JP2010001099A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a curl of paper carried from a paper feeding portion, according to an actual curl direction before image formation. <P>SOLUTION: The image forming device includes a paper feeding cassette 4 feeding paper; an image forming portion 40 forming an image on the paper carried from the paper feeding cassette 4 on the basis of image data; a detecting portion 80 detecting a curl direction of the paper carried from the paper feeding cassette 4; a curl correcting portion 90 correcting the curl of the paper carried in a carrying path between the image forming portion 40 and the paper feeding cassette 4, and capable of changing a curl correcting direction; and a control portion setting the curl correcting direction of the curl correcting portion 90 in the opposite direction to the curl of the paper detected by the detecting portion 80, and making the curl correcting portion correct the curl of the paper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an image forming apparatus such as an electrophotographic copying machine is known. In this image forming apparatus, since fixing is performed by heating and pressing after the toner image is formed on the paper, a phenomenon that the paper after fixing is curled is known.

  For this reason, an image forming apparatus having a paper curl correction function has been considered. For example, an image amount to be formed on a sheet is acquired from image information input for image formation, a curl correction direction is determined according to the image amount, and a sheet after fixing processing is determined by two curl correction units. An image forming apparatus that performs curl correction in the curled correction direction and discharges the paper to a post-processing apparatus is considered (for example, see Patent Document 1). This is because, even if fixing is performed by the same fixing device, the direction of curl changes depending on the amount of image on the paper. The curl correction device is composed of a pair of rollers having different radii, and the sheet passes through the nip portion of the pair of rollers, so that the sheet is curled in the direction of the roller having a small radius to correct the sheet.

Further, an image forming apparatus that detects the length of the sheet in the conveyance direction after the fixing process with an optical sensor, corrects the curl of the sheet after the fixing process with a curl correction roller according to the detected length, and discharges the sheet. It is considered (for example, refer to Patent Document 2).
JP 2000-229758 A JP 2002-326754 A

  In recent years, in an image forming apparatus, in order to make effective use of resources in consideration of environmental problems, an opportunity to form an image on a white paper surface (front surface) of paper (back paper) that has been formed and discharged on one side has increased. ing. Unlike the opened paper, the backing paper is printed once, so curl wrinkles at the time of fixing often remain on the paper. When such a backing paper is set in a paper feed cassette or a manual feed tray and transported from the paper feed cassette or the manual feed tray to the image forming unit, the paper is caught by the guide or roller shaft of the transport path due to the curl and the paper is transported. There was a possibility of causing a defect (jam: JAM).

  Further, since the leading edge of the curled paper does not enter the registration roller, the function of the registration roller is impaired, and there is a possibility that the skew correction in the paper feeding / conveyance is not sufficiently performed. Furthermore, there is a possibility that print misalignment may occur due to a shift in timing of transferring the toner image in the image forming unit.

  However, in the conventional image forming apparatus having the curl correction function, since the curl correction apparatus is provided downstream of the fixing unit, it is possible to improve the stacking of the paper (printed matter) after being discharged, but the back paper is an image. The curl correction could not be performed before being conveyed to the forming unit. Further, since the conventional image forming apparatus having the curl correction function predicts the curl direction according to the image amount and performs the curl correction, there is a possibility that an appropriate curl correction direction may not be obtained.

  For this reason, there is a possibility that the productivity and quality of the print may be reduced due to a jam or the like caused by the curling of the backing paper. In order to solve this, there is a method in which the user corrects the curl by hand when setting the backing paper in the paper feed cassette or the manual feed tray, but the work burden on the user is large.

  An object of the present invention is to perform curl correction on a sheet conveyed from a sheet feeding unit according to an actual curl direction before image formation.

In order to solve the above-described problem, an image forming apparatus according to a first aspect of the present invention provides:
A paper supply unit for supplying paper;
An image forming unit that forms an image on a sheet conveyed from the sheet feeding unit based on image data;
A curl correction unit that corrects curl of a sheet conveyed along a conveyance path between the image forming unit and the sheet feeding unit, and the curl correction direction can be changed;
A detection unit for detecting a direction of curling of the paper conveyed from the paper supply unit;
A control unit that sets a curl correction direction of the curl correction unit to a direction opposite to a curl direction of the paper detected by the detection unit, and causes the curl correction unit to correct the curl of the paper.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
A registration roller for conveying the paper to the image forming unit;
The curl correcting unit corrects curl of a sheet conveyed along a conveyance path between the registration roller and the sheet feeding unit.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The curl correction unit includes a first roller and a second roller, and a third roller having an elastic body around it, and the first and second rollers and the third roller are pressed against each other. And the state where the first roller and the third roller are pressed against each other and the state where the first and second rollers and the third roller are separated can be switched. .

  According to the first aspect of the present invention, based on the curl direction of the paper detected by the detection unit, the back paper conveyed from the paper supply unit can be curled according to the actual curl direction before image formation. .

  According to the second aspect of the present invention, it is possible to prevent misalignment of prints and jamming of the image forming unit based on misalignment of skew correction in the registration roller and sheet misalignment of the registration roller.

  According to the third aspect of the present invention, three rollers are sufficient, and the configuration of the curl correction unit can be simplified, and the first, second, and third rollers in the case of curl correction in a predetermined direction. Can be freely pressed, a state in which the third roller and the third roller are pressed against each other in the case of curl correction in the direction opposite to the predetermined direction, and a state of being spaced apart in the case of no curl correction. You can switch to

  Exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the illustrated example. The embodiment of the present invention represents the most preferable embodiment of the invention, and the use and terms of the invention are not limited to this.

  First, the apparatus configuration of the present embodiment will be described with reference to FIG. FIG. 1 shows a schematic configuration of an image forming apparatus 1 according to the present embodiment.

  The image forming apparatus 1 detects the curl direction of the paper being transported to form an image, and when there is curl on the paper according to the detection result, performs the curl correction according to the curl direction to form the image. The image forming apparatus performs image formation without performing curl correction when the sheet is not curled. The backing paper is more likely to have a curl than the opened paper (new paper), and the direction of the curl is not constant. For this reason, mainly when the paper is a back paper, the curl correction is performed according to the curl direction. However, even when the paper is a curled open paper or the like, if the paper has curl, the curl direction is corrected. Perform curl correction. The image forming apparatus 1 is a color page printer, particularly a tandem type color page printer.

  As shown in FIG. 1, the image forming apparatus 1 includes a housing 2, a paper discharge tray 3, a paper feed cassette 4 as a paper feed unit, a manual feed tray 5 as a paper feed unit, an image forming unit 40, and a transport unit 60. , A detection unit 80, a curl correction unit 90, and the like. The image forming unit 40 includes an image forming main body 40a and a fixing unit 40b.

  The transport unit 60 includes a paper feed roller 61, transport rollers 62A and 62B, a transport guide 63, registration rollers 65A and 65B, a pressure roller 66, and transport rollers 67A and 67B. These rollers are in this order in the paper feed cassette. 4 to the paper discharge tray 3 are provided on a paper conveyance path 60a. Further, the transport unit 60 includes transport rollers 68A, 68B, 69A, 69B, 70A, and 70B, and these rollers are provided on the reversing path 60b in this order. Further, the transport unit 60 includes paper feed rollers 64A and 64B.

  The conveyance rollers 62A and 62B are a pair of rollers that are pressed against each other and have a nip portion, and are rotated so that the sheet passes through the nip portion. The registration rollers 65A and 65B, the transport rollers 67A and 67B, the transport rollers 68A and 68B, the transport rollers 69A and 69B, the transport rollers 70A and 70B, and the paper feed rollers 64A and 64B are respectively transport rollers 62A, The configuration is the same as 62B. The conveyance guide 63 is a guide member for the sheet to be conveyed.

  The paper feed cassette 4 stores paper P and supplies the paper P. The paper P is an open paper or a backing paper on which an image is formed (printed) on one side. When the paper P is a back paper, the paper P is set in the paper feed cassette 4 so that the white paper surface of the back paper faces up. This is because an image is formed on the white side of the backing paper. The paper P set in the paper feed cassette 4 is taken out from the uppermost portion one by one by the rotational drive of the paper feed roller 61 and is transported to the transport rollers 62A and 62B. The sheet P is conveyed to the registration rollers 65A and 65B via the conveyance guide 63. Similarly, the paper P is set on the manual feed tray 5, and the paper P is taken out from the top one by one by the rotational driving of the paper feed rollers 64A and 64B and conveyed to the registration rollers 65A and 65B. The registration rollers 65A and 65B are driven to rotate, convey the paper P conveyed from the conveyance guide 63 to the image forming main body 40a, adjust the conveyance timing, and perform skew correction of the paper P.

  The image forming main body 40a includes a yellow image forming unit 40Y, a magenta image forming unit 40M, a cyan image forming unit 40C, a black image forming unit 40K, an intermediate transfer belt 47, a secondary transfer driving roller 48, a driven roller 49, and a cleaning unit 50. Have The fixing unit 40 b includes a fixing roller 51 and a pressure roller 52.

  The yellow image forming unit 40Y includes a photosensitive drum 41, a charging unit 42, an exposure unit 43, a developing unit 44, a primary transfer roller 45, and a cleaning unit 46 which are sequentially arranged around the photosensitive drum 41. ) Is formed on the intermediate transfer belt 47.

  Specifically, in the yellow image forming unit 40Y, the photosensitive drum 41 charged by the charging unit 42 is irradiated with light according to yellow image data from the exposure unit 43, and an electrostatic latent image is formed. . Then, the developing unit 44 attaches a charged yellow toner to the surface of the photosensitive drum 41 on which the electrostatic latent image is formed, and the electrostatic latent image is developed to form a toner image. The photosensitive drum 41 and the primary transfer roller 45 are rotated, and the yellow toner image formed on the photosensitive drum 41 is primarily transferred onto the intermediate transfer belt 47 to the transfer position where the primary transfer roller 45 is disposed. After the yellow toner image is primarily transferred to the intermediate transfer belt 47, the cleaning unit 46 removes residual charges, residual toner, and the like on the surface of the photosensitive drum 41.

  The magenta image forming unit 40M has an apparatus configuration similar to that of the yellow image forming unit 40Y, and forms a magenta (M) image on the intermediate transfer belt 47. Similarly, the cyan image forming unit 40 </ b> C forms a cyan (C) image on the intermediate transfer belt 47. Similarly, the black image forming unit 40 </ b> K forms a black (K) image on the intermediate transfer belt 47.

  The intermediate transfer belt 47 is an endless belt. The secondary transfer driving roller 48 is disposed on the conveyance path 60a side in the housing 2 and is driven to rotate. The driven roller 49 is disposed at a horizontal position with the secondary transfer driving roller 48. The primary transfer rollers 45 of each color of YMCK are sequentially arranged between the driven roller 49 and the secondary transfer drive roller 48. The intermediate transfer belt 47 is hung on the secondary transfer drive roller 48, the primary transfer roller 45, and the driven roller 49, and rotates around by the rotational drive of the secondary transfer drive roller 48. The driven roller 49 and the primary transfer roller 45 rotate according to the circumferential movement of the intermediate transfer belt 47.

  The pressure roller 66 is pressed against the secondary transfer driving roller 48 via the intermediate transfer belt 47. The sheet P conveyed from the registration rollers 65A and 65B passes between the secondary transfer driving roller 48 and the pressure roller 66 and is formed on the intermediate transfer belt 47 formed by the image forming units 40Y, 40M, 40C, and 40K. The toner image is secondarily transferred and conveyed to the fixing unit 40b. The cleaning unit 50 removes residual toner and the like on the intermediate transfer belt 47.

  The fixing roller 51 is rotatable and has a heat source to heat the paper P. The pressure roller 52 is pressed against the fixing roller 51 to form a nip portion. The fixing unit 40b fixes the toner image secondarily transferred to the paper P by heating and pressurizing when the conveyed paper P passes through the nip portion, and transports the toner image to the transport rollers 67A and 67B.

  The transport rollers 67A and 67B discharge the paper P transported from the fixing unit 40b to the paper discharge tray 3 by the rotational drive of the transport roller 67B. In the double-sided image formation, after the first surface of the paper P is formed, the transport rollers 67A and 67B discharge the paper P halfway to the paper discharge tray 3 side by the rotational driving of the transport roller 67B. The paper P is transported to the transport rollers 68A and 68B in the reverse path 60b by the reverse rotation of the transport roller 67B. The transported paper P is reversed and is transported in turn by transport rollers 68A and 68B and transport rollers 69A, 69B, 70A and 70B in the reverse path 60b, and transported to the registration rollers 65A and 65B in the transport path 60a. Is done. Then, the image forming unit 40 forms an image on the second surface (blank surface) of the sheet P.

  The detection unit 80 is a detection unit provided in the conveyance guide 63 between the conveyance rollers 62A and 62B and the registration rollers 65A and 65B on the conveyance path 60a, and detects the curl direction of the conveyed paper P.

  The curl correcting unit 90 is provided in a transport guide 63 between the detection unit 80 and the registration rollers 65A and 65B on the transport path 60a, and corrects the paper P transported by the transport guide 63. The curl correction unit 90 can switch the curl correction direction.

  The position where the curl correction unit 90 is provided is not limited to the example of FIG. 1, and the position between the paper supply unit (the paper supply cassette 4 or the manual feed tray 5) and the image forming unit 40 in the transport path 60 a. The position may be any position (position upstream of the paper feed unit and downstream of the image forming unit 40 in the transport direction of the transport path 60a), and a position between the paper feed unit and the registration rollers 65A and 65B is more preferable. This is because when the paper P is curled, there is a possibility that the skew of the skew correction of the registration rollers 65A and 65B, the print misalignment of the image forming unit 40 based on the paper misalignment of the registration rollers 65A and 65B, and jamming may occur. It is.

  Next, the curl correction unit 90 will be described in detail with reference to FIGS. FIG. 2 shows a configuration of the curl correction unit 90 in a normal state.

  As shown in FIG. 2, the curl correction unit 90 includes metal rollers 91 and 92 as first and second rollers, a rubber roller 93 as a third roller, a curl correction cam 94, and a spring unit 95. The metal roller 91 has a metal part 91a and a shaft part 91b. The metal portion 91a is made of metal and does not deform, and is provided around the shaft portion 91b. The metal material of the metal part 91a is steel such as SUM (sulfur free-cutting steel) and SUS (stainless steel). The metal part 91a may be made of a resin such as POM (polyacetal) or the like in addition to the metal. The shaft portion 91 b is a shaft of the metal roller 91. Similar to the metal roller 91, the metal roller 92 has a metal portion 92a and a shaft portion 92b. The metal rollers 91 and 92 are arranged so that the upper axis position in FIG. 2 is the same in the horizontal direction.

  The rubber roller 93 is a roller provided at a position separated from the metal rollers 91 and 92 in a normal state as shown in FIG. 2, and is controlled by a moving mechanism (not shown) constituted by a spring or the like. It can be moved so as to be in pressure contact with or spaced from 92. During this movement, the curl correcting cam 94 and the spring portion 95 are also moved together with the rubber roller 93. The metal rollers 91 and 92 are moved by a moving mechanism (not shown) so as to be pressed against or separated from the rubber roller 93, or the metal rollers 91 and 92 and the rubber roller 93 (and the curl correction cam 94 and the spring portion 95). It is good also as a structure which moves and presses or mutually separates.

  The rubber roller 93 has a rubber part 93a and a shaft part 93b. The rubber part 93a is made of rubber and can be deformed, and is provided around the shaft part 93b. The rubber part 93a may be configured by an elastic body other than rubber. The shaft portion 93b is a shaft of the rubber roller 93 and has a portion exposed at an end portion in the axial direction. Further, the rubber roller 93 is movable in the vertical direction in FIG. 2 by the rotation of the curl correction cam 94.

  The curl correction cam 94 is a mechanical element that is driven to rotate and has a curve in which the distance from the rotation axis to the spring portion 95 changes according to the rotation angle. The spring portion 95 is pressed between the shaft portion 93 b of the rubber roller 93 and the curl correction cam 94, and transmits the pressure applied by the rotation of the curl correction cam 94 to the rubber roller 93.

  Next, the detection unit 80 and the curl correction unit 90 during curl correction will be described with reference to FIGS. FIG. 3A shows a state of the curl correction unit 90 at the time of curl correction in the second direction. FIG. 3B shows a sheet P1 having a curl in the first direction.

  First, at the time of curl correction, the rubber roller 93, the curl correction cam 94, and the spring portion 95 are moved so that the metal rollers 91, 92 and the rubber roller 93 are pressed against each other by the control of the moving mechanism (not shown). Further, the first direction and the second direction are the left direction and the right direction in FIG. As shown in FIG. 3B, consider a case where the paper P1 is a back paper and has a curl in the first direction. The curl in the first direction is a curl in which the first direction is a concave surface. The blank sheet surface of the sheet P1 is the concave surface side.

  In order to correct the curl of the paper P1, it is necessary to correct the curl in the second direction opposite to the first direction. When the curl correction is performed in the second direction, the curl correction unit 90 is brought into a state shown in FIG. Specifically, the curl correcting cam 94 is rotationally driven to maximize the distance to the spring portion 95, the downward pressure applied to the rubber roller 93 is increased, and the axial position of the rubber roller 93 is adjusted to the metal rollers 91 and 92. The rubber roller 93 and the metal rollers 91 and 92 are pressed against each other at the same height as the intermediate position. Then, a concave nip portion N <b> 1 is formed in the second direction between the rubber roller 93 and the metal rollers 91 and 92. For this reason, the conveyed paper P1 passes through the nip portion N1, and is subjected to curl correction.

  FIG. 4A shows a state of the curl correction unit 90 at the time of curl correction in the first direction. FIG. 4B shows a sheet P2 having a curl in the second direction. As shown in FIG. 4B, consider a case where the paper P2 is a back paper and has a curl in the second direction. The curl in the second direction is a curl in which the second direction is concave. The blank surface of the paper P2 is the convex surface side.

  In order to correct the curl of the paper P2, it is necessary to correct the curl in the first direction opposite to the second direction. When curl correction is performed in the first direction, the curl correction unit 90 is in the state shown in FIG. Specifically, the curl correction cam 94 is rotationally driven so as to minimize the distance to the spring portion 95, the downward pressure applied to the rubber roller 93 is reduced, and the shaft position of the rubber roller 93 is the axis of the metal roller 91. The rubber roller 93 and the metal roller 91 are pressed against each other at the same height as the position. Then, a concave nip portion N2 is formed between the rubber roller 93 and the metal roller 91 in the first direction. For this reason, the conveyed paper P2 passes through the nip portion N2 and is subjected to curl correction.

  FIG. 5A shows the detection unit 80 and the curl correction unit 90 at the time of curl correction in the second direction. FIG. 5B shows the detection unit 80 and the curl correction unit 90 at the time of curl correction in the first direction.

  As shown in FIG. 5A, the detection unit 80 includes a curl direction detection sensor 81 provided on the first direction side of the conveyance guide 63 and a curl direction provided on the second direction side of the conveyance guide 63. And a detection sensor 82. The curl direction detection sensors 81 and 82 are sensors based on mechanical switches, and when the curl direction detection sensors 81 and 82 are pressed by the conveyed paper, the detection signals are output to the control unit 11 described later. The curl direction detection sensors 81 and 82 may include an optical paper detection sensor.

  As shown in FIG. 5A, when the paper P is detected by the curl direction detection sensor 81 and the paper P is not detected by the curl direction detection sensor 82, the paper P is curled in the first direction. For this reason, the curl correction unit 90 is set in a curl correction state in the second direction, and the curl correction of the paper P is performed. Further, as shown in FIG. 5B, when the paper P is not detected by the curl direction detection sensor 81 and the paper P is detected by the curl direction detection sensor 82, the paper P curls in the second direction. ing. For this reason, the curl correction unit 90 is set in the curl correction state in the first direction, and the curl correction of the paper P is performed.

  Next, the circuit configuration of the image forming apparatus 1 will be described. FIG. 6 shows a circuit configuration of the image forming apparatus 1.

  As shown in FIG. 6, the image forming apparatus 1 includes a control unit 11, an operation unit 20, a display unit 30, an image memory 12, a ROM (Read Only Memory) 13, a communication unit 14, an image forming unit 40, a transport unit 60, The detection unit 80, the curl correction unit 90, and the like are connected to each other via the bus 15.

  The control unit 11 centrally controls each unit of the image forming apparatus 1. The control unit 11 includes a CPU (Central Processing Unit) and a RAM (Random Access Memory). In the control unit 11, the CPU expands various programs stored in the ROM 13 in the RAM, and the CPU executes various processes using the programs expanded in the RAM.

  During normal image formation, the control unit 11 receives image data input from an external device (not shown) via the communication unit 14 and feeds the paper from the paper cassette 4 to the transport unit 60 for transport. Based on the received image data, the image forming unit 40 forms an image on a sheet. In addition, the control unit 11 executes a curl correction process to be described later using a curl correction program stored in the ROM 13.

  The operation unit 20 includes a key operation unit having various keys, receives various operation inputs from the user to the key operation unit, and outputs an operation signal of the operation input to the control unit 11. The display unit 30 includes a display panel such as an LCD (Liquid Crystal Display), and performs various displays according to display signals input from the control unit 11.

  The image memory 12 is a storage unit that temporarily stores information such as image data received from an external device. The ROM 13 is a storage unit dedicated to reading information. The ROM 13 stores various programs such as a curl correction program and various data.

  The communication unit 14 is connected to an external device (not shown) such as a PC (Personal Computer) via a communication line such as a LAN (Local Area Network). Communicate.

  As described with reference to FIG. 1, the image forming unit 40 includes the image forming main body 40 a and the fixing unit 40 b, and forms an image on the paper conveyed by the conveying unit 60 (toner on the paper) according to an instruction from the control unit 11. Image transfer and fixing). As described with reference to FIG. 1, the transport unit 60 includes various rollers such as a paper feed roller 61, and feeds paper from the paper feed cassette 4 or the manual feed tray 5 in accordance with instructions from the control unit 11. The paper is transported on the path 60 a and the reverse path 60 b and discharged to the paper discharge tray 3.

  As described with reference to FIG. 1, the detection unit 80 includes the curl direction detection sensors 81 and 82, detects the curl direction of the paper conveyed by the conveyance unit 60, and outputs the image signal to the control unit 11. As described with reference to FIG. 1, the curl correction unit 90 includes metal rollers 91 and 92, a rubber roller 93, and the like, and performs curl correction of the paper conveyed by the conveyance unit 60 in accordance with instructions from the control unit 11.

  Next, curl correction processing will be described as an operation of the image forming apparatus 1 with reference to FIG. FIG. 7 shows the flow of curl correction processing.

  The curl correction process is a process for determining whether or not the paper before image formation fed from the paper feed cassette 4 is a back paper, and when the paper is a back paper, the curl correction is performed on the back paper. For example, after an instruction to form an image on a sheet in the sheet cassette 4 is given, the control unit is triggered by the sheet being conveyed to a position where the curl direction detection sensors 81 and 82 in the conveyance guide 63 can be pressed. 11, the curl correction process is executed. The detection that the sheet has been conveyed to a position where the curl direction detection sensors 81 and 82 of the conveyance guide 63 can be pressed is performed by, for example, providing a sheet detection sensor (not shown) at that position and using the sheet detection sensor. It is assumed that this is done.

  First, based on the curl direction signal of the paper detected by the detection unit 80, it is determined whether or not there is curl in the paper being conveyed in the conveyance guide 63 (step S1). When the curl direction detection sensor 81 or 82 is pressed and a detection signal (curl direction signal) of the curl direction is input from the detection unit 80, it is determined that the paper being conveyed has curl. If the curl direction detection sensors 81 and 82 are not pressed and a curl direction signal in that direction is not input from the detection unit 80, it is determined that there is no curl on the sheet being conveyed.

  When the paper being conveyed has curl (step S1; YES), it is determined whether or not the curl direction is the first direction based on the paper curl direction signal detected by the detection unit 80 (step S2). . When the curl direction is the first direction (step S2; YES), the curl correction unit 90 is set to perform the curl correction in the second direction, and the paper being conveyed is curled in the second direction ( Step S3), the curl correction process is completed. Specifically, in step S3, as shown in FIG. 3A, the curl correction unit 90 is configured such that the metal rollers 91 and 92 and the rubber roller 93 are pressed against each other by a moving mechanism (not shown), and the curl correction cam. 94 is driven to rotate so that a nip portion N1 is formed between the metal rollers 91 and 92 and the rubber roller 93. The paper subjected to the curl correction by the curl correction unit 90 is conveyed to the registration rollers 65A and 65B, the image forming timing is adjusted, the image is formed by the image forming unit 40, and is discharged to the paper discharge tray 3, or the double-sided image. It is formed. For this reason, it is possible to prevent a skew correction shift in the registration rollers 65A and 65B, a print shift in the image forming unit 40, and a jam.

  When the curl direction is the second direction (step S2; NO), the curl correction unit 90 is set to perform the curl correction in the first direction, and the paper being conveyed is curled in the first direction ( Step S4), the curl correction process is completed. Specifically, in step S4, as shown in FIG. 4A, the curl correction unit 90 is configured such that the metal roller 91 and the rubber roller 93 are pressed by a moving mechanism (not shown) and the curl correction cam 94 is moved. The nip portion N2 is formed between the metal roller 91 and the rubber roller 93 by being driven to rotate. The paper subjected to the curl correction by the curl correction unit 90 is conveyed to the registration rollers 65A and 65B, the image forming timing is adjusted, the image is formed by the image forming unit 40, and is discharged to the paper discharge tray 3, or the double-sided image. It is formed. For this reason, it is possible to prevent a skew correction shift in the registration rollers 65A and 65B, a print shift in the image forming unit 40, and a jam.

  When there is no curl (step S1; NO), the curl correction unit 90 is set to a state where no curl correction is performed, and the paper being conveyed is passed through the curl correction unit 90 without being curled (step S5). The correction process ends. Specifically, in step S5, as shown in FIG. 2, in the curl correction unit 90, the metal rollers 91 and 92 and the rubber roller 93 are separated by a moving mechanism (not shown). The paper that has passed through the curl correction unit 90 is conveyed to the registration rollers 65A and 65B, the timing of image formation is adjusted, the image is formed by the image forming unit 40, and is discharged to the paper discharge tray 3, or the double-sided image is formed. The Since the paper is not curled, there is no skew correction deviation in the registration rollers 65A and 65B, print deviation in the image forming unit 40, or jamming.

  As described above, according to the present embodiment, the detection unit 80 detects the curl direction of the paper conveyed from the paper feed cassette 4, and the curl correction unit 90 determines whether the registration rollers 65 </ b> A and 65 </ b> B and the paper feed cassette 4 are connected. The control unit 11 curls the paper in a direction opposite to the curl direction of the detection result when the paper being conveyed has curl according to the detection result by the detection unit 80. The correction unit 90 performs curl correction, and when there is no curl, the paper passes through the curl correction unit 90 without being curled. For this reason, the paper conveyed from the paper feed cassette 4 can be subjected to curl correction according to the actual curl direction before image formation, skew correction misalignment in the registration rollers 65A and 65B, print misalignment in the image forming unit 40, jamming. Can be prevented.

  The curl correction unit 90 includes metal rollers 91 and 92 and a rubber roller 93. The metal rollers 91 and 92 and the rubber roller 93 are pressed against each other by a curl correction cam 94, a spring unit 95, and a moving mechanism (not shown). The state in which the metal roller 91 and the rubber roller 93 are pressed against each other and the state in which the metal rollers 91 and 92 and the rubber roller 93 are separated from each other are switched. For this reason, the number of rollers may be three, the configuration of the curl correction unit 90 can be simplified, the metal rollers 91 and 92 and the rubber roller 93 in the case of curl correction in the second direction, It is possible to freely switch between a state in which the metal roller 91 and the rubber roller 93 are pressed against each other in the case of curl correction in the direction 1 and a state in which the metal roller 91 and the rubber roller 93 are not separated from each other.

  The description in the above embodiment is an example of a suitable image forming apparatus according to the present invention, and the present invention is not limited to this.

  For example, at least two of the above embodiments and the following configurations may be appropriately combined.

  In the above embodiment, the image forming apparatus is an electrophotographic color printer. However, the present invention is not limited to this. For example, an apparatus such as an electrophotographic black-and-white printer, a black-and-white or color copier, or a multifunction peripheral may be used as the image forming apparatus.

  In the above-described embodiment, the detection unit 80 and the curl correction unit 90 are provided in the transport path between the registration rollers 65A and 65B and the paper feed cassette 4, and curl the paper transported from the paper feed cassette 4. Although it was a structure, it is not limited to this. For example, a detection unit 80 and a curl correction unit 90 are provided on the conveyance path between the registration rollers 65A and 65B (or the image forming unit 40) and the manual feed tray 5 (and the paper feed cassette 4), and the manual feed tray 5 (or The paper conveyed from the paper feed cassette 4) may be configured to correct the curl. In the image forming apparatus, a plurality of paper feed cassettes may be provided.

  In the above embodiment, the curl correcting unit 90 has the three rollers that are pressed against each other at the time of curl correction. However, the present invention is not limited to this. As the curl correction unit, for example, a plurality of roller pairs that perform curl correction in different directions may be provided to switch the curl correction direction. Also, an endless belt hung on a plurality of rollers and a pressure roller are provided, and the belt and the pressure roller are pressed against each other during curl correction, and the paper passes through the nip portion to perform curl correction in different directions. A plurality of devices may be provided to switch the curl correction direction. In addition, a curling correction direction may be switched by providing a plurality of apparatuses that include ironing materials such as blades and that curl paper in the different directions by squeezing paper with the ironing material during curl correction.

  Further, the detailed configuration and detailed operation of each part constituting the image forming apparatus 1 in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the curl correction part at the normal time. (A) is a figure which shows the state of the curl correction part at the time of the curl correction to a 2nd direction. FIG. 5B is a diagram illustrating a sheet having curl in a first direction. (A) is a figure which shows the state of the curl correction part at the time of the curl correction to the 1st direction. FIG. 6B is a diagram illustrating a sheet having curl in a second direction. (A) is a figure which shows a detection part and the curl correction part at the time of the curl correction to a 2nd direction. (B) is a figure which shows a detection part and the curl correction part at the time of the curl correction to a 1st direction. 1 is a block diagram illustrating a circuit configuration of an image forming apparatus. It is a flowchart which shows a curl correction process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Housing | casing 3 Paper discharge tray 4 Paper feed cassette 5 Manual feed tray 11 Control part 20 Operation part 30 Display part 12 Image memory 13 ROM
14 Communication section 15 Bus 40 Image forming section 40a Image forming main body section 40Y Yellow image forming section 40M Magenta image forming section 40C Cyan image forming section 40K Black image forming section 41 Photosensitive drum 42 Charging section 43 Exposure section 44 Development section 45 Primary transfer Roller 46 Cleaning unit 47 Intermediate transfer belt 48 Secondary transfer drive roller 49 Driven roller 50 Cleaning unit 40b Fixing unit 51 Fixing roller 52 Pressing roller 60 Conveying units 61, 64A, 64B Paper feed rollers 62A, 62B, 67A, 67B, 68A, 68B, 69A, 69B, 70A, 70B Conveying roller 63 Conveying guide 65A, 65B Registration roller 66 Pressure roller 60a Conveying path 60b Reversing path 80 Detection unit 81, 82 Curl direction detection sensor 90 Curl correction unit 91, 92 Metal rollers 91a, 92a Money Genus parts 91b, 92b Shaft part 93 Rubber roller 93a Rubber part 93b Shaft part 94 Curl correction cam 95 Spring part

Claims (3)

A paper supply unit for supplying paper;
An image forming unit that forms an image on a sheet conveyed from the sheet feeding unit based on image data;
A detection unit for detecting a direction of curling of the paper conveyed from the paper supply unit;
A curl correction unit that corrects curl of a sheet conveyed along a conveyance path between the image forming unit and the paper feeding unit, and the curl correction direction can be changed;
An image forming apparatus comprising: a control unit that sets a curl correction direction of the curl correction unit to a direction opposite to a curl direction of the paper detected by the detection unit, and causes the curl correction unit to correct the curl of the paper. A registration roller for conveying the paper to the image forming unit;
The image forming apparatus according to claim 1, wherein the curl correction unit corrects curl of a sheet conveyed along a conveyance path between the registration roller and the sheet feeding unit.   The curl correction unit includes a first roller and a second roller, and a third roller having an elastic body around it, and the first and second rollers and the third roller are pressed against each other. And the state where the first roller and the third roller are pressed against each other and the state where the first and second rollers and the third roller are separated can be switched. The image forming apparatus according to claim 1.

Images