JP2001282053A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device where the magnification of an image is made correct on both sides of paper where double-sided printing processing has been performed after the temperature of the paper is restored to ambient temperature and where also arithmetic processing time for such adjustment is easily secured and which has few restrictions in terms of constitution. SOLUTION: The paper is fed to an image forming position A from a paper supply part 2 through a first carrying path 21 and, after forming the image on the first side of the paper, the paper is reversed from the front surface to the back surface through a second carrying path 22 and the image is formed on the second side of the paper. This device is equipped with an elongation ratio storage means 3 for storing the elongation ratio of the paper associated with temperature changes and a temperature sensor 30 for detecting the temperature of the paper passing through the downstream part 21d of the first carrying path 21. An adjusting means 4 adjusts a parameter concerning image formation on the basis of the elongation ratio of the paper and the result outputted from the sensor 30 so that the magnification of the image formed on the paper is correct after the temperature of the paper is restored to the ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms an image on one side of a sheet and then performs a double-sided printing process for forming an image on the other side of the sheet. .

[0002]

2. Description of the Related Art In this type of image forming apparatus, a double-sided printing process is often performed as follows. First, a sheet is fed from a paper feeding unit to a predetermined image forming position through a conveyance path, and an image is formed on the first surface of the sheet at the image forming position. Thereafter, the sheet is turned over through another transport path (a so-called circulating transport path or switchback transport path), and the sheet is fed back to the image forming position. Then, an image is formed on the second surface of the sheet at the image forming position. Note that “forming” an image includes heating for fixing the image to paper.

Usually, the sheet is heated by forming an image on the first side of the sheet. Therefore, when the sheet is fed again to the image forming position in order to form an image on the second side of the sheet. (At the time of refeeding), the temperature of the sheet becomes higher than the temperature at the time of the first sheet feeding. That is, due to the coefficient of thermal expansion of the sheet, the sheet size at the time of the first sheet feeding and the sheet size at the time of re-feeding are different. Therefore, if no measures are taken, even if the user attempts to place an image of the same size on both sides of the sheet, for example, and uses the same size original image, the sheet returns to the ambient temperature after the two-sided printing process. As a result, the size (magnification) of the image differs between the two sides of the sheet.

Therefore, conventionally, the paper length at the time of the first paper feeding and the paper length at the time of re-feeding are measured by using a paper sensor provided in the conveying path, and based on the measured values, both sides are measured. When the paper returns to the original temperature after the printing process, the image size (magnification) is the same between both sides of the paper,
A technique for adjusting the reading speed of an original image, a reference clock of an image processing system, a fine adjustment correction magnification, a paper speed at the time of image formation, and the like has been proposed (Japanese Patent Application Laid-Open No. 9-50222,
JP-A-10-133519).

[0005]

However, in the above-mentioned prior art, since the adjustment is performed based on the paper length measured by using the paper sensor, the time for measuring the paper length (the time during the conveyance) It takes a long time from when the leading edge of the sheet is detected to when the trailing edge is detected. For this reason, there is a problem that there is a short time from the completion of the measurement of the sheet length to the start of the image formation, that is, a short calculation processing time for adjusting the parameters related to image formation. In addition, since the trailing edge of the paper must be detected before the leading edge of the paper being transported reaches the drum at the image forming position, the configuration of the paper sensor is largely restricted.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to correct the magnification of an image on both sides of a sheet that has been subjected to double-sided printing after the temperature of the sheet has returned to the ambient temperature, and to shorten the calculation processing time for the adjustment. It is an object of the present invention to provide an image forming apparatus which can secure the image forming apparatus with few restrictions on the configuration.

[0007]

According to a first aspect of the present invention, an image forming apparatus includes:
The paper is sent to a predetermined image forming position through the transport path,
After forming an image on the first surface of the sheet at the image forming position, the sheet is turned upside down through a second transport path, and the sheet is passed through at least a downstream portion of the first transport path to the image forming position. An image forming apparatus for forming an image on the second surface of the sheet at the image forming position, an expansion / contraction ratio storage means for storing an expansion / contraction ratio of the sheet due to a temperature change, and the downstream portion of the first transport path. A temperature sensor for detecting the temperature of the sheet passing through the sheet, and a magnification of an image formed on the sheet based on the expansion ratio of the sheet and an output result of the temperature sensor, so that the magnification of the image formed on the sheet becomes correct after the sheet temperature returns to the ambient temperature. And an adjusting means for adjusting parameters relating to image formation.

In the image forming apparatus of the first aspect, the adjusting means determines the magnification of the image formed on the sheet based on the expansion ratio of the sheet due to the temperature change and the output result of the temperature sensor so that the sheet temperature is the ambient temperature. The parameters related to image formation are adjusted so as to be correct after returning to. In particular, since the sheet temperature is higher than the ambient temperature when forming an image on the second surface of the sheet, this parameter adjustment works effectively.
Therefore, after the temperature of the sheet subjected to the double-sided printing process returns to the ambient temperature, the magnification of the image becomes correct on both sides of the sheet. In addition, the time for the temperature sensor to detect the temperature of the sheet (sampling time) is instantaneous compared to the time for measuring the length of the sheet, so that there is a time margin from the completion of the temperature measurement to the start of image formation. That is, the calculation processing time for adjusting the parameters related to image formation is easily secured. Further, since the temperature sensor only needs to detect the temperature of the sheet passing through the downstream portion of the first transport path irrespective of the sheet length, there is little restriction on the arrangement of the temperature sensor.

According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, further comprising a sheet temperature storage unit for storing a sheet temperature detected by the temperature sensor.

In the image forming apparatus according to the second aspect, since the sheet temperature storage means stores the sheet temperature detected by the temperature sensor, the adjusting means sends the sheet temperature to the image forming position to form an image on the first surface. Temperature (hereinafter referred to as a "first temperature") and a sheet temperature when the sheet is fed to an image forming position to form an image on the second surface (this is referred to as a "second temperature"). The ratio of the sheet size between the first temperature and the second temperature can be obtained based on the difference between the first and second temperatures, and the parameters relating to image formation can be adjusted based on the ratio of the sheet sizes. Therefore, the adjustment of the parameters related to image formation is performed with high accuracy.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the parameter relating to image formation adjusted by the adjusting means is a magnification of image data. .

In the image forming apparatus according to the third aspect, the adjusting means determines the magnification of the image formed on the sheet based on the expansion rate of the sheet due to the temperature change and the output result of the temperature sensor. Adjust the magnification of the image data so that it becomes correct after returning to. Then, an image is formed on a sheet using the scaled image data. Therefore,
After the temperature of the sheet subjected to the double-sided printing process returns to the ambient temperature, the magnification of the image becomes correct on both sides of the sheet.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus further includes a document reading unit that optically reads a document image and converts the read document image into an electric signal. The parameter relating to the image formation to be adjusted is the operating frequency of the solid-state imaging device that transfers the electric signal.

In the image forming apparatus according to the fourth aspect, the adjusting means determines the magnification of the image formed on the sheet based on the expansion ratio of the sheet due to the temperature change and the output result of the temperature sensor. The operating frequency of the solid-state imaging device is adjusted so as to be correct after returning to. Then, an image is formed on a sheet using the image data output by the solid-state imaging device. Therefore, after the temperature of the sheet subjected to the double-sided printing process returns to the ambient temperature, the magnification of the image becomes correct on both sides of the sheet.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 schematically shows a block configuration of a printer 90 according to an embodiment of the present invention.

The printer 90 includes a paper feed tray 2 as a paper feed unit and a fixing roller 1 provided at an image forming position A.
It has. The paper feed tray 2 stores a plurality of sheets P of the same type (plain paper of A4 size). A temperature sensor 30 for detecting the temperature of the sheet P passing through the portion 21d is provided opposite to the downstream portion 21d of the first transport path 21 from the sheet feed tray 2 toward the image forming position A. The first transport path 21 includes transport roller pairs 31 and 32, and transports the paper P from the paper feed tray 2 to the image forming position A. The discharge conveyance path 23 includes a conveyance roller pair 34,
The sheet P on which an image is formed at the image forming position A is discharged onto a discharge tray (not shown). The second transport path 22 branches off from the middle of the discharge transport path 23 and joins the first transport path 21 upstream of the location where the temperature sensor 30 is provided. The second transport path 22 has a transport roller pair 35 and has a form of a circulating transport path in which the sheet P having an image formed on the first surface is turned over and returned to the first transport path 21. The sheet P conveyed through the discharge conveyance path 23 is transferred to the second conveyance path 2
Switching claw 3
6 can be switched according to the angle.

The printer 90 includes a control unit 10 for controlling the operation of the entire apparatus and an image processing unit 5 for performing processing such as shading correction, color discrimination, scaling, and image quality correction on input image data. And a laser control unit 6 that outputs a laser beam in accordance with the image data from the image processing unit 5.
And the laser light from the laser controller 6
It includes a polygon mirror section 7 for scanning upward, a thermal expansion coefficient table 3 as expansion / contraction rate storage means, and a magnification correction circuit 4 as paper temperature storage means and adjustment means. The coefficient of thermal expansion table 3 stores the coefficient of thermal expansion of the paper for each type of paper used in the printer 90.

FIG. 2 shows a flow of a double-sided printing process by the control unit 10 of the printer 90.

When a double-sided print start command is input, first, in order to form an image on the first side of the sheet P, the image forming position A is fed from the paper feed tray 2 through the first conveying path 21.
The paper P is conveyed to (S1). At this time, the temperature sensor 3
0 detects the temperature T1 (° C.) of the sheet P passing through the downstream portion 21d of the first transport path 21 (S2), and the magnification correction circuit 4 stores the output result of the temperature sensor 30 (S3). The sheet temperature T1 (° C.) at this time is equal to the ambient temperature Ta (° C.) because the sheet P has not been heated by fixing.

On the other hand, in synchronization with the conveyance of the sheet P, the image processing section 5 performs shading correction, color discrimination, scaling, and the like on the image data input for the first side of the sheet P.
Processing such as image quality correction is performed (S4), and the image data is sent to the laser control unit 6. The laser controller 6 outputs a laser beam according to the received image data (S5), and the polygon mirror 7 scans the fixing roller 1 with the laser beam.
Thereby, an image is formed on the fixing roller 1. Then, the image is fixed on the first surface of the sheet P sent to the image forming position A (S6).

Thereafter, the sheet P on which an image is formed on the first surface
Is transported halfway through the discharge transport path 23, and the switching claw 3
Then, the sheet is sent to the second conveyance path 22 by the switching by S6 (S7). Then, the sheet P is passed through the second transport path 22.
(S8), and the sheet P is transferred to the first transport path 2
It returns to the upstream side of the location where the first temperature sensor 30 is provided, and is conveyed again to the image forming position A through the downstream portion 21d of the first conveyance path 21. At this time, the temperature sensor 30
Temperature T2 of sheet P passing through downstream portion 21d of transport path 21
(C) is detected (S9), and the magnification correction circuit 4 stores the output result of the temperature sensor 30 (S10). Subsequently, the magnification correction circuit 4 calculates the difference between the thermal expansion coefficient α (/ ° C.) of the paper P stored in the thermal expansion coefficient table and the paper temperature at the time of re-feeding and the paper temperature at the first paper feeding ( T2-T1) (° C.), the ratio (elongation) (L2 / L) of the paper size L2 at the time of re-feeding and the paper size L1 at the time of the first paper feeding is calculated according to the following equation (1).
1) is calculated (S11).

(L2 / L1) = 1 + α (T2-T1) = 1 + α (T2-Ta) (1) On the other hand, in synchronization with the conveyance of the sheet P, the image processing unit 5
The image data input for the second side of the sheet P is subjected to processing such as shading correction, color discrimination, scaling, and image quality correction (S12). In the process of the image processing unit 5, the magnification correction circuit 4 determines the magnification of the image formed on the second surface of the paper P based on the determined elongation rate (L2 / L1) as the paper temperature T2 (° C.). The magnification of the image data is corrected (adjusted) so as to be correct after returning to the ambient temperature Ta (° C.). Specifically, the magnification of the image data is enlarged by the calculated elongation rate (L2 / L1). Image processing unit 5
Sends the image data whose magnification has been corrected after the image processing to the laser control unit 6. The laser controller 6 outputs a laser beam according to the received image data (S13), and the polygon mirror 7 scans the fixing roller 1 with the laser beam. Thereby, an image is formed on the fixing roller 1. And
The image is fixed on the second surface of the sheet P sent to the image forming position A (S14).

Thereafter, the sheet P on which images are formed on both sides
Is discharged onto the paper discharge tray through the discharge conveyance path 23.
The temperature of the discharged sheet P returns to the ambient temperature Ta (° C.) after a while (usually, after several minutes).

In this case, after the temperature of the sheet P subjected to the double-sided printing process returns to the ambient temperature Ta (° C.), the magnification of the image on both sides of the sheet P becomes correct. In particular, when an image is formed on both sides of the sheet P using the same image data, the size (magnification) of the image on both sides of the sheet P becomes exactly the same. Moreover, the time (sampling time) for the temperature sensor 30 to detect the temperatures T1 and T2 (° C.) of the sheet P is instantaneous as compared with the time for measuring the sheet length. It is possible to easily secure a time margin until the start of image formation, that is, a calculation processing time for correcting the magnification of the image data. The temperature sensor 30
Is the downstream portion 2 of the first transport path 21 regardless of the paper length.
Since the temperature T (° C.) of the sheet P passing through 1 d only needs to be detected, there is little restriction on the arrangement of the temperature sensor 30 in the configuration.

FIG. 3 schematically shows a block configuration of a copying machine 190 according to an embodiment of the present invention.

The copying machine 190 has a document transport section 180 on a main body 191 and a document reading section IR for optically reading an image of a document transported by the document transport section 180 and converting the image into an electric signal. I have. Document transport unit 180
Is a pair of the feed transport roller 181 and the receiving transport roller pair 1
A plurality of documents 82 placed on a document tray (not shown) are transported one by one through a document transport path 171 and a glass plate 172. The document reading section IR includes a document sensor 11 that detects a document conveyed through the document conveyance path 171.
4, a document counter 111 for counting the number of documents detected by the document sensor 114, and a CCD solid-state image pickup device (hereinafter referred to as "CCD") for optically reading an image of a document passing over the glass plate 172 and converting the image into an electric signal. Sensor ”) 113 and a CCD control unit 112 that controls the operation of the CCD sensor 113. CCD controller 1
Reference numeral 12 denotes C based on whether the count value of the document counter 111 is an odd number or an even number at the time of double-sided copy processing.
The operating frequency of the CD sensor 113 is switched and set (the details will be described later).

The copying machine 190 includes a paper feed tray 102 as a paper feed unit, and a fixing roller 101 provided at an image forming position A. In the paper feed tray 102,
A plurality of sheets P of the same type (plain paper of A4 size) are stored. A temperature sensor 130 for detecting the temperature of the sheet P passing through the portion 121d is provided opposite to the downstream portion 121d of the first transport path 121 from the sheet tray 102 to the image forming position A. First transport path 12
1 includes a pair of conveying rollers 131 and 132, and conveys the sheet P from the sheet feeding tray 102 to the image forming position A. The discharge conveyance path 123 includes a conveyance roller pair 134, and discharges the sheet P on which an image is formed at the image forming position A onto a discharge tray (not shown). The second transport path 122 branches from the middle of the discharge transport path 123 and joins the first transport path 121 on the upstream side of the location where the temperature sensor 130 is provided. The second transport path 122 has a transport roller pair 135, and has a form of a circulating transport path in which the sheet P having an image formed on the first surface is turned over and returned to the first transport path 121. Whether the paper P conveyed through the discharge conveyance path 123 is sent to the second conveyance path 122 or discharged onto a discharge tray is switched according to the angle of the switching claw 136.

The copying machine 190 includes a control unit 110 for controlling the operation of the entire apparatus, and an image processing unit for performing processing such as shading correction, color discrimination, scaling, and image quality correction on input image data. 105 and the image processing unit 1
A laser controller 106 for outputting a laser beam in accordance with the image data from the camera unit 05; a polygon mirror unit 107 for scanning the laser beam from the laser controller 106 onto the fixing roller 101; A thermal expansion coefficient table 103, an arithmetic circuit 108 as a sheet temperature storage means and an adjusting means, and an arithmetic result table 109 for storing the arithmetic results of the arithmetic circuit 108 are provided. The coefficient of thermal expansion table 103 stores the coefficient of thermal expansion of each type of paper used in the copying machine 190.

FIG. 4 shows a control unit 110 of the copying machine 190.
2 shows a flow of a double-sided printing process.

When a double-sided print start command is input, first, the paper P is transported from the paper feed tray 102 to the image forming position A through the first transport path 121 in order to form an image on the first surface of the paper P. (S101). At this time, the temperature sensor 130 detects the temperature T1 (° C.) of the sheet P passing through the downstream portion 121d of the first transport path 121 (S102), and the arithmetic circuit 108 stores the output result of the temperature sensor 30 (S103). At this time, the sheet temperature T1 (° C.)
Is equal to the ambient temperature Ta (° C.) since the sheet P has not yet been heated by fixing.

On the other hand, in synchronization with the conveyance of the sheet P, the image processing unit 105 performs shading correction, color discrimination, scaling, and image quality correction on the image data input for the first side of the sheet P. The image data is sent to the laser control unit 106. The laser controller 106 outputs a laser beam according to the received image data, and the polygon mirror 107 scans the fixing roller 1 with the laser beam.
Thus, an image is formed on the fixing roller 101. Then, the first sheet P fed to the image forming position A is
The image is fixed on the surface (S104).

Thereafter, the sheet P on which an image is formed on the first surface
Is transported halfway through the discharge transport path 123, and is fed into the second transport path 122 by switching by the switching claw 136 (S105). Then, the sheet P is turned upside down through the second transport path 122 (S106), and the sheet P
To the upstream side of the first transport path 121 where the temperature sensor 130 is provided.
The sheet is conveyed again to the image forming position A through 1d. At this time, the temperature sensor 130 is connected to the downstream portion 12 of the first conveyance path 121.
The temperature T2 (° C.) of the sheet P passing through 1d is detected (S10).
7), the arithmetic circuit 108 stores the output result of the temperature sensor 130 (S108).

On the other hand, in synchronization with the conveyance of the sheet P, the image processing unit 105 performs shading correction, color discrimination, scaling, and image quality correction on the image data input for the second side of the sheet P. The image data is sent to the laser control unit 106. The laser controller 106 outputs a laser beam according to the received image data, and the polygon mirror 107 scans the fixing roller 101 with the laser beam. Thus, an image is formed on the fixing roller 101. Then, the sheet P sent to the image forming position A
The image is fixed on the second surface (S109). Thereafter, the paper P on which images are formed on both sides is transferred to the discharge conveyance path 12.
3, and is discharged onto a discharge tray.

Further, the arithmetic circuit 108 determines the coefficient of thermal expansion α of the sheet P stored in the coefficient of thermal expansion table and the step S10.
3 based on the sheet temperature T1 (° C.) at the time of the first sheet feeding and the sheet size L1 at the time of the first sheet feeding according to the following equation (2).
Then, the ratio (elongation) (L1 / L0) of the sheet size L0 at the standard temperature 23 (° C.) is calculated (S110). Also,
The coefficient of thermal expansion α of the paper P stored in the coefficient of thermal expansion table;
Sheet temperature T2 (° C.) at the time of refeeding obtained in step S108
Then, the ratio (elongation) (L2 / L0) between the paper size L2 at the time of refeeding and the paper size L0 at the standard temperature of 23 (° C.) is calculated according to the following equation (3) (S110).
And these elongation percentages (L1 / L0), (L2 / L
0) is stored in the calculation result table (S111).

Thereafter, when a double-sided copy start command is input, the document transport unit 180 transports the document through the document transport path 171 and the glass plate 172 (S121).
A document sensor 114 of the document reading section IR detects a document, and a document counter 111 counts the number of documents. Based on whether the count value of the document counter 111 is an odd number or an even number, the CCD control unit 112 determines whether the document is a document for forming an image on the first side of a sheet or forms an image on the second side of the sheet. It is checked whether the document is a document to be read (S122). If the original being conveyed is an original for forming an image on the first surface of the sheet, data of the elongation rate (L1 / L0) is extracted from the calculation result table 109 (S123), and the elongation rate (L1 / L0) is obtained. ) Based on the CCD sensor 113
Is corrected and set (S124). Specifically, the operating frequency f0 to be set when the sheet temperature is at the standard temperature 23 (° C.) is divided by the elongation rate (L1 / L0) and changed to the obtained operating frequency f1 for setting. .

F1 = f0 / (L1 / L0) (4) The sheet P is fed from the paper feed tray 102 to the image forming position A through the first transport path 121 in synchronization with the reading of the document image by the document reading unit IR. Sending, the image forming position A
Then, an image is formed on the first surface of the paper P using the above-mentioned original image data (S125).

On the other hand, if the document being transported is a document for forming an image on the second side of the sheet, the calculation result table 109
Data of the elongation (L2 / L0) is extracted from
3) The operating frequency of the CCD sensor 113 is corrected and set based on the elongation rate (L2 / L0) (S12).
4). Specifically, the operating frequency f0 to be set when the paper temperature is at the standard temperature 23 (° C.) is determined by the elongation rate (L2 /
L0), and change and set the obtained operating frequency f2.

F2 = f0 / (L2 / L0) (5) In synchronization with the reading of the document image by the document reading section IR, the sheet P on which the image is formed on the first surface is discharged to the discharge conveyance path 12.
3 to the second transport path 122 and the second transport path 122
Then, the sheet P is turned over and sent again to the image forming position A, and an image is formed on the second surface of the sheet P at the image forming position A using the original image data (S12).
5).

In this case, the magnification of the image on both sides of the sheet P becomes correct after the temperature of the sheet P subjected to the double-side copy processing returns to the ambient temperature Ta (° C.). In particular, when an image is formed on both sides of the sheet P using the same image data, the size (magnification) of the image on both sides of the sheet P becomes exactly the same. Moreover, the temperature sensor 30 detects the temperature T of the paper P.
Since the time (sampling time) for detecting 1, T2 (° C.) is instantaneous as compared with the time for measuring the paper length, a time margin from the completion of temperature measurement to the start of image formation, that is, An arithmetic processing time for correcting the magnification of the image data can be easily secured. In addition, the temperature sensor 130
Only needs to detect the temperature T (° C.) of the sheet P passing through the downstream portion 121 d of the first transport path 121 irrespective of the sheet length.

In this embodiment, the expansion / contraction rate of the sheet due to the temperature change is calculated as being caused by the thermal expansion rate α of the sheet. However, the present invention is not limited to this. The expansion and contraction of the sheet due to the temperature change may be caused by evaporation of moisture contained in the sheet, deterioration of the sheet, and other various factors. By storing the expansion and contraction ratio of the paper in consideration of such various factors by the expansion and contraction ratio storage means, according to the present invention, after the temperature of the paper P returns to the ambient temperature Ta (° C.) after the double-sided print / copy processing, The magnification of the image is correct on both sides of the sheet P.

[0042]

As is apparent from the above description, according to the image forming apparatus of the first aspect, thanks to the function of the adjusting means, after the temperature of the sheet subjected to the double-sided printing process returns to the ambient temperature, The image magnification is correct on both sides. In addition, it is possible to easily secure a time margin from the completion of the temperature measurement to the start of the image formation, that is, a calculation processing time for adjusting parameters related to the image formation. In addition, there are few restrictions on the configuration of the temperature sensor.

In the image forming apparatus according to the second aspect, since the sheet temperature storage means stores the sheet temperature detected by the temperature sensor, the parameters relating to image formation are adjusted with high accuracy.

In the image forming apparatus according to the third aspect, since an image is formed on the sheet using the scaled image data, the temperature of the sheet that has been subjected to the double-sided print processing returns to the ambient temperature. The image magnification is correct on both sides of the paper.

In the image forming apparatus according to the fourth aspect, the operating frequency of the solid-state imaging device is adjusted, and an image is formed on a sheet using the image data output by the solid-state imaging device. After the temperature of the received paper returns to the ambient temperature, the magnification of the image on both sides of the paper becomes correct.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a block configuration of a printer according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation flow of the printer.

FIG. 3 is a diagram illustrating a block configuration of a copying machine according to an embodiment to which the present invention is applied;

FIG. 4 is a diagram showing an operation flow of the copying machine.

[Explanation of symbols]

 A Image forming position P Paper 1,101 Fixing roller 3,103 Thermal expansion rate table 21 First transport path 22 Second transport path 23 Discharge transport path 30,130 Temperature sensor 90 Printer 190 Copier

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Minami 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. (reference) 2C062 RA06 2H027 DA11 DC00 EC02 EC06 ED04 ED30 EE07 EE08 2H028 BB00 BD03 5C076 AA21 BA02 BA03 BA04 BA05 BA06 BB13 9A001 HH23 JJ35 KZ42

Claims (4)

[Claims] 1. A sheet is fed from a paper feeding unit to a predetermined image forming position through a first conveying path, an image is formed on a first surface of the sheet at the image forming position, and then the sheet is passed through a second conveying path. In an image forming apparatus in which the sheet is turned over and sent to the image forming position through at least a downstream portion of the first conveyance path and an image is formed on the second surface of the sheet at the image forming position, Expansion / contraction ratio storage means for storing the expansion / contraction ratio of the paper associated with the above, a temperature sensor for detecting the temperature of the paper passing through the downstream portion of the first transport path, and an output result of the paper expansion / contraction ratio and the temperature sensor. An image forming apparatus, comprising: an adjusting unit that adjusts parameters related to image formation such that a magnification of an image formed on a sheet becomes correct after the sheet temperature returns to an ambient temperature based on the sheet temperature. 2. The image forming apparatus according to claim 1, further comprising a sheet temperature storage unit that stores a sheet temperature detected by the temperature sensor. 3. The image forming apparatus according to claim 1, wherein the parameter related to image formation adjusted by the adjustment unit is a magnification of image data. 4. The image forming apparatus according to claim 1, further comprising: a document reading unit that reads a document image optically and converts the document image into an electric signal; An image forming apparatus, wherein the operating frequency is the operating frequency of a solid-state imaging device that transfers an electric signal.