JP2687582B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus. More specifically, it is an image carrier such as an electrophotographic photosensitive member and an electrostatic recording dielectric, and an image forming unit for forming a toner image on the image carrier, the image carrier being in contact with the image carrier. An image forming unit including a charging member that charges the image carrier, a transfer member that forms a nip portion with the image carrier, and a transfer member that transfers the toner image from the image carrier to a transfer material at the nip portion, And an image forming apparatus having the following.

(Prior Art) As a transfer means, a transfer member that forms a nip portion with an image carrier and transfers a toner image from the image carrier to a transfer material at the nip portion, generally a transfer roller is adopted. When the image is formed up to the rear end of the transfer material surface, the developer (toner) on the surface of the image carrier scatters and the transfer roller is easily soiled with the developer. Since this causes troubles such as winding of the transfer material around the transfer roller, it is necessary to add complicated means for cleaning the transfer roller.

As one of effective means for preventing or reducing the developer stain on the transfer roller, for example, 5 mm at the rear end of the transfer material is used.
A surface area having a width of about a non-image portion (margin portion) is set, that is, a transferable image is not formed on a surface portion of the image carrier corresponding to the width surface area at the rear end of the transfer material.

As means for making the rear end of the transfer material surface a non-image area in order to prevent / reduce the developer stain on the transfer roller, conventionally, for example, in the case of an electrophotographic apparatus, a surface of a photosensitive member, which is an image bearing member, is charged. The required area was subjected to an exposure process by the following means to form a non-image area portion (non-charged area portion) to which the developer does not adhere.

. It is exposed by a light source for forming a non-image area.

. A movable reflector is provided, and the light of the image forming light source is branched and exposed.

. When a non-image area is formed at the front end or the rear end of the transfer material, white plates are provided before and after the back surface of the document table.

(Problems to be solved by the invention) However, the conventional example has a drawback that the device is complicated and large.

When the non-image portion is formed at the rear end by this method, it is difficult for a small-sized transfer material.

Further, in a sheet-through type image forming apparatus without a document table, the above method cannot be adopted.

The present invention has been proposed in view of the above, and the developer (toner) scatters at the trailing edge of the transfer material regardless of whether the image forming apparatus has a document table or a sheet-through type image forming apparatus having no document table. In order to prevent the transfer member from being contaminated by the developer, the desired portion on the rear end side of the transfer material surface can be easily made into a non-image area, and the means structure is simple and the overall size and simplification of the apparatus can be simplified. It is an object of the present invention to provide an image forming apparatus of this type that enables cost reduction.

(Means for Solving the Problem) The present invention is an image forming apparatus having the following configuration.

(1) An image forming unit for forming an image bearing member and a toner image on the image bearing member, the image forming unit including a charging member that contacts the image bearing member to charge the image bearing member, An image forming apparatus having a transfer member that forms a nip portion with an image carrier, the transfer member transferring the toner image from the image carrier to the transfer material at the nip portion. An image forming apparatus, further comprising switching means for switching a voltage applied to the charging member to form a blank portion.

(2) The image forming apparatus according to claim 1, wherein the switching unit switches a voltage applied to the charging member in order to form a blank portion at a leading end portion of the transfer material.

(3) The image forming apparatus according to claim 1 or 2, wherein an oscillating voltage is applied to the charging member, and the switching unit switches a vibration center of the oscillating voltage.

(Function) As a means for uniformly charging the surface of an object to be charged such as an image bearing member, a corona discharger such as a corotron or a scorotron having a good uniform charging property is widely used. However, the corona discharger requires an expensive high-voltage power supply, requires space such as itself and a shield space for the high-voltage power supply, and often generates corona products such as ozone.
There is a problem that a mechanism is required, and these are factors that increase the size and cost of the device.

Therefore, recently, the use of contact charging means (direct charging means) is being considered in place of the corona discharger, which has many problems. Contact charging is performed by contacting a conductive member (charging member) to which a voltage (for example, a DC voltage of about 1 to 2 KV, or a superimposed voltage of a DC voltage and an AC voltage) is applied by a power source to the surface of the image bearing member as a member to be charged. By charging the surface of the image carrier directly, the surface of the image carrier is charged to a predetermined potential by a roller charging method (JP-A-56-91253) or a blade charging method (JP-A-56-194349). No. 60-147756), charging / cleaning combined type (JP-A-56-165166) and the like have been devised.

This contact charging means has a characteristic that the applied voltage can be lowered even if a corona product is generated, and the applied voltage is low, and the charging width is narrow, the rise after voltage application is fast, and the voltage application is stopped. Alternatively, it has a feature that the charging process on the surface of the image carrier can be rapidly stopped by lowering the applied voltage level or separating the charging member from the surface of the image carrier.

The present invention positively utilizes the above characteristics of the contact charging means.

That is, as described above, the contact charging means is used as the uniform charging processing means for the image carrier, and the contact charging means is synchronized with the transfer material conveyance or the document conveyance or the exposure scanning in a predetermined manner, for example, the transfer material or the document. Of the front end or the rear end of the charging member is provided, and the voltage applied to the charging member is controlled in a predetermined manner based on the detection signal, for example, the ON / OFF control of the voltage applied to the charging member, or the applied voltage is controlled. In the case of an oscillating voltage, the center of the oscillating voltage is shift-controlled, that is, by switching the oscillating center of the oscillating voltage, the surface of the image carrier is moved at a predetermined position along the relative surface moving direction with the charging member. It is possible to easily perform alternating charging / non-charging processing with an arbitrary width by sharply dividing the charging processing area surface portion having a predetermined potential and the non-charging processing area surface portion to which the developer does not adhere.

Since the surface portion of the non-charge-treated area of the image carrier is a non-image area for the transfer material, the contact charging means is controlled as described above in a predetermined synchronization with the conveyance of the transfer material, the conveyance of the document, or the exposure scanning. Thus, in order to prevent / reduce the developer stain on the transfer member, the predetermined width area at the rear end of the transfer material can be easily made into a non-image area portion with a simple configuration.

Since the charging width of the charging member is narrow, the boundary between the blank area and the image area can be sharpened, and the small blank area can prevent the transfer member from being contaminated due to the scattering of the developer at the trailing edge of the transfer material.

The invention can be applied to an image forming apparatus having a document table or a sheet-through type image forming apparatus having no document table without any problem.

Since this is not a static elimination method by exposure, a dielectric (insulator) is used as the image carrier, its surface is uniformly charged, and the charged surface is selectively neutralized by static elimination means other than exposure to form a latent image. It can also be applied to a transfer type image forming apparatus based on the image principle.

(Embodiment) FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The apparatus of this example is a transfer type electrophotographic copying machine equipped with a reciprocating type document table 50.

In the figure, 1 is a machine, 2 is a drum type electrophotographic photosensitive member (hereinafter abbreviated as photosensitive member) as an image bearing member,
It is rotationally driven around the support shaft 2a in the clockwise direction indicated by the arrow at a predetermined peripheral speed (process speed).

Reference numeral 3 is a contact charging member as a means for uniformly charging the peripheral surface of the photoconductor. The contact charging member 3 of this example is a blade type member made of conductive rubber or the like, and is pressed against the surface of the photoconductor 2 at a predetermined constant pressure.

Reference numeral 4 denotes a voltage application source for the contact charging member 3, and in this example, an oscillating voltage obtained by superimposing a pulsating voltage having a peak-to-peak voltage that is at least twice the charging start voltage and a DC voltage that defines the charging potential is applied. The peak voltage is 1500V.
The oscillating voltage (AC + DC) that superimposes the AC voltage AC of and the DC voltage of -750V is applied. The DC voltage DC becomes the center of the oscillating voltage. The photoconductor 2 is a charging member 3 to which this voltage is applied.
As a result of the contact, the peripheral surface thereof is sequentially and uniformly charged to a predetermined electric potential as it rotates and processed.

The surface of the photoconductor 2 that has been uniformly charged by the charging member 3 is then sequentially subjected to slit exposure 6 of the document image in the exposure unit 5 so as to be post-processed. As a result, electrostatic latent images corresponding to the exposure light image pattern are sequentially formed on the surface of the photoconductor 2.

The latent image is then visualized (developed) as a toner image in sequence by the developing device 7, and a transfer roller as a transfer member is formed.
It reaches the transfer section, which is the nip section between 8A and photoreceptor 2.

On the other hand, the stacked transfer material P in the paper cassette 15 set in the paper feeding unit is conveyed into the single-sheet addressing device by the cooperation of the paper feeding roller 16 and the separating claw member, and the guide 17, the pair of conveying rollers 18, and the guide 19 are conveyed.
・ Timing roller pair (registration roller pair) 20 ・ Guide
In the route of 21, the sheet is fed to the transfer portion, which is the nip portion between the transfer roller 8A and the photosensitive member 2, in synchronization with the rotation of the photosensitive member 2,
The formed and carried toner images on the side of the photoconductor 2 are sequentially transferred onto the surface of the feeding transfer material.

The transfer material that has passed through the transfer section is separated from the surface of the photoconductor 2,
The image is fixed by being introduced into the fixing device 12 by the conveying device 9 and output from the carry-out port 13 to the paper discharge tray 14.

After the transfer material is separated, the surface of the photoconductor 2 is cleaned by a cleaning device 10 after removal of adhered contaminants such as transfer residual toner and erasing of electric memory by a static eliminator such as a full-face exposure device 11,
The image formation is repeatedly performed.

In the reciprocating platen 50, 51 is a platen glass that is driven to reciprocate on the top plate of the machine 1 in the left-right direction in the drawing, and 52.
Is a document pressure plate that can be freely opened and closed on the platen glass.
The original 0 is placed on the original table glass 51 with the image side facing downward, and the original pressure plate 52 is tilted over the original 0 to set the original. When the image forming start key is pressed, reciprocating movement of the platen glass 51 is started, and in the process of passing through the slit illumination section 53, the downward image surface of the set original 0 on the platen glass 51 is illuminated by the illumination lamp 30, and the illumination thereof is performed. The light reflected from the original surface of the document is image-wise exposed by the lens array 31 on the surface of the photoconductor 2 in the exposure unit 5.

As described above, in the image forming apparatus using the transfer member that forms a nip with the image carrier as the transfer means and transfers the image from the image carrier to the transfer agent at the nip portion, the transfer material is used. When an image is formed up to the rear end, the developer on the image carrier scatters and the transfer member is contaminated.

In this embodiment, the developer (toner) stain on the transfer roller 8A as a transfer member is prevented and reduced.

That is, since the charging of the sheet-corresponding area surface of the photosensitive member 2 can be turned off by controlling the applied voltage to the contact charging member 3, in this example, the sheet feeding sensor S1 detects the passage of the trailing edge of the transfer material P. The charging member 3 based on the detection signal.
DC applied voltage to the inside of the transfer material
Image formation after 5 mm is prohibited.

That is, the contact charging member 3 has an AC voltage AC (peak-to-peak voltage 15
00V) only is applied. When the direct current voltage DC-750V is set to OV and only the alternating voltage AC is applied to the contact charging member 3, the surface of the photoconductor 2 is neutralized to the surface potential OV,
No developer is applied. This is the vibration center of vibration voltage -750V
You have switched to OV.

As a result, it is possible to prevent the transfer roller 8A from being contaminated due to toner scattering at the trailing end of the transfer material, and it becomes possible to provide an image forming apparatus that does not require a complicated means for cleaning the transfer roller.

Reference numeral 40 denotes a control circuit section (microcomputer) of the apparatus, the applied voltage source 4 for the contact charging member 3 is controlled by this control circuit section 40 in a predetermined sequence, and the control circuit section 40 applies an applied voltage source for the contact charging member 3. 4 functions as a switching unit that switches the voltage applied to the contact charging member 3 as described above in order to form a margin at the rear end of the transfer material.

The contact charging method is characterized by a quick rise after voltage application and a narrow charging width.
In the case of this example, it is possible to precisely control the formation of the charged area and the non-charged area on the photoconductor with a desired division width simply by switching the DC applied voltage DC.

That is, since the charging width of the charging member is narrow, the boundary between the blank portion and the image portion can be sharpened, and the small blank portion can prevent the transfer member from being soiled due to the scattering of the developer at the rear end of the transfer material.

The DC switching level will be described with reference to FIG. Normally, the photoconductor potential is developed between V _{D and} V _L in the V _D area as the development bias.
The development bias is set to V _DC during that time so as not to develop to V _L. Forming a blank space at the rear end means not developing the portion, preferably OV, but the same applies to the E zone below Vdev in the figure.

In the above, the image area and non-image area were formed by turning on / off the DC applied voltage.
You may FF.

The transfer material fed to the transfer section and closely contacted with the surface of the image carrier to receive the image is passed through the transfer section and sequentially separated from the surface of the image carrier and conveyed to the image fixing unit. In order to always and easily perform the separation of the transfer material from the sheet, it is preferable that the front end portion of the transfer material is easily separated from the surface of the image carrier. If the leading edge of the transfer material is easily separated from the surface of the image carrier, the transfer material after passing through the transfer part will be easily and smoothly separated from the surface of the image carrier from the front end to the rear end due to the curvature of the image carrier. Trouble such as transfer material jam due to poor separation is extremely rare.

As one of effective means for making the front end portion of the transfer material easily separated from the surface of the image carrier, a surface area of the front end portion of the transfer material, for example, about 5 mm width is made a non-image area (blank portion). That is, it is possible to adopt a treatment configuration in which a transferable image is not formed on the surface portion of the image carrier corresponding to the above-mentioned width surface region of the transfer material front end portion.

As described above, it is easy to separate the transfer material from the surface of the image carrier.
Even when the predetermined width surface area of the transfer material tip is made to be a non-image area portion for smoothness, the voltage applied to the charging member 3 is switched by the control circuit section 40 as a switching means to change the tip portion of the transfer material. It is possible to form a margin portion.

Figure 3 shows a sheet-through type document feeder (ADF) 2
It is a transfer type electrophotographic copying machine equipped with 2. Since the structure of the copying machine main body is the same as that of the copying machine shown in FIG. 1, the description thereof will be omitted.

The document conveying device 22 is installed on the top plate of the casing 1, and one sheet document O stacked on the document placing tray 23 with the image surface facing downward is placed in the device 22 by a pair of separating and feeding rollers 24. Sheets are drawn in and the first transport roller 25 → platen glass
The sheet is conveyed through the path of 26 → second conveying roller 27 → sheet discharging roller 28 → sheet discharging tray 29. The transported original O passes through the upper surface of the platen glass 26 in close contact with it, and in the course of the transport, the original illumination lamp 30 illuminates the downward image surface through the platen glass 26, and the reflected light of the illumination light on the original surface is a short focus lens. The array 31 forms an image on the surface of the rotating photoconductor 2 in the exposure unit 5, and the document image is sequentially exposed 6 from one end side to the other end on the photoconductor 2 surface uniformly charged by the charging member 3.

The image forming apparatus of this example controls the voltage applied to the contact charging member 3 to form a non-image area having a width of 5 mm at the tip of the transfer material P, thereby separating the transfer material from the surface of the photoconductor 2 after passing through the transfer portion. To make it easier.

That is, the transfer material P is conveyed from the paper supply unit when the paper supply sensor
S1 (photo sensor in this example) detects, the photoconductor 2 starts to rotate, and the original O is also conveyed. Only the AC voltage AC (peak-to-peak voltage 1500V) is applied to the contact charging member 3, and then the DC voltage 750V is superposed at the timing of forming an image from the tip 5 mm of the transfer material P in synchronization with the timing roller pair 20. The photoconductor 2 starts to be charged.

The applied voltage to the charging member 3 is DC voltage OV,
When only the AC voltage AC is applied, the surface of the photoconductor 2 is discharged and the surface potential becomes OV, and the developer is not applied. When the DC voltage DC is applied, the charging of the surface of the photoconductor 2 is started.

That is, the sequence is such that the voltage application to the contact charging member 3 is controlled so that the charging process of the surface of the photosensitive member 2 by the contact charging member 3 is started from the inside of the tip of the corresponding photosensitive member surface area of the transfer material P by 5 mm. As a result, the transfer material P that has passed through the transfer portion and has undergone image transfer and is in close contact with the surface of the photoconductor 2 has a non-image area portion (margin portion) where the tip 5 mm width area does not have a toner image. Since the adhesion to the two surfaces is weak and the tip of the transfer material is easily separated from the surface of the photosensitive member, it is easily separated by the curvature of the photosensitive member 2, and troubles such as transfer material jam due to improper separation are prevented and reduced. .

(Effects of the Invention) As described above, according to the present invention, in the contact transfer type image forming apparatus having the transfer member that forms the nip portion with the image carrier, the transfer by the scattering of the developer (toner) at the trailing end of the transfer material is performed. Easily and appropriately to prevent the developer from being contaminated with the developer, make the desired area on the trailing edge of the transfer material surface a non-image area (make a blank area)
Further, it is possible to provide an image forming apparatus of this kind, which has a simple means structure and which enables downsizing, simplification and cost reduction of the entire apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus of one embodiment, FIG. 2 is an explanatory diagram of a DC voltage switching level of an applied voltage to a contact charging member, and FIG. 3 is a schematic configuration diagram of an image forming apparatus of another embodiment. is there. 2 is a rotary drum type electrophotographic photosensitive member as an image bearing member,
3 is a contact charging member, 4 is a voltage application source for the member, 40
Is a control circuit section, 8A is a transfer roller, 22 is a sheet document feeder (ADF), 50 is a reciprocating document table, P is a transfer material, and O is a document.

Front page continued (72) Inventor Norifumi Koitabashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Taka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Arai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroyuki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-58-121063 (JP, A) JP-A-59-229580 (JP, A) JP-A-63-85768 (JP, A) JP-A-57-49965 (JP, A)

Claims (3)

(57) [Claims] 1. An image carrier, and an image forming unit for forming a toner image on the image carrier, the image forming unit comprising a charging member for contacting the image carrier and charging the image carrier. ,
A transfer member forming a nip portion with the image carrier,
In an image forming apparatus having a transfer member that transfers the toner image from the image carrier to a transfer material at the nip portion, a voltage applied to the charging member to form a blank portion at the rear end of the transfer material. An image forming apparatus having a switching means for switching between. 2. The image forming apparatus according to claim 1, wherein the switching means switches the voltage applied to the charging member to form a blank portion at the leading end of the transfer material. 3. The image forming apparatus according to claim 1, wherein an oscillating voltage is applied to the charging member, and the switching means switches a vibration center of the oscillating voltage.