JP6809210B2 - Double feed detection device and its control method, and image forming device - Google Patents

Description

The present invention relates to a double feed detection device for detecting double feed of a sheet transported along a transport path, a control method thereof, and an image forming apparatus.

An image forming apparatus such as a printer forms an image while taking out papers (sheets) one by one from a paper storage unit and transporting them. In addition, an automatic document feeder provided in a scanner, a copier, a facsimile machine, or the like transports documents (sheets) stacked on a document tray one by one to a reading position.

One of the troubles related to the transfer of sheets is a phenomenon called "double transfer" in which a plurality of sheets are conveyed in a state of being displaced and overlapped in the transfer direction. Double feeding occurs when one sheet is taken out from a group of sheets in a laminated state by a pickup roller or the like, and the sheet in contact with the sheet is dragged by friction or electrostatic adsorption with the sheet being taken out.

Conventionally, a technique using an ultrasonic sensor has been proposed for detecting double feed. In this technology, the transmitter and the receiver that make up the ultrasonic sensor are placed in the transport path so that the sheet passes between them, and are based on the received signal of ultrasonic waves that penetrate the sheet being transported. Judge whether it is a double feed.

There is a technique described in Patent Document 1 as a prior art for improving the reliability of detection of double feed by an ultrasonic sensor. In Patent Document 1, the double feed detection device is described by adjusting the threshold value so that the difference between the threshold value for determining the suitability of the reception level and the average value of the history of the reception level becomes a predetermined value. It is disclosed to prevent false detections due to aging deterioration.

Japanese Unexamined Patent Publication No. 2013-75746

The double feed detection device using the ultrasonic sensor operates by the electric power supplied from the power supply circuit.

Generally, the power supply circuit is used not only as a double feed detection device but also as a power source for other loads such as a drive source of a mechanism for transporting a sheet. In the circuit configuration in which the power supply circuit is shared between the double feed detection device and the other load in this way, the output voltage of the power supply circuit may fluctuate momentarily as the other load is turned on and off.

If the voltage supplied to the double feed detection device fluctuates, the transmission / reception of ultrasonic waves and the amplification of the received signal are disturbed, and the accuracy of double feed detection deteriorates. Adding a high-performance DC-DC converter or regulator to the power supply circuit as a measure to suppress fluctuations in the power supply voltage will result in a significant cost increase.

The technique described in Patent Document 1 deals with aged deterioration, and cannot solve the problem of sudden decrease in accuracy due to the voltage fluctuation described above.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a detection device capable of detecting double feed even if there is a fluctuation in power supply voltage, and a control method thereof.

The double feed detection device according to the embodiment of the present invention is a double feed detection device for detecting double feed of a sheet transported along a transport path, and is opposed to the sheet in the transport path. It has an ultrasonic sensor including an ultrasonic transmitter and an ultrasonic receiver arranged in the above, and a sensor control unit that controls the ultrasonic sensor and outputs a determination result of whether or not it is a double feed. The sensor control unit is based on a drive unit that outputs a pulse train consisting of a set number of pulses to drive the ultrasonic transmitter and an output signal output from the ultrasonic receiver corresponding to the pulse train. It has a determination unit for determining whether or not it is a double feed, and a voltage fluctuation detection unit for detecting fluctuations in the voltage of the power supplied to the sensor control unit and the ultrasonic sensor. In response to the fluctuation of the voltage detected by the unit, the set number of pulses output by the drive unit or the timing of the pulse is changed , and the drive unit receives the voltage detected by the voltage fluctuation detection unit. When it is lower than the reference voltage range, the set number of the pulses is increased, and when it is higher than the reference voltage range, the set number of the pulses is decreased .

The control method according to the embodiment of the present invention is a control method of a double feed detection device for detecting double feed of a sheet transported along a transport path, and the double feed detection device is the same in the transport path. An ultrasonic sensor including an ultrasonic transmitter and an ultrasonic receiver arranged so as to face each other across a sheet, and a sensor control that controls the ultrasonic sensor and outputs a determination result of whether or not it is a double feed. The sensor control unit outputs a pulse train consisting of a set number of pulses to drive the ultrasonic transmitter, and outputs the pulse train from the ultrasonic receiver in response to the pulse train. Based on the output signal, it is determined whether or not the feed is double-fed, and the fluctuation of the voltage of the operating power supplied from the power supply is detected, and the pulse is set in response to the detected fluctuation of the voltage. The number of the pulses or the timing of the pulses is changed, and when the detected voltage is lower than the reference voltage range, the set number of the pulses is increased, and when the voltage is higher than the reference voltage range, the set number of the pulses is decreased .

According to the present invention, double feeding can be detected even if the power supply voltage fluctuates.

It is a figure which shows the outline of the structure of the image forming apparatus provided with the double feed detection apparatus which concerns on one Embodiment of this invention. It is a figure which shows the hardware composition of the image forming apparatus. It is a figure which shows the internal structure of an automatic document feeder and a scanner. It is a figure which shows typically the change by the sheet of the ultrasonic wave from the ultrasonic sensor. It is a figure which shows the relationship between the threshold value for discriminating double feed and the output of an ultrasonic sensor. It is a figure which shows the structure of the double feed detection device. It is a figure which shows the structure of the voltage fluctuation detection part in the double feed detection device. It is a figure which shows the example of the fluctuation of a power supply voltage. It is a figure which shows the example of the input / output of an ultrasonic sensor. It is a figure which shows the example of the timing of the fluctuation of a power supply voltage. It is a figure which shows the relationship between the number of pulses of the drive pulse signal input to an ultrasonic sensor, and the output. It is a figure which shows an example of the correction of the input / output of an ultrasonic sensor. It is a figure which shows another example of the correction of the input / output of an ultrasonic sensor. It is a figure which shows the example of the setting range of the set number N of pulses. It is a figure which shows the example of the processing flow in an image forming apparatus. It is a figure which shows another example of the structure of the voltage fluctuation detection part in a double feed detection device.

FIG. 1 shows an outline of the configuration of an image forming apparatus 1 provided with a double feed detection device 18 according to an embodiment of the present invention, FIG. 2 shows a hardware configuration of the image forming apparatus 1, and FIG. 3 shows an automatic original document. The internal configurations of the feeder 10 and the scanner 20 are shown, respectively.

The image forming apparatus 1 shown in FIG. 1 is an MFP (Multi-functional Peripheral) that integrates the functions of a copier, a printer, a facsimile machine, an image reader, and the like. The image forming apparatus 1 includes an automatic document feeder (ADF: Auto Document Feeder) 10, a flatbed type scanner 20, a printer unit 30, a paper feeding unit 40, an operation panel 60, and the like.

The automatic document feeder 10 is provided so as to be openable and closable as a cover that covers the platen glass of the scanner 20. The automatic document feeder 10 is provided with a double feed detection device 18. The configurations of the automatic document feeder 10 and the scanner 20 will be described in detail later.

The printer unit 30 forms an image on a sheet (recording paper) supplied from the paper feed unit 40. The method of image formation is an electrophotographic method. However, an inkjet method or another method may be used.

The paper feed unit 40 includes a plurality of paper feed cassettes for storing the recording paper, and the recording paper is fed out from the selected paper feed cassette by the pickup roller and supplied to the printer unit 30.

The operation panel 60 has a touch panel display that displays a screen for input operations by the user, and a key input unit in which hard keys and LEDs (light emitting diodes) are arranged, and outputs a signal corresponding to the input operations. ..

As shown in FIG. 2, the image forming apparatus 1 includes a main control unit 50 that is in charge of overall control of the image forming apparatus 1, a power supply circuit 70 that supplies electric power necessary for its operation to each portion of the image forming apparatus 1, and an automatic. It has an ADF control unit 100 that is in charge of controlling the document feeder 10.

In FIG. 3, the automatic document feeding device 10 includes a document tray 11, a transport mechanism 12, a transport path 13, a transport motor 14, an image sensor 15, a paper output tray 16, and the like.

The document tray 11 is provided with a plurality of mechanical sensors 19a and 19b for detecting the presence or absence of the sheet (original) 5. The output signals of the sensors 19a and 19b are input to the ADF control unit 100 (see FIG. 2), and are used for determining whether or not the sheet 5 is set, determining the document size, and the like.

The transport mechanism 12 transports a plurality of sheets 5 stacked on the document tray 11 one by one from the document tray 11 toward the reading position P1, and after passing through the reading position P1, the paper output tray. Transport to 16. The transport mechanism 12 includes a pickup roller 12a, a paper feed roller pair 12b, a plurality of feed roller pairs 12c, 12d, 12e, 12f, 12g, a transport guide forming the transport path 13, a sheet sensor 17a, 17b, and the like.

The pickup roller 12a takes out the top sheet 5 from the document tray 11. The paper feed roller pair 12b feeds the taken-out sheet 5 into the transport path 13. The feed roller pairs 12c to 12g are arranged at intervals along the transport path 13, transport the sheet 5 taken out from the document tray 11, pass through the reading position P1, and then eject the sheet 5 to the paper output tray 16. To do.

The sheet sensors 17a and 17b detect the presence or absence of the sheet 5 in the transport path 13. The sheet sensor 17a is arranged near the downstream side of the paper feed roller pair 12b, and the sheet sensor 17b is arranged near the upstream side of the feed roller pair 12c. Based on the output of the sheet sensor 17a, the ADF control unit 100 controls the timing of feeding (feeding) the sheets 5 to the transport path 13 so that the plurality of sheets 5 are conveyed at intervals.

When the fed sheet 5 passes through the reading position P1 between the feed roller pair 12d and the next feed roller pair 12e in the transport path 13, the image of the lower surface of the sheet 5 is captured by the image sensor 27 of the scanner 20. Read. Then, while the sheet 5 is moving from the feed roller pair 12e to the paper output tray 16, the image of the upper surface of the sheet 5 is read by the contact image sensor (CIS) 15.

The scanner 20 includes an image sensor 27 including a light source unit 22, a mirror unit 23, an imaging lens 26, and a CCD (Charge Coupled Device). The light source unit 22 has a light source 24 that irradiates the sheet 5 and a mirror 25a that guides the reflected light from the sheet 5 to the mirror unit 23. The mirror unit 23 has mirrors 25b and 25c that turn back the light incident from the light source unit 22 and incident it on the image sensor 27. The light source unit 22 and the mirror unit 23 are configured to be movable in parallel with the platen glass 21.

By the way, an ultrasonic sensor 80 for detecting double feeding of the sheet 5 conveyed along the conveying path 13 is arranged in the vicinity of the downstream side of the sheet sensor 17a in the automatic document feeder. The ultrasonic sensor 80 is a transmissive type, and includes a transmitter and a receiver which are arranged so as to face each other across the sheet 5 in the transport path 13 and transmit and receive ultrasonic waves.

Hereinafter, the configuration and operation of the image forming apparatus 1 will be further described with a focus on the function of detecting double feeding using the ultrasonic sensor 80.

FIG. 4 schematically shows the change of the ultrasonic wave emitted by the ultrasonic sensor 80 due to the sheet 5, and FIG. 5 shows the threshold value Vth for discriminating the double feed and the output values V80a and V80b of the ultrasonic sensor 80. The relationship with is shown.

The ultrasonic sensor 80 has a transmitter (transmitter) 81 and a receiver (receiver) 82. The transmitter 81 emits (transmits) ultrasonic waves in a direction inclined with respect to the transport direction M1 of the sheet 5. The receiver 82 is arranged directly in front of the transmitter 81 to receive ultrasonic waves. The ultrasonic sensor 80 outputs a signal according to the intensity of this reception.

As shown in FIG. 4A, the transmitter 81 transmits ultrasonic waves during the period in which the sheet 5 passes between the receiver 81 and the receiver 82. The transmitted ultrasonic waves are divided into a transmitted wave that passes through the sheet 5 and a reflected wave that is reflected on the surface of the sheet 5 (the interface with the atmosphere). Since the receiver 82 receives only the transmitted wave, the reception intensity is weaker than that without the sheet 5.

As shown in FIG. 4B, when a plurality of sheets 5, 5b are overlapped and transported between the transmitter 81 and the receiver 82 (during double feeding), the sheet 5b on the side closer to the transmitter 81 Ultrasonic waves are reflected on the surface of the sheet 5 and also on the surface of the sheet 5 on the far side. In addition, ultrasonic waves are attenuated when passing through the sheets 5 and 5b. Therefore, the reception strength is weaker than that in the case where one sheet 5 passes through as shown in FIG. 4A (single feed). That is, as shown in FIG. 5, there is a difference in the output values V80a and V80b of the ultrasonic sensor 80 between the single feed and the double feed. The output value V80a at the time of single feed is larger than the output value V80b at the time of double feed.

Therefore, by setting an appropriate value between the output value V80a and the output value V80b to the threshold value Vth and comparing the output value V80 of the ultrasonic sensor 80 with the threshold value Vth, the double feed is performed. It can be determined whether or not. When the output value V80 of the ultrasonic sensor 80 is smaller than the threshold value Vth, it may be determined that the double feed is performed, and when it is larger than the threshold value Vth, it may be determined that the double feed is not performed.

FIG. 6 shows the configuration of the double feed detection device 18, FIG. 7 shows the configuration of the voltage fluctuation detection unit 88 in the double feed detection device 18, and FIG. 8 shows an example of fluctuations in the power supply voltage Vs. ..

In FIG. 6, the double feed detection device 18 includes the ultrasonic sensor 80 described above and a sensor control unit 85 that controls the ultrasonic sensor 80 and outputs a determination result D1 of whether or not the double feed is performed. .. The ultrasonic sensor 80 and the sensor control unit 85 are supplied with power required for their respective operations from the power supply circuit 70.

The transmitter 81 of the ultrasonic sensor 80 has a piezoelectric element 811 for transmitting ultrasonic waves, and the receiver 82 has a piezoelectric element 821 for converting ultrasonic waves into an electric signal and an amplification for amplifying the electric signal. It has a circuit 822.

The sensor control unit 85 includes an oscillation circuit 86, a determination unit 87, a voltage fluctuation detection unit 88, a basis weight acquisition unit 89, and the like.

The oscillation circuit 86 is a drive unit that drives the transmitter 81 by outputting a drive pulse signal S1 including a pulse train PL composed of a set number of pulses.

The determination unit 87 determines whether or not the double feed is performed based on the output signal S80 output from the receiver 82 corresponding to the pulse train PL, and notifies the ADF control unit 100 of the determination result D1. When the determination unit 87 determines that the double feed is performed, the ADF control unit 100 controls the transport mechanism 12 so as to stop the transport of the sheet 5, and notifies the main control unit 50 of the occurrence of the double feed, for example. To do. The main control unit 50 causes the operation panel 60 to display a message prompting the user to remove the sheet 5 from the transport path 13.

The voltage fluctuation detection unit 88 detects fluctuations in the voltage of the electric power supplied from the power supply circuit 70, that is, the output voltage of the power supply circuit 70 (hereinafter, referred to as “power supply voltage Vs”). As shown in FIG. 7, the voltage fluctuation detection unit 88 predicts fluctuations in the power supply voltage Vs of the power supply circuit 70 based on the operation modes of the voltage measurement unit 881 that measures the power supply voltage Vs in real time and the image forming apparatus 1. It has an operation mode monitoring unit 882.

In the operation mode monitoring unit 882, for example, depending on the operation mode such as the standby mode, the print mode, the continuous print mode, and the double-sided print mode in the image forming apparatus 1, the size of the recording paper, the presence or absence of automatic reading and post-processing, and the like. , The operation timing of the motor and the like is predicted, thereby predicting the fluctuation of the power supply voltage Vs.

In this way, the voltage fluctuation detection unit 88 can detect the presence / absence and the amount of fluctuation of the power supply voltage Vs by actually measuring the power supply voltage Vs or predicting it based on the operation mode.

The basis weight acquisition unit 89 acquires the basis weight of the sheet 5 as an index of ultrasonic transmission. By adjusting parameters such as the threshold value Vth or the gain of the amplifier circuit 82 according to the basis weight, the reliability of the determination of double feed can be improved. The basis weight acquisition unit 89 inquires of the main control unit 50 via the ADF control unit 100 about the basis weight input by the user of the image forming apparatus 1 using, for example, the operation panel 60. If there is no input by the user, the main control unit 50 notifies the basis weight acquisition unit 89 of the default basis weight. The double feed detection device 18 determines the parameter change range according to the basis weight of the sheet 5 acquired by the basis weight acquisition unit 89.

The power supply circuit 70 that supplies electric power to the double feed detection device 18 also includes a motor group 140 including the motor 14, a fan 165, an LED group 160 of the operation panel 60, and a sensor group 170 including the seat sensors 17a and 17b. Supply power.

Therefore, the operation of the supply destination other than the double feed detection device 18 affects the power supply voltage Vs. For example, at the time when the motor 14 of the automatic document feeder 10 starts to rotate, as shown in FIG. 8A, a larger motor drive current I flows than in the steady state where the motor 14 rotates at a constant speed. That is, the load becomes heavy when viewed from the power supply circuit 70. At this time, as shown in FIG. 8B, the power supply voltage Vs temporarily decreases. At regular times, the motor drive current I is substantially constant, and the power supply voltage Vs is maintained at the rated voltage Vs0. At the time of braking to stop the rotation, the motor drive current I sharply decreases. At this time, the power supply voltage Vs temporarily increases.

When the power supply voltage Vs fluctuates in this way, the transmission intensity of ultrasonic waves in the ultrasonic sensor 80 fluctuates, and the value of the output signal S80 of the ultrasonic sensor 80 becomes low or high accordingly. Therefore, the determination result of the double feed by the determination unit 87 may be incorrect.

Therefore, the double feed detection device 18 changes the set number N of pulses output by the oscillation circuit 86 or the timing of the pulses in response to the fluctuation of the power supply voltage Vs detected by the voltage fluctuation detection unit 88. Various parameters can also be corrected. The details are as follows.

FIG. 9 shows an example of input / output of the ultrasonic sensor 80.

In the actual determination of double feeding, the pulse train PL is transmitted a plurality of times with a predetermined interval T2 during the period in which the sheet 5 passes through the arrangement position of the ultrasonic sensor 80. That is, a burst signal including a plurality of pulse trains PL is input to the transmitter 81 as the drive pulse signal S1, and ultrasonic waves are intermittently transmitted. The frequency of each pulse train PL is, for example, about 300 kHz, and the maximum number of pulses of each pulse train PL is about 15. The interval T2 is about several ms, and the number of transmissions of the pulse train PL is, for example, about 10 to 20.

Each time the pulse train PL is transmitted, the peak value of the output signal S80 of the receiver 82 is read, and it is determined whether or not the double transmission is performed based on the reception results for a plurality of times obtained. For example, if the average value of the peak values is equal to or less than the threshold value Vth, it may be determined to be double feed, or if the number of times the peak value is equal to or less than the threshold value Vth is equal to or greater than a predetermined number, it is determined to be double feed. You may.

When the ultrasonic sensor 80 is used, several hundreds determined by the clearance dimension between the transmitter 81 and the receiver 82 from the start of transmission of one pulse train PL to the completion of reception corresponding to the pulse train PL. A time T3 of about several ms from μs is required. This time T3 is a combination of the reception delay period T4 from the start of transmission until the vibration of the sheet 5 due to ultrasonic waves starts to be transmitted to the receiver 82 and the reception period T5 from the start of the vibration of the sheet 5 to the convergence. Is the length of. The next pulse train PL is transmitted after the margin time T6 has elapsed from the end of the reception period T5.

The double feed detection device 18 partially changes the process of determining double feed according to the relationship between the time T3, the timing at which the power supply voltage Vs fluctuates, and the continuous time.

FIG. 10 shows an example of the timing of fluctuation of the power supply voltage Vs.

In FIG. 10A, a sudden fluctuation of the power supply voltage Vs occurs during the transmission period T1 for transmitting ultrasonic waves, and the fluctuation ends before the start of the reception period T5. When such a short-time fluctuation occurs, the power supply voltage Vs returns to the rated voltage Vs0 immediately after the fluctuation is detected, so it is difficult to deal with the fluctuation by correcting the transmission / reception parameters. is there. Therefore, in order to prevent erroneous determination of double feed, the reception result in this case is excluded from the target of determination of double feed. In FIG. 10A, it is assumed that fluctuation occurs at the time of transmission, but even if it occurs at the time of reception, the reception result is similarly excluded from the target of the determination of double feed.

In FIG. 10B, the power supply voltage Vs continues to be higher than the rated voltage Vs0 over the transmission period T1 and the reception period T5 corresponding to one pulse train PL. In this case, it is possible to deal with the fluctuation by correcting the transmission / reception parameters. Therefore, in order to prevent erroneous determination of double transmission, the transmission timing or transmission / reception parameters are corrected.

FIG. 11 shows the relationship between the number of pulses of the drive pulse signal S1 input to the ultrasonic sensor 80 and the reception intensity.

As shown in FIG. 11A, when the number of pulses of the drive pulse signal S1 is small, the transmitted energy is small, so that the sheet 5 cannot be vibrated. That is, ultrasonic waves cannot pass through the sheet 5. In order for ultrasonic waves to pass through the sheet 5, the number of pulses in the pulse train PL needs to be set to a predetermined value or more determined by the type (basis weight) of the sheet 5. When the value is set to a predetermined value or more, the amplitude of the output of the receiver 82 increases as the number of pulses increases. Therefore, by setting the number of pulses so as to cancel the increase / decrease of the peak value of the pulse train PL due to the fluctuation of the power supply voltage Vs, it is possible to obtain the same transmission / reception state as when there is no fluctuation and correctly determine the presence / absence of double feeding. ..

From this, the oscillation circuit 86 increases the set number of pulses N when the power supply voltage Vs detected by the voltage fluctuation detection unit 88 is lower than the reference voltage range, and increases the set number of pulses N when it is higher than the reference voltage range. To reduce. The reference voltage range can be a certain range centered on the rated voltage Vs0, for example, a range of ± a% centered on the rated voltage Vs0, or a range of ± α. As a, for example, it can be in the range of 0 to 10. In this case, specifically, the range may be ± 1%, ± 3%, ± 5%, ± 10%, or the like. Further, when the power supply voltage Vs is, for example, DC power of 24 volts, α can be in the range of 0 to 2.4, for example. In this case, specifically, the range may be ± 0.24 volt, ± 1 volt, ± 2 volt, or the like.

FIG. 12 shows an example of input / output correction of the ultrasonic sensor 80.

In FIG. 12, the power supply voltage Vs is higher than the rated voltage Vs0 during the period from the transmission of the first pulse train PL1 to the completion of the reception corresponding to the second pulse train PL2. However, the power supply voltage Vs returns to the rated voltage Vs0 before t7 when the third pulse train PL2 is transmitted.

When such a transition of the power supply voltage Vs is predicted based on the operation mode of the image forming apparatus 1, the set number N of the pulses of the first and second pulse trains PL1 and PL2 is set to the number N in the normal state (for example, 8). ) Is less than (6 in the figure). For the third and subsequent pulse trains PL3, the set number N of pulses is the normal number. That is, no correction is performed.

Instead of reducing the set number N of pulses of the pulse trains PL1 and PL2, the gain of the amplifier circuit 822 of the receiver 82 is lowered, the AD conversion rate of the output voltage V80 is lowered, or the threshold value Vth is raised. Corrections such as lowering the read value of the output voltage V80 by the determination unit 87 may be performed.

FIG. 13 shows another example of input / output correction of the ultrasonic sensor 80.

In FIG. 13A, the power supply voltage Vs is higher than the rated voltage Vs0 from before the transmission of the first pulse train PL1 to the time point t8 in the middle of transmission of the second pulse train PL2. That is, if the first pulse train PL1 is transmitted and then the second pulse train PL2 is transmitted at the default interval T2, the influence of the fluctuation of the power supply voltage Vs appears on the pulse train PL2.

Therefore, as shown in FIG. 13B, the second pulse train PL2 is transmitted at the timing of providing the interval T2b longer than the default interval T2, that is, at the timing delayed from the normal. The interval between subsequent pulse trains may be the default interval T2.

Corrections such as reducing the set number N of pulses may be performed for the first pulse train PL1, but in the example of FIG. 13, transmission of the first pulse train PL1 is stopped. Therefore, the determination as to whether or not the double feed is performed is performed based on the reception result corresponding to the second and subsequent pulse trains PL2 and PL3.

According to the example of FIG. 13, only by shifting the transmission timing of the pulse trains PL2 and PL3 with respect to the normal timing, the power supply voltage Vs in the determination of double feed is performed without correcting the set number of pulses N or the transmission / reception parameter. It is possible to eliminate the influence of fluctuations in.

FIG. 14 shows an example of a setting range of the set number N of pulses.

In FIG. 14A, the setting range of the set number N of pulses is in the range of 4 to 10. The reference set number Nk, which is the set number N in the normal time when the power supply voltage Vs is within the reference voltage range BV, is set to "7". Here, the reference voltage range BV is set as a minute range centered on the rated voltage Vs0. However, as described above, the reference voltage range BV can be set in various ways.

When the power supply voltage Vs exceeds the reference voltage range BV, the set number N of pulses is set to 4 to 6 according to the power supply voltage Vs (drive condition 1), and when it is smaller than the reference voltage range BV, it is set. The number N is 8 to 9 depending on the power supply voltage Vs (drive condition 2).

When changing the set number N of pulses, the set number N of pulses after the change is multiplied by the reciprocal 1 / Kv of the fluctuation ratio Kv of the power supply voltage Vs to the reference set number Nk, which is the set number of pulses before the change ( It can be an integer value rounded up to the nearest whole number (Nk / Kv). That is, the set number N is determined so that the product of the power supply voltage Vs and the set number N of the pulses to be transmitted is always equal to or more than a predetermined value.

In FIG. 14B, the setting range of the number of pulses N is in the range of 2 to 12. That is, as the sheet 5 suitable for the automatic document feeder 10, various sheets including thinner and thicker sheets than in the case of FIG. 14A are assumed.

The reference set number Nk is set to "6". When the power supply voltage Vs exceeds the reference voltage range BV, the set number N is set to 2 to 5 according to the power supply voltage Vs (drive condition 1), and when it is smaller than the reference voltage range BV, the set number N Is 7 to 12 depending on the power supply voltage Vs (drive condition 2).

That is, in FIG. 14, the set number N above the diagonal line shown by the chain line is selected. As a result, even when the power supply voltage Vs is lower than the reference voltage range BV, the minimum energy required for passing through the sheet 5 can be secured.

FIG. 15 shows an example of the processing flow in the image forming apparatus.

The transfer of the sheet 5 is started (# 101), and the fluctuation of the power supply voltage Vs is detected (# 102). When a fluctuation during transmission or reception of ultrasonic waves is detected (YES in # 103), the reception result is excluded from the target of the determination of double feeding (# 104).

If the fluctuation is expected to converge by the time the ultrasonic waves are transmitted (YES in # 105), the ultrasonic waves are transmitted in a burst period (cycle of transmission of the pulse train PL) in which the interval T2 between the pulse trains is changed (#). 106).

If the time required for the fluctuation of the power supply voltage Vs to converge is longer than the burst period (YES in # 107), the set number of pulses N or the transmission / reception processing parameter is corrected according to the variable amount (# 108). ..

In other cases (NO at # 107), the ultrasonic wave is transmitted after waiting for the fluctuation to converge (# 109). Then, based on the obtained reception result, it is determined whether or not the double feed is performed (# 110).

FIG. 16 shows another example of the configuration of the voltage fluctuation detection unit 88b in the double feed detection device 18. The voltage fluctuation detection unit 88b has a load condition monitoring unit 883. The load state monitoring unit 883 monitors the operating state of the load (for example, the motor group 140) connected to the power supply circuit 70 and predicts the fluctuation of the output voltage (power supply voltage Vs) of the power supply circuit 70. For example, as in the operation mode monitoring unit 882 described above, the operation timing of the motor or the like is predicted based on the operation mode of the device or other factors, and the fluctuation of the power supply voltage Vs is predicted.

According to the above embodiment, the double feed of the sheet 5 can be detected even if the power supply voltage Vs fluctuates.

In the above-described embodiment, the upper and lower limits of the correction values of the parameters such as the amplification factor of the amplifier circuit 822 of the receiver 82 are determined based on the fact that the smaller the basis weight of the sheet 5 is, the easier it is for ultrasonic waves to pass through. Can be left. As a result, it is possible to prevent the circuit components from being destroyed by setting the amplification factor too high, and it is possible to prevent the output level of the receiver 82 from becoming too high and the double feed detection accuracy from being lowered.

When the set number N of pulses is corrected, the time from the reception of ultrasonic waves to the convergence of vibrations is different from the normal time, so the period T2 is changed accordingly. That is, when the set number N is increased, the period T2 is lengthened, and when the set number N is decreased, the period T2 is shortened. Specifically, when the frequency of the pulse train PL is 300 kHz, the transmission period T1 becomes longer or shorter by 3.33 μs by increasing or decreasing one pulse, and the vibration time becomes longer on the receiving side by a time proportional to this 3.33 μs. Or get shorter. Therefore, the period T2 is increased or decreased by the time required for the vibration convergence on the receiving side.

The pulse width or crest value of the pulse trains PL, PL1, PL2, PL2b, PL3 may be modulated. That is, the configuration of the oscillation circuit 86, the output pulse, the waveform of the pulse train PL, and the like may differ depending on the operating principle and structure of the ultrasonic sensor 80. In the waveform of modulated pulses, it is necessary to distinguish the number and timing of pulses according to the modulation method.

In the above-described embodiment, if the fluctuation amount of the power supply voltage Vs is less than or equal to the predetermined range, only the parameters on the receiving side are corrected, and if it is equal to or more than the predetermined range, the set number N of pulses on the transmitting side is corrected. It may be done and the parameters on the receiving side may be corrected as necessary. Correcting the parameters on the receiving side has a smaller effect when there is a variation in the receiving sensitivity than correcting the set number N of pulses. Therefore, when the influence of the fluctuation of the power supply voltage Vs can be eliminated only by correcting the parameters on the receiving side, the detection accuracy of the double feed can be kept high by correcting only the parameters on the receiving side.

In the above-described embodiment, the case of detecting the double feeding of the sheet 5 (manuscript) conveyed by the automatic document feeding device 10 has been given as an example. Not limited to this, the present invention can also be applied to detect double feeding of a sheet (recording paper) different from the sheet 5 conveyed from the paper feeding unit 40 to the printer unit 30.

The configuration of all or each part of the image forming apparatus 1, the automatic document feeder 10, and the double feed detecting apparatus 18, the content, order, or timing of processing, the configuration of the ultrasonic sensor 80, and the like are in accordance with the gist of the present invention. Can be changed as appropriate.

1 Image forming device 5 Sheet 14 Motor 18 Double feed detection device 30 Printer unit 70 Power supply circuit (power supply unit)
80 Ultrasonic sensor 81 Transmitter (ultrasonic transmitter)
82 Receiver (Ultrasonic receiver)
85 Sensor control unit 86 Oscillation circuit (drive unit)
87 Judgment unit 88,88b Voltage fluctuation detection unit 89 Basis weight acquisition unit 113 Transport path 881 Voltage measurement unit 882 Operation mode monitoring unit 883 Load status monitoring unit D1 Judgment result PL, PL1, PL2, PL2b, PL3 Pulse train S80 Output signal Vs Power supply Voltage (output voltage of power supply)
BV reference voltage range

Claims (14)

It is a double feed detection device for detecting double feed of sheets transported along a transport path.
An ultrasonic sensor including an ultrasonic transmitter and an ultrasonic receiver arranged so as to face each other across the sheet in the transport path.
It has a sensor control unit that controls the ultrasonic sensor and outputs a determination result of whether or not it is double feed.
The sensor control unit
A drive unit that outputs a pulse train consisting of a set number of pulses to drive the ultrasonic transmitter, and
A determination unit that determines whether or not double feed is performed based on the output signal output from the ultrasonic receiver corresponding to the pulse train.
It has a sensor control unit and a voltage fluctuation detection unit that detects fluctuations in the voltage of electric power supplied to the ultrasonic sensor.
In response to variation of the voltage detected by the voltage variation detecting unit, as well as changes the setting number or timing of pulses of the output pulse of the drive unit, the drive unit is detected by the voltage variation detecting unit When the voltage is lower than the reference voltage range, the set number of the pulses is increased, and when the voltage is higher than the reference voltage range, the set number of the pulses is decreased.
A double feed detection device characterized by this. When changing the set number of pulses, the product of the detected voltage and the set number of pulses is always set to a predetermined value or more.
The double feed detection device according to claim 1 . When changing the set number of pulses, the set number N of the pulses after the change is multiplied by the reciprocal 1 / Kv of the voltage fluctuation ratio Kv to the reference set number Nk, which is the set number of the pulses before the change. The integer value after the decimal point of (Nk / Kv) is rounded up.
The double feed detection device according to claim 1 or 2 . The drive unit repeats the pulse train at a set cycle and outputs the pulse train to the ultrasonic transmitter.
When the set number of the pulses is increased, the period of the pulse train is increased accordingly.
The double feed detection device according to any one of claims 1 to 3 . The voltage fluctuation detection unit is
It has a voltage measuring unit that measures the output voltage of the power supply unit that supplies power in real time.
The set number of the pulses is determined based on the output voltage measured by the voltage measuring unit.
The double feed detection device according to any one of claims 1 to 4 . When the voltage fluctuation is detected by the voltage fluctuation detection unit during transmission by the ultrasonic transmitter or reception by the ultrasonic receiver, the sensor control unit outputs a determination result of double feed. do not do,
The double feed detection device according to claim 5 . The voltage fluctuation detection unit is
It has a load condition monitoring unit that monitors the operating state of a load connected to the power supply unit that supplies electric power and predicts fluctuations in the output voltage of the power supply unit.
The double feed detection device according to any one of claims 1 to 3 . The drive unit repeats the pulse train at a set cycle and outputs the pulse train to the ultrasonic transmitter.
When the voltage fluctuation detection unit predicts the fluctuation of the output voltage of the power supply unit, the output of the pulse train from the drive unit is stopped during the period in which the fluctuation is predicted.
The double feed detection device according to claim 7 . The drive unit repeats the pulse train at a set cycle and outputs the pulse train to the ultrasonic transmitter. The sensor control unit predicts the voltage fluctuation by the voltage fluctuation detection unit, and the fluctuation is predicted by the voltage fluctuation detection unit. When the predicted period is longer than the period, the parameter of the determination unit is changed according to the magnitude of the fluctuation.
The double feed detection device according to claim 7 . The determination unit compares the amplitude of the output signal output from the ultrasonic receiver corresponding to the pulse train with the threshold value, and double feeds when the amplitude of the output signal is equal to or less than the threshold value. Judging that
When changing the parameters of the determination unit according to the magnitude of the fluctuation, the threshold value is changed.
The double feed detection device according to claim 9 . It has a basis weight acquisition unit that acquires the basis weight of the sheet.
The change range of the parameter is determined according to the basis weight of the sheet acquired by the basis weight acquisition unit.
The double feed detection device according to claim 9 or 10 . The double feed detection device according to any one of claims 1 to 11 .
A power supply unit that supplies electric power to the sensor control unit and the ultrasonic sensor,
A motor that is a drive source for transporting the sheet along the transport path and is rotated by being supplied with electric power from the power supply unit.
It has a printer unit that forms an image on the sheet or another sheet.
An image forming apparatus characterized in that. The voltage fluctuation detection unit has an operation mode monitoring unit that predicts fluctuations in the output voltage of the power supply unit based on the operation mode of the image forming apparatus.
The image forming apparatus according to claim 12 . It is a control method of a double feed detection device for detecting double feed of a sheet transported along a transport path.
The double feed detection device is
An ultrasonic sensor including an ultrasonic transmitter and an ultrasonic receiver arranged so as to face each other across the sheet in a transport path.
A sensor control unit that controls the ultrasonic sensor and outputs a determination result of whether or not it is double feed.
Have,
The sensor control unit
A pulse train consisting of a set number of pulses is output to drive the ultrasonic transmitter, and whether or not double feed is performed based on an output signal output from the ultrasonic receiver corresponding to the pulse train. At the same time as determining, the fluctuation of the voltage of the operating power supplied from the power supply is detected, and the set number of the pulses or the timing of the pulse is changed and detected in response to the detected fluctuation of the voltage. When the voltage is lower than the reference voltage range, the set number of the pulses is increased, and when the voltage is higher than the reference voltage range, the set number of the pulses is decreased.
A control method for a double feed detection device.

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