JPH04149564A - Image forming device - Google Patents

Abstract

PURPOSE:To rapidly carry in a recording material so that it may not be caught in the joint part of a carrying means by providing a means for detecting a joint several times while an endless type recording material carrying means provided with the joint is rotated nearly once. CONSTITUTION:In the case that a distance from a mark 18 provided on a posi tion near the joint part 81 of a carrying belt 8 to a sensor 17 in the moving direction of the belt 8 is <= nearly L/2 when the carrying belt 8 is started to be actuated, that means, in the case that the mark 18 passes through the sensor 17 earlier than a mark 19, a timing is calculated by a signal from the sensor 17 so that the joint part 81 on the belt 8 can reach a point (A point) where the recording material 6 is carried in exact timing with passing of the mark 18 through the sensor 17, and then, a roller 13 is actuated so that the recording material 6 may be carried in just after the joint part 81 passes by.

Description

DETAILED DESCRIPTION OF THE INVENTION [Higashijou five-plate ball 1] The present invention provides a method for transferring a visible image formed on an image carrier such as a photoreceptor, an insulator, or a magnetic material to a recording material conveyed by a conveyance means. Regarding an image forming apparatus configured to transfer, for example, but not limited to, a plurality of images of different colors are formed on a plurality of image carriers such as an electrophotographic photoreceptor,
This invention is suitable for color copying machines, printers, and the like that sequentially transfer these images onto the same recording material conveyed by a conveyance means.

[i.Response I] Conventionally, a plurality of image forming sections are provided, each image forming section forms a developed image (toner image) of a different color, and these toner images are transferred to the same recording material conveyed by a conveying means. A variety of image forming apparatuses have been proposed, which produce a composite color image by sequentially overlapping transfers and uniform review, and among these, the most commonly used is electrophotographic color copying. It is a machine.

An example of such an electrophotographic color copying machine is shown in FIG. Inside the main body of this color copying machine are the first and second
, a third and a fourth image forming section Pa, Pb, Pc, and Pd are arranged in parallel, and each image forming means Pa, Pb,
Pc and Pd have substantially the same configuration, and are each equipped with a dedicated image carrier, in this example, electrophotographic photosensitive drums 1a, 1b, IC, and 1d, which are rotationally driven in the direction of the arrow in the figure as usual. are doing. Around each of the photoreceptor drums 18 to 1d, there are dedicated image forming process means, such as electrostatic latent image forming sections 2a, 2b, 2C and 2d, and a developing section 3a.
, 3b, 3C and 3d, cleaning parts 5a, 5b, 5
C, 5d, etc. are arranged sequentially in the drum rotation direction.

Further, an endless recording material conveying means, in this example, a recording material conveying belt 8, is arranged below each image forming section Pa, Pb, Pc, Pd, and inside this conveying belt 8, each image forming section P At the bottom of the photoreceptor drums 18 to 1d of a to Pd,
Transfer parts 4a, 4b, 4C and 4d are provided.

In the color copying machine having such a configuration, when the recording material 6 is placed from the recording material cassette 60 through the pair of registration rollers 13 and onto the conveyor belt 8 serving as recording material conveying means, the conveyor belt 8 moves in the direction of the arrow in FIG. As the photosensitive drums 1a, 1b, of the corresponding image forming units Pa to Pd move to
The image forming process for 1c and ld is started sequentially.

First, a latent image of the black component color of the original image is formed by the latent image forming section 2a on the photosensitive drum la of the first image forming section Pa. The latent image is made into a visible image by a developer containing black toner in the developing section 3a, and this black toner image is transferred to the recording material 6 conveyed by the conveying belt 8 at the transfer section 4a. While this black toner image is being transferred to the recording material 6, a latent flaw of magenta component color is formed on the photosensitive drum 1b of the second image forming section pb by the latent image forming section 2b, and then a latent scratch of magenta component color is formed on the photosensitive drum 1b of the second image forming section pb. When the recording material 6 on which a visible image is formed using magenta toner and the transfer at the first image forming section Pa has been completed is carried into the transfer section 4b below the photosensitive drum 1b of the second image forming section PB. , this magenta toner image is transferred to a predetermined position on this recording material 6.

Thereafter, in the same manner, yellow toner images and cyan toner images formed on the photoreceptor drums 1c and 1d of the third and fourth image forming portions Pc and Pd, respectively, are transferred to the transfer portions 4c and 4d below these photoreceptor drums. The images are superimposed and transferred to predetermined positions on the conveyed recording material 6, thus completing the process of transferring the four-color full-color image onto the recording material 6. When the transfer process is completed, the recording material 6 is separated from the conveyor belt 8 by a separating means (not shown) and sent to the fixing section 7, where the superimposed and transferred color toner images are melted and fixed onto the recording material 6. After that, the image is ejected to an ejection tray, and the desired full color image is thus obtained.

On the other hand, each photosensitive drum 1a has completed the transfer. 1b, 1c
and 1d, residual toner is removed by cleaning sections 5a, 5b, 5C, and 5d in preparation for the next latent image formation to be performed subsequently.

Incidentally, in the above image forming apparatus, generally, as a recording material conveying belt, both ends of a dielectric resin film sheet such as a polyethylene terephthalate resin film sheet, a polyfukkavinylidene resin film sheet, or a polyurethane resin film sheet are overlapped with each other. Many are used that are joined together to form an endless shape. This is because so-called seamless belts having no seams are difficult to manufacture and are very expensive, resulting in a great disadvantage in terms of cost.

When using a belt with such a seam, if transfer is performed on a recording material at a location corresponding to the seam, the physical properties of the seam are different from those of the surrounding areas, so transfer omissions may occur, or the seam may be damaged. If it is convex, it will strongly hit the photoreceptor, causing image defects such as image disturbance. Therefore, a mechanism is provided to detect this seam part during preliminary rotation prior to image formation, and the seam part is detected and, for example, immediately after this seam part passes the part where the recording material is conveyed to the belt, the recording material Conventionally, a method has been taken in which the above-mentioned problem is avoided by carrying the belt into the belt.

However, in the conventional image forming apparatus having the above configuration, the position of the seam on the conveyor belt is detected before starting the actual image forming operation.
In the worst case, the image forming operation cannot be started while the conveyor belt makes approximately one revolution, resulting in a prolonged rotation before image forming, resulting in a long so-called first copy time. In addition, the conveyor belt and devices, parts, members, etc. that operate at the same time as the conveyor belt, such as photoreceptor drums and fixing devices, are operated redundantly due to rotation before image formation. It also had the disadvantage of shortening its lifespan.

Therefore, an object of the present invention is to be able to quickly transport the recording material to the endless recording material conveyance means without getting caught in the joint portion of the conveyance means, thereby significantly shortening the first copy time, and to reduce the first copy time. An object of the present invention is to provide an image forming apparatus that can extend the life of parts, members, devices, etc. that are forced to operate during rotation before image formation by reducing copy time.

1. The above objects are achieved by an image forming apparatus according to the present invention. To summarize, the present invention provides an image forming apparatus that forms an image on an image carrier and transfers the image to a recording material conveyed by an endless recording material conveying means having a seam. The image forming apparatus is characterized in that it includes means for detecting the seam a plurality of times during approximately one rotation of an endless recording material conveying means having a seam.

According to an embodiment of the present invention, the means for detecting the seam a plurality of times during approximately one rotation of the endless recording material conveying means includes a plurality of marks provided on the recording material conveying means and a plurality of marks provided on the recording material conveying means. and one mark reading sensor arranged around the recording material conveyance means to read the marks.

According to another embodiment of the present invention, the means for detecting the seam a plurality of times during approximately one rotation of the endless recording material conveying means detects one mark provided on the recording material conveying means. and a plurality of mark reading sensors arranged around the recording material conveyance means to read the marks.

According to still another embodiment of the present invention, the means for detecting the seam a plurality of times during approximately one revolution of the endless recording material conveying means includes a plurality of marks provided on the recording material conveying means. and a plurality of mark reading sensors arranged around the recording material conveyance means to read these marks.

EMBODIMENT OF THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 6 is a sectional view schematically showing the overall configuration of a color image forming apparatus to which the present invention is applied, and shows a case where the apparatus is applied to an electrophotographic color copying machine. Before explaining the main parts of the present invention, first, the overall operation of the color copying machine shown in FIG. 6 will be explained.

As shown in the figure, this color copying machine includes a copying machine main body 10
There are four image forming units Pa, first, second, third and fourth.
, Pb, Pc and Pd are arranged in parallel. Each of the image forming units Pa, Pb, Pc, and Pd has substantially the same configuration, and includes dedicated electrophotographic photosensitive drums 1a, lb, which are image carriers that are rotationally driven in the direction of the arrow in the figure, as usual. Including 1c and 1d. For example, chargers 15a, 15b, 15c for uniformly charging the photoreceptor drum are provided around each photoreceptor drum.
and tsct, developing devices 3a, 3b, 3c, and 3d that develop the electrostatic latent image formed on the five-photo drum, a transfer discharge device 4a that transfers the developed toner images of each color onto the recording material 6,
4b, 4c and 4d, cleaning means 5a, 5b, 5c and 5d for removing toner remaining on the photoreceptor drum;
etc. are arranged sequentially in the drum rotation direction.

Furthermore, laser beam scanners 16a, 16b, 16c and 16d are provided above each of the photosensitive drums 1a, 1b, 1c and 1d, respectively. These laser beam scanners 16a, 16b, 16c, and 16d are composed of a semiconductor laser, a polygon mirror, an fθ lens, etc., and upon receiving an electric digital pixel signal, send a laser beam modulated in accordance with this signal to the charger 15a. , 15b,
The drum surface is exposed by scanning in the drum generatrix direction between the developing devices 15c and 15d and the developing devices 3a, 3b, 3c and 3d.

On the other hand, below the photoreceptor drums 1a, 1b, 1c, and 1d, there is an endless recording material conveying member having a joint that rotates in the direction of the arrow in the figure so as to cross each image forming section Pa, Pb, Pc, and Pd. In the example, a recording material conveying means including a conveying belt 8 is arranged. The conveyor belt 8 having this seam is stretched between the drive roller 11 and the idler roller 12 via a tension adjusting roller 76, and is endlessly driven by the drive roller 11 in the direction shown by the arrow in FIG. The recording material 6 fed from the cassette 60 is supported and sequentially conveyed to each of the transfer positions of the aforementioned image forming sections Pa, Pb, Pc, and Pd.

In the color image forming apparatus having the above configuration, when an image forming work start signal is input to the image forming apparatus, the photosensitive drum 1a of the first image forming section Pa starts rotating in the direction of the arrow shown in the figure, and the charger 15a After that, the laser beam scanner 16a writes a laser beam modulated by an image signal corresponding to the black component image of the original image, thereby forming a latent image. Next, the latent image is developed by the developing device 3a containing black toner.
A black toner image is formed on the photoreceptor la.

On the other hand, the recording material 6 in the recording material cassette 60 is taken out by the pickup roller 9 and sent to the registration roller 13. The recording material 6 once stopped by this registration roller 13
is sent onto the conveyor belt 8, which has already started rotating, by the registration rollers 13 in synchronization with the toner image formed on the photoreceptor la. The recording material 6 fed onto the conveyor belt at the right timing is transferred from the back side of the conveyor belt 8 by the transfer discharger 4a while moving through the transfer section below the photoreceptor drum 1a of the first image forming section Pa. The black toner image on the photosensitive drum la is transferred onto the recording material 6 by corona discharge. While this black toner image is being transferred to the recording material 6, the second
A visible image of magenta toner is formed on the photoreceptor drum 1b of the image forming section pb, and the recording material 6, which has been transferred at the first image forming section Pa, is transferred to the photoreceptor drum 1b of the second image forming section pb. While moving through the lower transfer section, the magenta toner image is transferred to a predetermined position on the recording material 6 by the action of the transfer discharge device 4b.

Thereafter, the third and fourth image forming portions P are formed by similar steps.
The yellow toner image and the cyan toner image formed on the photoreceptor drums lc and 1d of Pd and lc are transported to the transfer position below the photoreceptor drums by the action of the transfer dischargers 4c and 4d, respectively, on the recording material 6. The four-color full-color image is transferred onto the recording material 6 in a superimposed manner, thus completing the process of transferring the four-color full-color image onto the recording material 6. When the transfer process is completed, the recording material 6 is separated from the conveyor belt 8 while being subjected to AC static electricity removal by a separation charger 61 almost directly above the roller 12 at the left end of the conveyor belt 8, and sent to the fixing section 7, where it is fixed. After the color toner images superimposed and transferred in the section 7 are fused and fixed on the recording material 6, they are discharged from the discharge port 14 to the outside of the copying machine main body 10, thus obtaining a desired full-color image.

After the transfer, residual toner is removed from each photosensitive drum by cleaning means 5a, 5b, 5c, and 5d in preparation for the next latent image formation to be performed subsequently.

Next, the main parts of the present invention will be explained in detail.

FIG. 1 is a schematic sectional view showing the main parts of an embodiment of an image forming apparatus according to the present invention. In this embodiment, when the distance from the image exposure position E of the photoreceptor drum 1a to the transfer lower part along the rotational direction of the photoreceptor drum 1a is ET, from the transfer portion T to the upstream side in the moving direction of the conveyor belt 8. Almost distance ET
In this embodiment, the optical sensor 17 for reading the mark provided on the conveyor belt 8 is placed at a point S that is traced back by ET, that is, at a point S where ET→TS changes. to be installed. Of course, this sensor 17 may be installed inside or outside the conveyor belt 8. On the other hand, a mark 18 indicating the joint 81 is provided near the joint 81 on the conveyor belt 8 and near the front end thereof, and a mark 18 is provided on the downstream side of the conveyor belt 8 from this mark 18 in the direction of movement of the conveyor belt 8. A mark 18 is located on the conveyor belt at a distance of approximately L/2, which is approximately half the circumferential length of the conveyor belt 8, and indicates that the distance is approximately L/2 from the joint portion 81. A different mark 19 is provided. When an optical sensor is used as in this embodiment, the marks 18 and 19 are one slit and the mark 19 is two slits, for example, as shown in FIG. I set up something like this.

Note that these marks are preferably provided outside the area on the conveyor belt 8 where the recording material 6 is placed, that is, outside the image forming area.

Further, in this embodiment, the marks 18 and 19 are slits, but they may be made of any material that can be identified by the optical sensor 17 (for example, a paint having a different optical reflectance from the surrounding conveyor belt 8). It goes without saying that methods such as coating may also be used.

Further, although an optical type sensor is used in this embodiment as a sensor for reading marks, it is of course possible to use a different type of sensor such as an electric type, a magnetic type, or a mechanical type. It goes without saying that it is better to use one that suits your needs.

Now, in an image forming apparatus equipped with such a sensor and mark, when a signal indicating the start of image formation is input, the photoreceptor drums 18 to 1d and the conveyor belt 8 are driven in the directions of the arrows, and at the same time the paper is fed. The mechanism is activated to take out the recording material 6 from the recording material cassette 60 and drive it in the direction indicated by the arrow.

After the recording material 6 is conveyed to the registration rollers 13, it is temporarily stopped there by the action of the registration rollers 13, and enters a standby state.

Next, the operation of the conveyor belt 8 will be explained using the following two cases.

When the conveyor belt 8 starts to operate, the conveyor belt 8 starts from the mark 18 provided near the joint 81 of the conveyor belt 8
The distance to the sensor 17 in the direction of movement is approximately L/
2 or less, that is, when the mark 18 passes the sensor 17 earlier than the mark 19, when the mark 18 passes the sensor 17, the position of the registration roller 13! When the recording material 6 is waiting, the seam 8 on the conveyor belt 8
1 arrives at the point where the recording material 6 is carried onto the conveyor belt 8 (point A shown in FIG. 1).
A synchronization timing is calculated by a calculation means (not shown) based on a signal from the sensor 17, and the registration roller 13 is operated by a motor (not shown) so that the recording material 6 is carried in immediately after the joint portion 81. On the other hand, photoreceptor drum 1
At point a, almost at the same time as the mark 18 passes the sensor 17, a light image is irradiated onto the point E on the photosensitive drum 1a in synchronization with the movement of the recording material 6.

Begins forming a latent image. At this time, since the distance ET:TS is established as described above, when the leading edge of the recording material 6 reaches the transfer position T of the photosensitive drum 1a, it is precisely synchronized with the leading edge of the toner image on the photosensitive drum la. , enabling efficient operation.

On the other hand, if the recording material 6 is not waiting at the position of the registration roller 13 when the mark 18 passes the sensor 17, the recording material 6 is not waiting at the position of the registration roller 13. The recording material 6 is carried in on the downstream side of the joint portion 81 in the belt conveyance direction.

Furthermore, from this state, the recording material 6 is continuously transferred to the conveyor belt 8.
In other words, in the continuous image forming mode, the signal generated when the mark 18 passes the sensor 17 is used to determine the position at which the first recording material 6 is transported to the conveyor belt 8 and the recording material. The recording material 6 is conveyed onto the conveyor belt 8 by the action of the registration rollers 13 while always changing the distance between the recording materials so that the recording material does not overlap the seam 81, taking into consideration the size of the recording material. It was also found that good results could be obtained.

Next, regarding a case in which the mark 19 provided at a position approximately L/2 apart from the joint 81 of the conveyor belt 8 passes the sensor 17 earlier than the mark 18 when the conveyor belt 8 starts operating. explain.

In this case as well, the general operation is that the mark 18 mentioned above is the mark 1.
This is the same as the case where the sensor 17 is passed before the sensor 9.

However, in this case, if the circumferential length of the conveyor belt 8 is shorter than twice the length in the conveyance direction of the recording material to be carried in at this time, and if image formation is performed continuously, the mark 19 will be It is preferable to carry the recording material 6 in such a way that the recording material 6 does not always touch the seam 81 using the signal when it passes the sensor 17 .

When an image is formed using an image forming apparatus having a configuration in which two marks are provided on the conveyor belt 8 to indicate the distance from the joint 81 as in this embodiment, even if the first copy time is the worst, Good results were obtained in that the first copy time was shortened to almost half of the maximum value of , and on average to almost half of that of the conventional method, and the lifespan of the conveyor belt, photoreceptor drum, fixing device, etc. was also extended.

In this embodiment, two marks are provided on the conveyor belt 8 to indicate the joints, but it goes without saying that even better results can be obtained if three or more marks are provided.

In addition, until the mark on the conveyor belt passes the sensor, the moving speed of the conveyor belt is set faster than after the mark has passed the sensor, that is, after the actual image formation has started (this will produce even better results). Needless to say, you can get it.

FIG. 3 is a schematic sectional view showing the main parts of a second embodiment of the image forming apparatus according to the present invention. In this embodiment, when the distance from the image exposure position E of the photoreceptor drum 1a to the transfer portion T along the rotational direction of the photoreceptor drum 1a is ET,
At a point S that is approximately a distance ET back from the transfer portion T toward the upstream side in the moving direction of the conveyor belt 8, that is, at a point S where ET''=TS,
The first one is for reading marks provided on the conveyor belt 8.
and a second optical sensor 20 at a distance of about L/2, which is approximately half the circumference of the conveyor belt 8, from the point S. Install it near the front side of 8. Of course, these first and second optical sensors 17 and 20 may be installed inside or outside the conveyor belt 8. On the other hand, near the joint 81 on the conveyor belt 8 and near the front end.

A mark 18 indicating this joint portion 81 is provided.

When an image is formed using the image forming apparatus having the above configuration, when the mark 18 indicating the seam 81 passes the first or second sensor 17 or 20, the same result as shown in the first embodiment is detected. It became possible to start image formation with the following operating procedure, and good results similar to those of the first embodiment were obtained. In other words, even in the worst case, the first copy time is approximately half of the maximum value of the conventional first copy time.
On average, the lifespan of the conveyor belt, photoreceptor drum, fixing device, etc. has been reduced to about half that of the conventional method.

In this embodiment, two sensors are installed to detect the mark 18 indicating the joint 81 provided on the conveyor belt 8, but if three or more sensors are installed, even better results can be obtained. Needless to say, you can obtain

In addition, better results can be obtained by moving the conveyor belt faster until the mark on the conveyor belt passes the sensor than after the mark has passed the sensor, that is, after the actual image formation begins. Needless to say, it can be done.

FIG. 4 is a schematic cross-sectional view showing the main parts of a third embodiment of the image forming apparatus according to the present invention. In this embodiment, when the distance from the image exposure position E of the photoreceptor drum 1a to the transfer portion along the rotational direction of the photoreceptor drum 1a is ET,
A first optical sensor for reading a mark provided on the conveyor belt 8 is located at a point S that is approximately a distance ET from the lower part of the transfer section toward the upstream side in the moving direction of the conveyor belt 8, that is, at a point S at ET@TS. 17, and a second optical sensor 20 at a distance of about L/2, which is approximately half the circumferential length of the conveyor belt 8, from the point S, respectively, on the front side of the conveyor belt 8. Install it nearby. Of course, these first and second
The optical sensors 17 and 20 may be installed inside or outside the conveyor belt 8. On the other hand, the conveyor belt 8
A mark 18 indicating the seam 81 is provided in the vicinity of the upper seam 81 and near the front end, and furthermore, a mark 18 indicating the seam 81 is provided in the vicinity of the upper seam 81 and on the downstream side in the moving direction of the conveyor belt 8 and around the circumference of the conveyor belt 8. The distance that is approximately % of the length is approximately L/
A mark 21 is provided at a position on the conveyor belt that is approximately L/4 away from the seam 81. In this embodiment, the mark 21 is provided on the conveyor belt at a position approximately L/4 away from the mark 18 on the downstream side in the direction of travel of the conveyor belt, but at a position approximately L/4 on the upstream side.
It goes without saying that they may be provided at positions on the conveyor belt that are separated by 4 degrees.

When the image forming apparatus having the above configuration is used to form an image, when the mark 18 or mark 21 indicating the seam 81 passes the first or second sensor 17 or 2 degrees, the first and second sensors It became possible to start image formation using the same operating procedure as shown in the example, and good results similar to those of the first and second examples were obtained. In other words, even in the worst case, the first copy time is shortened to almost the maximum value of the conventional first copy time, and on average it is shortened to almost the same as that of the conventional method, and the life of the conveyor belt, photoreceptor drum, fixing device, etc. is extended. became.

In this embodiment, two marks indicating the seam 81 of the conveyor belt 8 are provided, and these marks are detected by two sensors. However, if three or more marks and three or more sensors are provided, It goes without saying that even better results can be obtained by providing three or more of either one of them.

In addition, until the mark on the conveyor belt passes the sensor, the moving speed of the conveyor belt is set faster than after the mark has passed the sensor, that is, after the actual image formation has started (this will produce even better results). Needless to say, you can get it.

FIG. 5 is a schematic sectional view showing the main parts of a fourth embodiment of the image forming apparatus according to the present invention. In this embodiment, when the distance from the image exposure position E of the photoreceptor drum 1a to the transfer portion T along the rotational direction of the photoreceptor drum 1a is ET,
A first optical system for reading marks provided on the conveyor belt 8 is located at a point S that is approximately a distance ET back from the transfer portion T toward the upstream side in the moving direction of the conveyor belt 8, that is, at a point S where ET:TS. The sensor 17 is also connected to a second optical sensor at a position downstream from the point S in the moving direction of the conveyor belt 8 and at a distance of approximately L/4, which is approximately the length of the circumference of the conveyor belt 8. The sensors 22 are installed near the front side of the conveyor belt 8, respectively. These first and second optical sensors 17 and 2
2 may be installed inside or outside the conveyor belt 8.

On the other hand, a mark 18 indicating the joint 81 is provided near the joint 81 on the conveyor belt 8 and near the front end thereof,
Furthermore, a distance of approximately half the circumferential length of the conveyor belt 8 from the position of the mark 18 is approximately L/2, and a distance of approximately L/2M from the joint portion 81 is located on the conveyor belt. 0, which has a mark 19 indicating the position.
In this embodiment, the sensor 22 is provided at a position approximately L/4 away from the sensor 17 on the downstream side in the direction of travel of the conveyor belt.
Needless to say, it may be provided at a position approximately L/4 away from the upstream side.

When the image forming apparatus having the above configuration is used to form an image, when the mark 18 or mark 19 indicating the seam 81 passes the first or second sensor 17 or 22, the first to third embodiments are performed. It became possible to start image formation using the same operating procedure as shown in the example, and good results similar to those of the first to third embodiments were obtained. In other words, even in the worst case, the first copy time is almost the same as the maximum value of the conventional first copy time, and on average it is shortened to almost the same as the conventional first copy time, and the lifespan of the conveyor belt, photoreceptor drum, fixing device, etc. is also long. became.

In this embodiment, two marks indicating the seam 81 of the conveyor belt 8 are provided, and these marks are detected by two sensors. However, if three or more marks and three or more sensors are provided, It goes without saying that even better results can be obtained by providing three or more of either one of them.

In addition, better results can be obtained by moving the conveyor belt faster until the mark on the conveyor belt passes the sensor than after the mark has passed the sensor, that is, after the actual image formation begins. Needless to say, it can be done.

In addition, although the above embodiment shows the case where the present invention is applied to an electrophotographic color image forming apparatus, the present invention can be applied to various copying machines using an electrophotographic method, an electrostatic recording method, etc. other than the embodiments,
It is equally applicable to image forming apparatuses such as printers. Furthermore, it goes without saying that various modifications and changes can be made as necessary.

As is clear from the above description, the image forming apparatus according to the present invention is capable of moving the joint portion of the endless recording material conveying means during one revolution of the endless recording material conveying means having the seam. Since the detection can be performed multiple times, and based on the detection results, the recording material is quickly transported to the conveyance means without being caught in the seam, the first copy time can be reduced even in the worst case to the maximum of the conventional first copy time. The value can be reduced to approximately H or less, and on average to approximately less than the conventional value. Therefore, the first copy time can be significantly shortened, and by reducing the first copy time, parts, members, devices, etc. that are forced to operate during rotation before image formation, such as conveyor belts, photoreceptor drums, fixing devices, etc. It has the remarkable effect of prolonging the lifespan of

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing the main parts of a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is an enlarged plan view showing a portion of the conveyor belt used in the image forming apparatus of FIG. 1. FIG. 3 is a schematic sectional view showing the main parts of a second embodiment of the image forming apparatus according to the present invention. Figure 4 shows an image forming bag according to the present invention! FIG. 3 is a schematic cross-sectional view showing main parts of a third embodiment of the invention. FIG. 5 is a schematic sectional view showing the main parts of a fourth embodiment of the image forming apparatus according to the present invention. FIG. 6 is a sectional view schematically showing the overall configuration of a color image forming apparatus to which the present invention is applied. FIG. 7 is a schematic cross-sectional view showing an example of a conventional color image forming apparatus. 18 to 1d: Recording material conveying belt having two joints of photoreceptor drums 6 and 8. 20.22: Sensor 18.19.21 = Mark 81: Joint portion Figure Figure Figure Figure Figure Figure Figure Figure

Claims (1)

[Scope of Claims] 1) An image forming apparatus that forms an image on an image carrier and transfers the image to a recording material conveyed by an endless recording material conveying means having a seam. An image forming apparatus comprising means for detecting the seam a plurality of times during approximately one rotation of an endless recording material conveying means having a seam. 2) The means for detecting the seam a plurality of times during approximately one rotation of the endless recording material conveying means detects a plurality of marks provided on the recording material conveying means and the recording material in order to read these marks. 2. The image forming apparatus according to claim 1, further comprising one mark reading sensor arranged around the conveying means. 3) The means for detecting the seam a plurality of times during approximately one rotation of the endless recording material conveying means detects one mark provided on the recording material conveying means and the recording material conveying means for reading the mark. The image forming apparatus according to claim 1, further comprising a plurality of mark reading sensors arranged around the means. 4) The means for detecting the seam a plurality of times during approximately one rotation of the endless recording material conveying means detects a plurality of marks provided on the recording material conveying means and the recording material in order to read these marks. The image forming apparatus according to claim 1, further comprising a plurality of mark reading sensors arranged around the conveyance means.