JP6780409B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Patent Document 1 detects and corrects how much the left edge of the electrostatic recording paper is displaced with respect to the first pass or how much the electrostatic recording paper expands and contracts in a direction perpendicular to the transport direction. A color image recording device for sending image data including the above to a recording driver is disclosed.

In Patent Document 2, the transfer paper position detection signal is output to the timing control circuit, the detection signal is incorporated into the timing control circuit, and the laser writing position in the main scanning direction is determined every time the transfer paper is conveyed by 1 mm by the laser writing timing signal. An image forming apparatus for performing correction is disclosed.

In Patent Document 3, the light emitted from the CIS is reflected by a high-reflectivity object and a recording medium, and the photoelectric conversion element pixel capable of receiving more reflected light than the threshold value is regarded as no recording member, and the photoelectric conversion element pixel that receives less light is excluded. There is disclosed an edge detection device having a recording member.

Japanese Unexamined Patent Publication No. 3-219271 Japanese Unexamined Patent Publication No. 9-219776 Japanese Unexamined Patent Publication No. 2012-198073

The image forming apparatus may be provided with a detection unit for detecting an image formed on the recording medium or detecting a side surface of the recording medium. However, if the detection unit is provided corresponding to each of the detection targets. , The number of detectors increases, which leads to an increase in cost and an increase in size of the device.
An object of the present invention is to reduce the number of detection units installed in the image forming apparatus as compared with the case where the detection units are provided corresponding to each of the detection targets provided in the image forming apparatus.

In the invention according to claim 1, an image is formed on the first surface of the recording medium, an image is formed on the second surface of the recording medium whose front and back sides are inverted, and the first surface is formed. In image formation, an image forming unit capable of forming an image for alignment used for positioning an image formed on the first surface and an image formed on the second surface on the first surface, and the image. when the forming unit the image formation on the first surface of the recording medium is performed, when the side of the recording medium detects the image formation on the by the image forming portion second surface is performed, A detection unit for detecting the alignment image formed on the first surface is provided , and a protrusion along a direction in which the downstream tip of the recording medium in the recording medium transport direction intersects the recording medium transport direction. This is an image forming apparatus in which the alignment image is detected by the detection unit when the movement of the recording medium to the downstream side in the recording medium transport direction is stopped by hitting the contact portion .
According to the second aspect of the present invention, an image is formed on the first surface of the recording medium, an image is formed on the second surface of the recording medium whose front and back sides are inverted, and the first surface is formed. In image formation, an image forming unit capable of forming an image for alignment used for positioning an image formed on the first surface and an image formed on the second surface on the first surface, and the image. When an image is formed on the first surface of the recording medium by the forming unit, a side surface of the recording medium is detected, and an image is formed on the second surface by the image forming unit. A detection unit that detects the alignment image formed on the first surface, a guide member that guides the conveyed recording medium, and the alignment image formed on the conveyed recording medium are described above. An image forming apparatus including a pressing means for pressing a portion of the recording medium facing the detection unit against the guide member when detected by the detection unit.
The invention according to claim 3, the transport destination of the recording medium on which the image for the positioning is formed, further comprising Claim switching means for switching between conveyance destination of the recording medium for the alignment image is not formed The image forming apparatus according to any one of 1 and 2 .

According to the invention of claim 1, the recording medium is stopped as compared with the configuration in which the movement of the recording medium is stopped again for the detection of the alignment image after the movement is stopped due to the recording medium hitting the abutting portion. The efficiency of the image forming process can be improved.
According to the second aspect of the present invention, the accuracy of detecting the alignment image by the detection unit is improved as compared with the configuration in which the recording medium is not pressed against the guide member.
According to the invention of claim 3 , as compared with the case where all the recording media are transported to one transport destination, the recording medium on which the alignment image is formed and the recording medium on which the alignment image is not formed are formed. The sorting work with and can be made simpler.

It is a figure which showed the structural example of the image forming apparatus of this embodiment. It is a figure which showed the structure around the cash register roll. (A) is a view when the periphery of the register roll is viewed from the direction of arrow III in FIG. 2, and FIG. (B) is an enlarged view of region IIIb in FIG. 3 (a). (A) and (b) are diagrams showing a state in which an image is formed on a paper longer than a reference value due to a cutting error when double-sided printing is performed. (A) and (b) are diagrams showing a state in which an image is formed on a paper formed by tilting one side due to a cutting error when double-sided printing is performed. It is a figure which showed the state of the paper when the cross image formed on the paper is detected. It is a flowchart which showed the flow of the detection process at the time of double-sided printing of a paper. It is a flowchart which showed the flow of the process when the special paper is output for every predetermined number of sheets.

Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a configuration example of the image forming apparatus 1 of the present embodiment.
The image forming apparatus 1 shown in FIG. 1 includes an image forming unit 100 that forms a toner image on paper P (recording medium) by, for example, an electrophotographic method.
Further, the image forming apparatus 1 includes a paper transport path 17 for transporting the paper P and a paper accommodating portion 18 for accommodating the paper P.
Further, the image forming apparatus 1 includes a detection device 30 that detects the paper P conveyed along the paper conveying path 17.

Further, the image forming apparatus 1 includes a register roll 20 as an example of an abutting portion that aligns the tips of the paper P by abutting the paper P transported on the paper transport path 17 and then transports the paper P to the downstream side. .. Further, the image forming apparatus 1 includes a pre-registration roll 22 as an example of a pressing means for transporting the paper P to the registration roll 20. The pre-registration roll 22 is provided on the upstream side of the registration roll 20.
Further, the image forming apparatus 1 includes an optical sensor 23 that detects the tip of the paper P conveyed by the register roll 20.

The image forming unit 100 includes a plurality of image forming units 11 (11Y, 11M, 11C, 11K) of yellow (Y), magenta (M), cyan (C), and black (K).
In the present embodiment, the image forming unit 100 that forms an image by an electrophotographic method is illustrated, but the image forming unit 100 may be configured by, for example, an inkjet printer.

Each image forming unit 11 includes a photoconductor drum 111 and a charging device 112 for charging the photoconductor drum 111. Further, the image forming unit 11 includes an exposure device 113 that exposes the surface of the photoconductor drum 111 charged by the charging device 112 to form an electrostatic latent image.
Further, the image forming unit 11 includes a developing device 114 that develops an electrostatic latent image formed on the photoconductor drum 111 by the exposure device 113 and forms a toner image on the photoconductor drum 111. Further, the image forming unit 11 includes a cleaning device 116 for removing waste toner on the photoconductor drum 111.

Further, the image forming unit 100 includes an intermediate transfer belt 12 on which each color toner image formed by the photoconductor drum 111 is multiplex transferred. Further, the image forming unit 100 includes a primary transfer roll 115 that sequentially transfers (primary transfer) each color toner image formed by the photoconductor drum 111 to the intermediate transfer belt 12.
Further, the image forming unit 100 includes a secondary transfer roll 13 that collectively transfers (secondary transfer) the toner image formed by superimposing the toner image on the intermediate transfer belt 12 onto the paper P which is a recording medium. The secondary transfer roll 13 is provided on the downstream side of the registration roll 20. Further, the image forming unit 100 includes a fixing unit 14 for fixing the secondary transferred toner image on the paper P.
Further, the image forming apparatus 1 includes a control unit 16 that controls the entire image forming apparatus 1.

The paper transport path 17 is provided with a first paper transport path R1 through which the paper P transported from the paper storage unit 18 toward the secondary transfer roll 13 passes. Further, as the paper transport path 17, a second paper transport path R2 through which the paper P passes after passing through the secondary transfer roll 13 is provided.

Further, as the paper transport path 17, a third paper transport path R3 that reverses the paper P and transports the inverted paper P to the first paper transport path R1 on the upstream side of the secondary transfer roll 13 It is provided. Further, as the paper transport path 17, a fourth paper transport path R4 and a fifth paper transport path R5 branched from the second paper transport path R2 are provided. The fourth paper transport path R4 and the fifth paper transport path R5 are transport paths through which the paper P transported toward the discharge unit (not shown) of the image forming apparatus 1 passes.

Further, the image forming apparatus 1 is provided with a switching gate 24 as an example of the switching means. The switching gate 24 projects onto the fourth paper transport path R4 and retracts from the fourth paper transport path R4.
When the switching gate 24 projects onto the fourth paper transport path R4, the paper P is transported to the fifth paper transport path R5, and when the switching gate 24 is retracted from the fourth paper transport path R4, the paper P is transported. Is transported to the fourth paper transport path R4.

The image forming apparatus 1 executes a series of image forming processes under the operation control by the control unit 16. That is, the image data acquired from a PC (not shown), a scanner, or the like (not shown) is subjected to image processing by the image processing unit (not shown), and is sent to the exposure device 113 as image data of each color. Then, in each image forming unit 11, exposure is performed by the exposure device 113, and further development is performed by the developer 114 to form a toner image on the photoconductor drum 111.

Each color toner image formed on the photoconductor drum 111 of each image forming unit 11 is sequentially electrostatically transferred (primary transfer) on the intermediate transfer belt 12 by the primary transfer roll 115, and each color is sequentially transferred on the intermediate transfer belt 12. A superimposed toner image on which toner is superimposed is formed.
The superimposed toner image on the intermediate transfer belt 12 is conveyed to the secondary transfer region T in which the secondary transfer roll 13 is arranged as the intermediate transfer belt 12 moves.

On the other hand, when the paper P fed from the paper accommodating portion 18 and conveyed through the first paper transport path R1 hits the register roll 20, the tips of the paper P are aligned. In other words, when the paper P hits the cash register roll 20, the cash register roll 20 is stopped, and in the present embodiment, the paper P hits the stopped cash register roll 20 and the inclination of the tip of the paper P is corrected. The registration roll 20 is an example of a stopping means.
After that, the rotation of the register roll 20 is started, and the paper P is sent to the downstream side. At this time, in the present embodiment, the tip of the paper P is detected by the optical sensor 23 while the paper P is sandwiched between the registration rolls 20.

When the tip of the paper P is detected, the register roll 20 conveys the paper P to the secondary transfer region T at a speed that matches the transfer timing of the superimposed toner image on the intermediate transfer belt 12.
In other words, in the present embodiment, the rotation speed of the register roll 20 is adjusted (the transport speed of the paper P is adjusted) based on the detection result of the tip of the paper P, and the paper P is supplied to the secondary transfer region T. Is done.

Then, the superimposed toner image on the intermediate transfer belt 12 is collectively electrostatically transferred (secondary transfer) on the conveyed paper P by the transfer electric field formed by the secondary transfer roll 13 in the secondary transfer region T. ). The paper P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing unit 14 and fixed on the paper P by the fixing unit 14.

The paper P after fixing passes through the fourth paper transport path R4 or the fifth paper transport path R5 and is conveyed to the paper loading section provided in the discharge section of the image forming apparatus 1.
When performing so-called double-sided printing in which an image is formed on the other side of the paper P having an image formed on one side, the paper P is conveyed to the third paper transport path R3 and the paper P is inverted. Then, the paper P is conveyed to the secondary transfer region T again to form an image.

FIG. 2 is a diagram showing a configuration around the cash register roll 20. More specifically, FIG. 2 shows a state when the configuration around the cash register roll 20 is viewed from above.
In the present embodiment, the pre-registration roll 22, the detection device 30, the registration roll 20, the optical sensor 23, and the secondary transfer roll 13 are arranged in order from the upstream side in the transport direction of the paper P (direction of arrow A in the drawing).

The register roll 20 is formed along a direction intersecting the transport direction of the paper P. Further, the register roll 20 is provided so as to be movable in a direction intersecting the transport direction of the paper P (see the arrow B1 direction and the arrow B2 direction in the drawing).
Further, a moving mechanism 20a for moving the register roll 20 is provided. The moving mechanism 20a is composed of, for example, a rack gear (not shown) interlocked with the register roll 20 and a pinion gear (not shown) rotated by a motor.

The detection device 30 includes a CIS (Contact Image Sensor) 31 as an example of a detection unit that detects a side side (side side along the transport direction of the paper P) of the paper P transported along the paper transport path 17. In addition to detecting the side edges of the paper P, the CIS 31 can also detect an image formed on the paper P.
Further, the CIS 31 is provided on one end side of the register roll 20 in the axial direction.

FIG. 3A is a view when the periphery of the register roll 20 is viewed from the direction of arrow III in FIG. 2, and FIG. 3B is an enlarged view of region IIIb in FIG. 3A.
More specifically, FIG. 3A shows a state in which the configuration around the cash register roll 20 is viewed from one end side (the side opposite to the side where the CIS 31 is provided) in the axial direction of the cash register roll 20. Is shown.

As shown in FIG. 3A, a guide member 21 for guiding the paper P to be transported is provided between the pre-registration roll 22 and the registration roll 20 and beside the paper transport path 17. The guide member 21 is provided with an upward guide member 21a and a downward guide member 21b.
The upward guide member 21a is provided above the paper transport path 17. The downward guide member 21b is provided below the paper transport path 17 and is provided so as to face the upward guide member 21a. Further, the downward guide member 21b is provided with a curved portion 21c that is curved so as to bulge downward.

Further, as shown in FIG. 3B, the detection device 30 includes a reflector 32 that reflects light. The reflector 32 is made of a metal material such as silver. The reflector 32 has a higher light reflectance than the paper P. Further, the reflector 32 is attached to the upward guide member 21a.
Further, as shown in FIG. 2, the reflector 32 is provided on one end side of the register roll 20 in the axial direction. Further, the reflector 32 is provided so as to face the CIS 31.

As shown in FIG. 3A, the CIS 31 is attached to the downward guide member 21b. Specifically, the CIS 31 is attached to a portion of the downward guide member 21b on the downstream side of the curved portion 21c.
The CIS 31 is provided with a plurality of light emitting elements (not shown) and a plurality of light receiving elements (not shown). The plurality of light receiving elements are arranged in a grid pattern (two-dimensionally arranged).

During the transportation of the paper P, the light emitting element emits light upward. The light emitted from the light emitting element is reflected by the reflector 32 and the paper P (see FIG. 2) conveyed to the opposite portion of the light emitting element. The light reflected by the reflector 32 and the paper P is received by the light receiving element.
Here, in the present embodiment, more light reflected by the reflector 32 is received by the light receiving element than light reflected by the paper P. As a result, the CIS 31 detects the side side of the paper P based on the magnitude of the light receiving amount in the light receiving element.

The control unit 16 acquires the position of the side side of the paper P from the CIS 31. Further, the control unit 16 calculates the amount of deviation of the position of the side side of the paper P from the reference position.
After that, the control unit 16 moves the registration roll 20 (see FIG. 2) in a direction intersecting the transport direction of the paper P with the registration roll 20 sandwiching the paper P based on the calculated deviation amount. As a result, the misalignment of the side side on the paper P is corrected. Further, as described above, the register roll 20 transports the paper P to the secondary transfer region T after adjusting the transport speed of the paper P.
As a result, the paper P is conveyed to the secondary transfer region T in a state where the position of the paper P and the timing at which the paper P reaches the secondary transfer region T are adjusted.

Further, in the present embodiment, when double-sided printing of the paper P is performed, a cross image as an example of a positioning image having a cross shape is formed when forming an image on the first surface of the paper P.
Then, when the image is formed on the second surface of the paper P, the cross image formed on the first surface is detected by CIS31, and the cross image formed on the first surface is formed on the second surface based on the position of the detected cross image. The position of the formed image is corrected.

In the present embodiment, the position of the image formed on the paper P is based on the position of the paper P in the direction intersecting the transport direction and the timing at which the paper P (the tip of the paper P) reaches the secondary transfer region T. Is decided.
Further, when double-sided printing of the paper P is performed, the position where the image is formed on the first side of the paper P and the position where the image is formed on the second side do not deviate (front and back misalignment of the image). A cross image is formed on the first surface of the paper P.

Here, generally, the paper P is manufactured by cutting, but the length of the paper P may differ from a predetermined reference value due to a cutting error. If the length of the paper P deviates from the reference value, a misalignment may occur between the image formed on the first side and the image formed on the second side of the paper P during double-sided printing. ..

Here, in the present embodiment, as described above, the tip of the paper P is abutted against the cash register roll 20 to adjust the position of the paper P, but if the paper P has the above-mentioned cutting error or the like, the position is adjusted. Even if the above is performed, the position cannot be substantially adjusted. In this case, the image formed on the first surface of the paper P and the image formed on the second surface are displaced from each other.
Specifically, in the present embodiment, the front end and the rear end of the paper P are exchanged during double-sided printing, and the front end of the paper P that abuts on the register roll 20 when forming an image on the first surface and the image on the second surface. The tip of the paper P that abuts on the register roll 20 will be different from the tip of the paper P when forming the

In such a case, the criteria for forming an image will be different between the first surface and the second surface, and if there is a cutting error in the paper P, the image formed on the first surface and the second surface will be formed. There is a misalignment with the image.
In the present embodiment, in order to prevent this misalignment, a cross image is formed when the image is formed on the first surface, and when the image is formed on the second surface, the image is aligned with reference to this cross image. (Image is formed on the second surface).

Specifically, in the present embodiment, the position of forming the toner image on the photoconductor drum 111 is changed based on the position of the detected cross image to align the images.
More specifically, based on the position of the cross image, the exposure timing for the photoconductor drum 111 is shifted, the formation position of the toner image is changed, and the image formed on the first surface and the image formed on the second surface Align.

The alignment of the image formed on the first surface and the image formed on the second surface may be performed by changing the feeding timing of the paper P by the register roll 20 at the time of forming the image on the second surface. Good. More specifically, the delivery timing is delayed or earlier than the predetermined reference (predetermined delivery timing), and the image formed on the first surface and the image formed on the second surface are Alignment may be performed.

Further, due to a cutting error, the front edge and the rear edge of the paper P may not be parallel. Also in this case, there is a possibility that a misalignment may occur between the image formed on the first surface of the paper P and the image formed on the second surface during double-sided printing.
Specifically, the tip of the paper P is aligned by the cash register roll 20 when the image of the first surface is formed, but the front and rear ends of the paper P are exchanged by the cash register roll 20 again when the second image is formed, and the tip of the paper P is again formed by the cash register roll 20. Are aligned. Here, if the front edge and the rear edge of the paper P are not parallel, the paper P at the time of image formation on the second surface is tilted with respect to the arrangement of the paper P at the time of image formation on the first surface. Become.

In such a case, the image formed on the second surface is tilted (rotated) with respect to the image formed on the first surface of the paper P.
In the present embodiment, in order to prevent such misalignment (positional misalignment in which the second surface image is tilted with respect to the image on the first surface), a cross image is formed when the image is formed on the first surface, and the first image is formed. When forming an image on two surfaces, this cross image is detected and the image is aligned.

Specifically, in the present embodiment, the control unit 16 grasps the inclination of the paper P based on the detected position of the cross image, and then uses it for image formation on the second surface based on the grasped inclination. Rotate the image data. Then, in the present embodiment, an image is formed on the second surface based on the rotated image data. As a result, the position shift in which the second surface image is tilted with respect to the first surface image is less likely to occur.

Hereinafter, a specific example will be described.
4 (a) and 4 (b) are views showing a state in which an image is formed on a paper Pa longer than a reference value due to a cutting error when double-sided printing is performed. More specifically, FIG. 4A is a diagram showing a state in which a rectangular image G1 and a cross image F1 are formed on the first surface of the paper Pa. Further, FIG. 4B is a diagram showing a state in which a rectangular image G2b is formed on the second surface of the paper Pa (a state after double-sided printing is performed).

As shown in FIG. 4A, the paper Pa is formed to be longer than the reference value by a length C. Further, in this example, when the image is formed on the first surface, the side E1 is the front end in the transport direction of the paper Pa (direction of arrow A in the figure), and the side E2 is the rear end. By forming an image on the first surface of the paper Pa, an image G1 is formed on the first surface.
Further, when the image is formed on the first surface, the cross image F1 is formed. The cross image F1 is formed on one end side in a direction intersecting the transport direction of the paper P (direction of arrow A in the drawing). Further, the cross image F1 is formed at the front end and the rear end of the paper Pa, respectively.

As shown in FIG. 4B, when the image is formed on the second surface of the paper Pa, the front and back sides of the paper Pa are reversed. As a result, the side E2, which was the rear end of the paper Pa when the image is formed on the first surface, becomes the front end of the paper Pa when the image is formed on the second surface.

Here, for example, even if an attempt is made to form an image G2a on the second surface so as to overlap the image G1 on the first surface, since there is a cutting error on the paper P, the image G2a formed on the second surface and the first surface A misalignment occurs with the image G1 formed on the surface. Specifically, the image G2a is formed at a position closer to the side E2 by a length C than the image G1.

On the other hand, in the present embodiment, when the image is formed on the second surface, the cross image F1 formed on the first surface is detected by the CIS 31. Then, based on the detected position of the cross image F1, the exposure timing for the photoconductor drum 111 is changed to change the formation position of the toner image. As a result, in the present embodiment, the image G2b is formed with respect to the second surface.
As a result, the positions of the image G1 formed on the first surface and the image G2b formed on the second surface coincide with each other.

5 (a) and 5 (b) are views showing a state in which an image is formed on paper Pb formed with one side tilted due to a cutting error when double-sided printing is performed. More specifically, FIG. 5A is a diagram showing a state in which a rectangular image G3 and a cross image F1 are formed on the first surface of the paper Pb. Further, FIG. 5B is a diagram showing a state in which a rectangular image G4b is formed on the second surface of the paper Pb (a state after double-sided printing is performed).

As shown in FIG. 5A, one side of the paper Pb (the rear end side when the image is formed on the first surface) E2 is the other side (the front end side when the image is formed on the first surface). It is formed so as to be inclined with respect to E1.
The image G3 is formed by forming an image on the first surface of the paper Pb. Further, when forming an image on the first surface, a cross image F1 is formed.

Here, as shown in FIG. 5B, for example, even if an image G4a is formed on the second surface so as to overlap the image G3 on the first surface, there is a cutting error on the paper P, so that the second surface has a cutting error. A misalignment occurs between the image G4a formed on the first surface and the image G3 formed on the first surface. Specifically, the image G4a is formed in a state where the image G4a is tilted with respect to the image G3.

On the other hand, in the present embodiment, when the image is formed on the second surface, the cross image F1 formed on the first surface is detected by CIS31, and the inclination of the paper Pb is detected. Then, in the present embodiment, the image data used for image formation on the second surface is rotated based on the detected inclination. As a result, the image G3 formed on the first surface and the image G4b formed on the second surface come to match.

FIG. 6 is a diagram showing a state of the paper P when the cross image F1 formed on the paper P is detected.
When double-sided printing of the paper P is performed, in the present embodiment, when the image is formed on the first side of the paper P, the side side of the paper P is detected by the CIS 31 and at the position of the detected side side. Based on this, the position of the paper P in the direction intersecting the transport direction is adjusted. Specifically, the position of the paper P is adjusted by moving the register roll 20 in a direction intersecting the transport direction.

Further, when forming an image on the first surface of the paper P, a cross image F1 is formed on the first surface. Then, the paper P on which the image is formed on the first surface reaches the pre-registration roll 22 again after the front and back sides are reversed. Then, the pre-registration roll 22 conveys the paper P toward the registration roll 20. At this time, the registration roll 20 has stopped rotating.

As shown in FIG. 6, when the tip of the paper P conveyed by the pre-registration roll 22 abuts on the registration roll 20, a loop (deflection) along the shape of the curved portion 21c of the downward guide member 21b is formed on the paper P. Paper P is fed toward the cash register roll 20. At this time, the inclination (skew) of the paper P with respect to the conveying direction is corrected.

Further, at this time, due to the stiffness of the paper P, the portion of the paper P on the downstream side of the portion where the loop is formed is pressed against the upward guide member 21a. Specifically, the portion of the paper P on which the cross image F1 is formed presses against the portion of the upward guide member 21a facing the CIS 31 (CIS facing portion) 21d. At this time, in the present embodiment, the registration roll 20 has stopped rotating, whereby the movement of the paper P is also stopped, and the movement of the portion of the paper P on which the cross image F1 is formed is also stopped. ing.

Then, in the present embodiment, the cross image F1 is detected by the CIS 31 while the cross image F1 is stopped. Then, in the present embodiment, as described above, the control unit 16 adjusts the position of the image formed on the second surface of the paper P based on the detection result of the cross image F1.
Specifically, when the detected cross image F1 is deviated in the transport direction, the image formation position on the second surface is adjusted by shifting the exposure timing for the photoconductor drum 111 to match the image on the first surface. Align with the image on the second surface.
When the detected cross image F1 is tilted, the image data used for forming the image on the second surface is rotated to align the image on the first surface with the image on the second surface.

In the present embodiment, the side side of the paper P is detected by the CIS 31 when the image is formed on the first surface of the paper P. Further, since the first surface on which the cross image F1 is formed faces the CIS31 side when the image is formed on the second surface, the CIS31 is used when the image is formed on the second surface. The cross image F1 is detected. Then, as described above, the image on the first surface and the image on the second surface are aligned based on the detection result of the cross image F1.
In the present embodiment, the detection of the side side of the paper P and the detection of the cross image F1 are performed by one CIS 31.

Further, in the present embodiment, when forming an image on the second surface of the paper P, the cross image F1 is detected after the paper P hits the register roll 20. As a result, the misalignment between the image formed on the first surface and the image formed on the second surface is more reliably reduced.

Here, if the paper P abuts on the register roll 20 after the cross image F1 is detected, the inclination of the paper P may change after the cross image F1 is detected.
As described above, the side of the tip of the paper P may be inclined due to a cutting error or the like. In this case, the paper P abuts on the register roll 20 after the cross image F1 is detected. After the cross image F1 is detected, the paper P may be tilted.
In such a case, even if the image is formed on the second surface based on the detection result of the cross image F1, the occurrence of misalignment cannot be prevented. Therefore, in the present embodiment, as described above, the cross image F1 is detected after the paper P hits the registration roll 20.

Further, in the present embodiment, when the movement of the portion (cross image portion) of the paper P on which the cross image F1 is formed is stopped, the cross image F1 is detected by the CIS 31.
As a result, the detection accuracy of the cross image F1 is improved as compared with the case where the cross image F1 is detected when the portion where the cross image F1 is formed is moving.

Further, in the present embodiment, the paper P hits the register roll 20, and the cross image F1 is detected while the tip of the paper P is being aligned. As a result, the efficiency of the image forming process is improved.

Here, if the configuration is such that the transport of the paper P is stopped only for the detection of the cross image F1, the efficiency of the image forming process is reduced by the amount of the stop.
On the other hand, if the registration roll 20 detects the cross image F1 at the same time during the alignment process of the tip of the paper P as in the present embodiment, the paper P is not stopped only for the detection. The efficiency of the image formation process is improved.

Further, in the present embodiment, when the cross image F1 is detected, the portion of the paper P on which the cross image F1 is formed by the pre-registration roll 22 is the CIS facing portion 21d of the upward guide member 21a. It is pressed against (see FIG. 6). As a result, the detection accuracy of the cross image F1 by the CIS 31 is improved.
In the present embodiment, the focal length of the CIS 31 is the distance H (focal length H) from the CIS 31 (light emitting element) to the upward guide member 21a (see FIG. 6).

Here, if the paper P is not pressed against the upward guide member 21a, the cross image F1 is displayed in a state where the portion of the paper P facing the CIS 31 (the portion where the cross image F1 is formed) is floating. May be detected. In this case, the distance between the portion where the cross image F1 is formed and the CIS 31 tends to vary, and the detection accuracy of the cross image F1 may decrease.

On the other hand, when the cross image F1 is detected as in the present embodiment, when the portion where the cross image F1 is formed is pressed against the CIS facing portion 21d, the CIS 31 and the cross image of the paper P are formed. The distance to the portion is close to the focal length H. In this case, the detection accuracy of the cross image F1 is improved.

FIG. 7 is a flowchart showing the flow of the detection process when double-sided printing of the paper P is performed.
First, when the paper P transported through the paper transport path 17 abuts on the register roll 20, the tips of the paper P are aligned (step 701). After that, when the paper P moves to the downstream side, the tip of the paper P is detected by the optical sensor 23 (step 702).

When the tip of the paper P is detected, the control unit 16 adjusts the transport speed of the register roll 20 so that the paper P reaches the secondary transfer region T in accordance with the transport timing of the superimposed toner image on the intermediate transfer belt 12. (Step 703). When the tip of the paper P is detected, the CIS 31 detects the position of the side side of the paper P conveyed by the register roll 20 (step 704).
When the position of the side side on the paper P is detected, the control unit 16 adjusts the position in the direction intersecting the transport direction of the paper P based on the detection result (step 705).

Then, after adjusting the position of the paper P (the position in the direction orthogonal to the transport direction of the paper P) and the timing at which the paper P reaches the secondary transfer region T, the image on the first surface of the paper P is adjusted. Forming, the cross image F1 is formed on the first surface of the paper P. (Step 706).

The paper P on which the image is formed on the first surface hits the register roll 20 again after the front and back sides are reversed (step 707). Further, even while the paper P is in contact with the cash register roll 20, the paper P is fed to the cash register roll 20 by the pre-registration roll 22. As a result, the tips of the paper P are aligned while the loop is formed on the paper P (step 708).
Further, at this time, the portion of the paper P on which the cross image F1 is formed is pressed against the CIS facing portion 21d of the upward guide member 21a, and its movement is stopped (step 709).

Then, in the present embodiment, the cross image F1 is detected by the CIS 31 while the paper P is abutting against the register roll 20 (when the movement of the cross image F1 is stopped) (step 710). When the cross image F1 is detected, the control unit 16 calculates the amount of misalignment of the image formed on the second surface with respect to the image formed on the first surface based on the detection result of the cross image F1 (step). 711).
Then, the control unit 16 determines whether or not the calculated displacement amount is equal to or less than the reference value (step 712). Note that this reference value is a value for determining whether or not the position of the image can be adjusted.

If the amount of misalignment is not less than or equal to the reference value (No in step 712), the position of the image is not adjusted and an error is displayed on the user interface (not shown) of the image forming apparatus 1 (step 713). In addition, the transfer of the paper P is stopped (step 714).
On the other hand, when the amount of misalignment is equal to or less than the reference value (Yes in step 712), the control unit 16 adjusts the position of the image (the image formed on the second surface) (step 715). After that, the register roll 20 is rotationally driven, and the transfer of the paper P is restarted (step 716). After that, an image is formed on the second surface of the paper P.

In the above, when double-sided printing of the paper P is performed, the cross image F1 is formed when the image is formed on the first surface of the paper P, and the cross image F1 is formed when the image is formed on the second surface of the paper P. The case of detecting is explained. That is, a cross image F1 was formed on the paper P together with the image, and the image formed on the first surface and the image formed on the second surface were aligned.

By the way, not limited to this processing, a special paper for alignment (paper P on which only the cross image F1 is formed) is conveyed, and an image formed on the first surface and an image formed on the second surface are transferred. Alignment may be performed. When special paper is used, for paper P (normal paper for double-sided printing) other than special paper, an image formed on the first side and an image formed on the second side without forming a cross image F1. Align.

Specifically, when the special paper is used, first, the special paper is conveyed to form a cross image F1 on the first surface of the special paper. Then, the front and back sides of the special paper are reversed, and the cross image F1 is detected by using CIS31. Here, if there is a cutting error in this special paper, the detection timing of the cross image F1 will be different from the predetermined timing, or it will be detected that the cross image F1 is tilted.

Then, in the present embodiment, the position of the image formed on the paper P conveyed following the special paper is shifted or the image is tilted based on the detection result of the special paper. Specifically, when an image is formed on the second surface of the paper P, the position of the image is shifted or the image is tilted.

More specifically, when the detection timing of the cross image F1 is different from the predetermined timing, the exposure timing is changed, the feeding timing by the registration roll 20 is changed, or the like, and the paper P is changed. The positions of the images formed on the two surfaces are shifted. When it is detected that the cross image F1 is tilted, the image formed on the second surface of the paper P is rotated.

Here, in general, the paper P is formed by cutting a base paper in which a plurality of sheets are bundled in the manufacturing process. Therefore, when a cutting error occurs in the paper P, the paper P having the same error tends to occur continuously.
In such a case, the image forming apparatus 1 aligns the image formed on the first surface with the image formed on the second surface without forming the cross image F1 on all the sheets P. Specifically, as described above, the degree of cutting error can be grasped by using the special paper, and if the image is formed on the second surface of the paper P based on the grasping result, the first surface can be grasped. The image formed on the second surface can be aligned with the image formed on the second surface.

In this embodiment, special paper is output for each predetermined number of sheets.
In other words, only the cross image F1 is formed on the paper P for each predetermined number of sheets.
Here, different lots of paper P may be stored in the paper storage unit 18 of the image forming apparatus 1, and in this case, all subsequent alignments are performed based on the detection result of one dedicated paper. If this is done, the position will shift according to the change of lot.
Therefore, in the present embodiment, the special paper is output for each predetermined number of sheets.

FIG. 8 is a flowchart showing a processing flow when special paper is output for each predetermined number of sheets.
The control unit 16 determines whether or not the next sheet P to be conveyed is the nth sheet P (step 801). Here, the value of n is a predetermined integer.

If the paper P is not the nth sheet (No in step 801), the cross image F1 is not formed on the paper P. In other words, in this case, a normal image is formed on the paper P. In this case, after the side side detection process of the paper P is performed (step 802), the image is formed on the first surface (step 803).

Subsequently, an image is formed on the second surface of the paper P (step 804). At this time, the image formation position is determined (rotate when the image is rotated) based on the degree of cutting error obtained by transporting the special paper, and the image is formed on the second surface.
The paper P on which the image is formed on the second surface is conveyed to the downstream side. At this time, the switching gate 24 (see FIG. 1) is retracted from the fourth paper transport path R4, and the paper P is ejected from the image forming apparatus 1 after being transported to the fourth paper transport path R4 (step 805). Will be done.

After that, as shown in FIG. 8, the control unit 16 determines whether or not there is a paper P to be printed next (step 806). If there is a next sheet P (Yes in step 806), the processes after step 801 are executed. If there is no next sheet P (No in step 806), the process ends.

On the other hand, when the paper P is the nth sheet P (Yes in step 801), the special paper is output. Specifically, the transfer of the paper P is started, and the side side of the paper P is detected (step 807). Then, based on the detection result of the side side, the registration roll 20 is moved to correct the misalignment of the paper P. After that, the cross image F1 is formed on the first surface of the paper P (step 808).

After that, the front and back sides of the paper P are reversed, and the cross image F1 is further detected using CIS31 (step 809). The result of this detection is stored in a memory (not shown), and is later used for forming an image on the second surface of a normal paper which is a paper P other than the special paper.
After that, it is determined whether or not the discharge destination is specified (step 810). Then, if not specified (No in step 810), the paper is conveyed to the fourth paper transfer path R4 (step 811). That is, the paper is conveyed to the same transfer path as the normal paper.

On the other hand, if it is determined in step 810 that the ejection destination is specified (Yes in step 810), the paper P (dedicated paper) is transported to the fifth paper transport path R5, which is different from the fourth paper transport path R4. (Step 812). That is, the paper is transported to a destination different from the normal paper destination. In this case, it is possible to avoid mixing the normal paper and the special paper, and the sorting work of the normal paper and the special paper becomes easy.

1 ... Image forming apparatus, 11 ... Image forming unit, 12 ... Intermediate transfer belt, 13 ... Secondary transfer roll, 16 ... Control unit, 17 ... Paper transport path, 20 ... Registrar roll, 21a ... Upward guide member, 21b ... Downward guidance Member, 21c ... Curved part, 22 ... Pre-registration roll, 23 ... Optical sensor, 24 ... Switching gate, 30 ... Detection device, 31 ... CIS, 32 ... Reflector, 100 ... Image forming part

Claims (3)

An image is formed on the first surface of the recording medium, an image is formed on the second surface of the recording medium whose front and back sides are inverted, and an image is formed on the first surface on the first surface. An image forming unit capable of forming an image for alignment used for alignment between the image to be formed and the image formed on the second surface on the first surface, and
When the image formation on the first surface of the recording medium is performed by the image forming unit detects the side of the recording medium, when the image formation by the image forming unit to the second surface is performed In addition, a detection unit that detects the alignment image formed on the first surface and
Equipped with a,
When the tip of the recording medium on the downstream side in the recording medium transport direction abuts on the abutting portion along the direction intersecting the recording medium transport direction, the recording medium can be moved to the downstream side in the recording medium transport direction. An image forming apparatus in which the alignment image is detected by the detection unit when the image is stopped . An image is formed on the first surface of the recording medium, an image is formed on the second surface of the recording medium whose front and back sides are inverted, and an image is formed on the first surface on the first surface. An image forming unit capable of forming an image for alignment used for alignment between the image to be formed and the image formed on the second surface on the first surface, and
When the image forming unit forms an image on the first surface of the recording medium, the side side of the recording medium is detected, and the image forming unit forms an image on the second surface. In addition, a detection unit that detects the alignment image formed on the first surface and
A guide member that guides the recorded recording medium to be conveyed, and
When the positioning image formed on the conveyed recording medium is detected by the detection unit, a pressing means for pressing a portion of the recording medium facing the detection unit against the guide member, and
An image forming apparatus comprising. The image according to claim 1 or 2 , further comprising a switching means for switching between a transport destination of a recording medium on which the alignment image is formed and a transport destination of a recording medium on which the alignment image is not formed. Forming device.

Images