JP4669817B2 - Double feed detection device, double feed determination method, and image forming apparatus - Google Patents

Description

  The present invention relates to a multifeed detection device for cut paper (hereinafter simply referred to as paper) cut to a predetermined size, a multifeed determination method, and an image forming apparatus including the paper multifeed detection device.

Conventionally, as a paper double feed detection device in a paper transport device that transports paper, the number of sheets fed out in a paper stacking unit is counted, and the thickness of the paper is determined from the number of the paper and the height change of the stacked paper. An apparatus has been proposed in which a threshold value is determined and a double feed is determined if the sheet thickness measured on the sheet conveyance path is larger than the threshold value. (Patent Document 1)
In addition, when the paper accumulated in the paper accumulation unit is fed out, the thickness of the paper is measured, and the average thickness is obtained and stored. An apparatus for determining transmission is proposed. (Patent Document 2)
Japanese Patent Laid-Open No. 06-040604 JP-A-11-116101

  The paper double feed detection device described in Patent Document 1 counts the number of sheets fed out in the sheet stacking unit, and obtains the thickness of the sheet from the number of sheets and the change in height of the accumulated sheet. Therefore, it is not possible to determine the double feed of the paper first fed out from the paper stacking unit.

  In addition, since the thickness of the paper is obtained from the height change of the accumulated paper, it is difficult to accurately measure the thickness change of several sheets from the height of the paper when several hundred sheets are accumulated. Sending judgment is not possible.

  The prior art described in Patent Document 2 measures the thickness of the paper when the paper accumulated in the paper accumulation unit is fed out, obtains and stores the average value thereof, and measures the value thereafter. Even if it is determined that the paper is to be double-fed if the thickness of the paper to be printed is thick, it is difficult to determine whether the first paper is double-fed.

  Further, these sheet double feed detection devices cannot accurately determine double feed when sheets having different thicknesses are mixed in the sheet stacking unit.

  The object of the present invention is to eliminate the above-mentioned conventional disadvantages, to reliably detect double feed even for the first sheet fed out, and to detect double feed reliably even when sheets of different thicknesses are mixed. It is an object of the present invention to provide a detection device, a multifeed determination method, and an image forming apparatus.

In order to achieve the above object, the first means of the present invention includes a thickness detecting means for detecting the thickness of the cut sheet conveyed,
Stiffness detecting means for detecting the bending stiffness of the conveyed paper;
The thickness of the paper detected by the thickness detection means and the bending rigidity value of the paper detected by the rigidity detection means are set based on the thickness of one of the papers when stacked and the bending rigidity value at that time. And a double feed judging means for judging whether or not the double feed is made in comparison with the threshold value of the thickness of the sheet and the rigidity.

  According to a second means of the present invention, in the first means, the thickness detecting means includes a rotating driving roller, a driven roller pressed against the rotating roller, and the paper when the driven roller and the driving roller sandwich the sheet. Displacement detecting means for detecting a displacement amount between the driven roller and the driving roller is provided.

  According to a third means of the present invention, in the second means, the displacement detecting means has a rotating lever that supports the driven roller at one end, and the drive of the driven roller is detected from the displacement of the other end of the lever. The configuration is such that the amount of displacement between the shafts relative to the roller is detected.

  According to a fourth means of the present invention, in the third means, the amount of displacement of the other end of the lever from the pivot fulcrum of the lever is greater than the distance L1 from the pivot fulcrum of the lever to the support point of the driven roller. This is characterized in that the distance L2 to the detection unit for detecting the is longer.

  According to a fifth means of the present invention, in the second means, the rigidity detecting means is attached to a rotating shaft of the drive roller.

  According to a sixth means of the present invention, in the first or fifth means, the rigidity detecting means is a detection member that is supported so as to rotate when the leading edge of the paper comes into contact, and a part of the detection member. An elastic member that elastically energizes the paper so that it can be projected and retracted on the paper conveyance path, and a displacement detection unit that detects a rotational displacement amount of the detection member when the paper is bent in contact with a part of the detection member. It is characterized by having.

  According to a seventh means of the present invention, in the sixth means, the detection member has a first arm portion with which the leading end of the paper abuts, and a detection portion for detecting a rotational displacement amount by the displacement detection means. Two arm portions, and a rotation fulcrum is provided between the first arm portion and the second arm portion, and the rotation from the position where the paper front end of the first arm portion abuts. The distance L4 from the detection unit to the rotation fulcrum is longer than the distance L3 to the fulcrum.

The eighth means of the present invention comprises a thickness detection means for detecting the thickness of the cut sheet conveyed,
Stiffness detecting means for detecting the bending stiffness of the conveyed paper;
A double feed judging means for judging the double feed of the paper, by setting a threshold value of the paper thickness and the bending stiffness value based on one sheet of paper, the thickness at the time of stacking and the bending stiffness value at that time, and Memorize it in the memory part of the sending judgment means,
The sheet thickness detected by the thickness detecting unit and the bending stiffness value of the sheet detected by the stiffness detecting unit are input to the multi-feed determining unit and compared with the threshold value to determine whether or not the sheet is double-fed. It is characterized by judging.

The ninth means of the present invention deposits a photoconductor, an exposure means for forming an electrostatic latent image on the photoconductor, a developing means for forming a toner image on the photoconductor, and a cut sheet. A paper stacking unit; a transport mechanism that feeds the paper from the paper stacking unit toward the photoconductor; a transfer unit that transfers the toner image on the photoconductor to the paper; and a fixing that fixes the transferred toner image on the paper. An image forming apparatus comprising:
The double feed detection device according to any one of the first to seventh means is provided upstream of the transfer means in the paper conveyance direction.

  The tenth means of the present invention is characterized in that, in the ninth means, a double feed sheet retracting section for retracting the paper determined to be double fed by the double feed detecting device is provided.

  According to the present invention, it is possible to detect the double feed even for the first fed paper, and it is possible to reliably detect the double feed even when sheets of different thicknesses are mixed in the paper stacking unit. For example, it is possible to prevent the occurrence of paper jam, winding of paper around the conveyance roller, unfixed toner at the time of printing, etc., reducing the burden on the operator, and the printing efficiency can be improved in the image forming apparatus.

  In the present invention, when two or more sheets stacked with one sheet have different bending rigidity, and even when one sheet is thick, a thin sheet is stacked as a double leaf. It has been clarified that even when the thickness is the same as that of the one thick sheet, the bending rigidity of one thick sheet is different from the bending rigidity when a thin sheet is a double sheet. In the paper transport device, by detecting the thickness and bending rigidity of the paper, it is possible to easily and appropriately determine whether the paper is being transported as a single sheet or being double-fed.

  That is, the thickness of one sheet and the bending rigidity in that case, and the thickness of two or more sheets and the bending rigidity in that case are measured. Is set in advance. Then, the thickness and bending rigidity of the actually conveyed sheet are detected in the sheet conveying path, and the data is compared with the threshold value to determine whether the sheet is double-fed.

  FIG. 1 is a conceptual diagram showing the relationship between the thickness and rigidity of a sheet. The straight line A in the figure shows the change in bending rigidity when the thickness is changed by stacking two sheets, and the curve B shows the change in bending rigidity when the thickness of one sheet is changed. Yes.

  As is clear from this figure, the rigidity in the case of two sheets from the straight line A is almost twice the rigidity in the case of one sheet, and the rigidity increases in proportion to the number of stacks. On the other hand, when the thickness was changed by one sheet, it was found from the curve B that the rigidity increased in proportion to the cube of the thickness.

  Due to such a difference in bending rigidity, when sheets of the same thickness are being conveyed, a threshold value serving as a determination criterion is set at, for example, point C in the intermediate region between the thickness of one sheet and the thickness of two sheets. This threshold value is compared with the detected sheet thickness and bending rigidity value, and when the value falls below the threshold value, it can be determined that one sheet is conveyed, and more than that, double feeding is performed.

  In addition, a sheet thickness and bending stiffness threshold line D is set in an intermediate region between the straight line A and the curve B, the sheet thickness and the bending rigidity are detected, and the detected value of the sheet thickness and the bending rigidity are detected. If the intersection with the value is above the threshold line D, for example, point F in the figure, it is determined that one sheet is fed, and if it is below the threshold line D, for example, point E in the figure, it is determined that it is a double feed.

  Region G and region H in the figure show the variation width of the bending stiffness in consideration of the variation in the material and measurement of the sheet regarding the bending stiffness of one sheet and stacked sheets, and considering these variation ranges, That is, the threshold line D is set so as not to enter the regions G and H.

  The threshold value C and the threshold line D may be set for each type of paper to be used, stored in the storage unit of the double feed determination unit, and determined based on the stored data.

  In the present invention, it is necessary to measure the thickness and bending rigidity of the conveyed paper in the process of conveying the paper, and a known measurement method can be adopted for measuring the thickness and rigidity of the paper. The length can be easily measured by using a driving roller that conveys the paper and a driven roller that is pressed against the driving roller and monitoring the distance between the axes of both rollers.

  In particular, the method of measuring the distance between the shafts by supporting the driven roller at one end of the rotating lever and monitoring the displacement amount at the other end of the lever can measure with high accuracy.

  The bending rigidity of the paper is provided with a detection member that contacts the leading edge of the conveyed paper, and the detection member is urged to rotate in a direction to bend the leading edge of the paper by an elastic member, and the paper is bent by the detection member. If the configuration is such that the amount of rotational displacement of the detection member when detected is detected, the rigidity of the paper can be appropriately measured with a simple structure.

  In addition, the sheet thickness and bending rigidity are measured by a drive roller for conveying the sheet and a driven roller pressed against the sheet. The thickness detecting unit is attached to the driven roller, and the rigidity detecting unit is attached to the rotation shaft of the drive roller. By attaching, the number of parts can be reduced and the structure can be simplified.

  Next, a double feed detection device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic configuration diagram of the double feed detection device according to the first embodiment.

  As shown in the figure, a detection roller 23 is arranged to be movable up and down with respect to the transport roller 25 supported at a fixed position. The detection roller 23 is attached to the tip of the arm portion 211 of the L-shaped thickness detection lever 21 via a support shaft 231. The detection lever 21 is rotatably supported by a support shaft 24, and a spring 22 is connected in the middle of the arm portion 212, and the detection roller 23 is pressed against the conveying roller 25 side by the tension force of the spring 22. The transport roller 25 is rotated in the direction of arrow b by a motor (drive means) (not shown), and transports the paper 1 in the direction of arrow a with the paper 1 sandwiched between the transport roller 25. Accordingly, the transport roller 25 functions as a driving roller, and the detection roller 23 functions as a driven roller.

  Since the position of the transport roller 25 is fixed, and the detection roller 23 is supported by the rotating detection lever 21 and can move up and down, it is detected when the sheet 1 is sandwiched between the detection roller 23 and the transport roller 25. The roller 23 is pushed up by the thickness of the paper 1. With the displacement of the detection roller 23, the detection lever 21 rotates clockwise about the support shaft 24 toward the drawing as shown in FIG.

  A detection unit 213 such as a reflecting surface is set near the tip of the arm unit 212 of the detection lever 21, and a distance L <b> 2 between the detection unit 213 and the support shaft 24 corresponds to the support shaft 231 that supports the detection roller 23. Since the distance is set to several times the distance L1 from the shaft 24, the displacement of the detection roller 23 appears at the detection unit 213 after being amplified at a magnification of (L2 / L1). The displacement amount of the detection unit 213 enlarged in this way is detected by the first displacement sensor 20 including an optical sensor, a position sensitive detector (Position Sensitive Detector PSD), and the like.

  As described above, the change in the inter-axis distance X between the detection roller 23 and the transport roller 25 due to the sandwiching of the paper 1, that is, the thickness of the paper 1 can be automatically detected by the first displacement sensor 20 while the paper 1 is being transported. Data relating to the thickness of the sheet 1 obtained by the first displacement sensor 20 is transmitted to the double feed determination means 38.

  The transport roller 25 is preferably a rubber roller in order to secure a frictional driving force for transporting the paper 1, while an appropriate hardness is required to increase the thickness detection accuracy, and the transport roller 25 has a hardness of 50. It has been found from various experimental results that it is desirable to set the temperature to more than (JIS K6301A). In the second embodiment to be described later, it is preferable to use a transport roller having the hardness.

  Next, the sheet 1 is fed between the conveyance roller 31 and the driven roller 34. The transport roller 31 is supported at a fixed position and is rotationally driven in the direction of arrow c by a motor (drive means) (not shown). The driven roller 34 is pressed against the conveying roller 31 by the spring 35 and is rotated together with the conveying roller 31 to convey the sheet 1 in the direction of arrow a.

  A bent portion of a rigid detection lever 33 having a short arm portion 331 and a long arm portion 332 and having a rectangular shape is rotatably supported on the support shaft 36 of the transport roller 31. The short arm portion 331 is disposed so as to protrude in the vicinity of the exit side of the roller pair of the conveyance roller 31 and the driven roller 34 on the conveyance path of the paper 1. A spring 37 is connected to the middle of the long arm portion 332 and pulled in the direction of the arrow d, and a stopper 37 that contacts a part of the rigidity detection lever 33 is provided. By the spring 32 and the stopper 37, the rigidity detection lever 33 is held at a standby position where the paper 1 does not reach.

  Near the tip of the long arm portion 332, a second displacement sensor 30 made of an optical sensor, PSD, or the like that detects the amount of displacement of that portion is installed.

  As shown in FIG. 3, as soon as the leading end 10 of the conveyed paper 1 protrudes from between the conveyance roller 31 and the driven roller 34, it immediately hits the side surface of the arm portion 331 of the rigidity detection lever 33 and depends on the rigidity of the paper 1. The arm portion 331 sinks against the tensile force of the spring 32. This sinking amount is in balance with the tensile force of the spring 32. If the sheet 1 has low rigidity, the sinking amount is small, and if the sheet 1 has high rigidity, the sinking amount is large. The rigidity of the sheet 1 is preferably measured in a state where the portion slightly separated from the front end portion 10 of the sheet 1 is sandwiched between the conveyance roller 31 and the driven roller 34 because of the so-called strength of the sheet 1. The arm portion 331 of the rigidity detection lever 33 is disposed in the vicinity of the exit side of the joint between the transport roller 31 and the driven roller 34.

  As shown in FIG. 2, the joint portion between the transport roller 31 and the driven roller 34, that is, the distance L 3 from the position where the leading end portion 10 of the paper 1 straightly traveling from the joint portion contacts the arm portion 331 to the support shaft 36. Since the distance L4 from the support shaft 36 to the detection unit 333 is set long, the sinking amount of the arm unit 331 is amplified at a magnification of (L4 / L3). The displacement of the detection unit 333, that is, the change in the distance between the detection unit 333 and the second displacement sensor 30 is detected by the second displacement sensor 30. Data relating to the rigidity of the sheet 1 obtained by the second displacement sensor 30 is transmitted to the double feed determination means 38.

  From the thickness and bending rigidity values when there is one sheet 1 and from the thickness and bending rigidity values when two sheets 1 overlap, the threshold value C and threshold line D for double feeding are as follows. Is set in advance for each type, and the setting data is stored in the storage unit 381 of the double feed determination unit 38.

  The output signals from the displacement sensors 20 and 30 are captured by the determination unit 382 of the multifeed determination unit 38, and the threshold C and threshold line D data stored in the storage unit 381 are also captured and compared. If the thickness and bending stiffness of the sheet 1 detected at 30 are larger than the threshold C and fall below the threshold line D (see FIG. 1), it is determined that the sheet 1 is being double fed. If the value falls below the threshold C and falls above the threshold line D, it is determined that the sheet 1 is being conveyed by one sheet, and is further set to a value larger than the threshold C and above the threshold line D. If applicable, it is determined that the sheet is one sheet having a thickness different from that of the sheet 1 conveyed last time, and the determination result is sent to the control unit 100 that controls the apparatus main body.

  In this way, means for measuring the thickness and bending rigidity of the sheet are arranged in the sheet conveyance path, the thickness measured by these means, the measured value of the bending rigidity in that case, the preset threshold value and the threshold line, By comparing the above, even if it is the first paper to be transported, it can be determined whether or not it is accurately double-fed, and even if papers with different thicknesses are mixed, It becomes possible to judge whether.

  FIG. 6 is a characteristic diagram showing a specific setting example of the threshold line. In this test, the ratio of the distance L4 to the distance L3 shown in FIG. 2 (L4 / L3), the ratio of the distance L5 from the support shaft 36 to the tension point by the spring 32 (L5 / L3), and the tensile force F by the spring 32 shown in FIG. Was set as follows.

(L4 / L3) = 2
(L5 / L3) = 1
F = 5N
As the second displacement sensor 30, Z4D-B02 manufactured by OMRON Corporation was used. The rigidity of the sheet is obtained from the difference between the output voltage Sn of the second displacement sensor when no sheet is present and the output voltage Se of the second displacement sensor when the sheet is present. It is expressed.

St = Se-Sn
A curve I in FIG. 6 is a characteristic curve created by performing a test under the setting conditions as described above and plotting a relationship between the sheet thickness and the sheet rigidity voltage St in the case of one sheet, and the curve J is a sheet of two sheets. It is a characteristic curve created by plotting the relationship between the sheet thickness and the sheet rigidity voltage St when stacked. As is clear from this figure, the curve I and the curve J are separated from each other without overlapping, so that a line passing through the intermediate position between the curves I and J is drawn and set as a threshold line D.

  An example of the equation of the threshold line D when the paper stiffness voltage is St and the paper thickness is Tp is as follows.

St = 5.3 × Tp−0.53
Therefore, if St> 5.3 × Tp−0.53, one sheet is sent, and if St <5.3 × Tp−0.53, it is determined to be double feed.

  FIG. 4 is a schematic configuration diagram of a double feed detection device according to the second embodiment. In this embodiment, the thickness of the paper 1 and the bending rigidity are detected almost simultaneously by a single paper conveying means.

  The thickness detection roller 27 is supported so as to be movable up and down, and is pressed against the transport roller 25 by a spring 26. The detection roller 27 is pushed upward by the sheet 1 sandwiched between the conveyance roller 25 and the detection roller 27, and the first displacement sensor 20 detects the displacement of the support shaft 271 of the thickness detection roller 27, thereby detecting the thickness. The displacement amount of the inter-axis distance X between the support shaft 271 of the height detection roller 27 and the rotation shaft 251 of the transport roller 25 is measured.

  The rigidity detection lever 33 is supported so as to be rotatable about a support shaft 36 (on the rotation axis of the transport roller 25), and the spring 32 pulls the rigidity detection lever 33 in the direction of the arrow d, so that the arm portion 332 of the rigidity detection lever 33 is obtained. Against the stopper 37. The second displacement sensor 30 measures the amount of rotational displacement of the rigidity detection lever 33 when the arm portion 331 of the rigidity detection lever 33 is rotated by the bending rigidity of the paper 1.

  Similar to the first embodiment, the outputs of the displacement sensors 20 and 30 are input to the double feed determining means 38 and compared with the threshold C and the threshold line D to determine the presence or absence of double feed.

  A sheet detection sensor 29 that detects the presence or absence of the sheet 1 is disposed downstream of the rollers 25 and 27 in the sheet conveyance direction, and registration rollers 41 and 42 are disposed further downstream. The surface of the registration roller 41 is made of metal, and the surface of the registration roller 42 is formed of rubber. The registration roller 42 is rotated by a driving mechanism (not shown) to convey the paper 1 in the direction of arrow a.

  At this time, the paper detection sensor 29 detects the leading edge of the paper 1, and rotates the transport roller 25 by this detection signal to transport the paper 1 from there for a predetermined distance. As shown in FIG. 4, this distance is set to an amount capable of correcting the skew by pressing the leading end of the sheet against the nip portion of the registration rollers 41 and 42 and deflecting upward. Registration rollers 41 and 42 convey the paper 1.

  In this embodiment, the pair of conveyance rollers 25 and the detection roller 27 measure the thickness and bending rigidity of the paper 1 to detect double feed, and this roller pair uses the registration roller 41 to correct the skew of the paper 1. , 42 can be used in common for the paper 1 conveying means and the double feed detecting means for correcting the skew of the paper 1, and the apparatus can be miniaturized.

  In the first and second embodiments, the rigidity detection lever 33 is provided on the support shaft of the transport roller. However, the rigidity detection lever 33 is not necessarily provided coaxially, and the rigidity detection lever 33 is provided on a support shaft different from the support shaft of the transport roller. It can also be supported. However, if the rigidity detection lever 33 is provided on the support shaft of the transport roller, the structure can be simplified.

  FIG. 5 is a schematic configuration diagram of an image forming apparatus including a double feed detection device according to the second embodiment. In this image forming apparatus, four developing units 501 to 504 are arranged on the transfer belt 2, a color image is formed on the transfer belt 2 with toner, and the color image is formed on the paper 1 sent from the paper stacking means 4. The image is transferred and fixed by the fixing device 60 to obtain a color image.

  The developing units 501 to 504 individually contain black toner, cyan toner, magenta toner, and yellow toner. Each of the developing units 501 to 504 includes a photosensitive drum 54, a charger 55 that charges the photosensitive drum 54, an exposure device 56 that writes an electrostatic latent image on the photosensitive drum 54, a toner hopper 53 that stores toner, and a toner layer. The developing roller 52 is formed to bring the toner into contact with the photosensitive drum 54, and the drum cleaner 57 is used to clean the photosensitive drum 54.

  The intermediate transfer belt 2 is stretched by a plurality of rollers and is conveyed by a belt driving roller 3. The belt cleaner 91 removes residual toner on the intermediate transfer belt 2. The primary transfer roller 58 is disposed inside the intermediate transfer belt 2 so as to face the photosensitive drum 54.

  The paper conveyance path 8 passes between the secondary transfer roller 7 and the intermediate transfer belt 2 through the pick roller 9, the separation roller 11, the double feed detection device 201, and the registration rollers 41 and 42 from the paper accumulation unit 4 and is conveyed. From the belt 81 to the fixing device 60.

  A lever 701 that rotates about a support shaft 702 is mounted on the sheet conveyance path 8 on the downstream side of the double feed detection device 201 so as to be able to appear and retract from the conveyance path 8. Below the lever 701, a multi-feed paper retract path 71 branched from the paper transport path 8 and a tray-like multi-feed paper retract section 72 following the multi-feed paper retract path 72 are provided. The lever 701 also serves as the conveyance switching guide 70.

  The fixing device 60 includes a backup roller 64, an elastic roller 63, a heating roller 62, and a fixing belt 61. The fixing belt 61 is stretched over the elastic roller 63 and the heating roller 62, and is rotated by the rotation of the heating roller 62 or other rollers. Driven. The sheet 1 is conveyed by being pressed against the elastic roller 63 side by the backup roller 64, and the heating roller 62 has heating means such as a halogen heater in a metal hollow shaft to heat the fixing belt 61. The surface of the elastic roller 63 is formed of an elastic material such as silicon rubber, and the nip portion protrudes toward the elastic roller 63 by pressing the backup roller 64 to prevent the paper 1 from being wound around the fixing belt 61.

  The surface of the photosensitive drum 54 is charged by the charger 55 and light corresponding to image information is irradiated by the exposure device 56 to form an electrostatic latent image on the photosensitive drum 54. The electrostatic latent image reaches the developing roller 52 by the rotation of the photosensitive drum 54, and charged toner adheres to the electrostatic latent image when it comes into contact with the toner layer.

  As illustrated in the developing unit 501, the toner image on the photosensitive drum 54 is transferred onto the intermediate transfer belt 2 at a position where the primary transfer roller 58 presses the intermediate transfer belt 2, and then cyan, magenta, and yellow. In order, the toner images on the photosensitive drums of the developing units are transferred onto the intermediate transfer belt 2 to obtain a color toner image.

  Then, the toner image is transferred onto the sheet 1 conveyed at the position of the secondary transfer roller 7 by the conveyance of the intermediate transfer belt 2. The sheet 1 on which the toner image has been transferred is conveyed to the fixing device 60 by the conveying belt 81, and the toner is melted and fixed by heat and pressure to fix the color image on the sheet 1.

  In this example, the intermediate transfer belt 2 is used when the toner image is transferred to the paper 1. However, the intermediate transfer belt 2 is not always necessary, and the toner image may be directly transferred from the developing units 501 to 504 to the paper 1. Good.

  Next, detection of double feed of the paper 1 will be described. The paper 1 is fed from the paper stacking means 4 by the pick roller 9 and separated and conveyed one by one by the separation roller 11. However, the paper 1 is not reliably separated and may be conveyed in a state where a plurality of sheets are overlapped. As described above, the double feed detection device 201 (the first displacement sensor 20, the second displacement sensor 30, and the double feed determination means 38) constantly monitors the state of the sheet 1 being conveyed, and double feed is detected. Then, a double feed detection signal is sent to the control unit 100 that controls various operations of the image forming apparatus.

  In response to the double feed detection signal, the control unit 100 outputs a switching signal to the transport path switching guide 70, and rotates the guide 70 (lever 701) that has been waiting at a position away from the paper transport path 8 until now. As shown in the figure, the sheet conveying path 8 is blocked, and the sheet is guided to the double-feed sheet retracting path 71 side and stocked in the double-feed sheet retracting section 72. When the double-fed paper 1 is guided to the double-fed paper retraction path 71 side, the guide 70 (lever 701) is immediately returned to the standby position away from the paper conveyance path 8.

  By automatically evacuating the double-fed paper in this way, it is possible to avoid in advance that the device stops due to jam or the like due to double-fed, and further, the device to remove the double-fed paper by evacuating the double-fed paper There is no need to stop. Therefore, the operation efficiency of the apparatus is good, the printing efficiency is improved, and the burden on the operator is reduced.

  In the above-described embodiment, the double feed determination unit 38 and the control unit 100 are provided separately. However, the double feed determination unit 38 may be incorporated into the control unit 100.

  The multifeed detection device according to the present invention is not limited to a paper transport device for printing, but can also be applied to a paper transport device for confirming the number of printed papers or sorting printed papers.

It is a conceptual diagram which shows the relationship between the thickness of a paper, and bending rigidity. It is a schematic block diagram of the double feed detection apparatus which concerns on 1st Embodiment of this invention. It is a schematic block diagram which shows the detection operation of the double feed detection apparatus. It is a schematic block diagram of the double feed detection apparatus which concerns on 2nd Embodiment of this invention. FIG. 2 is a schematic configuration diagram of an image forming apparatus including the double feed detection device. It is a characteristic view which shows the specific example of a threshold line setting in embodiment of this invention.

Explanation of symbols

  1: paper, 2: intermediate transfer belt, 3: belt drive roller, 4: paper accumulation means, 7: secondary transfer roller, 8: paper conveyance path, 9: pickup roller, 10: leading edge of paper, 11: separation 20: First displacement sensor, 201: Double feed detection device, 21: Thickness detection lever, 211: Arm part, 212: Arm part, 213: Detection part, 22: Spring, 23: Thickness detection roller, 231: support shaft, 24: support shaft, 27: thickness detection roller, 271: support shaft, 29: paper detection sensor, 30: second displacement sensor, 31: transport roller, 32: spring, 33: rigidity detection lever 331: Arm unit, 332: Arm unit, 333: Detection unit, 34: Driven roller, 35: Spring, 36: Support shaft, 37: Stopper, 38: Double feed determination means, 381: Storage unit, 382: Determination unit 4 : Registration roller, 42: registration roller, 52: development roller, 53: toner hopper, 54: photosensitive drum, 55: charger, 56: exposure unit, 57: drum cleaner, 58: primary transfer roller, 501, 502, 503, 504: development unit, 60: fixing device, 61: fixing belt, 62: heating roller, 63: elastic roller, 64: backup roller, 70: conveyance switching guide, 701: lever, 702: spindle, 71: heavy Feeding / retracting path, 72: Multifeed sheet retracting unit, 81: Conveying belt, 91: Belt cleaner, 100: Control unit.

Claims (10)

A thickness detection means for detecting the thickness of the cut sheet conveyed;
Stiffness detecting means for detecting the bending stiffness of the conveyed paper;
The thickness of the paper detected by the thickness detection means and the bending rigidity value of the paper detected by the rigidity detection means are set based on the thickness of one of the papers when stacked and the bending rigidity value at that time. A double feed detection device comprising: double feed judgment means for judging whether or not double feed is made by comparing the thickness of the sheet and the threshold value of rigidity.   2. The multifeed detection device according to claim 1, wherein the thickness detection means includes: a rotating driving roller; a driven roller that is pressed against the rotating roller; and the driven roller when the paper is sandwiched between the driven roller and the driving roller. A multifeed detecting device comprising a displacement detecting means for detecting a displacement amount between shafts with respect to a driving roller.   3. The multifeed detection device according to claim 2, wherein the displacement detecting means has a rotating lever that supports the driven roller at one end, and the shaft between the driven roller and the drive roller is displaced from the displacement of the other end of the lever. A double feed detection device characterized in that the amount of displacement is detected.   4. The multifeed detection device according to claim 3, wherein the amount of displacement of the other end of the lever from the rotation fulcrum of the lever is detected from a distance L1 from the rotation fulcrum of the lever to the support point of the driven roller. A double feed detection device characterized in that the distance L2 to the section is longer.   3. The multifeed detection device according to claim 2, wherein the rigidity detection means is attached to a rotation shaft of the drive roller.   6. The multifeed detection device according to claim 1 or 5, wherein the rigidity detection means includes a detection member that is supported so as to rotate when the leading edge of the paper comes into contact, and a part of the detection member that conveys the paper. An elastic member that is elastically biased so as to appear and retract on the path; and a displacement detection unit that detects a rotational displacement amount of the detection member when the sheet is bent in contact with a part of the detection member. This is a double feed detection device. 7. The multi-feed detection device according to claim 6, wherein the detection member includes a first arm portion with which a leading end of the paper abuts and a detection portion that detects a rotational displacement amount by the displacement detection means. And a pivot point is provided between the first arm portion and the second arm portion,
The double feed detection device characterized in that a distance L4 from the detection unit to the rotation fulcrum is longer than a distance L3 from the position where the front end of the sheet of the first arm portion abuts to the rotation fulcrum. . A thickness detection means for detecting the thickness of the cut sheet conveyed;
Stiffness detecting means for detecting the bending stiffness of the conveyed paper;
A double feed judging means for judging the double feed of the paper, by setting a threshold value of the paper thickness and the bending stiffness value based on one sheet of paper, the thickness at the time of stacking and the bending stiffness value at that time, and Memorize it in the memory part of the sending judgment means,
The sheet thickness detected by the thickness detecting unit and the bending stiffness value of the sheet detected by the stiffness detecting unit are input to the multi-feed determining unit and compared with the threshold value to determine whether or not the sheet is double-fed. A multifeed judgment method characterized by judging. A photosensitive member, an exposing unit that forms an electrostatic latent image on the photosensitive member, a developing unit that forms a toner image on the photosensitive member, a paper accumulating unit that accumulates cut paper, and the paper accumulating unit An image forming apparatus comprising: a conveying mechanism that feeds the sheet from the photosensitive member to the photosensitive member; a transfer unit that transfers the toner image on the photosensitive member to the sheet; and a fixing unit that fixes the transferred toner image onto the sheet. ,
An image forming apparatus comprising the double feed detection device according to claim 1 provided upstream of the transfer unit in a paper conveyance direction.   The image forming apparatus according to claim 9, further comprising a multi-feed paper retreating unit that retreats a paper determined to be multi-feed by the multi-feed detection device.

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