JP2002207373A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove stuck toner and to prevent soil on the rear side of a transfer material and toner-scattering in a device, even in the case the margin of the transfer material is set small, and then, a toner image on a photoreceptor drum projects from the transfer material and sticks to a transfer roller. SOLUTION: In the case a small margin mode is selected, a cleaning bias (-1500 V) is applied on the transfer roller in a gap between papers, that is, the gap between the trailing end of the preceding transfer material and the leading end of the following transfer material. Then, the toner projecting from the transfer material and undesirably sticking to the transfer roller is shifted to the photoreceptor drum, and the transfer roller is cleaned. Such failures are prevented that the toner sticking to the transfer roller sticks to the rear side of the following transfer material and the toner is scattered in the device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a transfer member disposed in contact with an image carrier, for example, a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art FIG. 12 shows a schematic configuration of a conventional image forming apparatus. In the image forming apparatus shown in FIG.
When the toner image formed thereon is transferred onto the transfer material P such as paper, the toner adhered as dirt to the transfer roller 11 is applied with a transfer roller cleaning bias during the pre-rotation and the post-rotation when paper is not passed. The transfer roller 11 is transferred to the photosensitive drum 1 by applying a bias having the same polarity as the charge polarity of the toner to the transfer roller 11 by the power supply 23, and then collected by the cleaning device 5, thereby cleaning the surface of the photosensitive drum 1. I have.

FIG. 10 is a sequence diagram showing the relationship between the surface potential (photosensitive drum potential) of the photosensitive drum 1 of the image forming apparatus, the developing bias, the transfer bias, and the cleaning bias. The relationship between the surface potential of the photosensitive drum 1, the developing bias of the developing device 3, and the transfer bias of the transfer device 4 will be described with reference to the circumferential position of the photosensitive drum 1 with reference to FIGS.

The photosensitive drum 1 has a dark potential VD of -650 V from the previous rotation by a charging roller 6 as a primary charger.
The uniformly charged portion is exposed according to image information to form an electrostatic latent image.

The end of the last transfer material P starts from the time when the photosensitive drum 1 rotates before the charging position reaches the transfer nip portion N at the timing when the transfer material (transfer sheet) P reaches the transfer nip portion N. Until the charging position reaches the transfer nip N in accordance with the timing of passing through the transfer nip N,
The charging roller 6 charges the surface dark potential VD to −650V. In this case, the light potential VL of the image portion of the electrostatic latent image formed by the exposure light L is -200V.

The developing roller 9 develops the electrostatic latent image on the photosensitive drum 1 at the timing when the transfer material P reaches the transfer nip N, and rotates from the last rotation before the transfer to reach the transfer nip N. Until the toner image reaches the transfer nip portion N in accordance with the timing at which the transfer material P passes through the transfer nip portion N, the developing bias applying power source 10 supplies −500 to the toner image.
A DC developing voltage of V is applied.

When the surface potential of the photosensitive drum 1 at the time of pre-rotation and post-rotation is 0 V, a −1500 V cleaning bias is applied from the transfer roller cleaning bias applying power source 23 to the transfer roller 11, and the transfer material P A transfer bias VT is applied during paper passing, and a lower bias voltage VTo is applied between sheets between image formation (print) and image formation (print). The transfer bias VT in this case is a voltage for securing a necessary transfer current at the time of sheet passing, and varies depending on the resistance of the transfer roller 11. However, in order to correspond to the transfer material P of A3 size or letter size, A voltage for securing a current of about 10 μA is applied. VTo applies a voltage for securing the same transfer current as during paper passing in order to prevent transfer memory to the photosensitive drum 1, but the voltage is lower by the amount of the transfer material P.

As a method for cleaning the toner on the transfer roller 11, a method of applying a constant voltage as a cleaning bias as shown in FIG. 10 and a method of applying a negative and a positive voltage alternately as shown in FIG. There is also a way to do it. The toner adhering to the transfer roller 11 as dirt is not only a normally charged toner but also a toner charged to the opposite polarity in the developing device 3 and a toner originally originally charged due to a discharging action when a cleaning bias is applied. In some cases, the polarity was reversed. When the negative and positive toners are mixed on the transfer roller 11 as described above, the pre-rotation and the
In some cases, a negative or positive bias was applied to the transfer roller 11 as a cleaning bias in the post-rotation.

The components not described in FIG. 12 are the same as those in FIG. 1, and will be described in a first embodiment described later.

[0010]

However, in the above-mentioned conventional example, when an image is formed at the edge of the transfer material P, the dimensional accuracy of the transfer material P is poor and the transfer material P is smaller than the standard size. In some cases, the transfer material P is shifted to the front, rear, left and right at the transfer nip portion N due to the accuracy of the feeding position of the transfer material P. In such a case, in the transfer nip portion N, the toner image at the end portion is not transferred onto the transfer material P, and is transferred to the transfer roller 11, which may cause a back stain on the next transfer material P. . Further, the toner adhered to the back surface of the transfer material P scatters into the image forming apparatus main body, and is solidified by radiant heat from the fixing device, causing a transfer failure of the transfer material P,
Paper wrinkles and paper jams may occur. In addition,
As an example of forming an image at the edge of the transfer material P,
There is an example of an index of a design drawing, and an example of printing small characters at the end of a sheet as a reference number of a medical chart or a medical questionnaire.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and even when a transfer member is soiled with toner because an image on an image carrier protrudes from a transfer material and is transferred.
It is an object of the present invention to provide an image forming apparatus capable of preventing back contamination of a transfer material and scattering of toner in the apparatus.

[0012]

According to a first aspect of the present invention, an image formed on an image carrier is transferred onto a transfer material by using a charged toner, and the image is transferred to the transfer material. An image forming apparatus that forms a transfer nip between the image carrier and a transfer member; and a transfer member that transfers an image on the image carrier to a transfer material that is inserted into the transfer nip. A transfer bias application power supply for applying a transfer bias to the transfer member, a cleaning bias application power supply for applying a cleaning bias for transferring toner adhered to the transfer member onto the image carrier, and an image. For the margin at the end of the transfer material that is not formed, a normal margin mode in which the margin is set to a normal size and a small margin mode in which the margin is set smaller than normal are selected. With a margin selecting means, when said margin small mode is selected by the margin selecting means,
When the sheet interval between the rear end of the preceding transfer material and the front end of the subsequent transfer material comes to a position corresponding to the transfer nip portion,
The cleaning bias is applied to the transfer member by the cleaning bias application power supply.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the cleaning bias has a polarity opposite to that of the transfer bias.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the cleaning bias is an alternating of a polarity opposite to and the same as the polarity of the transfer bias. And

The present invention according to claim 4 is based on claims 1, 2,
Or the image forming apparatus according to claim 3, further comprising image size determining means for determining an image size to be transferred to a transfer material based on an image input signal, wherein the image size determining means determines the transfer nip based on a determination result. The number of sheets to be cleaned is changed among a plurality of sheets passing through the set.

The present invention according to claim 5 is based on claims 1, 2,
5. The image forming apparatus according to claim 3, wherein monitor means for monitoring a current value flowing through the transfer member when the transfer bias is applied to the transfer member, and a transfer material based on the current value monitored by the monitor means. And a synchronization confirmation unit that determines whether or not the transfer member is inserted into the transfer nip portion in synchronization with an image on the image carrier, and performs cleaning of the transfer member based on an output of the synchronization confirmation unit. Deciding whether to perform or not.

According to a sixth aspect of the present invention, in an image forming apparatus which is connected to an external device and forms an image on the transfer material based on an instruction from the external device, an image size transferred to the transfer material is determined. An image size judging unit for judging based on the image input signal, and when the image size is inappropriate with respect to the transfer material size, outputting a signal to that effect to the external device. It is characterized by.

According to a seventh aspect of the present invention, there is provided an image forming apparatus for forming an image by transferring an image formed on an image carrier with a toner having an electric charge onto a transfer material to form an image on the image carrier. A transfer member that transfers the transfer material to the transfer material, and a static eliminator that is grounded or biased by an electric machine to promote separation of the transfer material from the image carrier after image transfer,
A cleaning sheet passing mode for passing a cleaning sheet for cleaning the inside of the image forming apparatus, and when the cleaning sheet passing mode is selected, the discharging unit is floated, or the discharging unit is A different bias from that at the time of transfer is applied.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings referred to in the respective embodiments, members having the same configuration, members having the same operation, and the like are denoted by the same reference numerals, and redundant description will be appropriately omitted.

Embodiment 1 FIG. 1 shows a schematic configuration of an electrophotographic image forming apparatus as an example of an image forming apparatus according to the present invention.

The image forming apparatus shown in FIG. 1 includes a photosensitive member as an image carrier. The photoreceptor is a drum-type electrophotographic photoreceptor (hereinafter referred to as a “photosensitive drum”) in which a photosensitive layer of an organic photoreceptor (OPC) is coated on the surface of an aluminum cylinder.
The photosensitive drum 1 has an outer diameter of 30 mm, and is driven to rotate at a process speed (peripheral speed) of 150 mm / sec in the direction of the arrow.

Around the photosensitive drum 1, a charging device 2 for uniformly charging the photosensitive drum 1 is arranged around the photosensitive drum 1 in the direction of rotation, and an exposure light (for forming an electrostatic latent image on the photosensitive drum 1). An exposure apparatus (not shown) for irradiating laser light) L;
A developing device 3 for applying toner to the electrostatic latent image formed on the photosensitive drum 1 to develop (visualize) the toner image as a toner image; a transfer material P such as paper or an OHP sheet for transferring the toner image formed on the photosensitive drum 1 to paper; (Hereinafter, referred to as “paper” as appropriate) and a cleaning device 5 for cleaning the surface of the photosensitive drum 1 are provided.

The charging device 2 includes a charging roller 6 as a contact charging member, and a charging bias application power source 7 for applying a charging bias to the charging roller 6.

The developing device 3 includes a developing container 8 for storing a toner as a developer and a photosensitive drum 1 for transferring the toner.
Developing roller 9 as a developing member for developing the above electrostatic latent image
And a developing bias applying power source 10 for applying a developing bias to the developing roller 9.

The transfer device 4 includes a transfer roller 11 serving as a contact transfer member having an outer diameter of 20 mm, a transfer bias application power supply 12 for applying a transfer bias of about 1000 to 6000 V to the transfer roller 11, Roller 11
A transfer roller cleaning bias applying power source 23 for applying a transfer roller cleaning bias to the transfer roller 1;
Transfer bias application power supply 12
Or a changeover switch 39 for selecting any one of the transfer roller cleaning bias application power source (cleaning bias application power source) 23. And the transfer roller 1
Reference numeral 1 denotes a non-polar rubber EP on a metal core 11a.
It has a configuration in which a conductive elastic layer 11b whose main component is DM and whose resistance is adjusted by dispersing carbon or a metal oxide is applied, and the volume resistivity of the elastic layer 11b is 10 ⁶ to
It is about 10 ¹⁰ Ω · cm.

The cleaning device 5 includes a cleaning blade 13 for scraping toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 without being transferred to the transfer material P, and a transfer toner for scraping residual toner scraped off by the cleaning blade 13. And a collection container 14 for storing the same.

The transfer material P on which the toner image has been transferred is curvature-separated due to the small diameter of the photosensitive drum 1, and is neutralized by a neutralization needle unit 15 which is a separation assisting means. Accordingly, the electrostatic attraction between the transfer material P and the photosensitive drum 1 is weakened, and the transfer material P is separated from the photosensitive drum 1. The static elimination needle unit 15 includes a static elimination needle (static elimination means) 15a.
And an insulating member 15b, and the static elimination needle 15a is electrically grounded. Transfer material P separated from photosensitive drum 1
Is transported to the fixing device 17 while being guided on a transport guide 16 made of an insulating resin.

The fixing device 17 is formed by spray-coating or spray-coating PFA particles on an aluminum cylindrical cored bar 18a, and then baking and coating.
Roller 18 having a release layer 18b formed thereon, a halogen heater 19 for heating the same from the inside, and a transfer material P
And a fixing inlet guide 21 for guiding the transfer material P to a fixing nip portion between the fixing roller 18 and the pressing roller 20. When the transfer material P carrying the unfixed toner image passes through the fixing nip portion, the toner image is melted and fixed on the surface of the transfer material P and fixed.

In the above-described image forming apparatus, the photosensitive drum 1 is charged by the charging roller 6 by the charging bias applying power source 7.
About -650 V by applying a charging bias to
Is charged to a uniform negative dark potential VD, and then image-exposed by exposure light L, and the exposed portion becomes a bright potential VL to form an electrostatic latent image. In this case, the light potential VL is about -2.
It will be around 00V.

The electrostatic latent image on the photosensitive drum 1 is
Is developed. That is, when a developing bias is applied to the developing roller 9 by the developing bias applying power source 10, the negatively charged toner on the developing roller 9 is turned on the electrostatic latent image on the photosensitive drum 1. Potential VL
Is transferred to the area and developed as a toner image (visible image)
Is done.

The toner image on the photosensitive drum 1 is transferred to a transfer material P conveyed along a transfer guide 22 at a transfer nip N between the photosensitive drum 1 and the fixing roller 11.

The toner adhering to the transfer roller 11 as dirt during the transfer is charged to the transfer roller 11 by the fixing roller cleaning bias applying power supply 23 at the time of pre-rotation or post-rotation when paper is not passed. When a polarity bias is applied, the photosensitive drum 1 is transferred to the photosensitive drum 1 and collected by the cleaning device 5, whereby the surface of the photosensitive drum 1 is cleaned.

The image forming apparatus of the present embodiment shown in FIG. 1 further includes an engine control unit 40 and a formatter 42 in a printer engine 41.
The formatter 42 includes an external device 43 such as a personal computer.
It is connected to the.

At the time of image formation (printing), the image signal and the number signal are transmitted from the external device 43 to the formatter 42 of the image forming apparatus (hereinafter referred to as "printer"), and the image signal is turned on by the exposure apparatus. / Off signal.

The engine control unit 40 includes a formatter 4
2 to control the engine for printing while communicating with the formatter 42.

In the present embodiment, the application of the charging bias and the application of the transfer cleaning bias are performed as follows.

First, the printer driver of the software for controlling the printer on the external device 43 such as a personal computer is provided with a choice of whether or not to print in a format (small margin) where the margin of the transfer material P is small. Select whether to perform printing with normal margins or printing with small margins. Normally, the margin is set to about 5 to 10 mm in printer setting on the general external device 43. The selection between the normal margin print and the small margin print is made by the external device 4.
3 as well as the printer formatter 42
May be performed by a printer control panel (printer operation unit) 44 connected to the printer. In these cases, the external device 43 and the control panel 44 constitute the margin selecting means.

When the normal margin printing is selected, printing is performed in the same sequence as in the prior art as shown in FIG.

On the other hand, when small margin printing is selected, printing is performed in a sequence as shown in FIG.

In the sequence shown in FIG.
The printing (image formation) and post-rotation are the same as in the conventional example, but the paper interval is -15
A cleaning bias of 00 V is applied.

The time for applying the cleaning bias to the transfer roller 11 is such that at least the transfer roller 11
Rotation). If one round of the transfer roller 11 is configured to be shorter than the paper interval, even in the case of small margin printing, the time required for printing does not need to be long, and the number of prints per unit time (throughput) does not decrease. Yes.

For example, if the process speed is 150 mm /
In the image forming apparatus of sec, if the time between sheets is 470 msec due to the restriction of the performance of the paper sensor (sensor for detecting the transfer material P) disposed in the transfer path of the transfer material P, the space between the sheets is about 70 mm. And the transfer bias application power source 1
Even if the rise and fall of No. 2 are each expected to be 20 msec, the transfer roller 11 having an outer diameter of 20 mm or less can cope with small margin printing without changing the throughput.

However, when the diameter of the transfer roller must be increased due to the configuration of the apparatus, or when the rising and falling characteristics of the high voltage need to be delayed, the cleaning bias is applied to the transfer roller 11 between the sheets. Cannot be applied for more than one round of the transfer roller 11.

In such a case, the transfer roller 11 is cleaned by extending the sheet interval. Although the throughput is slightly slower, it is possible to prevent back stains due to the protrusion of the image from the transfer material P and paper jam due to toner scattering.

The potential of the surface of the photosensitive drum 1 corresponding to the portion to which the cleaning bias is applied to the transfer roller 11 may be the dark potential VD. However, in order to further improve the cleaning efficiency, 0 V (the broken line of the photosensitive drum potential in FIG. 2). It is desirable to set it to the portion indicated by A) or the light potential VL.

Further, usually, the transfer roller 11 is
The weak bias VTo is applied to make the transfer current flowing into the photosensitive drum 1 substantially equal between the transfer (printing) and the sheet interval to reduce the density difference due to the drum memory.

As described above, the bias applied during transfer is
In the case of a configuration that affects the drum potential, as shown in FIG. 3, after applying a cleaning bias to the transfer roller 11 between the sheets, the transfer weak bias VTo is applied to the transfer roller 11 for one rotation of the photosensitive drum 1 (see FIG. 3). The transfer step for the next transfer material P may be performed after applying the transfer bias of No. 3 (indicated by the solid line B) and making the potential of the photosensitive drum 1 substantially equal to that at the time of paper feeding.

By doing so, it becomes possible to form a good image while suppressing the occurrence of a memory even in an apparatus configuration in which a drum memory is likely to be generated.

When a polar rubber, such as NBR, epichlorohydricon rubber or urethane rubber, to which toner is easily adhered is used as the elastic layer 11b of the transfer roller 11, as shown in FIG. And the positive bias are alternately applied, thereby effectively removing the stain on the transfer roller 11 and preventing the back stain on the transfer material P.

The sequence of FIG. 4 is to apply a negative and positive alternating transfer roller cleaning bias to the transfer roller 11 even between sheets.

As a result, the transfer roller 1
1 can be effectively removed, and the occurrence of back contamination of the transfer material P can be prevented.

Second Embodiment FIG. 5 shows a second embodiment of the present invention.

Reference numeral 45 in the upper right of FIG. 5 denotes an image size judging unit for judging the size of a printing portion of an image signal sent from a personal computer or the like and the arrangement of characters. The form is a circuit dedicated to this function. May be provided or incorporated into the control of the formatter.

The operation of the image forming apparatus according to this embodiment will be described with reference to the flowchart of FIG.

In forming an image, first, the formatter 42 determines whether or not the print (image) signal is a print with a small margin (small margin).

If the image signal from the personal computer or the like is not instructed to print in the small margin mode, printing is performed in the normal mode. If so, the image size is determined next (S1). , S2).

The determination of the image size is made by comparing the size of the image with the size of the transfer material P.

Even if the print is specified in the small margin mode,
If the image is not located within 5 mm from the paper edge (S3),
Printing is performed in a normal sequence (S4).

On the other hand, if the image is within 5 mm from the edge of the sheet, it is next determined which position the image (the small margin portion) is.

Even if the paper edge is the same, the image protrudes from the leading and trailing edges (leading edge and trailing edge) and the left and right edges (left and right edges)
The amount of toner that adheres to the transfer roller 11 as dirt differs greatly from the case in which it runs off.

For example, a transfer roller 11 having a diameter of 17 mm
When printing is performed on leisure-size paper (length 432 mm in the transport direction) as the transfer material P, the transfer roller 11 rotates substantially eight times when performing transfer on the entirety of the paper. Then, when the image protrudes 1 mm at the leading and trailing ends, a 1 mm-wide band is only once or twice attached to the transfer roller 11. On the other hand, when the toner runs out in the left-right direction, the toner band for eight rotations adheres eight times on the transfer roller 11, and the amount of stain toner becomes extremely large.

For this reason, in the case where the image protrudes at the leading and trailing edges of the paper, the amount of toner adhering to the transfer roller 11 is not so large. If the image protrudes at the left and right ends of the image, there is a very high possibility that the image will be scattered in the apparatus or the back image will be generated due to the contamination of one sheet of paper.

Therefore, when a margin (margin) is smaller than 5 mm at the left and right ends of the paper when an image is formed,
The transfer roller is cleaned between each sheet (S6).

On the other hand, when an image is formed and the margin (margin) is small at the leading and trailing edges of the paper, further judgment may be made based on the margin amount (margin amount).

For example, the margin amount is usually 5 mm, but when an image is formed in a range that is less than 5 mm and is likely to be 2 mm or more (when the margin is definitely 2 mm or more in image information). (S6) The probability that the image protrudes from the paper is small, and even if the image protrudes, the amount of toner adhering to the transfer roller 11 as dirt is small. Therefore, in this case, cleaning of the transfer roller 11 is performed once every several sheets.
This may be performed once, for example, every time an image is formed on ten sheets of paper (S6, S7). If the margin is small, the cleaning interval may be changed more frequently and may be changed according to the margin amount. Further, it may be changed according to the printing rate. For example, when the printing rate is high, the number of sheets at the cleaning interval may be reduced.

When the margin at the front and rear ends is 2 mm or less, (S
6) Since the possibility of the image protruding from the paper increases, the cleaning may be performed between each paper.

In the above description, a margin of 5 mm and 2 mm have been adopted as criteria for judging the cleaning interval. However, regarding these numerical values, the configuration of the transfer path of the transfer material P of the image forming apparatus, the configuration of the transfer apparatus, etc. Therefore, they may be set appropriately according to the configuration.

<Embodiment 3> FIG. 7 shows this embodiment.

Reference numeral 46 shown near the transfer roller 11 in FIG.
Is a current detection circuit for detecting a transfer bias. This current detection circuit 46 monitors the transfer current when the margin at the leading end of the transfer material P is small.

Generally, the transfer voltage needs to be the voltage at the time of transfer at least for the portion where the transfer material P is present.

For this reason, at the leading end of the transfer material P, the transfer bias is quickly set to VT in consideration of the variation of the high voltage rise.
Switch from o to VT.

The trailing edge of the paper is very close to V.
Switching from T to VTo causes a high voltage fall, so that a bias higher than VTo is applied to the transfer roller 11 even after the rear end passes through the transfer nip N.

Therefore, in the present embodiment, the current value of the transfer bias is monitored by the above-described current detection circuit 46 to detect the sheet passing timing when the transfer material P passes through the transfer nip N. .

In general, the writing of an image on the photosensitive drum 1 is uniquely determined by the control of the exposure means, and does not shift. On the other hand, the transfer material P
The paper passing timing to the transfer nip N may be shifted due to the variation of the registration clutch or the like.

This shift can be detected by the current value detected by the current detection circuit 46 described above.

The transfer roller 11 is cleaned based on the relative relationship between the image-equivalent portion on the photosensitive drum 1 and the transfer material P, that is, from the actual measurement of the image position on the transfer material P and the timing at which the transfer material P passes. Synchronization confirmation means (not shown)
Judge by.

From the monitor value of the transfer current, if the sheet passing timing of the transfer material P matches the image, cleaning of the transfer roller is not performed. On the other hand, if there is a possibility that the image may run off the transfer material P due to a deviation of the sheet passing timing, the transfer roller 11 is cleaned.

With the above-described configuration, it is possible to automatically prevent the toner from scattering in the apparatus and the stain on the back of the transfer material P when printing is performed with a small margin, and to uniformly control the throughput. Since it is not necessary to reduce the size of the image forming apparatus, it is possible to perform printing while fully utilizing the performance of the image forming apparatus.

<Embodiment 4> In this embodiment, a case where the image size is larger than the transfer material size will be described. The configuration of the entire image forming apparatus is the same as that shown in FIG. 5 of the second embodiment.

When the image forming apparatus receives an image signal, the image size is determined by the image size determination unit 45. In this case, when the image size is larger than the transfer material size, the operation is performed in the following sequence. .

First, the cleaning of the transfer roller 11 is performed between each sheet.

In parallel with this, for example, if the image forming apparatus is a printer connected to a personal computer, a warning that the image size is too large for the transfer material P is displayed on the personal computer.

The printer always communicates with the personal computer via the formatter 42 and receives data one by one, but the printer outputs a signal indicating that data can be sent to the personal computer.

Apart from this signal, the formatter 42 issues a warning to the personal computer that the image size is too large for the transfer material P.

With the above-described configuration, the user can be alerted when the user tries to print an image larger than the transfer material size by mistake in the image size or the transfer material size.

In particular, when a large number of people share a printer like a network printer, it is not preferable to stop the printer due to an image size mismatch. This embodiment is effective as a configuration in which a printer is effectively shared and a failure of the image forming apparatus does not occur.

<Embodiment 5> FIG. 7 shows this embodiment.

In the first to fourth embodiments, the transfer roller 1
In the first embodiment, the removal of the toner scattered on the conveyance guide 16 and the fixing entrance guide 21 between the transfer and the fixing is described.

When printing is performed with a small margin, the image is transferred to the transfer material P.
The toner sticks out of the transfer roller 11 and scatters to the conveyance guide 16 from there, or the transfer material P
The toner adheres to the transport guide 16 and the like at the time of transport due to the toner adhering to the front and rear ends and the left and right ends. The toner adhered to the transport guide 16 in this manner adheres to the back of the next transfer material P at the time of the next printing and becomes back stain.

In the present embodiment, in order to prevent this,
A switch 47 capable of floating the ground bias of the static elimination needle 15a of the static elimination needle unit 15 is provided, and the switch 47 can be turned on / off by the engine control unit 40.

Normally, the potential of the transfer material P after the transfer is about +3 kV when the static elimination needle 15a is electrically grounded. After printing several prints with a small margin, the engine control unit 40 automatically or
The control panel 44 instructs the engine control unit 40 to pass the cleaning paper. When there are a plurality of paper feed ports, the engine control unit 40 that has received the command feeds paper of the maximum width as cleaning paper and performs solid white printing. At this time, the static elimination needle 15a turns off the switch 47 to be electrically floated. As a result, the potential of the transfer material P becomes approximately +5 kV, and negatively charged toner is electrostatically attracted while being transported on the transport guide 16.

The cleaning paper fixes the electrostatically attracted toner by fixing, and discharges the toner outside the image forming apparatus main body. As a result, all the toner that may become back stains on the conveyance guide 16 and the fixing entrance guide 21 can be discharged to the outside of the image forming apparatus main body. There is no.

Further, by applying a transfer bias larger than usual to the transfer roller 11 during the passage of the cleaning paper, the potential of the transfer material can be further increased, and the cleaning efficiency in the main body of the image forming apparatus is further improved. be able to.

In order to further improve the performance of separating the transfer material P from the photosensitive drum 1 at the transfer nip N, a bias having a polarity opposite to the polarity at the time of transfer may be applied to the charge removing needle 15a. Good. In this case, as shown in FIG. 9, the power supply 48 may be configured so that the bias of the static elimination needle can be switched to ground or float.

When the cleaning paper is passed, the same cleaning efficiency can be obtained by grounding the static elimination needle bias. For example, the static elimination needle 15a
When a voltage of 1 kV is applied, the potential of the transfer material P is about +2 kV.

Since the potential of the transfer material P is higher than usual by +3 kV by grounding the neutralization needle bias, scattered toner can be collected.

Of course, also in this case, the static elimination needle 15a may be electrically floated.

In an image forming apparatus having an automatic double-sided mechanism, since the transfer material P dries on the second surface of the transfer material when the first surface is fixed, the transfer material P is more easily charged. Therefore, by performing the cleaning according to the present embodiment in the image forming apparatus having the automatic double-sided mechanism, a further cleaning effect can be expected.

Further, as the voltage applied to the static elimination needle 15a when the cleaning paper passes, instead of being electrically floated or grounded, a voltage having the same polarity but smaller than usual or a voltage having the opposite polarity may be used.

[0100]

As described above, according to the present invention,
Even if the transfer member is contaminated with toner because the small margin mode is selected and the image on the image carrier protrudes from the transfer material and is transferred, it prevents the back contamination of the transfer material and toner scattering in the device. can do.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram of a sequence according to the first embodiment.

FIG. 3 is an explanatory diagram of another sequence according to the first embodiment.

FIG. 4 is an explanatory diagram of still another sequence of the first embodiment.

FIG. 5 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment.

FIG. 6 is a flowchart illustrating the operation of the second embodiment.

FIG. 7 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a third embodiment.

FIG. 8 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a fifth embodiment.

FIG. 9 is a longitudinal sectional view illustrating a schematic configuration of another image forming apparatus according to the fifth embodiment.

FIG. 10 is an explanatory diagram of a conventional sequence.

FIG. 11 is another sequence explanatory diagram of the related art.

FIG. 12 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image carrier (photosensitive drum) 11 transfer member (transfer roller) 12 transfer bias application power supply 15 a static elimination means (static elimination needle) 23 cleaning bias application power supply (transfer roller cleaning bias application power supply) 43 margin selection means (external device) 44 margin Selection means (control panel) 45 Image size determination means (image size determination section) 46 Monitor means (current detection circuit) N transfer nip section P transfer material

Claims (7)

[Claims] 1. An image forming apparatus for forming an image by transferring an image formed on an image carrier with a toner having a charge onto a transfer material, wherein a transfer nip portion is formed between the image carrier and the image carrier. A transfer member, a transfer bias application power source for applying a transfer bias for transferring an image on the image carrier to a transfer material inserted into the transfer nip portion, to the transfer member, A cleaning bias application power source for applying a cleaning bias to transfer the toner onto the image carrier to the transfer member; and a normal setting of the margin with respect to a margin at a transfer material end where no image is formed. And a margin selecting means for selecting a margin mode and a small margin mode for setting the margin smaller than usual. Is selected, when the sheet interval between the trailing end of the preceding transfer material and the leading end of the succeeding transfer material reaches a position corresponding to the transfer nip portion, the transfer member is activated by the cleaning bias application power supply. Applying the cleaning bias to the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the cleaning bias has a polarity opposite to that of the transfer bias. 3. The image forming apparatus according to claim 1, wherein the cleaning bias is an alternation of a polarity opposite to and the same as the polarity of the transfer bias. 4. An image size judging means for judging an image size to be transferred to a transfer material based on an image input signal, wherein the image size judging means passes through the transfer nip portion based on the judgment result. 4. The image forming apparatus according to claim 1, wherein the number of papers to be cleaned is changed among the papers. 5. 5. A monitor for monitoring a value of a current flowing through the transfer member when the transfer bias is applied to the transfer member, and a transfer material on the image carrier is determined based on a current value monitored by the monitor. And a synchronization confirmation unit that determines whether or not the transfer member has been inserted into the transfer nip portion in synchronization with an image, and determines whether to perform cleaning of the transfer member based on an output of the synchronization confirmation unit. The image forming apparatus according to claim 1, 2, 3, or 4, wherein: 6. An image forming apparatus which is connected to an external device and forms an image on a transfer material based on an instruction from the external device, determines an image size to be transferred to the transfer material based on an image input signal. An image forming apparatus for determining whether the image size is inappropriate for the transfer material size, and outputting a signal indicating that to the external device. . 7. An image forming apparatus for forming an image by transferring an image formed on an image carrier with a toner having a charge to a transfer material, wherein the image on the image carrier is transferred to a transfer material. A cleaning sheet for cleaning the inside of the image forming apparatus, comprising: a member; and a charge removing unit grounded or biased by an electric machine to promote separation of the transfer material after image transfer from the image carrier. A cleaning paper-passing mode for passing paper, and when the cleaning paper-passing mode is selected, the discharging unit is floated, or a bias different from that during transfer is applied to the discharging unit, Image forming apparatus.