JP2010139889A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for reducing mis-registration of an image, in an image forming device. <P>SOLUTION: This image forming device (U) includes a conveyance passage (SH1) on which a medium (S) is conveyed, an image recording section (U1b) for recording the image on the medium (S) at an image recording position (Q3) disposed on the conveyance way (SH1), a medium attitude correcting member (Rr) that is disposed on the upstream side of the medium conveying direction of the image recording position (Q3) and corrects the attitude of the passing medium (S) toward a preset reference attitude, an attitude detecting member (SN1) that is disposed on the upstream side of the medium conveying direction of the medium attitude correcting member (Rr) and detects the attitude of the medium, a residual amount arithmetic means (C9) for calculating the residual amounts (S3 and S3'), which are difference between the reference attitude and the attitude of the medium (S) corrected by the medium attitude correcting member (Rr), based on the detection result of the attitude detecting member (SN1), and an image rotating means (C11) for rotating the image to be formed on the medium (S) based on the residual amounts (S3 and S3'). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

In the image forming apparatus, techniques described in Patent Documents 1 and 2 below are known as techniques for correcting a positional deviation of an image recorded on a medium.
Japanese Patent Laid-Open No. 10-319674 as Patent Document 1 describes a so-called electrophotographic image forming apparatus having a photosensitive drum (9) and the like, and the transfer paper (P) is conveyed to the transfer position. In this case, the transfer paper (P) is detected by the two deviation detection units (5) provided in the direction perpendicular to the transport direction, and the skew, which is the inclination of the transfer paper (P), is corrected. The registration roller pair (3) provided with the skew correction means (13) conveys the transfer paper (P) and adjusts the inclination of the transfer paper (P) to correct the registration error, which is skew and image positional deviation. The technology to do is described.
In the technique described in Patent Document 1, the skew amount (S) of the transferred transfer paper (P) at the time of skew correction or registration deviation correction, or the measurement pattern (19) recorded at the time of double-sided printing, The registration roller pair (3) is detected by the detection unit (5) on the downstream side, and based on the detection result, one shaft end of the registration roller pair (3) is driven in the transport direction by driving the motor (17). And the inclination of the transfer sheet (P) with respect to the axial direction of the photosensitive drum (9) is adjusted.

  Japanese Patent Laid-Open No. 2000-335010 as Patent Document 2 is provided on the downstream side of a registration roller (185) that conveys transfer paper (P) to an image forming unit (50) in an electrophotographic image forming apparatus. In accordance with the passing position of the transfer paper (P) detected by the position detection sensor (220) in the main scanning direction, the image itself written on the photosensitive drum (51) is shifted in the main scanning direction, thereby shifting the position of the image. A technique for correcting the error is described.

JP-A-10-319674 ("0008" to "0010", "0013" to "0018", FIGS. 1 to 5) JP 2000-335010 A (“0075” to “0076”, “0096” to “0101”, “0117”, FIGS. 3 to 5 and FIG. 8)

  An object of the present invention is to reduce image displacement.

In order to solve the technical problem, an image forming apparatus according to claim 1 is provided.
A transport path through which the medium is transported;
An image recording unit for recording an image on the medium at an image recording position provided in the conveyance path;
The medium posture correction member that is provided upstream of the image recording position in the medium conveyance direction and corrects the posture of the medium passing toward a preset reference posture;
An attitude detection member that is provided upstream of the medium attitude correction member in the medium conveyance direction, and detects the attitude of the medium;
A residual amount calculating means for calculating a residual amount which is a difference between the posture of the medium after being corrected by the medium posture correcting member and the reference posture based on the detection result of the posture detecting member;
Image rotating means for rotating an image formed on the medium based on the remaining amount;
It is provided with.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
Correspondence information for specifying the relationship between the detection result by the posture detection member and the remaining amount corresponding to the detection result, and storing the correspondence information measured in advance for each type of medium Means,
Medium type determining means for determining the type of the medium;
The residual amount calculating means for calculating the residual amount based on the correspondence information according to the type of the medium determined by the medium type determining means;
It is provided with.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect,
A second attitude detection member that is provided downstream of the medium attitude correction member in the medium conveyance direction and detects the attitude of the medium after being corrected by the medium attitude correction member;
Based on the correspondence information in which the detection result by the posture detection member is associated with the residual amount that is the difference between the detection result by the second posture detection member and the reference posture, the correspondence information storage unit stores the correspondence information. Correspondence information updating means for updating the correspondence information;
It is provided with.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
An inversion path connecting the downstream side of the image recording position of the transport path in the medium transport direction and the upstream side of the transport path of the posture detection member in the transport direction of the image. The reversing path for reversing the front and back of the medium and retransmitting it to the posture detection member;
A second attitude detection member that is provided downstream of the medium attitude correction member in the medium conveyance direction and detects the attitude of the medium after being corrected by the medium attitude correction member;
A difference amount calculation that calculates a difference amount that is a difference between the residual amount calculated by the residual amount calculation means and a detection residual amount that is a difference between the detection result by the second posture detection member and the reference posture. Means,
Based on the residual amount calculated based on the detection result of the posture detection member and the difference amount with respect to the medium that has been retransmitted to the position of the posture detection member through the reversing path, The image rotating means for rotating the image formed on the second surface;
It is provided with.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
An inversion path connecting the downstream side of the image recording position of the transport path in the medium transport direction and the upstream side of the transport path of the posture detection member in the transport direction of the image. The reversing path for reversing the front and back of the medium and retransmitting it to the posture detection member;
A rear end posture that is provided on the upstream side of the medium posture correction member in the medium conveyance direction and detects a posture of the medium by detecting a rear end portion of the medium passing through the position of the medium posture correction member. A detection member;
A rear end detection residual that calculates a rear end detection residual amount that is a difference between the medium posture corrected by the medium posture correction member and the reference posture based on the detection result of the rear end posture detection member. A quantity calculation means;
Difference amount calculation means for calculating a difference amount which is a difference between the remaining amount calculated by the residual amount calculation means and the rear end detection residual amount calculated by the rear end detection residual amount calculation means;
Based on the residual amount calculated based on the detection result of the posture detection member and the difference amount with respect to the medium that has been retransmitted to the position of the posture detection member through the reversing path, The image rotating means for rotating the image formed on the second surface;
It is provided with.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect,
The posture detection member that also serves as the rear end posture detection member;
It is provided with.

According to the first aspect of the present invention, it is possible to reduce the image misalignment as compared with the configuration in which the image is not rotated.
According to the second aspect of the present invention, the remaining amount can be calculated based on the correspondence information corresponding to the type of the medium, and the image can be rotated.
According to the third aspect of the invention, the correspondence information can be updated based on the detection result of the posture of the medium after the posture correction by the second posture detection member on the downstream side in the medium conveyance direction of the medium posture correction member. it can.

According to the invention of claim 4, based on the detection result of the second posture detection member, the positional deviation between the image recorded on the first surface and the front and back images of the image recorded on the second surface, This can be reduced compared to a configuration in which the rotation is not performed based on the difference amount.
According to the fifth aspect of the present invention, based on the detection result of the rear end posture detection member, the positional deviation between the front and back images of the image recorded on the first surface and the image recorded on the second surface is different. Compared to a configuration in which the rotation is not performed based on the amount, it can be reduced.
According to the sixth aspect of the present invention, the posture detection member and the rear end posture detection member can be shared, and an increase in the number of parts can be suppressed.

Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings, but the present invention is not limited to the following examples.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The direction indicated by Z and -Z or the indicated side is defined as the front side, the rear side, the right side, the left side, the upper side, the lower side, or the front side, the rear side, the right side, the left side, the upper side, and the lower side, respectively.
In the figure, “•” in “○” means an arrow heading from the back of the page to the front, and “×” in “○” is the front of the page. It means an arrow pointing from the back to the back.
In the following description using the drawings, illustrations other than members necessary for the description are omitted as appropriate for easy understanding.

FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment of the present invention.
In FIG. 1, a copying machine U as an example of an image forming apparatus includes a copying machine body U1 having a platen glass PG which is an example of a transparent document table on an upper surface, and an automatic removably mounted on the platen glass PG. And a document conveying device U2.
The automatic document feeder U2 has a document feed tray TG1, which is an example of a document storage unit in which a plurality of documents Gi to be copied are stored. Each of the plurality of documents Gi placed on the document feed tray TG1 sequentially passes through a copy position on the platen glass PG and is discharged to a document discharge tray TG2 which is an example of a document discharge unit. ing.

The copying machine main body U1 includes an operation instruction input unit UI through which an operator inputs instructions, an image reading unit U1a and an image recording unit U1b sequentially disposed below the platen glass PG, and the image reading unit U1a or image. And an image processing unit GS provided in the recording unit U1b.
An image reading unit U1a serving as a document reading device disposed below the transparent platen glass PG on the upper surface of the copying machine main body U1 includes an exposure system registration sensor Sp as an example of an exposure system position detection member disposed at a document reading position, and It has an exposure optical system A.

The movement and stop of the exposure optical system A are controlled by a detection signal of the exposure system registration sensor Sp, and are always stopped at a home position as an example of an image reading position, that is, an initial position.
In the case of an automatic document conveyance operation in which a document is automatically conveyed and copied using the automatic document conveyance device U2, the exposure optical system A is stopped at the home position, and the copy position on the platen glass PG. Each document Gi that sequentially passes through F1 is exposed.
In the case of a manual manual placement operation in which an operator places a document Gi on the platen glass PG by hand, the exposure optical system A exposes and scans the document on the platen glass PG while moving.
The exposed reflected light from the original document Gi passes through the exposure optical system A and is converged on the solid-state image sensor CCD. The solid-state imaging device CCD converts the document reflected light converged on the imaging surface into an electric signal.

Further, the image processing unit GS converts the read image signal input from the solid-state imaging device CCD of the image reading unit U1a into a digital image writing signal to convert the image writing light drive signal output device DL of the image recording unit U1b. Output to.
The image writing light driving signal output device DL outputs an image writing light driving signal corresponding to the input image data to an exposure device RS as an example of an image writing device.

  A photosensitive drum PR, which is an example of an image carrier disposed below the exposure apparatus RS, rotates in the direction of the arrow Ya. The surface of the photosensitive drum PR is charged by a charging roll CR as an example of a charger in a charging region Q0, and then laser as an example of latent image writing light of the exposure device RS at a latent image writing position Q1. Exposure scanning is performed with the beam L to form an electrostatic latent image. The surface of the photosensitive drum PR on which the electrostatic latent image is formed rotates and moves sequentially through a development area Q2 and a transfer area Q3 as an example of an image recording position.

A developing unit G that develops the electrostatic latent image in the developing area Q2 conveys a developer including toner and a carrier to the developing area Q2 by a developing roll R0 as an example of a developer holder, and the developing area Q2 is moved to the developing area Q2. The passing electrostatic latent image is developed into a toner image Tn as an example of an image. The toner image Tn on the surface of the photosensitive drum PR is conveyed to the transfer area Q3.
A cartridge K as an example of a developer supply container for supplying the developer consumed by the developing device G is detachably mounted on a cartridge mounting member KS as an example of a supply container mounting member. The developer in the cartridge K is conveyed while being stirred in the developer container RT, and is conveyed to the developing device G by the developer conveying device GH disposed in the developer container RT.

A transfer unit TU as an example of a transfer conveyance device disposed in the transfer region Q3 so as to face the photosensitive drum PR includes a transfer belt TB as an example of a medium conveyance member. The transfer belt TB is rotatably supported by a belt support roll Rd + Rf as an example of a medium transport member support system having a drive roll Rd as an example of a drive member and a driven roll Rf as an example of a driven member. A transfer roll TR, which is an example of a transfer unit, is disposed opposite the photoconductor drum PR with the transfer belt TB interposed therebetween. Further, a peeling claw SC as an example of a medium peeling member is disposed facing the drive roll Rd, and a belt cleaner CLb as an example of a medium transport member cleaner is disposed downstream of the peeling claw SC in the rotation direction of the transfer belt TB. Is arranged.
The transfer roll TR is a member that transfers the toner image Tn on the surface of the photosensitive drum PR onto a sheet S as an example of a medium, and has a transfer voltage having a polarity opposite to the charging polarity of the developing toner used in the developing device G. Supplied from the power supply circuit E. The power supply circuit E is controlled by a controller C as an example of a control unit.

  The sheet S accommodated in the sheet feed trays TR1 to TR4 as an example of the medium accommodation member is conveyed to the transfer region Q3 by the sheet supply path SH1 as an example of the conveyance path. That is, the sheets S of the respective paper feed trays TR1 to TR4 are taken out by a pick-up roll Rp as an example of a medium take-out member at a predetermined paper feed timing and separated one by one by a separating roll Rs as an example of a medium separating member. Then, it is transported by a transport roll Ra as an example of a plurality of medium transport members to a registration roll Rr as an example of a medium posture correction member and an example of a medium transport timing adjustment member.

The sheet S conveyed to the registration roll Rr is corrected in posture, and the toner image Tn on the photosensitive drum PR is moved to the transfer region Q3, that is, in accordance with the timing of the medium guide member before transfer. The sheet is conveyed from the pre-transfer sheet guide SG1 as an example to the transfer belt TB of the transfer unit TU. The transfer belt TB conveys the conveyed sheet S to the transfer area Q3.
The toner image Tn developed on the surface of the photosensitive drum PR is transferred to the sheet S by the transfer roll TR in the transfer region Q3. After the transfer, residual toner is removed from the surface of the photoreceptor drum PR by a photoreceptor cleaner CLp as an example of an image carrier cleaner, and the surface is recharged by the charging roll CR.

  The sheet S on which the toner image Tn has been transferred by the transfer roll TR in the transfer area Q3 is peeled from the surface of the transfer belt TB by the peeling claw SC on the downstream side of the transfer area Q3. The peeled sheet S is conveyed by an elastic sheet after the toner image Tn is heated and fixed by a fixing device F having a heating roll Fh as an example of a heat fixing member and a pressure roll Fp as an example of a pressure fixing member. The sheet passes through a mylar gate MG as an example of a path switching member and is conveyed to a transport roll Rb that can rotate forward and backward in a sheet discharge path SH2 as an example of a discharge path. The mylar gate MG is elastically deformed to direct the sheet S that has passed through the fixing device F toward the sheet discharge path SH2.

  The sheet S to be discharged to the paper discharge tray TRh is transported through a sheet discharge path SH2 in which a transport roll Rb capable of forward and reverse rotation and a plurality of transport rolls Ra are arranged. A switching gate GT1 as an example of a conveyance path switching member is disposed at the downstream end of the sheet discharge path SH2. When a post-processing device (not shown) is connected to the image forming apparatus, the switching gate GT1 is either a paper discharge tray TRh as an example of a medium discharge unit or a post-processing device (not shown). To be discharged. When the post-processing device is not mounted, the switching gate GT1 is switched so that the sheet S conveyed to the downstream end of the sheet discharge path SH2 is discharged to the discharge tray TRh. S is discharged to a discharge tray TRh by a discharge roll Rh as an example of a medium discharge member.

  When the image is recorded on both sides of the sheet S, the transport roll Rb capable of rotating in the forward and reverse directions is provided with the first side image when the first side image recorded sheet S on which the image is recorded on the first side is transported. The rear end of the recorded sheet S rotates reversely immediately before passing the transport roll Rb. Therefore, the first-surface image-recorded sheet S is returned to the sheet discharge path SH2 and is switched back. The mylar gate MG directs the sheet S switched back by the transport roll Rb to a sheet reversing path SH3 as an example of a reversing path. The sheet reversing path SH is connected to the upstream side in the medium transport direction of the registration roll Rr of the sheet supply path SH1, and the first-surface image recorded sheet S transported to the sheet reversing path SH3 is reversed in the state where the sheet is reversed. Retransmitted to the registration roll Rr. Then, in the same manner as when the image is recorded on the first surface, the registration roll Rr conveys the toner image Tn to the second surface of the first-surface image-recorded sheet S. .

FIG. 2 is an enlarged view of a main part of the sheet supply path of the first embodiment.
3A and 3B are explanatory views when the sheet passes through the sheet supply path of the first embodiment, FIG. 3A is an explanatory view seen from above, FIG. 3B is an explanatory view of the posture of the sheet detected by the sensor, and FIG. It is explanatory drawing of the detection signal of the sensor at the time of passing a detection area | region.
2 and 3, in the sheet supply path SH1 according to the first exemplary embodiment, a first sensor SN1 as an example of an attitude detection member that detects the attitude of the sheet S is provided upstream of the registration roll Rr in the medium conveyance direction. Has been placed.
The first sensor SN1 according to the first embodiment includes a pair of front and rear first front sensors SN1a and SN1b that are arranged side by side with a distance L1 in a direction orthogonal to the conveyance direction of the sheet S. ing.
In the first embodiment, the first front sensor SN1a and the first rear sensor SN1b are configured by so-called optical sensors. In the first detection region Q11, the presence of the sheet S and the difference in detection timing cause The posture of the sheet S is detected.

The sheet supply path SH1 is an example of a second attitude detection member that detects the attitude of the sheet S downstream of the registration roll Rr in the medium conveyance direction and upstream of the transfer area Q3 in the medium conveyance direction. 2nd sensor SN2 is arrange | positioned.
The second sensor SN2 is also configured in the same manner as the first sensor SN1, and a pair of front and rear second front sensors SN2a arranged in a direction perpendicular to the conveying direction of the sheet S with a distance L1 arranged therebetween. The second rear sensor SN2b is provided, and the posture of the sheet S is detected based on the presence / absence of the sheet S and the difference in detection timing in the second detection region Q12.

In the sheet supply path SH1, after the front end edge Sa as an example of the front end portion of the sheet S in the medium conveyance direction passes through the first detection region Q11, the pair of members of the registration roll Rr is opposed to the front end edge Sa of the sheet S. To reach the posture correction area Q13.
At this time, the driving of the registration roll Rr is temporarily stopped, and the front end edge Sa of the sheet S is abutted against the registration roll Rr and stops in the posture correction area Q13, while being driven upstream in the medium conveyance direction. The trailing end of the sheet S is continuously conveyed to the posture correction region Q13 side by the continuing conveyance roll Ra. As a result, the sheet S is curved by being pushed from the rear end side, and the posture is corrected so that the front end edge Sa is along the posture correction region Q13. That is, in the first exemplary embodiment, the registration roll Rr corrects the posture of the sheet S toward the reference posture in which the main scanning direction of the photosensitive drum PR and the front edge Sa of the sheet S are parallel to each other. The

At a preset time, the registration roll Rr resumes driving, and the sheet S reaches the transfer area Q3 after the front edge Sa passes through the second detection area Q12.
In the first exemplary embodiment, the axial direction of the registration roll Rr and the main scanning direction of the photosensitive drum PR are set in a direction perpendicular to the conveyance direction of the sheet S, and the posture correction area Q13 and the transfer area Q3 is set to be parallel.

(Description of the control part of Example 1)
FIG. 4 is a block diagram illustrating the functions of the controller of the image forming apparatus according to the first embodiment.
In FIG. 4, the controller C executes an input / output interface as an example of an input / output signal adjustment unit that performs input / output of an external signal and adjustment of an input / output signal level, so-called I / O, and necessary processing. A read-only memory, a so-called ROM, a random access memory for temporarily storing necessary data, a so-called RAM, and a process corresponding to the program stored in the ROM The computer is configured by a computer as an example of a computer having a central processing unit to be performed, a so-called CPU and a clock oscillator, and various functions can be realized by executing programs stored in the ROM.

(Signal output element connected to controller C)
The controller C receives an output signal of the next signal output element.
UI: operation instruction input unit The operation instruction input unit UI includes a copy start key UI1 as an example of a copy start button, a numeric keypad UI as an example of a numeric button, a copy number input key UI3 as an example of a copy number input button, and a display unit UI4, a sheet type input key UI5 as an example of a medium type input button, a duplex printing setting key UI6 as an example of a duplex printing setting button, and the like are detected. Input to controller C.
SN1: First sensor The first sensor SN1 detects the presence or absence of the sheet S by the first front sensor SN1a and the first rear sensor SN1b in the first detection region Q11, and inputs the detection signal to the controller C.
SN2: Second sensor The second sensor SN2 detects the presence or absence of the sheet S by the second front sensor SN2a and the second rear sensor SN2b in the second detection region Q12, and inputs the detection signal to the controller C.

(Controlled element connected to controller C)
The controller C outputs control signals for the following controlled elements D1, D2, E, and DL.
D1: Main motor drive circuit A main motor drive circuit D1 as an example of a main drive source drive circuit drives a main motor M1 as an example of a main drive source via a gear as an example of a drive force transmission member (not shown). The photosensitive drum PR, the separating roll Rs, the transporting rolls Ra and Rb, the developing roll R0 of the developing device G, the heating roll Fh of the fixing device F, and the like are driven to rotate.

D2: Registration Roll Drive Circuit The registration roll drive circuit D2 controls the operation of the registration roll drive motor M2 to rotationally drive the registration roll Rr.
DL: Image writing light driving signal output device The image writing light driving signal output device DL outputs an image writing light driving signal corresponding to the input image data to the exposure device RS.

E: Power Supply Circuit The power supply circuit E includes a development power supply circuit E1, a charging power supply circuit E2, a transfer roll power supply circuit E3, and a heating roll power supply circuit E4.
E1: Developing power circuit The developing power circuit E1 applies a developing voltage to the developing roll R0 of the developing device G.
E2: Charging power supply circuit The charging power supply circuit E2 applies a charging voltage to the charging roll CR.
E3: Transfer Roll Power Supply Circuit The transfer roll power supply circuit E3 applies a transfer voltage to the transfer roll TR.
E4: Heating Roll Power Supply Circuit The heating roll power supply circuit E4 applies heating power to a heater as an example of a heating member of the heating roll Fh of the fixing device F.

(Function of controller C)
The controller C has the following function realizing means by a program for controlling the operation of each controlled element in accordance with the operation instruction input unit UI, the output signals of the first sensor SN1 and the second sensor SN2. ing.
C1: Job control unit The job control unit C1 as an example of the image forming operation control unit performs operations of the exposure device RS, the charging roll CR, the transfer roll TR, the fixing device F, and the like according to the input of the copy start key UI1. Under control, a job as an example of an image forming operation is executed.

C2: Main motor rotation control means The main motor rotation control means C2 as an example of the main drive source control means controls the rotation of the main motor M1 via the main motor drive circuit D1, and the photosensitive drum PR and the developing device. The driving of the G developing roll R0, the heating roll Fh of the fixing device F, and the like are controlled.

C3: Power supply circuit control means The power supply circuit control means C3 controls the operation of the power supply circuit E, and the voltage and current to the developing roll R0, the charging roll CR, the transfer roll TR, the heater of the heating roll Fh of the fixing device F, etc. To control the supply.
C4: Registration Roll Rotation Control Unit A registration roll rotation control unit C4 as an example of a medium transport timing adjustment member control unit controls the rotation of the registration roll motor M2 via the registration roll driving circuit D2, thereby controlling the driving of the registration roll Rr. .
C5: Sheet Type Discriminating Unit The sheet type discriminating unit C5, which is an example of the medium type discriminating unit, discriminates the type of the sheet S that is conveyed and the image is recorded during the image forming operation.
The sheet type determination means C5 of Embodiment 1 determines the type of the sheet S as a type of the sheet S such as cardboard or plain paper, a medium standard such as A4LEF or B4SEF, and medium conveyance according to information input by the sheet type input key UI5. Determine the direction.
C6: Double-sided printing determination unit The double-sided printing determination unit C6 determines whether the job is a double-sided printing job according to the input information from the double-sided printing setting key UI6.

C7: Skew amount detecting means Skew amount detecting means C7 as an example of posture detecting means includes first sensor skew amount detecting means C7A and second sensor skew amount detecting means C7B, and the first sensor SN1, Based on the detection signal from the second sensor SN2, skew amounts S1 and S2 as an example of the posture of the sheet S are detected.
C7A: First sensor skew amount detection means The first sensor skew amount detection means C7A as an example of the first posture detection means detects the first skew amount S1 based on the detection signal of the first sensor SN1.
The first sensor skew amount detection unit C7A according to the first exemplary embodiment detects the first skew amount S1 based on a difference in detection timing of the presence or absence of the sheet S by the first front sensor SN1a and the first rear sensor SN1b.
Specifically, in FIG. 3B and FIG. 3C, the first sensor skew amount detection unit C7A according to the first exemplary embodiment changes from the no sheet state to the sheet present state by the first front sensor SN1a and the first rear sensor SN1b. When detected, the timing t1 when the detection signal of the first front sensor SN1a is switched, the timing t2 when the detection signal of the first rear sensor SN1b is switched, and the conveyance speed V1 of the sheet S determined based on the conveyance roll Ra, , The first skew amount S1 is detected as S1 = V1 × (t1−t2) / L1.

C7B: Second sensor skew amount detection means The second sensor skew amount detection means C7B as an example of the second posture detection means detects the second skew amount S2 of the sheet S based on the detection signal of the second sensor SN2. To do.
The second sensor skew amount detection means C7B of the first embodiment is based on the second front sensor SN2a and the second rear sensor SN2b of the second sensor SN2 in the same manner as the first sensor skew amount detection means C7A. The second skew amount S2 is detected.

FIG. 5 is an explanatory diagram of correspondence information according to the first embodiment.
C8: Correspondence information storage means Correspondence information storage means C8 is the difference between the detection result by the first sensor SN1 and the attitude of the sheet S after being corrected by the registration roll Rr corresponding to the detection result and the reference attitude. Corresponding information for specifying a relationship with a certain remaining amount S3, the correspondence information measured in advance for each type of sheet S is stored.
In the first embodiment, the reference posture corresponds to the posture of the sheet S with a skew amount of 0, and the correspondence information storage unit C8 of the first embodiment is a paper type such as cardboard or plain paper, a medium standard such as A4LEF or B4SEF, a medium For each type of sheet S such as the conveyance direction, correspondence information of the remaining amount S3 corresponding to the first skew amount S1 is stored.
Specifically, in FIG. 5, the correspondence information storage unit C8 according to the first embodiment includes a first skew amount S1 measured in advance by an experiment or the like when the integers m and n represent arbitrary integers of 1 or more, Coefficients a _mn and b _mn that are coefficients specifying the relationship with the remaining amount S3 are stored, and for each type of sheet S, a linear function of S3 = a _mn × S1 + b _mn is stored as correspondence information.

C9: Residual amount calculation means The residual amount calculation means C9 has correspondence information setting means C9A, and calculates the residual amount S3 after being corrected by the registration roll Rr based on the detection result by the first sensor SN1. .
Based on the first skew amount S1 as the detection result by the first sensor SN1, the residual amount calculation unit C9 of the first embodiment is based on a linear function of correspondence information set by the correspondence information setting unit C9A described later. The residual amount S3 is calculated by S3 = a _mn × S1 + b _mn .
C9A: Correspondence information setting means Correspondence information setting means C9A determines the sheet S from the correspondence information stored in the correspondence information storage means C8 based on the type of the sheet S determined by the sheet type determination means C5. A linear function used for calculation of the residual amount S3 is set by reading out a linear function of the coefficients a _mn and b _mn corresponding to the type.

C10: Deviation amount calculation means The deviation amount calculation means C10 as an example of the difference amount calculation means includes the residual amount S3 calculated by the residual amount calculation means C9, the detection result by the second sensor SN2, and the reference posture. A deviation amount ΔS as an example of a difference amount that is a difference between the detected residual amount S4 and the difference between the detected residual amounts S4 is calculated.
When the double-sided printing determining unit C6 determines that the double-sided printing is performed, the misalignment amount calculating unit C10 according to the first exemplary embodiment is configured such that the residual amount S3, the second skew amount S2 as the detection result by the second sensor SN2, and the A deviation amount ΔS which is a difference between the detection residual amount S4 which is a difference from the reference posture is calculated.
Specifically, in the first embodiment, the reference posture is set as the posture of the sheet S with the skew amount of 0, and the detected residual amount S4 is equal to the second skew amount S2, and S4 = S2. Then, in the case of double-sided printing, the deviation amount calculation means C10 calculates a deviation amount ΔS that is the difference between the detected residual amount S4 and the residual amount S3 as ΔS = S3−S4.

6 is an explanatory diagram of a sheet and an image to be recorded in the transfer area according to the first exemplary embodiment. FIG. 6A is an explanatory diagram when an image having a linear portion in the main scanning direction is recorded on a sheet in a reference posture. FIG. 6C is an explanatory diagram when an image having a linear portion in the main scanning direction is rotated and recorded on a skewed sheet based on the remaining amount, and FIG. 6C is an explanatory diagram in the case of duplex printing, and the second surface of the skewed sheet FIG. 6 is an explanatory diagram when an image having a linear portion in the main scanning direction is rotated and recorded based on the remaining amount and the deviation amount.
In FIG. 6 and subsequent figures, in order to facilitate understanding of the operation of the present invention, the angles θ2, θ3, etc. based on the second skew amount S2 and the residual amount S3 are shown as relatively large angles. The second skew amount S2 and the remaining amount S3 are values of about 3 mm / 200 mm or less, and the angles θ2, θ3, etc. based on the second skew amount S2 and the remaining amount S3 are minute angles.

C11: Image Rotating Unit The image rotating unit C11 includes a first surface image rotating unit C11A and a second surface image rotating unit C11A, and is formed on the sheet S based on the residual amount S3 and the deviation amount ΔS. Rotate the image.
C11A: First surface image rotating unit The first surface image rotating unit C11A rotates an image formed on the sheet S based on the remaining amount S3.
In the first surface image rotating means C11A of Embodiment 1, for example, a latent image having a linear portion in the main scanning direction is formed on the photosensitive drum PR, and as shown in FIG. 6A, in the width direction of the sheet S in the reference posture. In the case of a document image on which an image 2 having a straight line portion 1 is recorded, when an image is recorded on a sheet S inclined with respect to a reference posture, that is, a sheet S with a skew remaining, an angle θ3 based on the residual amount S3. The original image is rotated by the minute.
As a result, a rotated latent image is formed on the photosensitive drum PR, and as shown in FIG. 6B, the skewed sheet S has a linear portion 1 along the width direction of the skewed sheet S. Image 2 is recorded.

C11B: Second surface image rotating means The second surface image rotating means C11B is the first sensor for the sheet S that has passed through the sheet reversing path SH3 and has been retransmitted to the first detection region Q11 of the first sensor SN1. The image formed on the second surface of the sheet S is rotated based on the residual amount S3 ′ calculated based on the detection result of SN1 and the deviation amount ΔS.
The second surface image rotation means C11B according to the first embodiment is based on the remaining amount S3 in a state where the skew remains by an angle θ2 corresponding to the skew amount S2 detected by the second sensor SN2 as shown in FIG. 6B, for example. When the linear image 3 is recorded on the first surface of the sheet S, when the image is recorded on the second surface, the angle θ3 ′ based on the residual amount S3 ′ and the angle Δθ based on the deviation amount ΔS , The latent image formed on the photosensitive drum PR is rotated.
As a result, a rotated latent image is formed on the photosensitive drum PR, and as shown in FIG. 6C, when the image is recorded on the second surface, an angle from the main scanning direction with respect to the sheet S on which the skew remains. The image 3 rotated by (θ3′−Δθ) is recorded.

FIG. 7 is an explanatory diagram of history correspondence information according to the first embodiment. FIG. 7A is a correspondence diagram between the first skew amount and the detected residual amount. FIG. 7B is the first skew amount on the horizontal axis and the detected residual amount on the vertical axis. FIG.
C12: Corresponding Information Updating Unit The corresponding information updating unit C12 includes a skew amount history information storage unit C12A, a skew amount history information updating unit C12B, and a correspondence information calculating unit C12C, and the detection result by the first sensor SN1. Further, the correspondence information stored in the correspondence information storage means C8 is updated based on the correspondence information in which the detection residual amount S4 that is the difference between the detection result by the second sensor SN2 and the reference posture is associated.
The correspondence information updating unit C12 according to the first embodiment updates the correspondence information based on the calculation result by the correspondence information calculation unit C12C described later.

C12A: Skew amount history information storage unit The skew amount history information storage unit C12A as an example of the remaining amount history information storage unit is set by the second sensor SN2 to the first skew amount S1 as the detection result by the first sensor SN1. The history correspondence information (S1; S4) that associates the detection residual amount S4 that is the difference between the second skew amount S2 as the detection result and the reference posture is stored for each type of the sheet S.
As shown in FIG. 7A, the skew amount history information storage unit C12A according to the first exemplary embodiment is corrected by the first skew amount S1 before the posture is corrected by the registration roll Rr and the registration roll Rr for each type of the sheet S. A predetermined number j of history correspondence information (S1; S4) = (S1 ₁ , S1 ₂ , S1 ₃ ,..., S1 _j ; S4 ₁ , S4 ₂ , S4 ₃ ,..., S4 _j ) are stored.
In the skew amount history information storage unit C12A according to the first embodiment, a plurality of history correspondence information (S1; S4) satisfying the linear expression stored in the correspondence information storage unit C8 is used as temporary information, so-called dummy information. The history correspondence information (S1; S4) is stored, but the first skew amount S1 and the detected residual amount S4 corresponding to the first skew amount S1 can be measured and stored in advance.

C12B: Skew amount history information updating unit The skew amount history information updating unit C12B as an example of the remaining amount history information updating unit uses the history correspondence information (S1; S4) stored in the skew amount history information storage unit C12A as a sheet. Update for each type of S.
The skew amount history information updating unit C12B according to the first exemplary embodiment includes the first skew amount S1 based on the detection result of the first sensor SN1 and the detection residual based on the detection result of the second sensor SN2 every time an image is recorded on the sheet S. Based on the amount S4, the history correspondence information (S1; S4) corresponding to the type of the sheet S stored in the skew amount history information storage means C12A is updated.
In the skew amount history information updating unit C12B according to the first embodiment, the oldest history correspondence information (S1; S4) is deleted from the plurality of history correspondence information (S1; S4), and the latest history correspondence information (S1) is deleted. Update by registering S4).

C12C: Correspondence Information Calculation Unit The correspondence information calculation unit C12C calculates the correspondence information stored in the correspondence information storage unit C8 based on the history correspondence information (S1; S4) stored in the skew amount history information storage unit C12A. To do.
In FIG. 7B, the correspondence information calculation unit according to the first embodiment satisfies S4 = a _mn × S1 + b _mn for the history correspondence information (S1; S4) stored in the skew amount history information storage unit C12A by the least square method. The coefficients a _mn and b _mn are calculated.
Therefore, the linear functions of the coefficients a _mn and b _mn of the correspondence information stored in the correspondence information storage unit C8 are updated to the linear functions of the coefficients a _mn and b _mn calculated by the response information calculation unit C12C.
In the first embodiment, every time the history correspondence information (S1; S4) of the skew amount history information storage unit C12A is updated, the coefficients a _mn and b _mn are calculated by the correspondence information calculation unit C12C. It is possible to employ a configuration in which calculation and updating are performed at an arbitrary time such as a preset time, for example, every preset number of recorded images, for example, every 100,000 images, or when the power is turned on.

(Description of Flowchart of Example 1)
Next, the process flow of the copying machine U according to the first embodiment of the present invention will be described with reference to a flowchart, a so-called flowchart.
(Description of Flowchart of Recording Position Correction Processing in Embodiment 1)
FIG. 8 is a flowchart of the recording position correction process according to the first embodiment of the present invention.
FIG. 9 is a flowchart of the recording position correction process according to the first embodiment of the present invention, and is a flowchart continued from FIG.
The processing of each step ST in the flowcharts of FIGS. 8 and 9 is performed according to a program stored in the controller C of the copying machine U. This process is executed in parallel with other various processes of the copying machine U in parallel.
The flowcharts shown in FIGS. 8 and 9 are started when the power of the copying machine U is turned on.

In ST1 of FIG. 8, it is determined whether or not the job is started. If yes (Y), the process proceeds to ST2, and if no (N), ST1 is repeated.
In ST2, the type of the set sheet S is determined, and the process proceeds to ST3.
In ST3, correspondence information corresponding to the type of sheet S is set, and the process proceeds to ST4.
In ST4, it is determined whether or not the first skew amount S1 based on the detection result of the first sensor SN1 is detected. If yes (Y), the process proceeds to ST5, and, if no (N), ST4 is repeated.
In ST5, a residual amount S3 corresponding to the skew amount S1 is calculated based on the linear function of the correspondence information, and the process proceeds to ST6.

In ST6, the original image is rotated based on the remaining amount S3, and the process proceeds to ST7.
In ST7, it is determined whether or not the second skew amount S2 based on the detection result of the second sensor SN2 is detected. If yes (Y), the process proceeds to ST8, and, if no (N), ST7 is repeated.
In ST8, the correspondence history information (S1; S4) of the first skew amount S1 and the detected residual amount S4 based on the second skew amount S2 is updated, and the process proceeds to ST9.
In ST9, a linear function of the correspondence information is calculated based on the correspondence history information (S1; S4), and the process proceeds to ST10.
In ST10, the linear function of the correspondence information is updated, and the process proceeds to ST11.

In ST11 of FIG. 9, it is determined whether or not double-sided printing is performed. If yes (Y), the process proceeds to ST12, and, if no (N), the process proceeds to ST20.
In ST12, a deviation amount ΔS is calculated based on the remaining amount S3 and the detected residual amount S4, and the process proceeds to ST13.
In ST13, it is determined whether or not the first skew amount S1 based on the detection result of the first sensor SN1 is detected. If yes (Y), the process proceeds to ST14, and, if no (N), ST13 is repeated.
In ST14, a residual amount S3 ′ corresponding to the first skew amount S1 is calculated based on the linear function of the correspondence information, and the process proceeds to ST15.
In ST15, the original image is rotated based on the remaining amount S3 ′ and the deviation amount ΔS, and the process proceeds to ST16.

In ST16, it is determined whether or not the second skew amount S2 based on the detection result of the second sensor SN2 is detected. If yes (Y), the process proceeds to ST17, and, if no (N), ST16 is repeated.
In ST17, the correspondence history information (S1; S4) of the first skew amount S1 and the detected residual amount S4 based on the second skew amount S2 is updated, and the process proceeds to ST18.
In ST18, a linear function of the correspondence information is calculated based on the correspondence history information (S1; S4), and the process proceeds to ST19.
In ST19, the linear function of the correspondence information is updated, and the process proceeds to ST20.
In ST20, it is determined whether or not the job is finished. If yes (Y), the process returns to ST1 in FIG. 8, and if no (N), the process returns to ST4.

(Operation of Example 1)
In the copying machine U according to the first embodiment having the above-described configuration, when a job as an example of an image forming operation is executed, a type of sheet S according to a user setting is fed from the sheet feeding trays TR1 to TR4. The The sheet S is conveyed through the sheet supply path SH1, an image is recorded in the transfer area Q3, and is discharged to the paper discharge tray TRh. In the case of double-sided printing, after the image is recorded on the first surface, the sheet S is conveyed through the sheet reversing path SH3 and retransmitted to the transfer area Q3 with the front and back sides reversed. In the same manner as the first surface, an image is recorded on the second surface of the sheet S and is discharged to the paper discharge tray TRh.

FIG. 10 is an explanatory diagram when an image is recorded on the first surface of the sheet, FIG. 10A is an explanatory diagram when an image is recorded on a skewed sheet of Example 1, and FIG. 10B is a configuration in which the image is not rotated. 6 is an explanatory diagram when an image is recorded on a sheet skewed in FIG.
In the copying machine U of Embodiment 1, the image S is recorded in the transfer area Q3 after the posture of the sheet S conveyed through the sheet supply path SH1 is corrected toward the reference posture by the registration roll Rr. At this time, the first skew amount S1 is detected based on the front edge Sa of the sheet S in the first detection region Q11 by ST3 to ST5 of the recording position correction process, and the transfer region Q3 based on the skew amount S1. A residual amount S3, which is a skew amount that is predicted to remain without being corrected, is calculated. In ST6 of the recording position correction process, the image based on the document information is rotated by an angle θ3 corresponding to the remaining amount S3. Then, based on the rotated image, a latent image is formed on the photosensitive drum PR, and as shown in FIG. 10A, the image 11 is recorded on the sheet S in which the skew remains in the transfer region Q3.

Here, in the conventional configuration in which the image based on the document information is not rotated, the orientation cannot be corrected by the registration roll Rr, and the skew remains on the sheet S corresponding to the reference orientation in the transfer region Q3. An image is recorded, and an image 12 inclined relative to the sheet S is recorded as shown in FIG. 10B.
On the other hand, in the first embodiment, the posture of the sheet S that cannot be corrected by the registration roll Rr is calculated as the remaining amount S3, and the image 11 is rotated by rotating the image based on the document information based on the remaining amount S3. As shown in FIG. 10A, an image 11 having a relatively reduced inclination with respect to the sheet S with the skew remaining is recorded, and the positional deviation of the image is reduced compared to a configuration in which the image is not rotated. Has been.

Further, when the image is rotated, the detection result of the sheet S after correction by the detection member provided on the downstream side in the medium transport direction from the registration roll Rr as the posture correction member, as in the past, When the image is rotated based on the two skew amount S2 or the like, the time from the detection of the posture to the recording of the image is the same as that in the first embodiment after detecting the posture of the sheet S before correction. Compared to the case where processing is performed, it becomes shorter.
That is, in a configuration in which image rotation processing, latent image formation processing, and the like are executed after correcting the posture of the sheet S, the arrival of the sheet S occurs when the image on the surface of the photosensitive drum PR reaches the transfer region Q3. In order to match the timings to be performed, it is necessary to delay the arrival timing of the sheet S to the transfer region Q3. Therefore, it is necessary to reduce the conveyance speed of the sheet S from the registration roll Rr to the transfer area Q3 or to increase the conveyance distance from the registration roll Rr to the transfer area Q3, and the productivity as the number of printed sheets per unit time is reduced. Or the copying machine U becomes larger.

  On the other hand, in the first embodiment, the image is rotated by predicting and estimating the residual amount S3 after the posture correction based on the posture of the sheet S before the posture is corrected by the registration roll Rr, and the posture is corrected. Compared to the configuration based on the posture of the sheet S after the reduction, the productivity and the enlargement of the copying machine U are reduced, and the correction accuracy of the posture of the sheet S in the transfer region Q3 by the registration roll Rr is also deteriorated. Has been reduced.

FIG. 11 is an explanatory diagram in the case of double-sided printing, FIG. 11A is an explanatory diagram when an image is recorded on the first surface of a sheet with skew left, and FIG. 11B is a second surface of a sheet with skew left. FIG. 11C is an explanatory diagram when an image rotated based on the remaining amount and the deviation amount is recorded. FIG. 11C shows an image rotated based only on the residual amount on the second surface of the skewed sheet. It is explanatory drawing in the case.
In the case of duplex printing, the sheet S on which the image is recorded on the first side is reversed on the sheet reversing path SH3 and retransmitted to the first detection area Q11. Then, an image is recorded on the second surface in the same manner as the first surface.
At this time, in the copying machine U according to the first embodiment, the detection based on the second skew amount S2 of the post-posture correction sheet S detected when the image is recorded on the first surface in ST12 of the recording position correction process. A deviation amount ΔS is calculated based on the remaining amount S4 and the remaining amount S3 when an image is recorded on the first surface. When the image is recorded on the second surface, the remaining amount S3 ′ of the second surface calculated in the same manner as the first surface by ST13 to ST15 of the recording position correction process, and the image on the second surface. Based on the shift amount ΔS calculated at the time of recording, the image 13 is recorded as shown in FIG. 11B.

Here, the remaining amount S3 is a value calculated based on a linear function of the correspondence information from the first skew amount S1 before posture correction, and the actual skew amount after posture correction due to individual differences of the sheet S and the like. May be different.
That is, when an image is recorded on the first surface, the angle θ2 based on the second skew amount S2 as the actual skew amount after posture correction may be different from the angle θ3 based on the residual amount S3. When an image rotated based on the remaining amount S3 is recorded on the sheet S where the skew remains, the image 11 is inclined with respect to the sheet S by an angle Δθ based on the deviation amount ΔS as shown in FIG. 11A. May be recorded.

Therefore, when an image is recorded on the second surface which is the back surface of the sheet S on which the image inclined by the amount of deviation ΔS is recorded on the first surface, the recording position correction process ST6 is performed as in the first surface. 11C, the inclination of the image 14 with respect to the sheet S is reduced as shown in FIG. 11C. However, there is a case where the deviation from the image 11 on the first surface remains by the deviation amount ΔS. is there.
On the other hand, in the first embodiment, when an image is recorded on the second surface, the image is rotated and recorded based on the residual amount S3 ′ when recording on the second surface and the shift amount ΔS. In addition, the inclination of the image 13 with respect to the sheet S is reduced, and the deviation between the front and back surfaces of the first surface and the second surface is reduced as compared with the case based only on the residual amount S3 ′.

In the copying machine U according to the first embodiment, when calculating the remaining amounts S3 and S3 ′, the remaining amounts S3 and S3 ′ are calculated based on the correspondence information set for each type of the sheet S. Compared to the case where the sheet S is not based on the type, the difference between the calculated residual amounts S3 and S3 ′ and the detected residual amount S4 based on the second skew amount S2 after the posture correction is reduced, and image recording is performed. The positional deviation is reduced.
In the copying machine U according to the first embodiment, the remaining detection amount S4 based on the first skew amount S1 before posture correction and the second skew amount S2 after posture correction is performed by ST8 to ST10 and ST17 to ST19 of the recording position correction process. Based on the above, the correspondence information between the first skew amount S1 and the remaining amounts S3, S3 ′ is updated.
Therefore, in the copying machine U according to the first embodiment, even when the correction ability of the sheet S by the registration roll Rr is changed due to a change over time, the remaining amounts S3 and S3 ′ based on the corresponding information corresponding to the change over time Compared to a configuration in which the image is rotated and the correspondence information is not updated, the positional deviation of the image due to a change with time is reduced.

Next, a second embodiment of the present invention will be described. In the description of the second embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. To do.
This embodiment is different from the first embodiment in the following points, but is configured in the same manner as the first embodiment in other points.
In the second embodiment, after the front edge Sa of the sheet S reaches the registration roll Rr in the sheet supply path SH1 and the posture of the sheet S is corrected, the rear edge Sb of the sheet S passes through the first detection region Q11. The position of the first detection region Q11 is set so as to pass.
That is, in the first detection region Q11 of the second embodiment, the first sensor SN1 as an example of the posture detection member that also serves as the rear edge posture detection member, and the front edge Sa of the sheet S before posture correction and the posture correction after The presence or absence of passage of the sheet S and the trailing edge Sb of the sheet S can be detected, and the posture of the sheet S can be detected.

(Description of Control Unit of Example 2)
FIG. 12 is a block diagram illustrating the functions of the controller of the image forming apparatus according to the second embodiment, and corresponds to FIG. 4 according to the first embodiment.
The control unit C ″ of the second embodiment replaces the first sensor skew amount detection means C7A, the deviation amount calculation means C10, and the second surface image rotation means C11B of the first embodiment with a first sensor skew amount detection means. C7A ″, displacement amount calculation means C10 ″, and second surface image rotation means C11B ″.
Further, the rear end detection correspondence information storage unit C8 ″ and the rear end detection residual amount calculation unit C9 ″ are added to the control unit C ″ of the second embodiment.

C7A ″: first sensor skew amount detection means The first sensor skew amount detection means C7A ″ of the second embodiment is based on the detection signal of the first sensor SN1 and the first skew amount S1 and the rear end first skew amount. S1 ″ is detected.
That is, in the first sensor skew amount detection unit C7A ″ of the second embodiment, the first skew amount S1 is detected based on the passage of the front edge Sa of the sheet S, similarly to the first sensor skew amount detection unit C7A of the first embodiment. At the same time, when the first front sensor SN1a and the first rear sensor SN1b detect the sheet absence state from the sheet presence state, the rear end first skew amount S1 ″ is detected.
Therefore, in the first sensor skew amount detection means C7 ″ of the second embodiment, the first skew amount S1 based on the front edge Sa is detected based on the detection signal for switching from the no sheet state to the sheet present state, and the sheet exists. Based on the detection signal for switching from the state of 1 to the state of no sheet, the trailing edge first skew amount S1 ″ based on the trailing edge Sb as an example of the trailing edge of the sheet S in the medium conveyance direction is detected.

C8 ″: rear end detection correspondence information storage means The rear end detection correspondence information storage means C8 ″ is a detection result of the sheet S by the first sensor SN1, the posture of the sheet S after being corrected by the registration roll Rr, and the The rear end detection correspondence information specifying the relationship between the rear end detection residual amount S4 ″, which is a difference from the reference posture, and the rear end detection correspondence information measured in advance for each type of the sheet S is stored.
The rear end detection correspondence information storage unit C8 ″ of the second embodiment replaces the correspondence information specifying the relationship between the first skew amount S1 and the remaining amount S3, and uses the first sensor SN1 as the detection result of the sheet S. Except for storing rear end detection correspondence information for specifying the relationship between the end first skew amount S1 ″ and the rear end detection residual amount S4 ″, the detailed configuration is the same as the correspondence information storage means C8. Description is omitted.

C9 ″: Rear end detection residual amount calculation means The rear end detection residual amount calculation means C9 ″ includes rear end detection correspondence information setting means C9A ″, and detects the rear end based on the detection result by the first sensor SN1. The remaining amount S4 ″ is calculated.
The rear end detection residual amount calculating unit C9 ″ of the second embodiment is configured to use the rear end detection correspondence information set by the rear end detection correspondence information setting unit C9A ″ and the rear end detection result of the rear end by the first sensor SN1. Since it is the same as the remaining amount calculating means C9 except that the rear end detected residual amount S4 "is calculated based on the end first skew amount S1", detailed description thereof will be omitted.

C10 ″: Deviation amount calculation means The deviation amount calculation means C10 ″ as an example of the difference amount calculation means of the second embodiment includes the residual amount S3 calculated by the residual amount calculation means C9 and the rear end detection residual amount calculation. A deviation amount ΔS ″ as an example of a difference amount that is a difference between the rear end detection residual amount S4 ″ calculated by the means C9 ″ is calculated.
The deviation amount calculation means C10 ″ of the second embodiment is a deviation amount ΔS that is a difference between the remaining amount S3 and the rear end detection residual amount S4 ″ when the duplex printing discrimination means C6 determines that the printing is duplex printing. ″ Is calculated as ΔS ″ = S3−S4 ″.

C11B ″: Second surface image rotating unit The second surface image rotating unit C11B ″ of the second embodiment passes through the sheet reversing path SH3 and is retransmitted to the first detection region Q11 of the first sensor SN1. The image formed on the second surface of the sheet S is rotated based on the residual amount S3 ′ calculated based on the detection result of the first sensor SN1 and the deviation amount ΔS ″.
The second surface image rotating means C11B ″ according to the second embodiment is the second surface image rotating means C11B according to the first embodiment, except that the image is rotated based on the displacement amount ΔS ″ instead of the displacement amount ΔS ″ according to the first embodiment. The detailed description thereof will be omitted.

(Explanation of flowchart of embodiment 2)
Next, the process flow of the copying machine U according to the second embodiment of the present invention will be described with reference to a flowchart, a so-called flowchart.
(Description of Flowchart of Recording Position Correction Process of Example 2)
FIG. 13 is a flowchart of the recording position correction process according to the second embodiment of the present invention, and corresponds to FIG. 8 according to the first embodiment.
FIG. 14 is a flowchart of the recording position correction process according to the second embodiment of the present invention, which is a continuation flowchart of FIG. 13 and corresponding to FIG. 9 according to the first embodiment.
In the flowchart of the second embodiment, ST3 ″, ST12 ″, and ST15 ″ are executed instead of ST3, ST12, and ST15 of the first embodiment. Also, in the flowchart of the second embodiment, between ST11 and ST12 ″, ST21 and ST22 are executed.
Next, the flowchart of the second embodiment will be described, but the description of the same processing as that of the first embodiment will be omitted, and only ST3 ″, ST21, ST22, ST12 ″, ST15 ″ will be described.

In ST3 ″ in FIG. 13, the following processes (1) and (2) are executed and the process proceeds to ST4. (1) Correspondence information corresponding to the type of sheet S is set.
(2) The rear end detection correspondence information corresponding to the type of the sheet S is set.
In ST21 of FIG. 14, it is determined whether or not the rear end first skew amount S1 ″ based on the detection result of the first sensor SN1 has been detected. If yes (Y), the process proceeds to ST22, and no (N). Repeats ST21.
In ST22, based on the linear function of the rear end detection correspondence information, a rear end detection residual amount S4 ″ corresponding to the rear end first skew amount S1 ″ is calculated, and the process proceeds to ST12 ″.
In ST12 ″, a deviation amount ΔS ″ is calculated based on the remaining amount S3 and the rear end detected residual amount S4 ″, and the process proceeds to ST13.
In ST15 ″, the document image is rotated based on the remaining amount S3 ′ and the deviation amount ΔS ″, and the process proceeds to ST16.

(Operation of Example 2)
FIG. 15 is an explanatory diagram when an image is recorded in the copying machine according to the second embodiment. FIG. 15A is an explanatory diagram when an image is recorded on the first surface of a sheet with a skew remaining, and FIG. FIG. 10 is an explanatory diagram when an image rotated based on a remaining amount and a deviation amount is recorded on a second surface of a sheet in which skew remains in printing.
In the copying machine U according to the second embodiment having the above-described configuration, the image is rotated based on the remaining amount S3, and the image is recorded on the first surface of the sheet S as shown in FIG. 15A. The image is rotated based on the residual amount S3 ′ and the shift amount ΔS ″ replaced with the shift amount ΔS of the first embodiment, and an image is recorded on the second surface as shown in FIG. 15B. Similarly, image misalignment is reduced.
In double-sided printing, the shift amount ΔS of the transfer region Q3 is calculated based on the first sensor SN1 and the second sensor SN2 in the first embodiment, but in the second embodiment, the shift amount ΔS of the transfer region Q3 is calculated. "" Is calculated based on the detection result of only the first sensor SN1.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is made in the range of the summary of this invention described in the claim. Is possible. Modification examples (H01) to (H09) of the present invention are exemplified below.
(H01) In each of the above-described embodiments, the copying machine U is illustrated as an example of the image forming apparatus. However, the present invention is not limited to this, and can be applied to a printer, a FAX, or a multifunction machine having a plurality of these functions. Further, the image forming apparatus is not limited to an electrophotographic image forming apparatus, and can be applied to an image forming apparatus of an arbitrary image forming system such as an ink jet recording system, a thermal head system, or a printing machine such as a lithograph. Further, the image forming apparatus is not limited to a single-color developing image forming apparatus, and can be configured by a multi-color, so-called color image forming apparatus.

(H02) In each of the above embodiments, when calculating the residual amounts S3 and S3 ′ from the first skew amount S1 and calculating the rear end detected residual amount S4 ″ from the rear end first skew amount S1 ″, Although the structure which calculates based on the correspondence information as a primary expression and the rear end detection correspondence information as a primary expression was illustrated, it is not limited to this. For example, a list of remaining amounts S3 and S3 ′ corresponding to the first skew amount S1, correspondence information constituted by a so-called lookup table, and a rear end detected residual amount S4 corresponding to the rear end first skew amount S1 ″. A configuration is also possible in which calculation is performed based on rear end detection correspondence information constituted by a look-up table corresponding to "".
Further, in each of the embodiments, the correspondence information and the rear end detection correspondence information can adopt not a linear expression but a multi-order expression or an arbitrary function according to a measurement result.
(H03) In each of the above embodiments, in the case of duplex printing, when an image is recorded on the second surface, the image is rotated and recorded based on the residual amount S3 ′ and the deviation amounts ΔS, ΔS ″. Although a configuration that reduces the positional deviation between the front and back images is desirable, a configuration in which an image is rotated and recorded based only on the remaining amount S3 ′ is also possible, as in the first surface.

(H04) In each of the above-described embodiments, the first sensor SN1 includes a pair of front and rear optical sensors including the first front sensor SN1a and the first rear sensor SN1b, and the second sensor SN2 includes the second front sensor SN2a. Although it was constituted by a pair of front and rear optical sensors by the second rear sensor SN2b, it is not limited to this, for example, by a so-called line sensor in which detectors are arranged side by side on the line, the first sensor SN1, It is also possible to configure the second sensor SN2.
(H05) In each of the above embodiments, the configuration in which the front end of the sheet S is abutted against the registration roll Rr as an example of the attitude correction member to correct the attitude of the sheet S is illustrated, but the present invention is not limited to this. For example, a configuration using a side guide as an example of an attitude correction member that corrects the attitude by aligning the width direction of the sheet S is also possible.
(H06) In each of the above embodiments, the correspondence information stored in the correspondence information storage means C8 is preferably updated, that is, a configuration having a learning function, but a configuration not updated is also possible. In this case, in the second embodiment, the second sensor SN2 can be omitted.

(H07) In the second embodiment, the rear end detection correspondence information stored in the rear end detection correspondence information storage unit C8 ″ is also updated in the same manner as the correspondence information stored in the correspondence information storage unit C8. Is also possible.
(H08) In the second embodiment, the rear end detection residual amount S4 ″ is preferably predicted and calculated based on the rear end first skew amount S1 ″. However, the rear end first skew amount S1 ″ is determined as the rear end. It is also possible to adopt a configuration in which each process is performed with S1 ″ = S4 ″, which is regarded as the detection residual amount S4 ″.
(H09) In each of the above embodiments, the skew amounts S1, S1 ″, S2, the remaining amounts S3, S3 ′, and the rear end detected residual amounts S4, S4 ″ are exemplified by the tangent, so-called tangent configuration. However, any function based on the angle as the attitude of the medium can be applied.

(H010) In each of the above embodiments, the configuration in which the posture of the sheet S after the posture is corrected by the registration roll Rr is detected by the second sensor SN2 installed on the upstream side in the medium conveyance direction of the transfer region Q3. A configuration is also possible in which the second sensor SN2 is installed downstream of the transfer region Q3 in the medium conveyance direction, and the posture of the sheet S after the posture is corrected by the registration roll Rr is detected.
(H011) In the second embodiment, the first sensor SN1 upstream of the registration roll Rr in the medium conveyance direction detects the trailing edge Sb, and detects the attitude of the sheet S after the attitude is corrected by the registration roll Rr. Although the configuration is desirable, a configuration in which a rear end posture detection member is provided separately from the first sensor SN1, the rear end edge Sb is detected, and the posture of the sheet S after the posture is corrected by the registration roll Rr is also detected. Is possible.
(H012) In each of the above embodiments, the first sensor SN1 upstream of the registration roll Rr in the medium conveyance direction detects the posture based on the front edge Sa of the sheet S before posture correction, and calculates the remaining amounts S3 and S3 ′. However, based on the trailing edge Sb of the sheet S before posture correction,
A configuration for detecting the posture is also possible. In this case, the first sensor SN1 is further upstream than the first embodiment and the like, and the position at which the rear edge Sb of the sheet S can be detected before the front edge Sa of the sheet S enters the registration roll Rr. Placed in.

FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the sheet supply path of the first embodiment. 3A and 3B are explanatory views when the sheet passes through the sheet supply path of the first embodiment, FIG. 3A is an explanatory view seen from above, FIG. 3B is an explanatory view of the posture of the sheet detected by the sensor, and FIG. It is explanatory drawing of the detection signal of the sensor at the time of passing a detection area | region. FIG. 4 is a block diagram illustrating the functions of the controller of the image forming apparatus according to the first embodiment. FIG. 5 is an explanatory diagram of correspondence information according to the first embodiment. 6 is an explanatory diagram of a sheet and an image to be recorded in the transfer area according to the first exemplary embodiment. FIG. 6A is an explanatory diagram when an image having a linear portion in the main scanning direction is recorded on a sheet in a reference posture. FIG. 6C is an explanatory diagram when an image having a linear portion in the main scanning direction is rotated and recorded on a skewed sheet based on the remaining amount, and FIG. 6C is an explanatory diagram in the case of duplex printing, and the second surface of the skewed sheet FIG. 6 is an explanatory diagram when an image having a linear portion in the main scanning direction is rotated and recorded based on the remaining amount and the deviation amount. FIG. 7 is an explanatory diagram of history correspondence information according to the first embodiment. FIG. 7A is a correspondence diagram between the first skew amount and the detected residual amount. FIG. 7B is the first skew amount on the horizontal axis and the detected residual amount on the vertical axis. FIG. FIG. 8 is a flowchart of the recording position correction process according to the first embodiment of the present invention. FIG. 9 is a flowchart of the recording position correction process according to the first embodiment of the present invention, and is a flowchart continued from FIG. FIG. 10 is an explanatory diagram when an image is recorded on the first surface of the sheet, FIG. 10A is an explanatory diagram when an image is recorded on a skewed sheet of Example 1, and FIG. 10B is a configuration in which the image is not rotated. 6 is an explanatory diagram when an image is recorded on a sheet skewed in FIG. FIG. 11 is an explanatory diagram in the case of double-sided printing, FIG. 11A is an explanatory diagram when an image is recorded on the first surface of a sheet with skew left, and FIG. 11B is a second surface of a sheet with skew left. FIG. 11C is an explanatory diagram when an image rotated based on the remaining amount and the deviation amount is recorded. FIG. 11C shows an image rotated based only on the residual amount on the second surface of the skewed sheet. It is explanatory drawing in the case. FIG. 12 is a block diagram illustrating the functions of the controller of the image forming apparatus according to the second embodiment, and corresponds to FIG. 4 according to the first embodiment. FIG. 13 is a flowchart of the recording position correction process according to the second embodiment of the present invention, and corresponds to FIG. 8 according to the first embodiment. FIG. 14 is a flowchart of the recording position correction process according to the second embodiment of the present invention, which is a continuation flowchart of FIG. 13 and corresponding to FIG. 9 according to the first embodiment. FIG. 15 is an explanatory diagram when an image is recorded in the copying machine according to the second embodiment. FIG. 15A is an explanatory diagram when an image is recorded on the first surface of a sheet with a skew remaining, and FIG. FIG. 10 is an explanatory diagram when an image rotated based on a remaining amount and a deviation amount is recorded on a second surface of a sheet in which skew remains in printing.

Explanation of symbols

C5: Medium type discrimination means,
C8 ... correspondence information storage means,
C9: Residual amount calculation means,
C9 ″: rear end detection residual amount calculating means,
C10, C10 ″... Difference amount calculation means,
C11: Image rotating means,
C12 ... correspondence information update means,
Q3: Image recording position,
Rr: medium posture correction member,
S ... medium,
Sb: Rear end of medium conveyance direction,
S3, S3 '... remaining amount,
S4: detection residual amount,
S4 ″ —the amount of residual trailing edge detection,
SN1 ... posture detection member, rear end posture detection member,
SN2 ... second posture detection member,
SH1 ... transport path,
SH2 ... reverse path,
U: Image forming apparatus,
U1b: Image recording unit,
ΔS, ΔS ″... Difference amount.

Claims (6)

A transport path through which the medium is transported;
An image recording unit for recording an image on the medium at an image recording position provided in the conveyance path;
The medium posture correction member that is provided upstream of the image recording position in the medium conveyance direction and corrects the posture of the medium passing toward a preset reference posture;
An attitude detection member that is provided upstream of the medium attitude correction member in the medium conveyance direction, and detects the attitude of the medium;
A residual amount calculating means for calculating a residual amount which is a difference between the posture of the medium after being corrected by the medium posture correcting member and the reference posture based on the detection result of the posture detecting member;
Image rotating means for rotating an image formed on the medium based on the remaining amount;
An image forming apparatus comprising: Correspondence information for specifying the relationship between the detection result by the posture detection member and the remaining amount corresponding to the detection result, and storing the correspondence information measured in advance for each type of medium Means,
Medium type determining means for determining the type of the medium;
The residual amount calculating means for calculating the residual amount based on the correspondence information according to the type of the medium determined by the medium type determining means;
The image forming apparatus according to claim 1, further comprising: A second attitude detection member that is provided downstream of the medium attitude correction member in the medium conveyance direction and detects the attitude of the medium after being corrected by the medium attitude correction member;
Based on the correspondence information in which the detection result by the posture detection member is associated with the residual amount that is the difference between the detection result by the second posture detection member and the reference posture, the correspondence information storage unit stores the correspondence information. Correspondence information updating means for updating the correspondence information;
The image forming apparatus according to claim 2, further comprising: An inversion path connecting the downstream side of the image recording position of the transport path in the medium transport direction and the upstream side of the transport path of the posture detection member in the transport direction of the image. The reversing path for reversing the front and back of the medium and retransmitting it to the posture detection member;
A second attitude detection member that is provided downstream of the medium attitude correction member in the medium conveyance direction and detects the attitude of the medium after being corrected by the medium attitude correction member;
A difference amount calculation that calculates a difference amount that is a difference between the residual amount calculated by the residual amount calculation means and a detection residual amount that is a difference between the detection result by the second posture detection member and the reference posture. Means,
Based on the residual amount calculated based on the detection result of the posture detection member and the difference amount with respect to the medium that has been retransmitted to the position of the posture detection member through the reversing path, The image rotating means for rotating the image formed on the second surface;
The image forming apparatus according to claim 1, further comprising: An inversion path connecting the downstream side of the image recording position of the transport path in the medium transport direction and the upstream side of the transport path of the posture detection member in the transport direction of the image. The reversing path for reversing the front and back of the medium and retransmitting it to the posture detection member;
A rear end posture that is provided on the upstream side of the medium posture correction member in the medium conveyance direction and detects a posture of the medium by detecting a rear end portion of the medium passing through the position of the medium posture correction member. A detection member;
A rear end detection residual that calculates a rear end detection residual amount that is a difference between the medium posture corrected by the medium posture correction member and the reference posture based on the detection result of the rear end posture detection member. A quantity calculation means;
Difference amount calculation means for calculating a difference amount which is a difference between the remaining amount calculated by the residual amount calculation means and the rear end detection residual amount calculated by the rear end detection residual amount calculation means;
Based on the residual amount calculated based on the detection result of the posture detection member and the difference amount with respect to the medium that has been retransmitted to the position of the posture detection member through the reversing path, The image rotating means for rotating the image formed on the second surface;
The image forming apparatus according to claim 1, further comprising: The posture detection member that also serves as the rear end posture detection member;
The image forming apparatus according to claim 5, further comprising:

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