JP6646965B2 - Sheet conveying device and image forming device - Google Patents

Description

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

  In an image forming apparatus and an image reading apparatus, a sheet conveying apparatus for conveying a sheet is used. It is assumed that the sheets are conveyed one by one (referred to as “single feed”), and when a plurality of sheets are conveyed in an overlapping manner (referred to as “double feed”), the conveyance of the sheets is stopped. You. According to Patent Literature 1, an ultrasonic sensor for detecting a double feed is proposed. The double feeding type includes a type in which a plurality of sheets are substantially overlapped, and a type in which the trailing end of the preceding sheet and the leading end of the succeeding sheet are overlapped (referred to as “double feeding”).

JP 2008-214046 A

  To detect these multiple types of double feeds, it would be promising to transmit and receive ultrasound throughout the sheet. However, Patent Document 1 does not consider the processing time required for one double feed detection. In general, double feed detection can be performed by the number of times obtained by dividing the conveyance time of the ultrasonic sensor by the processing time for conveying the sheet by the processing time. Needless to say, the transport time is not divisible by the processing time, so that there is a surplus. Therefore, unless appropriate consideration is given to in which section of the transport time the double feed detection is performed, the double feed detection cannot be performed at the rear end of the sheet, and the double feed cannot be detected. Therefore, an object of the present invention is to make it possible to detect a double feed more accurately than in the past.

The present invention provides, for example,
Ultrasonic transmission means for transmitting ultrasonic waves,
Ultrasonic receiving means for receiving the ultrasonic signal transmitted from the ultrasonic transmitting means,
A sheet conveyance path arranged so that a sheet is conveyed between the ultrasonic transmission unit and the ultrasonic reception unit,
While the sheet is passing between the ultrasonic transmission unit and the ultrasonic reception unit, the ultrasonic reception unit detects a plurality of sheets based on the reception level of the ultrasonic signal received from the ultrasonic transmission unit. Detecting means for performing multiple feed detection a plurality of times to detect a double feed that is being conveyed overlapped,
Have a, and control means for controlling the execution timing of the double feed detection to be performed over a plurality of times,
A rear end margin is provided that does not perform double feed detection of a predetermined length from the rear end of the sheet toward the front end side,
The control means is configured such that the double feed detection executed last among the multiple feed detections executed over a plurality of times is performed from the trailing edge margin to a detection time required for one double feed detection in the detection means. There is provided a sheet conveying apparatus characterized in that execution timing is controlled so as to be executed from a position distant to the front end side over a corresponding length .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to detect double feed more accurately than before.

Sectional view of image forming system Controller block diagram Diagram illustrating attenuation of ultrasonic waves by sheet Diagram for explaining the execution timing of double feed detection Diagram for explaining adjustment of execution timing of double feed detection FIG. 4 illustrates functions of a CPU. Flow chart showing double feed detection Diagram for explaining adjustment of execution timing of double feed detection Diagram for explaining adjustment of execution timing of double feed detection

<Example 1>
(overall structure)
FIG. 1 shows an image forming system. The image forming apparatus 1 may be realized as a printer, a copier, a multifunction peripheral, or a facsimile machine. The image forming apparatus 1 includes a sheet conveying device 18 that feeds and conveys sheets one by one from a sheet cassette 2 that stores a plurality of sheets. The pickup roller 3 picks up the uppermost sheet stored in the sheet cassette 2 and feeds it to the transport path. The paper feed roller 4 has an upper roller and a lower roller. The upper roller rotates so as to send the sheet from the upstream side to the downstream side in the transport direction, while the lower roller rotates in the reverse direction. Thus, the sheets are separated one by one and fed to the vertical path 5. In the vertical pass 5, the sheet is conveyed by a vertical pass roller 6 and guided to a horizontal pass 7. The vertical path 5 and the horizontal path 7 function as a sheet conveying path.

  The image forming unit 8 is an image forming unit that forms an image using toner. The image forming section 8 may employ any image forming method such as an ink jet method or a thermal transfer method. The toner images of different colors formed on the drums 81 to 84 are transferred onto the intermediate transfer body 85 in a superimposed manner. The secondary transfer unit 86 transfers the multicolor toner image transferred to the intermediate transfer body 85 to a sheet.

  The reference sensor 9 is a sheet sensor that detects a sheet. Based on the timing at which the reference sensor 9 detects the leading edge of the sheet, the execution timing for performing the double feed detection is controlled. The conveying distance of the sheet from the reference sensor 9 to the ultrasonic receiving unit 11 is known. The conveying speed of the sheet is also known (however, the conveying speed may be changed for each image forming mode such as the thick paper mode and the plain paper mode). Therefore, the movement time Twait from the timing when the sheet reaches the reference sensor 9 to the timing when the sheet reaches the double feed detection position P is obtained by dividing the transport distance by the transport speed. The double feed detection position P is a position on the sheet conveyance path where the ultrasonic receiving unit 11 and the ultrasonic transmitting unit 12 face each other. In the double feed detection, the ultrasonic signal transmitted from the ultrasonic transmitter 12 is received by the ultrasonic receiver 11 installed opposite thereto, and is determined based on the reception level and the degree of attenuation of the ultrasonic signal.

  The sheet is conveyed by conveyance rollers such as the pre-registration roller 10 and the registration roller 13, and is sent to the secondary transfer unit 86, where the toner image is transferred. The fixing unit 14 applies pressure and heat to the toner image transferred to the sheet to fix the toner image to the sheet. The discharge roller 15 discharges the sheet to a discharge tray 16. The user interface 17 has an input device for the operator to input information and instructions, and an output device for outputting information to the operator.

(Controller configuration)
FIG. 2 shows a controller that controls the entire image forming system. The printer controller 20 includes a CPU 21, a ROM 22, and a RAM 23. The CPU 21 executes a control program stored in the ROM 22, and controls the image forming unit 8, the image processing unit 19, the user interface 17, and the like. The RAM 23 temporarily stores control data and is used as a work area for arithmetic processing accompanying control. As a storage device other than the ROM 22 and the RAM 23, a hard disk drive, a solid state drive, or the like may be employed. The image processing unit 19 converts a digital image signal input from the computer 95 via the external I / F 94 into a video signal and outputs the video signal to the image forming unit 8. The image forming section 8 outputs a laser beam according to a video signal, and forms an electrostatic latent image on the drums 81 to 84 which are photosensitive members and image carriers. The electrostatic latent image is developed with toner to become a toner image. The input device of the user interface 17 has a plurality of keys for setting various functions related to image formation, and the output device may have a display unit for displaying information indicating a setting state. The user interface 17 outputs a key signal corresponding to each key operation to the printer controller 20 and displays corresponding information on the display unit based on the signal from the printer controller 20.

  A sheet feed motor 24 and a vertical path motor 25 exist as driving sources for driving the transport mechanisms arranged from the sheet cassette 2 to the vertical path 5. The paper feed motor 24 drives the pickup roller 3. The vertical path motor 25 drives the feed roller 4 and the vertical path roller 6. The registration motor 26 and the like exist as a drive source for driving a transport mechanism arranged from the horizontal path 7 to the secondary transfer unit 86. The registration motor 26 drives the pre-registration roller 10 and the registration roller 13. The drum motor 27 drives the drums 81 to 84, the intermediate transfer body 85, and the secondary transfer unit 86. The fixing motor 28 drives the fixing unit 14. The discharge motor 29 drives the discharge roller 15.

  The CPU 21 detects the leading edge of the sheet by the reference sensor 9 and determines the execution timing of the double feed detection. Further, when the execution timing of the double feed detection comes, the CPU 21 causes the ultrasonic transmission unit 12 to generate an ultrasonic signal, and causes the ultrasonic reception unit 11 to receive the ultrasonic signal. The CPU 21 determines whether double feed has occurred, for example, by comparing the received signal level with a threshold. The attenuation level and the threshold may be compared. The ultrasonic sensor 30 includes an ultrasonic receiving unit 11 and an ultrasonic transmitting unit 12.

  FIG. 3A shows an output signal output by the ultrasonic receiving unit 11 when the sheet is being fed in a single sheet. FIG. 3B illustrates an output signal output by the ultrasonic receiving unit 11 when the sheets are multi-fed. As shown in FIG. 3A, when a single sheet is fed, the amplitude of the output signal of the ultrasonic receiving unit 11 becomes relatively large. That is, the degree of attenuation of the ultrasonic signal is small. On the other hand, in the case of double feeding, as shown in FIG. 3B, the ultrasonic signal is greatly attenuated by the plurality of sheets and the air layer between the sheets, and the amplitude of the output signal becomes relatively small. As described above, the CPU 21 determines whether or not the sheet is multi-fed based on the amplitude of the output signal. When detecting double feeding, the CPU 21 stops the conveyance of the sheet by stopping a driving source related to the conveyance of the sheet, such as the registration motor 26.

  The outline of double feed detection will be described with reference to FIGS. 4A and 4B. Arrow F indicates the sheet conveyance direction. The double feed detection is performed not only at one point of the sheet but also at a plurality of different positions in the conveying direction by operating the ultrasonic sensor 30 while conveying the sheet. As shown in FIG. 4A, Tpap is a transport time required for one sheet to pass between the ultrasonic transmission unit 12 and the ultrasonic reception unit 11 (the double feed detection position P). . In other words, Tpap is a transit time from when the leading end of one sheet arrives at the double feed detection position P to when the rear end passes through the double feed detection position P. Tpap is calculated by dividing the length of the sheet in the transport direction by the transport time. Tdtct is a determination time required for one double feed detection (double feed determination). One double feed detection refers to a process of transmitting an ultrasonic wave from the ultrasonic transmission unit 12 and determining whether to perform single transmission or double transmission based on a difference in amplitude of an output signal received and received by the ultrasonic reception unit 11. . For one double feed detection, processing time (detection of the ultrasonic signal from the ultrasonic transmission unit 12, reception of the ultrasonic signal by the ultrasonic reception unit 11, and double determination by the CPU 21) is performed. A time Tdtct) is required. Tdtct is the same time for each multi-feed detection when a plurality of multi-feed detections are performed on one sheet, and does not change even when the size and thickness of the sheets are different. After performing the double feed detection once, a preparation time (standby time) is required until the amplitude of the ultrasonic signal falls and stabilizes. The preparation time required from the time when such double feed detection is performed to the time when double feed detection can be performed again is Tmin.

  By the way, the moving time from the passage of the sheet through the reference sensor 9 to the arrival at the double feed detection position P may be changed due to the sheet conveyance variation. For example, if the arrival of the sheet at the double feed detection position P is delayed, the double feed detection of the leading end section of the sheet is executed even though there is no sheet. In this case, double feed may not be detected. On the other hand, when the arrival of the sheet at the double feed detection position P is advanced, the double feed detection of the rear end section of the sheet is executed even though the rear end of the sheet has already passed the double feed detection position P. (The rear end section is a section behind the center of the seat). In this case, double feed may not be detected. This causes a reduction in the accuracy of double feed detection. In consideration of such a sheet conveyance variation, a leading edge margin Ttop and a trailing edge margin Ttail are provided in the leading end section and the trailing end section of the sheet as sections in which double feed detection is prohibited. The leading edge margin Ttop is a section from the leading edge position of the sheet to the first predetermined position. The rear end margin Ttail is a section from the second predetermined position of the sheet to the rear end position. Note that if the transport variation is sufficiently small, the leading edge margin Ttop and the trailing edge margin Ttail may be omitted. The leading edge margin Ttop is determined in advance in consideration of the nominal transfer time from the reference sensor 9 to the double feed detection position P and the transfer efficiency of the vertical path roller 6 and the pre-registration roller 10. Here, assuming that the nominal transport time is 100 ms and the transport efficiency is 70%, there is a possibility that the arrival of the sheet at the double feed detection position P is delayed by a maximum of 30 ms. Therefore, the tip margin Ttop is set to 30 ms. On the other hand, the trailing edge margin Ttail is a margin for preventing the trailing edge of the sheet from passing the double feed detection position P earlier than the nominal timing. Basically, it is unlikely that the sheet will be conveyed earlier than the nominal timing. Therefore, the rear end margin Ttail is a shorter time than the front end margin Ttop, and is set to, for example, 10 ms. These values are merely exemplary values to assist in understanding the embodiments. The maximum execution number N of the double feed detection for one sheet is calculated as the maximum integer satisfying the expression (1).

Tdtct × N + Tmin × (N−1) <Tpap− (Ttop + Ttail) (1)
As shown in FIG. 4A, the first double feed detection is executed when the leading edge margin Ttop elapses, and then the second double feed detection is executed when the preparation period Tmin elapses. Since the maximum number of executions N is an integer, an undetected time (undetected area) that is shorter than the detection time Tdct and in which double feed detection cannot be performed remains in the rear end section of the sheet. However, when the double feed occurs, as shown in FIG. 4B, the trailing end section of the preceding sheet and the vicinity of the leading end of the succeeding sheet overlap. As shown in FIG. 4A, since there is an undetected area in the trailing end section of the preceding sheet, there is a possibility that double feed cannot be detected.

  Therefore, the CPU 21 may adjust the detection interval Tintvl so that double feed detection can be performed substantially uniformly over the entire area in the transport direction. Specifically, the detection interval Tintvl is determined so as to satisfy Expression (2). The detection intervals Tintvl are determined to be equal, and the end timing of the Nth detection is determined to be immediately before the start timing of the trailing edge margin Ttail. By transforming Expression (2), Expression (3) for obtaining the detection interval Tintvl is obtained.

Tdtct × N + Tintvl × (N−1) = Tpap− (Ttop + Ttail) (2)
Tintvl = (Tpap− (Ttop + Tail) − (Tdtct × N)) / (N−1) (3)
The meanings of Expressions (2) and (3) will be described. By multiplying the maximum number of executions N by the detection time Tdtct, the total execution time required to execute the multi-feed detection with the maximum number of executions N is determined. By uniformly dispersing the time difference between the transport time Tpap (the leading margin and the trailing margin are excluded here) and the total execution time, N-1 detection intervals Tintvl are obtained.

  FIG. 5A shows an example of execution timing of double feed detection when the embodiment is applied to a sheet of B5 size (257 mm × 182 mm). Assuming that the sheet conveying speed is 1000 [mm / s], the conveying time Tpap is 182 [ms]. It is assumed that the detection time Tdtct = 57 [ms], the preparation time Tmin = 5 [ms], the leading edge margin Ttop = 30 [ms], and the trailing edge merge Ttail = 10 [ms]. In this case, N = 2 is calculated from equation (1). By substituting N = 2 into equation (3), the detection interval Tintvl = 28 [ms] is calculated.

  In the example shown in FIG. 5A, the first double feed detection is performed immediately after the leading edge margin has elapsed, and when the detection interval Tintvl (= 28 [ms]) has further elapsed, the second double feed detection is performed. Be executed. Immediately after the completion of the second double feed detection, the trailing edge margin arrives. Therefore, even when the double feed occurs, the double feed detection is executed in the rear end section of the preceding sheet, and the double feed is detected. Note that the rear end section may include a rear end margin, or may exclude the rear end margin. In this embodiment, the trailing margin is excluded from the trailing end section.

  FIG. 5B shows the execution timing of double feed detection when the embodiment is applied to an A3 size (210 mm × 420 mm) sheet. N = 6 is calculated from equation (1). By substituting N = 6 into equation (3), a detection interval Tinrvl = 7.6 [ms] is calculated. For A3 size sheets, double feed detection is performed six times at every 7.6 [ms] detection interval. In particular, double feed detection is performed in the rear end section of the A3 size sheet.

  In this way, the CPU 21 performs double feed detection as many times as possible for one sheet, and adjusts each detection interval so that the undetected area does not concentrate on the rear end side of the sheet. Thereby, the detection accuracy of the double feed will be improved as compared with the conventional case.

(Function of CPU)
FIG. 6 shows functions realized by the CPU 21 executing the control program. Some or all of these functions may be implemented by hardware such as a logic circuit or an ASIC (specific application integrated circuit).

  The ultrasonic transmission unit 12 that transmits the ultrasonic signal and the ultrasonic reception unit 11 that receives the ultrasonic signal transmitted from the ultrasonic transmission unit 12 are controlled by the double feed detection unit 31. The double feed detection unit 31 sets the reception level of the ultrasonic signal received from the ultrasonic transmission unit 12 by the ultrasonic reception unit 11 while the sheet passes between the ultrasonic transmission unit 12 and the ultrasonic reception unit 11. The multi-feed detection is performed a plurality of times based on the multi-feed detection. An attenuation level may be used instead of the reception level. The timer 32 starts timing when the reference sensor 9 detects the leading edge of the sheet. The control unit 33 controls the execution timing of double feed detection by the double feed detection unit 31 based on the timing at which the reference sensor 9 detects the leading edge of the sheet by referring to the count value of the timer 32.

  The control unit 33 determines the execution timing of the multiple feed detection performed a plurality of times so that at least the double feed detection executed last among the multiple feed detections performed a plurality of times is performed in the rear end section. Or adjust. The rear end section is a section from the rear end of the sheet (the start position of the rear end margin) to a position separated by a predetermined distance in the sheet conveyance direction. According to FIGS. 4A and 4B, the rear end section is illustrated as an undetected area.

  As shown in FIG. 5A and FIG. 5B, the determination unit 34 of the control unit 33 is executed a plurality of times so that the double feed detection executed last is executed in the rear end section. Each execution timing is determined so that double feed detection is performed at equal intervals. The size acquisition unit 35 acquires the size (length in the transport direction) of the sheet input through the user interface 17. The size acquisition unit 35 may analyze the print job input from the computer 95 and acquire the size of the sheet. The acquired sheet size is held in the RAM 23. The transport time calculator 36 calculates the transport time Tpap based on the sheet size and the transport speed. The number-of-times calculating unit 38 calculates the maximum number of executions N based on the transport time Tpap and Equation (1). The interval calculation unit 37 calculates the detection interval Tintvl using the maximum number of executions N, a known parameter stored in the ROM 22, and Expression (3).

(flowchart)
FIG. 7 is a flowchart showing the control operation of double feed detection. This flow is executed each time sheets are fed from the sheet cassette 2 one by one. In S101, the CPU 21 (size acquisition unit 35) acquires the size of the sheet stored in the RAM 23. In S102, the CPU 21 (the determination unit 34) determines the maximum number of executions N and the detection interval Tintvl in the double feed detection. For example, the CPU 21 (conveyance time calculation unit 36) calculates the conveyance time Tpap from the sheet size and the conveyance speed. The CPU 21 (number-of-times calculating unit 38) substitutes the transport time Tpap and the parameters stored in the ROM 22 into the equation (1) to calculate the maximum number of executions N. The CPU 21 (interval calculation unit 37) calculates the detection interval Tintvl by substituting the maximum number of executions N or the like into the equation (3).

  In S103, the CPU 21 (control unit 33) determines whether the reference sensor 9 has detected the leading edge of the sheet. The reference sensor 9 outputs a high-level signal while detecting a sheet, and when the sheet is no longer detected, the signal level changes to a low level. Therefore, the timing when the low level is changed to the high level is the timing when the leading edge of the sheet is detected. When the leading edge of the sheet is detected, the CPU 21 initializes a variable CNT for managing the number of executions of the double feed detection to 0, and advances the processing to S104. Further, the CPU 21 starts counting time of the timer 32. The variable CNT may be implemented by hardware such as a counter circuit.

  In S <b> 104, the CPU 21 (the control unit 33) determines whether or not the execution timing has arrived based on the count value of the timer 32. The execution timing of the first double-feed detection is a timing at which a time corresponding to the sum of the above-described movement time Twait and the leading edge margin Ttop has elapsed since the leading edge of the sheet was detected by the reference sensor 9. When the execution timing (start timing) of the first double feed detection comes, the CPU 21 advances the processing to S105. The control unit 33 instructs the double feed detection unit 31 to execute the double feed detection. In S105, the CPU 21 (the double feed detection unit 31) performs double feed detection. The double feed detecting unit 31 causes the ultrasonic transmitting unit 12 to transmit ultrasonic waves, causes the ultrasonic receiving unit 11 to receive ultrasonic waves, and receives an output signal from the ultrasonic receiving unit 11.

  In S <b> 106, the CPU 21 (the double feed detection unit 31) determines whether double feed has occurred based on the output signal from the ultrasonic receiving unit 11. For example, if the amplitude of the output signal does not exceed the threshold, the double feed detection unit 31 determines that double feed has occurred, and proceeds to S109. In step S109, the CPU 21 stops driving sources such as the sheet feeding motor 24 and the registration motor 26 in order to stop sheet conveyance. Further, the CPU 21 may display on the user interface 17 that multifeed has occurred, a method of removing the multiply fed sheet, and the like. On the other hand, if the amplitude exceeds the threshold value, CPU 21 determines that double feeding has not occurred, adds 1 to variable CNT, and advances the processing to S107.

  In S107, the CPU 21 (the control unit 33) determines whether or not all of the N-time double-feed detection has been completed based on the variable CNT. If the variable CNT is N, the control unit 33 ends this flow because all of the N times of double feed detection have been completed. On the other hand, if variable CNT is smaller than N, control unit 33 causes the process to proceed to S108.

  In S108, the CPU 21 (the control unit 33) determines whether or not the detection interval Tintvl has elapsed from the timing when the double feed detection has been completed. When the detection interval Tintvl has elapsed from the timing at which the double feed detection has been completed, the control unit 33 returns the processing to S105 in order to execute the next double feed detection.

  As described above, the execution timing is determined or adjusted so that the double feed detection is performed in the rear end section of the sheet, so that the double feed can be detected. Further, by making the detection interval Tintvl uniform, double feed detection is performed in almost the entire area of the sheet, so that not only double feed but also general double feed can be detected. In particular, since double feed detection is also performed in the leading end section of a sheet, double feed can be detected earlier.

<Example 2>
In the first embodiment, the execution timing is adjusted in accordance with Expression (3) so that the detection interval from the preceding double-feed detection to the subsequent double-feed detection is equal for all of the multiple-feed detections. Was done. However, it is not essential that all of the plurality of detection intervals be equal. This is because it is sufficient to perform the double feed detection at least in the rear end section of the preceding sheet. For example, the detection interval Tintvl for the first to (N-1) th multi-feed detections may be set to be constant (eg, the preparation period Tmin). Further, the detection interval Tintvl for the last (N-th) double feed detection may be set longer than the preparation period Tmin. As a result, at least the last (N-th) double feed detection is performed in the rear end section.

  FIG. 8 shows an example in which the execution timing is shifted to the rear end only for the last double-feed detection in the A3 size sheet. For A3 size sheets, N = 6 is calculated from equation (1). By adjusting the detection interval between the fifth double-feed detection and the sixth double-feed detection to be longer than the other detection intervals, the sixth double-feed detection is performed on the rear end side of the sheet. Thus, the execution timing of the sixth double feed detection shifts. The calculation method of the (N−1) -th and N-th detection intervals Tintvl is represented by, for example, the following equation (4).

Tintvl = Tpap− (Ttop + Ttail) − (Tdtct × N) −Tmin × (N−2) 4
The CPU 21 (the determination unit 34) adjusts the execution timing such that, for example, the process from the first double feed detection to the (N-1) th double feed detection is performed at Tmin intervals. Further, the CPU 21 (the interval calculation unit 37) calculates a detection interval Tintvl between the (N-1) th double feed detection and the Nth double feed detection by using the equation (4). As described above, the execution timing is determined or adjusted so that the double feed detection is performed in the rear end section of the sheet, so that the double feed can be accurately detected. Further, by making the detection interval Tintvl uniform, double feed detection is performed in almost the entire area of the sheet, so that not only double feed but also general double feed can be detected. In the case of performing the double feed detection N times, N-1 detection intervals are generated. One of these detection intervals is set as the detection interval Tintvl obtained by Expression (4), and the other detection interval is set as Tmin. However, the N-th double feed detection is performed in the rear end section. For example, as shown in FIG. 9A, an interval between the first double feed detection and the second double feed detection may be set as the detection interval Tintvl. As shown in FIG. 9B, an interval between the third double feed detection and the fourth double feed detection may be set as the detection interval Tintvl. In any case, the last double feed detection is performed in the rear end section. Note that a part of the detection interval Tintvl obtained by Expression (4) may be distributed to other detection intervals. In this case, the other detection intervals will be slightly longer than Tmin. The dispersion amounts may be equal or unequal. This is because it is sufficient to perform the double feed detection at least in the rear end section.
As described above, the double feed detection unit 31 performs the double feed detection a plurality of times while the sheet passes between the ultrasonic transmission unit 12 and the ultrasonic reception unit 11. The control unit 33 controls the execution timing of the multiple feed detection performed a plurality of times so that the double feed detection executed last among the multiple feed detections performed multiple times is performed in the rear end section of the sheet. I do. Double feed can be detected with higher accuracy than before. In particular, double feed that may occur in the rear end section can be detected.

  As described in the first embodiment, the determination unit 34 performs the multiple feed detection performed a plurality of times at equal intervals so that the double feed detection performed last is performed in the rear end section. Each execution timing may be determined. As a result, double feed that may occur in the rear end section can be detected.

  The number-of-times calculating unit 38 detects the time required for the double feed detection in the double feed detecting unit 31 and the time required for one sheet to pass between the ultrasonic transmitting unit 12 and the ultrasonic receiving unit 11. The maximum number of executions N may be determined from the required transfer time. N is the maximum number of times that double feed detection can be performed per sheet. The interval calculation unit 37 may determine the total execution time required to execute the double feed detection with the maximum execution number N based on the maximum execution number N and the detection time Tdtct. Further, the interval calculation unit 37 distributes the time difference between the transport time Tpap and the total execution time evenly so that the interval between the precedingly performed double feed detection and the subsequently performed double feed detection ( The detection interval Tintvl) may be determined. The transport time Tpap may exclude the leading edge margin Ttop for not performing double feed detection from the leading edge of the sheet to the first predetermined position. In addition, the rear end margin Ttail may be excluded from the transport time Tpap since double feed detection is not performed from the second predetermined position to the rear end of the sheet. By considering the front margin Ttop and the rear margin Ttail in this way, the influence of sheet conveyance variations will be reduced. If the transport variation is small, it is unnecessary to consider the front margin Ttop and the rear margin Ttail.

  As described in the first embodiment, the detection interval Tintvl is the preparation time Tmin required from the completion of the preceding double-feed detection to the subsequent execution of the double-feed detection. It may be longer. The determination unit 34 may be configured to determine N that is the maximum number of executions so that Expression (1) is satisfied. Further, the determination unit 34 may determine Tintvl such that Expression (3) is satisfied.

  As described with respect to the second embodiment, the determination unit 34 performs the double feed detection performed last from the execution timing of the double feed detection performed second to last so that the double feed detection is performed in the rear end section. It may function as an adjustment unit that adjusts the detection interval Tintvl until the timing. Also in the second embodiment, the determining unit 34 may determine the maximum number of executions N from the detection time Tdtct and the transport time Tpap. Further, the determination unit 34 determines the total execution time based on the maximum number of executions N and the detection time Tdtct, and disperses the time difference between the transport time Tpap and the total execution time to detect the preceding double feed and the subsequent double feed. An interval between detections may be determined. As illustrated in FIG. 8, the determination unit 34 determines each execution timing such that the detection interval from the (N−1) th double feed detection to the Nth double feed detection is longer than the other detection intervals. Is also good. Also in the second embodiment, the leading margin and the trailing margin may be considered. As a result, the influence of transport variations is reduced.

  The detection interval may be a time longer than the preparation time required from completion of the double feed detection performed in advance to execution of the double feed detection performed subsequently. For example, if a part of the detection interval Tintvl obtained by the equation (4) is distributed to other detection intervals, each detection interval will be longer than Tmin. At least in FIG. 8, the detection interval Tintvl from the (N-1) th double feed detection to the Nth double feed detection is set to be longer than Tmin.

  As shown in FIG. 8, the interval calculation unit 37 may set the detection interval from the first double feed detection to the (N−1) th double feed detection to the same time as the preparation time Tmin. The interval calculation unit 37 of the determination unit 34 may determine Tintvl, which is the interval from the (N-1) th multifeed detection to the Nth multifeed detection, so that the expression (4) is satisfied.

  A reference sensor 9 that detects the leading edge of the sheet may be provided upstream of the double feed detection position P between the ultrasonic receiving unit 11 and the ultrasonic transmitting unit 12 in the sheet conveyance direction. The control unit 33 may control the execution timing of the double feed detection based on the timing at which the reference sensor 9 detects the leading edge of the sheet. In this case, it is necessary to consider the influence of the transport variation occurring in the transport section from the reference sensor 9 to the double feed detection position P. That is, by considering the above-described leading edge margin and trailing edge margin, the influence of transport variations is reduced.

  The image forming apparatus 1 further includes an image forming unit 8 that forms an image on a sheet conveyed by the sheet conveying device 18 of the image forming apparatus 1. Since such a sheet conveying device 18 is provided, the image forming apparatus 1 can accurately detect the double feeding of the sheet and stop the conveyance of the sheet when the double feeding of the sheet occurs. As a result, it is possible to suppress complication of sheet jam and deterioration of the transport mechanism.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 7 ... Horizontal path, 11 ... Ultrasonic reception part, 12 ... Ultrasonic transmission part, 21 ... CPU, 31 ... Double feed detection part, 33 ..Control units

Claims (17)

Ultrasonic transmission means for transmitting ultrasonic waves,
Ultrasonic receiving means for receiving the ultrasonic signal transmitted from the ultrasonic transmitting means,
A sheet conveyance path arranged so that a sheet is conveyed between the ultrasonic transmission unit and the ultrasonic reception unit,
While the sheet is passing between the ultrasonic transmission unit and the ultrasonic reception unit, the ultrasonic reception unit detects a plurality of sheets based on the reception level of the ultrasonic signal received from the ultrasonic transmission unit. Detecting means for performing multiple feed detection a plurality of times to detect a double feed that is being conveyed overlapped,
Have a, and control means for controlling the execution timing of the double feed detection to be performed over a plurality of times,
A rear end margin is provided which does not perform double feed detection of a predetermined length from the rear end of the sheet toward the front end side,
The control means may be configured such that the double feed detection executed last among the multiple feed detections performed over a plurality of times is performed from the trailing edge margin to a detection time required for one double feed detection in the detection means. An execution timing is controlled so that execution is performed from a position distant to the front end side over a corresponding length . The control unit may be configured to perform the multiple-feed detection performed a plurality of times so that the last-performed double-feed detection is performed from a position away from the distal end for a length corresponding to the detection time. 2. The sheet conveying apparatus according to claim 1, wherein each execution timing is determined so as to be executed at intervals of. Said control means, said detection time, from a single sheet and said ultrasonic transmitting means and the and the transport time required to pass between the ultrasonic receiving means, double feed per one sheet Determine the maximum number of executions that can perform detection, determine the total execution time required to execute the multi-feed detection of the maximum number of executions based on the maximum number of executions and the detection time, and By determining the interval between the double feed detection performed earlier and the double feed detection performed subsequently by equally dispersing the time difference between the time and the total execution time, each execution timing is determined. The sheet conveying device according to claim 2, wherein the determination is made. A leading edge margin for not performing double feed detection of a second predetermined length from the leading end of the sheet toward the trailing end side is provided,
The transfer time, the sheet conveying device according to claim 3, wherein the leading end margin and the trailing margin has been removed. The interval is a time longer than a preparation time required until completion of detection of a double feed performed in advance and detection of a double feed performed subsequently can be performed. The sheet conveying device according to claim 4 . The control means includes:
Tdtct × N + Tmin × (N−1) <Tpap− (Ttop + Ttail)
Is configured to determine N that is the maximum number of executions such that
Tdtct is the detection time, Tmin is the preparation time, and Tpap is a transport time required for one sheet to pass between the ultrasonic transmitting unit and the ultrasonic receiving unit, 6. The sheet conveying apparatus according to claim 5 , wherein Ttop is the leading edge margin, and Ttail is the trailing edge margin. The control means includes:
Tintvl = (Tpap− (Ttop + Tail) − (Tdtct × N)) / (N−1)
The sheet conveying device according to claim 6 , wherein the interval Tintvl is determined so that the following condition is satisfied. The control means may be arranged such that the double feed detection executed last is separated from the rear end margin to the front end side for a length corresponding to a detection time required for one double feed detection in the detection means. And adjusting means for adjusting an interval from an execution timing of the double feed detection executed second to last to the execution timing of the double feed detection executed last so as to be executed from the position. The sheet conveying device according to claim 1. Said control means, said detection time, from a single sheet and said ultrasonic transmitting means and the and the transport time required to pass between the ultrasonic receiving means, double feed per one sheet Determine the maximum number of executions N that can perform detection, determine the total execution time required to execute the multi-feed detection of the maximum number of executions based on the maximum number of executions N and the detection time, The execution timing is determined by determining an interval between a preceding double feed detection and a subsequent double feed detection by dispersing a time difference between the transport time and the total execution time. Item 2. The sheet conveying device according to item 1 . A leading edge margin for not performing double feed detection of a second predetermined length from the leading end of the sheet toward the trailing end side is provided,
When performing the N- times double feed detection , the control means determines each execution timing so that the interval from the ( N-1) -th double feed detection to the N-th double feed detection is longer than other intervals. The sheet conveying device according to claim 9 , wherein: A leading edge margin for not performing double feed detection of a second predetermined length from the leading end of the sheet toward the trailing end side is provided,
The transfer time, the sheet conveying device according to claim 9, wherein the distal end margin and the trailing margin has been removed. The interval is a time longer than a preparation time required until completion of detection of a double feed performed in advance and detection of a double feed performed subsequently can be performed. The sheet conveying device according to claim 10 . The interval between the first double feed detection and the (N-1) th double feed detection is the same as the preparation time required from completion of the preceding double feed detection to execution of the subsequent double feed detection. The sheet conveying apparatus according to claim 10 , wherein the time is set to: The control means includes:
Tdtct × N + Tmin × (N−1) <Tpap− (Ttop + Ttail)
Is configured to determine N that is the maximum number of executions such that
Tdtct is the detection time, Tmin is the preparation time, and Tpap is a transport time required for one sheet to pass between the ultrasonic transmitting unit and the ultrasonic receiving unit, Ttop is the distal margin, the sheet conveying device according to claim 12 or 13, characterized in that Ttail is the rear end margin. The control means includes:
Tintvl = Tpap− (Ttop + Ttail) − (Tdtct × N) −Tmin × (N−2)
15. The sheet conveying apparatus according to claim 14 , wherein Tintvl, which is an interval from the (N-1) th double feed detection to the Nth double feed detection, is determined so that is satisfied. Further provided is a reference sensor that is disposed on the upstream side in the sheet conveying direction from a detection position between the ultrasonic receiving unit and the ultrasonic transmitting unit, and detects a leading edge of the sheet,
16. The sheet conveyance device according to claim 1, wherein the control unit controls execution timing of the double-feed detection based on a timing at which the reference sensor detects a leading edge of the sheet. 17. apparatus. A sheet conveying device according to any one of claims 1 to 16 ,
An image forming unit for forming an image on a sheet conveyed by the sheet conveying device.

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