JP2003035974A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the positional deviation of images on a 1st side and a 2nd side, as for the constitution capable of forming images on both sides of a paper. SOLUTION: As for the image forming device capable of forming the images on both sides of the sheet material, at the time of forming the image on the 1st side in order to form a timing of starting an image forming operation, the leading end of the sheet is detected by a 1st sheet detecting means 101, on the other hand, at the time of forming the image on the 2nd side, the position of the trailing end of the sheet is detected by a 2nd sheet detecting means 102.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus for forming images on both sides of a recording material in a copying machine, a printer or the like.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses have entered the market of light printing (short run printing) or have partially entered the market due to progress in colorization, digitization, and speedup. is there.

In this field, there are many applications for binding and binding recording materials discharged after image formation.

Basically, double-sided image formation is required for such applications, and when performing post-processing on the recording material as described above, more reliable double-sided image alignment performance than ever has been obtained. Is required.

Specifically, in the case where the recording materials are cut or bound together and the positions of the images are deviated, a margin may remain depending on the image or the image may be cut off after cutting. This is because problems such as

By the way, conventionally, the image position alignment for double-sided copying, which is often used in digital copying machines, is generally performed with reference to the end surface (paper edge) of a sheet material as a recording material. Is.

That is, after fixing the image on the first side of the recording material, during conveyance of the recording material (double-sided conveyance) for forming an image on the second side, an edge portion of the recording material is detected by using a flag type sensor or a CCD line sensor. The position of the leading edge and the lateral edge is detected, and the image position of the second surface (image writing position in the main scanning direction) on the recording material is corrected based on the information on the edge position.

Further, by taking into account the shrinkage of the sheet that has passed through the fixing device after the image formation on the first side, a predetermined magnification correction is performed at the time of image formation on the second side, and the images on the first and second sides are matched. There are also things.

By the way, as a means for aligning the positions of the paper and the image in a general image forming apparatus, a sheet leading edge detecting sensor is provided on the upstream side in the conveying direction of the image forming section, and the image forming timing is generated based on the passage timing thereof. However, the sheet and the image are synchronized.
During double-sided image formation, the first side of the image is formed and fixed, and then the sheet is inverted to reverse the front and back sides of the sheet, and the same timing as the passage timing of the sheet leading edge detection sensor is set as in the case of the first side. By generating the image formation timing for the second side based on the above, the image of the second side is synchronized with the sheet.

In this system, the leading edge position of the sheet on the second side becomes the trailing edge position of the sheet on the first side.

Although there is no problem if the length of the sheet is uniform, as described above, the sheet that has once passed through the fixing device contracts and is temporarily shortened.

In addition to this, the size (length) of the sheet also varies from sheet to sheet.

As a result, it is unavoidable that the positions of the images on the first side and the second side of the paper are deviated, and as a result, the positions of the images on the first side and the second side are displaced.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is an image forming apparatus which has a simple structure and which can minimize cost increase and can perform high-level double-sided image registration. Is to provide.

[0015]

In order to achieve the above object, the invention according to claim 1 is an image forming apparatus capable of forming an image on both sides of a sheet material, and starts image formation at the time of forming an image on the first side. In order to generate the timing, a first sheet detecting means for detecting the leading edge or the trailing edge of the sheet is provided, and the image forming start timing is generated at the time of forming the image on the second side, so that the position different from the first sheet detecting means is provided. Then, it has a second sheet detecting means for detecting the paper edge on the same side as that detected by the first sheet detecting means.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, a plurality of sheet detecting means for detecting the trailing edge are arranged according to the sheet size.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the sheet detecting means for detecting the trailing edge is movable according to the sheet size.

According to a fourth aspect of the present invention, there is provided a method for controlling an image forming apparatus capable of forming an image on both sides of a sheet material, which has a sheet detecting means for generating an image forming start timing by detecting the sheet edge position. A first detection step of generating an image formation start timing of the first surface by detecting a sheet front end or a rear edge position, and a first image formation step of forming an image on the first surface at a timing based on the detection step. When the sheet front end is detected in the first detection step at a position different from the inversion step in which the sheet is inverted to form an image on the second surface of the sheet material and the first detection step, the sheet rear The image formation start timing of the second surface is generated by detecting the edge position, and
When the trailing edge of the sheet is detected in the detecting step, a second detecting step of generating the image formation start timing of the second surface by detecting the sheet leading edge position, and the second surface at the timing based on the second detecting step. And a second image forming step for forming an image.

According to a fifth aspect of the present invention, there is provided a method for controlling an image forming apparatus capable of forming an image on both sides of a sheet material, which has a sheet detecting means for generating an image forming start timing by detecting an edge of the sheet. Since the image formation start timing is generated when the image is formed on the first side, the first detection step of detecting the leading edge or the trailing edge of the sheet,
At a position different from the reversing step of reversing the sheet to form the image on the first side and the image forming start timing at the time of forming the image on the second side, different from the first detecting step.
And a first detection step of detecting the paper edge position on the same side as that detected in the first detection step.

According to a sixth aspect of the present invention, in the control method of the image forming apparatus according to the fifth aspect, the first image forming step of forming an image on the first surface at a timing based on the detecting step, and the second image forming step. A second image forming step of forming an image on the second surface at a timing based on the detecting step.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

First, the overall structure and operation of the color image forming apparatus shown in FIG. 1 will be described.

The color image forming apparatus of this embodiment has two cassette paper feed units 1 and 2 and one manual paper feed unit 3, and these paper feed units 1, 2 and 3 can be selected selectively. The sheet material S, which is a recording material, is fed to.

In each of the sheet feeding units 1, 2, and 3, the sheet material S stacked on the cassette 4, 5 or the tray 6 is sequentially fed by the pickup roller 7 from the uppermost sheet material S.

The sheet material S fed out by the pickup roller 7 is separated only by the uppermost sheet material S by a separation roller pair 8 consisting of a feed roller 8A as a conveying means and a redert roller 8B as a separating means, and the rotation is stopped. Is sent to a pair of registration rollers 12 as a registration means.

Further, at this time, the sheet material S fed from the cassettes 4 and 5 having a long distance to the registration roller pair 12.
Is relayed to a plurality of roller pairs 9, 10, 11 and sent to the registration roller pair 12.

The sheet material S sent to the registration roller pair 12 is temporarily stopped when the leading end of the sheet material S hits the nip of the registration roller pair 12 to form a predetermined loop.

By forming the loop, the skewed state of the sheet material S is corrected.

A long conveyance belt (endless belt) 13 is installed downstream of the registration roller pair 12 in a substantially horizontal state. The conveyor belt 13 rotates counterclockwise in the figure. Then, above the conveyor belt 13, photosensitive drums 14, 15, 16 and 17 which are a plurality of image carriers for carrying color toner images of different colors are sequentially arranged along the sheet material conveying direction. .

The uppermost photosensitive drum 14 carries a magenta toner image, the next photosensitive drum 15 carries a cyan toner image, and the next photosensitive drum 16 carries a yellow toner image. The toner image is carried, and the most downstream photosensitive drum 17 carries a black toner image.

In this color image forming apparatus, a plurality of originals are sequentially set at a predetermined position on the original table (platen glass) 19 by the automatic original feeder 18. Then, the image of the document set on the document table 19 (here, a color image) is read by the reading optical system 20. This read color image is CCD
The element 21 separates the color components of magenta, cyan, yellow, and black, and temporarily stores them in an image memory (not shown).

The image information stored in the image memory is written by the writing optical system 22 including a laser scanner on the photosensitive drums 14 to 17 which are sequentially rotated clockwise in the figure for each color component.

First, the projection of the laser light LM based on the image of the magenta component is started on the most upstream photosensitive drum 14, and an electrostatic latent image is formed on the photosensitive drum 14. This electrostatic latent image is visualized by the magenta color manners supplied from the developing device 23.

Next, the projection of the laser beam LC based on the image of the cyan component is started on the photosensitive drum 15 to form an electrostatic latent image on the photosensitive drum 15. This electrostatic latent image is visualized by the cyan toner supplied from the developing device 24.

Next, after a lapse of a predetermined time from the start of projection of the laser beam LC onto the photosensitive drum 15, the photosensitive drum 1
The projection of the laser beam LY based on the image of the yellow component is started on the image forming device 6, and an electrostatic latent image is formed on the photosensitive drum 16. This electrostatic latent image is visualized by the yellow toner supplied from the developing device 25.

Next, after a lapse of a predetermined time from the start of projection of the laser beam LY onto the photosensitive drum 16, the photosensitive drum 1
The projection of the laser beam LB based on the image of the black component is started on the image forming device 7, and an electrostatic latent image is formed on the photoconductor drum 17. This electrostatic latent image is visualized by the black toner supplied from the developing device 26.

As the image forming means, the photoconductor drums 14 to 17, the writing optical system 22, and the developing units 23 to 26.
In addition, the primary chargers 27, 28, 29, 30 for uniformly charging the photoconductor drums 14 to 17 and the toner attached to the photoconductor drums 14 to 17 after the toner image transfer are removed. Cleaners 31, 32, 33, 34 and the like for performing the cleaning are installed.

The sheet material S sent from the registration roller pair 12 and having its skewed state corrected is located in the vicinity of the downstream side of the registration roller pair 12 at the position of the end portion of the paper constituted by a CCD line sensor or the like. Paper edge position detecting means 10 for detecting
0 is provided, and the output signal of the sensor 100 determines the writing timing of the image in the main scanning direction by the laser beams LM, LC, LY, and LB.

Similarly, on the downstream side of the registration roller pair 12, there is provided a paper edge detection sensor 101 for detecting the edge position of the paper.
According to the output signal of 1, laser light LM, LC, LY,
The writing timing of the image in the sub-scanning direction by LB is determined.

The arrangement of the paper edge position detection means 100 and the paper edge detection sensor 101 determines the irradiation position of the laser light LM and the irradiation start timing based on these sensor signals. Therefore, the irradiation start timing of the laser light LM is determined. Since the detection is required at an earlier timing, it is arranged upstream of the distance L1 from the irradiation position of the laser light LM to the photosensitive drum 14 to the transfer position in the transport direction.

The sheet material S sent onto the conveyor belt 13 is conveyed to the downstream side by the conveyor belt 13, and in the process of being conveyed downstream, the transfer portion between the photoconductor drum 14 and the transfer charger 90, the photoconductor drum 15, and the like. By sequentially passing through the transfer portion between the transfer charger 91, the transfer portion between the photosensitive drum 16 and the transfer charger 92, and the transfer portion between the photosensitive drum 17 and the transfer charger 93, On the surface of the sheet material S, toner images of magenta, cyan, yellow, and black are sequentially transferred in an overlapping manner while the paper and the image are synchronized and aligned.

The most downstream photosensitive drum 17 and the transfer charger 9
The sheet material S that has passed the transfer portion between
The sheet 3 is sent to a fixing roller pair 35 which constitutes a fixing device. Then, while the sheet material S passes through the nip of the fixing roller pair 35, it is heated by the fixing roller 35A and pressed by the pressure roller pair 35B to fix the transferred toner image on the sheet surface of the sheet material S.

The sheet material S that has undergone the fixing process after passing through the fixing roller pair 35 is discharged by the conveying roller pair 36 and the discharge roller 37.
And is discharged onto a discharge tray 38 outside the machine by this discharge roller pair 37.

In this color image forming apparatus, double-sided mode image formation is possible. The configuration of the color image forming apparatus will be described below along the flow of the sheet material S in the double-sided mode.

When the double-sided mode is designated, the fixing-processed sheet material S which has passed through the fixing roller pair 35 is sent to the reverse path 59 through the vertical path 58.

In the double-sided mode, the flapper 60 opens the vertical path 58, and the fixing-processed sheet material S is conveyed by the conveyance roller pairs 36, 61, 62 and the reverse rotation roller pair 63.

When the rear end of the fixing processed sheet material S conveyed in the direction of the arrow a by the reverse rotation roller pair 63 passes the point P, the reverse rotation roller pair 63 is rotated in the reverse direction, and the toner of the fixing processing sheet material S is rotated. The image transfer surface is on the upper side. At the same time, the leading edge and the trailing edge of the sheet are exchanged at this point.

At the point P, the flexibility is such that the sheet material S can enter from the vertical path 58 to the reversing path 59, and the sheet material S cannot enter from the reversing path 59 to the vertical path 58. A sheet 64 and a detection lever 65 for detecting that the rear end of the sheet material has passed the point P are provided.

The fixed sheet material S conveyed in the direction of arrow b by the reverse rotation of the reverse rotation roller pair 63 is conveyed by the conveyance roller pair 6.
6 is fed into the re-feeding path 67 and is relayed by a plurality of re-feeding path conveying roller pairs 68, 69, 70, 71, 72, 73 and the conveying roller pair 11, and is re-registered for image formation again. Sent to pair 12.

A sheet trailing edge detection sensor 102 for detecting the trailing edge position of the sheet is provided in the double-sided conveyance path. The arrangement of the sheet trailing edge detection sensor 102 will be described later in detail.

Now, the sheet material S is again used for the registration roller 1.
After the skewed state is corrected in 2, the paper edge position detecting means 100
The position of the paper edge in the main scanning direction and the sub-scanning direction is detected by the paper trailing edge detection means 102, and the laser light L
The writing timings of the image in the main scanning and sub-scanning directions by M, LC, LY, and LB are determined, the image formation on the second side is performed, and the colors of magenta, cyan, yellow, and black are adjusted while adjusting the position and synchronization of the image. Toner images are sequentially transferred in an overlapping manner. Thereafter, the sheet material S is discharged to the outside of the machine through the same process as the one-sided image formation.

Here, the sheet rear end detection sensor 102
The arrangement will be described with reference to FIG.

Assuming that the length of the sheet S is LS, the distance from the pair of registration rollers to the rear end detection sensor 102 is L2, and the distance from the exposure start timing position by the laser beam LM to the rear end detection sensor 102 is L3. The trailing edge detection sensor 102 is arranged so that the relationship of L2 <LS <L3 (1) is satisfied. With this arrangement, the exposure start timing of the laser light LM can be determined based on the trailing edge detection timing of the sheet S by the trailing edge detection sensor 102.

When the distance from the registration roller to the transfer position of the magenta station is L0 and the paper conveyance speed is V, laser irradiation is started from the paper front end position when the rear end of the sheet is detected by the rear end detection sensor 102. The distance Lx to the position is Lx = L0- (Ls-L2) -L1 (2). Therefore, the exposure start timing of the laser beam LM is set to t = Lx / V = (L0− (Ls−L2) −L1) / V (3) hours after the sheet rear edge detection timing by the rear edge detection sensor 102. Just decide.

As described above, the exposure start timing of the laser beam LM is determined based on the leading edge of the sheet when forming the image on the first side and the trailing edge of the sheet when forming the image on the second side. Even if the length of the sheet S varies, or if the sheet expands or contracts by passing through the fixing device,
Since the sheet end faces that determine the exposure start timing of the laser light LM are the same on the first side and the second side, there is no deviation between the position of the sheet and the image due to the length of the sheet S. It is possible to obtain an image with excellent printing accuracy without shifting the position of the image.

In this embodiment, the sheet leading edge detecting sensor 101 is used at the image forming start timing of the first side and the sheet trailing edge detecting sensor 102 is used at the image forming start timing of the second side. Conversely 1
A sheet trailing edge detection sensor may be used for the second side, and a sheet leading edge detection sensor may be used for the second side. In short, if the image formation start timing is generated by the detection timing of the same side of the first side and the second side, the same effect can be obtained. It goes without saying that you can get

Furthermore, the trailing edge detecting sensor 10 is located at a position satisfying the formula (1) in the above embodiment according to the paper size so as to correspond to the sheet S'of another size.
You may provide two or more 2 '.

Further, by using a driving source such as a stepping motor or the like, the rear edge detection sensor 102 is moved to a position satisfying the above expression (1) according to various paper sizes, so that sheets of various sizes can be obtained. Needless to say, it may be adapted to.

Further, the arrangement of the sheet trailing edge detection sensor 102 is most preferably the portion satisfying the above expression (1), but the arrangement is not limited to this, and the exposure start timing position by the laser beam LM is provided without providing the registration roller pair. The distance from the front end detection sensor 101 to the front end detection sensor 101 is Lt, and the rear end detection sensor 102 can also be arranged so as to have a relationship of Lt <LS <L3 (4).

[0060]

As described in detail above, according to the present invention, it is possible to obtain a double-sided image with high quality and excellent printing accuracy with a very simple structure. Further, by arranging a plurality of trailing edge detection sensors or by making them movable, it is possible to obtain a double-sided image with excellent printing accuracy regardless of the paper size.

[Brief description of drawings]

FIG. 1 is a main sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of a paper trailing edge detection sensor 102.

[Explanation of symbols]

100 Paper edge position detection sensor 101 Paper edge position detection sensor 102 Paper trailing edge detection sensor

Continued front page    F term (reference) 2H027 DA21 DC10 DE07 DE10 ED04                       ED17 EE02 EF09 FA13 FA28                       FB11                 2H028 BA06 BA09 BA16 BB04 BB06                 3F048 AA02 AA05 AB01 BA07 BB02                       CA03 CB12 CC03 CC04 DA06                       DB07 DC14                 3F100 AA01 BA17 CA15 EA02

Claims (6)

[Claims] 1. An image forming apparatus capable of forming an image on both sides of a sheet material, wherein a first sheet detection for detecting a leading edge or a trailing edge of a sheet for generating an image formation start timing when forming an image on the first side. Since the image forming start timing is generated at the time of forming the image on the second surface, the sheet edge on the same side as the sheet detected by the first sheet detecting unit is located at a position different from that of the first sheet detecting unit. An image forming apparatus having a second sheet detecting unit for detecting. 2. The image forming apparatus according to claim 1, wherein a plurality of sheet detecting means for detecting the rear end are arranged according to the sheet size. 3. The image forming apparatus according to claim 1, wherein the sheet detecting unit for detecting the rear end is configured to be movable according to the sheet size. 4. A method of controlling an image forming apparatus capable of forming an image on both sides of a sheet material, comprising a sheet detection means for generating an image formation start timing by detecting the edge of the sheet. A first detection step of generating an image formation start timing of the first surface by detecting, a first image formation step of forming an image on the first surface at a timing based on the detection step,
Detecting the sheet rear end position when detecting the sheet front end in the first detection process at a position different from the reversing process for reversing the sheet to form an image on the surface and the first detection process. A second detection step of generating the image formation start timing of the second surface, and generating the image formation start timing of the second surface by detecting the sheet front end position when the sheet rear end is detected in the first detection step. ,
A second image forming step of forming an image on the second surface at a timing based on the second detecting step. 5. A control method of an image forming apparatus capable of forming an image on both sides of a sheet material, which has a sheet detecting means for generating an image formation start timing by detecting an edge of the sheet. A first detection step of detecting the leading edge or the trailing edge of the sheet to generate the image formation start timing, an inversion step of inverting the sheet to form an image on the second side of the sheet material, and an image formation of the second side. Since the image formation start timing is sometimes generated, the image forming apparatus has a first detection step for detecting the paper edge position on the same side as that detected in the first detection step at a position different from the first detection step. Method for controlling an image forming apparatus. 6. A first image forming step of forming an image on the first surface at a timing based on the detecting step, and the second image forming step.
The control method of the image forming apparatus according to claim 5, further comprising a second image forming step of forming an image on the second surface at a timing based on the detecting step.