JP2003156974A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately aligning a double-sided image, correcting the deviation of the center part of the image and coping with the elongation/contraction of the image caused by the fixation of a 1st side. SOLUTION: This image forming apparatus capable of forming the image on both sides, that is, the 1st side and the 2nd side of recording material S has a detection means writing specified marks M1, M2, M3 and M4 on decided positions on the 1st side where the image is formed first and detecting the positions of the marks M1 to M4 before forming the image on the 2nd side after fixing the image formed on the 1st side. Based on two pieces of positional information L1' and L2' of the marks M1 to M4 detected by the detection means and two pieces of positional information L1 and L2 of the marks M1 to M4 at the time of writing the image on the 1st side, the positions of the image formed on the 2nd side in the carrying direction of the material S and a direction crossing with the carrying direction are corrected, and the magnification of the image on the 2nd side is corrected.

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 such as a copying machine or a printer for forming images on both sides of a recording material.

[0002]

2. Description of the Related Art Recent image forming apparatuses are entering the market of light printing (short run printing) due to progress in colorization, digitization, speeding up, etc. Is.

In this field, there is a great demand for binding or binding the recording materials discharged after image formation.

To meet such demand, it is basically necessary to form a double-sided image on both sides of the recording material, and the recording material on which the double-sided image is formed is subjected to post-treatment. In this case, more reliable double-sided image matching performance is required.

Specifically, in a case where recording materials are cut or bound together, if the positions of the images formed on the front and back sides are misaligned, a margin may remain depending on the image or the image may be cut and cut. This is because problems such as chipping occur.

Conventionally, the structure for image alignment during double-sided copying, which is often used in digital copying machines in general, is generally performed with reference to the end surface (paper edge) of a sheet material as a recording material.

That is, after the image on the front surface or the back surface which is the first surface of the recording material is fixed, it is provided in the transportation path for transporting the recording material (duplex transportation) for forming the image on the back surface or the front surface which is the second surface. The edge of the recording material is detected by using the flag type sensor etc., and the image position of the second surface (image writing position in the direction intersecting the recording material conveying direction) on the recording material is detected from the information of the edge position. It is to make a correction.

[0008]

However, in the case of the method of correcting the image position of the second surface using the flag type sensor described above, the image position of the image position relative to the position in the direction intersecting the conveying direction of the recording material is corrected. Since only the correction can be performed, the correction of the deviation between the center of the recording material and the image position center of the first surface is not effective, and due to this, the expansion and contraction of the image due to the contraction of the recording material due to the first surface fixing There was a problem that the images on one side and the two sides were misaligned.

Therefore, an object of the present invention is to perform high-level double-sided image registration and to correct the deviation of the central portion of the image.
An object of the present invention is to provide an image forming apparatus capable of coping with image expansion and contraction due to first surface fixing.

[0010]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the first aspect of the present invention is capable of forming an image on the first surface and the second surface of a recording material, and first forms an image in an image forming apparatus having fixing means for fixing the formed image. A predetermined mark is written at a predetermined position on the first surface, and after the image formed on the first surface is fixed, there is a detection means for detecting the position of the mark before image formation on the second surface, Based on the position information of the mark detected by the detecting means and the position information of the mark at the time of writing the first surface, the recording material of the image formed on the second surface intersects with the transportation direction of the recording material. There is provided an image forming apparatus characterized by correcting the position in the direction and correcting the magnification of an image on the second surface.

A second aspect of the present invention is an image forming apparatus capable of forming an image on the first surface and the second surface of a recording material and having a fixing means for fixing the formed image. A predetermined mark is written at a predetermined position on one surface, and after the image formed on the first surface is fixed, there is a detection means for detecting the position of the mark before image formation on the second surface,
Based on the position information of the mark detected by the detecting means and the position information of the mark at the time of writing the first surface, the recording material of the image formed on the second surface intersects with the transportation direction of the recording material. There is provided an image forming apparatus characterized by correcting the position in the direction, correcting the magnification of the image on the second surface, and further correcting the magnification of the image on the first surface.

According to one embodiment of the first and second aspects of the present invention,
The predetermined marks are written at four corners of the image formed on the first surface or at two locations in the image end portion in a direction intersecting the recording material conveying direction, and the detection means is formed on the first surface. After the image is fixed, the recording material is provided in a conveyance path that conveys the recording material toward the image formation on the second surface, and the position of the mark is detected.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. The present invention can be applied to an image forming apparatus such as a copying apparatus, an image recording apparatus, a printer, and a facsimile, and the dimensions, materials, shapes, relative positions, etc. of the constituent parts described in the following embodiments are Unless otherwise specified, the scope of the present invention is not limited to them.

Embodiment 1 First, the overall structure and operation of the color image forming apparatus of Embodiment 1 shown in FIG. 3 will be described. Although the first embodiment is an electrophotographic color image forming apparatus, the present invention can be applied to any type of image forming apparatus whether it is an electrostatic recording type or a single color image forming apparatus.

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 selectively used. The sheet material S, which is a recording material, is fed to. In addition, as the sheet material S, generally cut paper is often used.

In each of the sheet feeding units 1, 2, and 3, the sheet material S stacked on the cassettes 4, 5 or the tray 6 is sequentially fed out 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 pair of separation rollers 8 composed of a feed roller 8A as a conveying means and a redert roller 8B as a separating means. , And is sent to the pair of registration rollers 12 as the registration means whose rotation is stopped.

At this time, the sheet material S fed from the cassettes 4 and 5 provided at the position where the distance to the registration roller pair 12 is long is relayed to the plurality of roller pairs 9, 10 and 11, and the registration roller pair. Sent to 12.

The sheet material S sent to the pair of registration rollers 12 is temporarily stopped when the tip of the sheet material S hits the nip of the pair of registration rollers 12 to form a predetermined loop. By forming this loop, the skewed state of the sheet material S is corrected.

A long conveyor belt (endless belt) 13 is installed in a substantially horizontal state downstream of the pair of registration rollers 12 in the conveying direction of the sheet material S. 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 conveying direction of the sheet material S. There is.

Here, the most upstream photosensitive drum 14 carries a magenta toner image, the next photosensitive drum 15 carries a cyan toner image, and the next photosensitive drum 16 is carried.
Carries a yellow toner image, 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 predetermined positions 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 sequentially rotated clockwise in the figure for each color component by a writing optical system 22 including a laser scanner which is an exposing means constituting a latent image forming means. Photoconductor drums 14-17
Written on.

First, the projection of the laser beam LM based on the image of the magenta component is started on the uppermost photosensitive drum 14 uniformly charged by the primary charger 27, and the electrostatic latent image is formed on the photosensitive drum 14. Form an image. This electrostatic latent image is visualized by magenta toner supplied from the developing device 23 which is a developing means.

Next, the projection of the laser beam LC based on the image of the cyan component is started on the photosensitive drum 15 uniformly charged by the primary charger 28, and an electrostatic latent image is formed on the photosensitive drum 15. Form. This electrostatic latent image is visualized by the cyan toner supplied from the developing device 24 which is a developing means.

Next, after a lapse of a predetermined time from the start of projecting the laser light LC onto the photosensitive drum 15, the laser based on the image of the yellow component is formed on the photosensitive drum 16 uniformly charged by the primary charger 29. The projection of the light LY is started, 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 which is a developing means.

Next, after a lapse of a predetermined time from the start of the projection of the laser beam LY on the photosensitive drum 16, the photosensitive drum 17 is started.
The projection of the laser beam LB based on the image of the black component is started on the top, and an electrostatic latent image is formed on the photosensitive drum 17 uniformly charged by the primary charger 30. This electrostatic latent image is visualized by the black toner supplied from the developing device 26 which is the developing means.

As the image forming means constituting the image forming section, the photosensitive drums 14 to 17 and the primary chargers 27 to 3 are used.
0, the writing optical system 22 as the latent image forming means, the developing devices 23 to 26 as the developing means, and a cleaner for removing the toner adhering to the photosensitive drums 14 to 17 after the toner image transfer. 31, 32, 33, 34 are installed.

The sheet material S sent from the registration roller pair 12 and corrected in the skewed state is the most upstream photosensitive drum 1.
Registration roller pair 12 that starts rotation at the timing of aligning the position of the toner image on 4 with the leading edge of the sheet material S
Is sent onto the conveyor belt 13 rotating counterclockwise.

The sheet material S sent onto the conveyor belt 13 is conveyed to the downstream side, and the transfer portion between the photosensitive drum 14 and the transfer charger 90 as the transfer means, which is the position of the image forming portion. , A transfer portion between the photosensitive drum 15 and the transfer charger 91, a transfer portion between the photosensitive drum 16 and the transfer charger 92, and a transfer portion between the photosensitive drum 17 and the transfer charger 93. By sequentially passing, the toner images of magenta, cyan, yellow, and black are transferred and superposed on the surface of the sheet material S.

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 as fixing means. 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 which has undergone the fixing process after passing through the fixing roller pair 35 is discharged by the conveying roller pair 36 to the discharge roller 37.
And is discharged onto a discharge tray 38 outside the machine by this discharge roller pair 37.

The color image forming apparatus is capable of forming images in the double-sided mode. The configuration of the recording material conveying device in the color image forming apparatus will be described below along the flow of the sheet material S in the double-sided mode.

In the recording material conveying apparatus according to the present invention, at least the re-feeding path 67 is provided in the conveying path for conveying the recording material having the image formed on the first surface toward the image formation on the second surface. A conveyor belt 13, a registration roller 12 for conveying the sheet material S to an image forming unit on the conveyor belt 13, and a detection means (CCD line sensor) 74 for detecting the position of the recording material provided in the re-feed path 67. However, in the present embodiment, in addition to this, the transport rollers 68, 69, 70, 71, 72, 73 attached to the re-feeding path 67 and the reversing path 5 are added.
9 and the members associated therewith, the pickup roller 7, etc., and means the entire means relating to the conveyance of the recording material inside the image forming apparatus shown in FIG.

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 this case, the flapper 60 opens the vertical path 58, and the fixing-processed sheet material S is transported by the transport roller pairs 36, 61, 62 and the reverse rotation roller pair 63.

When the trailing edge of the fixing processed sheet material S which has been conveyed in the direction of the arrow a has passed the point P, the reverse rotation roller pair 63 reversely rotates and the toner image transfer surface of the fixing processed sheet material S is on the upper side. become.

At the point P, the flexible sheet 64 which allows the sheet material S to enter from the vertical path 58 to the reverse path 59 and prevents the sheet material S from entering from the reverse path 59 to the vertical path 58. And a detection lever 65 for detecting that the rear end of the sheet material S has passed the point P.
Therefore, the sheet material S whose image is already formed on the first surface by the reverse rotation roller pair 63 is transferred to the vertical path 5 before the point P.
8 will not be conveyed in the reverse direction.

The fixed sheet material S is fed in the direction of arrow b from the vertical path 58 by the reverse rotation of the reverse rotation roller 63,
The sheet is conveyed to the sheet re-feeding path 67 by the pair of conveying rollers 66.

After that, the sheet is relayed by a pair of conveying rollers 68, 69, 70, 71, 72, 73 in the re-feeding path 67 and the pair of conveying rollers 11, and again sent to the pair of registration rollers 12 for image formation.

Recording material (sheet material S) in the re-feed path 67
A CCD line sensor 74, which is a detection unit for reading the image of the fixed processing sheet material S from above, is arranged on the downstream side in the transport direction, and the image data formed on the second surface of the image is read by the CCD line sensor 74. The magnification in the main scanning direction and the sub-scanning direction, and the positional deviation of the image position in the main scanning direction and the sub-scanning direction are corrected.

Since the electrophotographic image forming apparatus shown in FIG. 3 is used as the image forming apparatus in this embodiment, the "main scanning direction" is the main scanning direction of the laser scanner with respect to the photosensitive drum. Yes, that is, the direction intersecting the recording material conveyance direction. The "sub-scanning direction" indicates the recording material conveyance direction.

After that, the sheet material S is re-registered on the registration roller 1.
After the skewed state is corrected in 2, the sheet is sent to the conveyor belt 13.

Then, based on the information in the sensor 74, a magnification correction in the main scanning direction and the sub-scanning direction, and a positional deviation correction in the main scanning direction and the sub-scanning direction are performed. An image formation on the second side is performed based on the stored image data, and thereafter, the sheet material S is discharged to the outside of the machine through the same process as the one-sided image formation.

Next, a detailed description will be given of the deviation correction in the main scanning direction and the sub-scanning direction, and the magnification correction in the main scanning direction and the sub-scanning direction of the second surface image, which are the features of the present invention.

Basically, the control for adjusting the position and the magnification of the image in the present embodiment is basically performed when the sheet material S finally discharged out of the machine is cut by a finishing device or a bookbinding device. This is done to match the size and position of the front and back images on the material.

Therefore, as shown in FIG. 1, on the sheet material S, marks M1, M2, M3, and M4, which serve as cutting marks in advance, are formed.
Are written in the four corners of the image area together with the image when the first surface image is formed. The positions of M1 to M4 are stored as image data in the image memory.

At this time, as the size for writing on the first surface, the distance between M1 and M2 (the distance between M3 and M4), which is the distance size in the main scanning direction in the direction intersecting the recording material conveyance direction of the image area, is An image is formed such that L1 is the size in the sub-scanning direction, that is, the size in the recording material conveyance direction, that is, the interval between M1 and M4 (the interval between M2 and M3) is the size of L2, here the cutting size.

The image of the first surface and, at the same time, the mark M
As described above, the sheet material S on which the sheets 1 to M4 have been formed is subjected to CC fixing at the re-feeding path 67, which is a conveyance path, by the reverse rotation roller pair 63 after the image is fixed by the fixing device 35.
It is conveyed to the position of the D line sensor 74, and the first surface on which the marks M1 to M4 are formed faces the CCD line sensor 74.

Then, as shown in FIG. 2, by reading these marks M1 to M4 from above by the CCD line sensor 74, the image data of the first surface of the sheet material S during the double-sided conveyance after the sheet material S is fixed. It is reading.

At this time, the sheet material S is temporarily fixed to the fixing device 3
Since it has passed through No. 5, the mark M1 formed before fixing
Since the positions of the marks M1 to M4 may be displaced due to the change in the size of the sheet material S, the distances L1 and L2 between the marks M1 to M4, which are the position information at the time of writing on the first surface, change. There is a possibility that here,
When the distances L1 and L2 at the time of writing on the first side are fixed on the first side,
The distance detected by the CCD line sensor 74 is L
1 ', L2'.

Regarding actual reading, in the CCD line sensor 74, an image is formed on the first surface, and after passing once through the fixing device 35, marks M1 to M1 shown in FIG.
When the sheet material S marked with M4 is conveyed, first, the distances L1 ′ and L3 described below are detected (measured).
Further, using the sensor unit 74 passing speed (conveying speed) of the sheet material S, L2 ′ and L4 described in are measured,
Calculate

Measurement of the distance L1 'between M1 and M2 Calculation of distance L3 from M1 determined reference position M5 Measurement of the distance L2 'between M2 and M3 (M1 and M4) Calculation of the distance L4 from the tip of the sheet material to M1 (M2)

Here, the determined reference position M in
5 is suitable for the writing (writing) reference position by the laser scanner as the latent image forming means or the image center (center of the image forming portion), and in this embodiment, the distance from the writing reference position M5 by the laser scanner is used. It is set to measure.

From the information obtained above, when the second surface image is formed on the sheet material S, the image writing position is first corrected from L3 and L4.

Regarding the image magnification, L1 and L
1 ', and the reduction amount of the image on the first surface is calculated from L2 and L2', and the image is written based on the above-described image writing standard.

Here, the position correction of the second surface image in the direction intersecting the recording material conveyance direction is carried out by the latent image forming means at the time of forming the second surface image, in this case, the writing position in the main scanning direction of the laser scanner. The position correction of the second surface image in the recording material conveying direction is performed by shifting the writing start timing of the laser scanner during the second surface image formation.

By the above method, the image on the first surface and the image on the second surface on the sheet material S are controlled so that the size and the position thereof match with each other with the cutting mark as a reference.

In the above, the CCD line sensor 74
Based on the detected position information of the marks M1 to M4 and the position information of the marks at the time of writing on the first surface, the main scanning direction and the sub-direction of the image formed on the second surface on the recording material (sheet material S). The image forming apparatus that corrects the position in the scanning direction and also corrects the magnification of the image on the second surface has been described.

Although only the magnification correction of the image on the second surface has been described here, when printing a plurality of recording materials, after printing the first sheet, the mark M1 detected by the CCD line sensor 74 on the first sheet. ~ M4 position information L
1 ', L2' and the mark M1 when writing the first side of the first sheet
Based on the position information L1 and L2 of M4, the magnification of the image on the first surface can be corrected in printing from the second sheet.

That is, from the dimension L1 at the time of writing L1 'and the dimension L2 at the time of writing L2' in the first surface image formation of the first sheet in advance, the main scanning direction of the first surface image from the second sheet. It is also possible to perform magnification correction in the sub-scanning direction,
The size of the image on the recording material that was finally discharged outside the machine is
It is possible to output in a desired size, that is, in a form in which there is no influence of image contraction due to fixing.

Therefore, by first using a test paper or the like as a recording material, the magnification of the first surface image is corrected to ensure the dimensions after the final cutting in the subsequent printing. Will also be possible.

Furthermore, since the cutting marks do not remain on the sheet after cutting, it is possible to align the front and back of the image without the need to write a special mark outside the image area. It is a feature.

In the present embodiment, the control is performed with the cutting mark as a reference, but the same effect can be obtained by using a mark written outside the image area for color misregistration correction.

Regarding the position adjustment of the image in the sub-scanning direction, it is possible to change the position by changing the writing timing of the laser scanner as well as by changing the rotation start timing of the registration roller.

Second Embodiment Next, a case where the image shrinkage ratio is obtained more simply than in the first embodiment will be described.

FIG. 4 shows an image forming apparatus according to this embodiment. In this embodiment, except for the position of the CCD line sensor, the structure is the same as that of the color image forming apparatus of the first embodiment shown in FIG. 1. Therefore, members having the same structure and function are designated by the same reference numerals. However, detailed description is omitted.

When simply obtaining the image shrinkage ratio, the shrinkage ratio from the size L1 at the time of writing on the first side to the size L1 'after fixing is directly changed from the size at the time of writing on the second side L2' to the size L2 at the time of fixing. May be applied to the shrinkage rate.

In this case, since the calculation based on the paper conveyance speed and the mark passage timing is not required, the CCD line sensor 75 for reading the mark is provided in the vicinity of the image transfer portion (image forming portion) as shown in FIGS. It is possible to dispose the sheet material S, which is a recording material, between the registration rollers 12 and the conveyor belt 13.

Therefore, as shown in FIG. 4, in the present embodiment, the recording material conveying device conveys the sheet material S having the image formed on the first surface toward the image formation on the second surface. Instead of the CCD line sensor 74 of the first embodiment provided on the sheet re-feeding path 67, the sheet material S passes through the sheet re-feeding path 67 in the conveying path and the registration roller 1
During the period from passing 2 to reaching the position of the image forming unit, C
A CD line sensor 75 is provided.

In this case, the image magnification and alignment method are performed as follows. The positions of the marks M1 and M2 and the distances L1 to L4 and L1′L2 ′ used here are
It is similar to that shown in FIG. In this embodiment, M3, M
4 is unnecessary.

The following numerical values are measured and calculated. even here,
The distance after fixing of the writing distances L1 and L2 is L1 ′,
L2 '.

The distance L1 'between M1 and M2 is measured. The distance L3 from the predetermined reference position M5 of M1 is calculated, and then the leading edge of the sheet material S of L2' is detected first, and then M1 (M2). Is detected, the distance L4 from the leading edge of the paper to M1 (M2)
Arithmetic

By the above method, the image of the first surface and the image of the second surface on the sheet material S are divided into two cutting marks M1,
Control is performed so that the size and the position match with M2 as a reference.

In this case as well, the same control can be performed by using other marks for color misregistration correction instead of the cutting marks.

Also in this case, as in the case of the above-mentioned embodiment,
Further, the magnification of the image on the first side is corrected and the size of the image on the first side is also controlled, so that the size of the image on the sheet finally discharged outside the machine becomes a desired size. That is, it is possible to output the image without the influence of image contraction due to fixing.

Further, a mark for cutting or the like is set to 2 in order to match the image.
Although only four pieces (M1, M2) are required, four marks (M1, M2, M3, M4) may be formed for actual cutting, or when the sheet material is folded at the center and then cut. Of course, it doesn't matter if there are two marks.

Further, in the present embodiment, since the image information on the first surface is read between the position of the image forming portion and the registration roller 12, the position of the skewed sheet material and the skew feeding of the sheet material when the sheet material is conveyed. The feature is that the influence of the deviation is very small.

Therefore, according to the present invention described in the first and second embodiments, the image position on the first surface of the recording material and the image shrinkage amount due to fixing and the like are detected, and the first image is detected based on the detected image shrinkage amount. To correct the image position and magnification when forming images on two sides,
Compensation for the deviation of the image position center of the recording material from the image of the second surface and the image position center of the first surface, and the expansion and contraction of the image due to the contraction of the recording material due to the fixing of the first surface It is possible to correct the deviation.

[0079]

As described above, according to the present invention, in an image forming apparatus capable of forming an image on both sides of a recording material, a predetermined mark is written at a predetermined position on the first surface on which an image is formed first. , The position of the mark is detected after the image formed on the first side is fixed and before the image is formed on the second side, and the position information of the detected mark and the position information of the mark at the time of writing on the first side are used. In addition, since the image forming apparatus corrects the position of the image formed on the second surface in the recording material conveyance direction and the direction intersecting the conveyance direction, and also corrects the magnification of the image on the second surface, The correction of the deviation between the image center of the recording material and the image position center of the first surface and the deviation of the image of the first surface and the second surface caused by the expansion and contraction of the image due to the contraction of the recording material due to the fixing of the first surface are corrected. It will be possible.

Since the image position or the expansion / contraction of the image is detected by using the cutting mark or the color misregistration correction mark, it is not necessary to write an unnecessary mark on the recording material.

Further, by correcting the magnification of the first surface image, it becomes possible to guarantee the dimensions in the state after the final cutting.

Therefore, it is possible to form a double-sided image with extremely high accuracy, and it is possible to obtain a high-quality double-sided image.

[Brief description of drawings]

FIG. 1 is a front view showing an example of a first surface of a recording material on which a mark according to the present invention is formed.

FIG. 2 is an explanatory diagram showing an example of a method for detecting a mark on the first surface of a recording material according to the present invention.

FIG. 3 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention.

FIG. 4 is a schematic configuration diagram showing another example of the image forming apparatus of the present invention.

FIG. 5 is an explanatory diagram showing another example of the method for detecting the mark on the first surface of the recording material according to the present invention.

[Explanation of symbols]

12 Registration Roller (Conveyance Path) 13 Conveyor Belt (Conveyance Path) 14-17 Photosensitive Drum (Image Carrier) 23-26 Developing Device (Developing Means) 22 Laser Scanner (Latent Image Forming Means) 35 Fixing Roller Pair (Fixing Means) ) 58 vertical path 59 reverse rotation path 63 reverse rotation roller pair 67 re-feed path (conveyance path) 68-73 re-feed path conveyance rollers 74, 75 CCD line sensor (detection means) 90-93 transfer charger (transfer means) S Sheet material (recording material) M1 to M4 marks

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 F term (reference) 2H027 DE02 DE07 DE09 EB04 EC01 EC06 EC09 ED04 ED17 EE02 EE04 EF06 FA13 FB12 FD03 FD06 2H028 BA06 BA09 BA16 BB04 BB06 2H076 AB02 AB16 AB67 AB73 DA41 EA01

Claims (9)

[Claims] 1. An image forming apparatus capable of forming an image on a first surface and a second surface of a recording material and having a fixing means for fixing the formed image, wherein the image is first formed on the first surface. Has a detection means for writing a predetermined mark at a predetermined position, fixing the image formed on the first surface, and before forming the image on the second surface. Based on the detected position information of the mark and the position information of the mark at the time of writing on the first surface, the position of the image formed on the second surface in the conveying direction of the recording material and the direction intersecting the conveying direction is determined. An image forming apparatus which corrects and corrects an image magnification on the second surface. 2. An image forming apparatus capable of forming an image on the first surface and the second surface of a recording material, and having a fixing means for fixing the formed image, on the first surface on which the image is formed first. Has a detection means for writing a predetermined mark at a predetermined position, fixing the image formed on the first surface, and before forming the image on the second surface. Based on the detected position information of the mark and the position information of the mark at the time of writing on the first surface, the position of the image formed on the second surface in the conveying direction of the recording material and the direction intersecting the conveying direction is determined. An image forming apparatus which corrects and corrects an image magnification on a second surface, and further corrects an image magnification on a first surface. 3. The predetermined marks are written at four corners of an image formed on the first surface or at two locations in the image end portion, which intersect with the recording material conveyance direction, and the detection means is provided on the first surface. 3. The image according to claim 1, wherein the position of the mark is detected by being provided in a conveyance path for conveying the recording material toward image formation on the second surface after fixing the image formed on the recording material. Forming equipment. 4. The image forming apparatus according to claim 1, wherein the predetermined mark is written on the recording material as a mark when the recording material is cut. 5. The image forming apparatus according to claim 1, wherein the predetermined mark is a mark written on a recording material for color misregistration correction of an image. 6. The image forming apparatus according to claim 1, wherein cut paper is used as the recording material. 7. A latent image forming means for forming an electrostatic latent image on an image carrier, a developing means for developing the electrostatic latent image to form an image, and a transfer means for transferring the image onto a recording material. In the image forming apparatus having the following, the position correction of the image formed on the second surface in the direction intersecting the recording material conveyance direction is performed in the direction intersecting the recording material conveyance direction when the second surface image is formed. 7. The image forming apparatus according to claim 1, wherein the writing start position of the latent image forming means is shifted. 8. A latent image forming means for forming an electrostatic latent image on an image carrier, a developing means for developing the electrostatic latent image to form an image, and a transfer means for transferring the image onto a recording material. In the image forming apparatus having the following, the position correction of the image formed on the second surface in the recording material conveyance direction is performed by shifting the writing start timing of the latent image forming means during the second surface image formation. The image forming apparatus according to any one of claims 1 to 7, wherein: 9. The position correction of the image formed on the second surface in the recording material conveyance direction is performed after correcting the skew of the recording material at the registration roller position for conveying the recording material to the position of the image forming unit.
The image forming apparatus according to any one of claims 1 to 7, wherein the rotation start timing of the registration roller is shifted.