JP2003241610A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of suppressing the deviation of images formed on both front and back surfaces of a sheet. <P>SOLUTION: The shrinkage factor of the sheet S is obtained by a control means 31 based on the detection signal from a detecting means 30 for detecting the shrinkage factor of the sheet S when the sheet S with a transferred toner image on the 1st surface passes through a fixing unit 19, and also, the size of the toner image to be transferred to the 1st surface of the sheet S or the 2nd back surface of the sheet S is controlled by the control means 31 based on the shrinkage factor. Besides, the transfer position is controlled by the control means 31 so that the reference position required when the toner image is transferred to the 2nd surface of the sheet S may become the same as the reference position required when the toner image is transferred to the 1st surface of the sheet S. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for forming an image on a sheet by developing a latent image formed on a photoreceptor with toner and then transferring and fixing the toner image on the sheet. More particularly, the present invention relates to forming an image on both front and back surfaces of a sheet.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, an electrophotographic image in which a latent image formed on a photoconductor is developed with toner, and then the toner image is transferred onto a sheet and fixed to form an image on the sheet. There is a forming apparatus, and such an image forming apparatus is used as an output device such as an image recording apparatus having a function of a copying machine, a printer or the like, a complex machine having such functions, or a workstation.

By the way, in such an electrophotographic image forming apparatus, a plurality of electrophotographic process units each having a charging device and a developing device arranged around a photoconductor are arranged side by side in the device, and the electrophotographic process units in each process unit are arranged in parallel. The latent image formed on the surface of the photoconductor is visualized with toner by the developing device by forming an optical image on the surface of the photoconductor with an exposure device using a laser, LED light, etc., and the visualized toner image is further visualized. In recent years, a structure in which a color image is formed on a transfer material by transferring it to a transfer material, which is a sheet, and then transferring the toner images to the transfer material at a time after transferring the intermediate transfer belt to the transfer material is collectively put into practical use. There is.

FIG. 9 is an example of such a conventional image forming apparatus and shows a schematic structure of a color image forming apparatus for forming an image by superposing four color toners of magenta, cyan, yellow and black. It is a figure.

In the figure, 10Y, 10M, 10C,
Reference numeral 10K denotes an image forming unit that forms yellow, magenta, cyan, and black toner images, and these image forming units 10Y, 10M, 10C, and 10K are the photosensitive drum 13 that is a photoconductor and the periphery of the photosensitive drum 13. The charging device 14, the exposure device 15, the developing device 16, the transfer device 17, and the cleaner 18 which are arranged in

Reference numeral 8 is an intermediate transfer belt formed of a conductive member and primary-transferred with yellow, magenta, cyan, and black toner images formed in the image forming section 10 (10Y, 10M, 10C, 10K). , 12 are image reading devices, and 1 is a cassette for accommodating a transfer material S which is a sheet.

When the image forming operation is started in the color image forming apparatus having such a structure, first, in each of the image forming sections 10Y, 10M, 10C and 10K, the document reading device 12 or a computer (not shown) is operated. A toner image corresponding to each color is formed on the photosensitive drum 13 by the image information signal sent from the output device. next,
The toner images of the respective colors formed on the photosensitive drum 13 in this way are sequentially and multiple-transferred onto the intermediate transfer belt 8, whereby a color image is formed on the intermediate transfer belt 8.

Further, in parallel with such a color image forming operation, the transfer material S accommodated in the cassette 1 is sent out from the cassette 1 by the paper feed roller 2 and then conveyed by the conveying rollers 3 to 6, It reaches the registration roller 7. After that, the skew of the transfer material S is corrected by the registration roller 7, and then the secondary transfer unit configured by the transfer roller 9 and the intermediate transfer belt 8 is synchronized with the image on the intermediate transfer belt. It is sent to T.

Next, the four-color toner images that have been multi-transferred to the intermediate transfer belt 8 at the secondary transfer portion T are collectively transferred to the transfer material S sent from the registration roller 7 in this way. After that, the transfer material S to which the four-color toner images have been collectively transferred in this way passes through the transport unit 29 and reaches the fixing roller pair 19.

The fixing roller pair 19 is heated by a heater (not shown). When the transfer material S passes through the fixing roller pair 19, the toner of each color is melted by heat and is fixed on the transfer material. Then, the color image is completed. Then, the transfer material S on which the toner image is fixed on the front surface (first surface) by the fixing roller pair 19 in this manner is discharged as it is to the outside of the apparatus.

By the way, this color image forming apparatus can also form an image on the back surface (second surface) of the transfer material S. When an image is formed on the back surface of the transfer material S, the transfer is performed. After the image is formed on the surface of the material S as described above, the material S is conveyed to the reversing unit 20 and is switched back in the reversing unit 20.

The transfer material S is reversed by being switched back in this way, and is conveyed to the secondary transfer portion T with the trailing end portion up to that point first. As a result, a new image formed through the same image forming process as the image formation on the front surface is additionally formed on the back surface, and thereafter, the transfer material S is formed.
Is discharged to the outside of the device.

[0013]

By the way, in the conventional color image forming apparatus having such a structure, in order to stabilize the toner image transferred on the transfer material, the toner is heated and melted. Although pressure is applied, when paper is used as the transfer material S at this time, the vertical and horizontal directions of the transfer material S are determined depending on the crevice direction of the fibers forming the paper and the evaporation rate of water contained in the transfer material. Contraction occurs.

The contraction amount of such a transfer material is, for example, when an A3 size transfer material is conveyed in the longitudinal direction and passed through a fixing device (fixing roller pair 19), the A3 longitudinal dimension is 0. Shrinkage of about 1% may occur.

Here, when an image is to be formed on the back surface (two surfaces) in the contracted state of the transfer material S, the position of the image on the transfer material is different from that at the time of forming the front surface (one surface). As a result, the image positional relationship between the two front and back surfaces, which would normally be substantially the same, may be displaced, causing a problem in image quality.

FIG. 10 is a diagram for explaining the deviation of the image positional relationship when images are formed on both surfaces of the transfer material S which causes such shrinkage. In the figure, is the state when the toner image is transferred to the transfer material surface (one surface),
Is the state when the toner image is fixed, is the transfer material S
Indicates a state in which the toner image is newly transferred to the back surface (two sides) of the transfer material, and the state in which the toner image is fixed is indicated by.

Here, the transfer material surface (1
When a toner image R is transferred to the surface), the length of the transfer material S in the transport direction (hereinafter, referred to as length) and the length in the width direction orthogonal to the transport direction (hereinafter, referred to as width) are X ₁ , Y. ₁ and the image is formed in G _1X and G _1Y sizes at the transfer material reference position, that is, at a position a ₁ from the leading end of the transfer material S in the transport direction and at a position b ₁ from one side end of the transfer material S.

Next, when the transfer material S passes through the fixing device as shown in (3), the transfer material S contracts and the length and width of the transfer material S are reduced to X ₁ 'and Y ₁ '. Accordingly, the image size is reduced to G _1X ′ and G _1Y ′, and the image position on the transfer material is changed to a ₁ ′ and b ₁ ′.

Next, the contracted transfer material S is switched back and inverted, and the toner image is transferred to this transfer material S, and the image size becomes the same as shown in. At this time, in order to make the image relationship with the surface the same, the entire image is reversed before and after the transfer. When the toner image is transferred in this way, the image position reference for the transfer material S is C ₁ and b ₁ ′. It should be noted that the light letter R shown in () indicates an image already formed on the front surface (one surface) of the transfer material S, and is clearly smaller than the letter R formed on the back surface.

When the toner image formed on the back surface is fixed, the size of the transfer material S finally becomes X ₂ and Y ₂ , and the image sizes become G _2X and G _2Y , as shown in.

As described above, when images are formed on both sides of one transfer material, the transfer material by fixing is fixed as shown in (1) (the image forming state is deformed for easy understanding). Due to the image contraction caused by the contraction and the difference in the image reference position with respect to the transfer material S, a shift occurs between the two-sided images.

When such a deviation between the two-sided images occurs, for example, when the image is folded along a fold line defined on the surface as shown in FIG. 11, the image is cut at the fold line and the image is excessively projected. Will end up. In addition, FIG.
When trying to construct a booklet-like product that is made by stacking and folding multiple transfer materials as shown in (A3 size transfer material, two A4 size images are arranged on the front and back, and stitched at the center) A deviation occurs between the front surface of the material and the back surface of another transfer material, resulting in discontinuous images.

Therefore, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image forming apparatus capable of suppressing the deviation of images formed on both front and back surfaces of a transfer material (sheet). It is intended.

[0024]

The present invention is directed to a first sheet
An image in which a toner image is transferred to a surface, the toner image is fixed by a fixing device to form an image on the sheet, and then the sheet is reversed to form an image on the second surface on the back side of the sheet. In the forming apparatus, a detection unit for detecting the size of the sheet after the sheet has passed through the fixing unit, and a size of the toner image transferred to the first surface or the second surface of the sheet are controlled. And a control unit for controlling a reference position when the toner image is transferred onto the second surface of the sheet, the control unit based on a detection signal from the detection unit, and controls the reference position after passing through the fixing device. The change rate of the sheet size is calculated, the size of the toner image transferred to the first surface or the second surface of the sheet is controlled based on the change rate, and the toner image is transferred to the second surface of the sheet. When setting the reference position It is characterized in that the controls to the same as the reference position when the toner image is transferred onto the first surface of the bets.

According to the present invention, the detecting means detects the length of the sheet in the sheet conveying direction before and after the sheet passes through the fixing device, and the control means detects the length of the sheet in the sheet conveying direction from the detecting means. It is characterized in that the rate of change upon passing through the fixing device is obtained.

In the present invention, the control means sets the reference position in the sub-scanning direction for transferring the toner image on the first surface to the leading end side in the sheet conveying direction, and sets the reference position in the sub-scanning direction on the second surface in the sheet conveying direction. It is characterized in that it is controlled so as to be on the rear end side.

In the present invention, the control means multiplies the image forming data of the image formed on the second surface of the sheet by the change rate so as to control the size of the toner image transferred to the second surface. It is a feature.

In the present invention, the control means multiplies the image forming data of the image formed on the first surface of the sheet by the reciprocal of the change rate so as to control the size of the toner image transferred to the first surface. It is characterized by that.

The present invention further comprises an image carrier on which the toner image is formed, and an exposure device which exposes the image carrier to form a latent image on the image carrier, and the control means comprises: The main scanning direction of the image forming data for forming the image on the second surface on the image carrier is scaled by modulating the writing time interval in the main scanning direction by the exposure device according to the change rate. It is characterized by forming a latent image.

Further, the present invention comprises an image carrier on which the toner image is formed, and an exposure device which exposes the image carrier to form a latent image on the image carrier, and the control means comprises: By changing the sheet conveyance speed at a constant rate in accordance with the change rate, the transfer toner image formed on the image bearing member in which the sub-scanning direction of the second surface image forming data is scaled is obtained. It is characterized by being formed on a sheet.

Further, the present invention comprises an image carrier on which the toner image is formed, and an exposure device using a rotary polygon mirror which exposes the image carrier to form a latent image on the image carrier. The control means changes the sub-scanning direction of the image forming data for forming an image on the second surface by changing the rotation speed of the rotary polygon mirror and the sheet conveying speed according to the change rate. It is characterized in that a latent image is formed.

Further, the present invention comprises an image carrier on which the toner image is formed, and an LED exposure device which exposes the image carrier to form a latent image on the image carrier, and the control means is provided. By changing the writing time interval in the sub-scanning direction by the exposure device according to the change rate, the sub-scanning direction of the image forming data for forming an image on the second surface on the image carrier is scaled. It is characterized in that a latent image is formed.

Further, the present invention is characterized in that the rate of change is stored, and the stored rate of change is called according to the sheet.

Further, the present invention comprises an image carrier on which the toner image is formed, and an exposure device which exposes the image carrier to form a latent image on the image carrier, and the control means comprises: The main scanning direction of the image forming data for forming an image on the first surface on the image carrier is changed by modulating the writing time interval in the main scanning direction by the exposure device according to the reciprocal of the change rate. It is characterized in that a doubled latent image is formed.

Further, the present invention comprises an image carrier on which the toner image is formed, and an exposure device using a rotary polygon mirror which exposes the image carrier to form a latent image on the image carrier. The control unit changes the conveyance speed of the sheet at a constant rate according to the reciprocal of the change rate, so that the transfer toner on the sheet in which the sub-scanning direction of the first surface image forming data is scaled is changed. It is characterized by forming an image.

The present invention further comprises an image carrier on which the toner image is formed, and an exposure device using a rotary polygon mirror which exposes the image carrier to form a latent image on the image carrier. The control means changes the sub-scanning direction of the image forming data for forming an image on the first surface by changing the rotation speed of the rotary polygon mirror and the sheet conveying speed according to the reciprocal of the change rate. It is characterized in that a latent image having a variable magnification is formed.

Further, the present invention comprises an image carrier on which the toner image is formed, and an LED exposure device which exposes the image carrier to form a latent image on the image carrier, and the control means is provided. , The sub-scanning direction of the image forming data for forming an image on the first surface on the image carrier is changed by changing the writing time interval in the sub-scanning direction by the exposure device according to the reciprocal of the change rate. It is characterized in that a latent image having a variable magnification is formed.

Further, the present invention is characterized in that the reciprocal of the change rate is stored, and the stored change rate is called according to the sheet.

Further, according to the present invention, the distance to the transfer portion for transferring the toner image onto the sheet on the transfer material conveying path where the detecting means conveys the sheet at a constant conveying speed is the maximum in the sheet conveying direction. It is characterized in that it is provided at a position longer than the length.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the schematic arrangement of a color image forming apparatus according to the first embodiment of the present invention. In addition,
In the figure, the same reference numerals as those in FIG. 9 indicate the same or corresponding portions.

In the figure, reference numeral 30 is a transfer material length detection unit, and this transfer material length detection unit 30 is installed in a part of the transfer material transport path upstream of the toner image transfer position. Here, the transfer material length detection unit 30 measures the passage time of the transfer material S sent at a predetermined constant speed in synchronization with the toner image formed on the intermediate transfer belt by the registration roller 7. By measuring the transit time of the transfer material S in this manner, the length of the transfer material S in the transport direction is indirectly measured.

The transfer material length detection unit 30 is provided on the transfer member T on the transfer material transfer path where the transfer speed of the transfer material S is constant.
Is provided at a position where the distance to is longer than the length of the transfer material S having the maximum length in the transport direction, and thus the length of the transfer material S can be reliably detected.

Further, reference numeral 31 is a CPU which is a control means, and the length information of the transfer material S in the carrying direction from the transfer material length detection section 30 is inputted to the CPU 31. Then, the CPU 31 thus receives the fixing roller pair 19 input from the transfer material length detection unit 30 which is the detection means.
Of the transfer material S before passing through the fixing roller pair 19 and the length information of the transfer material S after passing through the fixing roller pair 19 in the carrying direction before and after the fixing. The amount of change (contraction amount) is calculated.

Further, after the change amount (shrinkage amount) of the length of the transfer material S in the conveying direction is obtained in this way, the image data is scaled (reduced) to a size commensurate with the shrinkage amount during image formation on the second surface. Alternatively, the toner image is formed by enlarging the toner image, and the toner image that has been magnified according to the amount of change (contraction amount) is transferred to the transfer material
So that it is transferred and fixed at the desired position.

By the way, as described above, the toner image on the first side is fixed at a predetermined position on the transfer material with the leading end in the conveying direction as a reference, and the toner image on the second side is conveyed in the conveying direction by passing through the reversing mechanism. When the transfer is performed with reference to the leading edge of the transfer material S whose front and rear sides are replaced with each other (the trailing edge side in the transport direction when forming the first surface), that is, when the toner image position reference on the front and back sides is different, the positions of both images are changed. The relationship is relatively displaced (see FIG. 10).

Therefore, in the present embodiment, the toner image transfer reference position on the transfer material is set to be the same on the first surface and the second surface, that is, the first surface is on the front end side in the transfer material conveying direction and the second surface is also on the second surface. Uses the rear end side in the transfer material conveyance direction as the transfer position reference of the toner image. By thus setting the toner image transfer reference positions on the first and second surfaces to be the same, it is possible to obtain a good image with no relative positional deviation of the images on the front and back sides of the same transfer material.

FIG. 2 is a diagram for explaining an image formed on both surfaces of the transfer material S in this embodiment. In the figure, is the state when the toner image is transferred to the surface of the transfer material (first side), is the state when the toner image is fixed, is the reverse side of the transfer material, and newly displays the back side of the transfer material ( The second surface shows the state when the toner image is transferred, and the state when the toner image is fixed.

In the present embodiment, when the size of the transfer material S is X ₁ and Y _{1 as shown} by, when the heat at the time of fixing removes the water content of the transfer material S, as shown by. Then, the transfer material S is reduced in size, and the sizes thereof are X ₁ 'and Y ₁ '.

Here, the reduction ratio R at this time can be determined by the following method.

That is, the transfer material S before being fixed, which is conveyed at a constant speed Ps, by the transfer material length detection unit 30 described above.
The transit time t of is measured. The length X ₁ of the transfer material S in the transport direction before fixing can be obtained from the product Ps * t of the passing time t and the predetermined transport speed Ps. Also,
By performing the same measurement on the transfer material S after fixing, it is possible to estimate the transport direction length X ₁ ′ after fixing.

Next, the reduction ratio R can be determined by obtaining the ratio of the transporting direction lengths X ₁ and X ₁ ′ of the transfer material S before and after fixing thus obtained. Here, the length measurement in the main scanning direction may be performed using, for example, a contact image sensor, but it is empirically found that the reduction ratio R has the same value in the transfer material conveyance direction and its width direction. Since it is known, if the transfer material conveyance direction Rx is measured,
The orthogonal direction Ry can have the same value.

As a result, the reduction ratios Rx and Ry at this time are set.
Is R _X = X ₁ ′ / X ₁ (1) R _Y = Y ₁ ′ / Y ₁ (= R _X ) (2)

The sizes of the toner images before fixing on the transfer material are G _1X and G _1Y , and the image sizes G _1X 'and G _1Y ' at the time of fixing which are reduced according to the reduction of the transfer material S are as follows. It is expressed by the formula.

[0055] G_1X’= Rx * G_1X      (3) G_1Y’= Rx * G_1Y      (4) Then, as shown by, originally, as the second side image data, originally
G_1X, G_1YIf so, good image data, G_2X’= Rx * G_1X  (5) G_2Y’= Rx * G_1Y  (6) By shrinking and creating, the first surface and the second surface
There is no difference in the size of the image from the surface.

G _1X '= G _2X ' (7) G _1Y '= G _2Y ' (8)

After transferring such a toner image,
When the fixing is performed, both of them cause similar image reduction, but no new misalignment occurs.

As described above, when transferring the toner image on the second surface, the registration roller 7 is synchronized so that the toner image is transferred with the rear end portion (the front end portion of the first surface) of the transfer material S in the conveying direction as the image position reference. By transporting the toner, the toner position on the transfer material can be set from the same reference point, and relative image misalignment between the two front and back surfaces can be prevented from occurring.

As described above, the contraction rate before and after the transfer material S passes through the fixing roller pair 19 is obtained, and the size of the toner image transferred to the second surface is controlled based on this contraction rate. By controlling the reference position when the toner image is transferred to the second surface to be the same as the reference position when the toner image is transferred to the first surface, the deviation between the front and back images on a single transfer material, specifically, Specifically, it is possible to prevent a change in the size of the image on the first side and the second side due to the expansion and contraction of the transfer material at the time of fixing, and to prevent the image forming position shift due to the reversal of the transfer material S. Double-sided image formation is possible.

Generally, in many cases where double-sided image formation is performed, double-sided image formation is continuously performed on a large number of sheets, or the same type of transfer material is repeatedly used. In such a case, it is not necessary to measure the change of the transfer material every time, and the set value once set may be repeatedly used during the operation.

When the same condition is to be used again after a certain period of time, the set value once set may be stored in the memory in the apparatus and may be recalled and used for reuse.

By the way, in the above description, the case where the image shift on the front and back sides of the transfer material S is prevented by reducing or enlarging the image at the time of forming the image on the second side has been described, but the present invention is not limited to this. In consideration of contraction of the transfer material S, the image may be enlarged or reduced at the time of forming the image on the first surface.

Next, a second embodiment of the present invention will be described in which the image is enlarged at the time of forming the image on the first side.

In the present embodiment, first, the shrinkage amount of the preset transfer material S is calculated by the above-described transfer material length detection unit 30, and then the image size is adjusted so that the image size corresponds to the shrinkage amount. A latent image is formed by expanding in the scanning and sub-scanning directions.

Therefore, in the main scanning direction, for example, when the exposure device 15 has a structure using a polygon mirror which is a rotary polygon mirror, a slight expansion is performed with respect to the clock of the writing frequency to the polygon motor. Frequency modulation is applied as much as possible. Specifically, as shown in FIG. 3, the writing time t determined by the initial writing frequency in the main scanning direction.
On the other hand, by writing the writing time by frequency modulation by the time obtained by multiplying 1 / R, which is the reciprocal of the contraction rate, an image that is 1 / R times the actual data in the main scanning direction is written.

Incidentally, FIG. 4A schematically shows a latent image when no processing is performed in the main scanning. Then, when toner development, toner transfer and fixing are performed in this state, the transfer material S by fixing as shown in FIG.
The main scanning direction is multiplied by Lr * R due to contraction.

On the other hand, if the writing frequency of the main scanning is modulated as in this embodiment and the latent image length in the main scanning direction is set to 1 / R times as shown in FIG. It is possible to eliminate the influence of the reduction amount R of the material S, and as a result, it is possible to obtain a desired length in the main scanning direction as shown in FIG.

Further, the enlargement in the sub-scanning direction can be realized by increasing the conveying speed of the transfer material. Here, the writing interval in the sub-scanning direction is initially set to the exposure apparatus 1.
5 (see FIG. 1) and is determined by the transfer material conveying speed V ₀ of the photosensitive drum 13 in synchronism with 5.

FIG. 7A schematically shows a latent image when no processing is performed on the sub-scan. Then, when toner development, toner transfer, and fixing are performed in this state, the interval tr in the sub-scanning direction is multiplied by R due to contraction of the transfer material S due to fixing as shown in FIG.
* R.

Therefore, normally, as shown in FIG. 6A, the photosensitive drum and the transfer material conveying speed are driven at a constant speed of Vo, but as shown in FIG. 6B, the photosensitive drum 13 is transferred. When the transfer material transfer speed is V ₀ , the transfer material transfer speed is V
By increasing the speed to / R, the toner image on the transfer material can be expanded in the sub-scanning direction due to the relative speed difference.

If the transfer material conveying speed is increased as in the present embodiment and the toner image interval in the sub-scanning direction is multiplied by 1 / R as shown in FIG. 8A, the change of the transfer material S due to fixing is performed. It is possible to eliminate the influence of the minute R, and as a result, as shown in FIG.
As shown in (b), a desired sub-scanning direction interval can be obtained.

Next, a third embodiment of the present invention will be described.

In the present embodiment, for example, the contraction rate of the transfer material S having a different size or material, or its reciprocal, is obtained in advance by the transfer material length detection unit 30 or other detection means, respectively, and these are calculated. While storing a table summarizing the above, when a predetermined transfer material S is set, this table may be called automatically or manually, and the shrinkage rate or its reciprocal number may be selected based on this table.

Then, the main scanning direction and the sub-scanning direction of the image forming data for forming the image on the second surface are reduced so that the set transfer material S has an image size corresponding to the contraction rate (amount). Or a latent image in which the main scanning direction and the sub scanning direction of the image forming data for forming the image on the first surface are enlarged.

Specifically, for example, when the exposure device 15 uses a polygon mirror which is a rotary polygon mirror, the rotation speed of the polygon motor is slightly decreased to reduce the main scanning writing timing on the photosensitive member. In order to enlarge the latent image in the sub-scanning direction and compensate for the decrease in the polygon motor rotation speed, the frequency of the clock of the writing frequency to the polygon scanner is modulated so that it can be enlarged in the main scanning direction. As a result, a latent image can be formed by expanding in the main scanning direction and the sub scanning direction.

Alternatively, it is possible to enlarge the latent image in the sub-scanning direction by slightly lowering the light emission start timing of the LED exposure device in the sub-scanning direction. Further, enlargement in the main scanning direction can be dealt with by interpolating and enlarging the image data.

In each of the above-described embodiments, the case where the fixing sheet using heat is used and the fixed sheet shrinks due to heat has been described. When a pressure fixing device or the like that does not utilize is used, the size of the fixed sheet may change in the expanding direction. In such a case, the change rate of the sheet size may be obtained as the enlargement ratio, and various controls according to the enlargement ratio may be performed.

[0078]

As described above, according to the present invention, the first
The size of the toner image to be transferred to the first surface of the sheet or the second surface on the back side of the sheet and the second surface of the sheet based on the contraction rate of the sheet when the sheet on which the toner image is transferred passes through the fixing device. By controlling the reference position when the toner image is transferred to the surface to be the same as the reference position when the toner image is transferred to the first surface of the sheet, the deviation of the images formed on both the front and back surfaces of the sheet is suppressed. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus according to a first embodiment of the invention.

FIG. 2 is a diagram for explaining an image formed on both surfaces of a transfer material according to the present embodiment.

FIG. 3 is a diagram illustrating a main scanning direction clock of the image forming apparatus according to the second embodiment of the present invention.

FIG. 4 is a diagram illustrating a defect in a main scanning direction in a conventional image forming apparatus.

FIG. 5 is a diagram illustrating an effect in the main scanning direction according to the present embodiment.

FIG. 6 is a diagram illustrating a transfer material conveyance speed in the present embodiment.

FIG. 7 is a diagram illustrating a defect in the sub-scanning direction in the conventional image forming apparatus.

FIG. 8 is a diagram illustrating an effect in the sub-scanning direction according to the present embodiment.

FIG. 9 is a diagram showing a schematic configuration of a color image forming apparatus which is an example of a conventional image forming apparatus.

FIG. 10 is a diagram for explaining images formed on both surfaces of a conventional transfer material.

FIG. 11 is a diagram illustrating a problem in a conventional color image forming apparatus.

FIG. 12 is a diagram illustrating another problem in the conventional color image forming apparatus.

[Explanation of symbols]

1 cassette 7 Registration roller 8 Intermediate transfer belt 10 Image forming section 13 Photosensitive drum 15 Exposure equipment 19 Fixing roller pair 30 Transfer material length detector 31 CPU S transfer material T transfer part

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/04 15/043 F term (reference) 2C162 AE04 AE12 AE21 AE28 AE47 AF19 AF79 AF82 FA04 FA17 2C362 BA04 CB12 CB34 CB41 CB48 CB51 2H027 DA07 DC10 DE07 DE10 ED01 ED04 ED16 EE03 EF10 FA13 2H028 BA06 BA14 BB06 2H076 AB42 AB67 AB68 AB73

Claims (16)

[Claims] 1. A toner image is transferred to a first surface of a sheet, the toner image is fixed by a fixing device to form an image on the sheet, and then the sheet is inverted to form a second surface on the back side of the sheet. In an image forming apparatus configured to form an image on a sheet, a detection unit for detecting the size of the sheet after the sheet has passed through the fixing device, and a transfer unit for transferring the sheet to the first surface or the second surface. Controlling the size of the toner image to be transferred and controlling the reference position when the toner image is transferred to the second surface of the sheet, the control means based on the detection signal from the detection means. Then, the rate of change of the sheet size after passing through the fixing device is obtained, the size of the toner image transferred to the first surface or the second surface of the sheet is controlled based on the rate of change, and Toner image on the second side Image forming apparatus and controls so that the same as the reference position when transferring the toner image to the reference position when shooting the first surface of the sheet. 2. The fixing means detects the length of the sheet in the sheet transport direction before and after the sheet passes through the fixing device, and the control means detects the length of the sheet in the sheet transport direction from the detecting means. The image forming apparatus according to claim 1, wherein the change rate when passing through the image forming apparatus is obtained. 3. The control unit sets a sub-scanning direction reference position for transferring a toner image on the first surface to a leading end side in a sheet conveying direction, and sets a second scanning direction reference position on the second face in a sheet carrying direction rear end. The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus is controlled to be on the side. 4. The control means multiplies the image forming data of the image formed on the second surface of the sheet by the change rate so as to control the size of the toner image transferred to the second surface. The image forming apparatus according to claim 1. 5. The control means multiplies the image formation data of the image formed on the first surface of the sheet by the reciprocal of the change rate so as to control the size of the toner image transferred to the first surface. The image forming apparatus according to any one of claims 1 to 3. 6. An image carrier on which the toner image is formed,
An exposure device that exposes the image carrier to form a latent image on the image carrier, and the control means modulates a writing time interval in the main scanning direction by the exposure device according to the change rate. 4. A latent image in which a main scanning direction of image forming data for forming an image on the second surface is scaled is thereby formed on the image carrier. The image forming apparatus according to item. 7. An image carrier on which the toner image is formed,
And an exposure device that forms a latent image on the image carrier by exposing the image carrier, the control means, by changing the transport speed of the sheet at a constant rate according to the change rate, 4. The transfer toner image, which is formed on the image carrier and has the sub-scanning direction of the second surface image formation data scaled, is formed on a sheet. The image forming apparatus according to item 1. 8. An image carrier on which the toner image is formed,
And an exposure device using a rotary polygonal mirror that exposes the image carrier to form a latent image on the image carrier, wherein the controller controls the number of revolutions of the rotary polygonal mirror in accordance with the change rate and 4. The latent image in which the sub-scanning direction of the image forming data for forming an image is formed on the second surface by changing the conveying speed of the sheet to form a latent image. The image forming apparatus according to item 1. 9. An image carrier on which the toner image is formed,
An LED exposure device that exposes the image bearing member to form a latent image on the image bearing member, and the control means changes the writing time interval in the sub-scanning direction by the exposing device according to the rate of change. 4. The latent image in which the sub-scanning direction of the image forming data for forming an image on the second surface is scaled to form a latent image on the image carrier. The image forming apparatus according to item 1. 10. The change rate according to claim 1, wherein the change rate is stored and the stored change rate is called according to the sheet. Image forming apparatus. 11. An image carrier, on which the toner image is formed, and an exposure device, which exposes the image carrier to form a latent image on the image carrier, wherein the control unit includes the change rate. The main scanning direction of the image forming data for forming an image on the first surface on the image carrier is scaled by modulating the writing time interval in the main scanning direction by the exposure device according to the reciprocal of The image forming apparatus according to claim 5, wherein a latent image is formed. 12. An image carrier on which the toner image is formed, and an exposure device using a rotary polygon mirror that exposes the image carrier to form a latent image on the image carrier, the control comprising: The means forms a transfer toner image on the sheet in which the sub-scanning direction of the first-side image forming data is scaled by changing the transport speed of the sheet at a constant rate according to the reciprocal of the rate of change. 6. The method according to claim 5, wherein
The image forming apparatus described. 13. An image bearing member on which the toner image is formed, and an exposure device using a rotary polygonal mirror for exposing the image bearing member to form a latent image on the image bearing member. The means changes the sub-scanning direction of the image forming data for forming an image on the first surface by changing the rotation speed of the rotary polygon mirror and the sheet conveying speed according to the reciprocal of the change rate. An image forming apparatus according to claim 5, wherein the latent image is formed. 14. An image bearing member, on which the toner image is formed, and an LED exposure device, which exposes the image bearing member to form a latent image on the image bearing member, wherein the control unit changes the change. By changing the writing time interval in the sub-scanning direction by the exposure device according to the reciprocal of the ratio, the sub-scanning direction of the image forming data for forming an image on the first surface on the image carrier is scaled. An image forming apparatus according to claim 5, wherein the latent image is formed. 15. The reciprocal of the rate of change is stored, and the stored rate of change is called according to the seat, according to any one of claims 5 and 11 to 14. Image forming apparatus. 16. The distance from the detection unit to a transfer unit that transfers a toner image onto the sheet on the transfer material conveyance path where the conveyance speed of the sheet is constant is larger than the length of the sheet having the maximum length in the sheet conveyance direction. The image forming apparatus according to any one of claims 1 to 15, wherein the image forming apparatus is provided at a position where it becomes longer.