its components.

[Effect]

(a) Uniform charging of the surface of the image carrier is performed by contact (direct) charging by bringing a conductive member to which a voltage is applied into contact with the surface of the image carrier, without using a corona charging device;
In addition, by setting the voltage applied to the conductive member in that case 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 surface remains unchanged, each part of the image bearing surface is uniformly charged without the potential contrast of the previous electrostatic latent image remaining, and in practice, a ghost image appears in the output image due to the residual potential contrast of the previous electrostatic latent image. There is no.

Therefore, during the pre-rotation or pre-movement period of the image carrier or in each repeated image forming cycle, the surface of the image carrier is subjected to a pre-neutralization process (exposure) before the charging step.
There is no need to install equipment.

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) During the post-rotation or post-rotation period for at least one circumferential surface of the image carrier after the completion of image formation, the DC voltage applied to the conductive member that is in contact with the surface of the image carrier is changed to the first voltage at the time of image formation. A second voltage at a level lower than the DC voltage.
By setting the DC voltage to , 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 the DC voltage applied to it using a conductive member as a charging device, so a dedicated post-static discharge (exposure)
There is no need to install equipment.

[Embodiment] FIG. 1 shows a schematic configuration of an apparatus according to an embodiment. Components common to those of the apparatus shown in 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) charging device.

Reference numeral 20 denotes a conductive member serving as a charging member of a contact type charging device 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 its resistance is suitably 10 ² to ^{10 8} Ω, and in this example, a roller made of conductive urethane rubber with a resistance of 10 ⁵ Ω was used. The charging roller 20 applies a predetermined pressure (for example, a linear pressure of 0.01 to 0.01 to
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 to rotate in a non-rotational manner 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.

30 is a reciprocating type original table glass,
is set on this glass 30 with the image surface facing downward, and the downward image surface of the document O is illuminated and scanned sequentially from one end to the other end by the exposure lamp 31 during the forward or backward movement of the glass. The reflected light from the original image surface passes through the mirror 32 → mirror 33 → imaging lens 34 → mirror 35 → mirror 36 and reaches the exposure section 3 for the photoreceptor 1, and a light image of the original image is formed on the photoreceptor 1 surface. Exposure L is applied.

During the pre-rotation period of the photoreceptor 1 and in each repeated image forming cycle, the charging roller 20 is supplied with a DC power source 22.
by the first DC voltage V _DC and by the AC power supply 23
A superimposed voltage V _DC +V _AC with the AC voltage V _AC is applied. In this example, the first DC voltage V _DC is −700V.
and peak-to-peak voltage V _PP = 1500V, frequency 1000
A superimposed voltage with a sinusoidal AC voltage V _AC of Hz was applied. As a result, each part of the photoreceptor was uniformly charged to a surface potential of approximately -700V.

In this configuration, when the photoreceptor 1 is repeatedly used to form images, the electrostatic latent image formed by the previous image formation is removed because there is no pre-exposure on the surface of the photoreceptor just before the charging roller 20, which is conventionally required. Although a potential contrast remains, the surface of the photoreceptor immediately after passing through the charging roller 20 is uniformly charged to −700 V 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. The uniform electrical property is achieved by applying a voltage that is a superimposition of a DC voltage and an AC voltage during contact charging by the roller 20. By the way, if you charge the photoconductor only with DC voltage, the DC voltage will be -1200V ~
When −1300V is applied, the photoreceptor surface potential is approximately −
Although it was charged to 700 V, the uniformity of the charging was quite poor, and when the photoreceptor 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 AC voltage is not completely clear, but the charging mechanism is
This is thought to be due to a discharge phenomenon that occurs at or near the contact area between the photoreceptor 1 and the photoreceptor 1 due to the AC voltage.
It is thought that the uniformity of charging is improved because reverse discharge occurs from the charging roller 20 to the charging roller 20.

In this way, the photoreceptor 1 is repeatedly used to form images, and when the image formation is completed, the photoreceptor 1
The voltage supplied to the charging roller 20 is increased in order to attenuate the potential remaining in the charging roller 20 and enter the stop/standby state.
The level of the DC voltage is lowered from the first DC voltage -700V to the second DC voltage -100V. That is, during the post-rotation period for at least one circumferential surface of the photoreceptor 1 after the completion of image formation, the second DC voltage V _DC of -100V is applied.
and peak-to-peak voltage V _PP = 1500V, frequency 1000
A voltage superimposed on the Hz sinusoidal AC voltage V _AC is applied to the charging roller 20 .

As a result, the surface potential on the photoreceptor 1 is attenuated to approximately -100V over the entire surface, which is equivalent to the potential at which the entire surface of the photoreceptor is exposed and the charge is substantially removed. 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 the work was completed was set to -100V, but this value was set at a potential value that would not cause any change in the characteristics of the photoreceptor used even if it was left as it was. do it. More desirably, the potential is set to be lower than the potential at which the photoreceptor is substantially neutralized by intense exposure. For various ordinary photoreceptors, there will be no problem if the second DC voltage is set to 50V or less.

〔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 and 20 are charging devices, 3 is a photoimage 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, 21 is a power supply unit, 22 is a DC power supply, and 23 is an AC power supply.

Claims (1)

[Scope of Claims] 1. An image carrier, an image forming device that forms an image on the image carrier, a contact member that contacts the image carrier, and a voltage application device that applies voltage to the contact member; In the image forming apparatus, the voltage applying means applies a first voltage including a first DC component and an AC component to the contact member when charging the image carrier;
When discharging the image carrier, a second contact member is applied to the contact member.
an image forming apparatus comprising a second voltage applying means for applying a second voltage including a DC component and an AC component, the second DC component being smaller than the first DC component.