JPH0437776A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the occurrence of a toner fused part on the surface of a body to be electrified caused by a vibrating voltage component by applying a direct current voltage when an image is not formed, in this image forming device using a contact type electrifier applying the superimposed voltage of a direct current voltage component and the vibrating voltage component and carrying out the electrifying processing of the body to be electrified. CONSTITUTION:After getting the image forming period of a first sheet, a switch 6 is changed over to the side of a first contact point (a), the DC bias of a direct current power 4, an ac power 5 and the superimposed voltage of an AC bias are applied on an electrifying roller 2, and the processes of an exposure L, development and a transfer are executed. An interval till the copying of the first sheet is finished and the copying of a second sheet is executed is a sheet one, and a time not to form the image. The rotational driving of a drum 1 is continued in this sheet interval, but the switch 6 is changed over to the side of a second contact point (b), and only the DC bias of the direct current power 4 is applied on the electrifying roller 2. Therefore, the AC bias is not applied on the electrifying roller 2, so that the occurrence of the toner fused part causing that a developer is firmly stuck to the surface of the drum 1 by the AC bias is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is applicable to electrostatically charged devices, such as image forming devices such as transfer-type electrophotographic devices (copiers, optical printers, etc.) and electrostatic recording devices. Image formation is performed by applying an image forming process that includes a process of charging the surface of an image carrier (electrophotographic photoreceptor, electrostatic recording dielectric, etc.) as a body, and the image carrier is repeatedly subjected to image formation. The present invention relates to an image forming apparatus that provides a system for providing an image.

A transfer-type image in which the image formed on the surface of the image carrier is transferred to a recording material, the image carrier after the image transfer is cleaned by a cleaning means to remove residual developer, etc., and the image carrier is repeatedly used for image formation. In addition to the forming device, there is also an image display device (display device, reader, etc.) in which the formed image is removed from the image carrier surface by a cleaning means without being transferred after displaying or reading the image formed on the image carrier surface. It also includes an image forming apparatus configured to repeatedly perform image formation.

More specifically, the present invention relates to an image forming apparatus that uses a contact-type charging device as a charging processing means for a charged object, which charges the surface of the charged object by bringing a charging member to which a voltage is applied into contact with the charged object.

(Prior Art) In the above-mentioned image forming apparatus, a corona discharge device has been widely used as a device for charging the surface of an image carrier as a charged body.

A corona discharge device is effective as a means for uniformly charging the surface of an object to be charged, such as an image carrier, to a predetermined potential. but,
It requires a high-voltage power supply and has problems such as the generation of undesirable ozone due to corona discharge.

In contrast to such corona discharge devices, contact-type charging devices, which charge the surface of a charged object by bringing a conductive charging member to which a positive or negative voltage is applied, into contact with the surface of the charged object, can reduce the voltage of the power source. Because of its advantages such as low ozone generation, it can be used instead of a corona discharge device in image forming apparatuses to charge the surface of image carriers such as photoreceptors, dielectrics, and other objects to be charged. It has attracted attention as a processing means device,
Research on its practical application is underway.

For example, the present applicant first proposed (Patent Application No. 62-51492
No. 62-230334, etc.), an oscillating voltage ( (Alternating voltage, voltage whose voltage value changes periodically over time; hereinafter referred to as AC voltage or AC component)
Applying a superimposed voltage of and a DC voltage to a charging member,
By using a charging member with a high resistance layer on its surface,
It is possible to improve the uniformity of charging of the charged object and to prevent leakage due to holes, scratches, etc. on the surface of the charged object such as a photoreceptor.

The charging member is generally of a roller type or a plate type, and may also be of a rond type, a pad type, a block type, or the like.

(Problems to be Solved by the Invention) A device that applies a superimposed voltage of a DC component and an AC component to a charging member to perform charging processing on the surface of the charged object has good uniformity and stability of charging, but this is not the case as described above. The following problems can be raised when the image forming apparatus is used as a charging processing means for the surface of an image carrier as a charged member in an image forming apparatus.

That is, after the image bearing member undergoes a transfer process or the like or after the image is read, it is cleaned by a cleaning means to remove residual developer, paper powder, and other adhering residues or images, and the clean surface or image is removed. The carrier is charged again by a charging member that is in contact with the carrier surface and used for image formation repeatedly.
In this case, residual adhesion such as untransferred developer on the surface of the image bearing member may slip through the cleaning means and reach the contact area between the image bearing member and the charging member.

Then, the spilled developer, etc., may be transferred to the contact area between the image carrier and the charging member due to the charging member due to the AC component being applied to the charging member, or due to the electrical/mechanical vibrations of the charging member and the image carrier. The toner is strongly pressed against the surface of the image carrier and firmly adheres to the surface of the image carrier in an embedded manner, and a so-called toner (developer) fused portion is likely to occur on the surface of the image carrier. The occurrence of toner fused portions on the surface of the image carrier impedes uniform charging of the surface of the image carrier, causing deterioration in the quality of the formed image.

The present invention is also an image forming apparatus using a contact type charging device that applies a superimposed voltage of a DC component and an AC component to a charging member to charge an image bearing member as a charged body. It is an object of the present invention to provide an image forming apparatus which can always and stably form high-quality images by suppressing the occurrence of toner fusion on the surface of an image carrier as much as possible.

(Means for Solving the Problems) The present invention executes image formation by applying an image forming process to a charged object including a charging process for the surface of the charged object, and the charged object is repeatedly subjected to image formation. It is a contact-type charging device in which the charge processing means for the charged object is a contact-type charging device that performs charging by bringing a charging member to which a voltage is applied into contact with the charged object, and performs image formation on the charged object. The image forming apparatus is characterized in that a superimposed voltage of a DC voltage component and an oscillating voltage component is applied to the charging member to perform charging processing on the surface of the charged object, and a DC voltage is applied when an image is not formed.

The present invention also provides the above-mentioned image forming apparatus, which is provided with a means for removing deposits such as developer transferred from the charging member to the charging member, and that when an image is not formed, the charging member and the charged member are separated from each other when an image is not formed. having a means for weakening the contact pressure of the
This image forming apparatus is characterized by the following.

(Function) That is, when an image is not formed on the image bearing member as a charged body in the driving state of the device other than when image formation is being executed, specifically, during a predetermined device warming period (image formation) after the device power is turned on. a predetermined pre-rotation period of the image carrier after the image formation start signal is input, a paper gap between one image formation and the next image formation, and the end of the last image formation. During a predetermined post-rotation period of the image bearing member, etc., the alternating current component of the voltage applied to the charging member is cut off and only the direct current component is used. Since the occurrence of toner fused areas on the surface of the image carrier due to the components is prevented, the occurrence of toner fused areas throughout the entire image forming cycle can be suppressed as much as possible. This makes it possible to continue to stably form high-quality images.

By providing a means for removing deposits such as developer that have migrated from the image carrier side as a charged body to the charging member from the charging member, it is possible to prevent deposits that have migrated to the charging member from re-adhering to the image carrier. The occurrence of toner fused areas is prevented.

When an image is not formed, by providing means for weakening the contact pressure between the image bearing member as a charged body and the charging member, the image of the spilled developer etc. is removed from the contact area between the image bearing member and the charging member. The pressing force against the surface of the image carrier becomes weaker, and the toner is transferred to the charging member side and is more easily removed from the surface of the image carrier, so that it is possible to further prevent the formation of toner fused portions on the surface of the image carrier.

(Embodiments) <Embodiment 1> FIG. 1 shows a schematic configuration of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a transfer type, rotating drum type copying machine or printer using an electrophotographic process.

Reference numeral 1 denotes an image bearing member as a charged member, and the one in this example is a drum-shaped electrophotographic photoreceptor (
(hereinafter referred to as drum). The tram 1 is rotated clockwise as indicated by an arrow at a predetermined circumferential speed (process speed).

Reference numeral 2 denotes a charging roller as a charging member that is brought into contact with the surface of this drum. The charging roller 2 consists of a central core bar 2C, a conductor roller portion 2b formed on the outer periphery of the core bar 2C, and a resistance layer 2a further formed on the outer periphery of the core bar 2C.Both ends of the core bar 20 are rotatably mounted on bearing members (not shown) is pressed against one surface of the drum with a predetermined pressing force by a pressing means (not shown),
It rotates as the drum I rotates.

Reference numeral 3 denotes a power supply unit for the charging roller 2, which includes a DC power supply 4, an AC power supply 5, and a changeover switch 6.

The switch 6 is automatically switched and controlled by a control unit (not shown), and by switching to the first contact a side, a superimposed voltage of DC voltage and AC voltage from the DC power source 4 and the AC power source 5 is applied to the charging roller 2. By switching to the second contact side, only the DC voltage from the DC power supply 4 is applied to the charging roller 2.

When performing image formation, the switch 6 is switched to the first contact a side, and the surface of the drum is uniformly and primarily charged to a predetermined polarity and potential.

The surface of the drum 1, which has been uniformly charged by the charging member 2, is then exposed to target image information (laser beam scanning exposure, slit exposure of the original image, etc.) by an exposure means (not shown), so that the target image is formed on its peripheral surface. An electrostatic latent image corresponding to image information is formed. The latent image is then sequentially visualized as a toner image by the developing means 11.

The toner image is then transferred to a transfer material 14 by the transfer means 12 from a paper feeding means (not shown) to a transfer section between the drum 1 and the transfer means 12 at an appropriate timing in synchronization with the rotation of the drum 1. The images are transferred one after another onto the surface of the screen.

The transfer material 14 to which the toner image has been transferred is separated from the surface of the drum and conveyed to the image fixing means 16, where the image is fixed.
It is output as an image formed product.

Alternatively, if an image is to be formed on the back side as well, the sheet is conveyed to a re-conveying means to the transfer section.

After the image has been transferred, the surface of the drum 1 is cleaned by cleaning means 13 (blade cleaning in this example) to remove adhered contaminants such as residual toner after transfer, and is further cleaned by static eliminating exposure device 15.
The charge is removed by the process, and the sample is repeatedly used for image formation.

FIG. 2 shows a voltage application control sequence by the power supply section 3 to the charging roller 2. As shown in FIG.

This example is for the case of continuous copying (or printing, hereinafter the same) of two sheets.

(2) When the device power is turned on, rotation of the tram 1 is started, and the device enters a predetermined period of warming period (pre-multi-rotation period), during which heating of the fixing device, etc. is executed. During this period, an image is not formed, the switch 6 is switched to the second contact side, and the charging roller 2 is connected to the DC power source 4.
Only the DC voltage (DC bias) is kept applied.

(2) When the predetermined device warming period ends, the rotation of the tram 1 is stopped, the DC bias to the charging roller 2 is turned off, and the device is in a standby state until the next copying (printing) start signal is input to the control unit. is maintained.

(2) When the copy start signal is input to the control unit, the tram 1 is driven to rotate and enters a predetermined pre-rotation period, during which no image is formed, and the switch 6 is switched to the second contact side and held. The charging roller 2 is maintained in a state where only the DC bias from the DC power source 4 is applied.

(2) When the predetermined pre-rotation period ends, the first image forming period begins, and the switch 6 is switched to the first contact a side and held, and the charging roller 2 is supplied with a predetermined DC bias of the DC power supply 4 and the AC power W5. A superimposed voltage of AC bias is applied, primary charging of the drum surface to a predetermined polarity and potential is performed, and the processes of exposure L, development, and transfer are performed, and the first copy is made. Ru.

(2) The period from the end of copying the first sheet until the copying of the next second sheet is executed is a paper interval and is a time when no image is formed. During this interval, the rotation of the drum unit continues, but the switch 6 is switched to the second contact side, and only the DC bias from the DC power supply 4 is applied to the charging roller 2.

(2) When the second image forming period begins, the switch 6 is switched to the first contact a side and held, and the charging roller 2 is connected to the DC power supply 4.
Then, a superimposed voltage of DC bias and AC bias from the AC power source 5 is applied, primary charging of the drum 1 surface to a predetermined polarity and potential is performed, and a second copy is made.

(2) When the second sheet (last sheet) has been copied, the tram 1 enters a predetermined post-rotation period, during which no image is formed, the switch 6 is switched to the second contact, and the charging roller 2 is maintained in a state where only the DC bias of the source 4 is applied.

(2) When the predetermined post-rotation period ends, the rotational drive of the tram 1 is turned off, the bias application to the charging roller 2 is turned off, and the apparatus is maintained in a standby state until a copy start signal is input again.

In this way, in a series of image forming cycles, when the drum 1 is not forming an image during the pre-multi-rotation period, pre-rotation period, inter-sheet period, post-rotation period, etc., the voltage applied to the charging roller 2 is cut off from the AC bias and only the DC bias is applied. By controlling the switch to the state in which the image is formed, even if there is developer that slips through the cleaning member such as the cleaning blade of the cleaning means 13 and spills onto the contact area between the drum 1 and the charging roller 2, charging is prevented. Since no AC bias is applied to the roller 2, the developer may adhere firmly to the surface of the drum due to electrical and mechanical vibrations caused by the AC bias, thereby creating a toner fused portion. Prevented. That is, the occurrence of toner fusion on the drum is suppressed as much as possible throughout the entire image forming cycle, and high quality images can be stably formed and output.

<Embodiment 2> In this embodiment, the DC bias applied to the charging roller 2 during non-image formation is set to be a polarity bias opposite to that of the toner (developer).

In the power supply section 3 in FIG. 3, 4a is a first DC power supply;
b is a second DC power supply. During image formation, the switch 6 is switched to the first contact a side, so that the charging roller 2 is supplied with the DC bias of the first DC power supply 4a and the AC power supply 5, and the AC
By applying a bias superimposed voltage, the surface of the drum is uniformly and primarily charged at a predetermined polarity and potential. During non-image formation, the switch 6 is switched to the second contact side, and a DC bias having a polarity opposite to that of the toner from the second DC power source 4b is applied to the charging roller 2 (sequence diagram in FIG. 4). reference).

By applying a DC bias of the opposite polarity to the toner to the charging roller 2 during non-image formation in this way, the toner does not slip through the cleaning means 13 and fall into the contact area between the tram 1 and the charging roller 2. The charged toner is transferred to charging roller 2.
By actively adhering to the side by electrostatic force and being removed (cleaned) from the surface of the drum, fusion to the surface of the drum can be more effectively prevented.

<Embodiment 3> In this embodiment (Fig. 5), as in the above-mentioned Embodiment 2 (Fig. 3), a DC bias having a polarity opposite to that of the toner is applied to the charging roller 2 during non-image formation. At this time, the toner that is adhered from the drum 1 side to the charging roller 2 side by electrostatic force and removed from the drum 1 side is collected by a cleaning means 7 (cleaning plate type in this example) arranged to act on the charging roller 2. This is to keep the two surfaces of the charging roller clean.

That is, the toner adhering to the charging roller 2 side is scraped off from the surface of the charging roller 2 by the plate 7a and the pick sheet 7b due to the driven rotation of the charging roller 2 as the tram 1 rotates.
Since it is collected in the cleaner container 7c, charging failures due to dirt such as toner adhering to the circumferential surface of the charging roller 2 are prevented, and re-adhesion of dirt such as toner to the surface of the drum 1 is prevented.
This prevents toner from fusing on the drum.

By providing the charging roller cleaning means 7 in this way, the charging roller 2 can also be used as a cleaning means for the drum 1, and the dedicated drum surface cleaning means 13 on the upstream side of the drum surface movement direction of the charging roller 2 can be used as a cleaning means for the drum 1. It is also possible to omit it.

Embodiment 4 This embodiment is similar to Embodiment 2, in which a DC bias of opposite polarity to the toner is applied to the charging roller 2 when not forming an image, but when forming an image (see FIG. A
)) means 8 for bringing the charging roller 2 into pressure contact with the surface of the drum;
For example, the pressure contact force of the charging roller by the electromagnetic pressure contact means is maintained in a strong state, the pressure contact nip portion Na between the tram 1 and the charging roller 2 is increased, and a desired pressure contact state is ensured. In (B)), the charging roller pressing force by the pressing means is switched to a weakened state so that the pressing nip Nb between the drum 1 and the charging roller 2 is kept small.

That is, during non-image formation, the contact pressure of the charging roller 2 against the drum 1 is weakened, so that toner adhering to the surface of the drum 1 is easily removed from the charging roller 2 by electrostatic force.

In this embodiment as well, the charging roller 2
By providing the cleaning means 7, the same effect as in the third embodiment can be obtained.

The roller-type charging member 2 may be driven to rotate by the image carrier 1 as a charged member which is driven in plane movement, or it may be non-rotating, or it may be rotated in the forward direction in the plane movement direction of the image carrier 1. Alternatively, it may be actively rotated in the opposite direction at a predetermined circumferential speed. It is also possible to use a belt member that is rotationally driven or rotationally driven.

In addition to the roller type and belt type, the charging member 2 is also available in blade type, block type, lot type, etc.
It can be configured in a web-like form.

Blade-shaped, rod-shaped, etc. are rotatable, and in the case of a roller type, there is no sliding contact for power supply required to apply a bias voltage to the cored metal member 2c. The lead wire leading to power supply #3 can be connected directly, with the advantage of eliminating electrical noise that may be generated from the power supply sliding contact.
According to the present invention, as described above, the superimposed voltage of the DC voltage component and the oscillating voltage component is applied to the charging member. For image forming apparatuses that use contact-type charging devices that charge the charged object by applying voltage to the charged object, this method is effective in reducing the occurrence of toner fusion on the surface of the charged object due to electrical and mechanical vibrations caused by oscillating voltage components. This means that it is possible to reduce the amount of noise and to consistently form high-quality images in a stable manner, and the intended purpose is well achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. FIG. 2 is a sequence diagram of applying bias to the charging roller. FIG. 3 is a diagram of another configuration example of the bias application power supply section. FIG. 4 is a sequence diagram of applied bias control by the power supply section. FIG. 5 is a schematic diagram of the structure of an example in which a cleaning means is added to the charging roller. FIG. 6 is a schematic diagram of the configuration of an example in which a means for controlling the strength of the contact pressure of the charging roller against the drum is provided. FIG. 6 (A) is a state diagram during image formation, and FIG. 6 (B) is a state diagram during non-image formation. state diagram. 1 is an image carrier (electrophotographic photosensitive drum) as a charged body
, 2 is a charging roller as a charging member, 3 is a bias application power supply section, 4, 4a, 4b are DC power supplies, 5 is an AC "a" power supply,
6 is a changeover switch.

Claims (3)

[Claims] (1) An image forming apparatus that forms an image by applying an image forming process that includes a charging process on the surface of the charged body to a charged body, and repeatedly subjects the charged body to image formation; The body charging processing means is a contact-type charging device that performs charging by bringing a charging member to which a voltage is applied into contact with the charged object, and when performing image formation on the charged object, a DC voltage component and an oscillating voltage are applied to the charging member. An image forming apparatus characterized in that a superimposed voltage of components is applied to perform a charging process on a surface of a charged object, and a DC voltage is applied when an image is not formed. (2) The image forming apparatus according to claim 1, further comprising means for removing deposits such as developer transferred from the charging member to the charging member. (3) The image forming apparatus according to claim 1, further comprising means for weakening the contact pressure between the charged member and the charging member when an image is not formed.