JP6957866B2 - Sheet discrimination device and image forming device - Google Patents

Description

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

An image forming apparatus such as a copier and a printer that forms an image on a sheet has a function of setting operating conditions so that an appropriate image can be obtained according to the type of the sheet. Patent Document 1 discloses that the resist roller unit detects the type of sheet by a sensor and determines the transfer speed by the resist roller based on the detection result.

For example, in an electrophotographic image forming apparatus, sheets are classified according to the basis weight, and the transfer speed, transfer voltage, fixing temperature, and the like are set according to the basis weight. With this setting, it is possible to prevent jams, transfer defects, fixing defects, and the like.

As a method for the image forming apparatus to specify the basis weight of the sheet, there is a method in which the user selects and specifies the type of the sheet from several options (plain paper, thick paper 1, thick paper 2, etc.). The image forming apparatus specifies the basis weight associated with the type specified by the user in advance as the basis weight of the sheet, and sets the 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 have been diversified, it has become difficult to appropriately set the operating conditions by 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 a type of sheet is discriminated by using a distributed inductance type capacitance sensor. Further, in order to eliminate erroneous detection of the sensor output and perform the discrimination reliably, it has been proposed to perform the discrimination when the sheets are continuously conveyed. Specifically, the preceding sheet is stopped at the detection position to measure the electrostatic coupling amount, and while the preceding sheet is stopped, the succeeding sheet is conveyed to the detection position and stopped, and the measurement is performed again with the two sheets overlapping. Is disclosed, and a method for determining the type of sheet based on the difference between the two measured values obtained is disclosed.

Japanese Unexamined Patent Publication No. 2006-330698 JP-A-2007-107976

Capacitance sensors have advantages such as small restrictions on placement space due to the small size of the detection unit and low cost as compared with other sensors such as ultrasonic sensors. However, fluctuations in the distance to the detection target greatly affect the output. For this reason, when 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 discrimination based on the sensor output in a state where the seat is stopped, this problem cannot be solved.

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

The present invention has been made in view of the above problems, and an object of the present invention is to provide a sheet discriminating device and an image forming device capable of discriminating while transporting a sheet.

The sheet discriminating device according to the embodiment of the present invention is a sheet discriminating device that discriminates the sheet carried into the transport passage for transporting the sheet, and is a first roller for transporting the sheet and the first roller. A second roller that is arranged on the downstream side of the roller and conveys the sheet, a transfer control unit that controls the rotational drive of the first roller and the second roller, and the first of the transfer passages. It has a capacitance sensor arranged at a detection position between the first roller and the second roller, and a discrimination processing unit for discriminating the sheet, and the transport control unit is the first roller. And when the sheet is in contact with both of the second roller, the downstream speed, which is the speed of transportation by the second roller, is higher than the upstream speed, which is the speed of transportation by the first roller. The tension control for controlling the rotation drive is performed, and the discrimination processing unit discriminates the sheet based on the output of the capacitance sensor during the period during which the tension control is performed .
The portion of the transport passage between the first roller and the second roller is a curved transport path through which the sheet is curved, and the detection position is the curved transport path of the curved transport path. It is an inner position, and the curved transport path is formed by a curved inner transport guide and an outer transport guide, and the inner transport in a stretched state during the period during which the tension control is performed. The capacitance sensor is arranged so as to come into contact with the guide, and the capacitance sensor is arranged so as to detect the sheet in a stretched state in the vicinity of the inner transport guide, and the discrimination processing unit starts the tension control. The output of the capacitance sensor after the time required for the sheet to come into contact with the inner transport guide at the detection position has elapsed since the sheet was generated, and the capacitance during the period during which the tension control is performed is performed. Used for discrimination as the output of the sensor, the capacitance sensor has a metal plate as a detection surface, and the metal plate is arranged at a portion outside the curved transport path in the inner transport guide. Has been done.

According to the present invention, it is possible to discriminate while transporting a sheet.

It is a figure which shows the structure of the image formation system provided with the sheet discrimination apparatus which concerns on one Embodiment of this invention. It is a figure which shows the hardware composition of the image forming apparatus 2 in an image forming system. It is a figure which shows the outline of the transport passage in an image formation system. It is a figure which shows the example of the structure of the capacitance sensor. It is a figure which shows the functional structure of the sheet discriminating device. It is a figure which shows typically the state of the sheet during transportation. It is a figure which shows the example of the change of the output of a capacitance sensor. It is a figure which shows the example of the relationship between the output of a capacitance sensor, and the basis weight. It is a figure which shows the state of the sheet in the curved transport passage when tension control is performed. It is a figure which shows the timing which performs the measurement by a capacitance sensor. It is a figure which shows the example of the arrangement of the electrode part of a capacitance sensor. It is a figure which shows the modification of the arrangement position of a capacitance sensor. It is a figure which shows the position of the sheet when the measurement by the capacitance sensor is performed when the sheet is supplied from the adjacent sheet supply mechanism. It is a figure which shows the flow of the process in a sheet discriminating device. It is a figure which shows the 1st example of the process flow of the sheet state determination. It is a figure which shows the 2nd example of the process flow of the sheet state determination. It is a figure which shows the 3rd example of the process flow of the sheet state determination. It is a figure which shows the 4th example of the process flow of the sheet state determination. It is a figure which shows the flow of the paper feed control processing in an image forming apparatus. It is a figure which shows the flow of the paper feed start processing in the paper feed control.

FIG. 1 shows the configuration of the image forming system 1 provided with the sheet discriminating device 5 according to the embodiment of the present invention, and FIG. 2 shows the hardware configuration of the image forming apparatus 2 in the image forming system 1. There is.

As shown in FIG. 1, the image forming system 1 is composed of an image forming device 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 or more sheets. The finisher 4 is a post-processing device that performs processing such as tri-folding, punching, and staple binding on the printed sheet discharged from the image forming apparatus 2.

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

The main control unit 20 is in charge of overall control of the image forming system 1. That is, the image forming apparatus 2, the paper feed cabinet set 3, and the finisher 4 are controlled. 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.

A computer program for controlling the operation of the image forming system 1 is stored in the ROM 20c or the auxiliary storage device 28. Further, a sheet discriminating program for operating a part of the components of the image forming apparatus 2 as the sheet discriminating device 5 is stored. These programs are loaded into the RAM 20b as needed 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 a process of compressing / decompressing image data, a process of generating raster data to be output to the printer unit 23, and the like.

The automatic document feeder 21 conveys the sheet set in the document tray to the reading position of the scanner 22. The scanner 22 is a flatbed type, and generates image data by reading images written on a sheet-shaped document or various documents set on a platen glass conveyed from the automatic document feeder 21. ..

The printer unit 23 forms an image on a sheet based on the raster data generated by the image processing unit 20d in print jobs 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 that is useful when printing on an infrequently used sheet such as a color sheet or a long sheet.

The network interface 26 communicates with another device 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), an SSD (Solid State Drive), or the like is used.

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

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

The paper feed 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 has a printer engine 30B that forms an image by an electrophotographic method. The printer engine 30B has four imaging stations 31, 32, 33, 34, and parallelizes four color toner images of yellow (Y), magenta (M), cyan (C), and black (K). To form. Each of the imaging stations 31, 32, 33, 34 has a cylindrical photoconductor, a charging charger, a developing device, a light source for exposure, and the like.

The four-color toner image is primarily transferred to the intermediate transfer belt 35, and is secondarily transferred to the sheet 9 conveyed via the resist roller 67 by the transfer roller 68. After the secondary transfer, the sheet 9 is sent out to the finisher 4 through the inside of the fuser 37. When passing through the fuser 37, the toner image is fixed on the sheet 9 by heating and pressurizing.

By the way, the image forming system 1 has a transport passage 50 shown by a thick solid line in the figure. The transport passage 50 is configured such that a plurality of paper feed passages 51, 52, 55, 56 merge into one upstream of the printer engine 30B, and passes through the paper feed unit 24, the printer engine 30B, and the fuser 37 in order. It extends to the finisher 4. The transport passage 50 is a space provided for transporting the sheet 9 in the direction along the surface thereof.

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

The transport passage 50 feeds the sheet 9 into the discharge passage 57 extending from the printer engine 30B to the finisher 4, the reversing passage 58 for inverting the front and back of the sheet 9 and returning it to the resist roller 67 during double-sided printing, and the reversing passage 58. Includes a switchback passage 59 for.

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 highest sheet 9 of the group of sheets stacked on the storage cassette. The paper feed roller 62 sends the taken out sheet 9 to the paper feed passage 51. That is, it is carried into the transport passage 50. The carried-in sheet 9 is conveyed by the paper feed roller 62 and proceeds to the intermediate roller 63 downstream. Hereinafter, carrying the sheet 9 into the transport passage 50 may be referred to 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 seat supply mechanism 24B is the same as the configuration of the seat supply mechanism 24A. That is, the sheet supply mechanism 24B has 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 advances to the intermediate roller 66 through the paper feed passage 52, is further sent to the intermediate roller 66, and proceeds 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 via the clutch 82. The motor 71 is common to the seat supply mechanism 24A, but the clutches 81 and 82 are individual. Therefore, the intermittent control of the clutches 81 and 82 can be used to feed the paper from the sheet supply mechanism 24A and the sheet supply mechanism 24B. 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 resist roller 67. The resist roller 67 sends the sheet 9 to the transfer roller 68 at the timing of aligning the toner image secondarily transferred to the intermediate transfer belt 35 with the sheet 9.

The intermediate roller 63 is rotationally driven by the motor 72, the intermediate roller 66 is rotationally driven by the motor 73, and the resist roller 67 is rotationally driven by the motor 74. That is, the rotation speeds and on / off of the intermediate rollers 63 and 66 and the resist rollers 67 can be controlled independently of each other. Further, the paper feed rollers 62 and 65, which are rotationally driven by the motor 71, can be rotated at a different speed and turned on and off at different timings.

The image forming apparatus 2 automatically specifies the basis weight of the fed sheet 9 regardless of the user's specification, and appropriately adjusts the operating conditions of the printer engine 30B, the fuser 17 and the like according to the specified basis weight. It has a function to set so that a simple image is formed.

Capacitance sensors 40a, 40b and a plurality of other capacitance sensors are arranged at appropriate positions in the image forming system 1 in order to specify the basis weight of the sheet 9. The capacitance sensor 40a is arranged in the paper feed passage 51, and the capacitance sensor 40b is arranged in the paper feed passage 52. It is also arranged in the paper feed passages 55, 56 and the like. That is, regardless of which of the paper feed passages 51, 52, 55, 56 is passed through, the paper feed sheet 9 can be discriminated and the basis weight can be specified. Hereinafter, the capacitance sensors 40a and 40b and other capacitance sensors may be collectively referred to as “capacitance sensor 40”.

By arranging the capacitance sensors individually for each of the paper feed passages 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 capacitance sensor 40 is a sensor that is also called a capacitance type proximity sensor, and is composed of an electrode portion 410 that serves as a detection surface and a detection circuit portion 420.

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

The detection circuit unit 420 includes a capacitor 421, a switch 422, a current / frequency conversion unit (current control 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 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 consisting of a capacitor 421 to become a DC current. Then, the DC current is converted into a frequency by the current / frequency conversion unit 423. When the capacitance of the electrode portion 410 increases, the current during charging and 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 shown in 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 stack two sheets 9 to measure the capacitance, and even one sheet 9 can measure the capacitance. Can be measured.

FIG. 5 shows the functional configuration of the sheet discriminating device 5, and FIG. 6 schematically shows the state of the sheet 9 during transportation. Further, 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 device 5 includes a first roller 60A that conveys the sheet 9, a second roller 60B that is arranged downstream of the first roller 60A and conveys the sheet 9, and these rollers 60A. It has a rotary drive unit 250 that rotationally drives 60B.

In addition, the seat discrimination device 5 is arranged at the transfer control unit 202 that controls the rotational drive of the rollers 60A and 60B, and at the detection position P40 (see FIG. 6) between the rollers 60A and 60B in the transfer passage 50. It has a capacitance sensor 40. Further, the sheet discriminating device 5 has a discriminating processing unit 203 for discriminating the sheet 9 using the basis weight information D1 and a timer 204 for determining the discriminating timing.

The rollers 60A and 60B are rollers arranged upstream of the printer engine 30B in the transport passage 50. The rotary 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 executing the above-mentioned program by the CPU 20a.

The transfer control unit 202 controls the rotation drive unit 250 so as to feed the sheet 9 and then transfer the sheet 9 in accordance with a command from the print job control unit 201 in the main control unit 20. At the same time, as shown in FIG. 6B, the transport control unit 202 is the speed of transport by the roller 60B on the downstream side in transport in the transport direction M1 when the sheet 9 is in contact with both the rollers 60A and 60B. Tension control is performed to control the rotational drive so that the downstream speed V2 becomes larger than the upstream speed V1 which is the speed of transportation by the upstream roller 60A.

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

Due to the tension control, as shown in FIG. 6B, the sheet 9 is in a stretched state at the detection position P40, which is the detection target range by the capacitance sensor 40 in the transport passage 50, and the capacitance sensor 40 is in a stretched state. It is conveyed in a state where the distance d1 to and from is kept constant.

On the other hand, as shown in FIG. 6A, when the tip of the sheet 9 has passed through the roller 60A on the upstream side but is not in contact with the roller 60B on the downstream side, the sheet 9 and the capacitance sensor 40 The distance d1 to and from changes with the movement of the seat 9.

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

C = k (A / d1) + Cp
However, 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 with the change of the distance d1. Therefore, the transport control unit 202 performs tensile control so that the change in the capacitance C can be suppressed and the detection can be performed in a stable state. Thereby, the basis weight can be specified by discriminating while transporting the sheet 9, and the conditions for the operation of image formation can be set according to the basis weight without lowering the productivity of image formation.

The discrimination processing unit 203 describes the output of 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 during which tension control is being performed. Determine the sheet based on the output.

Specifically, the difference dS4 between the measured value S4a of the detection signal S4 when the sheet 9 is absent and the measured value S4b of the detection signal S4 when the sheet 9 is present is calculated and shown in FIG. The basis weight BW of the sheet 9 is specified by using the basis weight information D1 indicating the relationship between the difference dS4 and the basis weight BW. Then, the specified basis weight BW is notified to the print job control unit 201 as the determination result of the sheet 9. As the measured values S4a and S4b, an average value of the detection signals S4 at a predetermined time or a value intermediate between the maximum value and the minimum value can be used.

The basis weight information D1 may be a table for associating the count value of the frequency that can be the difference dS4 with the basis weight BW, or an arithmetic expression expressing 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, for example, by the non-volatile memory in the main control unit 20.

Upon receiving 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 set the operation 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 a command. Further, the print job control unit 201 sets the fixing temperature of the fixing device 37 according to the basis weight BW, and commands the transfer control unit 202 to set the paper feeding speed.

Next, the tension control will be described in more detail.

FIG. 9 shows the state of the seat 9 in the curved transport passage 51A when the tension control is performed, and FIG. 10 shows the timing of measurement by the capacitance sensor 40a.

In FIG. 9, the upstream roller 60A (first roller) described with reference to FIG. 6 is a paper feed roller 62 of the sheet supply mechanism 24A, and the downstream roller 60B (second roller) is an intermediate roller 63. Is.

The portion of the transport passage 50 between the paper feed roller 62 and the intermediate roller 63 is a curved transport path 51A through which the sheet 9 is curved. The curved transport path 51A includes a part of the paper feed passage 51.

The curved transport path 51A is formed by the curved inner transport guide 511 and the outer transport guide 512, and the inner transport guide 511 with the sheet 9 stretched as shown in FIG. 9 during the period when the tension control is performed. It is designed to come into contact with. The capacitance sensor 40a is arranged so as to detect the sheet 9 in a stretched state in the vicinity of the inner transport guide 511. The detection position P40 is a position inside the curve in the curved transport path 51A.

With reference to FIG. 10, the rotary drive of the paper feed roller 62 is started at the time point t1, and the tip of the sheet 9 enters the curved transport path 51A. The sheet 9 advances horizontally along the transport guide 512 as shown by the broken line in FIG. 9, and is guided by the transport guide 512 and bends upward.

Rotational drive of the intermediate roller 63 is started at a time point t2 before the tip of the sheet 9 arrives at the intermediate roller 63. However, for example, the rotary drive of the intermediate roller 63 may be started at the time point t1.

The rotation of the paper feed roller 62 at the time when the sheet sensor 91 arranged near the downstream side of the intermediate roller 63 detects the sheet 9, that is, at the time t4 immediately after the tip of the sheet 9 passes through the nip portion of the intermediate roller 63. The drive is stopped. The rotational drive of the intermediate roller 63 is continued. That is, at the time point t4, the tension control is started.

The detection signal S4 is measured in order to obtain the measured value S4a when the sheet 9 is absent at the time point before the tension control is started, for example, the time point t3 between the time points t1 and the time point t4.

At the time point t4, the tension control is started and the time T1 is started by the timer 204. The time T1 is only 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 the seat 9 travels along the inner transport guide 511. This is the time required for transportation. The time T1 can be determined, for example, experimentally.

At the time t5 when the time T1 is finished, the sheet 9 is in a stretched state as shown by a solid line in FIG. Therefore, at this time point t5, the detection signal S4 is measured in order to obtain the measured 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 discrimination processing unit 203 outputs the output of the capacitance sensor 40a after the time (T1) required for the sheet 9 to come into contact with the inner transport guide 511 at the detection position P40 has elapsed since the tension control was started. It is used to discriminate the sheet 9 as the output of the capacitance sensor 40a during the period when the tension control is performed.

The paper feed roller 62 rotates when a rotation torque equal to or higher than a predetermined value is applied in a state where the rotation drive is stopped. Therefore, when the sheet 9 is conveyed by the intermediate roller 63 in a stretched state by tension control, the paper feed roller 62 takes a period until the rear end of the sheet 9 passes through the nip portion (shown by a broken line in FIG. 10). The peripheral surface is dragged by the moving sheet 9 and rotates.

At the time point t6, when the rear end of the seat 9 passes through the intermediate roller 63 and the output of the seat 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 the period during which the tension control is performed.

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

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

The inner transport guide 511 is made of, for example, resin. As shown in FIG. 11B, a plurality of protrusions 511A are provided on the surface on the curved transport path 51A side in order to reduce the contact area with the sheet 9. In the example of FIG. 11B, the protrusions 511A have a long strip shape in the transport direction M1 of the sheet 9, and are regularly formed at predetermined intervals by resin molding. The electrode portion 410 is arranged 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 transport 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. 11C. Therefore, the electrode portion 410 is arranged at a portion outside the curved transport path 51A in the inner transport guide 511. The exposed surface, which is the detection surface of the electrode portion 410, and the sheet 9 hardly rub against each other.

The electrode portion 410 may be provided on the surface of the inner transport guide 511 that does not face the curved transport path 51A, or may be embedded inside the inner transport guide 511.

FIG. 12 shows a modified example of the arrangement position of the capacitance sensor 40. In this modification, the capacitance sensors 40 are not individually provided for the plurality of paper feed passages 51, 52, 55, 56, but the positions where the paper feed passages 51, 52, 55, 56 merge into one. One capacitance sensor 40 is provided downstream of the capacitance sensor 40. Specifically, it is provided between the intermediate roller 63 and the resist 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 resist 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 of the paper feed passages 51, 52, 55, 56 is passed through, the paper feed sheet 9 can be discriminated before the secondary transfer to specify the basis weight.

Since the number of capacitance sensors 40 is reduced as compared with the configuration in which the capacitance sensors 40 are individually provided for each of the paper feed passages 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 the capacitance sensor 40b is used to supply the sheets 9a and 9b from the adjacent sheet supply mechanisms 24A and 24B.

In a print job in which a plurality of sheets 9a and 9b are continuously fed, for example, by feeding the sheet 9a as a preceding sheet from the sheet supply mechanism 24A, the sheet supply mechanism 24A becomes empty and the subsequent sheet 9b is fed. Paper may be fed from the sheet supply mechanism 24B.

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

Therefore, when feeding paper from the adjacent sheet feeding mechanism 24B following the feeding from the sheet feeding mechanism 24A, the capacitance sensor is performed after the time when the preceding sheet 9a is separated by a distance d2 or more that does not affect the measurement. The output of 40b is measured. In the example of FIG. 13, the time when the rear end of the preceding seat 9a is detected by the seat sensor 91 is the time when the distance is d2 or more.

Instead of 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 and measuring the output of the capacitance sensor 40b, the distance is separated by a distance d2 or more. After that point, the subsequent sheet 9b may be fed.

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

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

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

The sheet state determination process for determining whether or not the sheet 9 is in a stretched state is executed (# 105). When it is determined that the sheet 9 is in a stretched state, the capacitance in the state with the sheet is measured (# 106).

The difference dS4 between the measured value S4a without the sheet and the measured value S4b with the 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 (# 107). 108). Then, the specified basis weight BW is output to the print job control unit 201 as a determination 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 T1 timed by the timer 204 ends (YES in # 112), it is determined that the sheet 9 is in a stretched 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 a predetermined amount (YES in # 122), it is determined that the sheet 9 is in a stretched state (# 123). According to this, it is possible to reduce the influence of the variation in the transport amount due to the slip or the like for each paper feed 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 time T1 is timed by the timer 204 (YES in # 132), it is checked whether or not there is a preceding sheet 9a in the paper feed passage 51 adjacent to the paper feed passage 52 in which paper feeding is started (# 133). ..

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

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

On the other hand, if the set time elapses (YES in # 142) before the amount of change in the value of the detection signal S4 becomes equal to or less than the predetermined amount, it is determined that an abnormality has occurred (# 145). If the sheet 9 is the second and subsequent sheets in continuous paper 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). Therefore, in the printing job using the plurality of sheets 9, the main control unit 20 can specify the basis weight BW for the second and subsequent sheets 9 that are sequentially carried in from the paper feeding unit 24 to the transport passage 50. If not, the formation of an image on the sheet 9 is controlled according to the basis weight BW specified for the sheet 9 previously carried in.

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

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

In FIG. 19, a paper feed start process for starting paper feed to any of the paper feed passages 51, 52, 55, and 56 is executed according to the designation of the print job (# 201). Then, check whether the next paper feed is required (# 202). If the print job being executed is a job that continuously feeds paper and the next paper feed is required (YES in # 202), the process returns to step # 201 and the paper feed of the next sheet 9 is started. .. If the final paper feed has already been completed and the next paper feed is not required (NO in # 202), the process ends.

It should be noted that the other sheet 9 that is already feeding is not within the range that affects the measurement by the capacitance sensor 40 arranged in the feeding passage for which the feeding start process is to be executed. It may be a condition. That is, for example, as described in the example of FIG. 13, the sheet feeding mechanism 24B waits for the fed sheet 9a to move away from the capacitance sensor 40b at a distance d2 or more, and then executes the paper feeding start process. You may. In that case, after executing step # 201, the process proceeds to step # 202 after waiting for the sheet 9 to pass the 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 paper 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 the open state or pushed in to be in the closed state.

When it is in the open state (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 being fed. It is determined that there is no effect on the determination of the above, and paper feeding is started (# 213).

On the other hand, when it is closed (NO at # 212), a preparatory operation (lift-up) is performed to bring the seat storage cassette closer to the pickup roller 64 (or 61) immediately after being pushed in, which causes paper feeding. This may affect the determination of the sheet 9 on which the sheet 9 is being used. Therefore, wait for the preparatory operation to finish (# 214). When the preparatory operation is completed (YES at # 214), paper feeding is started (# 213).

According to the above embodiment, it is possible to discriminate while transporting the sheets 9, 9a and 9b. Since the basis weight BW can be specified while transporting the sheets 9, 9a, 9b, it is possible to set the operation conditions of image formation according to the basis weight BW without lowering 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 without the sheet and the measured value S4b with the sheet, it is related to the dielectric constant k and the parasitic capacitance Cp. The effects of changes in environmental conditions such as temperature and humidity can be reduced.

According to the embodiment described above, the number of capacitance sensors 40 arranged at one detection position P40 can be one. Compared with the case where the capacitance sensors 40 are arranged on both sides of the sheet 9 in the thickness direction to reduce the influence of the fluctuation of the distance d1 between the capacitance sensor 40 and the sheet 9, 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 from each other in the transport passage 50, the design of the image forming apparatus 2 becomes easy.

In the embodiment described above, the content of the basis weight information D1 is 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 is not the proportional relationship shown in FIG. can.

The difference dS4 between the measured value S4a without the sheet and the measured value S4b with the sheet was calculated, but instead of the difference dS4, the ratio between the measured value S4a and the measured value S4b was calculated, and the ratio and the basis weight BW The basis weight BW may be specified by using the information indicating the relationship with.

As the tension control, the upstream roller 60A is stopped, but the upstream speed V1 may be slower than the downstream speed V2. That is, a speed difference may be provided so that the roller 60B on the downstream side rotates faster than the roller 60A on the upstream side, and the sheet 9 may pass through the detection position P40 in a stretched state.

In addition, the configuration, processing content, order, timing, etc. of the entire or each part of the image forming system 1, the image forming apparatus 2, and the sheet discriminating apparatus 5 can be appropriately changed according to the gist of the present invention.

2 Image forming device 5 Sheet discrimination device 9, 9a, 9b Sheet 20 Main control unit (control unit)
24 Paper feed section (sheet supply section)
24A, 24B Sheet supply mechanism 30B Printer engine 40, 40a, 40b Capacitance sensor 50 Transport passage 51, 52, 55, 56 Paper feed passage 51A Curved transport path 60A Upstream roller (first roller)
60B Downstream roller (second roller)
202 Transport 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 (8)

It is a sheet discriminating device that discriminates the sheet carried into the transport passage for transporting the sheet.
The first roller that conveys the sheet and
A second roller arranged on the downstream side of the first roller and conveying the sheet, and a second roller.
A transport control unit that controls the rotational drive of the first roller and the second roller, and
Capacitance sensors arranged at detection positions between the first roller and the second roller in the transport passage.
It has a discrimination processing unit for discriminating the sheet and
In the transport control unit, when the sheet is in contact with both the first roller and the second roller, the downstream speed, which is the speed of transport by the second roller, is the transport by the first roller. Tension control is performed to control the rotational drive so that the speed is higher than the upstream speed, which is the speed.
The discrimination processing unit discriminates the sheet based on the output of the capacitance sensor during the period during which the tension control is performed.
The portion of the transport passage between the first roller and the second roller is a curved transport passage through which the sheet is curved.
The detection position is a position inside the curve in the curved transport path.
The curved transport path is formed by a curved inner transport guide and an outer transport guide so as to abut the inner transport guide in a stretched state during the period during which the tension control is performed. It has become
The capacitance sensor is arranged so as to detect the sheet in a stretched state in the vicinity of the inner transport guide.
The discrimination processing unit outputs the output of the capacitance sensor after the time required from the start of the tension control to the contact of the sheet with the inner transport guide at the detection position has elapsed. Used for discrimination as the output of the capacitance sensor during the period being performed,
The capacitance sensor has a metal plate as a detection surface, and has a metal plate.
The metal plate is arranged at a portion outside the curved transport path in the inner transport guide.
A sheet discriminating device characterized by this. The discrimination processing unit is the output of 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 the period during which the tension control is performed. The sheet is discriminated based on the output of
The sheet discriminating device according to claim 1. The discrimination processing unit calculates the 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, and calculates the difference. The basis weight of the sheet is specified by using the information indicating the relationship between the basis and the basis weight, and the specified basis weight is output as the discrimination result of the sheet.
The sheet discriminating device according to claim 2. An image forming device that forms an image on a sheet.
A sheet supply unit that can store multiple sheets,
A printer engine that forms an image on the sheet supplied from the sheet supply unit, and
A first roller for transporting the sheet carried into the transport passage from the sheet supply unit to the printer engine, a second roller arranged on the downstream side of the first roller, and a second roller.
Capacitance sensors arranged at detection positions between the first roller and the second roller in the transport passage.
Control unit and
It has a discrimination processing unit for discriminating the sheet and
In the control unit, when the sheet is in contact with both the first roller and the second roller, the downstream speed, which is the speed of transportation by the second roller, is the speed of transportation by the first roller. Tension control is performed to control 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. The basis weight of the sheet is specified based on the output of the sensor, and the image forming apparatus is controlled according to the specified basis weight.
The portion of the transport passage between the first roller and the second roller is a curved transport passage through which the sheet is curved.
The detection position is a position inside the curve in the curved transport path.
The curved transport path is formed by a curved inner transport guide and an outer transport guide so as to abut the inner transport guide in a stretched state during the period during which the tension control is performed. It has become
The capacitance sensor is arranged so as to detect the sheet in a stretched state in the vicinity of the inner transport guide.
The discrimination processing unit outputs the output of the capacitance sensor after the time required from the start of the tension control to the contact of the sheet with the inner transport guide at the detection position has elapsed. Used for discrimination as the output of the capacitance sensor during the period being performed,
The capacitance sensor has a metal plate as a detection surface, and has a metal plate.
The metal plate is arranged at a portion outside the curved transport path in the inner transport guide.
An image forming apparatus characterized in that. In a job using a plurality of the sheets, the control unit cannot specify the basis weight for the second and subsequent sheets of the sequential delivery from the sheet supply unit to the transport aisle. The formation of an image on the sheet is controlled according to the basis weight specified for the sheet brought in in advance.
The image forming apparatus according to claim 4. The sheet supply unit has a plurality of sheet supply mechanisms.
The transport passage is configured such that a plurality of paper feed passages 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 passages, and the capacitance sensor is provided for each of the plurality of paper feed passages.
The control unit uses the capacitance sensor provided in the paper feed passage corresponding to the sheet supply mechanism for carrying the sheet into the transport passage among the plurality of sheet supply mechanisms, and the basis weight of the sheet. To identify,
The image forming apparatus according to claim 4 or 5. In the job of carrying in the sheet in order from one of the plurality of sheet supply mechanisms and the other one, the control unit detects the preceding sheet and the succeeding sheet by the respective capacitance sensors. The basis weight of each sheet is specified based on the output of the capacitance sensor when they are separated from each other by a distance that does not affect them.
The image forming apparatus according to claim 6. The sheet supply unit has a plurality of sheet supply mechanisms.
The transport passage is configured such that a plurality of paper feed passages 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 the position where the plurality of paper feed passages merge into one.
The image forming apparatus according to claim 4 or 5.

Images