JPH09211916A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a toner image on a photoreceptor from being transferred on a transferring/transporting belt itself, in the image forming system transferring the toner image on the photoreceptor to a recording medium being statically attracted on the transfer-transporting belt. SOLUTION: The image forming operation is started, on making the detection of recording medium 1 as a trigger by a resist sensor 20 arranged in the medium transporting path 4 on the upstream side of the transfer position TP of the toner image. After the recording medium is detected by the resist sensor 20, even if the transporting defect occurs on the upstream side of the detecting position PDP on the medium transporting path 4, the image forming operation is continued by forcibly transporting the recording medium 1 detected by the resist sensor 20. Therefore, the toner image is prevented from being transferred on the transferring/transporting belt 7, and the recording medium 1 itself is also discharged without staying on the transferring/transporting belt 7 part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for forming a desired image on a recording medium electrostatically adsorbed on a transfer / transport belt by an electrophotographic process.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, a recording medium, for example, a transfer paper is electrostatically adsorbed on a transfer / transport belt, and a toner image on a photoconductor is transferred to the transfer paper by using an electrophotographic process. The method of forming the is known. Especially,
In a tandem type color copying machine or a color printer that requires strict alignment of each color, if the transfer paper is electrostatically adsorbed on the transfer / conveying belt, the misalignment of each color hardly occurs. The image forming method of the method is widely used. However, when there is no transfer paper at a predetermined position on the transfer / transport belt due to paper jam or the like, or when the transfer paper on the transfer / transport belt is peeled off due to some accident, the image forming operation is performed as it is. Then, the toner image on the photoconductor is transferred onto the transfer / transport belt, and the transfer / transport belt is contaminated with the toner and adheres to the subsequent transfer paper. In this case, even if the image forming operation is immediately stopped, if the toner image is already developed on the photoconductor, it is inevitable that the toner image is transferred and adhered to the transfer / conveying belt after the restart. I can't.

Therefore, conventionally, the transfer / conveyance belt can be freely contacted / separated with respect to the photoconductor, and when the transfer paper has a conveyance failure, the transfer / conveyance belt is separated from the photoconductor and the toner image is transferred to the transfer / conveyance belt. Inventions have been made to prevent this. Such an invention is disclosed in, for example, JP-A-63-472.
45 and Japanese Patent Laid-Open No. 63-296078. According to such an invention, the transfer of the toner image onto the transfer / conveyance belt is reliably prevented, and the jam processing operation at the transfer / conveyance belt portion becomes extremely easy.

[0004]

Problems to be Solved by the Invention JP-A-63-4724
In the electrophotographic apparatus disclosed in Japanese Patent Laid-Open No. 5-296078, Japanese Patent Laid-Open No. 63-296078, and the like, when a transfer sheet has a conveyance failure, a process of separating the transfer belt from the photoconductor is uniformly performed at that time. The image forming operation is stopped. Then, the image forming operation is restarted after all the transfer papers existing in the transfer paper conveyance path are removed. However,
Depending on the position where the transfer paper is poorly conveyed, there is a case where the image forming operation currently in progress is not affected and there is no problem even if the image forming operation is continued. It must be said that the suspension of the image forming operation in such a case is an unnecessary suspension.

Further, in the electrophotographic apparatus disclosed in JP-A-63-47245, JP-A-63-296078, etc., a large-scale structure in which the transfer / transport belt is brought into contact with and separated from the photosensitive member, When the transfer paper is not properly conveyed, a complicated operation of separating the transfer conveyance belt from the photoconductor is required. Therefore, the structure and operation are complicated,
The device also becomes large.

[0006]

According to another aspect of the present invention, there is provided an electrophotographic apparatus, which is provided with a medium conveying path having a transfer conveying belt for electrostatically adsorbing and conveying a recording medium, and a transfer conveying belt. An electrophotographic process section that includes a photoconductor, and that transfers a toner image formed on the surface of the photoconductor through the electrophotographic processes of charging, exposing, and developing to a recording medium that is electrostatically adsorbed on a transfer conveyance belt, and the electrophotographic process unit. A registration sensor that detects the recording medium on the upstream side of the medium conveyance path from the transfer position of the toner image by the photographic process unit, and a document that causes the electrophotographic process unit to start the image forming operation triggered by the detection of the recording medium by the registration sensor. The registration start unit, the conveyance failure detection unit that independently detects the conveyance failure of the recording medium on the upstream side and the downstream side of the medium conveyance path with respect to the registration sensor, and the registration sensor are described. After the medium is detected, the recording medium detected by the registration sensor is forcibly conveyed by the electrophotographic process section even if the conveyance failure detection means detects a conveyance failure on the upstream side of the medium conveyance path with respect to the registration sensor. And a forcing means for continuing the image forming operation.

Therefore, when the registration sensor detects the recording medium, the electrophotographic process section starts the image forming operation by using this as a trigger. At this time, when a recording medium conveyance failure occurs on the upstream side of the medium conveyance path with respect to the registration sensor, the recording medium is forcibly conveyed by the compulsion unit and the image forming operation is continued. Therefore, the transfer of the toner image onto the transfer / transport belt is reliably prevented. Since the recording medium itself is also ejected without remaining on the transfer / conveying belt portion, it is not necessary to jam the recording medium detected by the registration sensor. On the contrary, in some cases, the desired image is correctly formed on the recording medium without inconvenience. Moreover, since the structure and control for retracting the transfer / conveyance belt from the photoconductor are not required, the structure and operation are not complicated, and the apparatus is not upsized.

According to a second aspect of the present invention, in the electrophotographic apparatus according to the first aspect, the registration sensor detects the recording medium in the medium conveying path at an upstream side of a touchdown position of the recording medium with respect to the transfer / conveying belt. . Here, the distance from the registration sensor to the transfer position (hereinafter referred to as the timing length) in the medium transport path needs to be at least the length of the outer circumference of the photoconductor from the exposure position to the transfer position. On the other hand, if the recording medium detection position of the registration sensor is on the upstream side of the touchdown position, the length from the detection position of the registration sensor to the touchdown position in the medium conveyance path can also be used as part of the timing length. is there.
Therefore, it is possible to set the distance from the touchdown position to the transfer position to be short and downsize the entire apparatus.

According to a third aspect of the present invention, in the electrophotographic apparatus according to the second aspect, a forced transport roller for transporting the recording medium is arranged at a position upstream of the recording medium detection position by the registration sensor in the medium transport path. At least one medium conveying unit that conveys the recording medium is arranged on the upstream side of the medium conveying path with respect to the compulsory conveying roller, and the compulsory unit causes the conveying force of the forced conveying roller to exceed the holding force of the recording medium by the medium conveying unit. The recording medium detected by the registration sensor is forcibly conveyed by increasing the strength. Therefore, after the recording medium is detected by the registration sensor, even if the medium conveying unit stops its operation due to defective conveyance, for example, the conveying force of the forced conveying roller is larger than the holding force of the recording medium by the medium conveying unit. The recording medium is forcibly conveyed toward the transfer / conveying belt because it wins.

According to a fourth aspect of the present invention, in the electrophotographic apparatus according to the third aspect, the forced transport roller is driven by a drive source of the transfer transport belt. Therefore, the force of the recording medium to be conveyed by the forced conveying roller becomes extremely strong, and it becomes extremely easy to make the force of conveyance stronger than the holding force of the recording medium by the medium conveying section.

According to a fifth aspect of the present invention, in the electrophotographic apparatus according to the second aspect, a toner image formed by the electrophotographic process section is located downstream of the touchdown position of the recording medium with respect to the transfer conveyance belt in the medium conveyance path. When the medium detection sensor detects the recording medium on the upstream side of the transfer position and when the registration sensor detects the recording medium and the medium detection sensor does not detect the recording medium even after a lapse of a predetermined timing, the forced operation by the forcing means is performed. A forced operation prohibiting means for prohibiting is further provided. Therefore, since the medium detection sensor does not detect the recording medium after a lapse of a predetermined timing after the registration sensor detects the recording medium, the defective conveyance of the recording medium after the detection by the registration sensor is detected. Then, in that case, the forced operation prohibiting means prohibits the forced operation by the forcing means, and it is possible to prevent the situation in which the conveyance failure occurs.

According to a sixth aspect of the present invention, in the electrophotographic apparatus according to the second aspect, the resist sensor is located in the medium conveying path, downstream of the touchdown position of the recording medium with respect to the transfer / conveying belt and in the electrophotographic process. The recording medium is detected on the upstream side of the transfer position of the toner image by the unit. At this time, the recording medium is detected by the registration sensor while being electrostatically attracted to the transfer / transport belt. Therefore, the recording medium is less likely to be displaced until it reaches the transfer position after being detected by the registration sensor, and the accuracy of image formation is improved.

[0013]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. The present embodiment is an example of application to a tandem type color laser printer.

First, a conveyance path 4 is provided as a medium conveyance path from a paper feed section 2 that stores and holds a transfer sheet 1 as a recording medium to a paper ejection section 3. The transport path 4 partially includes a transfer transport belt 7 that is stretched between a belt drive roller 5 that is driven by a drive source (not shown) to rotate and a rotatable belt driven roller 6. The transfer / conveyance belt 7 is charged by a belt charger 8 arranged at an upstream position of the conveyance path 4 and discharged by a belt charge eliminator 9 arranged at a downstream position of the conveyance path 4. That is, the transfer paper 1 is electrostatically adsorbed by being charged by the belt charger 8, and the belt static eliminator 9
It is a structure in which the electrostatic attraction of the transfer paper 1 is released by removing the charge by.

Four electrophotographic process units 10 for yellow, magenta, cyan, and black are sequentially arranged on the transfer / transport belt 7. The electrophotographic process unit 10 mainly includes a photosensitive drum 11 as a photosensitive member that contacts the transfer / conveyance belt 7, and the photosensitive drum 11
A charger 12, an exposure unit (not shown), a developer 13,
A transfer device 14 and a static eliminator 15 are formed in this order. That is, the periphery of the photosensitive drum 11 is uniformly charged by the charging device 12, the exposure portion irradiates the exposure position EP with laser light to form an electrostatic latent image, and the electrostatic latent image is developed by the developing device 13. The toner image is formed into a toner image, and this toner image is transferred onto the transfer paper 1 on the transfer / transport belt 7 by the transfer device 14, which is a known structure. The transfer position TP by the transfer device 14
Is a position where the transfer / conveyance roller 7 and the photosensitive drum 11 come into contact with each other.

The paper feed unit 2 has a pickup roller 16 for picking up the uppermost transfer paper 1 stacked and stored in the paper feed unit 2, and the uppermost paper when a plurality of transfer papers 1 are picked up. And a separation roller 17 for separating and feeding only the transfer paper 1 of FIG.

In the conveying path 4 communicating with the sheet feeding section 2, a plurality of conveying rollers 18 as a medium conveying section for conveying the fed transfer sheet 1 are arranged in order at predetermined intervals, and are transferred. Immediately before the conveyor belt 7, a forced conveyor roller 19 is arranged. These rollers 18 and 19 are composed of a pair of rollers. The forced conveyance roller 17 rotates by being given a driving force from a driving source of a belt driving roller that rotationally drives the transfer conveyance belt 7. Then, the carrying force of the forced carrying roller 17 is equal to that of all the carrying rollers 1 that are stopped.
It is set to be stronger than the holding force of the transfer paper 1 by 8.

In the transport path 4, the transfer as a recording medium detection position where the fed transfer paper 1 first contacts the transfer transport belt 7, that is, a recording medium detection position on the upstream side of the touchdown position TDP. The registration sensor 20 is arranged at the paper detection position PDP. This registration sensor 2
Reference numeral 0 denotes a photoelectric detection sensor configuration that detects the recording paper 1 with high or low light reflectance based on a predetermined threshold value, and is configured by, for example, a photo interrupter or a photo reflector.

On the downstream side of the transfer / transport belt 7 in the transport path 4, the unfixed toner image transferred onto the transfer paper 1 is fixed to the fixing device 2.
1 is provided.

Here, the color laser printer of the present embodiment is provided with a control unit (not shown) having a microcomputer mainly composed of a CPU and a memory, and the control unit controls the operation of each unit. The structure and basic processing of such a control unit are the same as the known structure and processing, and therefore description thereof will be omitted.

Next, the color laser printer according to the present embodiment is provided with a writing start means, a conveyance failure detection means, and a compulsion means as various means executed by the control unit having a microcomputer configuration. These various means are
According to the operation program stored in M, it is executed based on a basic process in which the CPU outputs a control signal to each unit.

The writing start means is triggered by the detection of the transfer paper 1 by the registration sensor 20 and is used as the electrophotographic process unit 1.
It is a means for starting the image forming operation of 0. Here, the image forming operation is started by using the output signal of the registration sensor 20 as a trigger, but it is not started at the same time as the output signal. That is, the electrophotographic process unit 1 for each color
In the case of 0, it is necessary to shift the start timing of each image forming operation by the transfer delay timing of the transfer sheet 1. Therefore, the image forming operation in each electrophotographic process section 10 is started by using the output signal of the registration sensor 20 as a trigger and being shifted by a predetermined timing by a delay circuit (not shown). As a result, a color image is formed on the transfer paper 1 without color misregistration.

The defective conveyance detecting means is the registration sensor 20.
Transfer sheet 1 independently on the upstream side and the downstream side of conveyance path 4
Is a means for detecting the conveyance failure of. More specifically, a plurality of photoelectric detection sensors (not shown) are arranged at various positions in the transport path 4, and the timing of the transfer paper 1 entering the photoelectric detection sensors and the timing from the entry to the exit are detected. By doing so, it is possible to detect whether the transfer paper 1 is conveyed properly.

After the registration sensor 20 detects the transfer sheet 1, the compulsion means is configured to move the conveyance path 4 more than the registration sensor 20.
Even if the transport failure detection means detects a transport failure on the upstream side,
It is means for forcibly conveying the transfer paper 1 detected by the registration sensor 20 and continuing the image forming operation by the electrophotographic process unit 10. More specifically, when a conveyance failure occurs on the upstream side of the registration sensor 20 in the conveyance path 4, the conveyance roller 18 is stopped. Therefore, the state is preserved in the transport path 4 immediately after the paper feed unit 2, and measures are taken to prevent a situation in which a transport failure occurs, for example, a paper jam from further worsening. At this time, if the transfer paper 1 is already detected by the registration sensor 20, the detected transfer paper 1 is forcibly conveyed to the forced conveyance roller 19 or the transfer conveyance belt 7 in some cases, and the electrophotographic process unit 10 is operated.
The image forming operation is continued. In this case, the stopped conveyance roller 18 becomes a load to convey the transfer paper 1,
The carrying force of the forced carrying roller 19 is set to be stronger than this load.

In such a structure, the uppermost transfer sheet 1 stored in the sheet feeding section 2 is separated and fed to the conveying path 4 by the pickup roller 16 and the separating roller 17 and detected by the registration sensor 20. And the registration sensor 20
Output value fluctuates. Then, with this as a trigger, the image forming operation by the electrophotographic process unit 10 is started.
That is, charging by the charger 12, exposure at the exposure position EP,
A toner image is formed on the photosensitive drum 11 through each electrophotographic process of development by the developing device 13, and the toner image is transferred to the transfer paper 1 which is electrostatically adsorbed by the transfer conveyance belt 7 charged by the charging device 8. Transferred by 14. At this time, the toner images of yellow, magenta, cyan, and black are sequentially transferred onto the transfer paper 1. Then, the transfer paper 1 after the transfer of the toner image is conveyed to the fixing device 21, where the toner image is fixed, and the paper is discharged to the paper discharge unit 3. As a result, a desired color image is formed on the transfer paper 1.

On the other hand, when the transfer sheet 1 has a conveyance defect in the conveyance path 4, the conveyance defect detection means detects it. Here, there are two conditions, that is, the condition that the transfer paper 1 is detected by the registration sensor 20 and the condition that the transfer paper 1 is not properly conveyed upstream of the registration sensor 20 in the conveyance path 4. If it does, the processing by the compulsory means is executed. That is, the holding force of the transfer paper 1 by the transfer roller 18 is overcome and the forced transfer roller 19
Forcibly conveys the transfer paper 1 detected by the registration sensor 20, and the image forming operation by the electrophotographic process unit 10 on the transfer conveyance belt 7 is continued. The reason for performing such a forced operation will be described below.

When the two conditions for executing the process by the forcing means are satisfied, it can be inferred that the conveyance failure does not occur downstream of the registration sensor 20 in the conveyance path 4.
Then, when the transfer paper 1 is detected by the registration sensor 20 which is one of the two conditions, the image forming operation is started by using this as a trigger, so that the toner image is already formed on the photosensitive drum 11. It may have been formed. Therefore, if the conveyance of the transfer sheet 1 and the image forming operation are stopped at this stage, the toner that may have already been formed on the photosensitive drum 11 when the cause of the conveyance failure is removed and the image forming operation is restarted next. Image transfer transfer belt 7
May adhere to. Therefore, in the color laser printer according to the present embodiment, when the above two conditions are satisfied, the transfer sheet 1 detected by the registration sensor 20 is forcibly conveyed and the image forming operation is executed on the transfer sheet 1.
As a result, the transfer of the toner image onto the transfer / transport belt 7 is reliably prevented. Further, the transfer paper 1 itself is not retained on the transfer / conveyance belt 7 but is discharged to the paper discharge unit 3,
The jam processing is not necessary for the recording medium detected by the registration sensor 20. On the contrary, in some cases, a desired image may be correctly formed on the transfer paper 1. The above is the reason why the forcing means performs the forcing operation.

In the color laser printer according to the present embodiment, the transfer of the toner image onto the transfer / transport belt 7 is prevented by the execution of the forcing means, and the jam processing at the transfer / transport belt 7 portion becomes unnecessary. In this case, since the structure and operation of retracting the transfer / conveyance belt 7 from the photosensitive drum 11 are not necessary, the structure and operation do not become complicated, and the apparatus does not become large.

Further, the distance from the registration sensor 20 to the transfer position TP (denoted by γ in FIG. 1) in the transport path 4 is at least the length of the outer circumference of the photosensitive member from the exposure position EP to the transfer position TP ( 1 (represented by α in FIG. 1) is required. In contrast, the transfer paper detection position P of the registration sensor
If DP is upstream of the touchdown position TDP, the length from the detection position of the registration sensor 20 to the touchdown position TDP in the transport path 4 can also be used as part of the distance γ. Therefore, the touchdown position TDP
It is possible to reduce the size of the entire apparatus by setting a short distance from the transfer position TP to the transfer position TP.

The relationship between the carrying roller 18 and the forced carrying roller 19 when the forcing means is executed is as follows.
The content of the transfer sheet 1 is not limited as long as 8 does not hinder the transfer of the transfer sheet 1 by the forced transfer roller 19. Therefore, in practice, the roller pair constituting the transport roller 18 may be separated from each other when the forcing means is executed, and may be used in a bicycle in a driving force transmission mechanism (not shown) for the transport roller 18. The free roller may be interposed, and when the driving force is not applied to the carrying roller 18, the carrying roller 18 may be freely rotated. Further, as in the present embodiment, in order to increase the carrying force of the transfer sheet 1 on the forced carrying roller 19 side over the holding force of the transfer sheet 1 on the carrying roller 18 side, for example, the carrying roller 18
It is conceivable to adopt a structure in which a roller and a belt are used together.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted (same in the following embodiments). In the color laser printer of the present embodiment, the touchdown position TD of the transfer paper 1 with respect to the transfer / transport belt 7 is set.
A transfer sheet detection sensor 31 as a medium detection sensor is provided between P and the transfer position TP. The transfer paper detection sensor 31 has a photoelectric detection sensor configuration for detecting the recording paper 1 with high and low light reflectances based on a predetermined threshold value.

A forced operation prohibiting means is provided as various means executed by the control unit having a microcomputer configuration. The forced operation prohibiting unit is a unit that prohibits the forced operation by the forcing unit when the transfer sheet detecting sensor 31 does not detect the transfer sheet 1 even after a predetermined timing has elapsed after the registration sensor 20 detects the transfer sheet 1. That is, it is a means for prohibiting the compulsory conveyance and image forming operation of the transfer paper 1 which has already been detected by the registration sensor 20 when the transfer paper detection sensor 31 does not detect the transfer paper 1 under a predetermined condition. Here, “when the transfer paper detection sensor 31 does not detect the transfer paper 1 even after a predetermined timing has elapsed”
When the length of the outer periphery of the photoconductor from the exposure position EP to the transfer position TP is α and the length from the detection position of the transfer paper 1 by the transfer paper detection sensor 31 to the transfer position TP is β, This means a case where the transfer paper 1 is not detected by the transfer paper detection sensor 31 even after the time when the transfer paper 1 should be conveyed by the distance of α-β after the start of the exposure operation on the photosensitive drum 11. That is, in this case, the transfer paper 1 does not reach the transfer position TP by the time the toner image formed on the photosensitive drum 11 reaches the transfer position TP.

In such a configuration, if the transfer paper detection sensor 31 does not output the detection signal of the transfer paper 1 even after a predetermined timing has passed after the registration sensor 20 detected the transfer paper 1, the registration sensor 20 detects the transfer paper 1. It is conceivable that the detected transfer paper 1 has a conveyance failure. Therefore, in this case, the forced operation prohibiting means stops the forced operation by the forcing means. This prevents the toner image from adhering to the transfer / transport belt 7.

A third embodiment of the present invention will be described with reference to FIG. In the color laser printer according to the present embodiment, the registration sensor 20 is arranged between the touchdown position TDP of the transfer sheet 1 with respect to the transfer / transport belt 7 and the transfer position TP.

In such a structure, the transfer paper 1 is electrostatically attracted to the transfer / conveying belt 7 and then the registration sensor 2
The detection signal from the registration sensor 20 is used as a trigger to start the image forming operation by the electrophotographic process unit 10. Therefore, the transfer sheet 1 detected by the registration sensor 20 does not shift in position until it reaches the transfer position TP, whereby accurate image formation is performed on the transfer sheet 1.

[0036]

According to the first aspect of the present invention, after the registration sensor detects the recording medium, even if the conveyance error occurs on the upstream side of the medium conveyance path with respect to the registration sensor, the registration sensor detects it. Since the recording medium is forcibly conveyed and the image forming operation by the electrophotographic process section is continued, it is possible to reliably prevent the transfer of the toner image to the transfer / conveyance belt. The jam processing can be facilitated because the paper is discharged without staying, and in some cases, a predetermined image can be correctly formed on the recording medium without inconvenience,
It is possible to avoid unnecessary operation stop. In addition, since the structure and control for retracting the transfer / conveyance belt from the photoconductor are not required, it is possible to avoid complication of the structure and operation and increase in size of the apparatus.

According to the second aspect of the invention, the recording medium is detected by the registration sensor on the upstream side of the touchdown position of the recording medium with respect to the transfer / transport belt in the medium transport path. The distance to the position can be set short and the entire device can be downsized.

According to the third aspect of the present invention, the compulsory conveying roller is arranged at a position upstream of the medium conveying path from the recording medium detecting position by the registration sensor, and is arranged on the upstream side of the medium conveying path from the compulsory conveying roller. The recording medium is conveyed by at least one medium conveying unit, and the recording medium detected by the registration sensor is forcibly conveyed by making the conveying force of the forced conveying roller stronger than the holding force of the recording medium by the medium conveying unit. After the recording medium is detected by the registration sensor, even if the medium conveyance unit stops its operation due to a conveyance error, for example, the holding force of the recording medium by the medium conveyance unit is stronger than the holding force of the recording medium. Since the carrying force of the forced carrying roller is stronger, the recording medium can be forcibly carried toward the transfer carrying belt.

According to the fourth aspect of the present invention, since the forced conveying roller is driven by the drive source of the transfer / conveying belt, the conveying force of the recording medium by the forced conveying roller becomes extremely strong. It can be easily made stronger than the holding force of the recording medium by the portion.

According to a fifth aspect of the present invention, the recording medium is located downstream of the touchdown position of the recording medium with respect to the transfer / transport belt in the medium transport path and upstream of the toner image transfer position by the electrophotographic process section. A medium detection sensor for detecting and a forced operation prohibiting means for prohibiting the forced operation by the forcing means when the medium detecting sensor does not detect the recording medium even after a lapse of a predetermined timing after the registration sensor detects the recording medium are further provided. Therefore, since the medium detection sensor does not detect the recording medium after a predetermined timing has elapsed after the registration sensor detected the recording medium, it is possible to easily and reliably detect the conveyance failure of the recording medium that occurs after the detection by the registration sensor. it can. In this case, since the forced operation by the forcing means is prohibited, it is possible to prevent the situation in which the poor conveyance occurs.

According to the sixth aspect of the invention, the recording medium is detected by the registration sensor on the upstream side of the touchdown position of the recording medium with respect to the transfer / conveyance belt in the medium conveyance path. It is possible to make it difficult for the recording medium to be displaced until it reaches the transfer position, and thus it is possible to improve the accuracy of image formation.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional front view of a part of an apparatus showing a positional relationship between a registration sensor and a transfer position as a first embodiment of the present invention.

FIG. 2 is a vertical sectional front view schematically showing the entire structure of the apparatus.

FIG. 3 is a schematic vertical sectional front view of a part of an apparatus showing a positional relationship between a registration sensor, a medium detection sensor, and a transfer position according to a second embodiment of the present invention.

FIG. 4 is a schematic vertical sectional front view of a part of the apparatus showing the positional relationship between the registration sensor and the transfer position as the third embodiment of the present invention.

[Explanation of symbols]

 1 Recording Medium 4 Medium Conveying Path 7 Transfer Conveying Belt 10 Electrophotographic Process Section 11 Photoconductor 18 Medium Conveying Section 19 Forced Conveying Roller 20 Registration Sensor 31 Medium Detection Sensor TP Transfer Position TDP Touchdown Position PDP Recording Medium Detection Position

Claims (6)

[Claims] 1. A medium transport path having a transfer transport belt for electrostatically attracting and transporting a recording medium, and a photosensitive member arranged in contact with the transfer transport belt, the surface of the photosensitive member being charged, exposed, and exposed. An electrophotographic process section for transferring a toner image formed through each electrophotographic process of development to the recording medium electrostatically adsorbed on the transfer / transport belt, and the medium rather than the transfer position of the toner image by the electrophotographic process section. A registration sensor that detects the recording medium on the upstream side of the conveyance path, a writing start unit that causes the electrophotographic process unit to start an image forming operation by using the detection of the recording medium by the registration sensor as a trigger, and the registration sensor Also, a conveyance failure detection unit that independently detects a conveyance failure of the recording medium on the upstream side and the downstream side of the medium conveyance path, and the registration sensor described above. After detecting the medium, the recording medium detected by the registration sensor is forcibly conveyed by the conveyance sensor even if the conveyance defect detection unit detects the conveyance defect on the upstream side of the medium conveyance path with respect to the registration sensor. An electrophotographic apparatus comprising: a compulsory unit for continuing the image forming operation by the electrophotographic process unit. 2. The electrophotographic apparatus according to claim 1, wherein the registration sensor detects the recording medium at an upstream side of a touchdown position of the recording medium with respect to the transfer / conveying belt in the medium conveying path. 3. A forced transport roller for transporting the recording medium is arranged at a position upstream of the medium transport path from a recording medium detection position by the registration sensor, and the recording medium is upstream of the forced transport roller from the medium transport path. At least one medium transporting unit that transports the recording medium is disposed, and the forcing unit detects the registration sensor by making the transporting force by the forced transporting roller stronger than the holding force of the recording medium by the medium transporting unit. The electrophotographic apparatus according to claim 2, wherein the recording medium is forcibly conveyed. 4. The electrophotographic apparatus according to claim 3, wherein the forced transport roller is driven by a drive source of the transfer transport belt. 5. A medium detection device for detecting the recording medium on the downstream side of a touchdown position of the recording medium with respect to the transfer / transport belt in the medium transport path and on the upstream side of the transfer position of the toner image by the electrophotographic process section. A sensor, and a forced operation prohibiting unit that prohibits the forced operation by the forcing unit when the medium detection sensor does not detect the recording medium even after a predetermined timing has elapsed after the registration sensor detected the recording medium. The electrophotographic apparatus according to claim 2, wherein: 6. A registration sensor controls the recording medium in the medium conveyance path at a downstream side of a touchdown position of the recording medium with respect to a transfer conveyance belt and an upstream side of a transfer position of a toner image by an electrophotographic process section. The electrophotographic apparatus according to claim 1, wherein the electrophotographic apparatus detects.