JP2003054784A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus capable of making the writing reference of the image of the first surface and that of the second surface coincide when writing an image on both sides of a sheet. SOLUTION: Sensors 35a and 35b for measuring the length of the recording paper 50 in the transport direction are provided near the recording paper transport path.
Is provided, and the image transfer position on the recording paper 50 is controlled to align the image centers of the first and second surfaces of the recording paper 50. Further, by controlling the size of the image transferred to the recording paper, the image size deviation between the first surface and the second surface of the recording paper is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to alignment of image writing positions in an image forming apparatus such as a copying machine, and in particular, image position deviation occurring on a first surface and a second surface when images are recorded on both sides of a sheet. Is related to the prevention technology.

[0002]

2. Description of the Related Art An image forming apparatus utilizing an electrophotographic process such as a copying machine or a laser printer reproduces an original on a recording paper by using toner as a coloring medium as an image forming means. The image information to be reproduced is digital information transmitted from a computer or digital information read by a document reading unit in accordance with the progress of digitization technology in recent years. By modifying this information, the image to be reproduced is changed. It is also possible to let them.

In the electrophotographic process, first, image exposure is performed on a drum, which is a photoconductor, and toner is attached onto the drum.
Then, the developed toner image is transferred onto the recording paper, and the toner is fixed on the recording paper.

In order to fix the toner on the recording paper,
It is necessary to apply heat, but since the recording paper contains water at this time, the application of heat causes the recording paper to contract due to evaporation of water. This shrinkage causes a difference in shrinkage rate depending on the type of recording paper. Shrinkage is the size of the recording paper before fixing,
The size of the recording paper after fixing is shown, and the length of the recording paper before fixing is L1 and the length of the recording paper after fixing is L2, which is represented by L2 / L1.

[0005]

Therefore, when images are formed on both sides, the paper size is smaller when the images are formed on the second side than when the images are formed on the first side. In other words, when the recording paper on which one side has been recorded is corrected by the registration roller positioned immediately before the transfer position and image transfer is started, the position of the finished first image and the second image will be different. If they are folded in half, problems such as image breakage will occur.

Further, in order to form a double-sided image, it is necessary to reverse the recording paper. Therefore, when the leading edge of the recording paper is used as a reference as in the conventional case, the reference of the second surface is the reference of the first surface. It becomes the rear side, and the standards for the first and second sides are different. Therefore, the center of the image to be transferred is further off,
When folded in two, for example, when saddle stitch processing as shown in FIG. 3 is performed, a problem such as image cutoff occurs on the second surface as shown in FIG.

However, it has been unknown in the past how much the recording paper shrinks, and it has been difficult to accurately match the image centers of the first and second surfaces.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to form an image in which the image writing position can be accurately controlled by measuring the length of the sheet. To provide a device.

[0009]

In order to achieve the above object, according to the present invention, in an image forming apparatus for recording an image on a sheet, the sheet size in the conveying direction is set during conveyance before image recording on the sheet. It is characterized in that a length measuring means for measuring the length is provided.

The image forming apparatus is an image forming apparatus for recording images on both sides of one sheet, and the sheet size may be measured by the length measuring means for each image recording on the first side and the second side. .

Image writing position control means for controlling the image writing positions of the first side and the second side may be provided with the position of 1/2 of the sheet size measured by the length measuring means as an image writing reference.

Image size control means for writing the image size of the second side at a magnification of the sheet size of the second side with respect to the first side measured by the length measuring means may be provided.

It is preferable that a fixing means for fixing the image recorded on the sheet is provided, and after fixing the image recorded on the first side by the fixing means, the image is recorded on the second side by reversing the image.

The length measuring means may obtain the sheet size from the sheet passage time and the passage speed of a sheet sensor provided on the way of the conveying path.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions of the components described in this embodiment,
Unless otherwise specified, the material, the shape, the relative arrangement, and the like are not intended to limit the scope of the present invention thereto.

(First Embodiment) FIG. 1 is a schematic configuration diagram of a digital copying machine as an image forming apparatus according to a first embodiment of the present invention.

This digital copying machine includes a document reading section 1
0, a main body image forming unit 20, a paper cassette unit 30, and a recording paper reversing unit 40.

The recording sheets 50 as sheets stacked in the paper cassette section 30 are fed upward by a sheet feeding roller 31 which is disposed close to the upper surface of the end portion of the recording sheet bundle and is rotationally driven at a predetermined timing. The nip is carried by the carrying roller pair 32 and carried to the registration roller pair 33.

On the other hand, in the image forming unit 20 including the photoconductor 21, the charging unit 22, the developing unit 23, the cleaning unit 24, etc., the original reading unit is placed on the photoconductor 21 uniformly charged by the charging unit 22. The image information obtained by 10 is written by irradiating a laser beam emitted from the light source 25 to form a latent image.

This latent image is visualized as a toner image by the developing means 23, and the registration roller pair 33 is rotationally driven in accordance with the movement timing of the visualized image to convey the recording paper onto the transfer means 26, and the recording paper. Transfer the image onto 50. By controlling this timing, the position timing of the image front end can be matched.

The recording paper 50 to which the image has been transferred is conveyed by the conveying means 27 to the fixing section 28 as a fixing means to be fixed, and the toner is fixed on the recording paper 50. At this time, since the recording paper 50 is heated by the fixing unit 28,
The contained water evaporates and contracts. For this reason, the fixed image also contracts, and the distance from the front end of the recording paper 50 to the image center at the time of image transfer differs from the distance from the front end of the recording paper to the image center after the fixing is completed.

The recording paper reversing unit 40 is located on the discharge side of the fixing unit 28, and is conveyed to the reversing unit by a flapper 29 which switches the conveying direction, and is conveyed so that the recording paper surface on which the recording has been performed is the upper surface. 41 again, the image forming unit 2
0 is conveyed to the upstream side.

After that, the image is transferred to the registration roller pair 33 again, and the image is transferred onto the back surface of the recording paper by the transfer means 26.
After fixing by the fixing unit 28, the flapper 29, which switches the conveying direction, conveys the sheet to the sheet discharge unit and discharges the sheet.

When the second side is fixed, the amount of shrinkage is smaller than that when the first side is fixed because the amount of water contained is smaller.

A sensor for detecting the lateral registration of the recording paper (lateral registration detection sensor) is provided in the vicinity of the registration roller pair 33.
34, the lateral registration detection sensor 34 can correct the lateral misalignment of the recording paper conveyed to correct the lateral misalignment of the image.

Since the lateral registration is adjusted here, the registration roller pair 33 is then rotationally driven to transfer the recording paper to the transfer means 2.
The image position in the carrying direction is adjusted by adjusting the carrying timing to 6.

This control configuration will be described with reference to FIG.

That is, there is provided a length measuring unit 110 as a length measuring means for measuring the recording paper size in the conveyance direction during the conveyance before recording an image on the recording paper 50. In the case of this embodiment, the length measuring unit 110 measures the recording paper size for each image recording job on the first side and the second side. The image writing position control unit 1 that controls the image writing positions of the first side and the second side with the position of 1/2 of the recording paper size measured by the length measuring unit 110 as the image writing reference.
Equipped with 20.

The length measuring unit 110 determines the sheet passing time and the passing speed of the sensor 35a, which is a sheet sensor provided in the middle of the conveying path of the first surface, and the sensor 35b provided in the middle of the conveying path of the second surface. It is for obtaining the recording paper size.

The sensor 35a on the first surface is provided in the conveyance path of the pair of registration rollers 33 from the paper cassette unit 30, detects the leading end and the trailing end of the recording paper 50, and the passing time t1 (s) of the sensor 35a is detected. ) Is measured. Sensor 35a
When the speed when passing through is s1 (mm / s),
The length L1 of the recording sheet in the transport direction is s1 × t1.

The sensor 35b on the second side is arranged in the middle of being conveyed to the registration roller pair 33 after the fixing on the first side is completed and conveyed to the recording sheet reversing section 40, and the leading end portion of the recording sheet 50. Then, the rear end portion is detected and the passage time t2 (s) of the sensor 35b is measured.

When the speed at which the recording paper 50 passes the sensor 35b is s2 (mm / s), the length L2 of the recording paper 50 in the transport direction is s2 × t2.

The recording paper size L1 on the first side is determined by the fixing unit 28.
Since it is the length of the recording paper 50 in the conveyance direction before entering, the relationship with L2, which is the length of the recording paper 50 in the conveyance direction after passing through the fixing unit 28, is L1> L2.

The image writing position control unit 120 controls the image writing position on the first surface so that the image center is (1/2).
If it is at L1, the image center after the recording paper 50 has passed through the fixing unit 28 is at (1/2) L2, so the image writing position on the second side is controlled so that the image center becomes (1/2). ) L2
When the image is transferred so that it comes to
Even after passing through, the image center of the first side and the image center of the second side coincide with each other, and it is possible to prevent the image from being cut off when the output paper is folded in two.

Therefore, not only can the image centers be aligned independently of the water content of the recording paper 50, but
The image centers can be aligned without depending on the difference in shrinkage amount due to the difference in paper type. As a result, as shown in FIG. 3, the output product subjected to the saddle stitch process can be produced without the image cutout as shown in FIG.

(Second Embodiment) FIG. 2B shows an example of the control configuration of an image forming apparatus according to the second embodiment of the present invention.

Since the outline of the image forming apparatus constituting the second embodiment is the same as that of FIG. 1 described in the first embodiment, the description thereof will be omitted.

In the digital copying machine having such a structure, as shown in the first embodiment, since the recording paper 50 contains water, it shrinks in the carrying direction when heat is applied at the fixing section 28. Resulting in. For this reason, in an image forming apparatus having a double-sided copying function, it is necessary to transfer an image in consideration of shrinkage of a recording sheet on which one side has been recorded before and after fixing.

A sensor for detecting the lateral registration of the recording paper (lateral registration detection sensor) is provided near the registration roller pair 33.
34, the lateral registration detection sensor 34 can correct the lateral misalignment of the recording paper conveyed to correct the lateral misalignment of the image.

Since the lateral registration is adjusted here, the registration roller pair 33 is rotationally driven next, and the timing of carrying the recording paper to the transfer means is adjusted to adjust the image position in the carrying direction.

This control configuration will be described with reference to FIG.

That is, there is provided a length measuring unit 110 as a length measuring means for measuring the recording paper size in the conveyance direction during the conveyance before recording an image on the recording paper 50. In the case of this embodiment, the length measuring unit 110 measures the recording paper size for each image recording job on the first side and the second side. The image writing position control unit 1 that controls the image writing positions of the first side and the second side with the position of 1/2 of the recording paper size measured by the length measuring unit 110 as the image writing reference.
Equipped with 20.

The length measuring unit 110 determines the sheet passing time and the passing speed of the sensor 35a, which is a sheet sensor provided in the middle of the conveying path of the first surface, and the sensor 35b provided in the middle of the conveying path of the second surface. It is for obtaining the recording paper size.

The sensor 35a on the first surface is provided in the conveyance path of the pair of registration rollers 33 from the paper cassette unit 30, detects the leading end and the trailing end of the recording paper 50, and the passing time t3 (s) of the sensor 35a is detected. ) Is measured. Sensor 35a
When the speed when passing through is s3 (mm / s),
The length L3 of the recording paper in the transport direction is s3 × t3.

The sensor 35b on the second surface is arranged in the middle of being conveyed to the registration roller pair 33 after the fixing on the first surface is completed and conveyed to the recording paper reversing unit 40, and the leading end portion of the recording paper 50. Then, the rear end portion is detected and the passage time t4 (s) of the sensor 35b is measured.

When the speed at which the recording paper 50 passes the sensor 35b is s4 (mm / s), the length L4 of the recording paper 50 in the transport direction is s4 × t4.

The recording paper size L3 on the first side is determined by the fixing unit 28.
Since it is the length of the recording paper 50 in the conveyance direction before entering, the relationship with L4, which is the length of the recording paper 50 in the conveyance direction after passing through the fixing unit 28, is L3> L4.

The image writing position control unit 120 controls the image writing position on the first surface, and the image center is (1/2).
If it is at L3, the image center after the recording paper 50 has passed the fixing unit 28 is at (1/2) L4, so the image writing position on the second side is controlled so that the image center becomes (1/2). ) L4
When the image is transferred so that it comes to
Even after passing through, the image center of the first side and the image center of the second side coincide with each other, and it is possible to prevent the image from being cut off when the output paper is folded in two.

Furthermore, since the first surface and the second surface have different water contents when passing through the fixing section 28, the sizes of the finished images differ between the first surface and the second surface.

When the second side enters the fixing section 28,
The amount of shrinkage is very small because most of the water is evaporated when the first surface passes through the fixing unit 28.

Therefore, the image size control section 130 writes the image size of the second side at a magnification of the sheet size of the second side with respect to the first side measured by the length measuring section 110.
Is provided.

That is, not only is the image center aligned with the length L3, L4 of the recording paper 50 in the transport direction measured by the sensor, but the image size written on the second surface is L.
By multiplying by 4 / L3 and aligning the image centers, the image sizes of the first side and the second side are substantially the same.

Therefore, the image size can be aligned with the image center without depending on the water content of the recording paper, and the image center and the image can be adjusted without depending on the difference in shrinkage amount due to the difference in paper type. The size can be adjusted.

As a result, as shown in FIG. 3, the output product subjected to the saddle stitch process can be produced without any image breakage.

[0055]

As described above, according to the present invention, since the length measuring means for measuring the sheet size in the conveying direction during the conveyance before the image recording on the sheet is provided, it is possible to adjust the sheet size according to the sheet size. Images can be written at precise positions.

If the sheet size is measured for each of the image recording jobs for the first side and the second side, it is possible to match the image writing standard even if the sheet shrinks.

Particularly, if the image writing positions on the first side and the second side are controlled with the position of 1/2 of the sheet size measured by the length measuring means as the image writing reference, the water content of the sheet and the paper It becomes possible to align the image centers of the first side and the second side without being affected by the difference in species, and for example, output products that have undergone saddle stitch processing have the effect of being able to produce images without interruption. To be

Further, by providing the image size control means for writing the image size of the second side with the magnification of the sheet size of the second side with respect to the first side measured by the length measuring means, the image size control means for the first side and the second side is provided. It is possible to suppress the image size deviation of the surface.

In the present invention, a fixing means for fixing the image recorded on the sheet is provided, and the contracted sheet after fixing the image recorded on the first surface is reversed to record the image on the second surface. Especially effective for.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a digital color copying machine as an image forming apparatus according to an embodiment of the present invention.

FIG. 2A is a control block diagram according to a first embodiment of the present invention, and FIG. 2B is a control block diagram according to a second embodiment of the present invention.

FIG. 3 is a schematic perspective view of an output product of a saddle stitch.

FIG. 4 is a diagram showing a first side and a second side of a saddle stitch output product by a conventional image forming apparatus.

[Explanation of symbols]

10 Document reading section 20 Image Department 21 photoconductor 22 charging means 23 Developing means 24 Cleaning means 25 light sources 26 Transfer means 27 transportation means 28 fixing means 29 flapper 30 Paper cassette part 31 paper feed roller 32 Conveyor roller pair 33 Pair of registration rollers 34 Horizontal registration detection sensor 35a, 35b sensors 40 Recording paper reversing section 41 Conveyor roller pair 50 recording paper 110 Length measurement unit 120 Image writing position control unit 130 Image size control unit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 3F100 F term (reference) 2C087 AA09 AC08 CA02 CB12 2H027 DA20 DA38 DC10 DE02 DE07 DE09 ED04 EE02 EE07 EF09 EH02 FA13 2H028 BA06 BA09 BA16 BB06 2H072 AA07 AA16 AA23 CB01 CB03 3F048 AA03 AA05 AB01 BA07 BB02 CA03 CC02 CC11 DA06 DB12 DC00 EB37 3F100 AA02 CA13 CA15 CA17 DA04

Claims (6)

[Claims] 1. An image forming apparatus for recording an image on a sheet, characterized by comprising length measuring means for measuring a sheet size in a conveying direction during conveyance before image recording on the sheet. 2. An image forming apparatus for performing image recording on both sides of one sheet, wherein the length measuring means measures the sheet size for each image recording of the first side and the second side. The image forming apparatus according to claim 1. 3. An image writing position control means for controlling the image writing positions of the first side and the second side with the position of 1/2 of the sheet size measured by the length measuring means as an image writing reference. The image forming apparatus according to claim 2, wherein: 4. An image size control means for writing the image size of the second side at a magnification of the sheet size of the second side with respect to the first side measured by the length measuring means. The image forming apparatus according to item 3. 5. A fixing means for fixing the image recorded on the sheet, wherein the image recorded on the first surface is fixed by the fixing means and then reversed to record the image on the second surface. The image forming apparatus according to any one of 2 to 4. 6. The length measuring means obtains the sheet size from the sheet passing time and the passing speed of a sheet sensor provided in the middle of the conveying path, according to any one of claims 1 to 5. Image forming device.