JP2018080038A - Sheet discrimination device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet discrimination device capable of discriminating a sheet while transporting.SOLUTION: A sheet discrimination device comprises a first roller 62, a second roller 63, a transport control unit for controlling rotational drive of the first roller 62 and the second roller 63, an electrostatic capacity sensor 40a arranged on a detection position P40 between the first roller 62 and the second roller 63 in a transporting passage 51A, and a discrimination processing unit for discriminating a sheet 9. The transport control unit, when the sheet 9 is in contact with both the first roller 62 and the second roller 63, performs tension control for controlling the rotational drive so that a downstream-side velocity V2 being a velocity of transport by the second roller 63 becomes larger than an upstream-side velocity V1 being a velocity of transport by the first roller 62. The discrimination processing unit discriminates the sheet 9 based on an output of the electrostatic capacity sensor 40a during a period in which the tension control is performed.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a sheet discrimination device and an image forming apparatus.

  An image forming apparatus that forms an image on a sheet, such as a copier or a printer, has a function of setting operation conditions so that an appropriate image can be obtained according to the type of the sheet. Japanese Patent Application Laid-Open No. H10-228667 discloses that a type of a sheet is detected by a sensor at a registration roller unit, and a conveyance speed by the registration roller is determined based on a detection result.

  For example, in an electrophotographic image forming apparatus, sheets are classified by basis weight, and a conveyance speed, a transfer voltage, a fixing temperature, and the like are set according to the basis weight. This setting can prevent jamming, transfer failure, and fixing failure.

  As a method for specifying the basis weight of the sheet by the image forming apparatus, there is a method in which the user selects and designates the sheet type from several options (plain paper, thick paper 1, thick paper 2, etc.). The image forming apparatus specifies the basis weight associated with the type designated by the user in advance as the basis weight of the sheet, and sets operation conditions according to the specified basis weight.

  However, in recent years, since the types of sheets that can be used in the image forming apparatus are diversified, it is difficult to appropriately set the operation conditions in the method of specifying the basis weight according to the user's specification.

  As a prior art for the image forming apparatus to automatically discriminate a sheet, there is a technique described in Patent Document 2.

  Patent Document 2 discloses that the type of a sheet is determined using a distributed inductance type capacitance sensor. Further, it has been proposed to perform the determination when the sheets are continuously conveyed in order to reliably perform the determination without erroneous detection of the sensor output. Specifically, the amount of electrostatic coupling is measured by stopping the preceding sheet at the detection position, the subsequent sheet is conveyed to the detection position and stopped while the preceding sheet is stopped, and the measurement is performed again with the two sheets overlapped. And a method for discriminating the sheet type based on the difference between the two obtained measurement values is disclosed.

JP 2006-330698 A JP 2007-107976 A

  The capacitance sensor has advantages such as a small size of the detection unit, a small restriction on arrangement space, and a low cost compared to other sensors such as an ultrasonic sensor. However, fluctuations in the distance to the detection target greatly affect the output. For this reason, in the case of discriminating a sheet using a capacitance sensor, there is a problem that erroneous discrimination is likely to occur if the sheet is discriminated while being conveyed. Since the techniques of Patent Documents 1 and 2 perform determination based on the sensor output with the sheet stopped, this problem cannot be solved.

  In the image forming apparatus, it is preferable to make a determination while conveying a sheet in order to increase the productivity of image formation.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet determination apparatus and an image forming apparatus that can determine a sheet while conveying the sheet.

  A sheet determination apparatus according to an embodiment of the present invention is a sheet determination apparatus that determines the sheet carried into a conveyance path for conveying a sheet, the first roller conveying the sheet, and the first roller A second roller that is disposed downstream of the first roller and conveys the sheet; a conveyance control unit that controls rotational driving of the first roller and the second roller; and the first of the conveyance paths. An electrostatic capacitance sensor disposed at a detection position between the first roller and the second roller, and a determination processing unit for determining the sheet, wherein the conveyance control unit includes the first roller. When the sheet is in contact with both the second roller and the second roller, the downstream speed, which is the conveyance speed by the second roller, is greater than the upstream speed, which is the conveyance speed by the first roller. To said rotation Perform tension control for controlling the movement, the determination processing unit determines the sheet based on an output of the capacitive sensor during a period in which the tension control is performed.

  According to the present invention, it is possible to make a determination while conveying a sheet.

1 is a diagram illustrating a configuration of an image forming system including a sheet discrimination device according to an embodiment of the present invention. 2 is a diagram illustrating a hardware configuration of an image forming apparatus 2 in the image forming system. FIG. It is a figure which shows the outline | summary of the conveyance path | route in an image forming system. It is a figure which shows the example of a structure of an electrostatic capacitance sensor. It is a figure which shows the functional structure of a sheet | seat discrimination | determination apparatus. It is a figure which shows typically the state of the sheet | seat in conveyance. It is a figure which shows the example of the change of the output of an electrostatic capacitance sensor. It is a figure which shows the example of the relationship between the output of an electrostatic capacitance sensor, and basic weight. It is a figure which shows the state of the sheet | seat in the curved conveyance path when tension control is performed. It is a figure which shows the timing which performs the measurement by an electrostatic capacitance sensor. It is a figure which shows the example of arrangement | positioning of the electrode part of an electrostatic capacitance sensor. It is a figure which shows the modification of the arrangement position of an electrostatic capacitance sensor. It is a figure which shows the position of a sheet | seat when measuring by a capacitance sensor in the case of supplying a sheet | seat from an adjacent sheet supply mechanism. It is a figure which shows the flow of the process in a sheet | seat discrimination | determination apparatus. It is a figure which shows the 1st example of the flow of a process of sheet state judgment. It is a figure which shows the 2nd example of the flow of a process of sheet state judgment. It is a figure which shows the 3rd example of the flow of a process of sheet state judgment. It is a figure which shows the 4th example of the flow of a process of sheet state judgment. FIG. 10 is a diagram illustrating a flow of processing for paper feed control in the image forming apparatus. FIG. 9 is a diagram illustrating a flow of paper feed start processing in paper feed control.

  FIG. 1 shows a configuration of an image forming system 1 including a sheet discrimination device 5 according to an embodiment of the present invention, and FIG. 2 shows a hardware configuration of the image forming device 2 in the image forming system 1. Yes.

  As shown in FIG. 1, the image forming system 1 includes an image forming apparatus 2, a paper feed cabinet 3, and a finisher 4. The image forming apparatus 2 is, for example, an MFP (Multi-functional Peripheral) and has functions such as a copying machine, a printer, and a facsimile machine. The paper feed cabinet 3 is a large-capacity sheet supply device capable of storing, for example, 3000 sheets or more. The finisher 4 is a post-processing device that performs processing such as tri-folding, punch punching, and stapling on the printed sheet discharged from the image forming apparatus 2.

  2, the image forming apparatus 2 includes a main control unit 20, an automatic document feeder (ADF) 21, a scanner 22, a printer unit 23, a paper feeding unit 24, a manual paper feeding unit 25, a network interface 26, A facsimile unit 27, an auxiliary storage device 28, and an operation panel 29 are provided.

  The main control unit 20 is responsible for overall control of the image forming system 1. That is, it controls the image forming apparatus 2, the paper feed cab set 3, and the finisher 4. The main control unit 20 includes a CPU (Central Processing Unit) 20a, a RAM (Random Access Memory) 20b, a ROM (Read Only Memory) 20c, and an image processing unit 20d.

  The ROM 20 c or the auxiliary storage device 28 stores a computer program for controlling the operation of the image forming system 1. Further, a sheet discrimination program for operating some of the components of the image forming apparatus 2 as the sheet discrimination device 5 is stored. These programs are loaded into the RAM 20b as necessary and executed by the CPU 20a.

  The image processing unit 20d performs processing related to the characteristics of the reading optical system, such as shading correction or chromatic aberration correction, on the image data sent from the scanner 22. Further, it performs compression / decompression processing of image data, processing for generating raster data to be output to the printer unit 23, and the like.

  The automatic document feeder 21 conveys the sheet set on the document tray to the reading position of the scanner 22. The scanner 22 is of a flat bed type, and reads image data written on a sheet-like document conveyed from the automatic document feeder 21 or various documents set on a platen glass and generates image data. .

  The printer unit 23 forms an image on a sheet based on raster data generated by the image processing unit 20d in a print job such as copying, network printing (PC printing), and facsimile reception.

  The paper feed unit 24 is a sheet supply unit capable of storing a large number of sheets. The manual paper feed unit 25 is a sheet supply unit useful for printing on a low-use sheet such as a color sheet or a long sheet.

  The network interface 26 communicates with other devices via a communication line by a protocol such as TCP / IP (Transmission Control Protocol / Internet Protocol).

  The facsimile unit 27 exchanges image data with an external facsimile terminal using a protocol such as G3.

  The auxiliary storage device 28 stores the image data sent from the main control unit 20. As the auxiliary storage device 28, an HDD (Hard Disk Drive) or an SSD (Solid State Drive) is used.

  The operation panel 29 includes a touch panel display that displays a screen for an input operation by a user, and a key input unit on which hard keys such as a start key and a stop key are arranged, and controls a signal corresponding to the input operation. Send to 20.

  FIG. 3 shows a configuration of a main part related to the conveyance of the sheet 9 in the image forming system 1.

  The sheet feeding unit 24 of the image forming apparatus 2 is a four-stage drawer type and has four sheet supply mechanisms. However, in FIG. 3, the first sheet supply mechanism 24A and the second sheet supply mechanism 24B from the top are shown.

  The image forming apparatus 2 includes a printer engine 30B that forms an image by electrophotography. The printer engine 30B includes four imaging stations 31, 32, 33, and 34, which are arranged in parallel with four color toner images of yellow (Y), magenta (M), cyan (C), and black (K). To form. Each of the imaging stations 31, 32, 33, and 34 includes a cylindrical photosensitive member, a charging charger, a developing device, a light source for exposure, and the like.

  The four-color toner images are primarily transferred to the intermediate transfer belt 35 and secondarily transferred by the transfer roller 68 to the sheet 9 conveyed through the registration roller 67. After the secondary transfer, the sheet 9 passes through the inside of the fixing device 37 and is sent to the finisher 4. When passing through the fixing device 37, the toner image is fixed on the sheet 9 by heating and pressing.

  Now, the image forming system 1 has a conveyance path 50 indicated by a thick solid line in the drawing. The conveying path 50 is configured such that a plurality of sheet feeding paths 51, 52, 55, and 56 merge together into one upstream of the printer engine 30B, and passes through the printer engine 30B and the fixing device 37 in order from the sheet feeding unit 24. To the finisher 4. The conveyance path 50 is a space provided for conveying the sheet 9 in a direction along the surface.

  The sheet feeding path 51 corresponds to the first sheet supply mechanism 24A of the sheet feeding unit 24, and the sheet feeding path 52 corresponds to the second sheet supply mechanism 24B. The paper feed path 55 corresponds to the manual paper feed unit 25, and the paper feed path 56 corresponds to the paper feed cabinet 3. The positions of the paper feed paths 51, 52, 55, and 56 are below the printer engine 30B.

  The conveyance path 50 is a discharge path 57 extending from the printer engine 30B to the finisher 4, a reversing path 58 for reversing the front and back of the sheet 9 and returning it to the registration rollers 67 in double-sided printing, and a sheet 9 to the reversing path 58. A switchback passage 59 is included.

  The sheet supply mechanism 24A includes a pickup roller 61, a paper feed roller 62, and a storage cassette (not shown). The pickup roller 61 takes out the uppermost sheet 9 from the sheet group stacked on the storage cassette. The paper feed roller 62 sends out the taken sheet 9 to the paper feed path 51. That is, it is carried into the conveyance path 50. The loaded sheet 9 is conveyed by the paper feed roller 62 and proceeds to the downstream intermediate roller 63. Hereinafter, carrying the sheet 9 into the conveyance path 50 may be expressed as “feeding”.

  The rotational driving force of the motor 71 is transmitted to the pickup roller 61 and the paper feed roller 62 via the clutch 81.

  The configuration of the sheet supply mechanism 24B is the same as the configuration of the sheet supply mechanism 24A. That is, the sheet supply mechanism 24B includes a pickup roller 64, a paper feed roller 65, and a storage cassette. The sheet 9 fed by the pickup roller 64 and the paper feed roller 65 passes through the paper feed path 52 to the intermediate roller 66, and is further sent to the intermediate roller 66 to advance to the downstream intermediate roller 63.

  The rotational driving force of the motor 71 is transmitted to the pickup roller 64 and the paper feed roller 65 through the clutch 82. The motor 71 is common to the sheet supply mechanism 24A, but the clutches 81 and 82 are separate. Therefore, the sheet supply from the sheet supply mechanism 24A and the sheet supply from the sheet supply mechanism 24B are controlled by the intermittent control of the clutches 81 and 82. It can be done selectively.

  The intermediate roller 63 conveys the sheet 9 fed from the sheet supply mechanism 24A or the sheet supply mechanism 24B to the downstream registration roller 67. The registration roller 67 sends the sheet 9 to the transfer roller 68 at a timing for aligning the toner image secondarily transferred to the intermediate transfer belt 35 and the sheet 9.

  The intermediate roller 63 is rotationally driven by a motor 72, the intermediate roller 66 is rotationally driven by a motor 73, and the registration roller 67 is rotationally driven by a motor 74. That is, the rotational speed and on / off of the intermediate rollers 63 and 66 and the registration roller 67 can be controlled independently of each other. Further, it can be rotated at a speed different from that of the paper feed rollers 62 and 65 driven to rotate by the motor 71, and can be turned on and off at different timings.

  The image forming apparatus 2 automatically specifies the basis weight of the fed sheet 9 without specifying by the user, and appropriately sets the operation conditions of the printer engine 30B and the fixing device 17 according to the specified basis weight. A function of setting so that a clear image is formed.

  In order to specify the basis weight of the sheet 9, electrostatic capacity sensors 40a and 40b and a plurality of other electrostatic capacity sensors are arranged at appropriate positions of the image forming system 1. The capacitance sensor 40 a is disposed in the paper feed path 51, and the capacitance sensor 40 b is disposed in the paper feed path 52. Further, they are also arranged in the paper feed paths 55 and 56. That is, the basis weight can be specified by discriminating the fed sheet 9 regardless of which sheet feeding path 51, 52, 55, 56 is passed. Hereinafter, the capacitance sensors 40a and 40b and other capacitance sensors may be collectively referred to as “capacitance sensor 40”.

  By arranging a capacitance sensor individually for each of the paper feed paths 51, 52, 55, and 56, the basis weight can be specified at an early timing after paper feed.

  FIG. 4 shows an example of the configuration of the capacitance sensor 40.

  The electrostatic capacity sensor 40 is a sensor also called an electrostatic capacity type proximity sensor, and includes an electrode section 410 and a detection circuit section 420 serving as a detection surface.

  The electrode part 410 is a metal plate (including metal foil) having a size of about 10 mm square, for example, a copper plate. The electrode unit 410 is connected to the detection circuit unit 420 via a lead wire and a connector. Note that the position where the capacitance sensor 40 is disposed in the transport path 50 means a position where the electrode portion 410 is disposed.

  The detection circuit unit 420 includes a capacitor 421, a switch 422, a current / frequency conversion unit (current controlled oscillator: ICO) 423, and a frequency counter 424. The detection circuit unit 420 is configured to generate a signal S3 whose frequency changes according to the capacitance of the electrode unit 410, and to output a count value of the frequency of the signal S3 to the CPU 20a as a detection signal S4.

  The switch 422 is switched by a pulse output from the frequency counter 424 and repeats charging and discharging. The resulting AC current is smoothed by a low-pass filter made up of a capacitor 421 and becomes a DC current. The DC current is converted into a frequency by the current / frequency converter 423. When the capacitance of the electrode portion 410 increases, the current during charging / discharging increases and the DC current also increases. Therefore, the frequency changes linearly (proportional) with respect to the capacitance.

  The configuration of the capacitance sensor 40 is not limited to the configuration of FIG. However, a circuit configuration in which the frequency is linear with respect to the capacitance is preferable. When the relationship between the capacitance and the frequency is linear, unlike the conventional example, it is not necessary to measure the capacitance by stacking two sheets 9, and the capacitance can be reduced even with one sheet 9. Can be measured.

  FIG. 5 shows a functional configuration of the sheet discriminating apparatus 5, and FIG. 6 schematically shows a state of the sheet 9 being conveyed. FIG. 7 shows an example of a change in the output of the capacitance sensor 40, and FIG. 8 shows an example of the relationship between the output of the capacitance sensor 40 and the basis weight BW.

  In FIG. 5, the sheet discriminating apparatus 5 includes a first roller 60A that conveys the sheet 9, a second roller 60B that is disposed downstream of the first roller 60A and conveys the sheet 9, and these rollers 60A, It has the rotation drive part 250 which rotationally drives 60B.

  In addition, the sheet discriminating device 5 is disposed at a conveyance control unit 202 that controls the rotational driving of the rollers 60A and 60B, and a detection position P40 (see FIG. 6) between the rollers 60A and 60B in the conveyance path 50. The electrostatic capacitance sensor 40 is provided. Further, the sheet determination apparatus 5 includes a determination processing unit 203 that determines the sheet 9 using the basis weight information D1, and a timer 204 for determining the determination timing.

  The rollers 60A and 60B are rollers disposed upstream of the printer engine 30B in the conveyance path 50. The rotation drive unit 250 includes motors 71, 72, 73, 74, clutches 81, 82, and the like.

  The functions of the transport control unit 202 and the discrimination processing unit 203 are realized by the hardware configuration of the main control unit 20 and by the CPU 20a executing the program described above.

  The conveyance control unit 202 controls the rotation driving unit 250 to feed the sheet 9 and perform subsequent conveyance in accordance with a command from the print job control unit 201 in the main control unit 20. At the same time, the conveyance control unit 202 is the conveyance speed by the downstream roller 60B in the conveyance in the conveyance direction M1 when the sheet 9 is in contact with both the roller 60A and the roller 60B as shown in FIG. 6B. Pulling control is performed to control the rotational drive so that the downstream speed V2 is greater than the upstream speed V1, which is the speed of conveyance by the upstream roller 60A.

  The discrimination processing unit 203 discriminates the sheet 9 based on the detection signal S4 that is the output of the capacitance sensor 40 during the period in which the tension control is performed.

  With the tension control, as shown in FIG. 6B, the sheet 9 is stretched at the detection position P <b> 40 that is the detection target range by the capacitance sensor 40 in the conveyance path 50, and the capacitance sensor 40. And the distance d1 is kept constant.

  On the other hand, as shown in FIG. 6A, at the stage where the leading edge of the sheet 9 has passed through the upstream roller 60A but is not in contact with the downstream roller 60B, the sheet 9 and the capacitance sensor 40 The distance d1 changes as the sheet 9 moves.

  Here, the capacitance C detected by the capacitance sensor 40 is expressed by the following equation.

C = k (A / d1) + Cp
Here, k is the dielectric constant of the sheet 9, A is the area of the electrode, and Cp is the parasitic capacitance.

  From this equation, it can be seen that the capacitance C changes as the distance d1 changes. Therefore, the conveyance control unit 202 performs tension control so that the change in the capacitance C can be suppressed and detected in a stable state. As a result, the basis weight can be specified by discriminating while conveying the sheet 9, and the conditions of the image forming operation can be set according to the basis weight without reducing the productivity of image formation.

  The discrimination processing unit 203 outputs the capacitance sensor 40 when the sheet 9 is not present at the detection position P40 and the capacitance sensor 40 when the sheet 9 is present at the detection position P40 during the period in which the tension control is performed. The sheet is determined based on the output.

  Specifically, the difference dS4 between the measurement value S4a of the detection signal S4 when there is no sheet 9 shown in FIG. 7 and the measurement value S4b of the detection signal S4 when there is the sheet 9 is calculated, and as shown in FIG. The basis weight BW of the sheet 9 is specified using basis weight information D1 indicating the relationship between the difference dS4 and the basis weight BW. The specified basis weight BW is notified to the print job control unit 201 as the discrimination result of the sheet 9. As the measurement values S4a and S4b, an average value of the detection signal S4 in a predetermined time or an intermediate value between the maximum value and the minimum value can be used.

  The basis weight information D1 may be a table that associates the count value of the frequency that can be the difference dS4 with the basis weight BW, or an arithmetic expression that represents the relationship between the count value and the basis weight BW (proportional relationship in FIG. 8). It may be. The basis weight information D1 is stored in, for example, a nonvolatile memory in the main control unit 20.

  When the print job control unit 201 receives the notification of the basis weight BW, the print job control unit 201 instructs the engine control unit 30A that controls the printer engine 30B to perform operation setting according to the notified basis weight BW. The engine control unit 30A sets, for example, a transfer voltage applied to the transfer roller 68 according to the command. Further, the print job control unit 201 sets the fixing temperature of the fixing device 37 according to the basis weight BW, or instructs the conveyance control unit 202 to set the paper feed speed.

  Next, tension control will be described in more detail.

  FIG. 9 shows the state of the sheet 9 in the curved conveyance path 51A when the tension control is performed, and FIG. 10 shows the timing at which measurement by the capacitance sensor 40a is performed.

  In FIG. 9, the upstream roller 60A (first roller) described in FIG. 6 is the sheet feeding roller 62 of the sheet supply mechanism 24A, and the downstream roller 60B (second roller) is the intermediate roller 63. It is.

  A portion of the conveyance path 50 between the paper feed roller 62 and the intermediate roller 63 is a curved conveyance path 51A through which the sheet 9 is curved. The curved conveyance path 51 </ b> A includes a part of the sheet feeding path 51.

  The curved conveyance path 51A is formed by a curved inner conveyance guide 511 and an outer conveyance guide 512, and the inner conveyance guide 511 in a state where the sheet 9 is stretched as shown in FIG. 9 during a period in which the tension control is performed. It comes to contact with. The electrostatic capacity sensor 40a is disposed so as to detect the sheet 9 that is stretched in the vicinity of the inner conveyance guide 511. The detection position P40 is a position inside the curve in the curved conveyance path 51A.

  Referring also to FIG. 10, the rotation of the sheet feeding roller 62 is started at time t1, and the leading edge of the sheet 9 enters the curved conveyance path 51A. As shown by a broken line in FIG. 9, the sheet 9 proceeds in the horizontal direction along the conveyance guide 512, and is guided upward by the conveyance guide 512 and bends upward.

  At a time point t2 before the leading edge of the sheet 9 arrives at the intermediate roller 63, the rotational driving of the intermediate roller 63 is started. However, for example, the rotational driving of the intermediate roller 63 may be started at time t1.

  When the sheet sensor 91 disposed in the vicinity of the downstream side of the intermediate roller 63 detects the sheet 9, that is, at a time point t4 immediately after the leading edge of the sheet 9 passes through the nip portion of the intermediate roller 63, the rotation of the paper supply roller 62 is rotated. Driving is stopped. The rotational driving of the intermediate roller 63 is continued. That is, tension control is started at time t4.

  At a time before starting the tension control, for example, at a time t3 between the time t1 and the time t4, the detection signal S4 is measured in order to obtain a measurement value S4a when the sheet 9 is not present.

  At time t4, the tension control is started, and the time measurement by the timer 204 is started. Time T1 is the length of the difference between the distance (long distance) that the sheet 9 travels along the curved transport path 51A along the outer transport guide 512 and the distance (short distance) when it travels along the inner transport guide 511. This is the time required for conveyance. The time T1 can be obtained by experiment, for example.

  At the time point t5 when the timing of the time T1 is completed, the seat 9 is in a stretched state as indicated by a solid line in FIG. Therefore, at this time t5, the detection signal S4 is measured to obtain the measurement value S4b when the sheet 9 is present.

  Based on the value S4a obtained by the measurement at the time point t3 and the value S4b obtained by the measurement at the time point t5, the difference dS4 is calculated as described above, and the basis weight BW of the sheet 9 is calculated using the basis weight information D1. Is identified.

  That is, the determination processing unit 203 outputs the output of the capacitance sensor 40a after the time (T1) required for the sheet 9 to contact the inner conveyance guide 511 at the detection position P40 after the tension control is started. It is used for discrimination of the sheet 9 as an output of the capacitance sensor 40a during the period in which the tension control is performed.

  The sheet feeding roller 62 rotates when a rotational torque of a predetermined level or more is applied in a state where the rotation driving is stopped. Accordingly, when the sheet 9 is conveyed by the intermediate roller 63 in a state where the sheet 9 is stretched by the tension control, the sheet feeding roller 62 is in a period (shown by a broken line in FIG. 10) until the rear end of the sheet 9 passes through the nip portion. The peripheral surface is dragged by the moving sheet 9 to rotate.

  When the rear end of the sheet 9 passes through the intermediate roller 63 at time t6 and the output of the sheet sensor 91 is turned off, the rotational drive of the intermediate roller 63 is stopped. That is, the period T2 from the time point t4 to the time point t6 is a period during which the tension control is performed.

  FIG. 11 shows an example of the arrangement of the electrode portions 410 of the capacitance sensor 40a. 11A shows the arrangement position of the electrode portion 410 in the cross section of the curved conveyance path 51A, and FIG. 11B shows the arrangement of the electrode portion 410 when the inner conveyance guide 511 is viewed in plan from the curved conveyance path 51A. Show. FIG. 11C shows the arrangement of the electrode portions 410 in the cross section taken along the line CC in FIG.

  As shown in FIG. 11A, the electrode portion (metal plate) 410 can be provided on the inner conveyance guide 511, for example, on the surface on the curved conveyance path 51A side by pasting, embedding, or vapor deposition.

  The inner conveyance guide 511 is made of resin, for example. As shown in FIG. 11B, a plurality of protrusions 511 </ b> A are provided on the surface on the curved conveyance path 51 </ b> A side to reduce the contact area with the sheet 9. In the example of FIG. 11B, the protrusions 511A have a strip shape that is long in the conveyance direction M1 of the sheet 9, and are regularly formed with a predetermined interval by resin molding. The electrode part 410 is disposed between two adjacent protrusions 511A.

  As shown in FIG. 11C, the thickness of the electrode portion 410 is smaller than the height of the protrusion 511A. The curved conveyance path 51A is a space through which the sheet 9 passes and is a space above the top surface of the protrusion 511A in FIG. Accordingly, the electrode portion 410 is disposed at a portion of the inner conveyance guide 511 that is outside the curved conveyance path 51A. The exposed surface that becomes the detection surface of the electrode portion 410 and the sheet 9 are hardly rubbed.

  The electrode portion 410 may be provided on the surface of the inner conveyance guide 511 on the side not facing the curved conveyance path 51A, or may be embedded in the inner conveyance guide 511.

  FIG. 12 shows a modified example of the arrangement position of the capacitance sensor 40. In this modification, the electrostatic capacity sensor 40 is not individually provided for the plurality of paper feed paths 51, 52, 55, 56, but the positions where the paper feed paths 51, 52, 55, 56 join together. One electrostatic capacity sensor 40 is provided further downstream. Specifically, it is provided between the intermediate roller 63 and the registration roller 67.

  In this case, the upstream roller 60A in the tension control is the intermediate roller 63, and the downstream roller 60B is the registration roller 67. The upstream roller 60A, the downstream roller 60B, and the capacitance sensor 40 are arranged upstream of the printer engine 30B. Therefore, regardless of which paper feed path 51, 52, 55, 56 passes, the fed sheet 9 can be identified before the secondary transfer and the basis weight can be specified.

  Since the number of capacitance sensors 40 is reduced as compared with the configuration in which the capacitance sensors 40 are individually provided for the paper feed paths 51, 52, 55, and 56, the cost of the image forming apparatus 2 can be reduced.

  FIG. 13 shows the position of the sheet 9a when measurement is performed by the capacitance sensor 40b when the sheets 9a and 9b are supplied from the adjacent sheet supply mechanisms 24A and 24B.

  In a print job for continuously feeding a plurality of sheets 9a and 9b, for example, when the sheet 9a is fed as a preceding sheet from the sheet feeding mechanism 24A, the sheet feeding mechanism 24A becomes empty, and the succeeding sheet 9b is There is a case where paper is fed from the sheet supply mechanism 24B.

  The subsequent sheet 9b is determined based on the output of the capacitance sensor 40b. At this time, even if the sheet 9b is tensioned by the tension control and the distance d1 (see FIG. 6) is constant, if the preceding sheet 9a moves around the capacitance sensor 40b, The output of the capacitance sensor 40b may become unstable due to the influence.

  Therefore, when feeding from the adjacent sheet supply mechanism 24B following the sheet supply from the sheet supply mechanism 24A, the capacitance sensor after the time when the preceding sheet 9a is separated by more than the distance d2 that does not affect the measurement. The output of 40b is measured. In the example of FIG. 13, the time when the trailing edge of the preceding sheet 9a is detected by the sheet sensor 91 is the time when the distance is greater than or equal to the distance d2.

  Instead of measuring the output of the capacitance sensor 40b after waiting for the preceding sheet 9a to move away from the capacitance sensor 40b by a distance d2 or more after feeding the succeeding sheet 9b, the sheet 9b is separated by a distance d2 or more. The subsequent sheet 9b may be fed after that time.

  FIG. 14 shows the flow of processing in the sheet discriminating apparatus 5.

  Waiting for the start of paper feeding (# 101), and when paper feeding is started (YES in # 101), the capacitance in the absence of sheet is measured (# 102).

  When the sheet 9 arrives at the downstream roller 60B (YES in # 103), the tension control is started (# 104). For example, the rotation driving of the upstream roller 60A is stopped, and the rotation driving of the downstream roller 60B is continued.

  A sheet state determination process for determining whether or not the sheet 9 is in a tensioned state is executed (# 105). If it is determined that the sheet 9 is in the tensioned state, the capacitance in the state where the sheet is present is measured (# 106).

  A difference dS4 between the measurement value S4a in the absence of sheet and the measurement value S4b in the presence of sheet is calculated (# 107), and the basis weight BW of the sheet 9 is specified by the basis weight information D1 based on the calculated difference dS4 (# 108). Then, the specified basis weight BW is output to the print job control unit 201 as a discrimination result (# 109).

  FIG. 15 shows a first example of the flow of the sheet state determination process, and FIG. 16 shows a second example of the flow of the sheet state determination process.

  In FIG. 15, the timer 204 is set (# 111). When the time measurement by the timer 204 is completed (YES in # 112), it is determined that the sheet 9 is in a tensioned state (# 113).

  In FIG. 16, the detection signal S4 from the capacitance sensor 40 is monitored (# 121). When the amount of change in the value of the detection signal S4 is equal to or less than the predetermined amount (YES in # 122), it is determined that the sheet 9 has been stretched (# 123). According to this, it is possible to reduce the influence of the variation in the conveyance amount due to the slip or the like for each sheet feeding in FIG.

  FIG. 17 shows a third example of the flow of the sheet state determination process, and FIG. 18 shows a fourth example of the flow of the sheet state determination process.

  In FIG. 17, the timer 204 is set (# 131). When the timer 204 finishes counting the time T1 (YES in # 132), it is checked whether or not there is a preceding sheet 9a in the paper feed path 51 adjacent to the paper feed path 52 that has started feeding (# 133). .

  If there is a preceding sheet 9a (YES in # 133), it waits for the preceding sheet 9a to move to a predetermined position that is more than a predetermined distance d2 (# 134). When the preceding sheet 9a moves to a predetermined position (YES in # 134), it is determined that the sheet 9b is in a tensioned state (# 135).

  In FIG. 18, the detection signal S4 from the capacitance sensor 40 is monitored (# 141). While the time set for abnormality determination does not elapse (NO in # 142), when the amount of change in the value of the detection signal S4 becomes equal to or less than a predetermined amount (YES in # 143), the sheet 9 is stretched. It is determined that it has become (# 144).

  On the other hand, if the set time elapses before the amount of change in the value of the detection signal S4 becomes equal to or less than the predetermined amount (YES in # 142), it is determined that an abnormality has occurred (# 145). If the sheet 9 is the second and subsequent sheets in continuous feeding (YES in # 146), the basis weight BW specified for the preceding sheet 9 is output as the determination result for the sheet 9 (# 147). Accordingly, the main control unit 20 can specify the basis weight BW for the second and subsequent sheets 9 sequentially fed from the sheet feeding unit 24 to the conveyance path 50 in a print job using a plurality of sheets 9. If not, the image formation on the sheet 9 is controlled according to the basis weight BW specified for the sheet 9 that has been carried in earlier.

  If the sheet 9 to be identified is not the second or subsequent sheet 9 (NO in # 146), the occurrence of abnormality is notified to the print job control unit 201 of the main control unit 20 (# 148).

  FIG. 19 shows the flow of paper feed control processing in the image forming apparatus 2, and FIG. 20 shows the flow of paper feed start processing in paper feed control.

  In FIG. 19, paper feed start processing for starting paper feed to any of the paper feed paths 51, 52, 55, and 56 is executed according to the designation of the print job (# 201). Subsequently, it is checked whether or not the next sheet feeding is necessary (# 202). If the print job being executed is a job that continuously feeds and the next feed is necessary (YES in # 202), the process returns to step # 201 to start feeding the next sheet 9. . If the final paper feeding is already finished and the next paper feeding is not necessary (NO in # 202), the process is finished.

  It should be noted that when the sheet feeding start process is executed, another sheet 9 that is already being fed is not in a range that affects the measurement by the capacitance sensor 40 arranged in the sheet feeding path to start feeding. This may be a condition. That is, as described in the example of FIG. 13, for example, the sheet supply mechanism 24B performs the sheet feeding start process after waiting for the fed sheet 9a to move away from the capacitance sensor 40b by a distance d2 or more. May be. In that case, after step # 201 is executed, the process proceeds to step # 202 after waiting for the sheet 9 to pass a predetermined position.

  In FIG. 20, it is checked whether or not the sheet supply mechanism 24B (or 24A) adjacent to the sheet supply mechanism 24A (or 24B) to start feeding has been opened or closed (# 211). That is, it is checked whether the sheet supply mechanism 24B (or 24A) is pulled out to be in an open state or pushed in to be in a closed state.

  When the sheet is opened (YES in # 212), the sheet storage cassette of the pulled out sheet supply mechanism 24B (or 24A) is out of the image forming apparatus 2 and the sheet 9 to be fed is supplied. If it is determined that there is no influence on the discrimination, the paper feeding is started (# 213).

  On the other hand, in the closed state (NO in # 212), a preparation operation (lift up) is performed to bring the sheet storage cassette closer to the pickup roller 64 (or 61) immediately after being pushed in, which is the paper feed. This may affect the determination of the sheet 9 that is about to be performed. Therefore, it waits for the preparation operation to end (# 214). When the preparation operation is finished (YES in # 214), paper feeding is started (# 213).

  According to the above embodiment, it is possible to make a determination while conveying the sheets 9, 9a, 9b. Since the basis weight BW can be specified while the sheets 9, 9a, 9b are conveyed, it is possible to set the conditions of the image forming operation according to the basis weight BW without reducing the productivity of image formation. become.

  According to the embodiment described above, since the basis weight BW is specified based on the difference dS4 between the measured value S4a in the absence of the sheet and the measured value S4b in the presence of the sheet, it is related to the dielectric constant k and the parasitic capacitance Cp. The influence of changes in environmental conditions such as temperature and humidity can be reduced.

  According to the embodiment described above, one electrostatic capacity sensor 40 can be arranged at one detection position P40. Compared with the case where the capacitance sensor 40 is disposed on both sides in the thickness direction of the sheet 9 and the method of reducing the influence of the fluctuation of the distance d1 between the capacitance sensor 40 and the sheet 9 is adopted, the capacitance sensor. Since the required number of 40 is small, the cost can be reduced. Further, since it is not necessary to insulate the electrode portions 410 in the transport passage 50, the design of the image forming apparatus 2 is facilitated.

  In the embodiment described above, the content of the basis weight information D1 shows an example. The content of the basis weight information D1 depends on the configuration and characteristics of the capacitance sensor 40, and may indicate the relationship between the difference dS4 and the basis weight BW which are not the proportional relationship shown in FIG. it can.

  The difference dS4 between the measurement value S4a in the absence of the sheet and the measurement value S4b in the presence of the sheet was calculated, but instead of the difference dS4, the ratio between the measurement value S4a and the measurement value S4b was calculated. The basis weight BW may be specified using information indicating the relationship between

  As the tension control, the upstream roller 60A is stopped, but the upstream speed V1 may be controlled to be slower than the downstream speed V2. That is, it is only necessary to provide a speed difference so that the downstream roller 60B rotates faster than the upstream roller 60A and pass the detection position P40 while the sheet 9 is stretched.

  In addition, the overall configuration of each of the image forming system 1, the image forming apparatus 2, and the sheet determination apparatus 5, the contents of processing, the order, or the timing can be appropriately changed in accordance with the spirit of the present invention.

2 Image forming apparatus 5 Sheet discriminating apparatus 9, 9a, 9b Sheet 20 Main control section (control section)
24 Paper Feeder (Sheet Feeder)
24A, 24B Sheet supply mechanism 30B Printer engine 40, 40a, 40b Capacitance sensor 50 Conveyance path 51, 52, 55, 56 Feed path 51A Curved conveyance path 60A Upstream roller (first roller)
60B Downstream roller (second roller)
202 Conveyance control unit 203 Discrimination processing unit 410 Electrode unit (metal plate)
511 Inner transport guide 512 Outer transport guide BW Basis weight d2 Distance dS4 Difference D1 Basis weight information (information)
P40 Detection position S4 Detection signal (output)
T1 Time T2 Period V1 Upstream speed V2 Downstream speed

Claims (12)

A sheet discriminating apparatus for discriminating the sheet carried into a conveyance path for conveying a sheet,
A first roller for conveying the sheet;
A second roller disposed downstream of the first roller to convey the sheet;
A conveyance control unit that controls rotational driving of the first roller and the second roller;
A capacitance sensor disposed at a detection position between the first roller and the second roller in the transport path;
A determination processing unit for determining the sheet,
When the sheet is in contact with both the first roller and the second roller, the conveyance control unit has a downstream speed, which is a conveyance speed by the second roller, of the conveyance by the first roller. Performing tension control to control the rotational drive so as to be higher than the upstream speed which is the speed,
The discrimination processing unit discriminates the sheet based on an output of the capacitance sensor during a period in which the tension control is performed.
A sheet discrimination apparatus characterized by the above. The discrimination processing unit is configured to output the capacitance sensor when the sheet is not present at the detection position and the capacitance sensor when the sheet is present at the detection position during a period in which the tension control is performed. And determining the sheet based on the output of
The sheet discrimination apparatus according to claim 1. The discrimination processing unit calculates a difference between the output of the capacitance sensor when the sheet is not present at the detection position and the output of the capacitance sensor when the sheet is present at the detection position. The basis weight of the sheet is specified using information indicating the relationship between the basis weight and the basis weight is output as the discrimination result of the sheet.
The sheet discrimination apparatus according to claim 2. A portion of the conveyance path between the first roller and the second roller is a curved conveyance path through which the sheet is curved,
The detection position is a position inside the curve in the curved conveyance path.
The sheet discriminating apparatus according to any one of claims 1 to 3. The curved conveyance path is formed by an inner conveyance guide and an outer conveyance guide, and is in contact with the inner conveyance guide while the sheet is stretched during the period in which the tension control is performed. And
The capacitance sensor is arranged to detect the sheet in a tensioned state in the vicinity of the inner conveyance guide.
The sheet discrimination apparatus according to claim 4. The discrimination processing unit outputs the output of the capacitance sensor after the time required for the sheet to come into contact with the inner conveyance guide at the detection position after the tension control is started. Used for discrimination as the output of the capacitance sensor during the period being performed,
The sheet discrimination apparatus according to claim 5. The capacitance sensor has a metal plate that serves as a detection surface,
The metal plate is disposed in a portion that is outside the curved conveyance path in the inner conveyance guide.
The sheet discrimination apparatus according to claim 6. An image forming apparatus for forming an image on a sheet,
A sheet supply unit capable of storing a plurality of sheets;
A printer engine for forming an image on the sheet supplied from the sheet supply unit;
A first roller and a second roller disposed on the downstream side of the first roller for conveying the sheet carried into the conveyance path from the sheet supply unit to the printer engine;
A capacitance sensor disposed at a detection position between the first roller and the second roller in the transport path;
A control unit,
When the sheet is in contact with both the first roller and the second roller, the control unit is configured such that a downstream speed, which is a conveyance speed by the second roller, is a conveyance speed by the first roller. And performing the tension control for controlling the rotational drive of the first roller and the second roller so as to be larger than the upstream speed, and the capacitance during the period during which the tension control is performed. Identifying the basis weight of the sheet based on the output of the sensor, and controlling the image forming apparatus according to the identified basis weight;
An image forming apparatus. In a job using a plurality of the sheets, the control unit is unable to specify the basis weight for the second and subsequent sheets of sequential carry-in from the sheet supply unit to the conveyance path. Control the formation of an image on the sheet according to the basis weight specified for the sheet carried in advance.
The image forming apparatus according to claim 8. The sheet supply unit has a plurality of sheet supply mechanisms,
The conveying path is configured such that a plurality of sheet feeding paths respectively corresponding to the plurality of sheet supply mechanisms merge into one upstream of the printer engine,
The capacitance sensor is provided for each of the plurality of paper feed paths;
The control unit uses the capacitance sensor provided in the sheet feeding path corresponding to a sheet feeding mechanism that carries the sheet into the transport path among the plurality of sheet feeding mechanisms, and uses a basis weight of the sheet. Identify
The image forming apparatus according to claim 8 or 9. The control unit detects a preceding sheet and a succeeding sheet by the respective capacitance sensors in a job for carrying in the sheet in order from one of the plurality of sheet supply mechanisms and the other one. Identifying the basis weight of each sheet based on the output of the capacitance sensors when they are separated from each other by more than a distance that does not affect,
The image forming apparatus according to claim 10. The sheet supply unit has a plurality of sheet supply mechanisms,
The conveying path is configured such that a plurality of sheet feeding paths respectively corresponding to the plurality of sheet supply mechanisms merge into one upstream of the printer engine,
The first roller, the second roller, and the capacitance sensor are provided downstream from a position where the plurality of paper feed paths merge together.
The image forming apparatus according to claim 8 or 9.

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