JP2013227120A - Image forming apparatus and thickness detection method of recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately detecting a thickness of a sheet even if a conveyance interval of sheets is narrow.SOLUTION: An image forming apparatus includes: a driving roller 47a that conveys a sheet by being rotated and driven; a driven roller 47c that is set to be pressed into the driving roller 47a and sandwiches the sheet between the driving roller 47a; a variation detection sensor 61 that detects a variation of the driven roller 47c caused by sandwiching the sheet; a sheet thickness detection part 601 that detects a sheet thickness based on detection data from the variation detection sensor 61; a sheet existence detection part 602 that detects existence of the sheet between the driving roller 47a and the driven roller 47c; and a driving control part 603 that performs rotation driving control of the driving roller 47a based on the detection data of the sheet existence detection part 602.

Description

  The present invention relates to an image forming apparatus that conveys a recording medium such as paper and forms an image on the recording medium, and a method for detecting the thickness of the recording medium.

  2. Description of the Related Art Conventionally, electrophotographic image forming processing has been performed in image forming apparatuses such as copying machines, facsimile machines, and printers. In electrophotographic image forming processing, an electrostatic latent image is formed on a photosensitive drum, the formed electrostatic latent image is developed with toner, and the developed toner image is transferred to a recording medium to form an image. The In order to perform such process processing accurately, conditions for each process are set according to characteristics such as the thickness of the recording medium. Therefore, when performing image processing on a recording medium, the thickness of the recording medium to be transported is detected in advance to determine whether or not a recording medium with a non-standard thickness is transported. In the case of this recording medium, the image forming process is stopped.

  Regarding such a recording medium thickness detection technique, for example, in Patent Document 1, for the purpose of increasing detection accuracy, an output value that varies depending on the thickness of a recording medium that is transported through a predetermined position of the transport path is detected. Based on the output value when there is no recording medium and the output value when there is no recording medium detected by the detecting means before the recording medium is transported through the predetermined position of the transport path and after the previous recording medium passes, An image forming apparatus for detecting the thickness of the image is described.

  In Patent Document 2, an encoder is installed on a roller shaft for detecting thickness, and data corresponding to one rotation of the roller between sheets is collected from the measurement data between a plurality of sheets, and the value is averaged. An image forming apparatus to be used is described.

In the above-mentioned patent documents, in order to improve the accuracy of thickness detection of a recording medium, detection is performed based on an output value in the presence or absence of a recording medium, or an average value of measurement data is used. However, when detecting based on the amount of displacement of the roller that conveys the recording medium according to the thickness of the recording medium, it is necessary to take into account variations due to the eccentricity of the rotating shaft of the roller. In order to measure the amount of eccentricity of the rotation axis of the roller, it is necessary to carry the roller at least once during the detection of the thickness of the recording medium. It becomes difficult to perform one rotation of the roller in the absence, and the thickness cannot be detected accurately.
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can accurately detect the thickness of a recording medium even when the conveyance interval of the recording medium is narrow.

  An image forming apparatus according to the present invention is an image forming apparatus that conveys a sheet-like recording medium to form an image on the recording medium, the driving roller being rotated to convey the recording medium, and the driving roller A driven roller that is set so as to be in pressure contact with the drive roller and sandwiches the recording medium, a variation detection unit that detects a variation of the driven roller caused by sandwiching the recording medium, and the variation detection unit A recording medium thickness detecting means for detecting the thickness of the recording medium based on detection data from the recording medium; a recording medium presence detecting means for detecting the presence or absence of the recording medium between the driving roller and the driven roller; Drive control means for performing rotational drive control of the drive roller based on detection data of the recording medium presence / absence detection means.

  Since the present invention has the above-described configuration, it is possible to accurately detect the thickness of the recording medium by detecting the fluctuation of the driven roller by performing rotational drive control of the driving roller in the absence of the recording medium. Even when the transport interval is narrow, the thickness of the recording medium can be accurately detected.

It is a schematic block diagram regarding embodiment which concerns on this invention. It is a schematic block diagram regarding the apparatus which detects paper thickness. It is explanatory drawing which shows the state which pinched | interposed the paper. It is a time chart regarding the example of a detection output of a change detection sensor. It is a time chart regarding the example of a detection output when the space | interval of the paper to convey is narrow. It is a time chart regarding the example of a detection output at the time of enlarging the rotational speed of a drive roller within the time when there is no paper.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram relating to an embodiment of the present invention. The image forming apparatus includes an image forming processing unit 1, a paper feeding unit 2, a reading unit 3, and a document conveying unit 4. The image formation processing unit 1 forms a toner image on a sheet that is a sheet-like recording medium. An intermediate transfer unit is disposed in the center of the image forming processing unit 1, and an intermediate transfer belt 10 that is an endless belt is provided in the intermediate transfer unit. The intermediate transfer belt 10 is composed of, for example, a multi-layer belt in which an elastic layer is provided on a base layer made of a material that hardly stretches, such as a fluororesin material having a small elongation or a rubber material having a large elongation, and a canvas or the like. As the elastic layer, for example, a surface obtained by coating a fluorine resin material on the surface of a fluorine rubber material or an acrylonitrile-butadiene copolymer rubber material to form a smooth coat layer can be used.

  The intermediate transfer belt 10 is stretched around the three support rollers 14 to 16 and is driven to rotate clockwise. A transfer belt cleaning unit 17 for removing residual toner remaining on the intermediate transfer belt 10 after the transfer of the toner image is provided on the downstream side of the third support roller 16. An image forming unit 20 for each color is disposed so as to face the intermediate transfer belt 10 between the first support roller 14 and the second support roller 15. The image forming unit 20 arranges color units of black (K), yellow (Y), magenta (M), and cyan (C) along the moving direction of the intermediate transfer belt 10. Each image forming unit 20 includes a photoreceptor unit 40, a charger unit 18, a developing unit, and a cleaning unit. The image forming unit 20 includes an IC tag and is detachably attached to the image forming apparatus. Above the image forming unit 20, a writing unit 21 for irradiating a laser beam for forming an electrostatic latent image on the photosensitive drum of the photosensitive unit 40 of each color is provided.

  Below the intermediate transfer belt 10 is a secondary transfer unit 22. The secondary transfer unit 22 is configured such that a secondary transfer belt 24, which is an endless belt, is stretched between a pair of conveying rollers 23, and the intermediate transfer belt 10 is pushed up and pressed against the third support roller 16. Has been. The secondary transfer belt 24 transfers the toner image formed on the intermediate transfer belt 10 and transfers the transferred toner image onto a sheet. A fixing unit 25 for fixing the toner image transferred onto the paper is provided on the side of the secondary transfer unit 22, and the paper on which the toner image has been transferred is conveyed to the fixing unit 25. The fixing unit 25 includes a fixing belt 26 that is an endless belt and a heating and pressing roller 27 that is in pressure contact with the fixing belt 26. Below the secondary transfer unit 22 and the fixing unit 25, there is provided a sheet reversing unit 28 for reversing and conveying the sheet on which the image is fixed on one side and the sheet on the other side to form an image. .

  The paper feed unit 2 includes a paper feed unit 43, and the paper feed unit 43 includes a plurality of stages of paper feed trays 44. At the side of the paper feed tray 44, a paper feed roller 42 that feeds the paper stacked on the paper feed tray 44 one by one, and the paper fed by the paper feed roller 42 is separated one by one so as not to double feed. A separation roller 45 that is carried out and a conveyance roller 47 that conveys the paper carried out from the separation roller 45 to the paper feed path 46 are provided. The sheet is transported toward the upper image forming processing unit 1 by the transport roller 47 and is transported into the transport roller unit 48. The conveyance roller unit 48 is provided with a registration roller 49. The leading edge of the conveyed sheet is abutted against the registration roller 49 to correct the inclination of the sheet, and from the registration roller 49 according to the timing of the image forming process. The sheet is conveyed to the secondary transfer unit 22. The paper can be set on the manual feed tray 51 and fed by the paper feed roller 50. The paper drawn by the paper feed roller 50 is conveyed one by one by the separation roller 52, butted against the registration roller 49 and conveyed to the secondary transfer unit 22.

  When a start switch of an operation unit (not shown) is pressed, when a document is set on the document feeder 30 of the automatic document feeder (ADF) that is the document transport unit 4, a known ADF is used. Is conveyed onto the contact glass 32. When no document is set on the ADF, the scanner of the reading unit 3 is driven to read and move the first carriage 33 and the second carriage 34 in order to read the document placed on the contact glass 32. Then, light is irradiated from the light source provided on the first carriage 33 toward the contact glass 32, and reflected light from the document surface is transmitted toward the second carriage 34 by the reflection mirror provided on the first carriage 33. . In the second carriage 34, the transmitted light is reflected by a mirror and incident on an imaging lens 35 to form an image on an image reading sensor 36 composed of a CCD (Charge Coupled Device) image sensor. The image reading sensor 36 generates image data of each color of black (K), yellow (Y), magenta (M), and cyan (C) based on the read image signal.

  Further, when the start switch is pressed, the rotational driving of the intermediate transfer belt 10 is started and preparation for image formation of each color unit of the image forming unit 20 is started. Then, an image forming sequence of each color is started, and an exposure laser modulated based on the image data of each color is projected onto the photosensitive drum corresponding to each color, thereby forming an electrostatic latent image. A toner image corresponding to the color image is formed on the electrostatic latent image formed on the photosensitive drum by forming each color toner image by the image forming process, transferring the toner image onto the intermediate transfer belt 10 and superimposing the toner images. Is done. When the leading edge of the toner image formation region of the intermediate transfer belt 10 enters the secondary transfer unit 22, the sheet is carried in such that the leading edge of the sheet enters the secondary transfer unit 22, whereby the intermediate transfer belt 10. The upper toner image is transferred to the paper. The sheet on which the toner image has been transferred passes through the fixing unit 25 and is fixed on the sheet. Then, the sheet is conveyed to the discharge roller 56 and discharged to the discharge tray 57 by the discharge roller 56. The intermediate transfer belt 10 can perform the image forming process again by cleaning the residual toner remaining on the belt after transferring the toner image by the intermediate transfer belt cleaning unit 17 and removing it.

  The sheet transported to the secondary transfer unit 22 is selectively rotated by driving one of the plurality of sheet feeding rollers 42 of the sheet feeding unit 2 and from one sheet feeding tray 44 of the sheet feeding units 43 arranged in a plurality of stages. Feed out the paper. Then, the fed paper is separated by one sheet by the separation roller 45, is carried out to the paper feed path 46, and is conveyed by the conveyance roller 47. The paper transported by the transport roller 47 is introduced into the transport roller unit 48 and abuts against the registration roller 49 of the transport roller unit 48 to correct the inclination of the paper. Then, as described above, the toner image is carried into the secondary transfer unit 22 in synchronization with the transfer timing of the toner image. In the case of paper feed by manual feed, paper is set on the manual feed tray 51, the paper feed roller 50 is driven to rotate, the paper set on the manual feed tray 51 is drawn, and the paper is conveyed one by one by the separation roller 52. The paper is separated and conveyed along the manual paper feed path 53, and the leading edge of the paper is brought into contact with the registration roller 49 in the same manner as the paper fed from the paper feed tray 44 and is carried into the secondary transfer unit 22. The

  The paper feed unit 43 is equipped with a paper end sensor that detects the remaining amount or presence of paper stored in the paper feed tray 44, a size detection sensor that detects the size and orientation of the paper, and each paper feed tray 44. Various sensors such as a tray set detection sensor for detecting whether or not there is provided. Such a sensor can be configured using a known photosensor. In addition, in order to monitor the transport state of the paper, a paper transport sensor for detecting whether or not a transport jam (paper jam) has occurred is provided at a necessary location.

  When the image forming process is performed on the remaining one side of the sheet fixed on one side in the fixing unit 25, the sheet is conveyed to the sheet reversing unit 28. First, the switching claw 55 is operated and guided to the discharge roller 56, and the paper is once transported to the paper discharge tray 57 by the discharge roller 56, and the discharge roller 56 is reversed to pull the paper into the paper reversing unit 28. The carried-in paper is returned to the registration roller 49 again through the reverse path, and the remaining one-side image forming process is performed. It is also possible to operate the switching claw 55 so as to guide the sheet on which image formation processing has been performed on one side to the sheet reversing unit 28 side, perform the reversing conveyance process, and return the sheet to the registration roller 49 again. The sheet that has undergone image formation processing on both sides is discharged to a discharge tray 57 by a discharge roller 56 after fixing processing.

  The registration roller 49 is normally used while being grounded, but it is also possible to apply a bias voltage to remove paper dust from the paper. For example, a bias voltage can be applied using a conductive rubber roller. A conductive rubber roller having a diameter of 18 mm and a conductive layer made of a conductive NBR rubber material having a thickness of 1 mm is used on the surface. The electric resistance of the conductive layer is about 109 Ωcm, which is the volume resistance of the rubber material. As described above, the surface of the sheet after passing through the registration roller 49 to which the bias voltage is applied is slightly charged on the negative side. For this reason, in the transfer process from the intermediate transfer belt 10 to the sheet, it may be necessary to change the transfer conditions as compared with the case where no bias voltage is applied to the registration roller 49. A voltage of about −800 V is applied to the intermediate transfer belt 10 on the toner transfer side (front side), and a voltage of about +200 V is applied to the opposite side (back side) by the transfer roller 62.

  FIG. 2 is a schematic configuration diagram relating to an apparatus for detecting the sheet thickness. In this example, the sheet thickness is detected using the conveyance roller 47. The conveying roller 47 includes a driving roller 47a and a driven roller 47c. The driven roller 47c is urged by an elastic member (not shown) and is in pressure contact with the driving roller 47a. It is designed to be held and transported. A drive motor 62 is connected to the rotation shaft 47b of the drive roller, and the drive roller 47a is rotationally controlled by controlling the drive motor 62 by the control unit 60.

  A fluctuation detection sensor 61 is attached to the rotation shaft 47d of the driven roller 47c, and the fluctuation detection sensor 61 detects the fluctuation of the rotation shaft 47d. Examples of the fluctuation detection sensor 61 include a lever type encoder, a magnetic type linear sensor, an optical distance measuring sensor, and a direct-acting minute displacement sensor. In the case of a lever-type encoder, the change can be detected by setting the detection lever in contact with the rotation shaft 47d and quantitatively detecting the displacement of the detection lever accompanying the change in the rotation shaft 47d with the encoder. . With respect to other sensors, the fluctuation can be detected by quantitatively detecting the fluctuation of the rotating shaft 47d magnetically or optically.

  The control unit 60 includes a paper thickness detection unit 601, a paper presence / absence detection unit 602, and a drive control unit 603. As shown in FIG. 3, the sheet P is sandwiched between the driving roller 47a and the driven roller 47c, so that the rotation shaft 47d varies as the driven roller 47c moves away from the driving roller 47a. The fluctuation detection sensor 61 detects such fluctuation of the rotating shaft 47d due to the presence or absence of the paper P, and based on the detection data, the paper presence / absence detection unit 602 detects the presence or absence of the paper between the driving roller 47a and the driven roller 47c. . Further, the sheet thickness detection unit 601 detects the sheet thickness from the variation amount based on the detection data of the variation detection sensor 61. The drive control unit 603 controls the driving speed by rotating the drive motor 62 based on the presence / absence of the paper detected by the paper presence / absence detection unit 602. For example, when the time when there is no paper is shorter than the time of one rotation of the driven roller 47c, the rotational drive control increases the rotational speed of the drive roller 47a so that the driven roller 47c can make one or more rotations within the time when there is no paper. I do.

FIG. 4 is a time chart regarding a detection output example of the fluctuation detection sensor 61. Since the displacement level, which is detection data, changes according to the presence or absence of paper, the paper thickness detection unit 601 obtains the displacement level when there is paper and the displacement level when there is no paper at predetermined time intervals and obtains an average value. And the difference between the average values is detected as the sheet thickness.
However, the detection output includes an eccentric component accompanying the rotation of the rotating shaft 47d due to the influence of the eccentricity of the rotating shaft 47d. As shown in FIG. 4, the eccentric component is alternately generated with the same amount of displacement increase and displacement decrease during one rotation of the rotating shaft 47d. For this reason, since the detection accuracy of the detection data varies depending on the acquisition timing of the displacement level, it is necessary to remove the eccentric component in order to improve the detection accuracy of the paper thickness. In order to remove the eccentric component, the detection data is acquired in the detection range of one rotation or more of the rotating shaft 47d and the average value is obtained, thereby canceling out the displacement increase and displacement decrease occurring during one rotation. Can do.

  In the example shown in FIG. 4, since the time interval with paper and the time interval without paper are long, the detection data is acquired in the detection range of one rotation or more of the rotation shaft 47d within the time with paper and the time without paper. be able to. Therefore, the paper thickness detection unit 601 can accurately detect the paper thickness by removing the influence of the eccentric component based on the detection data acquired during the time when the paper is present and during the time when the paper is not present.

  FIG. 5 is a time chart regarding an example of detection output when the interval between sheets to be conveyed is narrow. In this example, since the time interval T when there is no paper is shorter than the time required for one rotation of the rotation shaft 47d, it cannot be detected in a detection range of one rotation or more, and the eccentric component accompanying the rotation of the rotation shaft 47d is excluded. Therefore, the paper thickness cannot be detected with high accuracy.

  FIG. 6 is a time chart relating to a detection output example when the rotational speed of the drive roller 47a is increased within the time when there is no paper. In this example, when the paper presence / absence detection unit 602 detects that there is no paper based on the decrease in the displacement level, the drive control unit 603 causes the drive roller to rotate the rotation shaft 47d one or more times within the time when there is no paper. Rotation drive control is performed so as to increase the rotation speed of 47a. By controlling the drive in this way, the driven roller 47c rotates more than one rotation in the absence of paper, and therefore, by performing detection output in a detection range of more than one rotation, the average value of the displacement level excluding the eccentric component is obtained. Can be obtained.

  In the above-described example, the fluctuation of the rotation shaft 47d of the driven roller 47c is detected. However, the fluctuation detection is performed by detecting an identifiable portion such as a protrusion or a hole provided on the driven roller 47c. You can also. Further, the presence / absence of the paper in the transport roller 47 is performed based on the detection output of the fluctuation detection sensor, but another paper presence / absence detection sensor may be provided for detection. Further, the rotation drive control of the drive roller 47a can also be performed at a timing when there is no sheet in the transport roller 47 after a predetermined time has elapsed from the transport start timing from the paper feed unit 43. Further, when the rotational speed of the drive roller 47a is increased, the rotational speed may be set to be increased to a predetermined rotational speed, and the drive control is performed so that the rotational speed is changed according to the time interval when there is no paper. You can also.

  DESCRIPTION OF SYMBOLS 10 ... Intermediate transfer belt, 14-16 ... Support roller, 17 ... Transfer belt cleaning unit, 18 ... Charger unit, 20 ... Image forming unit, 21 ... Writing unit, 22. .. Secondary transfer unit, 23... Conveying roller, 24... Secondary transfer belt, 25... Fixing unit, 26... Fixing belt, 27. Paper reversing unit, 32 ... contact glass, 33 ... first carriage, 34 ... second carriage, 35 ... imaging lens, 36 ... image reading sensor, 40 ... photoconductor unit , 42 ... paper feed roller, 43 ... paper feed unit, 44 ... paper feed tray, 45 ... separation roller, 46 ... paper feed path, 47 ... transport roller, 48 ...・ Conveyor roller unit 49 ... registration roller 50 ... feed roller, 51 ... manual feed tray, 55 ... switching claw, 56 ... discharge roller, 57 ... output tray.

Japanese Patent No. 4623436 JP 2009-234698 A

Claims (6)

  An image forming apparatus for conveying a sheet-like recording medium to form an image on the recording medium, wherein the driving roller is rotated to convey the recording medium, and is set to be in pressure contact with the driving roller. A driven roller that sandwiches the recording medium with a driving roller, a variation detection unit that detects a variation of the driven roller due to the sandwiching of the recording medium, and the recording based on detection data from the variation detection unit The detection data of the recording medium thickness detecting means for detecting the thickness of the medium, the recording medium presence / absence detecting means for detecting the presence / absence of the recording medium between the driving roller and the driven roller, and the detection data of the recording medium presence / absence detecting means An image forming apparatus comprising: drive control means for performing rotational drive control of the drive roller based on the drive control means. The image forming apparatus according to claim 1,
The drive control unit performs rotation drive control of the drive roller so that the driven roller rotates one or more times without the recording medium when the recording medium presence / absence detection unit detects the absence of the recording medium. Forming equipment. The image forming apparatus according to claim 1 or 2,
The image forming apparatus that detects the thickness of the recording medium based on a difference between detection data of the fluctuation detecting unit when the recording medium is present and when the recording medium is absent. The image forming apparatus according to claim 3.
The recording medium thickness detecting unit calculates an average value of detection data of the variation detecting unit in a detection range of one rotation or more of the driven roller and detects the thickness of the recording medium. The image forming apparatus according to claim 1, wherein:
The recording medium presence / absence detection unit is an image forming apparatus that detects the presence / absence of the recording medium based on detection data of the variation detection unit. A method for detecting a thickness of a recording medium in an image forming apparatus that conveys a sheet-like recording medium and forms an image on the recording medium,
A step of detecting a change in a driven roller which is set so as to be in pressure contact with a driving roller which is driven to rotate and conveys the recording medium and sandwiches the recording medium with the driving roller;
A step of rotationally controlling the drive roller so that the driven roller rotates one or more times without the recording medium between the drive roller and the driven roller;
Detecting the thickness of the recording medium based on a difference in detection data in a detection range of one or more rotations of the driven roller when the recording medium is present and when the recording medium is absent. Detection method.

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