JP2015117979A - Sheet shape measurement apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet shape measurement apparatus configured to convey a sheet and measure a shape of the sheet accurately, and an image forming apparatus.SOLUTION: A sheet shape measurement apparatus measures a bend shape of a sheet passing through a measurement position arranged on a sheet conveyance path, at the measurement position. The sheet shape measurement apparatus includes: a shape measurement unit for measuring the bend shape of the sheet at the measurement position; and a plurality of conveyance roller pairs arranged from upstream to downstream of the measurement position on the sheet conveyance path, to convey the sheet. The sheet conveyance path in at least the measurement position is arranged vertically downward by the conveyance roller pairs.

Description

  The present invention relates to a paper shape measuring apparatus capable of accurately measuring a curved shape of a paper and an image forming apparatus including the paper shape measuring apparatus. More specifically, the present invention relates to a paper shape measuring device capable of measuring the shape of a paper being conveyed while conveying the paper, and an image forming apparatus including the paper shape measuring device.

  In a general image forming apparatus using an electrophotographic method such as a printer or a copying machine, a process for fixing a toner image transferred onto a sheet is performed. In the fixing process, the paper carrying the toner image is pressurized while being heated. The sheet after the fixing process may be curled due to curling or undulation. When the paper is curled or the like, the paper is hindered on the paper discharge tray. In addition, when binding a plurality of sheets, binding quality may be deteriorated due to curling or the like. Therefore, it is preferable that curling and undulation of the discharged paper is reduced as much as possible.

  Therefore, in order to reduce curling and the like, a decurling device that appropriately feeds back the heating temperature in the fixing processing unit and performs correction for removing the curling or the like is provided. Both the feedback of the heating temperature of the fixing processing unit and the adjustment of the curl correction amount in the decurling apparatus are performed based on the measured curl degree by measuring the shape of the paper after the fixing process. For this reason, it is necessary to accurately measure the shape of the paper.

  For example, Japanese Patent Application Laid-Open No. 2004-151867 is cited as a technique related to sheet shape measurement. In Patent Document 1, a sheet having a pattern arranged on a paper surface is conveyed horizontally, and a plurality of patterns on the paper surface are read by a sensor arranged in a direction orthogonal to the paper conveyance direction. A method of measuring the shape of the paper from the read pattern on the paper is described.

JP 2005-257456 A

  However, the above-described conventional technique for measuring the shape of a sheet while conveying the sheet horizontally has a problem that the actual shape of the sheet cannot be measured accurately. That is, when a sheet with curl or the like is conveyed horizontally, the degree of curl or the like becomes different from the actual one due to the influence of gravity.

  The present invention has been made for the purpose of solving the problems of the prior art described above. That is, the object is to provide a paper shape measuring apparatus and an image forming apparatus that can accurately measure the shape of a paper while conveying the paper.

  The paper shape measuring device of the present invention, which has been made for the purpose of solving this problem, is a paper shape measuring device that measures the curved shape of a paper at the measurement position while passing the paper through the measurement position provided on the conveyance path. A shape measuring unit that measures the curved shape of the sheet at the measurement position, and a plurality of conveyance roller pairs that are provided from the upstream to the downstream of the measurement position on the sheet conveyance path, The paper shape measuring apparatus is characterized in that at least a paper conveyance path at a measurement position is provided downward in the vertical direction by a plurality of conveyance roller pairs.

  In the paper shape measuring apparatus of the present invention, the paper shape can be measured while transporting the paper downward in the vertical direction at the measurement position for measuring the paper shape. Thereby, it is possible to measure the paper shape that is not deformed by the influence of gravity. That is, the paper shape can be accurately measured while the paper is being conveyed.

  In the paper shape measuring apparatus described above, at least one of the plurality of transport roller pairs at a position adjacent to the upstream side of the measurement position and a position adjacent to the downstream side has a nip for sandwiching the paper. The axial length of the outer peripheral surface to be formed is in the range of 1 mm or more and 50 mm or less, and the outer peripheral surface is in an intermediate region between one end and the other end of the paper passing region in the axial direction. A pair of narrow conveying rollers provided is preferable. With such a pair of narrow conveying rollers, it is possible to sandwich the paper without deforming the shape of the paper on which curling or the like has occurred. This is because the sheet can be passed to the measurement position without being deformed.

  In the sheet shape measuring apparatus described above, the narrow conveying roller pair is preferably provided at a distance within a length in the sheet conveying direction from the measurement position on the sheet conveying path. This is because at least a part of the paper passing through the measurement position can be transported only by the pair of narrow transport rollers that hardly deform the shape.

  Further, in the paper shape measuring apparatus described above, at least one of the transport roller pairs located at a distance within the length in the paper transport direction from the measurement position may be pressed or separated toward the other. A pressure separation roller pair that has a pressure separation control unit that switches the pressure separation roller pair between a pressure contact state and a separation state, and the pressure separation control unit is configured such that when at least a part of the paper passes the measurement position, Of the pair of pressure rollers located between the leading edge and the trailing edge of the paper, the first one from the leading edge of the paper or the first and second one from the leading edge of the paper is brought into a pressure contact state. It is preferable that a state other than the pair of pressure separating rollers in the pressure contact state is set in a separated state. This is because the deformation of the sheet being conveyed can be suppressed by conveying only the leading one on the leading end side of the sheet, or the second pair of conveying rollers.

  According to another aspect of the present invention, there is provided an image forming apparatus including: an image forming unit that transfers a toner image onto a sheet; and a fixing unit that performs a fixing process of the transferred toner image on the sheet. The sheet shape measuring apparatus also extends to an image forming apparatus characterized in that it is provided downstream of the fixing unit in the sheet conveyance direction.

  According to the present invention, there is provided a paper shape measuring apparatus and an image forming apparatus that can accurately measure the shape of a paper while conveying the paper.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating an outline of a control configuration of an image forming apparatus according to the present embodiment. It is a schematic block diagram of a shape measurement part. It is a figure for demonstrating the curl of a paper. It is a figure for demonstrating a narrow conveyance roller pair with the short length of the outer peripheral surface in an axial direction. It is a figure for demonstrating the shape measurement of a paper when two measurement positions are provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is embodied in an electrophotographic printer.

  FIG. 1 shows a schematic configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes an image forming unit 2, a fixing processing unit 3, and a correction unit 4. The image forming unit 2 forms a toner image and transfers the formed toner image onto the paper P. The fixing processing unit 3 fixes the toner image on the paper P by heating and pressurizing the paper P carrying the toner image. The correction unit 4 removes curling and undulation of the paper P after the fixing process.

  First, the image forming unit 2 will be described. The image forming apparatus 1 is a so-called tandem color printer having an intermediate transfer belt 30 in the image forming unit 2. The intermediate transfer belt 30 is an endless belt member having conductivity, and both ends in the figure are supported by rollers 31 and 32. At the time of image formation, the roller 31 on the right side in FIG. 1 is driven to rotate counterclockwise. As a result, the intermediate transfer belt 30 and the left roller 32 in FIG. 1 are driven to rotate.

  A secondary transfer roller 40 is provided on the outer peripheral surface of the portion of the intermediate transfer belt 30 supported by the right roller 31 in FIG. The secondary transfer roller 40 and the outer peripheral surface of the intermediate transfer belt 30 are in contact with each other, and a secondary transfer region is formed by the contact transfer nip N1.

  Also, a belt cleaner 41 is provided on the outer peripheral surface of the portion of the intermediate transfer belt 30 supported by the left roller 32 in FIG. The belt cleaner 41 is in pressure contact with the outer peripheral surface of the intermediate transfer belt 30, and a collection area 42 for collecting the transfer residual toner is formed by the contacting portion.

  In the lower part of the intermediate transfer belt 30 in FIG. 1, image forming units 10Y, 10M, 10C for yellow (Y), magenta (M), cyan (C), and black (K) are sequentially arranged from left to right. 10K is arranged. The image forming units 10Y, 10M, 10C, and 10K are all for transferring the toner images of the respective colors onto the intermediate transfer belt 30. The image forming units 10Y, 10M, 10C, and 10K all have the same configuration. For this reason, in FIG. 1, the image forming unit 10 </ b> Y is represented by a reference numeral.

  That is, the image forming units 10Y, 10M, 10C, and 10K include a photosensitive member 11 that is a cylindrical electrostatic latent image carrier, a charger 12, a developing unit 14, and a photosensitive member cleaner 16 disposed around the photosensitive member. have. A primary transfer roller 15 is disposed at a position facing the photoconductor 11 with the intermediate transfer belt 30 therebetween. Further, an exposure device 13 is disposed below the image forming units 10Y, 10M, 10C, and 10K for each color in FIG.

  The charger 12 is for uniformly charging the surface of the photoconductor 11. The exposure device 13 is for irradiating the surface of the photoconductor 11 with laser light based on image data to form an electrostatic latent image. The developing unit 14 is for applying toner to the surface of the photoreceptor 11 by the developing roller 17.

  Above the intermediate transfer belt 30 in FIG. 1, hoppers 18Y, 18M, 18C, and 18K are arranged. The hoppers 18Y, 18M, 18C, and 18K are equipped with toner bottles 19Y, 19M, 19C, and 19K that store toner of the corresponding color, respectively. Each hopper 18 is connected to the developing unit 14 of the image forming unit 10 of the corresponding color. The hopper 18 is for appropriately supplying toner contained in the toner bottle 19 to the corresponding developing unit 14.

  A density sensor for detecting the image density of the toner image transferred onto the intermediate transfer belt 30 is located downstream of the image forming unit 10K in the rotation direction of the intermediate transfer belt 30 and upstream of the transfer nip N1. 20 is provided. The density sensor 20 uses the outer peripheral surface of the intermediate transfer belt 30 as a detection position. The density sensor 20 includes, for example, a light projecting unit that irradiates light toward a detection position and a light receiving unit that receives the reflected light, which are used for adjusting the image density.

  In FIG. 1, the charger 12 is a roller charging type having a roller shape, but the present invention is not limited to this. A corona discharge charging charger, a blade charging member, a brush charging member, or the like may be used. Further, although the photosensitive member cleaner 16 is a plate and has one end portion in contact with the outer peripheral surface of the photosensitive member 11, the present invention is not limited to this. Other cleaning members, for example, a fixed brush, a rotating brush, a roller, or a combination of a plurality of them can be used. Alternatively, if a cleaner-less system in which the untransferred toner on the photoconductor 11 is collected by the developing unit 14 is employed, the photoconductor cleaner 16 may be omitted.

  A detachable paper feed cassette 51 is mounted at the lower part of the image forming apparatus 1. A conveyance path 50 is provided above the right side in FIG. Then, the sheets P stored in the sheet feeding cassette 51 by stacking are sent out one by one from the uppermost one to the conveying path 50 by the sheet feeding roller 52.

  A pair of registration rollers 53 and a transfer nip N1 are arranged in this order on the conveyance path 50 of the paper P in the image forming unit 2 sent out by the paper feed roller 52. The registration roller 53 is for adjusting the timing of feeding the paper P to the transfer nip N1. Further, the toner image on the intermediate transfer belt 30 is transferred to the paper P at the transfer nip N1. A fixing processing unit 3 is provided further downstream of the transfer nip N1 in the conveyance path 50.

  The fixing processing section 3 is for performing a fixing process on the paper P of the toner image transferred from the intermediate transfer belt 30 to the paper P in the transfer nip N1. The fixing processing unit 3 is provided with a heating roller 60 and a pressure roller 61 facing the heating roller 60 with the conveyance path 50 interposed therebetween. The heating roller 60 has a heater 62 inside. The pressure roller 61 is pressed against the heating roller 60 in a direction perpendicular to the axis. Due to the pressure contact, a fixing nip N <b> 2 for fixing the paper P is formed between the heating roller 60 and the pressure roller 61.

  The heating roller 60 is driven to rotate counterclockwise during image formation. The pressure roller 61 is driven and rotated by the rotation of the heating roller 60. The fixing processing unit 3 performs fixing processing of the toner image carried by the paper P by heating and pressurizing the paper P passing through the fixing nip N2. A correction unit 4 is provided further downstream of the fixing nip N <b> 2 of the conveyance path 50. The correction unit 4 is for correcting and removing curls and undulations generated on the paper P. The curling and undulation of the paper P occurs, for example, when the paper P is heated during the fixing process. That is, the degree of moisture evaporation from the paper P during heating is not uniform, and the paper P is curled.

  In the correction unit 4, a shape measuring unit 100, a decurling device 80, and a paper discharge roller 54 are provided along the conveyance path 50. A paper discharge tray 55 is provided at the lower part of the correction unit 4 further downstream of the paper discharge roller 54. As will be described in detail later, the shape measuring unit 100 is for measuring the shape of the paper P being conveyed while the paper P is being conveyed.

  The decurling device 80 is for correcting curling or the like of the generated paper P when the paper P is curled or wavy. The decurling device 80 has a plurality of decurling rollers 81 that are roller pairs arranged along the transport path 50. Then, the paper P is passed through the correction nip N3 of each decurling roller 81 to correct the curl or the like.

  In the decurling device 80 of this embodiment, the pressure contact force in the correction nip N3 of each decurling roller 81 can be adjusted. By adjusting the pressure contact force, it is possible to adjust the amount of correction and the direction of correction for correcting curling and undulation occurring on the paper P. The correction amount and correction direction in the decurling device 80 are obtained based on the shape of the paper P measured by the shape measuring unit 100.

  Next, an example of a normal image forming operation by the image forming apparatus 1 of this embodiment will be briefly described. The following description is an example of an image forming operation in a print mode in which a color image is formed on the paper P stored in the paper feed cassette 51 using four color toners.

  During normal image formation, the intermediate transfer belt 30 and the photoreceptors 11 of the respective colors are rotated at a predetermined peripheral speed in the directions indicated by arrows in FIG. First, the outer peripheral surface of the photoconductor 11 is charged almost uniformly by the charger 12. Next, light corresponding to the image data is projected onto the outer peripheral surface of the charged photoconductor 11 by the exposure device 13 to form an electrostatic latent image. Subsequently, the electrostatic latent image is developed with toner supplied by the rotation of the developing roller 17 of the developing unit 14, and a toner image is formed on the photoreceptor 11.

  The toner images of the respective colors formed on the photosensitive member 11 are transferred (primary transfer) onto the intermediate transfer belt 30 by the primary transfer roller 15. That is, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30 in this order. The transfer residual toner that is not transferred to the intermediate transfer belt 30 and remains on the photoconductor 11 even after passing the primary transfer roller 15 is scraped off by the photoconductor cleaner 16 and removed from the photoconductor 11. . The superimposed four color toner images are conveyed by the intermediate transfer belt 30 to the transfer nip N1.

  On the other hand, the paper P stored in the paper feed cassette 51 is pulled out from the uppermost one by one to the transport path 50 by the paper feed roller 52. The drawn paper P is conveyed along the conveyance path 50, and reaches the transfer nip N1 by the registration roller 53 in synchronization with the toner image placed on the intermediate transfer belt 30. Then, the superimposed four color toner images are transferred (secondary transfer) onto the paper P in the transfer nip N1. The toner image remaining on the intermediate transfer belt 30 even after passing through the transfer nip N1 is scraped off by the belt cleaner 41 in the collection area 42. As a result, the intermediate transfer belt 30 is removed.

  The paper P on which the toner image has been transferred is further conveyed downstream of the conveyance path 50. That is, the paper P is transported to the correction unit 4 after the fixing processing unit 3 performs the toner image fixing process. Then, in the correction unit 4, the shape measurement unit 100 measures the shape of the paper P, corrects by the decurling device 80 based on the shape of the paper P, and then is discharged to the paper discharge tray 55 by the paper discharge roller 54. The

  FIG. 2 shows an outline of the control configuration of the image forming apparatus 1. The image forming apparatus 1 includes a controller unit 90 and an engine control unit 91 in order to control each unit. The engine control unit 91 is configured around a CPU 92 that performs control processing for the entire apparatus.

  For example, the CPU 92 controls various loads 94 to form an image. That is, the toner image is formed in the image forming unit 10 and the temperature of the heater 62 in the fixing processing unit 3 is controlled. Further, the correction unit 4 at the time of image formation controls the reading of the shape of the paper P in the shape measuring unit 100 and calculates the correction amount and the correction direction of the decurling device 80 based on the read shape of the paper P. Do. Further, the decurling device 80 is controlled so that the calculated correction amount and correction direction are obtained.

  The engine control unit 91 includes a nonvolatile memory 93 attached to the main body and a nonvolatile memory 95 attached to various units. The CPU 92 performs writing and reading of the nonvolatile memory 93 attached to the main body. That is, the nonvolatile memory 93 stores data calculated by the CPU 92 and the like. Further, the non-volatile memory 93 also stores the rotational speed of the roller 31, the rotational speed of each photoconductor 11, the system speed such as the transport speed of the paper P in the transport path 50, and the like.

  Further, the CPU 92 performs writing and reading of the nonvolatile memory 95 attached to various units. In the nonvolatile memory 95 attached to the various units, for example, the remaining amount of toner is stored in the memory attached to the toner bottle 19, and the number of prints is stored in the memory attached to the imaging unit.

  The controller unit 90 is connected to an external personal computer or the like and receives an instruction input. Further, various information such as a dot counter value is exchanged between the engine control unit 91 and the controller unit 90.

  FIG. 3 is a schematic diagram of the shape measuring unit 100 of the present embodiment. As shown in FIG. 3, the shape measuring unit 100 includes a plurality of transport roller pairs A as a configuration for transporting the paper P. In addition, the shape measuring unit 100 includes an imaging unit 70 and an irradiating unit 71 as a configuration for reading the shape of the paper P at the measurement position M in the transport path 50.

  The plurality of transport roller pairs A1 to A7 are provided in this order along the transport path 50 from the downstream side of the fixing nip N2, and the transport path 50 faces downward in the vertical direction from the downstream side of the fixing nip N2. It is provided towards. Furthermore, in this embodiment, the conveyance path 50 is provided downward in the vertical direction from the conveyance roller pair A3 located upstream of the measurement position M to the conveyance roller pair A5 located downstream of the measurement position M. And it is horizontally provided downstream of the transport roller pair A6 downstream of the transport roller pair A5.

  The measurement position M is located in a section provided downward in the vertical direction in the transport path 50. Specifically, it is located between the transport roller pair A4 and the transport roller pair A5. The imaging unit 70 and the irradiation unit 71 are provided on the right side of the measurement position M. The imaging unit 70 and the irradiation unit 71 are for measuring the shape of the paper P being conveyed along the conveyance path 50 in a non-contact manner at the measurement position M by a light cutting method.

  The imaging unit 70 is a CCD camera, and reads the shape of the paper P being conveyed on the conveyance path 50 at the measurement position M. The measurement position M has a length in the depth direction in FIG. As shown in FIG. 3, the irradiating unit 71 irradiates the laser beam L toward the measurement position M from an oblique direction with respect to the paper surface of the paper P. The laser beam L has a slit shape in the width direction (depth direction in FIG. 3) orthogonal to the transport direction of the paper P.

  Then, by irradiation with the laser beam L, a linear line of light in the width direction is formed on the surface of the sheet P at the measurement position M. The imaging unit 70 can read the shape of the paper P by imaging the linear light streaks formed on the paper P at the measurement position M with the laser light L.

  Specifically, the paper P is transported along the transport path 50 by the transport roller pair A and passes through the measurement position M where the laser beam L is irradiated. Therefore, a streak of light by the laser beam L is formed on the paper P at the measurement position M. The imaging unit 70 continuously captures the light streaks on the paper P at the measurement position M, and outputs the captured data to the CPU 92.

  When the paper P is not curled or wavy, the streak of light on the paper P at the measurement position M imaged by the imaging unit 70 is straight. On the other hand, when the paper P is curled or wavy, the light streaks on the paper P at the measurement position M imaged by the imaging unit 70 is distorted depending on the degree of the curl or wavy.

  That is, the CPU 92 can obtain the shape of the paper P at the measurement position M by calculation from the shape of the streak of light imaged by the imaging unit 70. Further, the CPU 92 can obtain the overall shape of the sheet P by calculation from data obtained by the imaging unit 70 continuously imaging a plurality of times from the leading end to the trailing end in the transport direction of the sheet P passing the measurement position M. . Thereby, the shape of the paper P can be measured.

  Here, in the present embodiment, the paper P is transported downward in the vertical direction to the measurement position M by a plurality of transport roller pairs A. The effect of this will be described with reference to FIG. FIG. 4 shows an example of the paper P in a curled state by a solid line. A two-dot chain line indicates a state in which no curling occurs. In FIG. 4, X indicates the transport direction of the paper P, and Y indicates the width direction orthogonal to the transport direction of the paper P.

  When the paper P is arranged horizontally, as shown in FIG. 4, gravity acts perpendicularly to the paper surface of the paper P in a state where no curling occurs. For this reason, even if the paper P is actually curled as shown by the solid line in FIG. 4, it is deformed as shown by the broken line due to the influence of gravity. That is, in the example of FIG. 4, the end in the width direction of the paper P is actually lifted by curl, but the lifted end is lowered by gravity by being horizontally arranged. . For this reason, when the shape measurement of the paper P is carried out horizontally, for example, so that the paper surface of the paper P intersects the direction of gravity, the actual degree of curl is measured. It cannot be detected accurately.

  On the other hand, in the shape measuring unit 100 of this embodiment, the shape of the paper P is not affected by gravity at the measurement position M. This is because the paper P is conveyed downward in the vertical direction by the conveyance roller pair A at the measurement position M. Therefore, the imaging unit 70 of the shape measuring unit 100 can capture the actual shape of the paper P that is not affected by gravity.

  Therefore, the CPU 92 determines the amount of curl correction and the direction of correction in the decurling device 80 based on the degree of curling of the measured paper P before the paper P reaches the decurling device 80 after passing through the measurement position M. Adjust. Specifically, the pressure contact force at the correction nip N3 of each decal roller 81 is adjusted. Therefore, the paper P passes through the decurling device 80 in which the correction amount and the correction direction of the curl and the like are adjusted. After the curl and the like are corrected, the paper P is discharged to the paper discharge tray 55 by the paper discharge roller 54.

  Any of the sheets P discharged in this way has no trouble in stacking on the sheet discharge tray 55. This is because the correction amount and the correction direction of the paper P in the decurling device 80 are determined based on the actual shape of the measured paper P. That is, curling and undulation are appropriately removed by the decurling device 80. Furthermore, even when a plurality of discharged sheets P are bound and bound, the bookbinding quality is high.

  Alternatively, the temperature of the heater 62 in the fixing processing unit 3 can be fed back based on the measured shape of the paper P. Thereby, the degree of curl or the like in the next paper P can be reduced. This is because the feedback of the temperature of the heater 62 can be performed based on the actual shape of the paper P imaged by the imaging unit 70.

  Moreover, it is preferable that the conveyance roller pair A of the shape measurement part 100 is a narrow thing as shown in FIG. FIG. 5 shows transport roller pairs A3, A4, and A5. Each of the transport roller pairs A3, A4, and A5 has a narrow width in which the axial length B of the outer peripheral surface sandwiching the paper P is narrower than the width of the paper P. The narrow conveying roller pairs A3, A4, and A5 are all arranged in the center of the paper P in the width direction.

  Usually, the pair of transport rollers used for transporting the paper is wide and longer in the axial direction than the width of the paper P. With such a wide conveying roller pair, when the paper P is sandwiched, the curl generated in the width direction Y as shown in FIG. 4 is deformed. That is, with the wide conveying roller pair, the end portion in the width direction Y of the paper P shown in FIG. 4 is also sandwiched and deformed straight at the sandwiched position.

  On the other hand, the narrow conveying roller pairs A3, A4, and A5 sandwich only the center in the width direction Y of the paper P even when curling occurs in the width direction Y of the paper P as shown in FIG. Can be transported. Therefore, the end portion in the width direction Y of the paper P is not sandwiched and deformed. For this reason, at the measurement position M, the actual shape of the paper P that is not deformed can be measured. In addition, in order to reduce deformation due to the conveyance roller pair A of the paper P at the measurement position M, at least the conveyance roller pairs A4 and A5 adjacent to the upstream and downstream of the measurement position M should be narrow. preferable.

  Moreover, when making the conveyance roller pair A into a narrow thing, it is preferable that the length B of the axial direction of the outer peripheral surface exists in the range of 1 mm or more and 50 mm or less. This is because the pair of transport rollers A within this range can sandwich the paper P without being deformed. In addition, it is preferable that the outer peripheral surface of the narrow conveying roller pair A has a certain degree of elasticity. This is because, since the width of the paper P is narrow, if the outer peripheral surface is hard, there is a risk that the paper P that has been pinched will have a habit of being caught.

  Furthermore, it is preferable that all the conveyance roller pairs A positioned at a distance within the sheet length that is the length in the conveyance direction of the sheet P from the measurement position M upstream and downstream of the measurement position M are narrow. For example, when the leading edge of the paper P is sandwiched between the narrow conveying roller pair A and the trailing edge is sandwiched between the wide conveying roller pair A, naturally, the trailing edge side of the paper P cannot accurately detect curl. Moreover, it is because there exists a possibility that it may deform | transform in the front end side under the influence that the rear end is pinched | interposed uniformly in the width direction.

  Then, by making all the conveyance roller pairs A within a distance within the paper length of the paper P from the measurement position M narrow, the paper P at least part of which passes through the measurement position M is conveyed in a narrow width. It can be conveyed only by the roller pair A. This is because the deformation of the paper P due to the sandwiching of the transport roller pair A at the measurement position M can be further reduced, and the shape of the paper P can be measured more accurately.

  Further, when at least a part of the paper P passes the measurement position M, it is preferable that the paper P is always transported by only two or less transport roller pairs A positioned on the leading end side in the transport direction of the paper P. . When the paper length of the paper P is long, the paper P is transported in a state of straddling a number of transport roller pairs A. However, the sheet P sandwiched between a large number of transport roller pairs A has a correspondingly large deformation amount due to the sandwiching, resulting in a shape different from the actual shape.

  Therefore, all the conveying roller pairs A positioned at a distance within the paper length of the paper P from the measurement position M upstream and downstream of the measurement position M can be pressed or separated toward at least one of them toward the other. . Then, while the paper P passes through the measurement position M, for example, the paper P is transported only by the two transport roller pairs A positioned on the leading end side. Specifically, for example, the transport roller pair A upstream from the transport roller pair A3 is set in a separated state after the leading edge of the paper P reaches the measurement roller M after reaching the transport roller pair A4.

  Thereafter, the paper P is transported, and when the leading edge reaches the transport roller pair A5, the transport roller pair A3 is separated. In this manner, the transport roller pair A is sequentially separated when the leading edge of the paper P reaches the transport roller pair A that is two downstream. As a result, the sheet P passing through the measurement position M can be transported only by the two transport roller pairs A located on the leading end side, and deformation at the measurement position M can be reduced. The separated transport roller pair A is kept in a separated state until the trailing edge of the paper P passes. In addition, after the separation state, the pressure contact state may be returned before the leading edge of the next sheet P arrives.

  In the case where the paper P is transported by only one transport roller pair A positioned on the leading end side, the transport roller until the front end of the paper P reaches the measurement position M after reaching the transport roller pair A4. What is necessary is just to make it the separation state about the conveyance roller pair A upstream from the pair A4. After that, the transport roller pair A may be sequentially separated when the leading edge of the paper P reaches the transport roller pair A adjacent downstream thereof.

  Further, it is not always necessary to return to the pressure contact state before the leading edge of the paper P reaches. After the leading edge of the paper P passes through the transport roller pair A, it may be in a pressure contact state before reaching the transport roller pair A adjacent downstream. Thereby, even when the curl on the leading end side of the paper P is large, the leading end can be appropriately passed through the nip of the conveying roller pair A.

  Note that the arrival or passage of the paper P to each pair of transport rollers A or the measurement position M can be detected by, for example, providing sensors for confirming the paper P at these positions. Alternatively, the CPU 92 grasps the position of the paper P fed from the paper feed cassette 51 and being transported through the transport path 50 at the system speed. This is because the position of each device on the transport path 50 and the system speed for transporting the paper P are known by design. For this reason, it is possible to know the arrival and passage of the paper P to each pair of transport rollers A and the measurement position M depending on the position of the paper P on the transport path 50. Further, the control of the press contact and separation of the transport roller pair A can be performed by the CPU 92.

  Further, when the paper P is transported only by the two transport roller pairs A on the leading end side, when using a narrow transport roller pair A, the measurement position is located upstream of the measurement position M. Two conveying roller pairs A3 and A4 close to M may be narrow. This is because when the leading edge of the paper P passes the measurement position M, the transport roller pair A on the upstream side of the transport roller pair A3 is in a separated state. In addition, it is preferable that all the transport roller pairs A positioned at a distance within the sheet length of the sheet P from the measurement position M are narrower than the measurement position M. Further, when the paper P is transported by only one transport roller pair A on the leading end side, only the transport roller pair A3 adjacent upstream of the measurement position M may be narrow.

  Further, a plurality of measurement positions M may be provided. This will be described with reference to FIG. In the shape measuring unit 200 shown in FIG. 6, among the conveyance roller pair A, the conveyance roller pairs A3, A4, and A5 shown by hatching are narrow. On the other hand, the conveyance roller pair A upstream from the conveyance roller pair A3 and downstream from the conveyance roller pair A5 is not narrow but wide and sandwiches the paper P in the width direction.

  For this reason, when the paper P is curled, the deformation of the paper P at the portion of the paper P sandwiched between the narrow conveying roller pairs A3, A4, A5 is small. On the other hand, the deformation of the portion sandwiched by the other wide conveying roller pair A is large. Further, in FIG. 6, it is assumed that the transport roller pair A remains in a pressed state and does not take a separated state.

  In FIG. 6, a measurement position M1 is provided between the conveyance roller pair A3 and A4 in the conveyance path 50, and a measurement position M2 is provided between the conveyance roller pair A4 and A5. On the right side in FIG. 6, an imaging unit 70 and an irradiation unit 71 for measuring the shape of the paper P at the measurement positions M1 and M2 are provided. In FIG. 6, the distances on the conveyance path 50 from the wide conveyance roller pair A2 to the measurement positions M1 and M2 are indicated by Z1 and Z2, respectively. In addition, it is also possible to perform shape measurement at the measurement positions M1 and M2 by a pair of the imaging unit 70 and the irradiation unit 71.

  In the configuration shown in FIG. 6, it is preferable that the shape measurement of the paper P is performed at the measurement position M2 on the leading end side and at the measurement position M1 on the rear end side. As shown in FIG. 6, when the leading edge of the paper P sandwiched between the transport roller pairs A1, A2, and A3 reaches the measurement position M1, the leading edge of the paper P is transported wide upstream of the measurement position M1. There is a risk of deformation under the influence of pinching by the roller pair A2. This is because the distance Z1 from the transport roller pair A2 to the measurement position M1 is short.

  On the other hand, when the leading edge of the paper P reaches the measurement position M2, the curl at the leading edge of the paper P is not significantly affected by the pinching by the wide conveying roller pair A2. This is because the distance Z2 from the transport roller pair A2 to the measurement position M2 is longer than the distance Z1. Therefore, it can be seen that it is preferable to measure the shape of the front end side of the paper P at the measurement position M2. Similarly, since the distance from the wide conveyance roller pair A6 downstream of the measurement position M2 to the measurement position M1 is longer than the distance from the conveyance roller pair A6 to the measurement position M2, the rear end side of the paper P is It can be seen that it is preferable to measure the shape at the measurement position M1.

  As described above in detail, the image forming apparatus 1 according to the present embodiment includes the shape measuring unit 100 in the correction unit 4. The shape measuring unit 100 includes a plurality of transport roller pairs A that transport the paper P to the measurement position M. The conveyance path 50 by the plurality of conveyance roller pairs A is provided downward in the vertical direction at the measurement position M. For this reason, the paper P is conveyed downward in the vertical direction at the measurement position M. Thus, a paper shape measuring device that can accurately measure the shape of the paper while transporting the paper, and an image forming apparatus including the paper shape measuring device are realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the above embodiment, the shape of the paper P is measured by the light cutting method, but the shape of the paper P may be measured by other non-contact methods. For example, the shape of the paper P is measured by irradiating a certain area on the paper surface of the paper P with a lattice-shaped laser beam and photographing the irradiation region of the paper P that is being irradiated with the laser beam with an imaging unit. You can also. Further, for example, the pair of narrow conveyance rollers may not sandwich the sheet at the center in the width direction. This is because the paper can be transported with almost no deformation even when the narrower transport roller pair sandwiches the portion from the end than the center in the width direction of the paper. In addition, the number of transport roller pairs in the shape measuring unit is an example, and may be appropriately different.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 70 ... Imaging part 71 ... Irradiation part 100 ... Shape measurement part A ... Conveyance roller pair L ... Laser beam M ... Measurement position P ... Paper

Claims (5)

In a paper shape measuring apparatus for measuring a curved shape of a paper at the measurement position while passing the paper through a measurement position provided on the conveyance path,
A shape measuring unit for measuring the curved shape of the paper at the measurement position;
A plurality of transport roller pairs for transporting paper, which are provided from upstream to downstream of the measurement position on the paper transport path;
A paper shape measuring apparatus, wherein a plurality of the conveyance roller pairs are provided so that at least a paper conveyance path at the measurement position is directed downward in the vertical direction. In the paper shape measuring device according to claim 1,
Among the plurality of transport roller pairs, at least a position adjacent to the upstream side of the measurement position and a position adjacent to the downstream side are the axial lengths of the outer peripheral surfaces forming a nip for sandwiching the paper. Is within a range of 1 mm or more and 50 mm or less, and the pair of narrow conveying rollers provided in the intermediate region between one end and the other end of the sheet passing region in the axial direction of the outer peripheral surface. A paper shape measuring apparatus characterized by the above. In the paper shape measuring apparatus according to claim 2,
The paper shape measuring apparatus, wherein the narrow conveying roller pair is provided at a distance within the length in the paper conveyance direction from the measurement position on the paper conveyance path. In the paper shape measuring apparatus according to any one of claims 1 to 3,
Among the transport roller pairs, those located at a distance within the length of the paper transport direction from the measurement position are pressure roller pairs that can be pressed or separated at least one of them toward the other,
A pressure separation control unit that switches the pressure separation roller pair between a pressure contact state and a separation state;
The pressure separation control unit
When at least part of the paper passes through the measurement position,
Of the pair of press rollers located between the leading edge and the trailing edge of the paper,
The first one from the leading edge of the paper, or the first one from the leading edge of the paper and the second one are in pressure contact state,
A paper shape measuring apparatus characterized in that a member other than the pressure roller pair in the pressure contact state is placed in a separated state. An image forming unit for transferring a toner image to paper;
In an image forming apparatus having a fixing unit that fixes a transferred toner image onto a sheet,
A paper shape measuring device according to any one of claims 1 to 4,
The image forming apparatus according to claim 1, wherein the sheet shape measuring device is provided downstream of the fixing unit in the sheet conveyance direction.

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