JPH09274344A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately adjust a position where an image is formed on printing paper by controlling the operation timing of a resist mechanism corresponding to the operation timing of a processing unit. SOLUTION: The printing paper 6 is fed to a paper feeding path 12 by a paper feeding mechanism 7. When the paper 6 is detected by a paper detection sensor 25, the resist mechanism 8 is set to a stopped state and feeding the paper 6 is temporarily stopped. An image is started to be formed by a process unit 10 corresponding to the detection by the sensor 25. The image forming start timing and paper feeding restart timing by the resist mechanism 8 are appropriately controlled. By the control of timing, the paper 6 passes through the resist mechanism 8 and is fed to a belt carrying mechanism 9. The paper 6 is electrostatically attracted by a circulating transfer belt 21 and successively carried to the positions of four processing units 10.

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 that conveys printing paper by means of a circulating endless transfer belt.

[0002]

2. Description of the Related Art At present, an image forming apparatus for forming an image by an electrophotographic method is widely used as a laser printer or a copying machine. In such an image forming apparatus, there are various types of mechanisms for transporting printing paper, but for example, many color printers employ a belt transport mechanism.

In this case, an electrophotographic mechanism for transferring toner to printing paper to form an image is provided as a process unit, and a plurality of process units are sequentially arranged at positions facing one belt conveying mechanism. The belt transport mechanism includes an endless transfer belt that electrostatically attracts printing paper, and the transfer belt is stretched linearly by a plurality of rotating rollers. In such a color printer, printing paper is electrostatically adsorbed by a transfer belt and sequentially transported, and toner of each color is sequentially transferred by the plurality of process units to the printing paper thus transported to form a color image. .

Further, in a general image forming apparatus, a jam may occur on the printing paper to be carried. Therefore, when this is detected, the operation of each unit related to the transportation of the printing paper is stopped. However, in the image forming apparatus in which the process unit is arranged to face the belt transport mechanism as described above, the print sheet is jammed before reaching the process unit, and if the detection is delayed, the image is transferred to the transfer belt. . In order to solve this, JP-A-63
In the image forming apparatus described in JP-A-47245 or JP-A-63-296078, the process unit transfers the toner to the transfer belt by separating the transfer belt and the process unit when the occurrence of a jam is detected. Prevent that.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the image forming apparatus described in Japanese Patent Laid-Open No. 45-296078 and Japanese Patent Laid-Open No. 63-296078, when the occurrence of a jam is detected, the transfer belt and the process unit are separated from each other, so that the process unit does not transfer toner to the transfer belt. It can be prevented.

However, this requires a mechanism for bringing the transfer belt and the process unit into contact with each other, and the structure is complicated, which hinders reduction in size and weight of the image forming apparatus and improvement in productivity. Further, in the above-described image forming apparatus, when a jam occurs, the transfer belt and the process unit are separated from each other regardless of the position, so that, for example, the image forming operation is unnecessarily hindered. That is, in the case where images are continuously formed on a plurality of printing papers, even if a jam occurs on a certain printing paper, this may not hinder the transfer belt from carrying the other printing papers. In the forming device,
Even in such a case, the image forming operation is stopped by separating the transfer belt from the process unit.

[0007]

According to the first aspect of the present invention,
A paper feeding mechanism that sequentially feeds printing paper, a registration mechanism that temporarily stops printing paper that is sequentially fed, and an endless transfer belt that can circulate the printing paper that has been paused and then resumed feeding. A belt transport mechanism that electrostatically attracts and sequentially transports a process unit that forms an image on a printing sheet that is electrostatically attracted to the transfer belt and sequentially transported, and the registration mechanism corresponding to the operation timing of the process unit. And timing control means for controlling the operation timing of. Therefore, when the registration mechanism pauses the printing paper sequentially fed by the paper feeding mechanism and then restarts the feeding, the belt feeding mechanism electrostatically adsorbs the printing paper by the endless transfer belt. Are sequentially conveyed, and the process unit forms an image on the sequentially conveyed printing paper. Since the timing control means controls the operation timing of the registration mechanism in accordance with the operation timing of this process unit,
The position where the image is formed on the printing paper is adjusted appropriately.

According to a second aspect of the invention, a sheet feeding mechanism for sequentially feeding the printing sheets, a registration mechanism for temporarily stopping the printing sheets sequentially fed, and a resumption of the feeding after being temporarily stopped. A belt transport mechanism that electrostatically attracts and sequentially transports printing paper with a circulating endless transfer belt,
A process unit that forms an image on a printing sheet that is electrostatically attracted to the transfer belt and is sequentially conveyed; and a timing control unit that controls the operation timing of the registration mechanism corresponding to the operation timing of the process unit
The transfer belt has a paper detection unit that detects the print paper in a range that communicates from the position where the print paper is attracted to the position of the process unit. Therefore, when the registration mechanism temporarily stops the printing paper sequentially fed by the paper feeding mechanism and then restarts the feeding, this printing paper is electrostatically adsorbed by the endless transfer belt which can be circulated by the belt transportation mechanism. Are sequentially conveyed, and the process unit forms an image on the sequentially conveyed printing paper. Since the timing control means controls the operation timing of the registration mechanism in accordance with the operation timing of the process unit, the position where the image is formed on the printing paper is properly adjusted. Further, since the paper detection unit detects the printing paper in a range in which the position where the printing paper is attracted to the transfer belt and the position of the process unit is communicated, the printing paper is adsorbed to the transfer belt at this detection timing, for example. The occurrence of a jam is detected in the range that communicates from the position to the position of the process unit.

According to a third aspect of the present invention, in the first aspect of the present invention, a jam detecting unit for detecting a jam of the printing paper together with the occurrence position is provided, and when the occurrence of the jam is detected, the printing paper is conveyed. An operation stop means for stopping the operation of each part is provided, and passage detection means for detecting that at least the leading edge of the printing paper has passed through the registration mechanism is provided, and at a position where a certain printing paper does not interfere with the operation of the belt transport mechanism. Operation control means is provided for continuing the operations of the registration mechanism and the belt transport mechanism when a jam occurs and at least the leading edge of another printing sheet passes through the registration mechanism. Therefore, when the jam detecting unit detects the jam of the printing paper together with the generation position, the operation stopping unit stops the operation of each unit related to the conveyance of the printing paper. However, if a print sheet causes a jam at a position that does not hinder the operation of the belt transport mechanism and the passage detection unit detects that at least the leading edge of another print sheet has passed the registration mechanism, the operation control is performed. Since the means continues the operation of the registration mechanism and the belt conveyance mechanism, even if a jam occurs on a certain print sheet, image formation that can be executed on another print sheet is continued.

According to a fourth aspect of the invention, in the third aspect of the invention, the registration mechanism and the belt transport mechanism operate independently of the sheet feeding mechanism. Therefore, even if a jam occurs on the printing paper at the position of the paper feeding mechanism, the registration mechanism and the belt transport mechanism operate to continue image formation on another printing paper.

According to the invention of claim 5, in the invention of claim 4, the conveying force of the registration mechanism is stronger than that of the sheet feeding mechanism. Therefore, the registration mechanism can forcibly pull out the printing paper from the paper feeding mechanism even if the end of the printing paper whose front end is located at the position of the registration mechanism is located inside the paper feeding mechanism.

According to a sixth aspect of the present invention, in the third aspect of the present invention, a sheet detecting means for detecting the printing sheet is provided within a range in which the transfer belt is in communication with a position where the printing sheet is attracted to the position of the process unit. The operation control unit suspends the continuation of the operations of the registration mechanism and the belt transport mechanism unless the printing paper that has passed through the registration mechanism is detected by the paper detection unit before the elapse of a predetermined time. Therefore, if the printing paper that has passed through the registration mechanism is not detected by the paper detection means before the elapse of a predetermined time, the operation control means stops the continuation of the operation between the registration mechanism and the belt transport mechanism. If a jam occurs on the printing paper during the transportation, the continuation of image formation is stopped.

[0013]

FIG. 1 shows a first embodiment of the present invention.
1 to 3 will be described below. Although the front side of FIG. 1 is described as the front side of the image forming apparatus here, this does not limit the direction of the present invention.

First, as shown in FIG. 2, the color printer 1 which is the image forming apparatus of the present embodiment has a paper supply block 2 and an image forming block 3. The paper supply block 2 has a paper feed tray 4 and a paper discharge tray 5, and supplies printing paper 6 to the image forming block 3. The image forming block 3 has a sheet feeding mechanism 7, a registration mechanism 8, a belt conveying mechanism 9, four process units 10, a fixing unit 11 and the like as main parts, and a sheet communicating these positions. The transport path 12 is formed by the feed roller 13, the guide plate 14, and the like.

The process unit 10 has a rotatable photosensitive drum 15. Around the photosensitive drum 15, a static elimination lamp 16, a charging charger 17, a laser scanner 18, a developing device 19, etc. are arranged in order. It is arranged. The four process units 10 are sequentially arranged at positions facing the belt transport mechanism 9, and the four developing units 19 have YMCK (Yellow, Magenta,
Cyanide, Black) toner is stored individually.

The belt conveying mechanism 9 has a plurality of rotating rollers 20 which are rotatably supported, and an endless transfer belt 21 is stretched around the rotating rollers 20 in a freely circulating manner. The transfer belt 21 is made of a material such as polyimide having a good dielectric property, and electrostatically adsorbs the printing paper 6 by its charging potential. Four transfer devices 22 are arranged inside the transfer belt 21,
These four transfer devices 22 individually oppose the four photosensitive drums 15 via the transfer belt 21. The process unit 10 is provided outside the transfer belt 21.
One charging charger 23 is arranged at a position corresponding to the upstream side of the above, and one static elimination charger 24 is arranged at a position corresponding to the downstream side of the process unit 10.

Below the registration mechanism 8, a paper detection sensor 25 for detecting the printing paper 6 by a reflective photosensor or the like is arranged. Similarly, various sensors for detecting a jam of the printing paper 6 are arranged in each part of the paper transport path 12, and these sensors are connected to a central control circuit. Various drive control circuits are connected to the central control circuit, and these drive control circuits are individually connected to the mechanisms 7 to 9 and the units 10 and 11 related to the conveyance of the printing paper 6. There is.

The color printer 1 of the present embodiment has timing control means, jam detection means, operation stop means, passage detection means, operation control means, and the like. The timing control unit controls the operation timing of the registration mechanism 8 in accordance with the operation timing of the process unit 10 to temporarily stop the conveyance of the printing paper 6 by the registration mechanism 8 to change the image forming position. adjust. The jam detection unit is the paper detection sensor 25.
The jamming of the printing paper 6 conveyed by various sensors such as the above is detected together with the generation position, and the operation stopping means, when the occurrence of the jam is detected, the mechanisms 7 to 9 and the units related to the conveyance of the printing paper 6 are detected. The operation of each unit such as 10, 11 is stopped.

However, since the passage detecting means detects that at least the leading end portion of the printing paper 6 has passed the registration mechanism 8 by the paper detecting sensor 25, the operation control means detects that a certain printing paper 6 is present. If a jam occurs at a position that does not hinder the operation of the belt transport mechanism 9 and at least the leading edge of the other printing paper 6 passes through the registration mechanism 8, the registration mechanism 8 and the belt transport mechanism 9 are separated from each other. Let the operation continue. Further, the operation control means stops the continuation of the operations of the registration mechanism 8 and the belt transport mechanism 9 when the detection time of the printing paper 6 by the passage detection means exceeds a predetermined time. Therefore, for example, the drive motors of the mechanisms 7 to 9 are independent of each other,
The registration mechanism 8 and the belt transport mechanism 9 operate independently of the paper feeding mechanism 7.

With such a configuration, the color printer 1 of the present embodiment forms a color image on the printing paper 6. In that case, the printing paper 6 stored in the paper supply block 2 is fed to the paper conveyance path 12 by the paper feeding mechanism 7, and when the printing paper 6 is detected by the paper detection sensor 25, the registration mechanism 8 stops. Printed paper 6
Feeding is suspended. On the other hand, the image formation by the process unit 10 is also started in response to the detection of the sheet detection sensor 25, and the start timing of the image formation by the process unit 10 and the resumption timing of the sheet feeding by the registration mechanism 8 are the same. Properly controlled.

By this timing control, the printing paper 6 passes through the registration mechanism 8 and is fed to the belt conveying mechanism 9, so that the belt conveying mechanism 9 circulates the transfer belt 21.
Thus, the printing paper 6 is electrostatically adsorbed and sequentially conveyed to the positions of the four process units 10. Since these process units 10 sequentially transfer the YMCK toner onto the printing paper 6 to form a color image, the printing paper 6 is ejected after the color image is fixed by the fixing unit 11.

In the color printer 1 of the present embodiment, when the printing paper 6 is sequentially conveyed to form a color image as described above, the image forming start timing by the process unit 10 and the printing paper 6 by the registration mechanism 8 are changed. Since the feeding timing is synchronized, an image can be formed at an appropriate position on the printing paper 6.

More specifically, as shown in FIG. 1, the distance between the latent image exposure position and the image transfer position on the surface of the photosensitive drum 15 of the first process unit 10 is α, and the registration mechanism in the paper transport path 12 is. If the distance between the image transfer position and the image transfer position is β, the process unit 10 if α = β
The image formation by and the resumption of the feeding by the registration mechanism 8 are simultaneously executed. In the case of α> β, the paper feeding by the registration mechanism 8 is restarted after the lapse of a predetermined time after the image formation by the process unit 10 is started, and in the case of α <β, the paper feeding by the registration mechanism 8 is started. The image formation by the process unit 10 is started after a lapse of a predetermined time from the restart of the process.

Actually, the printing paper 6 temporarily stopped by the registration mechanism 8 is elastically curved by the feeding force of the paper feeding mechanism 7, and the printing paper 6 whose feeding is restarted has a curved length γ. Since it protrudes only by
Needs to be subtracted from the above-mentioned distance β.

Further, the color printer 1 of the present embodiment
When a jam occurs on the printing paper 6 conveyed through the paper conveyance path 12 as described above, various sensors detect the jam and the mechanisms 7 to 9 related to the conveyance of the printing paper 6 and the units 10, 11 and the like. By stopping the operation, the progress of jam is prevented. However, when a plurality of printing papers 6 are continuously conveyed to form an image in order, a certain printing paper 6 causes a jam at a position that does not hinder the operation of the belt conveyance mechanism 9, and the leading edge of another printing paper 6 is generated. If the part has passed the registration mechanism 8, the operations of the registration mechanism 8, the belt conveyance mechanism 9, and the process unit 10 are continued.

More specifically, as shown in FIG. 3, when it is detected by the paper detection sensor 25 that the first printing paper 6 has passed through the registration mechanism 8, it is transferred to this printing paper 6. Image forming process unit 10
Has been started by. In this state, even if the second printing paper 6 causes a jam at the position of the paper feeding mechanism 7,
The jam of the second printing paper 6 is the first printing paper 6
It does not hinder the transport and image formation. Therefore, in such a case, the sheet feeding mechanism 7 is stopped to stop the conveyance of the second printing sheet 6 in which the jam has occurred, and the operations of the registration mechanism 8, the belt conveyance mechanism 9, and the process unit 10 are performed. The image is conventionally transferred onto the first printing paper 6 by continuing.

Therefore, in the color printer 1 according to the present embodiment, even if a jam occurs on a certain print sheet 6, the image formation that can be executed on another print sheet 6 can be continued, and the progress of the jam can be continued. It is possible to perform the image forming work with high efficiency while preventing it. Moreover, the presence or absence of the printing paper 6 passing through the registration mechanism 8 at the time when a certain printing paper 6 is jammed is detected by the paper detection sensor 25, and if the printing paper 6 is present, the registration mechanism 8 and the belt are detected. Since the conveyance with the conveyance mechanism 9 is continued, it is possible to prevent the image formed on the photosensitive drum 15 of the process unit 10 from being transferred to the transfer belt 21 at this point.

In the color printer 1 of the present embodiment, the registration mechanism 8 and the belt conveyance mechanism 9 on the downstream side of the paper feeding mechanism 7 located upstream of the paper conveyance path 12 operate independently of each other. Even when the conveyance of the printing paper 6 that has jammed on the upstream side of the paper conveyance path 12 is stopped as described above, the conveyance of the printing paper 6 on the downstream side can be easily continued.

However, even if the leading edge of the printing paper 6 passes through the position of the registration mechanism 8 as described above, the printing paper 6 may cause a jam inside the registration mechanism 8. If the operation of the registration mechanism 8, the belt transport mechanism 9 and the process unit 10 is continued in this state, the image is transferred to the transfer belt 21. However, the color printer 1 of the present embodiment compares the detection time of the printing paper 6 by the paper detection sensor 25 with a predetermined time in the above-described state, and when the detection time exceeds the predetermined time, the registration mechanism The continuation of the operations of 8, the belt transport mechanism 9, and the process unit 10 is stopped. That is,
If the transfer of the print paper 6 by the registration mechanism 8 is not completed within a predetermined time, it is determined that a jam has occurred and the transfer of the print paper 6 is not continued. Therefore, it is preferable that the image is transferred to the transfer belt 21. Can be prevented.

However, when the occurrence of a jam of the printing paper 6 is judged from the detection time by the paper detection sensor 25 in front of the registration mechanism 8 as described above, for example, printing in which the trailing edge passes the position of the paper detection sensor 25 is performed. Even if the leading edge of the sheet 6 causes a jam on the surface of the transfer belt 21, it cannot be detected. If this causes a problem, as shown in FIG. 4, the second paper detection sensor 26 corresponding to the paper detection means is connected from the position where the printing paper 6 is attracted to the transfer belt 21 to the position of the process unit 10. If the second paper detection sensor 26 does not detect the printing paper 6 before the elapse of a predetermined time from the restart of the feeding by the registration mechanism 8, the registration mechanism 8 and the belt conveyance mechanism 9 are arranged.
It is preferable to stop the continuation of the operations with and.

In such a color printer 31, if a jam occurs on the printing paper 6 in the process of moving from the registration mechanism 8 to the process unit 10, the image formation is stopped and the image is transferred to the transfer belt 21. This can be effectively prevented. More specifically, if a jam does not occur on the printing paper 6 that has been re-fed by the registration mechanism 8, the printing paper 6 is detected by the second paper detection sensor 26 before the elapse of a predetermined time. The printing paper 6 not detected in this way is judged to have caused a jam.

For example, the distance between the latent image exposure position and the image transfer position on the surface of the photosensitive drum 15 of the first process unit 10 is α, and the distance between the second paper detection sensor 26 and the image transfer position in the paper transport path 12 is If the distance is β, and if the occurrence of a jam is detected before the image is formed on the surface of the photosensitive drum 15 beyond the α-β range, the image is not transferred to the transfer belt 21.

The color printer 1 of the present embodiment
In some cases, the registration mechanism 8 continues to convey the printing paper 6 with the paper feeding mechanism 7 stopped as described above. However, the rear portion of the printing paper 6 which is continuously conveyed by the registration mechanism 8 is It may be located in the sheet feeding mechanism 7. In such a case, the registration mechanism 8 needs to pull out the printing paper 6 from the paper feeding mechanism 7. Therefore, in order to realize this, the conveyance force of the registration mechanism 8 is set larger than that of the paper feeding mechanism 7. The paper feeding mechanism 7 includes a one-way clutch to facilitate the pulling out of the printing paper 6 and a mechanism for releasing the holding of the printing paper 6 in association with the stop of the conveyance in the paper feeding mechanism 7. To keep
Are preferred.

The present invention is not limited to the above method, and allows various modifications. For example, in the above-described color printer 1, since the registration mechanism 8 and the belt transport mechanism 9 are operated while the paper feeding mechanism 7 is stopped,
Although it has been illustrated that these drive motors are provided independently,
For example, it is possible to operate the mechanisms 7-9 independently by providing an electromagnetic clutch in the connection with the mechanisms 7-9 as one drive motor.

[0035]

According to the first aspect of the present invention, the paper feeding mechanism for sequentially feeding the printing paper, the registration mechanism for temporarily stopping the printing paper sequentially fed, and the resumption of the feeding after being temporarily stopped. A belt transport mechanism that electrostatically attracts the printed printing paper by a circulating endless transfer belt and sequentially transports it, and a process unit that forms an image on the printing paper that is electrostatically attracted to the transfer belt and transported sequentially. By having the timing control means for controlling the operation timing of the registration mechanism corresponding to the operation timing of the process unit, the printing paper temporarily stopped by the registration mechanism is fed to the position of the process unit at an appropriate timing. Therefore, the position where the image is formed on the printing paper can be properly adjusted.

According to a second aspect of the present invention, a sheet feeding mechanism for sequentially feeding the printing sheets, a registration mechanism for temporarily stopping the printing sheets sequentially fed, and a resumption of the feeding after being temporarily stopped. A belt transport mechanism that electrostatically attracts and sequentially transports printing paper with a circulating endless transfer belt,
A process unit that forms an image on a printing sheet that is electrostatically attracted to the transfer belt and that is sequentially conveyed, a timing control unit that controls the operation timing of the registration mechanism corresponding to the operation timing of this process unit, and the printing on the transfer belt. By having the paper detection means for detecting the printing paper in the range that communicates from the position where the paper is attracted to the position of the process unit, the printing paper temporarily stopped by the registration mechanism is properly placed at the position of the process unit. Since it can be fed at the timing, it is possible to properly adjust the position where the image is formed on the printing paper.
Since the presence or absence of the printing paper can be detected by the paper detection means in the range in which the position where the printing paper is attracted to the transfer belt to the position of the process unit can be detected, for example, the jam occurrence in the above range can be detected by this detection timing You can

According to the third aspect of the present invention, a jam detecting means for detecting the jam of the printing paper together with the occurrence position is provided.
Provided is an operation stopping means for stopping the operation of each part related to the conveyance of the printing paper when the occurrence of a jam is detected, and a passage detecting means for detecting that at least the leading end of the printing paper has passed the registration mechanism. , If a print sheet causes a jam at a position that does not hinder the operation of the belt transport mechanism and at least the leading edge of another print sheet passes through the registration mechanism, the operation of the registration mechanism and the belt transport mechanism is continued. By providing the operation control means, it is possible to prevent the progress of the jam by detecting the occurrence of the jam and stopping each part, but if the jam of one printing paper does not hinder the conveyance of another printing paper. In this case, since the printing paper is conveyed to form an image, it is possible to improve the work efficiency of the image formation without advancing the jam, and the image to be formed on the printing paper is improved. Can also be prevented in the toner is transferred onto the transfer belt.

According to the fourth aspect of the present invention, the registration mechanism and the belt conveyance mechanism operate independently of the sheet feeding mechanism, so that even if a jam occurs on the printing paper at the position of the sheet feeding mechanism, the registration mechanism It is possible to easily realize the operation of the mechanism and the belt conveyance mechanism to continue the conveyance of the printing paper.

According to the fifth aspect of the present invention, since the conveying force of the registration mechanism is stronger than that of the sheet feeding mechanism, the end portion of the printing paper whose leading end is located at the position of the registration mechanism is located inside the sheet feeding mechanism. Even so, the registration mechanism can forcibly pull out the printing paper from the paper feeding mechanism.

According to a sixth aspect of the present invention, a paper detection unit for detecting the printing paper is provided within a range in which the printing paper is adsorbed to the transfer belt and the position of the process unit, and the operation control unit includes a registration mechanism. If the passed printing paper is not detected by the paper detection means before the elapse of a predetermined time, by stopping the continuation of the operation of the registration mechanism and the belt transport mechanism, even if the printing paper that has passed through the registration mechanism is jammed, This can be easily determined to stop the transportation of the printing paper.

[Brief description of drawings]

FIG. 1 is a side view showing a main part of a color printer which is an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side view showing the overall structure of a color printer.

FIG. 3 is a schematic diagram showing a state in which a jam has occurred on one of two printing sheets.

FIG. 4 is a side view showing a color printer of a modified example.

[Explanation of symbols]

 1,31 Image forming apparatus 6 Printing paper 7 Paper feeding mechanism 8 Registration mechanism 9 Belt transport mechanism 10 Process unit 12 Paper transport path 21 Transfer belt

Claims (6)

[Claims] 1. A paper feeding mechanism that sequentially feeds printing paper, a registration mechanism that temporarily stops the printing paper that is sequentially fed, and a printing paper that has been paused and then restarted feeding. Corresponds to the belt transport mechanism that electrostatically attracts and sequentially transports by the endless transfer belt, the process unit that forms an image on printing paper that is electrostatically attracted to the transfer belt and sequentially transported, and the operation timing of this process unit And a timing control unit for controlling the operation timing of the registration mechanism. 2. A paper feeding mechanism that sequentially feeds printing paper, a registration mechanism that temporarily stops printing paper that is sequentially fed, and a printing paper that has been paused and then restarted feeding. Corresponds to the belt transport mechanism that electrostatically attracts and sequentially transports by the endless transfer belt, the process unit that forms an image on printing paper that is electrostatically attracted to the transfer belt and sequentially transported, and the operation timing of this process unit Timing control means for controlling the operation timing of the registration mechanism, and paper detection means for detecting the printing paper in a range communicating from the position where the printing paper is attracted to the transfer belt to the position of the process unit. An image forming apparatus characterized in that. 3. A jam detecting unit for detecting a jam of a print sheet together with a position of occurrence of the print sheet, and an operation stopping unit for stopping the operation of each section related to the conveyance of the print sheet when the occurrence of the jam is detected. Is provided with passage detection means for detecting that at least the leading edge of the other printing paper has passed through the registration mechanism, and a certain printing paper causes a jam at a position where it does not hinder the operation of the belt transport mechanism, and at least the leading edge of another printing paper. 2. The image forming apparatus according to claim 1, further comprising operation control means for continuing the operations of the registration mechanism and the belt transport mechanism when passing through the registration mechanism. 4. The registration mechanism and the belt conveying mechanism operate independently of the sheet feeding mechanism.
The image forming apparatus as described in the above. 5. The image forming apparatus according to claim 4, wherein the registration mechanism has a stronger conveying force than the sheet feeding mechanism. 6. A paper detection means for detecting the printing paper in a range communicating from the position where the printing paper is attracted to the transfer belt to the position of the process unit is provided, and the operation control means is such that the printing paper that has passed through the registration mechanism is predetermined. 4. The image forming apparatus according to claim 3, wherein the continuation of the operations of the registration mechanism and the belt conveyance mechanism is stopped if the sheet detection unit does not detect the time before the passage of time.