JP2003295631A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To separate a transfer belt and a latent image carrier and clean the transfer belt, in order to prevent image quality degradation which is caused by mixture of toner in certain color into toner in another color via the transfer belt. <P>SOLUTION: The transfer belt 1 and each of photosensitive drums 30Y, 30M, 30C, and 30B are separated by a contact/separation means constituted of a crank mechanism composed of a first arm 61, a second arm 63, a connecting member 64, etc. In this condition, toner sticking to the surface of the transfer belt 1 is removed by cleaners 10 and 70. <P>COPYRIGHT: (C)2004,JPO

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 such as a copying machine, a facsimile, a printer, etc.
An image forming an image by sequentially transferring, to a recording material conveyed by a transfer belt, toner images formed by developing latent images on the surfaces of a plurality of latent image carriers, the toner images being composed of different color toners. The present invention relates to a forming device.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, a latent image is formed on the surface of a latent image carrier, for example, a photosensitive drum, by a well-known image forming process, and the latent image is developed by a developing device. An image forming apparatus that forms a toner image by using a toner image and transfers the toner image to a recording material to form an image.
A plurality of latent image carriers and a developing device are provided, each of which forms a toner image of a different color toner, and each toner image is sequentially transferred to a recording material conveyed by a transfer belt and superposed on the surface of the recording material. What forms a color image is known.

[0003]

DISCLOSURE OF THE INVENTION In this device,
The transfer belt is in contact with each latent image carrier. For this reason,
Toner of a certain color on the surface of the latent image carrier used for latent image formation adheres to the transfer belt, and the toner is conveyed by the transfer belt to the surface of the latent image carrier used for image formation of another color, and the toner is carried. May adhere to the body surface. When the toner of a certain color adheres to the surface of the latent image carrier in this manner, the toner is conveyed into the developing device used for the development of another color,
It may be mixed with toner of another color stored in the developing device. In this case, the mixed toner is used for toner image formation together with the toner of the color originally used for image formation,
There is a problem that color mixture may occur in the image.

However, when the image forming apparatus is operating normally, the amount of toner adhering to the transfer belt from the latent image carrier is insignificant, so that color mixing is not a serious problem in many cases. However, when the recording material is poorly conveyed in the image forming apparatus, a large amount of toner on the surface of the recording material may adhere to the transfer belt. This is because the latent image carrier on which the toner image is formed and the transfer belt come into contact with each other even though the recording material has not reached the transfer position due to poor conveyance.
In this case, a large amount of toner attached to the transfer belt is mixed with the toner stored in the developing device that is transported by the transfer belt and used for developing other colors,
This will have a considerable adverse effect on the image.

In particular, in a wet type image forming apparatus using a two-component type developing solution consisting of a toner and a carrier or a one-component developing solution consisting of a toner as the developing agent, the developing solution which is the developing agent is fluid. Since the toner has adhesiveness, the toner easily mixes into another developing device, and the image quality easily deteriorates due to color mixing.

Incidentally, as a specific case where the conveyance failure occurs, not only the case where the recording material is clogged in the conveyance path (so-called jam) and the conveyance is stopped further,
There is also a case where a deviation occurs in the synchronization between the conveyance of the recording material and the latent image formation. In the latter case, even though the recording material has not reached the transfer position, or the portion of the latent image carrier on which the toner image is formed regardless of whether the recording material has already passed the transfer position, The transfer belt comes into contact with the transfer belt, and the toner adheres to the transfer belt.

Here, it seems that such a harmful effect can be prevented by providing a cleaning device for removing the toner adhering to the transfer belt and removing the toner adhering to the surface of the transfer belt by this cleaning device. However, the ability of such a cleaning device is naturally limited, and when a large amount of toner adheres to the transfer belt, it is difficult to completely remove the toner from the transfer belt by simply providing a cleaning device, and the above-mentioned color mixture is caused. Completely hard to prevent.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a toner of a certain color, which tends to occur in a conventional image forming apparatus when forming a color image. An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in image quality due to color mixture caused by mixing in toner of another color and always forming a color image having a correct hue.

[0009]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention is provided with a plurality of latent image carriers on which a latent image is formed, and the plurality of latent image carriers. A plurality of developing devices for forming latent images formed on the toner images as toner images of different colors, a transfer belt for sequentially conveying a recording material to the plurality of latent image carriers, and a transfer belt driving means for rotationally driving the transfer belt. A cleaning unit for removing toner adhering to the surface of the transfer belt; a cleaning unit driving unit for driving the cleaning unit; a sensor for detecting a conveyance failure of the recording material; An image forming apparatus comprising: a contacting / separating unit for bringing the transfer belt into contact with and separating from the transfer belt. The latent image carrier and the transfer belt are separated from each other, and in this state, the transfer belt drive means rotationally drives the transfer belt, the cleaning means drive means drives the cleaning means, and the cleaning means transfers the transfer belt. It is characterized by having a control means for removing the toner on the surface.

According to the image forming apparatus of claim 1,
When the sensor detects a poor conveyance of the recording material, the control unit causes the contact / separation unit to separate the latent image carrier from the transfer belt,
In this state, the transfer belt drive means drives the transfer belt to rotate, and the cleaning means drive means drives the cleaning means. Therefore, from a certain developing device to a transfer belt, which occurs when the transfer belt is rotationally driven while the transfer belt and the latent image carrier are in contact with each other despite the poor conveyance of the recording material. Therefore, a large amount of toner does not adhere and the toner is not mixed into the other developing device from the transfer belt. Further, the toner once attached to the transfer belt is also removed by the cleaning device.

An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the cleaning unit is
The cleaning means is provided with a web and a pressing member that presses the web against the transfer belt.

Particularly, in the image forming apparatus according to the second aspect, for example, the hygroscopic web is pressed against the transfer belt by the pressing member to more effectively remove the toner on the transfer belt surface. Further, since the toner removed from the transfer belt adheres to the web, it is not necessary to separately provide a device for collecting the removed toner, which is necessary when the cleaning device is composed of a blade or a brush.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first aspect, wherein the cleaning means presses the web supply means on which the web is wound into a roll and the web onto the transfer belt. And a web winding unit that winds the web used for cleaning the transfer belt by being pressed against the transfer belt, and the cleaning unit driving unit is the web winding unit. Is a cleaning means driving means for driving the web winding means to wind the web onto the web winding means. The belt is separated from the belt, and in this state, the transfer belt driving means rotates the transfer belt to cause the web winding means to rotate the web. The take-up speed, is characterized in that it has a control means for rapidly than the winding speed of the web during the normal image formation.

Particularly, in the image forming apparatus according to the third aspect, the web winding means winds the web, so that the portion of the web on which the toner is not adhered is used for cleaning. Therefore, it is possible to prevent the deterioration of the cleaning performance due to the adhesion of the toner to the cleaning member, which occurs when the cleaning member such as the roller is used. Further, particularly in the image forming apparatus of claim 3, when the sensor detects the conveyance failure of the recording material, the control means makes the web winding speed of the web winding means faster than that at the time of normal image formation, and the cleaning device. Improve the cleaning performance of than usual. Therefore, in the case of poor conveyance, a large amount of toner adhering to the transfer belt is sufficiently removed, and more than the required amount of web is consumed during normal operation, so that the web is not wasted.

An image forming apparatus according to a fourth aspect is the image forming apparatus according to the first aspect, wherein the cleaning means presses the web supply means on which the web is wound into a roll and the web onto the transfer belt. And a web winding unit that winds the web used for cleaning the transfer belt by being pressed against the transfer belt, and the cleaning unit driving unit is the web winding unit. Is a cleaning unit driving unit that drives the web winding unit to wind the web, and causes the cleaning unit driving unit to drive the web winding unit every plural times of image formation during normal image formation. The web winding means has a control means for winding the web.

Particularly, in the image forming apparatus according to the fourth aspect, as in the image forming apparatus according to the third aspect, the web winding means winds the web, so that a portion of the web on which the toner is not adhered can be cleaned. Will be used. Therefore, it is possible to prevent the deterioration of the cleaning performance due to the adhesion of the toner to the cleaning member, which occurs when the cleaning member such as the roller is used. Further, particularly in the image forming apparatus of claim 4,
During normal image formation, the web is wound up every time image formation is performed a plurality of times. Therefore, the amount of the web used is smaller than when the web is wound up every image formation.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the control means causes the cleaning means driving means to include the web winding means a plurality of times during normal image formation. When the web winding means is driven for each image formation and the web is taken up by the sensor, and the sensor detects a conveyance failure of the recording member, the contact / separation means is provided with the latent image carrier and the latent image carrier. The transfer belt is separated from the transfer belt, and in this state, the transfer belt driving means rotationally drives the transfer belt, the cleaning means driving means continuously drives the web winding means, and the web winding means drives the web. It is characterized in that it is a control means for winding.

Particularly, in the image forming apparatus according to the fifth aspect, when the sensor detects the conveyance failure of the recording material, the control means causes the cleaning means to continuously drive the web winding means to the driving means. Therefore, a new portion of the web, that is, a portion where no toner adheres is used for cleaning, and the cleaning ability is improved.
Therefore, during normal image formation, when a large amount of toner adheres to the transfer belt surface due to poor conveyance of the recording material while suppressing the amount of use of the web by winding the web every plural times of image formation, The toner can be sufficiently removed.

Further, in the image forming apparatus according to a sixth aspect of the present invention, a plurality of latent image carriers having latent images formed on the surface thereof and latent images formed on the plurality of latent image carriers have different colors. A plurality of developing devices that form toner images, a transfer belt that sequentially conveys the recording material to the plurality of latent image carriers, a transfer belt driving unit that rotationally drives the transfer belt, and an outlet for ejecting the recording material. Separation means provided in the vicinity for separating the recording material from the transfer belt, a sensor for detecting a conveyance failure of the recording material, and each of the latent image carriers are brought into contact with the transfer belt and separated from each other. An image forming apparatus comprising: a contact / separation unit that allows the latent image carrier and the transfer belt to be separated by the contact / separation unit when the sensor detects a conveyance failure of the recording material. In this state, Gate drive means the transfer belt is driven to rotate in, is characterized in that it has a control means for separating said recording material from the transfer belt by the separating means.

According to the image forming apparatus of claim 6,
When the sensor detects a poor conveyance of the recording material, the control unit causes the contact / separation unit to separate the latent image carrier from the transfer belt,
In this state, the transfer belt driving unit drives the transfer belt to rotate, and the separating unit separates the recording material from the transfer belt. Therefore, a large amount of toner adheres to the transfer belt, which occurs when the transfer belt is rotationally driven while the transfer belt and the latent image carrier are in contact with each other, even though the conveyance failure occurs. It never happens. Further, the recording material in the image forming apparatus is conveyed to the vicinity of the paper discharge port by the transfer belt and separated by the separation means in the vicinity of the paper discharge port,
It is discharged to the outside of the device.

Incidentally, in the image forming apparatus of claim 6,
For example, when a recording material conveyance failure occurs in a recording material conveyance path portion other than the transfer belt, such as a portion for conveying the recording paper to the transfer belt, the recording material that causes the conveyance failure in the conveyance path portion The recording sheet remaining on the transfer belt may be conveyed out of the apparatus after the operator performs the removing operation.

Further, in the image forming apparatus according to a seventh aspect, a plurality of latent image carriers on which latent images are formed and latent images formed on the plurality of latent image carriers have different colors. A plurality of developing devices that form toner images, a transfer belt that sequentially conveys a recording material to each of the plurality of latent image carriers, a transfer belt drive unit that rotationally drives the transfer belt, and each of the latent image carriers. And contact the transfer belt with each other,
An image forming apparatus including a contact / separation unit that separates the contact image, and a control unit that separates the latent image carrier from the transfer belt when the image forming operation is completed. It is characterized by that.

In the image forming apparatus according to claim 7,
Upon completion of the image forming operation, the control means causes the contact / separation means to separate the latent image carrier from the transfer belt. Therefore, the toner remaining on the surface of the latent image carrier, which is generated when the latent image carrier and the transfer belt are in contact with each other at the time of completion of image formation, is transferred along the surface of the latent image carrier due to gravity acting on the toner, for example. It is prevented from flowing down and adhering to the transfer belt.

An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to the seventh aspect, wherein cleaning means for removing toner adhering to the surface of the transfer belt and cleaning means driving means for driving the cleaning means. When,
When the image forming operation is completed, the control means separates the latent image carrier from the transfer belt by the contact / separation means, and in this state, the cleaning means drive means by the cleaning means. Is a control unit that drives the toner to remove the toner on the surface of the transfer belt.

Particularly, in the image forming apparatus according to the eighth aspect, the control means drives the cleaning means by the cleaning means drive means in a state where the latent image carrier and the transfer belt are separated from each other. Therefore, the toner attached to the transfer belt when the image forming operation is completed is removed by the cleaning device.

An image forming apparatus according to a ninth aspect is the image forming apparatus according to the eighth aspect, wherein the cleaning means is
The cleaning means is provided with a web and a pressing member that presses the web against the transfer belt.

Particularly, in the image forming apparatus according to the ninth aspect, for example, the hygroscopic web is pressed against the transfer belt by the pressing member to more effectively remove the toner on the transfer belt surface. Further, since the toner removed from the transfer belt adheres to the web, it is not necessary to separately provide a device for collecting the removed toner, which is necessary when the cleaning device is constituted by a blade or a brush.

An image forming apparatus according to a tenth aspect of the present invention is the image forming apparatus according to the eighth aspect, in which the cleaning means includes a web supply means in which a web is wound in a roll shape, and the web on the transfer belt. Cleaning means comprising: a pressing member for pressing the transfer belt; and a web winding means for winding the web used for cleaning the transfer belt by being pressed against the transfer belt, wherein the cleaning means driving means is the web winding means. Cleaning means drive means for driving the means to wind the web around the web take-up means, and when the image forming operation is completed, the contact-separation means holds the latent image carrier and the transfer belt. In this state, the transfer belt driving means rotatably drives the transfer belt in this state, and the web winding means changes the web winding speed. It is to further comprising a control means for rapidly than the winding speed of the web during normal image formation.

Particularly, in the image forming apparatus according to the tenth aspect, the web winding means winds the web,
The portion of the web on which the toner is not adhered is used for cleaning. Therefore, it is possible to prevent the deterioration of the cleaning performance due to the adhesion of the toner to the cleaning member, which occurs when the cleaning member such as the roller is used. Further, particularly in the image forming apparatus of claim 10, when the image forming operation is completed, the control means sets the web winding speed of the web winding means to be faster than that during normal image formation, and the cleaning performance of the cleaning device is higher than usual. Also improve. Therefore, at the time of completion of the image forming operation, the toner adhering to the transfer belt is sufficiently removed, while in the normal state, the unnecessary web is not consumed,
The web is never wasted.

An image forming apparatus according to an eleventh aspect is the image forming apparatus according to the eighth aspect, wherein the cleaning means is a web supply means in which the web is wound in a roll shape.
A pressing member for pressing the web against the transfer belt,
A web winding means that winds the web used for cleaning the transfer belt by being pressed against the transfer belt;
A cleaning means driving means for driving the web winding means so that the web winding means winds the web onto the web winding means. It is characterized in that it has a control means for causing the means driving means to drive the web winding means for each of a plurality of times of image formation and to cause the web winding means to wind the web.

Particularly, in the image forming apparatus according to the eleventh aspect, during normal image formation, the web is wound up every time image formation is performed a plurality of times. Therefore, as compared with the case where the web is wound up every image formation. It requires less web usage.

An image forming apparatus according to a twelfth aspect is the image forming apparatus according to the eleventh aspect, wherein the control means causes the cleaning means driving means to include the web winding means a plurality of times during normal image formation. The web winding means is driven to drive the web for each image formation, and when the image formation is completed, the contact / separation means separates the latent image carrier from the transfer belt. Control means for rotating the transfer belt by the transfer belt driving means, continuously driving the web winding means by the cleaning means driving means, and causing the web winding means to wind the web. It is characterized by.

Particularly, in the image forming apparatus according to the twelfth aspect, when the image formation is completed, the control means causes the cleaning means driving means to continuously drive the web winding means. Therefore, a new portion of the web, that is, a portion to which no toner is attached is used for cleaning, and the cleaning ability is improved. Therefore, during normal image formation, the amount of the web used is kept small by winding the web every multiple image formations, and when the image forming operation is completed, the toner is removed if it adheres to the transfer belt surface. can do.

An image forming apparatus according to a thirteenth aspect is the image forming apparatus according to the eighth aspect, wherein the control means causes the contact / separation means to contact the latent image carrier when the image forming operation is completed. And the transfer belt are separated from each other, and in this state, the cleaning device is driven to drive the cleaning device to remove the toner on the surface of the transfer belt, and the contact / separation member is removed until the image is formed again. It is characterized in that it is a control means for keeping the latent image carrier and the transfer belt in a separated state.

Particularly, in the image forming apparatus according to the thirteenth aspect, when the image forming operation is completed, the control means separates the latent image carrier and the transfer belt from the contact / separation means and the cleaning means drive means with the cleaning means. The toner adhered to the surface of the transfer belt is removed by driving, and the contact / separation unit keeps the latent image carrier and the transfer belt in a separated state until the image is formed again. Therefore, when the latent image carrier and the transfer belt are in contact with each other, the toner remaining on the surface of the latent image carrier does not deteriorate in image quality caused by the toner adhering to the transfer belt. Further, the toner attached to the transfer belt is also removed by the cleaning device. Further, the latent image carrier does not come into contact with the surface of the transfer belt from which the toner has been removed again, and the toner does not adhere again.

According to a fourteenth aspect of the present invention, in the image forming apparatus, a plurality of latent image carriers are formed, and latent images are formed on the surfaces of the plurality of latent image carriers at latent image forming positions determined for each latent image carrier. Image forming means for forming a plurality of latent image forming members, a plurality of developing devices for forming a plurality of latent images formed on the plurality of latent image holding members as toner images of different colors, and a recording material for each of the latent image holding members. Formed on each of the latent image carriers at the respective transfer positions where the transfer belt sequentially conveyed to each other, the transfer belt driving means for rotationally driving the transfer belt, and the transfer belt and each of the latent image carriers are close to each other. A plurality of transfer devices for transferring the formed toner image to the recording material, and a latent image forming means for the latent image bearing member positioned on the most upstream side of the plurality of latent image bearing members in the conveying direction of the preceding recording material. The recording to start imaging An image forming apparatus including a recording material detection sensor for detecting a recording material detection sensor, wherein the recording material detection sensor is arranged in a direction more than a transfer position in a latent image carrier located in the most upstream position in the recording material conveyance direction. Upstream from the transfer position and at a position where the distance from the transfer position to the recording material detection sensor is longer than the distance from the transfer position to the latent image forming position on the image carrier. It is characterized by.

In the image forming apparatus according to the fourteenth aspect, when the recording material detection sensor detects the recording material, that is, when the recording material is conveyed well, the control means carries the latent image on the latent image forming means. Start the formation of a latent image on the body. On the other hand, when the recording material detection sensor does not detect the recording material, that is, when the conveyance failure of the recording material occurs, formation of the latent image on the latent image carrier is not started. Therefore, in this case, a toner image is not formed on the latent image carrier, and a latent image carrier on which a toner image is formed even though the recording material has not reached the transfer position due to poor conveyance. Toner is prevented from adhering to the transfer belt due to the contact of the transfer belt.

That is, in the image forming apparatus that forms a latent image at a predetermined timing from when the start switch of the image forming apparatus is operated or when the conveyance of the recording material is started, the conveyance failure of the recording material occurs. Even if it occurs, the latent image is formed and the latent image is developed, and the toner adheres to the transfer belt. Further, in such an image forming apparatus, the arrival of the recording material at the transfer position may be delayed due to slipping of the conveying roller during the conveyance of the recording material. In this case, the toner image is formed on the surface of the latent image carrier without considering the delay. Therefore, when the recording material does not reach the transfer position, the toner image on the transfer belt is formed on the latent image carrier. The transfer belt comes into contact with the transfer belt, and the toner adheres to the transfer belt. On the other hand, in this image forming apparatus, the latent image is formed after confirming that the recording material is being conveyed by the recording material detection sensor. Even if the delay occurs, the toner does not adhere to the transfer belt.

Further, the distance from the transfer position to the recording material detection sensor is shorter than the distance from the transfer position on the most upstream latent image carrier to the latent image forming position on the image carrier. If the position where the toner image to be transferred is formed on the front end of the recording material of the image carrier reaches the transfer position, the front end of the recording material has already passed the transfer position. As a result, the toner image cannot be transferred to the leading end of the toner image. On the other hand, in the image forming apparatus according to claim 14, the recording material detection sensor is located at a position higher than the transfer position in the latent image carrier (hereinafter referred to as the most upstream latent image carrier) located in the most upstream position in the recording material conveyance direction. It is provided upstream from the transfer position and at a position where the distance from the transfer position to the recording material detection sensor is longer than the distance from the transfer position to the latent image forming position on the image carrier. ing. Therefore, based on the signal from the recording material detection sensor provided at such a position, the distance between the leading edge of the recording paper and the transfer position is equal to the distance between the latent image forming position and the transfer position on the most upstream latent image carrier. If the latent image formation by the latent image forming means is started at that point, the toner image can be satisfactorily transferred from the leading end of the recording material.
Further, even though the trailing edge of the recording material has already passed the transfer portion, the toner image transfer operation is not performed at the transfer position, which prevents toner from adhering to the transfer belt. It

According to a fifteenth aspect of the present invention, in the image forming apparatus, a plurality of latent image carriers are formed, and latent images are formed on the surfaces of the plurality of latent image carriers at a latent image forming position determined for each latent image carrier. Image forming means for forming a plurality of latent image forming members, a plurality of developing devices for forming a plurality of latent images formed on the plurality of latent image holding members as toner images of different colors, and a recording material for each of the latent image holding members. Formed on each of the latent image carriers at the transfer positions where the transfer belt sequentially conveyed to each other, the transfer belt driving means for rotationally driving the transfer belt, and the transfer belt and each of the latent image carriers are close to each other. A plurality of transfer devices for transferring the formed toner images to the recording material, a recording material detection sensor for detecting the recording material being conveyed, each of the latent image carriers and the transfer belt, and An image type including a contact / separation unit for separating It said recording material detecting sensor A device in timing for detecting the recording material being conveyed,
When the recording material is not detected, the contact / separation unit has a control unit for separating the latent image carrier from the transfer belt.

In the image forming apparatus according to the fifteenth aspect, when the recording material detection sensor does not detect the recording material at the timing at which the recording material should be originally detected, it is considered that there is a conveyance failure upstream of the sensor. The control means causes the contact / separation means to separate the latent image carrier from the transfer belt.
Therefore, even if the recording material does not reach the transfer position due to poor conveyance, the toner on the transfer belt is brought into contact with the latent image carrier on which the toner image is formed and the transfer belt. Is prevented from adhering. Further, in the image forming apparatus provided with the cleaning device for removing the toner adhering to the transfer belt, the excessive burden of forcing the cleaning device to remove the toner beyond its capability is eliminated.

An image forming apparatus according to a sixteenth aspect is the image forming apparatus according to the fifteenth aspect, wherein the recording material detection sensor is the latent image carrier located at the most upstream side in the recording material conveying direction. The contact / separation unit separates the transfer belt from the latent image carrier upstream of the transfer position in this direction and after the sensor detects a conveyance failure at the moving speed of the latent image carrier surface. It is characterized in that it is provided at a position such that the distance from the transfer position to the sensor is longer than the distance multiplied by the time required for this.

In the image forming apparatus according to the sixteenth aspect, if the recording material detection sensor does not detect the recording material at the timing at which the recording material should be originally detected, it is considered that there is a conveyance failure of the recording paper, and the latent image is formed. The carrier and the transfer belt are separated from each other. Therefore, even if the recording material has not reached the transfer position, the toner does not adhere to the transfer belt due to the contact between the latent image carrier on which the toner image is formed and the transfer belt. To be prevented.

Here, if the image forming apparatus can immediately separate the transfer belt from the latent image carrier at the moment when the recording material detection sensor detects the conveyance failure of the recording material, the sensor is moved to the transfer position. Even if it is provided in the vicinity of, it is possible to prevent toner from adhering to the transfer belt. That is, in such a case, at the time when the toner image formed on the image carrier to be transferred to the front end of the recording material that should normally be conveyed reaches the transfer position, the transfer belt carries the latent image. The toner is prevented from adhering to the transfer belt because the toner is separated from the body. However, it usually takes a certain time (hereinafter referred to as a separation time) for the contact / separation unit to separate the transfer belt from the latent image carrier after the recording material detection sensor detects the conveyance failure. In such a case, if the recording material detection sensor is provided in the vicinity of the transfer position, the portion of the latent image carrier on which the toner image is formed reaches the transfer position during the separation time, and thus the transfer belt is not transferred. Toner will be attached.

Therefore, in the image forming apparatus of the sixteenth aspect, the recording material detection sensor is provided at a position separated from the transfer position by a certain distance or more, so that the latent image carrier moves from the latent image carrier to the conveyor belt while the separation time elapses. It prevents toner from adhering. That is, in the image forming apparatus according to the sixteenth aspect, the moving speed of the latent image carrier surface, which is the distance that the tip portion of the toner image of the latent image carrier moves while the separating time elapses, is multiplied by the separating time. The transfer belt is separated from the latent image carrier by the time the tip reaches the transfer position by providing the sensor at a position where the distance from the transfer position to the recording material detection sensor is longer than the distance. I am trying to do it. This more reliably prevents toner from adhering to the transfer belt from carrying the latent image.

The image forming apparatus according to claim 17 is the same as that according to claim 15.
The image forming apparatus of claim 1, wherein the latent image forming means is configured to start latent image formation by the latent image forming means on the latent image bearing body located at the most upstream side of the plurality of latent image bearing bodies in the conveying direction of the recording material. Upstream of the transfer position on the latent image carrier, which detects the material, in the transport direction,
Further, a latent image forming sensor provided at a position where the distance from the transfer position is longer than the distance from the transfer position on the latent image carrier to the latent image forming position on the image carrier, The recording material detection sensor is provided downstream of the latent image forming sensor in the conveying direction of the recording material.

In the image forming apparatus according to the seventeenth aspect, even if there is a conveyance failure of the recording paper downstream of the latent image forming sensor in the conveyance direction of the recording material, the position where the conveyance failure occurs is the recording material detection sensor. If it is upstream, the transfer belt is separated from the latent image carrier by detecting that there is a conveyance failure by the recording material detection sensor, and toner is prevented from adhering to the transfer belt. As described above, the latent image forming sensor must be provided at a position where the distance from the transfer position to the latent image forming position is longer than the distance from the transfer position to the latent image forming position. Therefore, the latent image forming sensor must be provided at a position having a certain distance from the transfer position, and when only the latent image forming sensor is used, it is downstream of the latent image forming sensor in the recording material conveyance direction. Therefore, it is impossible to prevent the toner from adhering to the transfer belt due to the conveyance failure that occurred in (2). In view of this, in the image forming apparatus according to claim 17, the latent image forming sensor and the recording material detection sensor are used together, and the toner to the transfer belt is caused due to a defective conveyance of the recording material that occurs downstream of the latent image forming sensor. It prevents the adherence of.

Here, if the transfer belt is separated from the latent image carrier when a recording material conveyance error occurs only by using the recording material detection sensor, it is possible to prevent toner from adhering to the transfer belt. Can However, if such a configuration is adopted, a latent image is formed on the surface of the latent image carrier and a toner image is formed even when conveyance failure occurs upstream of the latent image forming sensor. Will be. Therefore, in this case, the cleaning device that removes the toner from the surface of the latent image carrier will be overloaded. On the other hand, in the image forming apparatus according to claim 17, when a recording material conveyance failure occurs upstream of the latent image forming sensor, a latent image is not formed on the latent image carrier and a toner image is formed. Is not formed, the cleaning device is not overloaded.

The image forming apparatus according to claim 18 forms a latent image on a plurality of latent image carriers and on the surface of the plurality of latent image carriers at a latent image forming position determined for each latent image carrier. Latent image forming means, a plurality of developing devices that form a plurality of latent images formed on the plurality of latent image carriers with toner images of different colors, and a recording material sequentially on each of the latent image carriers. The transfer belt to be conveyed, the transfer belt driving means for rotationally driving the transfer belt, and the transfer belt and the latent image carrier are formed on each of the latent image carriers at respective transfer positions close to each other. A plurality of transfer devices for transferring a toner image to the recording material, a sensor for detecting a conveyance failure of the recording material, and a contact for bringing each of the latent image carriers and the transfer belt into and out of contact with each other. An image forming apparatus including a separating unit. When the sensor is provided in a region between the latent image carriers and the sensor detects a conveyance failure of the recording material, the contact / separation unit is provided with the latent image carrier and the transfer belt. It is characterized in that it has a control means for separating them.

In the image forming apparatus according to the eighteenth aspect, when the sensor detects a defective conveyance of the recording material that occurs in the area between the latent image carriers, the control unit causes the contact / separation unit to detect the latent image carrier. Separate from the transfer belt. Therefore, the toner adhesion to the transfer belt, which occurs when the transfer belt is rotationally driven while the transfer belt and the latent image carrier are in contact with each other, even though the recording material is poorly conveyed, Can be prevented or reduced.

An image forming apparatus according to a nineteenth aspect is the eighteenth aspect.
Image forming apparatus, wherein the sensor is provided in the immediate vicinity of the latent image carrier located upstream of the latent image carrier in the conveyance direction of the recording material among the latent image carriers provided in the area between them. To do.

In particular, in the image forming apparatus according to claim 19, of the latent image bearing members provided with the sensor in the area between them, the latent image bearing member is located immediately upstream of the latent image bearing member in the conveying direction of the recording material, that is, A sensor will be provided at the most upstream position in the recording material conveyance direction in this area, and a defective conveyance of the recording material will be detected at an earlier timing than when a sensor is provided downstream of the position. Will be done. As a result, the timing of the transfer belt from the latent image carrier based on the detection is advanced, and the amount of toner adhering to the transfer belt can be minimized.

In the image forming apparatus according to claim 19, the moving speed of the surface of the latent image carrier is multiplied by the time required for the transfer belt to separate from the latent image carrier after the sensor detects a conveyance failure. From the transfer position to the sensor in the latent image carrier (hereinafter referred to as the downstream side latent image carrier) located downstream of the latent image carrier in the conveyance direction of the recording material, rather than the distance, between the latent image carriers. If the sensor is provided at a position where the distance becomes long, it is possible to prevent the toner from adhering to the downstream latent image carrier.

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] A first embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. Figure 1
FIG. 1 is a front view showing a schematic configuration of a copying machine according to this embodiment.

In this apparatus, recording is carried by being electrostatically attracted to the transfer belt 1 in the vicinity of a carrying unit 4 including a transfer belt 1, a driving roller 2 as a transfer belt driving means, a driven roller 3 and the like. A yellow toner image forming unit Y, a magenta toner image forming unit M, a cyan toner image forming unit C, and a black toner image forming unit B, which sequentially form toner images on a recording paper 5 as a material, are provided.

The structure of each toner image forming unit Y, M, C, B will be described. FIG. 2 is a front view showing a schematic configuration of the yellow toner image forming unit Y. Since the toner image forming units Y, M, C, and B have the same configuration, the description is given only for the yellow toner image forming unit Y, and for the other toner image forming units, the yellow toner image forming unit is illustrated in the drawing. Y
The numbers corresponding to those in the yellow toner image forming section are given M, C, and B after the numbers assigned to those in the yellow toner image forming unit, and the description thereof is omitted. Around the photosensitive drum 30Y serving as a latent image carrier of the yellow toner image forming section Y, a charging device 31Y, an exposure device 32Y, and a developing device for forming a yellow toner image on the surface of the recording paper 5 by an electrophotographic process. A device 33Y, a transfer device 34Y, a charge eliminating device 35Y, and a cleaning device 36Y are arranged.

Here, the developing device 33Y is a two-component developing solution composed of toner and carrier, or a one-component developing solution composed of toner.
It is a wet type developing device that uses a component developer as a developer, and includes a developing roller 37Y that supplies the developer to the surface of the photoconductor drum 30Y, a reverse roller 38Y that removes excess developer on the surface of the photoconductor drum 30Y, and a case 39Y. It is composed of a developer supply port 40Y for supplying a developer. In the transfer device 34Y, the recording paper 5 in the state of being interposed between the photoconductor drum 30Y and the transfer belt 1 has the photoconductor drum 30Y.
It is composed of a transfer charger which gives electric charges to the transfer belt 1 so as to generate an electric field in a direction in which the toner image formed on the surface is electrostatically attracted.

Transfer belt 1 of yellow toner image forming section Y
A first transport guide plate 6 for supplying the recording paper 5 as a recording material to the transfer belt 1 from a paper feeding device (not shown) is provided on the upstream side in the rotation direction. On the other hand, a separation charger 7 for separating the recording paper 5 from the transfer belt 1 is provided downstream of the black toner image forming unit B in the rotation direction of the transfer belt 1. The separation charger 7 removes electric charges from the transfer belt 1 and the recording paper 5 to weaken the electric attraction between the transfer belt 1 and the recording paper 5, and thereby the recording paper 5
Is separated from the surface of the transfer belt 2 due to its rigidity. In the vicinity of the separating portion, a second paper for guiding the recording paper 5 separated from the surface of the transfer belt 1 to a fixing device (not shown) is provided.
A transport guide plate 8 is provided.

A transfer belt cleaning device 10 is provided downstream of the separation charger 7 in the rotational direction of the transfer belt 1 as a cleaning means for removing the developer, dust and the like adhering to the surface of the transfer belt 1. The transfer belt cleaning device 10 is provided in contact with the transfer belt 1 and rotates in the opposite direction to the transfer belt 1,
The blotter roller 11 that removes toner from the surface of the transfer belt 1 by frictional force, and an air flow directed to the surface of the blotter roller 11 as shown by an arrow a in FIG. And a fan 12 for evaporating and drying the surface. The surface of the blotter roller 11 is preferably made of synthetic leather, which has oil supply properties and has a roughened surface so that the toner can be wiped off. Also, the blotter roller 11 and the fan 12
Is driven by a motor (not shown) as a cleaning means driving means.

Further, in order to detect a conveyance failure of the recording paper 5, a first sensor 50 is provided in the vicinity of the first conveyance guide plate 6.
A second sensor 51 is provided near the second transport guide guide plate 8.

Further, this apparatus is provided with the respective photosensitive drums 30.
The Y, 30M, 30C, 30B and the transfer belt 1 are brought into contact with each other, and also have a contact / separation means for separating them. The contact / separation means includes a first arm 61 rotatably provided on the apparatus body by a shaft 60, a second arm 63 rotatably provided on the apparatus body by a shaft 62, and both arms 61, 63.
And a connecting member 64 for connecting the above. At the connecting portion between the first arm 61 and the connecting member 64,
The transfer belt 1 is connected to the photosensitive drums 30Y, 30M, 30
The first pressing member 65 for pressing in the C and 30B directions is
The transfer belt 1 is attached to the connection portion of the second arm 63 and the connection member 64 with the photosensitive drums 30Y, 30M, 30C, and 30B.
Second pressing members 66 for pressing in the respective directions are provided.

These pressing members 65 and 66 are provided with springs 67, which are urging means provided on the first arm 61, as long as no force is applied from the outside.
It is urged in a direction away from 0Y, 30M, 30C, and 30B. Further, both the pressing members 65 and 66 are connected to the photosensitive drums 30Y and 3Y against the bias of the spring 67.
The second arm 63 is provided with a solenoid 68 as a drive source for bringing the second arm 63 into contact with the 0M, 30C, and 30B.
That is, in this contact / separation means, the solenoid 68 is OF
When F, the transfer belt 1 and the photoconductor drums 30Y and 30Y
When M, 30C and 30B are separated from each other and the solenoid 68 is ON, the transfer belt 1 and the photoconductors 30Y,
The configuration is such that 30M, 30C, and 30B abut.

The operation of the apparatus configured as described above will be described separately for normal image formation and when the recording paper 5 is not conveyed properly.

First, the operation during normal image formation will be described. When forming an image, first, the solenoid 6
8 is turned on, and the transfer belt 1 and the respective photosensitive drums 30Y, 30M, 3 and 3 are driven by the first pressing member 65 and the second pressing member 66.
0C and 30B are in contact with each other. In this state, a sheet feeding device (not shown) supplies the recording paper 5 to the first conveyance guide plate 6, and the first conveyance guide plate 6 transfers the recording paper 5 to the transfer belt 1.
To the surface of. The transfer belt 1 is a transfer device 34Y.
The recording paper 5 conveyed by the first conveyance guide plate 6 is adsorbed on the surface thereof by the electric charge given by. Here, the transfer belt 1 is rotated in the direction of the arrow b by the rotational force transmitted from the drive roller 2, and the transfer paper 5 is transferred to each of the photoconductor drums 30 provided in the toner image forming portions Y, M, C, and B.
It is conveyed at the same speed as the peripheral speed of Y, 30M, 30C, and 30B.

On the surface of the photoconductor drum 30Y which rotates at the same speed as the transfer belt 1, each device arranged around the photoconductor drum forms a yellow toner image. That is, the charging device 31Y uniformly charges the surface of the photosensitive drum 30Y, the exposure device 32Y forms an electrostatic latent image on the surface of the photosensitive drum 30Y, and the developing device 33Y supplies yellow toner to the electrostatic latent image. Finally, a yellow toner image is formed.
Then, the transfer device 34Y transfers this yellow toner image to
Nip portion NY formed by the transfer belt 1 and the photosensitive drum 30Y
The image is transferred onto the surface of the recording paper 5 conveyed by the transfer belt 1. That is, the transfer device 34Y applies an electric charge to the transfer belt 1 to generate an electric field in the vicinity of the nip portion N, and electrostatically moves the charged yellow toner image on the surface of the photoconductor drum 36Y toward the transfer paper 5. Then, the yellow toner image is transferred onto the transfer paper 5. Then, the charge removing device 35 removes the residual charges on the surface of the photoconductor drum 36, and the cleaning device 36Y removes the yellow toner remaining on the surface of the photoconductor drum 36Y.

The transfer belt 1 transfers the recording paper 5 whose surface has the yellow toner image adhered thereto by the above operation.
Nip portion NM formed by transfer belt 1 and magenta toner image forming portion M, nip portion NC formed by transfer belt 1 and cyan toner image forming portion C, and nip formed by transfer belt 1 and black toner image forming portion B It is sequentially conveyed to the part NB. Then, the magenta toner image forming portion M forms a magenta toner image in the nip portion NM, the cyan toner image forming portion forms a cyan toner image in the nip portion NC, and the black toner image forming portion B forms a black toner image in the nip portion NB. Are sequentially transferred to the transfer paper 5, and the toner images are superposed on the surface of the transfer paper 5. The operation of each toner image forming unit M, C, B to form a toner image and the operation of transferring the toner image to the recording paper 5 are the same as the operation of the yellow toner image forming unit Y.

By the above operation, the separating device 7 separates the recording paper 5 in which the four color toner images are superposed from the surface of the transfer belt 1. That is, the separation device 7
Part of the electric charge electrostatically adsorbing the recording paper 5 distributed on the transfer belt 1 is removed, and the electrostatic adsorption force between the transfer belt 1 and the recording paper 5 is weakened. The weakened electrostatic attraction force and the rigidity of the recording paper 5 combine to separate the recording paper from the surface of the transfer belt 1. Then, the recording paper 5 separated from the surface of the transfer belt 1 is conveyed by the second conveyance guide plate 8 to a fixing device (not shown), and the fixing device fixes the toner image on the recording paper. The recording paper 5 on which the fixing is completed is discharged to the outside of the apparatus by a mechanism (not shown).

When the above copying operation is completed, the solenoid 68 is turned off, and the spring 67 separates the first pressing member 65 and the second pressing member 66 from the transfer belt 1 to transfer the transfer belt 1 and each photosensitive drum 30Y. , 30M, 3
0C and 30B are separated. Further, in this state, the transfer roller 1 is rotated by the driving roller 2 and the blotter roller 11 and the fan 12 are rotated by a motor (not shown), thereby removing the toner adhering to the surface of the transfer belt 1.
As described above, since the transfer belt 1 is separated from each of the photoconductor drums 30Y, 30M, 30C, and 30B after the completion of the copying operation, it is possible to prevent the toner remaining on the surface of the photoconductor drums from adhering to the transfer belt. You can That is, if the transfer belt 1 and the photosensitive drum are kept in contact with each other at the completion of the copying operation, the toner on the surface of the photosensitive drum may flow down along the surface of the photosensitive drum and adhere to the surface of the transfer belt 1. become. For example, in this embodiment, the transfer belt 1 is stretched across the driven roller 3 and the drive roller 2 in a substantially vertical transverse direction, and the photoconductor drums 30Y, 30M, 30C, and 30B are provided in the vicinity of the lateral direction. ,
The toner in the region from the uppermost end of each photoconductor drum to the position closest to the transfer belt 1 (A region in FIG. 2) flows down along the surface of the photoconductor drum and adheres to the transfer belt. . Therefore, in order to avoid such a situation, when the copying is completed, the transfer belt 1 is operated so as to be separated from the photosensitive drums 30Y, 30M, 30C and 30B as described above.

As described above, when the copying operation is completed,
That is, since the toner attached to the surface of the transfer belt 1 is removed by the transfer belt cleaning device 10 at the time of completion of the image forming operation, the toner attached to the surface of the transfer belt 1 at the time of completion of copying is to be copied next time. It is not mixed with a developing device of another color to cause color mixing and deteriorate the image quality.

Since the solenoid 68 is not turned on until the next copy is made, the transfer belt 1 and the photosensitive drums 30Y, 30M, 3 and 3 are kept until the next copy is made.
0C and 30B will be kept in a separated state.
Therefore, it is possible to prevent the toner remaining on the surface of the photosensitive drum from adhering to the transfer belt before the next copy is made.

Next, the operation when the recording paper 5 is poorly conveyed will be described. When the first sensor 50 or the second sensor 51 detects that the conveyance failure of the recording paper 5 has occurred, the control means (not shown) turns the solenoid 68 off.
As F, the transfer belt 1 and the photosensitive drums 30Y and 30Y
Separate M, 30C, and 30B. Then, in this state, the transfer belt 1 is rotated by the driving roller 2, and the blotter roller 11 and the fan 12 are rotated by a motor (not shown) to remove the toner on the surface of the transfer belt. In this way, when the recording paper 5 is not conveyed properly, the transfer belt 1 and the photosensitive drums 30Y, 30M, 30C,
Since 30B is separated, the transfer belt 1 and the photosensitive drums 30Y and 30Y
It is possible to prevent a large amount of toner from adhering to the transfer belt 1 when the transfer belt 1 is rotated while the M, 30C, and 30B are in contact with each other.

Further, the transfer belt 1 and the respective photosensitive drums 30
Even if the Y, 30M, 30C, and 30B are separated from each other, some toner may adhere to the transfer belt 1 when the conveyance is defective. Also in this case, as described above, since the transfer belt 1 is rotated by the driving roller 3 and the blotter roller 11 and the fan 12 are rotated by the motor (not shown),
The adhered toner is removed from the surface of the transfer belt 1.

Further, the first sensor 50 or the second sensor 5
When 1 detects a conveyance failure of the recording paper 5, it is desirable to operate the separation charger 7 in addition to the above operation. When the separation charger 7 is operated, the recording paper 5 in the copying machine is conveyed to the vicinity of the separation charger 7 by the rotation of the transfer belt 1, and the separation charger 7 causes the transfer belt 1 to move.
And is discharged to the outside of the copying machine. Therefore, the trouble of removing the recording paper 5 in the copying machine from the copying machine can be saved.

[Second Embodiment] A second embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. The present embodiment is the same as the first embodiment except that the structure of the cleaning device is different from that of the first embodiment, and therefore the description of the configuration and operation of the common parts will be omitted. FIG. 3 is a front view showing a schematic configuration of the cleaning device of the copying machine according to this embodiment.

First, the structure of the cleaning device of this embodiment will be described. The cleaning device 70 as a cleaning means according to this embodiment is a web type cleaning device that uses a so-called web that is made of fibrous material, such as tissue paper, has hygroscopicity, and is formed into a wrapping paper. The web 71 is fed from a supply roller 72 as a web supply means and wound around a take-up roller 73 as a web winding means. The take-up roller 73 is driven by a step motor (not shown) serving as a cleaning unit driving unit to wind up the web 71. Further, the portion of the web 71 from the supply roller 72 to the take-up roller 73 is pressed against the transfer belt 1 by a pressing roller 75 as a pressing member that is biased by a biasing means such as a spring 74.

The supply roller 72, the take-up roller 73, the spring 74, and the pressing roller 75 are attached to the case 76. A window 77 is provided near the supply roller 72 of the case 76,
The end sensor 78 provided on the outer side of the web 6 has an end mark 79 provided at the end of the web 71 through the window 77.
To detect. When the end sensor 78 detects the end mark 79, the fact is displayed on the operation panel of the copying machine, so that the operator knows that the web needs to be replenished.

Next, the operation of the cleaning device of this embodiment will be described separately for normal image formation and when the recording paper 5 is poorly conveyed. First, the operation during normal image formation will be described. During normal image formation, the take-up roller 73 is rotated by the step motor,
The toner adhering to the surface of the transfer belt 1 is removed while winding the web 71. For the amount of web 71 to be sent,
Although it depends on the kind of the image to be copied, the toner adsorbing property of the web 71, etc., usually about 2% of the image length is suitable. However, if the feeding amount is increased, the cleaning property of the surface of the transfer belt 1 is improved and the image quality is improved, but the consumption amount of the web 71 is increased. Further, if the feeding amount is reduced, the consumption amount of the web 71 can be suppressed to a small amount, but it cannot be denied that the image quality is deteriorated. Therefore, it suffices to balance the two and determine the amount to be sent out. Also,
Regarding the timing of feeding the web 71, the web 71 may be fed after each copying or may be fed after every plural copying. If the web 71 is sent out after each of a plurality of times of copying, the consumption amount of the web 71 can be suppressed to a small amount.

When copying is completed, the cleaning device
The transfer belt 1 is cleaned. The operation of the entire copying machine upon completion of copying is the same as in the first embodiment. When copying is completed, the solenoid 68 is turned off, and the transfer belt 1 and the photosensitive drums 30Y, 30M, 3
0C and 30B are separated. The transfer belt 1 rotates in this state, and the cleaning device 70 causes the transfer belt 1 to rotate.
Remove surface toner. The operation of the cleaning device 70 will be described below.

When the copying operation is completed, the take-up roller 73 is rotated by the rotation of the step motor to move the web 71 to the web 71.
And the toner adhering to the surface of the transfer belt 1 is removed. Here, when the copying operation is completed, the toner remaining on the surface of each photoconductor drum 30Y, 30M, 30C, 30B flows down along the surface of the photoconductor drum and adheres to the transfer belt 1. The amount of toner attached to the transfer belt 1 is larger than that of the transfer belt 1. Therefore, the cleaning performance of the cleaning device 70 also needs to be improved as compared with the normal copying operation. Therefore, it is desirable to increase the feeding amount of the web 71, that is, to increase the take-up speed of the web 71 of the take-up roller 73 faster than usual. Specifically, as described above, during normal copying, about 2% of the image length is appropriate, so it is desirable to set it to a value greater than that. Further, even when the web 71 is sent out every plural times of copying in order to reduce the consumption amount of the web 71 in the normal copying operation, the web is always sent out at the completion of the cleaning operation when the copying operation is completed. Thus, it is desirable to use a new web with no toner attached.

Next, the operation of the cleaning device 70 when the recording paper 5 is not conveyed properly will be described. In addition, when the conveyance failure of the recording paper 5 occurs, that is,
The operation of the entire copying machine when the first sensor 50 or the second sensor 51 detects a conveyance failure is the same as that of the first embodiment. That is, the first sensor 50 or the second sensor 5
When 1 detects a conveyance failure, the control means (not shown) turns off the solenoid 68 to separate the transfer belt 1 from the photosensitive drums 30Y, 30M, 30C and 30B.
In this state, the transfer belt 1 is rotated. In addition to these operations, it is desirable to operate the separation charger 7. Then, the transfer belt 1 is cleaned by the cleaning device 70.
Remove surface toner. The operation of the cleaning device 70 will be described below.

When the first sensor 50 or the second sensor 51 detects the conveyance failure, the step motor is rotated by the instruction of the control means (not shown), the take-up roller 73 starts winding the web 71, and the surface of the transfer belt 1 is started. The toner adhering to is removed. Here, when the recording paper 5 is not conveyed properly, the amount of toner adhering to the transfer belt 1 is larger than that during normal image formation. Therefore, the cleaning performance of the cleaning device 70 also needs to be improved as compared with the normal copying operation. Therefore, increasing the feed amount of the web 71, that is, the web 71 of the take-up roller 73.
It is desirable that the take-up speed of is faster than usual. Specifically, as described above, during normal copying, about 2% of the image length is suitable, but when conveyance failure of copy paper occurs, about 4% of the image length is suitable. is there. Further, even when the web 71 is sent out after every plural copies in order to reduce the consumption amount of the web 71 during a normal copying operation, the web is always sent out at the completion of the copying operation. It is desirable to use a new web that is completely free of toner.

When the web type cleaning device of this embodiment is used, the web 71 adsorbs the toner, so that the toner can be effectively removed from the surface of the transfer belt 1. Further, since the web 71 is wound up by the take-up roller 73, the cleaning performance does not deteriorate due to the toner adhering to the roller, which occurs when a roller is used as a cleaning device. Also, the toner is not scraped off but the web 71
Therefore, a device for collecting the scraped toner, which is required in a cleaning device of a type such as a cleaning device using a roller for scraping the toner, is unnecessary.

[Third Embodiment] A third embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. Since this embodiment is common to the first embodiment except that various sensors are added to the first embodiment, the description of the configuration and operation of the common parts will be omitted. FIG. 4 is a front view showing a schematic configuration of the copying machine according to this embodiment, and FIG. 5 is an explanatory diagram showing a main part of the copying machine. 4 and 5, some members are not shown.

As shown in FIGS. 4 and 5, this copying machine is upstream of the transfer position C of the photoconductor drum 30Y, which is the most upstream photoconductor drum in the conveyance direction of the recording paper 5, in that direction. Latent image forming sensor 1
00 (hereinafter, referred to as sensor 100) is provided. This sensor 100 is provided for each of the photosensitive drums 30Y, 3Y.
Exposure devices 32Y, 32 for 0M, 30C, 30B
It is provided to determine the timing to start the formation of the electrostatic latent image by M, 32C, and 32B. That is, to describe the latent image formation on the photosensitive drum 30Y by the exposure device 32Y as an example, when the leading end of the recording paper reaches the transfer position C based on the detection of the recording paper 5 by the sensor 100, The formation of an electrostatic latent image by the exposure device 30Y is started so that the toner image to be transferred to the front end portion of the photosensitive drum 30Y reaches the transfer position C. Then, similarly, latent images are formed on the photoconductor drums 30M, 30C, 30B by the exposure devices 32M, 32C, 32B.

As a result, when the sensor 100 does not detect the recording paper 5, that is, when the recording paper 100 is jammed upstream of the sensor 100, the toner is applied to the photosensitive drums 30Y, 30M, 30C and 30B. No image is formed. Therefore, even though the recording paper 5 is not conveyed, the photosensitive drums 30Y, 30Y
It is possible to avoid a situation in which the portions on which the M, 30C, and 30B toner images are formed reach the respective transfer positions and the toner adheres to the transfer belt 1.

Further, as shown in FIG. 5, when the exposure device 32Y forms a latent image forming position where the electrostatic latent image is formed on the photosensitive drum 30Y as B and the position where the sensor 100 is provided as position D, the sensor 100 Is a transfer position C and a latent image forming position B
Are provided at positions such that the distance between the transfer position C and the position D along the transfer belt 1 is longer than the length BC of the arc formed on the surface of the photosensitive drum 30Y. Then, when the recording paper 1 reaches the position F, which is the position of the length BC in the conveyance direction of the recording paper 1 from the transfer position C, the exposure device 3
The formation of a latent image by 2Y is started. As a result, when the front end of the toner image formed on the photosensitive drum 30Y reaches the transfer position C, the front end of the recording paper 5 may have already passed the transfer position C. Disappear.

The copying machine also includes a recording material detection sensor 10 for detecting the recording paper 5 being conveyed by the transfer belt 1.
1 (hereinafter, referred to as sensor 101). The sensor 101 is used to control the driving of the contact / separation unit including the first pressing member 65, the second pressing member 66, and the like. That is, if the sensor 101 should not detect the recording paper 5 at the timing when it should otherwise be detected, the transfer belt 1 is considered to have a defective conveyance of the recording paper 5 upstream of the sensor 101. Separated from the photoconductor drums 30Y, 30M, 30C, and 30B. As a result, toner is prevented from adhering to the transfer belt 1 from the respective photosensitive drums due to poor conveyance of the recording paper 1.

The sensor 101 is located upstream of the transfer position C of the photoconductor drum 30Y, which is the most upstream photoconductor drum in the conveyance direction of the recording paper 5, in that direction and at the same time. The distance from the sensor 101 to the transfer position C is more than the distance obtained by multiplying the linear velocity of 30Y by the time required for the contact / separation unit to separate the transfer belt 1 from the photoconductor drum after the sensor 101 detects the conveyance failure.
It is installed in such a position that the distance to As a result, in the case where the recording paper 5 is poorly conveyed,
Before the front end of the toner image formed on the photoconductor drum 30Y reaches the transfer position C, the transfer belt 1 moves to the photoconductor drum 3
Since it is separated from 0Y, the adhesion of toner to the transfer belt 1 is prevented.

Further, in this copying machine, as shown in FIG. 5, a sensor 101 is provided downstream of the sensor 100 in the conveying direction of the recording paper 5. Therefore, even when the conveyance failure of the recording paper 5 occurs at a position downstream of the sensor 100, if the position is upstream of the sensor 101, the transfer belt 1 is separated from the photosensitive drum 30Y. Become.

[Fourth Embodiment] A fourth embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. Since this embodiment is common to the third embodiment except that a sensor is newly added to the third embodiment, the description of the configuration and operation of the common part will be omitted. FIG. 6 is a front view showing a schematic configuration of the copying machine according to this embodiment. In addition, in FIG. 6, illustration of some members is omitted.

As shown in FIG. 6, in this copying machine, the area between the photosensitive drums, that is, the area between the photosensitive drum 30Y and the photosensitive drum 30M, the photosensitive drum 30M.
Sensors 102 are provided in the areas between the photoconductor drum 30C and the photoconductor drum 30C, and in the areas between the photoconductor drum 30C and the photoconductor drum 30B, respectively, in order to detect defective conveyance of the recording paper 5. Then, when any of these sensors 102 detects that the recording paper 5 is poorly conveyed, the contact / separation unit composed of the first pressing member 65, the second pressing member 66, etc. operates, and the transfer belt 1 Photoreceptor drums 30Y, 30M,
Separated from 30C and 30B. As a result, it is possible to prevent toner from adhering to the transfer belt 1 from each of the photoconductor drums due to poor conveyance of the recording paper 1 in the area between the photoconductors.

Further, these sensors 102 are provided in the immediate vicinity of the photosensitive drum on the upstream side in the transport direction of the recording paper 5, respectively. Therefore, as compared with the case where the sensor 102 is provided downstream of the relevant position, it is possible to detect the conveyance failure of the recording paper 5 at an earlier timing, which allows the photosensitive drums 30Y and 30M of the transfer belt 1 to be detected. , 30C, 30B are also separated at an early timing.

[0093]

According to the first aspect of the invention, when the sensor detects a defective conveyance of the recording material, the transfer belt and the latent image carrier are separated from each other. Therefore, a large amount of toner does not adhere to the transfer belt, and it is possible to prevent the toner from mixing with the developing device used for forming toner images of other colors.
As a result, it is possible to prevent the deterioration of the image quality due to the mixing of the toner of a certain color with the toner of the other color, and it is possible to always form a color image having a correct hue. Even if the toner adheres to the transfer belt, the toner is removed by the cleaning device, so that the toner does not mix with the toner of other colors. Therefore,
Prevents deterioration of image quality due to toner mixture,
It is possible to always form a color image having a correct hue.

In particular, according to the second aspect of the present invention, the toner adhering to the surface of the transfer belt can be removed more efficiently by pressing a hygroscopic web against the transfer belt. The deterioration can be prevented more efficiently, and a color image having a correct hue can always be formed. Further, since the toner removed from the transfer belt adheres to the web, it is not necessary to provide a device for collecting the removed toner, and the image forming apparatus can be downsized.

According to the third aspect of the invention, the web winding means winds the web, so that the portion of the web on which the toner is not adhered is used for cleaning. Therefore, the toner adhering to the surface of the transfer belt is removed more efficiently, so that the deterioration of the image quality due to the mixing of the toner can be prevented more efficiently. Further, when the sensor detects the conveyance failure of the recording material, the web take-up speed is increased and the cleaning performance of the cleaning device is improved as compared with the normal case. , The toner is sufficiently removed. Therefore, it is possible to more effectively prevent the deterioration of the image quality due to the mixing of the toner. Further, during normal image formation, the web is not consumed more than necessary, so running costs can be suppressed.

In particular, according to the invention of claim 4, the web winding means winds the web, so that the portion of the web on which the toner is not adhered is used for cleaning. Therefore, the toner adhering to the surface of the transfer belt is removed more efficiently, so that the deterioration of the image quality due to the mixing of the toner can be prevented more efficiently, as in the third aspect of the invention. Further, in particular, according to the invention of claim 4, during normal image formation, the web is wound up every plural times of image formation. Low consumption. Therefore, the running cost of the image forming apparatus can be suppressed.

In particular, according to the fifth aspect of the invention, when the sensor detects the conveyance failure of the recording material, the web winding means is continuously driven, so that the cleaning performance of the cleaning device is improved. As a result, even if a large amount of toner adheres to the transfer belt when the recording material is poorly conveyed, the toner is sufficiently removed, and deterioration of image quality due to toner mixing is prevented. Therefore, it is possible to always form a color image having a correct hue.

According to the invention of claim 6, when the sensor detects the conveyance failure of the recording material, the transfer belt and the latent image carrier are separated from each other, so that the transfer belt and the latent image carrier are in contact with each other. It is possible to prevent a large amount of toner from adhering to the transfer belt, which occurs when trying to remove a recording material that is still in a poorly conveyed state. Therefore, it is possible to prevent a large amount of toner adhering to the transfer belt from mixing with toner of other colors and to deteriorate the image quality, and it is possible to always form a color image having a correct hue. Further, when the recording material is not conveyed properly, the recording material is conveyed by the transfer belt to the vicinity of the discharge port, where the recording material is separated from the transfer belt and discharged from the apparatus main body. Therefore, it is possible to provide the image forming apparatus which is excellent in operability without the trouble of removing the poorly conveyed paper from the image forming apparatus.

According to the sixth aspect of the present invention, when the operator removes the recording material having a conveyance failure in the transfer belt portion or the recording material remaining on the transfer belt portion, toner is transferred from the recording to the transfer belt. The situation of adhesion does not occur. Further, according to the image forming apparatus of claim 6, the operator scratches the latent image carrier when removing the recording material or the like having the conveyance failure on the transfer belt portion, which may adversely affect the subsequent image formation. It is possible to prevent the situation that it causes.

According to the invention of claim 7, since the latent image carrier and the transfer belt are separated from each other when the image forming operation is completed, the toner remaining on the latent image carrier does not adhere to the transfer belt. Therefore, the toner is prevented from being mixed with the toner in the developing device used for the development of other colors, and the deterioration of the image quality such as the color mixture is prevented, and the color image having the correct hue can be always formed.

According to the eighth aspect of the invention, since the latent image carrier and the transfer belt are separated from each other when the image forming operation is completed, the toner remaining on the latent image carrier does not adhere to the transfer belt. . Therefore, the toner is prevented from being mixed with the toner in the developing device used for developing other colors. Further, since the toner attached to the transfer belt at the time of completion of the image forming operation is also removed by the cleaning device, the toner is prevented from being mixed with the toner in the developing device used for developing other colors. Therefore, the toner of a certain color is not mixed with the toner of another color to prevent the image quality from being deteriorated, so that a color image having a correct hue can be always formed.

In particular, according to the invention of claim 9, for example, by pressing a hygroscopic web against the transfer belt, the toner adhering to the surface of the transfer belt can be removed more efficiently, so that the image quality due to the mixing of toner can be improved. The deterioration can be prevented more efficiently, and a color image having a correct hue can always be formed. Further, since the toner removed from the transfer belt adheres to the web, it is not necessary to provide a device for collecting the removed toner, and the image forming apparatus can be downsized.

According to the tenth aspect of the invention, since the web winding means winds the web, the portion of the web on which the toner is not adhered is used for cleaning. Toner is removed more efficiently. When the image formation is completed, the web take-up speed is increased to increase the cleaning performance of the cleaning device more than usual. Therefore, even if a large amount of toner adheres to the transfer belt when the image formation is completed, the toner is sufficiently removed. To be done. Therefore, it is possible to prevent the toner of one color adhering to the transfer belt from being mixed with the toner of another color to deteriorate the image quality, and it is possible to always form a color image having a correct hue. Further, during normal image formation, the web is not consumed more than necessary, so running costs can be suppressed.

In particular, according to the invention of claim 11, since the web winding means winds the web, the portion of the web on which the toner is not adhered is used for cleaning. Similarly, the toner adhering to the surface of the transfer belt is removed more efficiently. Therefore, it is possible to prevent the toner of one color adhering to the transfer belt from being mixed with the toner of the other color and to deteriorate the image quality.
It is possible to always form a color image having a correct hue. According to the eleventh aspect of the invention, since the web is wound every time a plurality of images are formed during normal image formation, the web is wound up compared to a device that winds the web every time an image is formed. The consumption amount is reduced, and the running cost of the image forming apparatus can be suppressed.

According to the twelfth aspect of the invention, when the image forming operation is completed, the web winding means is continuously driven, so that the portion of the web on which the toner is not adhered is used for cleaning. Therefore, the cleaning performance of the cleaning device is improved, and even if a large amount of toner adheres to the transfer belt when the image forming operation is completed, the toner is sufficiently removed. Therefore, it is possible to prevent the toner of one color adhering to the transfer belt from being mixed with the toner of another color to deteriorate the image quality, and it is possible to always form a color image having a correct hue.

According to the invention of claim 13, the latent image carrier and the transfer belt are separated from each other when the image forming operation is completed, the toner on the surface of the transfer belt is removed, and the image is formed again on the transfer belt. The latent image carrier and the transfer belt are kept in a separated state. Therefore, the toner remaining on the latent image carrier does not adhere to the transfer belt. Therefore, the toner adhering to the surface of the transfer belt is mixed with the toner in the developing device that forms a toner image of another color,
Since image quality deterioration such as color mixing does not occur, it is possible to always form a color image having a correct hue.

According to the fourteenth aspect of the present invention, when the recording material is poorly conveyed, the latent image is not formed on the latent image carrier, and the latent image carrier is formed with the toner image. Toner is prevented from adhering to the transfer belt due to the transfer belt coming into contact with the transfer belt. Therefore, the toner adhering to the transfer belt does not mix with the toner of other colors and the deterioration of the image quality due to the mixing does not occur.

According to the fourteenth aspect of the invention, based on the signal from the recording material detection sensor, the distance between the leading edge of the recording paper and the transfer position is determined by the latent image forming position and the transfer position on the most upstream latent image carrier. When it becomes equal to the distance from the position,
By starting the latent image formation by the latent image forming means, the toner image can be satisfactorily transferred from the leading end of the recording material, and a good image can be formed.

According to the fourteenth aspect of the present invention, the toner image transfer operation is not performed at the transfer position even though the trailing edge of the recording material has already passed the transfer section. Therefore, the adhesion of the toner to the transfer belt due to this is prevented, and the deterioration of the image quality due to the mixing of the toner adhered to the transfer belt with the toner of another color does not occur.

According to the fifteenth aspect of the present invention, when the recording material detection sensor does not detect the recording material at the timing when the recording material should be originally detected, the latent image carrier and the transfer belt are separated from each other, and the conveyance failure occurs. Since the toner is prevented from adhering to the transfer belt at this time, the toner adhering to the transfer belt does not mix with the toner of another color and the deterioration of the image quality due to this mixing does not occur. Further, when the present invention is applied to the image forming apparatus provided with the cleaning device for removing the toner adhering to the transfer belt, the cleaning device is not excessively burdened with the removal of the toner beyond its capability. .

In particular, according to the sixteenth aspect of the invention, while the time from the detection of the conveyance failure by the recording material detection sensor to the separation of the transfer belt from the latent image carrier (hereinafter referred to as separation time) elapses. The distance from the transfer position to the recording material detection sensor is longer than the distance obtained by multiplying the moving speed of the latent image carrier surface, which is the distance at which the tip of the toner image of the latent image carrier moves, by the separation time. The sensor is provided at such a position that the transfer belt is separated from the latent image carrier before the tip reaches the transfer position. This makes it possible to more reliably prevent toner from adhering to the transfer belt from the latent image carrier, and the toner adhering to the transfer belt mixes with toner of other colors, resulting in deterioration of image quality due to this mixing. Is more reliably prevented.

According to the seventeenth aspect of the present invention, even if there is a conveyance failure of the recording paper downstream of the latent image forming sensor in the conveyance direction of the recording material, the position where the conveyance failure occurs is higher than the recording material detection sensor. If it is upstream, it is detected by the recording material detection sensor that there is a conveyance failure, and the transfer belt is separated from the latent image carrier to prevent toner from adhering to the transfer belt. Therefore, even if the recording material is poorly conveyed at such a position, toner is prevented from adhering to the transfer belt, and the toner adhering to the transfer belt mixes with the toner of another color, resulting in this mixing. The deterioration of the image quality can be prevented more reliably.

Further, according to the seventeenth aspect of the present invention, as in the case where the toner adhesion to the conveying belt is prevented by using only the recording material detecting sensor, the conveying failure occurs upstream of the latent image forming sensor. Even in this case, a situation in which a toner image is formed on the surface of the latent image carrier is avoided, and an excessive load is not imposed on the cleaning device that removes toner from the surface of the latent image carrier.

According to the eighteenth aspect of the present invention, when the sensor detects a conveyance failure of the recording material that has occurred in the area between the latent image carriers, the transfer belt and the latent image carrier are separated from each other. Therefore, it is possible to prevent or reduce a large amount of toner from adhering to the transfer belt, and prevent the deterioration of the image quality due to the toner adhering to the transfer belt being mixed with the toner of another color, or to prevent the deterioration of the image quality. The degree is reduced.

According to the nineteenth aspect of the present invention, the sensor is provided in the immediate vicinity of the latent image bearing member located upstream of the latent image bearing member in the area between the latent image bearing members in the conveying direction of the recording material. Compared to the case where a sensor is provided downstream of the position, the timing at which the transfer belt separates from the latent image carrier also becomes earlier, so that the amount of toner adhering to the transfer belt can be minimized. Become. As a result, the degree of deterioration of the image quality due to the toner adhering to the transfer belt being mixed with the toner of another color is further reduced.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a copying machine according to a first embodiment.

FIG. 2 is a front view showing a yellow toner image forming unit of the copying machine.

FIG. 3 is a front view showing a cleaning device provided in the copying machine according to the second embodiment.

FIG. 4 is a front view showing a schematic configuration of a copying machine according to a third embodiment.

FIG. 5 is an explanatory diagram showing a main part of the copying machine.

FIG. 6 is a front view showing a schematic configuration of a copying machine according to a fourth embodiment.

[Explanation of symbols]

1 transfer belt 2 drive roller 3 Driven roller 4 Transport unit 5 Recording paper (recording material) 6 First transport guide plate 7 Separation Charger 8 Second transport guide plate 10 Transfer belt cleaning device 11 Blotter roller 12 fans 30 Photosensitive drum (latent image carrier) 31 Charging device 32 exposure equipment 33 Developing device 34 Transfer device 35 Static eliminator 36 Cleaning device 37 developing roller 38 Reverse roller 39 cases 40 developer supply port 50 First sensor 51 Second sensor 60 axes 61 First Arm 62 axes 63 Second Arm 64 Connection member 65 First pressing member 66 Second pressing member 67 spring 68 solenoid 70 Cleaning device 71 web 72 Supply Roller 73 Take-up roller 74 spring 75 pressure roller 76 cases 77 windows 78 End sensor 79 End Mark 100 Latent image forming sensor 101 Recording material detection sensor 102 sensor Y Yellow toner image forming unit M Magenta toner image forming unit C Cyan toner image forming unit B Black toner image forming unit

[Procedure amendment]

[Submission date] June 12, 2003 (2003.6.1)
2)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Image forming apparatus

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc.
An image forming an image by sequentially transferring, to a recording material conveyed by a transfer belt, toner images formed by developing latent images on the surfaces of a plurality of latent image carriers, the toner images being composed of different color toners. The present invention relates to a forming device.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, a latent image is formed on the surface of a latent image carrier, for example, a photosensitive drum, by a well-known image forming process, and the latent image is developed by a developing device. An image forming apparatus that forms a toner image by using a toner image and transfers the toner image to a recording material to form an image.
A plurality of latent image carriers and a developing device are provided, each of which forms a toner image of a different color toner, and each toner image is sequentially transferred to a recording material conveyed by a transfer belt and superposed on the surface of the recording material. What forms a color image is known.

[0003]

DISCLOSURE OF THE INVENTION In this device,
The transfer belt is in contact with each latent image carrier. For this reason,
Toner of a certain color on the surface of the latent image carrier used for latent image formation adheres to the transfer belt, and the toner is conveyed by the transfer belt to the surface of the latent image carrier used for image formation of another color, and the toner is carried. May adhere to the body surface. When the toner of a certain color adheres to the surface of the latent image carrier in this manner, the toner is conveyed into the developing device used for the development of another color,
It may be mixed with toner of another color stored in the developing device. In this case, the mixed toner is used for toner image formation together with the toner of the color originally used for image formation,
There is a problem that color mixture may occur in the image.

However, when the image forming apparatus is operating normally, the amount of toner adhering to the transfer belt from the latent image carrier is insignificant, so that color mixing is not a serious problem in many cases. However, when the recording material is poorly conveyed in the image forming apparatus, a large amount of toner on the surface of the recording material may adhere to the transfer belt. This is because the latent image carrier on which the toner image is formed and the transfer belt come into contact with each other even though the recording material has not reached the transfer position due to poor conveyance.
In this case, a large amount of toner attached to the transfer belt is mixed with the toner stored in the developing device that is transported by the transfer belt and used for developing other colors,
This will have a considerable adverse effect on the image.

In particular, in a wet type image forming apparatus using a two-component type developing solution consisting of a toner and a carrier or a one-component developing solution consisting of a toner as the developing agent, the developing solution which is the developing agent is fluid. Since the toner has adhesiveness, the toner easily mixes into another developing device, and the image quality easily deteriorates due to color mixing.

Incidentally, as a specific case where the conveyance failure occurs, not only the case where the recording material is clogged in the conveyance path (so-called jam) and the conveyance is stopped further,
There is also a case where a deviation occurs in the synchronization between the conveyance of the recording material and the latent image formation. In the latter case, even though the recording material has not reached the transfer position, or the portion of the latent image carrier on which the toner image is formed regardless of whether the recording material has already passed the transfer position, The transfer belt comes into contact with the transfer belt, and the toner adheres to the transfer belt.

Here, it seems that such a harmful effect can be prevented by providing a cleaning device for removing the toner adhering to the transfer belt and removing the toner adhering to the surface of the transfer belt by this cleaning device. However, the ability of such a cleaning device is naturally limited, and when a large amount of toner adheres to the transfer belt, it is difficult to completely remove the toner from the transfer belt by simply providing a cleaning device, and the above-mentioned color mixture is caused. Completely hard to prevent.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a toner of a certain color, which tends to occur in a conventional image forming apparatus when forming a color image. An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in image quality due to color mixture caused by mixing in toner of another color and always forming a color image having a correct hue .

[0009]

[Means for Solving the Problems] To achieve the above object
The image forming apparatus according to claim 1, a plurality of latent image carriers,
Latent image forming means for forming a latent image on the surface of the plurality of latent image carriers at a latent image forming position determined for each latent image carrier, and a plurality of latent image carriers formed on the plurality of latent image carriers. a plurality of developing devices to a latent image respectively different color toner images, a transfer belt for sequentially conveying the recording material on each of the latent image bearing member, a transfer belt drive means for rotationally driven the transfer belt, A plurality of transfer devices that transfer the toner image formed on each of the latent image carriers to the recording material at each transfer position where the transfer belt and each of the latent image carriers are close to each other, A latent image forming sensor for detecting the recording material in order to start the latent image formation by the latent image forming means on the latent image carrying body located on the most upstream side of the image carrying body in the conveying direction of the previous recording material; Is an image forming apparatus equipped with The latent image forming sensors, an upstream with respect to the direction from the transfer position in the latent image carrier positioned at the most upstream in the conveying direction of the recording material,
And characterized in that than the distance from the transfer position to the latent image formation position in the image carrier, provided the distance becomes long position from the transfer position to the sensor <br/> over for the latent image formation It is what

According to the image forming apparatus of claim 1 ,
When the latent image forming sensor detects the recording material, that is, when the recording material is conveyed well, the control means causes the latent image forming means to start forming a latent image on the latent image carrier. On the other hand, when the latent image forming sensor does not detect the recording material, that is, when the recording material is poorly conveyed, formation of the latent image on the latent image carrier is not started. Therefore, in this case, a toner image is not formed on the latent image carrier, and a latent image carrier on which a toner image is formed even though the recording material has not reached the transfer position due to poor conveyance. Toner is prevented from adhering to the transfer belt due to the contact of the transfer belt.

That is, in the image forming apparatus that forms a latent image at a predetermined timing from when the start switch of the image forming apparatus is operated or when the conveyance of the recording material is started, the conveyance failure of the recording material occurs. Even if it occurs, the latent image is formed and the latent image is developed, and the toner adheres to the transfer belt. Further, in such an image forming apparatus, the arrival of the recording material at the transfer position may be delayed due to slipping of the conveying roller during the conveyance of the recording material. In this case, the toner image is formed on the surface of the latent image carrier without considering the delay. Therefore, when the recording material does not reach the transfer position, the toner image on the transfer belt is formed on the latent image carrier. The transfer belt comes into contact with the transfer belt, and the toner adheres to the transfer belt. On the other hand, in this image forming apparatus, since the latent image is formed after confirming that the recording material is being satisfactorily conveyed by the latent image forming sensor, conveyance failure occurs upstream of the latent image forming sensor. Even if there is a delay in transporting the toner, the toner will not adhere to the transfer belt.

Further, a latent image forming sensors, than the distance from the transfer position in the most upstream image bearing member to the latent image forming position in the image carrier, <br/> for the latent image formed from the transfer position If it is provided at a position where the distance to the sensor becomes short, the tip of the recording material will be moved when the portion of the image bearing member where the toner image to be transferred is formed on the tip of the recording material reaches the transfer position. Since the toner has already passed the transfer position, the toner image cannot be transferred to the tip of the transfer position. On the other hand, in the image forming apparatus of claim 1 ,
The latent image forming sensor is upstream of the transfer position in the latent image carrier (hereinafter referred to as the most upstream latent image carrier) located in the most upstream position in the recording material conveyance direction, and than the distance from the transfer position to the latent image formation position in the image bearing member, the distance to the latent image forming cell <br/> Nsa is provided in a long position of the transfer position. Therefore, based on the signal from the latent image forming sensor provided at such a position, the distance between the leading end of the recording paper and the transfer position is
If the latent image forming means starts the latent image formation when the distance between the latent image forming position and the transfer position on the most upstream latent image carrier becomes equal, the toner image is satisfactorily transferred from the leading end of the recording material. Will be able to do. Further, even though the trailing edge of the recording material has already passed the transfer portion, the toner image transfer operation is not performed at the transfer position, which prevents toner from adhering to the transfer belt. It

The image forming apparatus according to a second aspect of the present invention includes a plurality of latent image carriers and latent images on the surfaces of the plurality of latent image carriers at latent image forming positions determined for each latent image carrier. a latent image forming means for forming a plurality of developing devices Ru color toner image to <br/> of respectively different plurality of latent images to be formed on the plurality of latent image carriers, a recording medium wherein At each transfer position where the transfer belt sequentially conveying each of the latent image carriers, the transfer belt driving means for rotationally driving the transfer belt, and the transfer belt and each of the latent image carriers are close to each other, A plurality of transfer devices for transferring the toner image formed on each of the carriers to the recording material; a recording material detection sensor for detecting the recording material being conveyed; and each of the latent image carriers and the transfer belt. And a contacting / separating means for abutting and separating. It said recording material detecting sensor A forming apparatus in timing for detecting the recording material being conveyed,
When the recording material is not detected, the contact / separation unit has a control unit for separating the latent image carrier from the transfer belt.

In the image forming apparatus according to claim 2 ,
When the recording material detection sensor does not detect the recording material at the timing at which the recording material should be detected, it is considered that there is a conveyance failure upstream of the sensor, and the control unit causes the contact / separation unit to detect the latent image carrier. Separate from the transfer belt. Therefore, even if the recording material does not reach the transfer position due to poor conveyance, the toner on the transfer belt is brought into contact with the latent image carrier on which the toner image is formed and the transfer belt. Is prevented from adhering. Further, in the image forming apparatus provided with the cleaning device for removing the toner adhering to the transfer belt, the excessive burden of forcing the cleaning device to remove the toner beyond its capability is eliminated.

According to a third aspect of the present invention, there is provided the image forming apparatus of the third aspect.
2. The image forming apparatus according to the second aspect , wherein the recording material detection sensor is upstream in the transfer position of the latent image carrier located at the most upstream side in the recording material transport direction in the direction, and the latent image is The sensor from the transfer position is more than the distance obtained by multiplying the moving speed of the surface of the carrier by the time required for the contact / separation unit to separate the transfer belt from the latent image carrier after the sensor detects the conveyance failure. It is characterized in that it is provided at a position such that the distance to is long.

In the image forming apparatus according to claim 3 ,
If the recording material detection sensor does not detect the recording material at the timing when the recording material should be detected, it is considered that there is a conveyance failure of the recording paper, and the latent image carrier and the transfer belt are separated from each other. Therefore, even if the recording material has not reached the transfer position, the toner does not adhere to the transfer belt due to the contact between the latent image carrier on which the toner image is formed and the transfer belt. To be prevented.

Here, if the image forming apparatus can immediately separate the transfer belt from the latent image carrier at the moment when the recording material detection sensor detects the conveyance failure of the recording material, the sensor is moved to the transfer position. Even if it is provided in the vicinity of, it is possible to prevent toner from adhering to the transfer belt. That is, in such a case, at the time when the toner image formed on the image carrier to be transferred to the front end of the recording material that should normally be conveyed reaches the transfer position, the transfer belt carries the latent image. The toner is prevented from adhering to the transfer belt because the toner is separated from the body. However, it usually takes a certain time (hereinafter referred to as a separation time) for the contact / separation unit to separate the transfer belt from the latent image carrier after the recording material detection sensor detects the conveyance failure. In such a case, if the recording material detection sensor is provided in the vicinity of the transfer position, the portion of the latent image carrier on which the toner image is formed reaches the transfer position during the separation time, and thus the transfer belt is not transferred. Toner will be attached.

Therefore, in the image forming apparatus of the third aspect , the recording material detection sensor is provided at a position separated from the transfer position by a certain distance or more, so that the latent image carrier moves from the transfer belt to the conveyor belt while the separation time elapses. It prevents toner from adhering. That is, in the image forming apparatus of claim 3 , the moving speed of the surface of the latent image carrier, which is the distance that the tip portion of the toner image on the latent image carrier moves while the separating time elapses, is multiplied by the separating time. The sensor is installed at a position where the distance from the transfer position to the recording material detection sensor is longer than the distance, and the transfer belt separates from the latent image carrier until the tip reaches the transfer position. I am trying to do it. This more reliably prevents toner from adhering to the transfer belt from carrying the latent image.

An image forming apparatus according to a fourth aspect is the image forming apparatus according to the second aspect , in which the latent image carrier among the plurality of latent image carriers is located at the most upstream position in the transport direction of the recording material. The recording material is detected in order to start the latent image formation by the latent image forming means, and is upstream of the transfer position in the latent image carrier in the transport direction and in the latent image carrier. A latent image forming sensor provided at a position where the distance from the transfer position is longer than the distance from the transfer position to the latent image forming position on the image carrier, The recording material detection sensor is provided downstream in the conveying direction of the recording material.

In the image forming apparatus according to claim 4 ,
Even if a recording paper conveyance failure occurs downstream of the latent image forming sensor in the recording material conveyance direction, if the position where the conveyance failure occurs is upstream of the recording material detection sensor, the recording material detection sensor conveys the recording material. It is detected that there is a defect, the transfer belt is separated from the latent image carrier, and the adhesion of toner to the transfer belt is prevented. As described above, the latent image forming sensor must be provided at a position where the distance from the transfer position to the latent image forming position is longer than the distance from the transfer position to the latent image forming position. Therefore, the latent image forming sensor must be provided at a position having a certain distance from the transfer position, and when only the latent image forming sensor is used, it is downstream of the latent image forming sensor in the recording material conveyance direction. Therefore, it is impossible to prevent the toner from adhering to the transfer belt due to the conveyance failure that occurred in (2). Therefore, in the image forming apparatus according to claim 4 , the latent image forming sensor and the recording material detection sensor are used together, and the toner to the transfer belt is generated due to the defective conveyance of the recording material that occurs downstream of the latent image forming sensor. It prevents the adherence of.

Here, if the transfer belt is separated from the latent image carrier when a recording material conveyance error occurs using only the recording material detection sensor, toner adhesion to the transfer belt can be prevented. Can However, if such a configuration is adopted, a latent image is formed on the surface of the latent image carrier and a toner image is formed even when conveyance failure occurs upstream of the latent image forming sensor. Will be. Therefore, in this case, the cleaning device that removes the toner from the surface of the latent image carrier will be overloaded. On the other hand, in the image forming apparatus according to claim 4 , when a conveyance failure of the recording material occurs upstream of the latent image forming sensor, the latent image is not formed on the latent image carrier and the toner image is not formed. Is also not formed, so
The cleaning device is not overloaded.

An image forming apparatus according to a fifth aspect of the present invention forms a latent image on a plurality of latent image bearing members and a surface of the plurality of latent image bearing members at a latent image forming position determined for each latent image bearing member. a latent image forming means for a plurality of developing device for a color toner images of a plurality of latent images were different from each formed on the plurality of latent image carriers, a recording material on each of the latent image bearing member A transfer belt that is sequentially conveyed, a transfer belt driving unit that rotationally drives the transfer belt, and a transfer belt and each of the latent image bearing members are formed on each of the latent image bearing members at respective transfer positions that are close to each other. A plurality of transfer devices for transferring the toner images to the recording material, a sensor for detecting a conveyance failure of the recording material, and a contacting member for separating and contacting each of the latent image carriers with the transfer belt. An image forming apparatus including a contact / separation unit. When the sensor is provided in a region between the latent image carriers and the sensor detects a conveyance failure of the recording material, the contact / separation unit is provided with the latent image carrier and the transfer belt. It is characterized in that it has a control means for separating them.

In the image forming apparatus according to claim 5 ,
When the sensor detects a defective conveyance of the recording material that has occurred in the area between the latent image carriers, the control unit causes the contact / separation unit to separate the latent image carrier from the transfer belt. Therefore, the toner adhesion to the transfer belt, which occurs when the transfer belt is rotationally driven while the transfer belt and the latent image carrier are in contact with each other, even though the recording material is poorly conveyed. Prevention,
Or it can be reduced.

An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fifth aspect , wherein the latent image carrier located upstream of the latent image carrier in the area between which the sensor is provided. The sensor is provided in the immediate vicinity of the image carrier.

In particular, in the image forming apparatus according to the sixth aspect , a sensor is provided in the area between the latent image bearing members, which is located upstream of the latent image bearing member upstream in the recording material conveying direction, that is, A sensor is provided at a position corresponding to the most upstream portion in the recording material conveyance direction in the area, and defective conveyance of the recording material is detected at an earlier timing than when a sensor is provided downstream from the position. Will be done. As a result, the timing of the transfer belt from the latent image carrier based on the detection is advanced, and the amount of toner adhering to the transfer belt can be minimized.

In the image forming apparatus of claim 6 ,
The distance between the sensor and the latent image carrier is multiplied by the time required for the transfer belt to separate from the latent image carrier after the sensor detects a conveyance failure. If a sensor is provided at a position such that the distance from the transfer position to the sensor on the latent image carrier (hereinafter referred to as the downstream latent image carrier) located downstream of the recording material conveyance direction in the latent image carrier becomes long. It is possible to prevent the toner from adhering to the downstream latent image carrier.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] A first embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. Figure 1
FIG. 1 is a front view showing a schematic configuration of a copying machine according to this embodiment.

In this apparatus, recording is carried by being electrostatically attracted to the transfer belt 1 in the vicinity of a carrying unit 4 including a transfer belt 1, a driving roller 2 as a transfer belt driving means, a driven roller 3 and the like. A yellow toner image forming unit Y, a magenta toner image forming unit M, a cyan toner image forming unit C, and a black toner image forming unit B, which sequentially form toner images on a recording paper 5 as a material, are provided.

The structure of each toner image forming unit Y, M, C, B will be described. FIG. 2 is a front view showing a schematic configuration of the yellow toner image forming unit Y. Since the toner image forming units Y, M, C, and B have the same configuration, the description is given only for the yellow toner image forming unit Y, and for the other toner image forming units, the yellow toner image forming unit is illustrated in the drawing. Y
The numbers corresponding to those in the yellow toner image forming section are given M, C, and B after the numbers assigned to those in the yellow toner image forming unit, and the description thereof is omitted. Around the photosensitive drum 30Y serving as a latent image carrier of the yellow toner image forming section Y, a charging device 31Y, an exposure device 32Y, and a developing device for forming a yellow toner image on the surface of the recording paper 5 by an electrophotographic process. A device 33Y, a transfer device 34Y, a charge eliminating device 35Y, and a cleaning device 36Y are arranged.

Here, the developing device 33Y is a two-component developing solution composed of toner and carrier, or one composed of toner.
It is a wet type developing device that uses a component developer as a developer, and includes a developing roller 37Y that supplies the developer to the surface of the photoconductor drum 30Y, a reverse roller 38Y that removes excess developer on the surface of the photoconductor drum 30Y, and a case 39Y. It is composed of a developer supply port 40Y for supplying a developer. In the transfer device 34Y, the recording paper 5 in the state of being interposed between the photoconductor drum 30Y and the transfer belt 1 has the photoconductor drum 30Y.
It is composed of a transfer charger which gives electric charges to the transfer belt 1 so as to generate an electric field in a direction in which the toner image formed on the surface is electrostatically attracted.

Transfer belt 1 of yellow toner image forming section Y
A first transport guide plate 6 for supplying the recording paper 5 as a recording material to the transfer belt 1 from a paper feeding device (not shown) is provided on the upstream side in the rotation direction. On the other hand, a separation charger 7 for separating the recording paper 5 from the transfer belt 1 is provided downstream of the black toner image forming unit B in the rotation direction of the transfer belt 1. The separation charger 7 removes electric charges from the transfer belt 1 and the recording paper 5 to weaken the electric attraction between the transfer belt 1 and the recording paper 5, and thereby the recording paper 5
Is separated from the surface of the transfer belt 2 due to its rigidity. In the vicinity of the separating portion, a second paper for guiding the recording paper 5 separated from the surface of the transfer belt 1 to a fixing device (not shown) is provided.
A transport guide plate 8 is provided.

A transfer belt cleaning device 10 is provided downstream of the separation charger 7 in the rotational direction of the transfer belt 1 as a cleaning means for removing the developer, dust and the like adhering to the surface of the transfer belt 1. The transfer belt cleaning device 10 is provided in contact with the transfer belt 1 and rotates in the opposite direction to the transfer belt 1,
The blotter roller 11 that removes toner from the surface of the transfer belt 1 by frictional force, and an air flow directed to the surface of the blotter roller 11 as shown by an arrow a in FIG. And a fan 12 for evaporating and drying the surface. The surface of the blotter roller 11 is preferably made of synthetic leather, which has oil supply properties and has a roughened surface so that the toner can be wiped off. Also, the blotter roller 11 and the fan 12
Is driven by a motor (not shown) as a cleaning means driving means.

Further, in order to detect a defective conveyance of the recording paper 5, a first sensor 50 is provided in the vicinity of the first conveyance guide plate 6.
A second sensor 51 is provided near the second transport guide guide plate 8.

Further, this apparatus is provided with the respective photosensitive drums 30.
The Y, 30M, 30C, 30B and the transfer belt 1 are brought into contact with each other, and also have a contact / separation means for separating them. The contact / separation means includes a first arm 61 rotatably provided on the apparatus body by a shaft 60, a second arm 63 rotatably provided on the apparatus body by a shaft 62, and both arms 61, 63.
And a connecting member 64 for connecting the above. At the connecting portion between the first arm 61 and the connecting member 64,
The transfer belt 1 is connected to the photosensitive drums 30Y, 30M, 30
The first pressing member 65 for pressing in the C and 30B directions is
The transfer belt 1 is attached to the connection portion of the second arm 63 and the connection member 64 with the photosensitive drums 30Y, 30M, 30C, and 30B.
Second pressing members 66 for pressing in the respective directions are provided.

These pressing members 65, 66 are provided with a spring 67, which is a biasing means provided on the first arm 61, unless a force is applied from the outside.
It is urged in a direction away from 0Y, 30M, 30C, and 30B. Further, both the pressing members 65 and 66 are connected to the photosensitive drums 30Y and 3Y against the bias of the spring 67.
The second arm 63 is provided with a solenoid 68 as a drive source for bringing the second arm 63 into contact with the 0M, 30C, and 30B.
That is, in this contact / separation means, the solenoid 68 is OF
When F, the transfer belt 1 and the photoconductor drums 30Y and 30Y
When M, 30C and 30B are separated from each other and the solenoid 68 is ON, the transfer belt 1 and the photoconductors 30Y,
The configuration is such that 30M, 30C, and 30B abut.

The operation of the apparatus configured as described above will be described separately for normal image formation and for the case where the recording paper 5 is not conveyed properly.

First, the operation during normal image formation will be described. When forming an image, first, the solenoid 6
8 is turned on, and the transfer belt 1 and the respective photosensitive drums 30Y, 30M, 3 and 3 are driven by the first pressing member 65 and the second pressing member 66.
0C and 30B are in contact with each other. In this state, a sheet feeding device (not shown) supplies the recording paper 5 to the first conveyance guide plate 6, and the first conveyance guide plate 6 transfers the recording paper 5 to the transfer belt 1.
To the surface of. The transfer belt 1 is a transfer device 34Y.
The recording paper 5 conveyed by the first conveyance guide plate 6 is adsorbed on the surface thereof by the electric charge given by. Here, the transfer belt 1 is rotated in the direction of the arrow b by the rotational force transmitted from the drive roller 2, and the transfer paper 5 is transferred to each of the photoconductor drums 30 provided in the toner image forming portions Y, M, C, and B.
It is conveyed at the same speed as the peripheral speed of Y, 30M, 30C, and 30B.

On the surface of the photoconductor drum 30Y that rotates at the same speed as the transfer belt 1, each device arranged around the photoconductor drum forms a yellow toner image. That is, the charging device 31Y uniformly charges the surface of the photosensitive drum 30Y, the exposure device 32Y forms an electrostatic latent image on the surface of the photosensitive drum 30Y, and the developing device 33Y supplies yellow toner to the electrostatic latent image. Finally, a yellow toner image is formed.
Then, the transfer device 34Y transfers this yellow toner image to
Nip portion NY formed by the transfer belt 1 and the photosensitive drum 30Y
The image is transferred onto the surface of the recording paper 5 conveyed by the transfer belt 1. That is, the transfer device 34Y applies an electric charge to the transfer belt 1 to generate an electric field in the vicinity of the nip portion N, and electrostatically moves the charged yellow toner image on the surface of the photoconductor drum 36Y toward the transfer paper 5. Then, the yellow toner image is transferred onto the transfer paper 5. Then, the charge removing device 35 removes the residual charges on the surface of the photoconductor drum 36, and the cleaning device 36Y removes the yellow toner remaining on the surface of the photoconductor drum 36Y.

The transfer belt 1 transfers the recording paper 5 having the yellow toner image adhered to the surface thereof by the above operation.
Nip portion NM formed by transfer belt 1 and magenta toner image forming portion M, nip portion NC formed by transfer belt 1 and cyan toner image forming portion C, and nip formed by transfer belt 1 and black toner image forming portion B It is sequentially conveyed to the part NB. Then, the magenta toner image forming portion M forms a magenta toner image in the nip portion NM, the cyan toner image forming portion forms a cyan toner image in the nip portion NC, and the black toner image forming portion B forms a black toner image in the nip portion NB. Are sequentially transferred to the transfer paper 5, and the toner images are superposed on the surface of the transfer paper 5. The operation of each toner image forming unit M, C, B to form a toner image and the operation of transferring the toner image to the recording paper 5 are the same as the operation of the yellow toner image forming unit Y.

By the above operation, the separating device 7 separates the recording paper 5 on which the four color toner images are superposed from the surface of the transfer belt 1. That is, the separation device 7
Part of the electric charge electrostatically adsorbing the recording paper 5 distributed on the transfer belt 1 is removed, and the electrostatic adsorption force between the transfer belt 1 and the recording paper 5 is weakened. The weakened electrostatic attraction force and the rigidity of the recording paper 5 combine to separate the recording paper from the surface of the transfer belt 1. Then, the recording paper 5 separated from the surface of the transfer belt 1 is conveyed by the second conveyance guide plate 8 to a fixing device (not shown), and the fixing device fixes the toner image on the recording paper. The recording paper 5 on which the fixing is completed is discharged to the outside of the apparatus by a mechanism (not shown).

When the above copying operation is completed, the solenoid 68 is turned off, and the spring 67 separates the first pressing member 65 and the second pressing member 66 from the transfer belt 1 to transfer the transfer belt 1 and each photosensitive drum 30Y. , 30M, 3
0C and 30B are separated. Further, in this state, the transfer roller 1 is rotated by the driving roller 2 and the blotter roller 11 and the fan 12 are rotated by a motor (not shown), thereby removing the toner adhering to the surface of the transfer belt 1.
As described above, since the transfer belt 1 is separated from each of the photoconductor drums 30Y, 30M, 30C, and 30B after the completion of the copying operation, it is possible to prevent the toner remaining on the surface of the photoconductor drums from adhering to the transfer belt. You can That is, if the transfer belt 1 and the photosensitive drum are kept in contact with each other at the completion of the copying operation, the toner on the surface of the photosensitive drum may flow down along the surface of the photosensitive drum and adhere to the surface of the transfer belt 1. become. For example, in this embodiment, the transfer belt 1 is being passed only multiplied to the driven roller 3 and drive roller 2, the photosensitive drums 30Y in the lateral direction near, 30M,
Since 30C and 30B are provided, the toner in the region from the uppermost end of each photoconductor drum to the position closest to the transfer belt 1 (A region in FIG. 2) flows down along the surface of the photoconductor drum and is transferred. It will adhere to the belt. Therefore, in order to avoid such a situation, when the copying is completed, the transfer belt 1 is connected to each of the photosensitive drums 30Y and 3Y as described above.
It is operated so as to be separated from 0M, 30C and 30B.

As described above, when the copying operation is completed,
That is, since the toner attached to the surface of the transfer belt 1 is removed by the transfer belt cleaning device 10 at the time of completion of the image forming operation, the toner attached to the surface of the transfer belt 1 at the time of completion of copying is to be copied next time. It is not mixed with a developing device of another color to cause color mixing and deteriorate the image quality.

Further, since the solenoid 68 is not turned on until the next copy is made, the transfer belt 1 and the photosensitive drums 30Y, 30M, 3 and 3 are kept until the next copy is made.
0C and 30B will be kept in a separated state.
Therefore, it is possible to prevent the toner remaining on the surface of the photosensitive drum from adhering to the transfer belt before the next copy is made.

Next, the operation when the recording paper 5 is poorly conveyed will be described. When the first sensor 50 or the second sensor 51 detects that the conveyance failure of the recording paper 5 has occurred, the control means (not shown) turns the solenoid 68 off.
As F, the transfer belt 1 and the photosensitive drums 30Y and 30Y
Separate M, 30C, and 30B. Then, in this state, the transfer belt 1 is rotated by the driving roller 2, and the blotter roller 11 and the fan 12 are rotated by a motor (not shown) to remove the toner on the surface of the transfer belt. In this way, when the recording paper 5 is not conveyed properly, the transfer belt 1 and the photosensitive drums 30Y, 30M, 30C,
Since 30B is separated, the transfer belt 1 and the photosensitive drums 30Y and 30Y
It is possible to prevent a large amount of toner from adhering to the transfer belt 1 when the transfer belt 1 is rotated while the M, 30C, and 30B are in contact with each other.

Further, the transfer belt 1 and the respective photosensitive drums 30
Even if the Y, 30M, 30C, and 30B are separated from each other, some toner may adhere to the transfer belt 1 when the conveyance is defective. Also in this case, as described above, since the transfer belt 1 is rotated by the driving roller 2 and the blotter roller 11 and the fan 12 are rotated by the motor (not shown),
Adhering toner is divided et al or the surface of the transfer belt 1.

Further, the first sensor 50 or the second sensor 5
When 1 detects a conveyance failure of the recording paper 5, it is desirable to operate the separation charger 7 in addition to the above operation. When the separation charger 7 is operated, the recording paper 5 in the copying machine is conveyed to the vicinity of the separation charger 7 by the rotation of the transfer belt 1, and the separation charger 7 causes the transfer belt 1 to move.
And is discharged to the outside of the copying machine. Therefore, the trouble of removing the recording paper 5 in the copying machine from the copying machine can be saved.

[0047] [Embodiment 2] Hereinafter, the present invention an electrophotographic copying machine which is an image forming apparatus (hereinafter, referred to as a copying machine) a description of a second embodiment applied to. Since this embodiment is common to the first embodiment except that various sensors are added to the first embodiment, the description of the configuration and operation of the common parts will be omitted. FIG. 3 is a front view showing a schematic configuration of the copying machine according to this embodiment, and FIG. 4 is an explanatory view showing a main part of the copying machine. Note that some of the members are not shown in FIGS. 3 and 4 .

As shown in FIGS. 3 and 4 , this copying machine is upstream of the transfer position C of the photoconductor drum 30Y which is the most upstream photoconductor drum in the conveying direction of the recording paper 5 in that direction. Latent image forming sensor 1
00 (hereinafter, referred to as sensor 100) is provided. This sensor 100 is provided for each of the photosensitive drums 30Y, 3Y.
Exposure devices 32Y, 32 for 0M, 30C, 30B
It is provided to determine the timing to start the formation of the electrostatic latent image by M, 32C, and 32B. That is, to describe the latent image formation on the photosensitive drum 30Y by the exposure device 32Y as an example, when the leading end of the recording paper reaches the transfer position C based on the detection of the recording paper 5 by the sensor 100, The formation of an electrostatic latent image by the exposure device 30Y is started so that the toner image to be transferred to the front end portion of the photosensitive drum 30Y reaches the transfer position C. Then, similarly, latent images are formed on the photoconductor drums 30M, 30C, 30B by the exposure devices 32M, 32C, 32B.

As a result, when the sensor 100 does not detect the recording paper 5, that is, when the recording paper 100 is jammed upstream of the sensor 100, toner is applied to the photosensitive drums 30Y, 30M, 30C and 30B. No image is formed. Therefore, even though the recording paper 5 is not conveyed, the photosensitive drums 30Y, 30Y
It is possible to avoid a situation in which the portions on which the M, 30C, and 30B toner images are formed reach the respective transfer positions and the toner adheres to the transfer belt 1.

As shown in FIG. 4 , when the exposure device 32Y defines a latent image forming position where the electrostatic latent image is formed on the photosensitive drum 30Y as B and the position where the sensor 100 is provided as position D, the sensor 100 Is a transfer position C and a latent image forming position B
Are provided at positions such that the distance between the transfer position C and the position D along the transfer belt 1 is longer than the length BC of the arc formed on the surface of the photosensitive drum 30Y. Then, when the recording paper 1 reaches the position F, which is the position of the length BC in the conveyance direction of the recording paper 1 from the transfer position C, the exposure device 3
The formation of a latent image by 2Y is started. As a result, when the front end of the toner image formed on the photosensitive drum 30Y reaches the transfer position C, the front end of the recording paper 5 may have already passed the transfer position C. Disappear.

In the copying machine, the recording material detection sensor 10 for detecting the recording paper 5 being conveyed by the transfer belt 1.
1 (hereinafter, referred to as sensor 101). The sensor 101 is used to control the driving of the contact / separation unit including the first pressing member 65, the second pressing member 66, and the like. That is, if the sensor 101 should not detect the recording paper 5 at the timing when it should otherwise be detected, the transfer belt 1 is considered to have a defective conveyance of the recording paper 5 upstream of the sensor 101. Separated from the photoconductor drums 30Y, 30M, 30C, and 30B. As a result, toner is prevented from adhering to the transfer belt 1 from the respective photosensitive drums due to poor conveyance of the recording paper 1.

The sensor 101 is located upstream of the transfer position C of the photosensitive drum 30Y, which is the most upstream photosensitive drum in the conveying direction of the recording paper 5, in that direction and at the same time. The distance from the sensor 101 to the transfer position C is more than the distance obtained by multiplying the linear velocity of 30Y by the time required for the contact / separation unit to separate the transfer belt 1 from the photosensitive drum after the sensor 101 detects the conveyance failure.
It is installed in such a position that the distance to As a result, in the case where the recording paper 5 is poorly conveyed,
Before the front end of the toner image formed on the photoconductor drum 30Y reaches the transfer position C, the transfer belt 1 moves to the photoconductor drum 3
Since it is separated from 0Y, the adhesion of toner to the transfer belt 1 is prevented.

Further, in this copying machine, as shown in FIG. 4 , a sensor 101 is provided downstream of the sensor 100 in the conveying direction of the recording paper 5. Therefore, even when the conveyance failure of the recording paper 5 occurs at a position downstream of the sensor 100, if the position is upstream of the sensor 101, the transfer belt 1 is separated from the photosensitive drum 30Y. Become.

[0054] [Embodiment 3] Hereinafter, the present invention an electrophotographic copying machine which is an image forming apparatus (hereinafter, referred to as a copying machine) describes a third embodiment applied to. The present embodiment, since except for the newly added sensor to the second embodiment is common to Embodiment 2, the configuration of the intersection, and the description of the operation will be omitted. FIG. 5 is a front view showing a schematic configuration of the copying machine according to this embodiment. In addition, in FIG. 5 , illustration of some members is omitted.

As shown in FIG. 5 , in this copying machine, the area between the photosensitive drums, that is, the area between the photosensitive drum 30Y and the photosensitive drum 30M, the photosensitive drum 30M.
Sensors 102 are provided in the areas between the photoconductor drum 30C and the photoconductor drum 30C, and in the areas between the photoconductor drum 30C and the photoconductor drum 30B, respectively, in order to detect defective conveyance of the recording paper 5. Then, when any of these sensors 102 detects that the recording paper 5 is poorly conveyed, the contact / separation unit composed of the first pressing member 65, the second pressing member 66, etc. operates, and the transfer belt 1 Photoreceptor drums 30Y, 30M,
Separated from 30C and 30B. As a result, it is possible to prevent toner from adhering to the transfer belt 1 from each of the photoconductor drums due to poor conveyance of the recording paper 1 in the area between the photoconductors.

Further, these sensors 102 are provided in the immediate vicinity of the photosensitive drum on the upstream side in the conveying direction of the recording paper 5, respectively. Therefore, as compared with the case where the sensor 102 is provided downstream of the relevant position, it is possible to detect the conveyance failure of the recording paper 5 at an earlier timing, which allows the photosensitive drums 30Y and 30M of the transfer belt 1 to be detected. , 30C, 30B are also separated at an early timing .

【The invention's effect】

[0057] Claim1According to the invention, the recording material is not conveyed.
When the quality is good, the latent image is not formed on the latent image carrier.
Without transfer, transfer with the latent image carrier on which the toner image is formed
Transfer belt caused by the contact of the belt
Toner is prevented from adhering to the surface. Therefore, on the transfer belt
The adhered toner mixes with toner of other colors, and this mixture
It is possible to prevent the deterioration of the image quality due to.

According to the invention of claim 1 , the latent image is formed.
When the distance between the leading edge of the recording paper and the transfer position becomes equal to the distance between the latent image forming position and the transfer position on the most upstream latent image carrier, based on the signal from the sensor for use by the latent image forming means. By starting the latent image formation, the toner image can be satisfactorily transferred from the leading end of the recording material, and a good image is formed.

Further, according to the first aspect of the invention, the toner image transfer operation is not performed at the transfer position even though the trailing edge of the recording material has already passed the transfer section. Therefore, the adhesion of the toner to the transfer belt due to this is prevented, and the deterioration of the image quality due to the mixing of the toner adhered to the transfer belt with the toner of another color does not occur.

According to the second aspect of the present invention, when the recording material detection sensor does not detect the recording material at the timing when the recording material should be detected, the latent image carrier and the transfer belt are separated from each other, and the conveyance failure occurs. Since the toner is prevented from adhering to the transfer belt at this time, the toner adhering to the transfer belt does not mix with the toner of another color and the deterioration of the image quality due to this mixing does not occur. Further, when the present invention is applied to the image forming apparatus provided with the cleaning device for removing the toner adhering to the transfer belt, the cleaning device is not excessively burdened with the removal of the toner beyond its capability. .

In particular, according to the invention of claim 3 , the time from the recording material detection sensor detecting the conveyance failure to the transfer belt separating from the latent image carrier (hereinafter referred to as separation time).
From the transfer position to the recording material detection sensor, the distance from the transfer position to the recording material detection sensor is more than the distance obtained by multiplying the moving speed of the latent image carrier surface where the tip portion of the toner image of the latent image carrier moves while The sensor is provided at a position where the distance becomes long, and the transfer belt is separated from the latent image carrier by the time the tip reaches the transfer position. This makes it possible to more reliably prevent toner from adhering to the transfer belt from the latent image carrier, and the toner adhering to the transfer belt mixes with toner of other colors, resulting in deterioration of image quality due to this mixing. Is more reliably prevented.

According to the fourth aspect of the present invention, even if there is a conveyance failure of the recording paper downstream of the latent image forming sensor in the conveyance direction of the recording material, the position where the conveyance failure occurs is higher than the recording material detection sensor. If it is upstream, the recording material detection sensor detects that there is a conveyance failure, and the transfer belt is separated from the latent image carrier to prevent toner from adhering to the transfer belt. Therefore, even if the recording material is poorly conveyed at such a position, toner adhesion to the transfer belt is prevented, and the toner adhered to the transfer belt mixes with toner of other colors,
The deterioration of the image quality due to this mixing can be prevented more reliably.

According to the fourth aspect of the present invention, as in the case of using only the recording material detection sensor to prevent toner from adhering to the conveyor belt, a conveyance failure occurs upstream of the latent image forming sensor. Even in such a case, a situation in which a toner image is formed on the surface of the latent image carrier is avoided, and an excessive load is not imposed on the cleaning device that removes toner from the surface of the latent image carrier.

According to the fifth aspect of the present invention, when the sensor detects the conveyance failure of the recording material that has occurred in the area between the latent image carriers, the transfer belt and the latent image carrier are separated from each other. Therefore,
It is possible to prevent or reduce a large amount of toner from adhering to the transfer belt, and prevent the deterioration of image quality due to the toner adhering to the transfer belt being mixed with the toner of another color. Will be reduced.

According to the sixth aspect of the invention, the sensor is provided in the immediate vicinity of the latent image bearing member located upstream of the latent image bearing member provided in the region between the latent image bearing members in the conveying direction of the recording material. Compared with the case where a sensor is provided downstream of the position, the timing at which the transfer belt is separated from the latent image carrier becomes earlier, so that the amount of toner adhering to the transfer belt can be minimized. Become. As a result, the degree of deterioration of the image quality due to the toner adhering to the transfer belt being mixed with the toner of another color is further reduced.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a copying machine according to a first embodiment.

FIG. 2 is a front view showing a yellow toner image forming unit of the copying machine.

FIG. 3 shows a schematic configuration of a copying machine according to a second embodiment .
Front view.

FIG. 4 is an explanatory diagram showing a main part of the copying machine.

FIG. 5 shows a schematic configuration of a copying machine according to a third embodiment .
Front view.

[Description of Reference Signs] 1 transfer belt 2 drive roller 3 driven roller 4 transport unit 5 recording paper (recording material) 6 first transport guide plate 7 separation charger 8 second transport guide plate 10 transfer belt cleaning device 11 blotter roller 12 fan 30 Photoreceptor drum (latent image carrier) 31 Charging device 32 Exposure device 33 Developing device 34 Transfer device 35 Static eliminator 36 Cleaning device 37 Developing roller 38 Reverse roller 39 Case 40 Developer supply port 50 First sensor 51 Second sensor 60 Axis 61 the first arm 62 the shaft 63 the second arm 64 connecting member 65 first pressing member 66 the second pressing member 67 the spring 68 solenoids 1 00 latent image forming sensors 101 recording material detecting sensor 102 sensor Y yellow toner image forming unit M magenta Toner image forming section C Cyan toner image forming section B Kkutona image forming unit

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 5]

[Figure 4]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Satoshi Satoshi             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H027 DC04 DC14 DE02 DE07 DE09                       EB06 EC06 ED01 ED06 ED16                       ED24 ED27 EE02 EE03 EE05                       EE07 EF10 EH10 EK03 EK09                       FB07 FB19                 2H200 FA08 FA12 FA17 FA19 FA20                       GA12 GA23 GA33 GA44 GA47                       GB12 GB25 HA12 HB03 JA02                       JB07 JB12 JB17 JB18 JB25                       JB39 JB42 JB49 JB50 KA03                       KA07 LA15 LA24 LB02 LB08                       LB11 LB17 LB37 LB39 MC20                       PA10 PA11 PA18 PB12 PB26                       PB39                 2H300 EA18 EB04 EB07 EB12 ED07                       ED12 EF02 EF06 EF09 EF13                       EF16 EG03 EH15 EH35 EH36                       EJ09 EL04 EL06 EL09 EL10                       FF05 FF16 GG01 GG02 GG03                       GG19 GG29 HH15 HH24 MM30                       QQ10 QQ12 QQ28 QQ35 RR12                       RR19 RR26 RR50

Claims (19)

[Claims] 1. A plurality of latent image carriers on which latent images are formed, and a plurality of developing devices for forming latent images formed on the latent image carriers as toner images of different colors. A transfer belt that sequentially conveys the recording material to each of the plurality of latent image carriers, a transfer belt driving unit that rotationally drives the transfer belt, a cleaning unit that removes toner adhering to the transfer belt surface, A cleaning means driving means for driving a cleaning means; a sensor for detecting a conveyance failure of the recording material; and a contact / separation means for contacting and separating each of the latent image carriers with the transfer belt, In the image forming apparatus including, when the sensor detects a conveyance failure of the recording material, the contact / separation means separates the latent image carrier from the transfer belt,
In this state, there is provided control means for rotating the transfer belt by the transfer belt driving means, driving the cleaning means by the cleaning means driving means, and causing the cleaning means to remove toner on the surface of the transfer belt. Image forming apparatus. 2. The cleaning means is a cleaning means including a web and a pressing member for pressing the web against the transfer belt.
Image forming device. 3. The cleaning means is used for cleaning the transfer belt, a web supply means in which a web is wound in a roll shape, a press contact member for pressing the web against the transfer belt, and a press contact member for pressing the transfer belt. Cleaning means for winding the web, and cleaning means driving means for driving the web winding means by the cleaning means driving means to wind the web on the web winding means. And
When the sensor detects a conveyance failure of the recording material, the contact / separation unit separates the latent image carrier from the transfer belt, and in this state, the transfer belt drive unit rotationally drives the transfer belt, 2. The image forming apparatus according to claim 1, wherein the web winding means has a control means for making the winding speed of the web faster than the winding speed of the web during normal image formation. 4. The cleaning means is used for cleaning the transfer belt, a web supply means having a web wound around a roll, a pressure contact member for pressing the web against the transfer belt, and a pressure contact member for contacting the transfer belt. Cleaning means for winding the web, and cleaning means driving means for driving the web winding means by the cleaning means driving means to wind the web on the web winding means. And
The control means for causing the cleaning means driving means to drive the web winding means every time a plurality of times of image formation during normal image formation to cause the web winding means to wind up the web. 1. The image forming apparatus of 1. 5. The control means, during normal image formation,
When the cleaning means driving means drives the web winding means every plural times of image formation to cause the web winding means to wind the web, and when the sensor detects a conveyance failure of the recording target member, , The contact / separation unit separates the latent image carrier from the transfer belt, and in this state, the transfer belt drive unit rotationally drives the transfer belt,
The image forming apparatus according to claim 4, wherein the cleaning means driving means is a control means for continuously driving the web winding means to wind the web by the web winding means. 6. A plurality of latent image carriers on which latent images are formed, and a plurality of developing devices for forming latent images formed on the plurality of latent image carriers as toner images of different colors. A transfer belt that sequentially conveys the recording material to each of the plurality of latent image carriers, a transfer belt driving unit that rotationally drives the transfer belt, and a transfer belt that is provided in the vicinity of an outlet through which the recording material is discharged. A separation means for separating the recording material from the transfer belt, and a sensor for detecting a conveyance failure of the recording material,
An image forming apparatus comprising a contact / separation unit for bringing each of the latent image carriers into contact with the transfer belt and for separating the transfer belt from each other, and when the sensor detects a conveyance failure of the recording material, Control for separating the latent image carrier from the transfer belt by the contacting / separating means, rotating the transfer belt by the transfer belt driving means in this state, and separating the recording material from the transfer belt by the separating means. An image forming apparatus comprising means. 7. A plurality of latent image carriers on which a latent image is formed, and a plurality of developing devices for forming the latent images formed on the plurality of latent image carriers as toner images of different colors. A transfer belt that sequentially conveys a recording material to each of the plurality of latent image carriers, a transfer belt driving unit that rotationally drives the transfer belt, and a contact of each of the latent image carriers and the transfer belt. An image forming apparatus including a contact-separation unit that separates the contact-separation unit, and a control that causes the contact-separation unit to separate the latent image carrier from the transfer belt when the image forming operation is completed. An image forming apparatus comprising means. 8. A cleaning unit for removing toner adhering to the surface of the transfer belt, and a cleaning unit driving unit for driving the cleaning unit, wherein the control unit completes the image forming operation. The contact / separation means separates the latent image carrier from the transfer belt,
The image forming apparatus according to claim 7, wherein the image forming apparatus is a control unit that drives the cleaning unit in this state to drive the cleaning unit to remove toner on the surface of the transfer belt. 9. The cleaning means is a cleaning means including a web and a pressing member for pressing the web against the transfer belt.
Image forming device. 10. The cleaning means uses a web supply means in which a web is wound in a roll shape, a pressing member for pressing the web against the transfer belt, and a cleaning means for pressing the transfer belt to clean the transfer belt. And a web winding means for winding the formed web, the cleaning means driving means drives the web winding means so that the web winding means winds the web. When the image forming operation is completed, the contact / separation unit separates the latent image carrier from the transfer belt, and in this state, the transfer belt drive unit rotationally drives the transfer belt. Control for causing the web winding means to make the winding speed of the web faster than the winding speed of the web during normal image formation The image forming apparatus of claim 8 wherein a stage. 11. The cleaning means is used for cleaning the transfer belt, a web supply means in which a web is wound in a roll shape, a press contact member for pressing the web against the transfer belt, and a press contact member for contacting the transfer belt. Cleaning means for winding the web, and cleaning means driving means for driving the web winding means by the cleaning means driving means to wind the web on the web winding means. In the normal image formation, the cleaning means drive means has a control means for driving the web winding means for each image formation of a plurality of times so that the web winding means winds the web. The image forming apparatus according to claim 8. 12. The control means, during normal image formation, causes the cleaning means drive means to drive the web take-up means every time image formation is performed a plurality of times, and causes the web take-up means to take up the web. When the image formation is completed,
The contact / separation unit separates the latent image carrier from the transfer belt, and in this state, the transfer belt driving unit rotates the transfer belt, and the cleaning unit driving unit continuously connects the web winding unit. 12. The image forming apparatus according to claim 11, which is control means for driving the web to wind the web by the web winding means. 13. The control means causes the contact / separation means to separate the latent image carrier from the transfer belt when the image forming operation is completed, and in this state, the cleaning means drive means performs the cleaning. It is a control means for driving the means to remove the toner on the surface of the transfer belt, and for keeping the latent image carrier and the transfer belt separated from each other by the contact / separation member until the image is formed again. The image forming apparatus according to claim 8, wherein 14. A latent image carrier, and latent image forming means for forming a latent image on the surface of the latent image carrier at a latent image forming position determined for each latent image carrier. A plurality of developing devices for forming a plurality of latent images formed on the plurality of latent image carriers on toner images of different colors; a transfer belt for sequentially conveying a recording material to each of the latent image carriers; At the transfer position where the transfer belt driving unit that rotationally drives the transfer belt and the transfer belt and each of the latent image carriers are close to each other, the toner image formed on each of the latent image carriers is recorded on the recording material. A plurality of transfer devices for transferring, and a plurality of latent image carriers for starting latent image formation by the latent image forming means on the latent image carrier which is located on the most upstream side in the conveying direction of the recording material. A latent image forming sensor that detects the recording material. An image forming apparatus including: a latent image forming sensor, the latent image forming sensor being upstream of a transfer position of a latent image carrier located in the most upstream side in the recording material conveyance direction. And an image provided at a position where the distance from the transfer position to the latent image forming sensor is longer than the distance from the transfer position to the latent image forming position on the image carrier. Forming equipment. 15. A latent image carrier, and latent image forming means for forming a latent image on the surface of the latent image carrier at a latent image forming position determined for each latent image carrier. A plurality of developing devices for forming a plurality of latent images formed on the plurality of latent image carriers on toner images of different colors; a transfer belt for sequentially conveying a recording material to each of the latent image carriers; At the transfer position where the transfer belt driving unit that rotationally drives the transfer belt and the transfer belt and each of the latent image carriers are close to each other, the toner image formed on each of the latent image carriers is recorded on the recording material. A plurality of transfer devices for transferring, a recording material detection sensor for detecting a recording material being conveyed, and a contact / separation unit for contacting and separating each of the latent image carriers with the transfer belt. An image forming apparatus including the recording material detection sensor When the recording material is not detected at the timing when the recording material is being conveyed, the contact / separation means has a control means for separating the latent image carrier from the transfer belt. A characteristic image forming apparatus. 16. The image forming apparatus according to claim 15, wherein the recording material detection sensor is located upstream of a transfer position of the latent image carrier located at the most upstream side in the recording material transport direction in the direction. From the distance obtained by multiplying the moving speed of the latent image carrier by the time required for the contact / separation unit to separate the transfer belt from the latent image carrier after the sensor detects the conveyance failure. Also, the image forming apparatus is provided at a position such that the distance from the sensor to the transfer position is long. 17. The image forming apparatus according to claim 15, wherein a latent image formed by the latent image forming means with respect to a latent image carrier which is located on the most upstream side in the conveyance direction of the recording material among the plurality of latent image carriers. The image carrier is detected upstream of the transfer position of the latent image carrier with respect to the conveyance direction, and the image carrier is detected from the transfer position of the latent image carrier to start the formation. In the conveyance direction of the recording material, the latent image forming sensor is provided at a position where the distance from the transfer position is longer than the distance to the latent image forming position. In the image forming apparatus, the recording material detection sensor is provided on the downstream side. 18. A latent image carrier, and latent image forming means for forming a latent image on the surface of the latent image carrier at a latent image forming position determined for each latent image carrier. A plurality of developing devices for forming a plurality of latent images formed on the plurality of latent image carriers on toner images of different colors; a transfer belt for sequentially conveying a recording material to each of the latent image carriers; At the transfer position where the transfer belt driving unit that rotationally drives the transfer belt and the transfer belt and each of the latent image carriers are close to each other, the toner image formed on each of the latent image carriers is recorded on the recording material. A plurality of transfer devices for transferring, a sensor for detecting a conveyance failure of the recording material, and a contact / separation unit for contacting and separating each of the latent image carriers with the transfer belt. An image forming apparatus, wherein the sensor is Provided in a region between the image bearing member, and,
An image forming apparatus, wherein the contact / separation unit has a control unit for separating the latent image carrier from the transfer belt when the sensor detects a conveyance failure of the recording material. 19. The image forming apparatus according to claim 18, wherein the sensor is provided in the area between the latent image bearing members located upstream of the latent image bearing member upstream in the recording material conveying direction. An image forming apparatus comprising the sensor.