JP2007169000A - Double feeding detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double feeding detecting device capable of preventing erroneous detection of double feeding caused by vibration transmitted via paper and deflection of the paper, when the tip collides with a curved part and a butting member of a paper carrying passage, regardless of a kind of paper carried in the paper carrying passage. <P>SOLUTION: This double feeding detecting device is composed of a thickness information output means outputting thickness information on the paper carried in the paper carrying passage as a sensor output value, a sensor output value extracting means extracting a predetermined sensor output value of the thickness information output means, a storage means storing a preset value of the sensor output value, and a comparing means detecting that the paper is doubly fed when the sensor output value is a predetermined value or more, by comparing the extracted sensor output value with the preset value of the sensor output value stored in the storage means. The sensor output value extracting means 2 extracts the sensor output value up to detecting an impact acting time sensor output value indicating that impact acts on the tip of the paper after the tip of the paper passes through the thickness information output means 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a double feed detection device for detecting double feed of paper conveyed on a paper conveyance path used in an image forming apparatus such as a printer or a copying machine.

JP-A-6-32497

  Conventionally, in an image forming apparatus such as a printer or a copying machine, in response to a request from an external terminal or a user, a sheet stored in a sheet tray is conveyed one by one to a sheet conveyance path, and is applied to one or both sides of the sheet. An image is formed. At this time, when the force to convey the paper is strongly applied to the paper conveyed from the paper tray, there is a state where two or more papers are conveyed at a time (hereinafter simply referred to as “multiple feeding”). May occur.

  When such double feeding occurs, the sheet may not be normally conveyed along the sheet conveyance path, and the sheet may be jammed on the sheet conveyance path. Further, when a state occurs in which the leading end side of the conveyed sheet has a thickness of one sheet and the trailing end side has a thickness of two or more sheets (hereinafter, simply referred to as “multiple feeding”), one sheet of sheet is generated. Thus, a plurality of images that are supposed to be formed are formed, and paper is wasted. Therefore, in order to prevent such a problem due to double feeding, the image forming apparatus is generally provided with a double feeding detection device.

  As this type of multi-feed detection device, for example, after detecting the leading edge and the trailing edge of the paper being transported on the transport path, the center of the paper excluding these parts is optically or mechanically The thickness of the paper is detected by a typical measuring means, and the detected thickness is compared with a predetermined thickness. As a result, when the thickness exceeds the predetermined thickness, a double feed is detected, and the leading edge and the trailing edge of the paper are detected. There has been proposed a double feed detection device that prevents the occurrence of curling and other variations or erroneous detection of double feed due to posture (Patent Document 1). According to this multi-feed detection device, when only the thickness of the central part of the paper is detected, it is possible to judge multi-feed without misdetection if the leading edge and the rear edge of the paper are curled. Is possible.

  However, when the thickness of the central portion of the paper is detected by the measuring means, the leading edge of the paper enters the curved portion provided in the paper conveyance path or enters the paper conveyance path to correct the paper skew. When it hits against the abutting member provided, the paper vibrates or bends due to the impact applied to the leading edge of the paper, and the vibration or deflection of the paper is erroneously detected as the thickness of the paper. In some cases, erroneous detection of double feeding may occur even when the paper is not double fed. In particular, image formation corresponding to image formation on a plurality of types of special paper (hereinafter referred to as “special paper”) such as thick paper in addition to regular size normal paper (hereinafter referred to as “plain paper”). In the apparatus, for example, if the special paper is thick paper, the leading end of the paper enters the curved portion of the paper conveyance path, and when the paper strikes the abutting member, the paper is subjected to a relatively large vibration due to the strength of the stiffness. If the special paper is softer than plain paper, the leading edge of the paper enters the curved part of the paper transport path, and when the paper strikes the abutting member, the paper is weak. In any case, the thickness of the sheet is detected in an unstable state, and there is a problem that erroneous detection is likely to occur.

  The present invention has been made in view of such problems, and the object of the present invention is to make the leading end of the paper conveyance path bend or abut regardless of the type of paper conveyed on the paper conveyance path. It is an object of the present invention to provide a double feed detection device capable of preventing erroneous detection of double feed caused by vibration transmitted through a sheet or bending of the sheet when it collides with a member.

  In order to achieve the above object, a double feed detection device according to the present invention includes a thickness information output unit that outputs, as a sensor output value, thickness information of a sheet conveyed on a sheet conveyance path, and the thickness information output unit. Sensor output value extracting means for extracting a predetermined sensor output value from the output sensor output value, storage means for storing a preset value of the sensor output value, and sensor output extracted by the sensor output value extracting means A comparison unit configured to compare the value with a set value of the sensor output value stored in the storage unit, and to detect that the paper is being double fed when the sensor output value is equal to or greater than a predetermined value. In the feed detection device, the sensor output value extracting means is configured to detect a sensor output value at the time of an impact action indicating that an impact has been applied to the leading edge of the paper after the leading edge of the paper has passed through the thickness information output means. Between, It is characterized in that to extract the sensor output values for determining the thickness of the paper.

  In such a double feed detection device of the present invention, the thickness information output means is set at a set position associated with the passage of the paper of the detection section of the thickness information output means that is always in contact with the inner wall of the paper transport path. Any device that outputs displacement as a sensor output value may be used. Further, the displacement of the set position of the detection unit due to vibration or impact acting when the leading edge of the sheet collides with the curved part of the sheet conveyance path, the abutting member, or the nip part of the roll can be output as a sensor output value. Anything is acceptable.

  Next, the sensor output value extraction means is a period from when the leading edge of the paper passes through the thickness information output means until a sensor output value at the time of impact action indicating that an impact has acted on the leading edge of the paper is detected. The sensor output values may be extracted at least once or at a predetermined interval. In the latter case, it is preferable that the sensor output value extracting means is provided with a calculating means for calculating an average value of a plurality of sensor output values, and the number of times the sensor output value is measured is required by the double feed detecting device. It can be set as appropriate according to the accuracy of the image. The sensor output value serving as a reference for completing the extraction by the sensor output value extracting means is a curved portion in which the leading end of the paper is disposed on the downstream side of the thickness information output means in the paper conveyance path, or the paper It is good to set in advance the sensor output value when colliding with the abutting member for correcting the skew of the roll or the nip part of the roll, and the sensor output value is fixed in advance as a ROM (Read Only Memory) etc. Should be stored. In addition, as a method for the sensor output value extraction unit to finish extracting the sensor output value, the leading end of the sheet conveyed through the sheet conveyance path passes through the thickness information output unit, and then the bending portion, the abutting member, Alternatively, since the time until it collides with the nip portion of the roll can be estimated in advance, the number of times the sensor output value is extracted within that time is set in advance, and the extraction is performed after extracting the sensor output value a predetermined number of times. It is also possible to apply a method of terminating. As a result, after the leading edge of the paper passes through the thickness information output means, the sensor output value in a stable state until the sensor output value at the time of impact action indicating that the impact has acted on the leading edge of the paper is detected. Can be extracted.

Subsequently, the storage means stores in advance the average value of the sensor output values of the paper transported immediately before or the sensor output value of a size corresponding to the thickness of each paper type as the paper thickness information. The average value of the sensor output values may be rewritten every time the sheet is conveyed. Here, “paper transported immediately before” is
(1) In the case where a plurality of sheets are continuously conveyed, the sheet conveyed before the sheet passing through the thickness information output means
(2) Both sheets of the same size conveyed during the previous image forming operation in a state where the paper tray is not inserted or removed are applicable. As the storage means, for example, a RAM (Random Access Memory) capable of temporarily storing an average value of sensor output values can be applied.

  According to the double feed detection device of the present invention configured as described above, when the leading end collides with a curved portion or abutting member of the paper transport path regardless of the type of paper transported on the paper transport path In addition, it is possible to prevent erroneous detection of double feed caused by vibration transmitted through the paper and bending of the paper.

  The multifeed detection device of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing the configuration of the double feed detection device of the present invention. The double feed detection device according to the present invention includes a thickness information output unit 1 that outputs thickness information of a sheet conveyed through a sheet conveyance path as a sensor output value, and a sensor output value output from the thickness information output unit 1. Sensor output value extracting means 2 for extracting a predetermined sensor output value, storage means 3 for storing a preset value of the sensor output value, sensor output value extracted by the sensor output value extracting means 2 and storage means 3 Comparing means 4 for comparing with the set value of the sensor output value stored in. The sensor output value extraction unit 2 includes a calculation unit 2a that calculates an average value from the plurality of sensor output values when the plurality of sensor output values output by the thickness information output unit 1 are extracted. Yes.

  In this configuration, the sensor output value extracting means 2 starts extracting the sensor output value after the leading edge of the paper transported through the paper transport path passes through the thickness information output means 1, and an impact acts on the leading edge of the paper. When a sensor output value at the time of an impact action indicating that the detection has been performed is detected, a sensor output value serving as a reference for ending extraction is set in advance. As a sensor output value serving as a reference for ending this extraction, for example, a curved portion in which the leading end of the sheet is disposed on the downstream side of the thickness information output unit 1 in the sheet conveyance path or a skew of the sheet is corrected. For example, it is possible to set a sensor output value that is detected when it collides with the abutting member or the nip portion of the roll. The storage unit 3 stores in advance an average value of sensor output values of the paper transported immediately before the paper transport path or a sensor output value having a size corresponding to the thickness of each paper type. Here, a RAM (random access memory) that temporarily stores data for the average value of the sensor output values of the paper transported immediately before the paper transport path is rewritten every time the paper is transported. Then, ROM (read only memory) stored as fixed data can be applied to sensor output values having a size corresponding to the thickness of each type of paper. The comparison unit 4 compares the sensor output value of the conveyed paper with the set value of the sensor output value stored in advance in the storage unit 3, and is predetermined when the sensor output value is greater than or equal to a predetermined value. It is possible to apply a comparator that outputs the above signal.

  Next, an example of thickness information output means applicable to the present invention will be described with reference to FIG.

  The thickness information output means 1 in FIG. 2 rotates on the inner wall of the paper transport path C when the paper P does not pass through the paper transport path C, and rotates while the paper P passes. A rotating portion 10 that contacts the paper P; a rotating portion 10 that is rotatably supported at one end thereof; and a link portion 11 that has a D-shaped insertion hole (not shown) at the other end; The shaft 12 has a D-shaped cross section that is inserted into the insertion hole of the link portion 11, and the sensor portion 13 that outputs the rotational displacement θ of the shaft 12 as a sensor output value. The link part 11 is urged clockwise around the shaft 12 by a spring 14 whose one end is hooked on the hook part 15 and whose other end is hooked on the link part 11. It has become. Further, the shaft 12 inserted into the link portion 11 has a D-shaped cross section, and the link portion 11 and the shaft 12 are fixed to each other. The displacement of the set position of the moving part 10 becomes the rotational displacement θ of the shaft 12 via the link part 11, and a sensor output value corresponding to this rotational displacement θ is output from the sensor part 13.

In this arrangement, the sheet P is conveyed to the sheet conveying path C in the arrow P _D direction, rotating portion 10 when passing through the pivot portion 10 by the biasing force acting on the link portion 11, the surface of the paper P It abuts so as to follow (arrow M in the figure). Then, as the rotating unit 10 follows the surface of the paper P, the rotational displacement θ of the shaft 12 that rotates by the thickness of the paper P via the link unit 11 is output from the sensor unit 13 as a sensor output value. Therefore, the sensor output value can be processed as the thickness information of the paper P. In addition, when the leading edge of the paper P collides with a curved portion disposed on the downstream side of the rotating portion 10 in the paper conveyance path C, or an abutting member for correcting paper skew or a nip portion of the roll. Since the vibration and impact acting on the paper P are output from the sensor unit 13 as sensor output values at the time of impact action, these sensor output values are used as criteria for ending the sensor output value extraction means by the sensor output value extraction means. Can also be processed. The urging force for urging the link portion 11 by the spring 14 is preferably set as appropriate so as not to interfere with the conveyance of the paper P.

  Subsequently, in the paper transport path in which the abutting member is disposed on the downstream side of the thickness information output means, the leading edge of the paper enters the thickness information output means and the trailing edge passes through the thickness information output means. The movement of the paper in the paper conveyance path up to this point will be described with reference to FIGS.

  3 to 7 are a pair of pre-registration rolls 5 and 5 for transporting the paper P along the paper transport path, and a trigger for timing for starting the double feed detection of the paper P. Pre-registration sensor 6 used for (trigger), thickness information output means 1 that outputs the displacement of the set position as the sensor output value as the paper P passes, and transport of the paper P transported through the paper transport path The skew is corrected by changing the direction and further abutting the leading end of the sheet P against the nip portion where the loop is formed, and the sheet P is further moved downstream along the sheet conveyance path. A pair of abutting (registration) rolls 9 and 9 to be conveyed and conveyance of the paper P by the abutting rolls 9 and 9 are started, and when the rear end of the paper P passes, the switch is turned off (“OFF Has shall consist to) measurement (registration) sensor 8.

Here, the sheet P is a pre-registration rolls 5,5 is conveyed in the direction of arrow P _D, when entered the thickness information output means 1, the thickness information output unit 1 of the paper P in the direction of arrow M thickness The set position is displaced by the amount (FIG. 3). At this time, when the leading edge of the paper P reaches the pre-registration sensor 6, the switch is turned on ("ON"). The pre-registration sheet P by configuration rolls 5,5 is conveyed in the direction of arrow P _D to the downstream side of the sheet conveying path, the sheet to the curved portion 7 disposed on the downstream side of the thickness information output means 1 P When the leading edge of the sheet collides, an impact acting on the leading edge of the sheet P is transmitted to the thickness information output unit 1 through the sheet P, and the set position of the thickness information output unit 1 is displaced in the direction of the arrow M (FIG. 4). Furthermore, the paper P by the pre-registration rolls 5,5 is transported in the direction of arrow P _D to the downstream side of the sheet conveying path and impinges on the abutment roll 9, 9 disposed on the downstream side of the bending portion 7 The impact acting on the leading edge of the paper P is transmitted to the thickness information output means 1 through the paper P, and the set position of the thickness information output means 1 is displaced in the direction of the arrow M (FIG. 5). Then, when the paper P in a state of abutting against the nip of the rolls 9,9 abutting the leading end of the sheet P is conveyed by pre-registration rolls 5,5 in the direction of the arrow P _D, the sheet P is curved section 7 A loop is formed, and vibrations acting on the paper P at that time are transmitted to the thickness information output means 1 through the paper P, and the thickness information output means 1 is continuously displaced in the direction of the arrow M (see FIG. 6). Thereafter, the conveyance pre registration rolls 5,5 to form a loop of the sheet P is completed in the bending portion 7 is once stopped, the sheet P by the roll 9, 9 abut after a predetermined time has elapsed in the direction of arrow P _D When the trailing edge of the paper P exits the thickness information output means 1, the setting position of the thickness information output means 1 is displaced in the direction of the arrow M and returns to the state before the leading edge of the paper P enters ( Fig. 7). At this time, when the trailing edge of the paper P passes the pre-registration sensor 6, the switch is turned off ("OFF").

  As described above, when the paper P passes through the paper conveyance path having the configuration shown in FIGS. 3 to 7, not only the thickness of the paper P but also the impact and vibration acting on the paper P are thick. The displacement of the set position in the information output means 1 is output as a sensor output value. Then, by processing this sensor output value by a predetermined method, double feeding of the paper P is detected. In addition, for the double feed, the time from the start of conveyance of the paper P by the abutting rolls 9 and 9 until the trailing edge of the paper P passes the length measuring sensor 8 and the length measuring sensor 8 is switched off. Is measured (not shown), the length of the paper P is calculated from this time and the conveyance speed, and the designated paper length is compared with the calculated paper length. This is detected because the designated paper size does not match the conveyed paper size. When a plurality of sheets P are continuously conveyed along the sheet conveyance path, the movements of FIGS. 3 to 7 are repeated in order for each sheet.

  Next, FIG. 8 shows the fluctuation of the sensor output value output from the thickness information output means 1 when the paper P passes through the paper transport path having the configuration shown in FIGS. The flow of processing of the sensor output value output from the thickness information output means 1 will be described using the flowcharts shown in FIGS. In FIG. 8, time (ms: milliseconds) is taken on the horizontal axis, and the fluctuation of the sensor output value and the pre-registration sensor 6 shown in FIGS. 3 to 7 are switched on. The timing and timing to be cut off are shown as time passes. In addition, sensor output values in the respective states of FIGS. 3 to 7 are indicated by arrows together with the figure numbers.

  First, conveyance of the paper P is started (FIG. 9, step S1), and when the leading edge of the paper P conveyed by the pre-registration rolls 5 and 5 reaches the pre-registration sensor 6, the switch is turned on (same step). S2). Thereafter, when the leading edge of the paper P enters the thickness information output means 1 ("FIG. 3" in FIG. 8), the impact that acts on the paper P when it enters is output from the thickness information output means 1 as a sensor output value. The Then, after T milliseconds have elapsed since the pre-registration sensor 6 was turned on (step S3), the sensor output value extraction means 2 determines the sensor output value while the paper P is passing the thickness information output means 1. A plurality (N times) are extracted at predetermined intervals (step S4).

  Here, the elapsed time (T milliseconds) from when the pre-registration sensor 6 that starts extraction of the sensor output value by the sensor output value extracting means 2 is switched on is after the pre-registration sensor 6 is switched on. When the leading edge of the paper P enters the thickness information output means 1, the time until the impact acting on the paper P is settled and the sensor output value output from the thickness information output means 1 is stabilized is set. Good. As a result, it is possible to extract a stable sensor output value (region “(1)” in FIG. 8) while the paper P passes through the thickness information output unit 1.

Then, after starting to extract the sensor output value output from the thickness information output means 1, when the leading edge of the paper P collides with the curved portion 7 disposed on the downstream side of the thickness information output means 1, When an impact acting on the paper P is detected as a sensor output value through the paper P (“FIG. 4” in FIG. 8; FIG. 9, step S5), the extraction of the sensor output value by the sensor output value extracting means 2 is terminated. (Step S6). Further, among the sensor output values extracted a plurality (N times) by the calculation means 2a provided in the sensor output value extraction means 2, the maximum value and the minimum value are deleted because they may contain noise. , The average value A _{1 of} the (N−2) sensor output values is calculated (step S7). Thereafter, the average value A ₁ of the sensor output values while the paper P is passing through the thickness information output means ₁ is stored in the storage means 3 (step S8). In FIG. 9, “X” following step S <b> 8 indicates that the flowchart of FIG. 9 continues to “X” of FIG. 10.

The average value A ₁ of the sensor output values is calculated by the calculating means 2a (FIG. 9, step S7), and the leading end of the paper P is stored while the average value A ₁ is stored in the storage means 3 (step S8). When it collides with the abutting rolls 9, 9, the impact applied to the paper P is detected as a sensor output value through the paper P (“FIG. 5” in FIG. 8), and a loop is formed in the bending portion 7. The vibration is detected as a sensor output value through the paper P (region of FIG. 6 in FIG. 8).

  When the rear end of the paper P passes through the pre-registration sensor 6 while the loop is formed in the curved portion 7 (region of FIG. 6 in FIG. 8), the pre-registration sensor 6 is switched off ( Further, the rear end of the paper P passes through the thickness information output means 1 ("FIG. 7" in FIG. 8). After T milliseconds have elapsed since the pre-registration sensor 6 was switched off (step S12), the sensor output value after the paper P has passed through the thickness information output means 1 is obtained by the sensor output value extraction means 2. A plurality (n times) are extracted at predetermined intervals (step S13).

  Here, the elapsed time (T milliseconds) from when the pre-registration sensor 6 for starting the extraction of the sensor output value after the paper P passes the thickness information output means 1 by the sensor output value extraction means 2 is switched off. ), When the pre-registration sensor 6 is switched off, the impact when the trailing edge of the paper P passes through the thickness information output means 1 and the link portion of the thickness information output means 1 are initially caused by the biasing force of the spring. It is preferable to set the time until the sensor output value output from the thickness information output means 1 is stabilized after the banding when returning to the state is settled. As a result, it is possible to extract a stable sensor output value (region “(2)” in FIG. 8) after the paper P passes through the thickness information output means 1.

In the case of forming an image on a plurality of sheets of paper P, if the impact when the leading edge of the second sheet of paper P enters the thickness information output means 1 is output as a sensor output value, or 1 In the case of forming an image on a sheet of paper P, the extraction of the sensor output value after the paper P has passed through the thickness information output means 1 ends when the extraction of the preset sensor output value is completed. (FIG. 10, step S14). Further, among the sensor output values extracted by the computing means 2a (n times), the maximum value and the minimum value are deleted because there is a possibility that noise or the like is included, and (n−2) An average value A ₂ of the sensor output values is calculated (step S15). Thereafter, the average value A ₂ of the sensor output values after the sheet P passes through the thickness information output means 1 is stored in the storage means 3 (step S16). Then, the calculation unit 2a, the sensor output value A ₁ in passing through the paper sheet P thickness information output means 1 stored in the storage unit 3, the difference between the sensor output value A ₂ after passing through (the sheet P ΔA (corresponding to the thickness) is calculated (step S17), and ΔA of the conveyed paper P and ΔA of the paper P conveyed immediately before are compared by the comparison means 4, and the difference is a predetermined value. It is determined whether it is within (step S18).

Here, the “paper transported immediately before” is
(1) When a plurality of sheets are continuously conveyed, the sheet conveyed before the sheet passing through the thickness information output means 1
(2) Both sheets of the same size conveyed during the previous image forming operation in a state where the paper tray is not inserted or removed are applicable. Note that (2) also applies to those that straddle the image forming operation, but the “state where the paper tray is not inserted / removed” is a problem. When the paper tray is inserted / removed, other thickness paper is used. This is because there is a possibility of being set on the tray.

  When it is determined in step S18 in FIG. 10 that the difference between ΔA of the paper P conveyed by the comparison unit 4 and ΔA of the paper P conveyed immediately before is within a predetermined value, It is determined whether or not the time from when the butting rolls 9 and 9 start transporting the paper P to when the trailing edge of the paper P passes the length measuring sensor 8 is within a predetermined time (FIG. 10, step S19). If this time is within a predetermined time, it is confirmed whether the image forming operation is completed (step S20). At this time, when the image forming operation is completed, ΔA of the last sheet P in the image forming operation is stored in the storage unit 3, and a series of processing of the sensor output value output from the thickness information output unit 1 is performed. finish. On the other hand, if the image forming operation is not completed in step S20, the process proceeds from “Y” in FIG. 10 to “Y” in FIG. 9 to process the sensor output value of the next paper P. enter. Note that the predetermined value of the difference between ΔA of the conveyed paper P and ΔA of the paper P conveyed immediately before is set by, for example, setting the former to a value that is 1.5 times or more of the latter. Double feed can be detected reliably.

  On the other hand, when the comparison unit 4 determines that the difference between ΔA of the conveyed paper P and ΔA of the paper P conveyed immediately before is not within a predetermined value, the conveyed paper P Is detected as being double fed (FIG. 10, step S31). Further, the time from when the butting rolls 9 and 9 start transporting the paper P until the trailing edge of the paper P passes the length measuring sensor 8 is not within a predetermined time, that is, calculated from this time and the transport speed. If the length of the printed paper P differs from the designated paper length by ± 10 mm or more, the transported paper P is detected as being double fed because it does not match the designated paper size (same as above). Step S32). Regardless of whether the double feed (step S31) or the double feed (step S32) is detected, the conveyance of the paper P is stopped (step S33), and the user interface of the image forming apparatus or the personal computer is used. “Double feed occurrence” is displayed on the screen or the like, and the user is informed that a double feed has occurred (step S34).

  It should be noted that the control of the length measuring sensor 8 used when detecting the double feed and the abutting rolls 9 and 9 start conveying the paper P until the trailing edge of the paper P passes the length measuring sensor 8. The calculation of the length of the paper P by this time is preferably performed by providing a control unit or the like in the image forming apparatus.

  As described above, according to the double feed detection device of the present invention, after the leading edge of the paper P passes through the thickness information output means 1, the leading edge of the paper P is higher than the thickness information output means 1 in the paper conveyance path. In order to extract the sensor output value by the sensor output value extracting means 2 until it collides with the curved portion 7 or the abutting rolls 9, 9 arranged on the downstream side, a stable sensor output value is extracted, The double feed of the paper P can be detected. In addition, since the extraction of the sensor output value is completed before the leading edge of the paper P collides with the curved portion or the abutting member, the paper is not affected by the vibration or the bending of the paper P regardless of the type of the paper. It is possible to prevent erroneous detection in which P is lifted, and this is particularly effective for paper that is stiff, such as thick paper, because such lifting frequently occurs. Furthermore, since the paper conveyance is stopped after detecting the double feed, it is possible to prevent the paper being fed double from the image forming apparatus from being discharged.

It is a block diagram which shows the structure of the double feed detection apparatus of this invention. It is a perspective view of an example of the thickness information output means applicable to this invention. FIG. 6 is a diagram illustrating a state in which a leading edge of a sheet conveyed through a sheet conveyance path has entered a thickness information output unit. FIG. 6 is a diagram illustrating a state in which a leading edge of a sheet conveyed through a sheet conveyance path collides with a curved portion. FIG. 6 is a diagram illustrating a state in which a leading edge of a sheet conveyed through a sheet conveyance path collides with an abutting roll. FIG. 6 is a diagram illustrating a state where a loop is formed in a curved portion of a paper transport path. FIG. 6 is a diagram illustrating a state in which a rear end of a sheet conveyed through a sheet conveyance path has passed through a thickness information output unit. It is a figure which shows the fluctuation | variation of the sensor output value output from a thickness information output means. It is a flowchart which shows the flow of a process of the sensor output value output from the thickness information output means. It is a flowchart which shows the flow of a process of the sensor output value output from the thickness information output means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thickness information output means, 2 ... Sensor output value extraction means, 2a ... Calculation means, 3 ... Memory | storage means, 4 ... Comparison means

Claims (5)

Thickness information output means for outputting the thickness information of the paper transported on the paper transport path as a sensor output value, and a sensor output for extracting a predetermined sensor output value from the sensor output value output from the thickness information output means A value extraction unit, a storage unit in which a set value of the sensor output value is stored in advance, a sensor output value extracted by the sensor output value extraction unit, and a set value of the sensor output value stored in the storage unit In the double feed detection device constituted by comparison means for detecting that the paper is being double fed when the sensor output value is equal to or greater than a predetermined value,
The sensor output value extracting means is configured to detect the sensor output value at the time of impact action indicating that an impact has been applied to the leading edge of the paper after the leading edge of the paper has passed through the thickness information output means. A double feed detection device that extracts a sensor output value for determining a thickness of a sheet. The sensor output value at the time of impact action is a sensor output value detected when the leading edge of the paper collides with a curved portion disposed on the downstream side of the thickness information output means in the paper conveyance path. The multifeed detection device according to claim 1. The sensor output value at the time of impact action is detected when the leading edge of the sheet collides with an abutting member disposed on the downstream side of the thickness information output means or the nip portion of the roll in the sheet conveyance path. The multifeed detection device according to claim 1, wherein the multifeed detection device is a sensor output value. The sensor output value extraction unit extracts a plurality of sensor output values at predetermined intervals after the leading edge of the paper passes through the thickness information output unit and before the sensor output value at the time of impact is detected. The multifeed detection device according to claim 1, further comprising a calculation unit that calculates an average value of the plurality of sensor output values. The set value of the sensor output value stored in advance in the storage means is the average value of the sensor output value in the sheet conveyed immediately before being rewritten every time the sheet is conveyed, or the thickness for each type of sheet. The multifeed detection device according to claim 4, wherein the sensor output value has a corresponding magnitude.

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