JP2003248409A - Sheet material transport device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To early detect a jam by detection of the position of paper on a transport belt and to accurately align an image with paper by alteration of the timing of image writing according to a detected paper position. <P>SOLUTION: A voltage application means is provided for applying a voltage to paper on the transfer belt. The passage of the paper is detected by the change of a current value accompanying the change of the resistance of the paper being passed. According to the timing of the passage of the paper, JAM determination or adjustment of image writing position is performed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally forms a visible image (toner image) on an image carrier by an electrophotographic recording system or an electrostatic recording system and transfers the toner image onto a sheet material (sheet). The present invention relates to an image forming apparatus for obtaining an image by means of a sheet conveying method.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus adopting an electrophotographic recording system forms a latent image on a photosensitive drum, which is an image carrier, by utilizing light, magnetism, electric charge, etc., and visualizes the latent image. An image forming section for obtaining a visible image by means of a sheet material, a sheet material conveying means for conveying the sheet material to a transfer position of the image forming section, and a fixing device for fixing the image transferred on the sheet material onto the sheet material. Have

As the sheet material conveying means, a belt-shaped conveying member, that is, a sheet material conveying belt (hereinafter simply referred to as a conveying belt) is often used from the viewpoint of conveying ability, and the sheet material is conveyed to a transfer position and further to a fixing device. To do. At this time, the sheet material is held and conveyed on the conveyor belt by electrostatic attraction.

The transport belt is stretched and supported by one driving roller and at least one driven roller to move.

The conveyor belt is stretched with a constant force between the driving roller and the driven roller, and the conveyor belt forms an image on the most upstream side at a constant speed without sagging between the rollers. Section to the most downstream image forming section.

As described above, the sheet material is electrostatically attracted to the conveyor belt, and is conveyed to each image forming unit while being held on the conveyor belt, and the toner images of the respective colors are transferred, and A full-color image can be obtained by being fixed by the fixing unit. When a plurality of continuous images are formed, sheet materials corresponding to the number of formed images are arranged at predetermined intervals to form images.

Further, the sheet material conveying belt is "closed" to the belt due to external force during long-term rotation or jam processing.
A deviation regulating means for preventing the belt body from moving on the roller shaft in a direction orthogonal to the driving direction and for preventing the belt from falling off the roller is provided.

(Conventional Example) Here, the image forming process in the conventional example will be specifically described with reference to FIG.

FIG. 1 is a schematic view of a conventional full-color image forming apparatus. First, second, and third in the image forming apparatus CP main body
The fourth four image forming portions Pa, Pb, Pc and Pd are arranged in parallel. The first, second, third and fourth image forming sections P extending from the cassettes 7a and 7b accommodating the sheet materials in the image forming apparatus main body CP to the fixing device 11
Below the sheets a, Pb, Pc, and Pd, a sheet material conveying belt 8 (hereinafter simply referred to as a conveying means) which is a cyclically moving endless belt-like sheet material conveying means for sequentially conveying the sheet material to these image forming portions. A belt) is provided. The conveyor belt 8 is stretched by driven rollers 9a and 9b and a driving roller 10. Further, the driven roller 9a is provided with a means 9t for applying a tension to the conveyor belt.
Further, a deviation regulating means (not shown) is provided.

The conveyor belt 8 is a thin belt made of a dielectric material, which is driven by the driving roller 10 in the direction shown by the arrow A in FIG. 4, is fed from the cassettes 7a and 7b, and is synchronized with the registration roller pair R. The sheet material to be fed is electrostatically adsorbed and carried, and the sheet material is sequentially conveyed to the above-mentioned image forming portions Pa, Pb, Pc and Pd at a constant speed.

A suction assisting roller Er is disposed on the most upstream portion of the sheet transport path on the transport belt 8. The suction assisting roller Er is biased in the direction of the driven roller 9a by a biasing spring (not shown) included in the suction assisting roller mechanism E, and the transport belt 8 is sandwiched between the suction assisting roller Er and the driven roller 9a. Further, a predetermined voltage bias is applied to the attraction assisting roller Er by a voltage applying means (not shown).

When continuously forming a plurality of images, a required number of sheet materials are fed from the cassettes 7a and 7b in the first period,
The registration roller pair R supplies the sheet material to the conveyor belt 8 so that a predetermined space is provided between the sheet materials.

The fixing device 11 receives the sheet material discharged from the drive roller 10 side and receives the sheet materials from the image forming portions Pa, Pb, Pc.
In Pd and Pd, the toner images of the respective colors transferred and superposed on the sheet material are collectively fixed to form a permanent image.

Next, each section will be described in detail. The image forming sections Pa, Pb, Pc, and Pd have substantially the same structure and include the photosensitive drums 1a, 1b, 1c, and 1d that are image carriers that are rotationally driven in the direction of arrow B.
-1d are primary chargers 2a, 2b, 2c and 2d for uniformly charging the photosensitive drums 1a-1d, and a developing device for developing the electrostatic latent image formed on the photosensitive drums 1a-1d. 3a, 3b, 3c and 3d, transfer chargers 4a, 4b and 4 for transferring the developed toner images of respective colors to the sheet material.
c and 4d, and cleaning devices 5a, 5b, 5c and 5d for removing the toner remaining on the photosensitive drums 1a to 1d are sequentially arranged in the drum rotation direction (arrow B direction). Exposure means 6a, 6b, 6c and 6d are provided above the photosensitive drums 1a to 1d, respectively.

The transfer chargers 4a, 4b, 4c and 4d are provided with transfer voltage applying means 20a, 20b, 20c, respectively.
The transfer voltage is applied by 20d. FIG. 5 shows an enlarged view of the image forming portion Pa.

The developing device 3a contains yellow toner, the developing device 3b contains magenta toner and the developing device 3c.
Contains cyan toner, and the developing device 3d contains black toner.

When the sheet material is placed on the conveyor belt 8 in the above-described full-color image forming apparatus, the sheet material is pressed against the conveyor belt 8 by the attraction assisting roller Er to which a bias is applied, and electrostatically. Adsorbed.

With the movement of the conveyor belt 8 in the direction of arrow A, the image forming process for the corresponding photosensitive drums 1a, 1b, 1c and 1d is sequentially started. Ie the first
The yellow image on the photosensitive drum 1a of the image forming portion Pa, the magenta image on the photosensitive drum 1b of the second image forming portion Pb, the cyan image on the photosensitive drum 1c of the third image forming portion Pc, A black image is shared and formed on the photosensitive drum 1d of the fourth image forming portion Pd.

The sheet material is moved by the movement of the conveyor belt 8 to the photosensitive drums 1a to 1 of the first to fourth image forming portions Pa to Pd.
The toner images of the respective colors formed on the sheet material by the transfer chargers 4a, 4b, 4c and 4d of the respective image forming portions are transferred to the fixing device 11 by sequentially passing through the lower part of d. The images are transferred one on top of the other to form a full-color image.

After passing through the final fourth image forming portion Pd, the sheet material is separated from the conveyor belt 8 and sent to the fixing device 11, and the toner images of respective colors superposed and transferred in the fixing device are fused and fixed. After that, the paper is discharged to the paper discharge tray 12.

[0021]

In the image forming apparatus, a paper jam (JAM) sometimes occurs, and in that case, it is necessary to detect the JAM promptly and take an appropriate treatment sequence. Here, if the JAM detection is not performed promptly, the sheet material may be clogged in an accordion shape, and the JAM processing may sound complicatedly.

Further, in a color image forming apparatus for forming a color image, a plurality of color images are formed on a sheet material in an overlapping manner. Here, in order to form a color image with high quality, a plurality of color images are formed. It is required to precisely align the color image (when the color image of 200 μm is misaligned, it is clearly recognized as “color misregistration” by the human eye, and the sense of quality is significantly deteriorated).

Therefore, in the image forming apparatus, it is necessary to accurately detect the position of the sheet material in the apparatus.

Usually, as a method for detecting the position of the sheet material in the image forming apparatus, a flag is provided on the sheet material conveying path and the sheet position is detected by tilting the flag on the sheet material, or the sheet material is detected. A method is used in which an optical sensor is provided in opposition to the conveyance path, and "blocking" or "reflection" of light by the sheet material is detected to detect the sheet position.

However, in the image forming apparatus as described in the conventional example, since the sheet material is electrostatically attracted and conveyed on the conveyor belt, it is difficult to detect the position of the sheet material by the method of providing the flag on the conveyor path. Is. Further, the sheet material is selected as the material for the conveyor belt based on the electrostatic adsorption property, and a material which is usually opaque and glossy is used, so that it is difficult to detect the position of the sheet material by the optical sensor.

[0026]

An endless conveying means for adsorbing and conveying a sheet material, at least one image forming portion, and a transfer portion for transferring an image formed by the image forming portion onto the sheet material. An image forming apparatus including: a transfer voltage applying unit that applies a transfer voltage to the transfer unit; and a transfer unit resistance detecting unit that detects a change in the transfer unit resistance due to a sheet material reaching the transfer unit. CPU for judging the position of the sheet material on the conveyor belt from the output of the resistance detecting means
An image forming apparatus comprising:

An endless conveying means for adsorbing and conveying the sheet material, an adsorption assisting roller for assisting the adsorption when the sheet material is adsorbed by the conveying means, and at least one image forming facing the conveying means. And a suction assisting voltage applying means for applying a voltage to the suction assisting roller, and the suction assisting roller part for detecting a change in the resistance of the suction assisting roller part due to a sheet material reaching the suction assisting roller. An image forming apparatus comprising: a resistance detection unit; and a CPU that determines the position of the sheet material on the conveyance belt from the output of the suction auxiliary roller unit resistance detection unit.

An image forming apparatus according to claim 1 or 2, further comprising a paper jam judging means for judging a paper jam according to an output of said transfer portion resistance detecting means and an output timing thereof.

The image forming apparatus has a plurality of image forming units, and has an image forming timing changing unit for changing the image forming timing on the downstream side according to the output of the transfer unit resistance detecting unit of the image forming unit on the upstream side and the output timing thereof. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

(Operation) According to the present invention, since the position of the sheet material adsorbed on the conveyor belt can be detected with a simple structure, JAM can be detected early, and the sheet material is clogged on the accordion. It is possible to avoid the problem caused by the delay of JAM detection.

Further, by forming the image in accordance with the position of the sheet material, it is possible to reduce the deviation of the image position formed on the sheet material. Especially in the color image forming apparatus, since the color images can be more precisely aligned,
Color misregistration can be reduced and a higher quality color image can be formed on the sheet material.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) The present invention is, for example, the same full-color copying as the conventional example using a plurality of photosensitive drums as an image bearing member and a sheet material conveying belt as a sheet material conveying means. Embodied in the machine.

An embodiment of the present invention will be described below with reference to FIG. The same components as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted.

The image forming apparatus according to the present embodiment has current value detecting means 21a, 21b, 21c and 21d connected to transfer voltage applying means 20a, 20b, 20c and 20d, respectively.
And current value detecting means 21a, 21b, 21c,
21d Current change detection means 22 for detecting current value change
a, 22b, 22c, 22d and current change detection means 22
It has a CPU connected to a, 22b, 22c and 22d.

The operation will be described.

In the image forming apparatus Cp of this embodiment,
For image formation, the sheet material is electrostatically attracted to the conveyor belt 8 and conveyed. The sheet material passes through the facing portions of the photosensitive drums 1a to 1d and the transfer chargers 4a to 4d of the image forming portions Pa to Pd, respectively, and the toner image on the drum is transferred onto the sheet material.

For example, in the image forming portion Pa, when the sheet material passes between the drum 1a and the transfer charger 4a,
By sandwiching the sheet material between the drum 1a and the transfer charger 4a, the resistance value between the drum 1a and the transfer charger 4a changes. The change is shown in FIG.

When controlling the application of a constant voltage to the transfer charger, as shown in FIG. 2, when the sheet material passes between the drum 1a and the transfer charger 4a, the transfer current value sharply decreases. By detecting the change in the transfer current value by the current change detecting means 22a, it is possible to detect at what timing the sheet material has entered the image forming portion Pa.

Here, the CPU connected to the current change detecting means 22a has a certain amount or more at a timing when the sheet material should normally rush into the image forming portion Pa and a sheet rushing timing obtained from the current change detecting means 22a. If the difference occurs, it is determined that some abnormality has occurred in the sheet conveyance, and the JAM processing sequence is performed. Image forming unit Pb
With the same configuration, it is possible to detect the timing at which the sheet material rushes into the image forming unit in each of Pd to Pd.

As described above, according to the present configuration, it is possible to detect the position of the sheet material on the sheet conveying belt 8 which has been difficult in the related art, and when any abnormality occurs in the sheet conveying, the JAM processing sequence is immediately started. You can
It is possible to avoid a problem caused by a delay in JAM detection, such as a sheet material clogging the accordion.

(Second Embodiment) A second embodiment will be described with reference to FIG. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

(Structure) Adsorption roller voltage applying means 30 for applying a voltage to the adsorption auxiliary roller Er, adsorption auxiliary roller current value detecting means 31 connected to the adsorption roller voltage applying means 30, and adsorption auxiliary roller current value detecting means A suction assist roller current change detection means 32 for detecting a change in current value of 31;
CP connected to the adsorption auxiliary roller current change detection means 32
Exposure timing changing means 3 for changing the operation timing of the exposing means 6a to 6d in response to signals from U and the CPU.
Have three.

(Operation) In the image forming apparatus Cp of this embodiment, the attraction roller voltage applying unit 30 applies the attraction voltage to the auxiliary roller Er so that the sheet material is electrostatically attracted to the conveyor belt 8. Is applied. In the present embodiment, the current value detecting means 31 of the attraction roller voltage applying means 30 is provided, and the timing at which the sheet material is attracted to the conveyor belt is detected by the attraction assist roller current change detecting means 32, as in the first embodiment. Is.

Conventionally, the sheet material and the image formed by the image forming portions Pa to Pd are aligned with each other at the start timing of the registration roller pair R. However, if the conveyance timing of the sheet material is deviated between the registration roller pair R and the suction assisting roller Er for some reason, there is a problem that the sheet material and the image are not aligned with each other. Similarly, if a difference occurs between the sheet material conveying speed and the image forming speed between the image forming portions Pa to Pd, the color images formed by the image forming portions Pa to Pd are misaligned on the sheet material. was there.

Therefore, in this embodiment, as shown in FIG. 3, the distance Lf from the suction assisting roller Er to the image forming portion Pa and the distance Lt from the exposure means 6a to the transfer position of the image forming portion Pa are Lf. > Lt, and the exposure start timing of the exposure means 6a is changed by the exposure timing changing means 33 with reference to the timing when the sheet material obtained by the adsorption auxiliary roller current change detecting means 32 is attracted to the conveyor belt, and the position of the sheet material and the image is changed. Make a match.

Further, the interval Ld between the image forming portions Pa to Pd
Is set to be larger than the distance Lt from the exposure unit 6a to the transfer position of the image forming unit Pa, so that, for example, one sheet is provided based on the timing of the sheet that has entered the image forming unit Pa obtained by the current change detecting unit 22a. By determining the exposure start timing of the exposure unit 6b of the downstream image forming unit Pb, the image formed on the sheet material in the image forming unit Pa and the image formed on the sheet material in the image forming unit Pb are aligned. It can be performed with higher accuracy. After that, the image formation with less color misregistration can be performed by performing the image formation on the image forming unit on the further downstream side in the same manner according to the timing of the sheet that has entered the image forming unit on the one upstream side.

Here, when there is a difference of a certain amount or more between the timing at which the normal sheet material should rush into the image forming portion Pa and the sheet rushing timing obtained from the adsorption auxiliary roller current change detection means 32, the sheet is conveyed. It is also possible to determine that some abnormality has occurred in the above and shift to the JAM processing sequence.

In the first and second embodiments, the transfer voltage and the adsorption assist voltage are controlled to be constant, and the resistance change when the sheet material reaches the transfer position is detected as the current value change, and the sheet Although the material position is detected, the resistance change may be directly detected. Alternatively, the current value may be controlled to be constant, a change in voltage may be detected, and the position of the sheet material may be detected.

[0049]

As described above, according to the present invention, it is possible to detect the position of the sheet material that is electrostatically attracted to the conveyor belt and is conveyed with a simple structure, and effectively utilize the position information. It is possible to perform JAM early response and image matching of color images with higher accuracy.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration according to an embodiment.

FIG. 2 is a graph for explaining the embodiment.

FIG. 3 is a diagram for explaining a configuration in the embodiment.

FIG. 4 is a diagram for explaining a configuration in the embodiment.

FIG. 5 is a diagram for explaining a conventional example.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/00 500 G03G 21/00 372 F term (reference) 2H027 DA01 DC04 DC14 ED04 ED06 2H072 AA02 AA03 AA07 AA16 AB09 CA07 JA02 JA03 3F048 AA01 AB01 BA05 BA14 BB05 CC03 DA06 DC17 EB25 3F049 AA01 DA04 EA22 LA01 LB03 3F101 LA01 LB03

Claims (4)

[Claims] 1. An endless conveying means for adsorbing and conveying a sheet material, at least one image forming portion, a transfer portion for transferring an image formed by the image forming portion onto the sheet material, and a transfer portion. In an image forming apparatus having a transfer voltage applying unit that applies a transfer voltage, a transfer unit resistance detecting unit that detects a change in transfer unit resistance due to a sheet material reaching a transfer unit, and a transfer unit resistance detecting unit. An image forming apparatus comprising: a CPU that determines the position of the sheet material on the conveyor belt based on the output. 2. An endless conveying means for adsorbing and conveying a sheet material, an adsorption assisting roller for assisting adsorption when the sheet material is adsorbed by the conveying means, and at least one opposed to the conveying means. An attraction auxiliary voltage applying means for applying a voltage to the attraction assisting roller, and an attraction assisting means for detecting a change in resistance of the attraction assisting roller due to a sheet material reaching the attraction assisting roller. An image forming apparatus comprising: a roller resistance detecting unit; and a CPU that determines the position of the sheet material on the conveyor belt from the output of the suction assisting roller resistance detecting unit. 3. The image forming apparatus according to claim 1, further comprising a paper jam determining unit that determines a paper jam according to an output of the transfer unit resistance detecting unit and an output timing thereof. 4. An image forming timing changing unit that has a plurality of image forming units and changes the downstream image forming timing according to the output of the transfer unit resistance detecting unit of the upstream image forming unit and the output timing thereof. The image forming apparatus according to claim 1, further comprising: