JP2000259044A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make transferable and fixable an image in a more proper part of paper and to make highly precisely formable the image on the paper, by calculating a change in the state of the paper between a first speckle pattern detection means and a second speckle pattern detection means and correcting, based on the change in state, the state of the image to be formed onto an image carrier and transferred onto the paper. SOLUTION: A front detection light source 31 and a front optical sensor 32 and a back detection light source 33 and a back optical sensor 34 are provided on the path along which transfer paper Pa is carried and in different positions in the direction in which the transfer paper Pa is carried. A paper elongation quantitative calculating means 45 calculates a change in the state of the transfer paper Pa between the front detection light source 31 and front optical sensor 32 and the back detection light source 33 and back optical sensor 34. Based on the change in the state of the paper, an image data correction quantitative calculating mean 46 calculates a quantity of the correction of image data, and the image data correcting means 48 corrects the image data based on the quantity of the correction of the image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for transferring and fixing an image formed on an image carrier on a sheet using an electrophotographic method such as a laser beam copying machine and a printer.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
By correcting an image or the like formed on the image carrier so as to suppress the occurrence of sub-scan registration deviation, skew, main-scan writing start position deviation, main-scan magnification deviation, sub-scan magnification deviation, and the like, Images are transferred and fixed at appropriate positions. For example, Japanese Patent Application Laid-Open No. 3-36560 discloses that when printing on the back side, the occurrence of a shift in the main scanning magnification and a shift in the sub-scanning magnification due to the expansion of the sheet due to the heat at the time of fixing the front side is determined. There has been disclosed a technique for correcting the write signal group in consideration of the above problem and preventing the correction. In the apparatus disclosed in Japanese Patent Application Laid-Open No. 3-36560, a sensor for detecting a paper type is provided when correcting a write signal group in consideration of a paper elongation rate, and the sensor is determined in advance according to the detected paper type. The selected write signal group for correction (specifically, a write reference clock) is selected to correct an image to be transferred to a sheet.

[0003]

However, the sheets have different lengths, widths, and squarenesses. Further, even if the type of paper is the same, the elongation rates are different for papers having different basis weights, thicknesses, and the like, and the elongation rates are also different depending on the difference in the size of the paper. For example, the elongation of the paper at the time of fixing also differs depending on the paper basis weight, paper texture, thickness, and the like. Therefore, the above-mentioned Japanese Patent Laid-Open Publication No.
In the case where a sensor for detecting a paper type is provided and a predetermined write signal group for correction is selected according to the detected paper type, as in JP-A-6560, an image is actually transferred and fixed. The difference between the sheet elongation rate and the sheet tends to occur, and there is a limit in transferring and fixing an image to an appropriate position on the sheet.

As described above, if an image to be transferred to a sheet is corrected based on data or the like predetermined in accordance with the type of paper, the correction necessarily reflects the actual state of the sheet. Therefore, it is difficult to transfer and fix an image at an appropriate position on a sheet.

The present invention has been made in view of the above points, and corrects an image transferred and fixed on a sheet based on the actual state of the sheet, and transfers and fixes the image at an appropriate position on the sheet. It is an object of the present invention to provide an image forming apparatus capable of forming an image on a sheet with high accuracy.

[0006]

SUMMARY OF THE INVENTION An image forming apparatus according to the present invention is an image forming apparatus for transferring an image formed on an image carrier onto a sheet to be conveyed and fixing the transferred image to the sheet. There is provided in the middle position of the paper transport path,
First speckle pattern detecting means for irradiating a predetermined position on the sheet with coherent light and detecting a reference speckle pattern of diffused light reflected at the predetermined position; and first speckle as viewed in the sheet conveyance direction. A second type is provided on the rear side of the pattern detection means, irradiates the paper with coherent light, and detects a speckle pattern equivalent to the reference speckle pattern from a speckle pattern of diffused light reflected on the paper.
Speckle pattern detection means, a predetermined position where the reference speckle pattern is detected by the first speckle pattern detection means, and a speckle pattern equivalent to the reference speckle pattern are detected by the second speckle pattern detection means Paper state change calculating means for calculating a paper state change between the first speckle pattern detecting means and the second speckle pattern detecting means based on a positional relationship with the detected position; Image forming state correcting means for correcting the state of an image formed on the image carrier and transferred onto the sheet according to the change in the state of the sheet calculated by the calculating means.

[0007] According to this image forming apparatus, the first speckle pattern detecting means and the second speckle pattern detecting means are provided at different positions in the middle of the sheet conveying path when viewed in the sheet conveying direction. , The paper state change calculation means,
The positional relationship between the predetermined position at which the reference speckle pattern is detected by the first speckle pattern detecting means and the position at which a speckle pattern equivalent to the reference speckle pattern is detected by the second speckle pattern detecting means. Based on this, a change in the state of the sheet between the first speckle pattern detecting means and the second speckle pattern detecting means is calculated. For this reason, based on the actual state change of the sheet, the image forming state correcting means corrects the state of the image formed on the image carrier and transferred onto the sheet. Therefore, based on the actual state of the sheet, the image transferred and fixed on the sheet can be corrected, and the image can be transferred and fixed at a more appropriate position on the sheet, so that the image can be formed on the sheet with high accuracy. Becomes

[0008] Further, transfer means for transferring the image formed on the image carrier onto the paper, fixing means for fixing the image transferred on the paper to the paper, and paper on which the image is fixed by the fixing means Transport means for transporting the sheet fixed by the fixing means to the transfer means in order to transfer the image formed on the image carrier to the back surface of the image forming apparatus, wherein the first speckle pattern detecting means Is provided on the front side of the fixing unit when viewed in the paper transport direction, and the second speckle pattern detection unit is provided on the rear side of the fixing unit when viewed in the paper transport direction. The detecting means detects a predetermined position where the reference speckle pattern is detected by the first speckle pattern detecting means and a speckle pattern equivalent to the reference speckle pattern by the second speckle pattern detecting means. Based on the positional relationship with the set position, the amount of elongation of the sheet that occurs at the time of fixing is calculated, and the image forming state correction unit calculates the amount of elongation of the sheet based on the amount of elongation of the sheet calculated by the sheet state change calculation unit. This is characterized in that the state of the image formed on the paper and transferred to the back surface of the paper is corrected. In this case, a first speckle pattern detecting unit and a second speckle pattern detecting unit are provided at the front and rear positions of the fixing unit, respectively. The amount of elongation of the paper is calculated based on the paper on which the front surface image is actually fixed. For this reason, the image forming state correction unit corrects the state of the image formed on the image carrier and transferred to the back surface of the sheet based on the actual amount of elongation of the sheet on which the front image has been fixed. . Therefore, based on the actual elongation of the sheet after fixing, the image transferred and fixed on the back of the sheet is corrected,
The image can be transferred and fixed to a more appropriate position on the back surface of the paper, and highly accurate alignment of the image on the front and back surfaces of the paper can be performed.

Further, the amount of elongation of the sheet calculated by the sheet state change calculating means is an amount of change in an interval from the end of the sheet to a predetermined position, and the image forming state correcting means is provided by the sheet state change calculating means. The writing position of the image formed on the image carrier and transferred to the back surface of the sheet is corrected based on the calculated change amount of the interval from the end of the sheet to the predetermined position. In this case, the writing position of the image transferred to the back surface of the sheet is corrected based on the actual extension amount of the sheet on which the front image is fixed. As a result, the occurrence of a shift in the writing position of the back surface image formed on the image carrier is suppressed, and the image can be transferred and fixed at an appropriate position on the back surface of the sheet.

[0010] Further, the first speckle pattern detecting means may include: a plurality of predetermined positions having an interval in a predetermined direction;
Each reference speckle pattern is detected, and the amount of elongation of the sheet calculated by the sheet state change calculating means is a change amount of an interval between a plurality of predetermined positions, and the image forming state correcting means is:
The magnification in a predetermined direction of an image formed on an image carrier and transferred to the back surface of a sheet is corrected based on a change amount of an interval between a plurality of predetermined positions calculated by the sheet state change calculation unit. And In this case, the magnification in the predetermined direction of the image transferred to the back surface of the sheet is corrected based on the actual extension amount of the sheet on which the front image is fixed. As a result, the occurrence of a magnification shift in the predetermined direction of the back side image formed on the image carrier is suppressed, and an image of an appropriate size can be transferred and fixed to an appropriate position on the back side of the sheet.

Further, the above-mentioned predetermined direction is characterized in that it is set in the main scanning direction when forming an image on the image carrier. In this case, the actual elongation in the main scanning direction of the sheet on which the front surface image is fixed is detected, and the main scanning magnification of the image transferred to the back surface of the sheet is determined based on the actual elongation in the main scanning direction. Will be corrected. Accordingly, it is possible to suppress occurrence of a magnification shift in the main scanning direction of the image of the back surface image formed on the image carrier.

Further, the above-mentioned predetermined direction is set in a sub-scanning direction when an image is formed on the image carrier. In this case, the actual amount of elongation in the sub-scanning direction of the sheet on which the front surface image is fixed is detected, and the sub-scanning magnification of the image transferred to the back surface of the sheet is determined based on the actual amount of elongation in the sub-scanning direction. Will be corrected. Thus, it is possible to suppress occurrence of a magnification shift in the sub-scanning direction of the image of the back surface image formed on the image carrier.

[0013]

Embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a schematic structural view showing an embodiment of an image forming apparatus according to the present invention, and corresponds to, for example, a four-drum type color laser beam printer.

The color laser beam printer 1 includes a yellow image forming station 2Y, a magenta image forming station 2M, a cyan image forming station 2C, and a black image forming station 2K.
The yellow image forming station 2Y includes a cleaner 3
Y, a charger 4Y, a developing unit 5Y, and a photosensitive drum 6Y as an image carrier are provided. A yellow exposure unit 7Y for forming a latent image is provided for the photosensitive drum 6Y. Exposure unit 7Y for yellow
Has a laser scanning unit 8Y, and emits a scanning beam 9Y pulse-width-modulated based on an image signal to the photosensitive drum 6Y. The transfer belt 10 is stretched around a drive roller 12 driven by a drive motor (not shown) and a driven roller 13, and moves as the drive roller 12 rotates. A transfer unit for yellow 14Y is provided at a position facing the photosensitive drum 6Y with the transfer belt 10 therebetween. Transfer unit 14 for yellow
Y transfers the image formed on the photosensitive drum 6Y of the yellow image forming station 2Y onto the surface of the transfer belt 10 by the yellow image recording material.

The magenta image forming station 2M includes:
A cleaner 3M, a charger 4M, a developing unit 5M, and a photosensitive drum 6M as an image carrier are provided. A magenta exposure unit 7M for forming a latent image is provided for the photosensitive drum 6M. The magenta exposure unit 7M has a laser scanning unit 8M and emits a scanning beam 9M pulse-width-modulated based on an image signal to the photosensitive drum 6M. A magenta transfer unit 14M is provided at a position facing the photosensitive drum 6M with the transfer belt 10 therebetween. Magenta transfer unit 14
M transfers the image formed on the photosensitive drum 6M of the magenta image forming station 2M onto the surface of the transfer belt 10 by the magenta image recording material.

The cyan image forming station 2C is provided with a cleaner 3C, a charger 4C, a developing unit 5C, and a photosensitive drum 6C as an image carrier. An exposure unit 7C for cyan for forming a latent image is provided for the photosensitive drum 6C. The cyan exposure unit 7C has a laser scanning unit 8C, and outputs a scanning beam 9C pulse-width-modulated based on an image signal to the photosensitive drum 6C.
Fire at A transfer unit for cyan 14C is provided at a position facing the photosensitive drum 6C with the transfer belt 10 therebetween. The cyan transfer unit 14 </ b> C is provided on the surface of the transfer belt 10.
An image formed by the developed cyan image recording material is transferred onto the photosensitive drum 6C of C.

The black image forming station 2K is
A cleaner 3K, a charger 4K, a developing unit 5K, and a photosensitive drum 6K as an image carrier are provided. A black exposure unit 7K for forming a latent image is provided for the photosensitive drum 6K. The black exposure unit 7K has a laser scanning unit 8K, and emits a scanning beam 9K pulse-width-modulated based on an image signal to the photosensitive drum 6K. A black transfer unit 14K is provided at a position facing the photosensitive drum 6K with the transfer belt 10 interposed therebetween. Black transfer unit 14
K transfers the image formed on the photosensitive drum 6K of the black image forming station 2K onto the surface of the transfer belt 10 by the black image recording material.

Each color image forming station 2Y, 2M, 2
A transfer unit 15 for transfer paper is provided on the transfer path of the transfer belt 10 located below C and 2K. The transfer unit 15 for transfer paper has a pair of transfer rollers 15a and 15b with the transfer belt 10 interposed therebetween, and transfers each color image transferred on the surface of the transfer belt 10 to transfer paper. Here, the transfer unit for transfer paper 15 constitutes a transfer unit in each claim.

The transfer paper Pa as a sheet is stored in a plurality of cassettes 16a, 16b, 16c, and the transfer paper Pa on the upper surface is brought into contact with each of the pickup rollers 17a, 17b, 17c by a spring (not shown). Raised. The transfer paper Pa separated by each of the pickup rollers 17a, 17b, 17c is transported on the transport path 18 in the direction in which the transfer unit for transfer paper 15 is disposed. Transport path 18
, Transport rollers 18a are provided at predetermined intervals. The transfer paper Pa on which each color image has been transferred by the transfer paper transfer unit 15 is transported to the fixing unit 20 by the transport belt 19. The fixing unit 20 includes a heat fixing roller 20a and a pressure roller 20b.
The respective color images (toner images) transferred to a are fused and fixed by heat. Here, the fixing unit 20 constitutes a fixing unit in each claim.

The transfer paper Pa on which the respective color images are fixed by the fixing unit 20 is discharged to the outside of the color laser beam printer 1 through the discharge conveyance path 21. Discharge transport path 21
A transfer paper reversal conveyance path 22 for reversing the transfer paper for backside printing is provided to branch off from an intermediate portion of the transfer paper.
A transfer path 23 branches off from the transfer paper reversal transfer path 22, and the transfer path 23 is configured to be connected to an intermediate portion of the transfer path 18. The transport path 23 includes a transport roller 23a.
Are provided at predetermined intervals. Here, the transfer paper reversing conveyance path 22 and the conveyance path 23 constitute a conveyance unit in each claim.

At the front side of the fixing unit 20 in the transfer direction of the transfer paper Pa, a front side light source 31 and a front side optical sensor 32 as first speckle pattern detecting means are provided.
Is provided for the transfer paper Pa conveyed toward the fixing unit 20, as shown in FIG. Transfer paper Pa
The second side of the fixing unit 20 when viewed from the
The rear-side detection light source 33 and the rear-side optical sensor 34 as the speckle pattern detecting means are provided with the transfer paper Pa conveyed from the fixing unit 20 as shown in FIG.
It is provided for. The front-side detection light source 31 and the rear-side detection light source 33 have laser scanning means (not shown), and irradiate the transfer paper Pa with a detection light beam (laser beam) that is coherent light. Front optical sensor 3
2 and the rear optical sensor 34 have a CCD (not shown), and the detection light beams from the front detection light source 31 and the rear detection light source 33 are reflected by the transfer paper Pa and formed by diffused light. It is configured to detect a speckle pattern to be detected.

Front-side detection light source 31 and front-side optical sensor 3
2, speckle patterns at three detection positions A1, A2, and A3 set at predetermined positions are measured as shown in FIG. Each measured speckle pattern is set as a reference speckle pattern at each of the detection positions A1, A2, and A3. More specifically, a predetermined distance 11 and a predetermined distance from the front end with respect to the front end and one side end (the left end in FIG. 2) viewed in the transport direction B of the transfer paper Pa detected by an end detection unit (not shown). A light beam for detection is emitted from the front light source 31 for detection around the detection position A1 which is a predetermined distance 12 away from the end. The speckle pattern reflected by the vicinity of the detection position A1 and formed by the diffused light is detected by the front optical sensor 32. Based on the detection position A1,
Main scanning direction from detection position A1 (right direction in FIG. 2)
The detection light beam from the front-side detection light source 31 is also emitted from the front detection light source 31 around the detection position A2 at a predetermined distance 13 from the front side. The speckle pattern reflected by the vicinity of the detection position A2 and formed by the diffused light is also detected by the front optical sensor 32. Further, based on the detection position A1, the sub-scanning direction from the detection position A1 (in FIG. 2,
The detection light beam from the front-side detection light source 31 is also emitted from the front-side detection light source 31 around the detection position A3 at a predetermined distance 14 downward (downward). The speckle pattern reflected by the vicinity of the detection position A3 and formed by the diffused light is also detected by the front optical sensor 32.

Referring to FIGS. 3 and 4, an example of the detection of the reference speckle pattern in the front side light source 31 and the front side optical sensor 32 will be described. Front side detection light source 3
1 is the detection position A1 (and the detection position A on the transfer paper Pa).
3) a first front side light source 3 for irradiating a light beam for detection
1a, and a second step of irradiating the detection position A2 with a detection light beam.
And a front-side detection light source 31b. The front optical sensor 32 detects the speckle pattern formed by the diffused light reflected at the detection position A1 (and the detection position A3), and the diffuse light reflected at the detection position A2. A second front optical sensor 32b for detecting a speckle pattern formed by light.

The first front side detection light source 31a is connected to the transfer paper Pa
Is transported to a predetermined position on the transport path (before the transfer paper Pa enters the fixing unit 20), a detection light beam is emitted to the detection position A1. First front optical sensor 32a
Detects a speckle pattern formed by the diffused light reflected at the detection position A1. The speckle pattern detected by the first front optical sensor 32a is set as the reference speckle pattern at the detection position A1. Similarly, the second front-side detection light source 31b irradiates the detection position A2 with a detection light beam when the transfer paper Pa is transported to the above-described predetermined position on the transport path. The second front optical sensor 32b detects a speckle pattern formed by the diffused light reflected at the detection position A2. The speckle pattern detected by the second front optical sensor 32b is set as a reference speckle pattern at the detection position A2. Thereafter, when the transfer paper Pa is transported by a predetermined distance, the first front-side detection light source 31a irradiates the detection position A3 with a detection light beam. The first front optical sensor 32a detects a speckle pattern formed by the diffused light reflected at the detection position A3. The speckle pattern detected by the first front optical sensor 32a is set as a reference speckle pattern at the detection position A3.

Next, an example of speckle pattern detection in the rear detection light source 33 and the rear optical sensor 34 will be described with reference to FIGS. The rear-side detection light source 33 irradiates a first detection light beam onto the transfer paper Pa.
It has a rear-side detection light source 33a and a second rear-side detection light source 33b that irradiates a light beam for detection onto the transfer paper Pa. The rear optical sensor 34 is provided with the first rear detection light source 3.
The first rear optical sensor 34a for detecting a speckle pattern formed by the diffused light reflected at the position on the transfer paper Pa irradiated from 3a, and the second rear light source 33b also emits light. And a second rear optical sensor 34b for detecting a speckle pattern formed by diffused light reflected at a position on the transfer paper Pa.

The first rear detection light source 33a irradiates a light beam for detection onto the transfer paper Pa when the transfer paper Pa on which the image is fixed by the fixing unit 20 is transported to a predetermined position on the transport path. Begin to. The first rear-side detection light source 33a includes:
The detection light beam is scanned in the main scanning direction. The first rear optical sensor 34a detects a speckle pattern formed by diffused light reflected at a position on the transfer paper Pa irradiated from the first rear detection light source 33a. Similarly the second
The rear detection light source 33b starts irradiating the transfer paper Pa with a detection light beam when the transfer paper Pa is transported to the above-described predetermined position on the transport path. Second rear-side detection light source 33
b scans the detection light beam in the main scanning direction. The second rear optical sensor 34b detects a speckle pattern formed by diffused light reflected at a position on the transfer paper Pa irradiated from the second rear detection light source 33b. Thereafter, when the transfer paper Pa is transported a predetermined distance, the first rear-side detection light source 33a irradiates a detection light beam and scans in the main scanning direction. The irradiation of the detection light beam may be continued from the above-described irradiation start. First rear optical sensor 34
“a” detects a speckle pattern formed by diffused light reflected at a position on the transfer paper Pa irradiated from the first rear-side detection light source 33a.

Next, with reference to FIGS. 7 and 8, an example of detecting a change in the reference speckle pattern position based on the elongation of the sheet in the main scanning direction or the sub scanning direction will be described. Here, the change of the reference speckle pattern position at the detection position A1 is shown, but the change of each reference speckle pattern position is detected at the detection positions A2 and A3 by the same method.

First, based on FIG. 7, the main scanning direction (FIG.
In the following, a description will be given of the detection of a position change of the reference speckle pattern position with respect to the left-right direction. The detection light beam C1 emitted from the first front-side detection light source 31a to the detection position A1 is reflected at the detection position A1, and a reference speckle pattern Sp1 is formed by the reflected scattered light. It is detected by the front optical sensor 32a. The detection light beam C2 emitted from the first rear detection light source 33a scans the transfer paper Pa on which the image is fixed by the fixing unit 20, in the main scanning direction. At this time, the detection light beam C2 is reflected on the transfer paper Pa, and a speckle pattern Sp2 is formed by the reflected scattered light, and is detected by the first rear optical sensor 34a. The first rear optical sensor 34a detects the reference speckle pattern Sp1.
If a speckle pattern Sp2 equivalent to is detected,
The position where the speckle pattern Sp2 equivalent to the reference speckle pattern Sp1 is detected, that is, the detection position D1 where the detection light beam C2 is emitted from the first rear-side detection light source 33a corresponds to the detection position A1. become. Accordingly, the displacement X in the main scanning direction between the detection position A1 and the detection position D1 with respect to the paper side edge is caused by the elongation of the transfer paper Pa generated at the time of fixing. Will show the amount of change in position.

Further, based on FIG. 8, the sub-scanning direction (FIG. 7)
In the following, a description will be given of the detection of a position change of the reference speckle pattern position with respect to the vertical direction. Similar to the detection of the position change of the reference speckle pattern position in the main scanning direction shown in FIG. 7, the first rear optical sensor 34a detects a speckle pattern Sp2 equivalent to the reference speckle pattern Sp1. In this case, the position where the speckle pattern Sp2 equivalent to the reference speckle pattern Sp1 is detected, that is, the detection position D1 where the detection light beam C2 is emitted from the first rear-side detection light source 33a corresponds to the detection position A1. Will do. Accordingly, the deviation Y in the sub-scanning direction between the detection position A1 and the detection position D1 with respect to the front end of the paper is caused in the sub-scanning direction of the detection position A1 caused by the extension of the transfer paper Pa generated during fixing. Will be shown.

FIG. 12 is a block diagram showing a control system of the color laser beam printer 1 in this embodiment.

The control unit 41 includes the front optical sensor 3
2 and an output signal from the rear optical sensor 34 are input. The control unit 41 performs an operation according to a program stored in advance and outputs output signals as various control signals. This output signal is output to each of the color exposure units 7Y, 7M, 7C, 7K, the front side light source 31 and the rear side light source 33. The control unit 41 includes a light source control unit 42, a reference speckle pattern position setting unit 43, a speckle pattern position detection unit 44, a sheet elongation amount calculation unit 45, an image data correction amount calculation unit 46, an image data correction unit 48, an exposure unit It has a control means 49 and an image data memory (RAM) 47. Further, the control unit 41 controls each of the color image forming stations 2Y, 2M, 2C, 2K (each of the chargers 4Y, 4M,
4C, 4K, each developing unit 5Y, 5M, 5C, 5K
Etc.), image forming control means (not shown) for controlling each color exposure unit 7Y, 7M, 7C, 7K and each color transfer unit 14Y, 14M, 14C, 14K, and transfer paper for controlling transfer paper transfer unit 15. Transfer unit control means (not shown), a fixing unit control means (not shown) for controlling the fixing unit 20, and a transfer control means for back side printing for controlling the transfer state in the transfer sheet reversing transfer path 22 and the transfer path 23 ( (Not shown).

The light source control means 42 controls the light source 31 for front detection.
An output signal as a control signal for controlling the blinking of the rear detection light source 33, the irradiation position, and the like is output to the front detection light source 31 and the rear detection light source 33, and at the same time, the reference speckle pattern position setting means 43 and An output signal is also output to the speckle pattern position detecting means 44. The output signal from the front optical sensor 32 is input to the reference speckle pattern position setting means 43. The reference speckle pattern position setting means 43 starts its operation with the output signal from the light source control means 42 as a trigger, and the front optical sensor 32
Recognize the respective reference speckle patterns at the detection positions A1, A2, and A3 based on the output signal from the CPU, and store the recognition results as the respective reference speckle patterns at the detection positions A1, A2, and A3. The reference speckle pattern position setting means 43 outputs an output signal indicating the position (detection position A1, A2, A3) of each detected reference speckle pattern to the paper elongation amount calculation means 45. Further, the reference speckle pattern position setting means 43 outputs an output signal relating to the recognition result (shape and the like) of each detected reference speckle pattern to the speckle pattern position detection means 44.

The output signal from the rear optical sensor 34 is input to the speckle pattern position detecting means 44. The speckle pattern position detecting means 44 includes a light source controlling means 42
The operation of the transfer paper Pa is started based on the output signal from the rear optical sensor 34 with the output signal from
The upper speckle pattern is recognized, the recognition result is compared with the recognition result of the reference speckle pattern output from the reference speckle pattern position setting means 43, and the matching rate is calculated. When the calculated coincidence ratio is equal to or greater than a predetermined value, the speckle pattern detected by the rear optical sensor 34 and recognized by the speckle pattern position detecting means 44 is regarded as a reference speckle pattern, and the speckle pattern is determined. The position detecting means 44 calculates the position on the transfer paper Pa where the speckle pattern corresponding to the reference speckle pattern is obtained based on the output signal from the light source control means 42, and uses the calculation result as an output signal to extend the paper. Output to the amount calculation means 45. The matching rate is determined based on the shape, area, and the like of the speckle pattern. Since it is considered that the reference speckle pattern itself changes due to fixing, the speckle pattern position detecting means 44 determines that the coincidence rate is equal to or more than a predetermined value so as to correspond to the reference speckle pattern.

The paper elongation amount calculating means 45 calculates the elongation amount of the transfer paper Pa based on the output signal from the reference speckle pattern position setting means 43 and the output signal from the speckle pattern position detecting means 44. Transfer paper Pa
Image data correction amount calculating means 4 using the amount of elongation as an output signal
6 is output. In the sheet elongation amount calculating means 45, each of the detection positions A1, A
The position change amount for A2 and A3 is calculated. The signal output to the image data correction amount calculating means 46 includes a position change amount in the main scanning direction with respect to the detection position A1, a position change amount in the sub-scanning direction with respect to the detection position A1, the detection position A1 and the detection position A.
2 and the detection position A1 and the detection position A
3 shows the amount of change in the distance between them. Detection position A
1 in the main scanning direction is the predetermined distance l2
Shows how much has changed due to fixing. The position change amount in the sub-scanning direction with respect to the detection position A1 indicates how much the predetermined distance 11 has changed due to fixing. The amount of change in the distance between the detection position A1 and the detection position A2 indicates how much the predetermined distance 13 has changed due to fixing, and corresponds to the amount of elongation of the transfer paper Pa in the main scanning direction. The amount of change in the distance between the detection position A1 and the detection position A3 indicates how much the predetermined distance 14 has changed due to fixing, and corresponds to the amount of elongation of the transfer paper Pa in the sub-scanning direction.

The image data correction amount calculating means 46 controls the influence (e.g., image writing position, main scanning magnification, and sub-scanning) on the respective color images due to the expansion of the transfer paper Pa due to fixing based on the output signal from the paper elongation amount calculating means 45. An image data correction amount for correcting the magnification or the like is calculated, and the calculated correction amount is output to the image data correction unit 48 as an output signal. The image data correction unit 48 includes an image data correction amount calculation unit 46
Image data memory (RA) based on the output signal from
M) The output signal indicating the image data output from 47 is corrected, and the output signal indicating the corrected image data is output to the exposure unit control means 49. Exposure unit control means 49
Controls the respective color exposure units 7Y, 7M, 7C, 7K based on the output signal from the image data correcting means 48. Here, reference speckle pattern position setting means 4
Reference numeral 3 together with the front side light source 31 and the front side optical sensor 32 constitute a first speckle pattern detecting means in each claim. Speckle pattern position detecting means 44
, Together with the rear-side detection light source 33 and the rear-side optical sensor 34, constitute second speckle pattern detection means in each claim. The paper elongation amount calculating means 45 constitutes a paper state change calculating means in each claim, and the image data correction amount calculating means 46 and the image data correcting means 48 constitute an image forming state correcting means in each claim. .

Hereinafter, each control process performed by the control unit 41 at the time of double-sided printing will be described with reference to a flowchart shown in FIG.

First, as shown in S101, a writing system (each laser scanning means 8Y, 8M, 8C, 8K, etc.) and a driving system (transfer belt 10, photosensitive drums 6Y, 6M, 6C,
6K) (sub-scan registration error,
Skew, main scanning write start position deviation, main scanning magnification deviation, sub scanning magnification deviation, etc.) are detected. S1
When the detection of the error by the writing system and the driving system in 01 ends, the error correction process by the writing system and the driving system is started as shown in S103. Here, each color image data is corrected for each color image formed on each of the photosensitive drums 6Y, 6M, 6C, and 6K for front surface printing. Note that the error detection and correction processing by the writing system and the driving system in S101 and S103 have been performed conventionally, and a detailed description thereof will be omitted. Upon completion of the above-described correction processing, as shown in S105, writing (transfer) processing of writing a yellow, magenta, cyan, and black color image for front side printing is started. Exposure units 7Y, 7M, 7C, 7 for the respective colors are output from the control unit 41 (image forming control means).
K forms a latent image of each color image on each photosensitive drum 6Y, 6M, 6C, 6K by each scanning beam 9Y, 9M, 9C, 9K from each laser scanning means 8Y, 8M, 8C, 8K. The latent images of the respective color images formed on the respective photosensitive drums 6Y, 6M, 6C, 6K are developed on the respective photosensitive drums 6Y, 6M, 6C, 6K using the respective color recording materials. Finally, the respective color images developed on the respective photosensitive drums 6Y, 6M, 6C, 6K are transferred to the respective color transfer units 14Y, 14M, 1
By 4C and 14K, the images are sequentially transferred onto the transfer belt 10.

In S107, it is determined whether or not each color image writing / forming process for back side printing has been completed. If the process of writing and forming each color image for backside printing is not completed (“No” in S107), it is determined in S105 that each color image transferred on the transfer belt 10 is for front side printing, and the process proceeds to S108. Then, the transfer process is started.
The transfer unit 15 for transfer paper is used to transfer the transfer paper P
a, the respective color images transferred onto the transfer belt 10 are transferred. If the process of writing and forming each color image for back side printing is completed (“Yes” in S107), the process proceeds to S125.

When the transfer of each color image for front side printing to the transfer paper Pa in the transfer paper transfer unit 15 is completed and the transfer paper Pa is transported to a predetermined position, the reference speckles are displayed as shown in S109. The pattern detection process starts. In response to an output signal from the light source control means 42, the front-side detection light source 31 is turned on, and a detection light beam is applied to the detection positions A1, A2, and A3 on the transfer paper Pa.
The front optical sensor 32 detects a speckle pattern formed by scattered light reflected from A2 and A3. The front optical sensor 32 outputs the detection result to the reference speckle pattern position setting unit 43 as an output signal. Detected position A by reference speckle pattern position setting means 43
When the recognition of each reference speckle pattern in A1, A2, and A3 is completed, a fixing process of the transfer paper Pa on which each color image is transferred is started as shown in S111. The fixing unit 20 fixes each color image on the transferred transfer paper Pa to the transfer paper Pa.

When the fixing unit 20 completes the fixing of each color image onto the transfer paper Pa and conveys the transfer paper Pa to a predetermined position, a speckle pattern detection process is started as shown in S113. . The rear-side detection light source 33 is turned on by an output signal from the light source control unit 42, irradiates a light beam for detection onto the transfer paper Pa, and a speckle pattern formed by scattered light reflected from the transfer paper Pa. Is detected by the front optical sensor 32. Front optical sensor 32
Outputs the detection result as an output signal to the speckle pattern position detection means 44. The speckle pattern position detecting means 44 calculates a position at which a speckle pattern equivalent to each reference speckle pattern is detected. afterwards,
Proceeding to S115, back side print preparation processing is started.
Here, the transfer paper Pa on which fixing has been completed is conveyed to the conveyance path 18 in a reversed state by the control unit 41 (conveyance control means for back side printing) via the transfer paper reversal conveyance path 22 and the conveyance path 23.

In S113, the position at which the speckle pattern equivalent to each reference speckle pattern is detected by the speckle pattern position detecting means 44 is calculated, and when the back surface print preparation processing is being performed, as shown in S117. Then, the paper elongation amount calculation process is started. here,
Based on the output signal from the reference speckle pattern position setting means 43 and the output signal from the speckle pattern position detection means 44, the paper elongation amount calculation means 45 detects the position change amount in the main scanning direction with respect to the detection position A1. Position A1
The position change amount in the sub-scanning direction, the change amount of the distance between the detection position A1 and the detection position A2, and the change amount of the distance between the detection position A1 and the detection position A3 are calculated. In the paper elongation amount calculating means 45, the position change amount in the main scanning direction with respect to the detection position A1, the position change amount in the sub-scanning direction with respect to the detection position A1, the change amount of the distance between the detection position A1 and the detection position A2, and When the calculation of the amount of change in the distance between the detection position A1 and the detection position A3 ends, the calculation processing of the image data correction amount starts, as shown in S119. Here, based on the output signal from the paper elongation amount calculating means 45, the image data correction amount calculating means 46 influences each color image due to the elongation of the transfer paper Pa due to the fixing (image writing position, main scanning magnification, sub-scanning, sub-scanning). An image data correction amount for correcting the magnification or the like is calculated, and the calculated correction amount is output to the image data correction unit 48 as an output signal.

When the calculation of the image data correction amount by the image data correction amount calculation means 46 is completed, S121 and S123 are performed.
As shown in (5), the writing position correction processing, the main scanning magnification correction processing, and the sub scanning magnification correction processing are started. here,
The image data correction means 48 generates an image data memory 47 based on an output signal from the image data correction amount calculation means 46.
The image data as an output signal sent from is corrected. Thereafter, the process returns to S101, and in S101 and S103, an error detection and correction process by the writing system and the driving system for back side printing is performed. Each photosensitive drum 6Y, 6 for back side printing in S103
When the correction of each color image data is completed for each color image formed on M, 6C, 6K, in S105, the writing, forming (transfer) processing of the yellow, magenta, cyan, and black images for the back side printing is performed. Is started. After that, the transfer units for each color 14Y, 14M, 14C, 14
By K, each color image for back side printing is transferred to the transfer belt 10.
When the image is transferred to the upper side, the process proceeds to S107, and it is determined whether the process of writing and forming each color image for back side printing is completed. At this time, since each color image writing and forming process for back side printing has been completed (“Yes” in S107),
Proceed to S125. In S125, a transfer process for backside printing is started. The transfer paper transfer unit 15 transfers each color image for backside printing transferred onto the transfer belt 10 to the transferred transfer paper Pa. Then, the process proceeds to S127, where the fixing process of the transfer paper Pa on which the respective color images for the back side printing are transferred is started. The fixing unit 20 fixes each color image for back side printing on the transferred transfer paper Pa to the transfer paper Pa.

From the above, in this embodiment,
A front detection light source 31 and a front optical sensor 32, and a rear detection light source 33 and a rear optical sensor 34 are provided on the transfer path of the transfer paper Pa and at different positions when viewed in the transfer direction of the transfer paper Pa. Paper elongation amount calculation means 45
A predetermined position (A1, A2, A2) of the reference speckle pattern set by the reference speckle pattern position setting means 43.
A3) and a detection position at which a speckle pattern equivalent to the reference speckle pattern is detected, calculated by the speckle pattern position detection means, based on the front side light source 31 and the front side optical sensor 32, and the rear side. Light source for detection 3
A change in the state of the transfer paper Pa between the transfer paper 3 and the rear optical sensor 34 is calculated. For this reason, based on the actual change in the state of the paper, the image data correction amount calculating means 46 is used to calculate the image data correction amount of the image formed on each of the photosensitive drums 6Y, 6M, 6C and 6K and transferred onto the transfer paper Pa. Is calculated, and the image data correcting means 48 corrects the image data based on the image data correction amount. Therefore, based on the actual state of the transfer paper Pa, the image transferred and fixed on the transfer paper Pa can be corrected, and the image can be transferred and fixed at a more appropriate position on the transfer paper Pa. It is possible to form an image with high accuracy.

In particular, a front detection light source 31 and a front optical sensor 32, and a rear detection light source 33 and a rear optical sensor 34 are provided at front and rear positions of the fixing unit 20, respectively.
The paper elongation amount calculation unit 45 calculates the elongation amount of the transfer paper Pa at the time of fixing each color image for front surface printing in the fixing unit 20 based on the transfer paper Pa on which each color image for front surface print is actually fixed. I do. For this reason, the image data correction amount calculating means 46 is formed on each of the photosensitive drums 6Y, 6M, 6C and 6K and transferred based on the actual elongation amount of the transfer paper Pa on which each color image for front side printing is fixed. Paper Pa
Calculate the image data correction amount of the image transferred to the back side of
The image data correcting means 48 corrects the image data based on the image data correction amount. Therefore, the transfer paper Pa is determined based on the actual elongation of the transfer paper Pa after fixing.
The image transferred and fixed on the back surface can be corrected, and the image can be transferred and fixed to a more appropriate position on the back surface of the transfer paper Pa, and the image can be positioned with high accuracy on the front and back surfaces of the transfer paper Pa. .

Further, the sheet elongation amount calculating means 45 includes a reference speckle pattern detection position A1 set by the reference speckle pattern position setting means 43 and a reference speckle pattern position calculated by the speckle pattern position detecting means. Based on the detected position where the speckle pattern equivalent to the above is detected, the position change amount of the detection position A1 in the main scanning direction and the position change amount of the detection position A1 in the sub-scanning direction are calculated. As a result, the image data correction amount calculating unit 46 determines whether the image transferred to the back surface of the transfer paper Pa is based on the position change amount in the main scanning direction with respect to the detection position A1 and the position change amount in the sub-scanning direction with respect to the detection position A1. The correction amount of the writing position is calculated, and the image data is corrected by the image data correction means 48 according to the correction amount. Therefore, due to the elongation of the transfer paper Pa at the time of fixing,
The occurrence of displacement of the writing position of each color image for printing on the back surface formed on each of the photosensitive drums 6Y, 6M, 6C, and 6K is suppressed, and the image can be transferred and fixed to an appropriate position on the back surface of the transfer paper Pa.

Further, the front detection light source 31 is
A first front side detection light source 31a for irradiating the upper detection position A1 with the detection light beam, and a second front side detection for irradiating the detection light beam to a detection position A2 which is separated from the detection position A1 by a predetermined distance 13 in the main scanning direction. Light source 31b. Also,
The front optical sensor 32 detects a speckle pattern formed by the diffused light reflected at the detection position A1.
A front optical sensor 32a and a second front optical sensor 32b for detecting a speckle pattern formed by diffused light reflected at a detection position A2 that is separated from the detection position A1 by a predetermined distance 13 in the main scanning direction. ing. Then, detection positions A1 and A2 of the reference speckle pattern set by the reference speckle pattern position setting means 43 and a speckle pattern equivalent to the reference speckle pattern calculated by the speckle pattern position detection means are detected. Based on the detected position, the amount of change in the distance between the detected position A1 and the detected position A2 is calculated. Accordingly, in the image data correction amount calculating means 46, the main scanning magnification of the image transferred to the back surface of the transfer paper Pa is determined by the actual extension amount of the transfer paper Pa on which each color image for the front surface print is fixed (the detection position A1 The correction amount of the main scanning magnification of the image transferred to the back surface of the transfer paper Pa is calculated based on the amount of change in the distance from the detection position A2). Is corrected. Therefore, the transfer paper P at the time of fixing is
a, each of the photosensitive drums 6Y, 6M, 6C,
The occurrence of a shift in the main scanning magnification of each color image for back side printing formed on 6K is suppressed, and an image of an appropriate size can be transferred and fixed to an appropriate position on the back side of the transfer paper Pa.

Further, the first front detection light source 31a irradiates a detection light beam to a detection position A3 which is separated from the detection position A1 by a predetermined distance 14 in the sub-scanning direction while the transfer paper Pa is transported by a predetermined distance. Then, the first front optical sensor 32a detects a speckle pattern formed by the diffused light reflected at the detection position A3. Then, the detection positions A1 and A3 of the reference speckle pattern set by the reference speckle pattern position setting means 43 and the speckle pattern equivalent to the reference speckle pattern calculated by the speckle pattern position detection means are detected. Based on the detected position, the amount of change in the distance between the detected position A1 and the detected position A3 is calculated. Accordingly, in the image data correction amount calculating unit 46, the sub-scanning magnification of the image transferred to the back surface of the transfer paper Pa is determined by the actual amount of elongation of the transfer paper Pa on which each color image for front-side printing is fixed (the detection position A1 Transfer paper Pa based on the amount of change in the distance from the detection position A3).
A correction amount of the sub-scanning magnification of the image transferred to the back surface is calculated, and the image data is corrected by the image data correction unit 48 according to the correction amount. Therefore, the transfer paper Pa at the time of fixing is
Photosensitive drums 6Y, 6M, 6C, 6
The occurrence of a shift in the sub-scanning magnification of each color image for backside printing formed on K is suppressed, and an image of an appropriate size can be transferred and fixed to an appropriate position on the backside of the transfer paper Pa.

FIGS. 11 to 13 show modified examples of the front-side detection light source 31 and the front-side optical sensor 32. FIG. FIG.
In the modification shown in FIG. 1, one front optical sensor 52 is provided as a front optical sensor, and the front optical sensor 52 is formed by scattered light reflected at the detection position A1 and the detection position A2. Speckle pattern is detected. In this case, the front-side detection light source 31 is configured as shown in FIG.
As shown in (1), it has a first front side detection light source 31a and a second front side detection light source 31b.

In the modification shown in FIG. 12, one front detection light source 61 is provided as a front detection light source. The detection light beam from the front-side detection light source 61 is split by the beam splitter 62 and is applied to the detection position A1 and the detection position A2. In this case, the front optical sensor 32 is, as shown in FIG.
2a and a second front optical sensor 32b.

In the modification shown in FIG.
3, a front-side detection light source 71 and a front-side optical sensor 72 are newly provided as a front-side detection light source and a front-side optical sensor. The modification of the front-side detection light source 31 and the front-side optical sensor 32 has been described above.
Other than those described above, any one can be appropriately employed as long as it can irradiate a coherent detection beam to 1, A2, and A3 and detect a speckle pattern formed by reflected diffused light. Further, the same modifications as the front-side detection light source 31 and the front-side optical sensor 32 can be adopted for the rear-side detection light source 33 and the rear-side optical sensor 34.

In the embodiment described above, the reference speckle patterns at three locations (detection positions A1, A2, A3) are configured to be detected. The above-described reference speckle pattern is detected. For example, the reference speckle pattern is detected at a position separated by a predetermined distance from the detection position A2 in the main scanning direction, or at a position separated by a predetermined distance from the detection position A3 in the sub-scanning direction. May be configured. Transfer paper P
The amount of elongation at the time of fixing a may vary depending on the position on the transfer paper Pa. By setting a large number of positions for detecting the reference speckle pattern, the elongation at the time of fixing the transfer paper Pa can be more appropriately adjusted. Thus, the image can be corrected.

In the above-described embodiment, the image is corrected by detecting the elongation of the transfer paper Pa at the time of fixing. However, the present invention is not limited to this. For example, the cassettes 16a and 16b may be used. , 16c to the transfer unit 15 for the transfer paper, a front side light source 31 and a front side optical sensor 32 are provided at predetermined positions on the transfer path 18, and the transfer path 18
The rear-side detection light source 3 is located at a predetermined position behind the front-side detection light source 31 and the front-side optical sensor 32 when viewed in the transport direction.
3 and the rear optical sensor 34 may be provided to detect a change in the posture of the transfer paper Pa between the two predetermined positions, and to correct the image according to the change in the posture.

Further, the color laser beam printer 1 according to the present embodiment is configured to form each color image on the transfer belt 10 and transfer each color image formed on the transfer belt 10 to transfer paper. However, the transfer paper is placed on the transfer belt 10, the transfer paper is transported to each color image forming station 2Y, 2M, 2C, 2K, and each color image is transferred to each color image forming station 2Y, 2M, 2M.
The present invention can be applied to a color laser beam printer configured to transfer onto transfer paper in 2C and 2K, and can be applied to various image forming apparatuses other than those having an intermediate transfer belt or other color laser beam printers. It is possible to apply.

[0055]

The first position is different from the first position in the paper transport direction.
Speckle pattern detection means and second speckle pattern detection means are provided, and the paper state change calculation means detects a predetermined position at which the first speckle pattern detection means has detected the reference speckle pattern, Between the first speckle pattern detecting means and the second speckle pattern detecting means based on the positional relationship with the position where the speckle pattern equivalent to the reference speckle pattern is detected by the speckle pattern detecting means. Calculates the change in the state of the sheet at. For this reason, based on the actual state change of the sheet, the image forming state correcting means corrects the state of the image formed on the image carrier and transferred onto the sheet. Therefore, based on the actual state of the sheet, the image transferred and fixed on the sheet can be corrected, and the image can be transferred and fixed at a more appropriate position on the sheet, so that the image can be formed on the sheet with high accuracy. A simple image forming apparatus.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a detection position of a speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 3 is an explanatory diagram illustrating an example of detecting a reference speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 4 is an explanatory diagram illustrating an example of detecting a reference speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 5 is an explanatory diagram illustrating a detection example of a speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 6 is an explanatory diagram illustrating a detection example of a speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 7 is an explanatory diagram illustrating an example of detection of a change in reference speckle pattern position based on sheet elongation in the main scanning direction in the embodiment of the image forming apparatus according to the present invention.

FIG. 8 is an explanatory diagram illustrating an example of detection of a change in reference speckle pattern position based on elongation of a sheet in the sub-scanning direction in the embodiment of the image forming apparatus according to the present invention.

FIG. 9 is a block diagram showing a control system in the embodiment of the image forming apparatus according to the present invention.

FIG. 10 is a flowchart illustrating a control operation of front and back image formation in the embodiment of the image forming apparatus according to the present invention.

FIG. 11 is an explanatory diagram illustrating a modification of the detection of the reference speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 12 is an explanatory diagram illustrating a modification of the detection of the reference speckle pattern in the embodiment of the image forming apparatus according to the present invention.

FIG. 13 is an explanatory diagram illustrating a modification of the detection of the reference speckle pattern in the embodiment of the image forming apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Color laser beam printer, 2Y ... Image forming station for yellow, 2C ... Image forming station for cyan, 2K ... Image forming station for black, 2M ...
Magenta image forming station, 3Y, 3M, 3C,
3K: cleaner, 4Y, 4M, 4C, 4K: charger, 5
Y, 5M, 5C, 5K: developing unit, 6Y, 6M, 6
C, 6K: photosensitive drum, 7Y, 47Y: exposure unit for yellow, 7C, 47C: exposure unit for cyan, 7
K, 47K: Exposure unit for black, 7M, 47M ...
Exposure unit for magenta, 8Y, 8M, 8C, 8K: laser scanning means, 10: transfer belt, 12: drive roller,
13: driven roller, 14Y: transfer unit for yellow,
14C: transfer unit for cyan, 14K: transfer unit for black, 14M: transfer unit for magenta, 15 ...
Transfer unit for transfer paper, 18: conveyance path, 20: fixing unit, 21: discharge conveyance path, 22: transfer paper reverse conveyance path, 2
DESCRIPTION OF SYMBOLS 3 ... Conveyance path, 31 ... Front side detection light source, 31a ... 1st front side detection light source, 31b ... 2nd front side detection light source, 32 ... Front side optical sensor, 32a ... 1st front side optical sensor, 32b ... 2nd front side optical Sensor 33, light source for rear side detection, 33a light source for first rear side detection, 33b light source for second rear side detection, 34
... Rear optical sensor, 34a... First rear optical sensor, 34
b: second rear optical sensor, 41: control unit, 42:
Light source control means 43, reference speckle pattern position setting means 44, speckle pattern position detection means 45
Paper elongation amount calculation means, 46: Image data correction amount calculation means, 47: Image data memory, 48: Image data correction means, 49: Exposure unit control means, 52: Front optical sensor, 61: Front side light source, 62 ... Beam splitter,
71: front side light source for detection, 72: front side optical sensor, A1,
A2, A3: detection position, C1, C2: detection light beam,
Pa: transfer paper, Sp1: reference speckle pattern, Sp
2: Speckle pattern.

Continuation of the front page F term (reference) 2C262 AA05 AA24 AA26 AB15 DA15 DA19 FA03 FA06 GA04 GA36 GA40 GA42 2H027 DC00 DE02 DE10 EC09 2H030 AA01 AB02 AD04 AD12 BB42 2H076 AB02 AB67 AB68 9A001 HH21 HH24 HH34 JJ35 KK32 KK32 KK32 KK32

Claims (6)

[Claims] 1. An image forming apparatus for transferring an image formed on an image carrier onto a sheet to be conveyed and fixing the transferred image to the sheet, wherein the image forming apparatus is provided at an intermediate position in a sheet conveyance path. A first speckle pattern detecting means for irradiating coherent light to a predetermined position of the sheet and detecting a reference speckle pattern of diffused light reflected at the predetermined position; The speckle pattern is provided on the rear side of the first speckle pattern detection means, irradiates the paper with coherent light, and calculates a speckle pattern equivalent to the reference speckle pattern from a speckle pattern of diffused light reflected by the paper. Second speckle pattern detecting means for detecting a pattern, and the predetermined position at which the reference speckle pattern is detected by the first speckle pattern detecting means. And the second
The first speckle pattern detecting means and the second speckle pattern detecting means based on the positional relationship between the speckle pattern detecting means and a position at which a speckle pattern equivalent to the reference speckle pattern is detected. Paper state change calculation means for calculating a change in the state of the paper between the paper state, according to the change in the state of the paper calculated by the paper state change calculation means, formed on the image carrier, on the paper An image forming apparatus comprising: an image forming state correcting unit that corrects a state of an image to be transferred. A transfer unit configured to transfer the image formed on the image carrier to the sheet; a fixing unit configured to fix the image transferred on the sheet to the sheet; Transport means for transporting the sheet fixed by the fixing means to the transfer means, in order to transfer the image formed on the image carrier to the back surface of the sheet on which the image is fixed. Wherein the first speckle pattern detecting means is provided in front of the fixing means as viewed in the sheet conveying direction, and the second speckle pattern detecting means is provided in the sheet conveying direction. The paper position change calculation means is provided at the predetermined position where the reference speckle pattern is detected by the first speckle pattern detection means, Calculating the amount of elongation of the sheet that occurs at the time of fixing, based on a positional relationship with a position at which a speckle pattern equivalent to the reference speckle pattern is detected by the second speckle pattern detecting means; The correction unit corrects the state of the image formed on the image carrier and transferred to the back surface of the sheet based on the amount of elongation of the sheet calculated by the sheet state change calculation unit. The image forming apparatus according to claim 1. 3. The method according to claim 1, wherein the elongation amount of the sheet calculated by the sheet state change calculating unit is a change amount of an interval from an end of the sheet to the predetermined position. Writing of the image formed on the image carrier and transferred to the back surface of the sheet based on the change amount of the interval from the end of the sheet to the predetermined position calculated by the sheet state change calculation unit The image forming apparatus according to claim 2, wherein the position is corrected. 4. The method according to claim 1, wherein the first speckle pattern detecting means includes:
Detecting each reference speckle pattern, the amount of elongation of the sheet calculated by the sheet state change calculating unit is a change amount of an interval between the plurality of predetermined positions, and the image forming state correcting unit is The magnification in the predetermined direction of the image formed on the image carrier and transferred to the back surface of the paper is determined based on the change amount of the interval between the plurality of predetermined positions calculated by the paper state change calculation unit. The image forming apparatus according to claim 2, wherein the correction is performed. 5. The image forming apparatus according to claim 4, wherein the predetermined direction is set to a main scanning direction when forming the image on the image carrier. 6. The image forming apparatus according to claim 4, wherein the predetermined direction is set in a sub-scanning direction when forming the image on the image carrier.