JP7419063B2 - Sheet conveyance device, image forming device - Google Patents

Description

The present invention relates to a sheet conveyance device having a function of detecting a state in which two or more sheets are conveyed in an overlapping manner, and an image forming apparatus equipped with this sheet conveyance device.

The image forming apparatus performs image formation while conveying sheets one by one using a sheet conveying device. If a situation occurs in which two or more sheets are conveyed in an overlapping manner, a blank product may be discharged or a sheet jam may occur. A state in which two or more sheets are conveyed in an overlapping manner is called "multiple feeding." Double feeding is detected, for example, by the technique disclosed in Patent Document 1. The image forming apparatus of Patent Document 1 compares the length of the sheet in the conveyance direction measured during conveyance (sheet measurement length) with the length of the sheet in the conveyance direction set by the user (sheet setting length), Double feeding is detected when the measured sheet length is longer than the set sheet length by a reference value or more. When this image forming apparatus detects double feeding, it notifies the user that double feeding has occurred. Double feeding can also be detected by a double feeding detection sensor using ultrasonic waves. The double feed detection sensor emits ultrasonic waves toward the sheet and receives the ultrasonic waves that have passed through the sheet. Double feeding is detected based on the intensity of the received ultrasonic waves. Even when double feeding is detected using the double feeding detection sensor, the user is notified that double feeding has occurred.

The sheets that are determined to be double-fed are ejected, for example, through a different conveyance path than the conveyance path used during normal printing processing. By automatically ejecting a sheet and printing on another sheet when double feeding is detected, printing processing can be continued without bothering the user.

Double feeding may be detected by combining the detection results based on the sheet measurement length and the set sheet length, and the detection results from the double feed detection sensor. In this case, for example, the difference between the measured sheet length and the set sheet length may be greater than a reference value, and the double feed detection sensor may not detect double feed. This occurs, for example, because the sheet length set by the user is different from the length of the sheet actually conveyed in the conveying direction (sheet length), that is, because the user makes a mistake in setting the sheet length. In such a case, the image forming apparatus needs to prompt the user to change the set sheet length without printing on another sheet. Thereby, unnecessary printing processing can be prevented.

Japanese Patent Application Publication No. 2005-162423

After the double feed detection process using the sheet measurement length and the set sheet length, the double feed detection process using the double feed detection sensor is performed. This is to correctly distinguish between the double feed detection result based on the sheet measurement length and the set sheet length, and the double feed detection result based on the double feed detection sensor. Double feed detection processing by the double feed detection sensor is performed with the leading end of the sheet being conveyed in the conveyance direction as a reference. Therefore, if double feeding occurs at the trailing edge of the sheet, there is a possibility that double feeding will be detected ahead of the section where the double feeding occurs. In this case, the occurrence of double feeding should normally be notified, but the user will be notified of an error in setting the size (sheet setting length). As a result, although there is no need for the user to reset the sheet length, the sheet length is reset, resulting in unnecessary downtime.

The present invention has been made in view of the above-mentioned problems, and a main object of the present invention is to provide a sheet conveyance device that can suppress errors in detecting double feeding of sheets during conveyance.

The image forming apparatus of the present invention includes a sheet storage means for storing sheets, a transport means for transporting the sheets stored in the sheet storage means, and a length of the sheet stored in the sheet storage means in the transport direction. sheet setting means for setting a certain first length; double feeding detection means for detecting whether two or more sheets are being conveyed in an overlapping manner by the conveying means; and double feeding in the conveying direction. a sheet detecting means disposed upstream of the detecting means to detect the sheet being conveyed by the conveying means; and a sheet detecting means for detecting the sheet being conveyed by the conveying means based on the detection result by the sheet detecting means; sheet measuring means for detecting a second length, and when the second length is longer than the first length, the double feeding detecting means detects overlapping of the sheets based on the difference; The present invention is characterized by comprising: a control means for determining a starting position and causing the double feeding detection means to detect overlapping sheets from the determined position.

According to the present invention, it is possible to reliably detect double feeding of sheets during conveyance.

FIG. 1 is a configuration diagram of an image forming apparatus. A configuration diagram of a control system. An explanatory diagram of a double feed detection sensor. (a) and (b) are explanatory diagrams of reception levels. (a) to (c) are exemplary diagrams of size setting screens. Flowchart showing preprocessing for double feed detection. (a) to (c) are explanatory diagrams of the double feed detection start position. Flowchart showing double feed detection processing. A flowchart showing escape processing. 5 is a flowchart showing operation control processing for detecting double feeding.

Embodiments of the present invention will be described below with reference to the drawings. Note that the technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments.

(Configuration of image forming apparatus)
FIG. 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 101 includes a sheet feeding mechanism that feeds sheets, an image forming section 20 that forms images, a fixing device 12, and an operation section 306. The image forming apparatus 101 prints an image on a sheet by transferring an image generated by the image forming unit 20 to the sheet fed by a sheet feeding mechanism.

The sheet feeding mechanism includes a plurality of sheet storage sections (paper feeding cassettes 50, 55) each capable of storing a plurality of sheets, a conveying path, a vertical sheet feeding path, a horizontal path 30, and is provided in each path. The apparatus includes a roller for conveying a sheet and a sensor. In this embodiment, a configuration in which a plurality of two paper feed cassettes 50 and 55 are provided will be described, but the number of paper feed cassettes may be any number as long as it is one or more.

The sheets stored in the paper feed cassette 50 are fed one by one from the paper feed cassette 50 to the conveyance path by separation paper feed sections 51 and 52 such as pickup rollers. A conveyance sensor 61 is provided on the conveyance path. The conveyance sensor 61 is used to detect a sheet measurement length (second length) that is the length of the sheet being conveyed in the conveyance direction. The sheet conveyed from the paper feed cassette 50 to the conveyance path is conveyed to the paper feed vertical path. A vertical path roller 53 is provided in the paper feeding vertical path. The vertical path roller 53 conveys the sheet to the horizontal path 30.

The sheets stored in the paper feed cassette 55 are fed one by one from the paper feed cassette 55 to the conveyance path by separation paper feed sections 56 and 57 such as pickup rollers. A conveyance sensor 62 is provided on the conveyance path. The conveyance sensor 62 is used to detect a sheet measurement length (second length ) that is the length of the sheet being conveyed in the conveyance direction. The sheet conveyed from the paper feed cassette 55 to the conveyance path is conveyed to the paper feed vertical path. A vertical path roller 58 is provided in the paper feeding vertical path. Vertical path rollers 58 transport the sheet to horizontal path 30 .

The horizontal path 30 includes a conveyance roller 40 , a conveyance roller 41 , a conveyance roller 42 , a registration roller 11 , and a paper discharge roller 13 . The sheet guided from the paper feed cassette 50 or the paper feed cassette 55 to the horizontal path 30 is transported to the registration roller 11 by transport rollers 40 , 41 , and 42 . The registration rollers 11 correct the skew of the sheet conveyed along the horizontal path 30. Note that the fixing device 12 is provided on the horizontal path 30.

A reference sensor 64 is provided upstream of the conveyance roller 40 in the sheet conveyance direction. A double feed detection sensor 60 is provided between the conveyance roller 40 and the conveyance roller 41 to detect double conveyance in which two or more sheets are conveyed in an overlapping manner. The double feed detection sensor 60 is composed of an ultrasonic sensor. The double feed detection sensor 60 transmits an ultrasonic wave toward the sheet when the sheet passes the double feed detection position in response to the detection of the sheet passing by the reference sensor 64, and receives the ultrasonic wave transmitted through the sheet. do. Based on the intensity of the received ultrasonic waves, it is determined whether two or more sheets are being conveyed in an overlapping manner.

The image forming section 20 includes photoreceptors 22 to 25, an intermediate transfer body 26, and a secondary transfer section 21. Toner images of different colors are formed on the photoreceptors 22 to 25, respectively. For example, the surfaces of the photoreceptors 22 to 25 are uniformly charged and then exposed to laser light to form electrostatic latent images. On the photoreceptors 22 to 25, toner images of corresponding colors are formed by developing the electrostatic latent images with toner of corresponding colors. The toner images formed on each of the photoreceptors 22 to 25 are sequentially transferred onto the intermediate transfer member 26 in a superimposed manner. As a result, a full-color toner image is formed on the intermediate transfer member 26. Intermediate transfer body 26 conveys the toner image to secondary transfer section 21 . The secondary transfer section 21 is provided on the horizontal path 30.

The sheet feeding mechanism transports the sheet to the secondary transfer section 21 using the registration rollers 11 in accordance with the timing at which the toner image on the intermediate transfer body 26 is transported to the secondary transfer section 21 . The secondary transfer section 21 transfers the toner image on the intermediate transfer body 26 to a sheet. The secondary transfer unit 21 transports the sheet onto which the toner image has been transferred to the fixing device 12 . The fixing device 12 fixes the toner image on the sheet by heating and melting the toner and pressurizing the toner and the sheet. The sheet with the toner image fixed thereon is discharged from the fixing device 12 to the outside of the image forming apparatus 101 via a paper discharge roller 13 .

The image forming apparatus 101 includes an escape path 31 branching from the horizontal path 30 and a flapper 43 for switching the sheet conveyance direction from the horizontal path 30 to the escape path 31 between the conveyance rollers 41 and 42. Be prepared. The escape path 31 is provided with a conveyance roller 70, a conveyance roller 71, and a conveyance sensor 63. When the sheet measurement length detected by the conveyance sensor 61 or the conveyance sensor 62 is longer than a preset sheet size (the length in the sheet conveyance direction) by a predetermined threshold or more, the image forming apparatus 101 transfers the sheet to a flapper. 43 and conveys it to the escape path 31. Further, the image forming apparatus 101 also transports sheets determined to be double fed to the escape path 31. The sheet conveyed to the escape path 31 is discharged to the escape tray 32 by conveyance rollers 70 and 71. The conveyance sensor 63 detects the discharge of the sheet from the escape path 31 to the escape tray 32 . Since the escape path 31 does not pass through the secondary transfer section 21, no image is formed on the sheet discharged via the escape path 31.

The operation unit 306 is a user interface including an input interface and an output interface. The input interface is various key buttons or a touch panel. The output interface is a display or speaker.

(Control system configuration)
FIG. 2 is a configuration diagram of a control system that controls the operation of the image forming apparatus 101. The control system includes a control section 200 and a printer control section 201. Control unit 200 controls the overall operation of image forming apparatus 101 . The printer control unit 201 controls the operation of each unit in the image forming apparatus 101 according to instructions from the control unit 200.

The control unit 200 includes a CPU (Central Processing Unit) 301, a RAM (Random Access Memory) 302, and a ROM (Read Only Memory) 303. The CPU 301 controls the overall operation of the image forming apparatus 101 by executing a computer program stored in the ROM 303. The RAM 302 provides a work area when the CPU 301 performs various processes. A PDL (Page Description Language) control unit 304 and an internal interface (I/F) unit 305 are connected to the CPU 301 . The PDL control unit 304 is a processing circuit for processing , storing, image processing, etc. of print data. Internal I/F section 305 is a communication interface for communicating with printer control section 201.

An operation unit 306 is also connected to the CPU 301 . The CPU 301 receives various instructions and settings via the input interface of the operation unit 306. The CPU 301 controls the output interface of the operation unit 306 to display various screens and provide notifications.

The printer control unit 201 includes a CPU 311, a RAM 312, and a ROM 313. The CPU 311 controls each part of the image forming apparatus 101 by executing a computer program stored in the ROM 313. The RAM 312 provides a work area when the CPU 311 performs various processes. A device control section 314 and an internal interface (I/F) section 315 are connected to the CPU 311 .

The device control unit 314 is an electric circuit including input/output ports and the like for controlling each component provided inside the image forming apparatus 101. A double feed detection sensor 60, transport sensors 61, 62, 63, etc. are connected to the device control unit 314. Internal I/F section 315 is a communication interface for communicating with control section 200. Internal I/F section 315 and internal I/F section 305 transmit and receive image signals and timing signals. The CPU 311 and the CPU 301 communicate via internal I/F units 315 and 305, and cooperate to perform various processes.

The CPU 311 receives an image signal from the control unit 200 and controls the device control unit 314 to execute print processing. Further, the CPU 311 controls the operation of the double feed detection sensor 60 to determine double feed according to the detection result of the double feed detection sensor 60. Further, the CPU 311 determines double feeding according to the detection results of the conveyance sensors 61 and 62.

(Double feed detection sensor)
FIG. 3 is an explanatory diagram of the double feed detection sensor 60. The double feed detection sensor 60 detects the overlap of sheets conveyed between the two guide plates 402a and 402b forming the horizontal path 30 using ultrasonic waves. As described above, the double feed detection sensor 60 of this embodiment is composed of an ultrasonic sensor, and includes a transmitting section 401a and a receiving section 401b. The transmitting section 401a and the receiving section 401b are arranged diagonally opposite to each other with the horizontal path 30 in between.

The transmitter 401a is connected to the device controller 314 via, for example, a power amplifier circuit (not shown). The device control unit 314 outputs a pulse signal of a predetermined frequency under the control of the CPU 311. The pulse signal is amplified by a power amplification circuit and input to the transmitter 401a. The transmitter 401a is driven by a pulse signal obtained from the power amplification circuit and transmits ultrasonic waves toward the receiver 401b.

The receiving section 401b is connected to the device control section 314 via, for example, an output amplifying circuit and a rectifying and smoothing circuit (not shown). The receiving unit 401b outputs a detection signal of a level corresponding to the intensity of the ultrasonic wave received from the transmitting unit 401a. The detection signal is amplified by the output amplification circuit, rectified by the rectification and smoothing circuit, and input to the CPU 311 via the device control section 314. The CPU 311 detects double feeding based on the level of the detection signal. For example, when the intensity (reception level) of the received ultrasonic waves represented by the detection signal is equal to or less than a threshold value for determining double feeding, the CPU 311 determines that sheets are being double fed. When the CPU 311 determines that the sheets are being fed in duplicate, the CPU 311 notifies the user of the occurrence of the double feeding using the operation unit 306 via the control unit 200 . Such double feed detection processing is repeatedly performed during printing processing.

FIG. 4 is an explanatory diagram of the reception level received by the receiving section 401b of the double feed detection sensor 60. FIG. 4(a) illustrates the reception level when there is one sheet. FIG. 4(b) illustrates the reception level when two sheets are conveyed in an overlapping manner.

In FIG. 4A, ranges A and C represent reception levels when the sheet 501 is not within the range of the double feed detection sensor 60. Range B represents the reception level when the sheet 501 is within the range of the double feed detection sensor 60.
In ranges A and C, the ultrasonic waves emitted from the transmitter 401a are received by the receiver 401b without being attenuated by the sheet 501. Ideally, the ultrasonic waves emitted from the transmitter 401a are received by the receiver 401b at 100% intensity, with the same intensity as when the ultrasonic waves were emitted. However, in reality, attenuation occurs during propagation through the air. In this embodiment, it is assumed that the ultrasonic waves emitted from the transmitter 401a are attenuated by 5% as they propagate through the air. Therefore, the receiving unit 401b receives ultrasonic waves with an intensity of 95% in ranges A and C.
In range B, since there is only one sheet 501, the ultrasonic waves are attenuated by one sheet 501. In this embodiment, it is assumed that the ultrasonic waves emitted from the transmitter 401a are attenuated by 30% by passing through one sheet 501. Therefore, in range B, the receiving unit 401b receives ultrasonic waves with an intensity of 70%.

In FIG. 4B, ranges A and E represent reception levels when the sheets 501 and 502 are not within the range of the double feed detection sensor 60. Ranges B and D represent reception levels when one sheet 501 or 502 is within the range of the double feed detection sensor 60. Range C represents the reception level when two sheets 501 and 502 overlap within the range of double feed detection sensor 60.
In ranges A and E, the ultrasonic waves emitted from the transmitter 401a are received by the receiver 401b without being attenuated by the sheet 501. In this embodiment, the receiving unit 401b receives ultrasonic waves with an intensity of 95% in ranges A and E. In ranges B and D, the ultrasonic waves are attenuated by one sheet 501 or 502. In this embodiment, the receiving unit 401b receives ultrasonic waves with an intensity of 70% in ranges B and D.
In range C, the ultrasonic waves are attenuated by the two overlapping sheets 501 and 502. Ultrasonic waves are significantly attenuated by the air layer between the sheets 501 and 502. In this embodiment, the ultrasonic waves transmitted from the transmitter 401a are attenuated by 75% by passing through the two sheets 501 and 502. It will be attenuated. Therefore, in range C, the receiving unit 401b receives ultrasonic waves with an intensity of 25%.

The double feed detection sensor 60 transmits a predetermined number of ultrasonic waves using the transmitter 401a at the timing when the sheet reaches the double feed detection position. The receiving unit 401b receives a predetermined number of ultrasonic waves and outputs a detection signal that is an electrical signal according to the intensity of the received ultrasonic waves. The detection signal is an analog signal whose value increases as the intensity of the ultrasonic wave increases. The CPU 311 can determine double feeding by checking whether the value of the detection signal acquired from the receiving unit 401b corresponds to the intensity of the ultrasonic waves in range C in FIG. 4(b). For example, the CPU 311 sets the threshold value for double feed detection between the level of the detection signal in ranges B and D in FIG. 4(b) and the level of the detection signal in range C in FIG. 4(b). The occurrence of double feeding is determined by comparing the threshold value with the level of the detection signal.

(sheet size)
The size of the sheets stored in the paper feed cassettes 50 and 55 is set by the user using the operation unit 306. FIG. 5 is an exemplary diagram of a size setting screen for setting the size of sheets to be stored in the paper feed cassettes 50 and 55. Size setting screen 610 is displayed on the display of operation unit 306. The user sets the sheet size from the size setting screen 610. The CPU 301 of the control unit 200 displays a size setting screen 610 by pressing a size input button (not shown) prepared for each paper cassette 50, 55. 5(a) and 5(b) show a size setting screen 610 for a standard size sheet. FIG. 5C shows a size setting screen 610 for a sheet of irregular size. The CPU 301 stores the sheet size set on the size setting screen in the RAM 302.

The size setting screen 610 in FIGS. 5A and 5B includes standard size input buttons 611a and 611b, size category switching buttons 612a and 612b, and user-set size input switching button 613. The standard size input buttons 611a and 611b include a plurality of buttons corresponding to a plurality of standard sizes, respectively. When one of the standard size input buttons 611a and 611b is pressed, the CPU 301 inputs the size in the transport direction of the sheet and the width perpendicular to the transport direction, which are associated with the button in advance and stored in the ROM 303. Get the size of the direction. For example, when the A4 button in the standard size input buttons 611a is pressed on the size setting screen 610 of the paper feed cassette 50, the CPU 301 selects the size in the transport direction stored in the ROM 303: 210 [mm] and the size in the width direction: 297 [mm] is temporarily stored in the RAM 312. Note that the size in the conveyance direction is a sheet setting length (first length) that is the length of the sheet in the conveyance direction.

By pressing the size category switching buttons 612a and 612b, the CPU 301 switches the size setting screen 610. When the size category switching button 612a on the size setting screen 610 in FIG. 5(a) is pressed, the CPU 301 switches the display to the inch size setting screen 610 in FIG. 5(b). When the size category switching button 612b on the size setting screen 610 in FIG. 5(b) is pressed, the CPU 301 switches the display to the AB size type size setting screen 610 in FIG. 5(a).

By pressing the user setting size input switching button 613, the CPU 301 switches the size setting screen 610 shown in FIG. 5(a) or 5(b) to the size setting screen 610 shown in FIG. 5(c). On the size setting screen 610 in FIG. 5C, the user can input the size of the sheet numerically, for example, in units of 0.1 [mm]. The input window 631 accepts input of the size of the sheet in the X direction. The input window 632 accepts input of the size of the sheet in the Y direction.

(Double feed detection processing)
FIG. 6 is a flowchart showing preprocessing for detecting double feed according to this embodiment. In the preprocessing for double feed detection, the sheet measurement length is detected, the double feed detection start position is set, and it is determined whether sheet escape processing is possible. The double feed detection start position indicates the position of the sheet at which double feed detection starts in the sheet conveyance direction. The double feed detection sensor 60 performs double feed detection at the timing when the sheet double feed detection start position reaches the double feed detection position. The escape process is a process for discharging sheets for which double feeding has been detected to the escape tray 32 via the escape path 31. Preprocessing for detecting double feeding is started after the image forming apparatus 101 starts conveying sheets. FIG. 7 is an explanatory diagram of the double feed detection start position.

The CPU 311 determines whether a sheet measurement length, which is the length of the sheet being transported in the transport direction, has been detected (S701). The sheet measurement length is detected based on the detection result of the conveyance sensor 61 or the conveyance sensor 62. The sheet measurement length is expressed, for example, as the product of the time during which the conveyance sensors 61 and 62 detect the sheet and the conveyance speed of the sheet. For example, when the time during which the conveyance sensors 61 and 62 detect the sheet is 0.42 seconds and the sheet conveyance speed is 1000 [mm/s], the sheet measurement length is 420 [mm].

If the sheet measurement length has been detected (S701: Y), the CPU 311 compares the detected sheet measurement length with the sheet setting length, which is the preset size of the sheet in the transport direction, and determines that the difference is a predetermined size. It is determined whether or not the value is less than or equal to the threshold value (S702). The threshold value is, for example, a value of 5% of the set sheet length. This will be explained using FIG. 7(a) as an example. For example, when the sheet setting length 1101 is 420 [mm], the threshold value is 21 [mm]. If the sheet measurement length 1102 is greater than 399 [mm] and smaller than 441 [mm], the CPU 311 determines that the difference is smaller than the threshold value.

If the difference is less than or equal to the threshold (S702: Y), the CPU 311 sets the double feed detection start position to the leading edge of the sheet in the conveying direction (hereinafter simply referred to as "leading edge") (S703). The CPU 311 stores the distance from the leading edge of the sheet to the double feed detection start position in the RAM 312. The double feed detection start position may be, for example, 1 mm from the tip, with a margin. Further, the CPU 311 stores in the RAM 312 a flag indicating that double feeding is to be detected. Whether or not to perform escape processing in this case changes depending on the result of double feeding detection. For example, when the sheet setting length is 420 [mm], the threshold value is 21 [mm]. When the sheet measurement length 1102 is longer than 339 [mm] and shorter than 441 [mm], 0 [mm], which is the distance between the double feed detection start position and the leading edge of the sheet, is stored in the RAM 312 (Fig. 7(a) )). In this case, the double feed detection sensor 60 performs double feed detection within a predefined double feed detection execution distance 1103 from the leading edge of the sheet.

If the difference is larger than the threshold (S702:N), the CPU 311 compares the sheet measurement length 1102 and the sheet setting length 1101 again, and determines whether the sheet measurement length 1102 is longer (S704). . Here, the range of the threshold value is excluded, and it is determined whether the sheet measurement length is greater than 441 [mm] or smaller than 339 [mm].

If the sheet measurement length 1102 is longer (S704: Y), the CPU 311 sets the double feed detection start position to a predetermined value based on the rear end of the sheet in the conveyance direction (hereinafter simply referred to as the "rear end"). The position is shifted forward in the transport direction by a distance of (S705). The CPU 311 stores the distance from the leading edge of the sheet to the double feed detection start position in the RAM 312. Further, the CPU 311 stores in the RAM 312 a flag indicating that double feeding is to be detected. Further, the CPU 311 stores in the RAM 312 a flag indicating that escape processing is to be performed. For example, if the sheet setting length 1101 is longer than 420 [mm], the double feed detection execution distance 1103 is longer than 180 [mm], and the sheet measurement length 1102 is longer than 441 [mm], the double feed detection start position is based on the rear edge of the sheet. 180 [mm] forward. In other words, the double feed detection start position is set at a position 240 [mm] from the leading edge of the sheet. 240 [mm] is stored in the RAM 312 as the double feed detection start position (FIG. 7(b)). In this case, the double feed detection sensor 60 performs double feed detection within a double feed detection execution distance 1103 from a position 240 [mm] backward from the leading edge of the sheet.

If the sheet measurement length 1102 is shorter (S704:N), the CPU 311 determines not to perform double feed detection processing, and stores a flag indicating that double feed detection is not performed in the RAM 312 (S706). Further, the CPU 311 stores in the RAM 312 a flag indicating that printing is to be interrupted after performing the escape process. For example, if the sheet setting length 1101 is shorter than 420 [mm] and the sheet measurement length 1102 is shorter than 339 [mm], double feeding is not detected (FIG. 7(c)).

After the processes of S703, S705, and S706, the CPU 311 determines whether the reference sensor 64 has detected a sheet (S707). If not detected (S707: N), the CPU 311 determines whether the double feed detection start position has been determined (S708). The CPU 311 makes this determination based on whether the double feed detection start position is stored in the RAM 312. The CPU 311 considers that "the double feed detection start position has been determined" even if it is set in the process of S706 not to perform double feed detection. If the double feed detection start position has been determined (S708: Y), the CPU 311 returns to the process of S707. That is, if the double feed detection start position has been determined, the CPU 311 waits until the reference sensor 64 detects a sheet. If the double feed detection start position has not been determined (S708: N), the CPU 311 returns to the process of determining whether the sheet measurement length has been detected in S701.

If the reference sensor 64 detects a sheet (S707: Y), the CPU 311 determines whether the double feed detection start position has been determined (S709), similar to the process in S708. If the double feed detection start position has been determined (S709: Y), the CPU 311 ends the double feed detection preprocessing. If the double feed detection start position has not been determined (S709:N), the CPU 311 sets the double feed detection start position to a position shifted forward in the conveying direction of the sheet by a predetermined distance with respect to the rear edge of the sheet. (S710). The CPU 311 stores the distance from the leading edge of the sheet to the double feed detection start position in the RAM 312. Whether or not to perform escape processing in this case changes depending on the result of double feeding detection. With the above steps, the CPU 311 ends the preprocessing for detecting double feeding.

FIG. 8 is a flowchart showing the double feed detection process.
The CPU 311 determines whether the sheet being conveyed has reached the double feed detection position (S801). The CPU 311 can determine whether the sheet has reached the double feed detection position based on the elapsed time from the timing when the reference sensor 64 detected the sheet (S707 in FIG. 6). If the sheet has not reached the double feed detection position (S801:N), the CPU 311 waits until the sheet reaches the double feed detection position.

If it has reached (S801: Y), the CPU 311 performs double feed detection processing using the double feed detection sensor 60 (S802). The CPU 311 stores the result of double feeding detection in the RAM 312. The CPU 311 determines whether the double feed detection time has elapsed since the time when the double feed detection process was started (S803). “Double feed detection time” is a preset time required to execute double feed detection. The CPU 311 repeatedly detects double feed until the double feed detection time elapses (S803:N, S802). When the double feed detection time has elapsed (S803: Y), the CPU 311 determines whether the double feed detection result stored in the RAM 312 indicates that double feed has been detected (S804).

If it is detected that double feeding has occurred (S804: Y), the CPU 311 stores in the RAM 312 a flag indicating that escape processing is to be performed for the sheet, and a flag indicating that printing processing is to be restarted in the RAM 312. It is stored (S805).

If double feeding is not detected (S804: N), the CPU 311 compares the measured sheet length and the set sheet length of the sheet and determines whether they are equal (S806). Here, "equal" may mean that the difference between the measured sheet length and the set sheet length is less than a predetermined threshold. If they are equal (S806: Y), the CPU 311 stores in the RAM 312 a flag indicating that escape processing will not be performed on the sheet, and a flag indicating that the printing process will normally end (S807). If they are not equal (S806:N), the CPU 311 stores in the RAM 312 a flag indicating that escape processing is to be performed for the sheet, and a flag indicating that printing processing is to be interrupted (S808).
The double feed detection process is performed as described above.

FIG. 9 is a flowchart showing escape processing.
The CPU 311 conveys the sheet determined to undergo escape processing to the escape path 31 and starts discharging it onto the escape tray 32 (S901). The CPU 311 waits until the sheet is ejected to the escape tray 32 (S902:N). The CPU 311 determines that the sheet has been ejected to the escape tray 32 when the conveyance sensor 63 detects the sheet and then stops detecting the sheet.

When the ejection of the sheet to the escape tray 32 is completed (S902: Y), the CPU 311 increments the number of times the sheet is ejected to the escape tray 32 by one, and stores the incremented number of ejections in the RAM 312 (S903). The CPU 311 determines whether the number of discharges is a predetermined number or more (here, three or more times) (S904). If the number of discharges is less than three (S904:N), the CPU 311 ends the escape process. If the number of discharges is three or more (S904: Y), the CPU 311 stores a flag indicating that the printing process is to be interrupted in the RAM 312, and ends the escape process shown in FIG. 9 (S905).

FIG. 10 is a flowchart showing the operation control process for detecting double feeding. This process is executed every time a print process is performed on a sheet.

The CPU 311 performs processing for detecting the sheet measurement length of the sheet being conveyed, setting a double feed detection start position, and determining execution of escape processing (S1001). This process is the process shown in FIG. Next, the CPU 311 determines whether or not to perform double feed detection processing (S1002). The CPU 311 determines whether or not to perform double feed detection processing by checking a flag stored in the RAM 312 that indicates whether or not to perform double feed detection.

When performing the double feed detection process (S1002: Y), the CPU 311 performs the double feed detection process described with reference to FIG. 8 (S1003). When the double feed detection process ends, the CPU 311 determines whether to perform escape processing (S1004). The CPU 311 determines whether or not to perform the escape process by checking a flag stored in the RAM 312 that indicates whether or not the escape process is necessary. If the escape process is not performed (S1004: N), the CPU 311 normally ends the print process (S1005) and ends the double feed detection operation control process.

When performing the escape process (S1004: Y), the CPU 311 performs the escape process described in FIG. 9 (S1006). After the escape processing is completed, the CPU 311 determines whether to interrupt the printing process for the sheet by checking the flag stored in the RAM 312 that indicates that printing is to be interrupted (S1007). If it is determined that printing is to be interrupted (S1007: Y), the CPU 311 interrupts the printing process (S1008), and ends the double feed detection operation control process. If it is determined that printing is not to be interrupted (S1007: N), the CPU 311 escapes the sheet, performs the printing process again on a different sheet (S1009), and returns to the process of S1001.

The image forming apparatus 101 of the present embodiment as described above suppresses detection errors of double feeding of sheets being conveyed, thereby reducing the occurrence of unnecessary downtime such as re-inputting the set sheet length. Therefore, user convenience is improved. In addition, the image forming apparatus 101 detects double feeding in the minimum section compared to the case where double feeding is detected in the entire section from the leading edge to the trailing edge in the conveying direction of the sheet being conveyed. The life of the sensor 60 can be extended.

In this embodiment, double feed detection during sheet conveyance by the image forming apparatus 101 has been described. , it is possible to reliably detect the occurrence of double feeding. For example, the present embodiment can be applied to an automatic document feeder provided in a scanner.

Claims (11)

a sheet storage means for storing the sheet;
a conveyance means for conveying the sheet accommodated in the sheet accommodation means;
sheet setting means for setting a first length that is a length in the conveyance direction of the sheet accommodated in the sheet storage means;
double feed detection means for detecting whether two or more sheets are being conveyed in an overlapping manner by the conveyance means;
a sheet detection means that is arranged at a position upstream of the double feed detection means in the conveyance direction and detects the sheet conveyed by the conveyance means;
sheet measuring means for detecting a second length, which is a length in the conveying direction of the sheet being conveyed by the conveying means, based on a detection result by the sheet detecting means;
If the second length is longer than the first length, the double feed detection means determines a position at which to start detecting the sheet overlap based on the difference, and the double feed detection means A control means for detecting the overlapping of the sheets based on the position,
Sheet conveyance device. If the second length is longer than the first length, the control means starts detecting the overlap of the sheets at a position shifted forward by a predetermined distance from the rear end of the sheets in the conveyance direction. characterized by determining the position,
The sheet conveying device according to claim 1. The control means is characterized in that, when the second length is shorter than the first length, the control means determines not to detect the overlapping of the sheets by the double feed detection means.
The sheet conveying device according to claim 1 or 2. The control means is configured to move the sheet to a leading edge of the sheet in a conveying direction or at a position with a predetermined margin from the leading edge when a difference between the first length and the second length is less than or equal to a predetermined threshold. determining a position at which to start detecting the overlap of the
The sheet conveying device according to claim 1 . The control means causes the double feed detection means to start detecting the overlapping of the sheets from the determined position based on the detection of the sheets by the sheet detection means , but when the sheet detection means detects the sheets, If the position at which to start detecting the sheet overlap has not yet been determined , detecting the sheet overlap is started at a position shifted forward by a predetermined distance from the rear end of the sheet in the transport direction. characterized by determining the position,
The sheet conveying device according to claim 1 . The double feed detection means includes a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, and the ultrasonic waves transmitted from the transmitting means are transmitted through the sheet and received by the receiving means. The transmitting means and the receiving means are arranged such that the transmitting means and the receiving means are arranged so that the overlapping of the sheets is determined based on the intensity of the ultrasonic waves received by the receiving means,
The sheet conveying device according to any one of claims 1 to 5. The control means causes the double feed detection means to detect whether or not the sheets are conveyed in an overlapping manner within a predetermined distance range from the determined position at which detection of overlapping sheets is started. Characterized by
The sheet conveying device according to any one of claims 1 to 6. The sheet setting means is characterized in that it includes an operation means through which the first length is input by a user's operation.
The sheet conveying device according to any one of claims 1 to 7. The path along which the sheet is conveyed by the conveying means includes a first path and a second path different from the first path,
The control means is characterized in that when the double feed detection means detects that two or more sheets are conveyed in an overlapping manner, the control means causes the conveyance means to convey the sheets to the second pass.
The sheet conveying device according to any one of claims 1 to 7. If the second length is longer than the first length by a predetermined threshold value or more when the double feeding detection means does not detect that two or more sheets are conveyed in an overlapping manner, The sheet is transported to the second pass by the transporting means,
The sheet conveying device according to claim 9. A sheet conveying device according to any one of claims 1 to 10,
an image forming means for forming an image on the sheet conveyed by the sheet conveyance device;
Image forming device.

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