JP4558922B2 - Double feed detection device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a double feed detection device that detects double feed of a sheet material such as printing paper, and an image forming apparatus such as a printing machine, a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
Conventionally, a multifeed detection device is used in a printing machine, a copying machine, a printer, a facsimile machine, etc., for conveying various sheet materials such as printing paper, and is disclosed in Japanese Patent Laid-Open No. 58-212539, There are those described in Japanese Patent Laid-Open No. Hei 8-48439.
[0003]
Japanese Patent Laid-Open No. 58-212539 discloses a multifeed detecting device that detects a sheet material by a light emitting element and a light receiving element that are arranged across a passage through which the sheet material is conveyed, and detects the first sheet material. Amplifies a signal proportional to the amount of transmitted light of the sheet material obtained by the light receiving element during conveyance, averages it for a certain period of time with an integration circuit, holds the voltage in a capacitor with a sample hold circuit, and integrates the above during conveyance of the second sheet material The output voltage of the circuit is compared with the voltage held by the sample-and-hold circuit by a comparator to determine the double feeding of the sheet material.
[0004]
JP-A-8-48439 discloses a sheet material detected by a light emitting element and a light receiving element arranged with a passage through which the sheet material is conveyed, and a transmitted light amount of the sheet material obtained by the light receiving element. After the signal proportional to is amplified, it is compared with a reference voltage by a comparator to determine whether the sheet material is double-fed.
[0005]
[Problems to be solved by the invention]
The amount of transmitted light of the sheet material is not constant. For example, if the light transmittance of a paper weighing 60 kg often used in a printing press is 30%, for example, the light transmittance of a paper weighing 180 kg used in the printing press is 2 It becomes very small with 7%. Therefore, when detecting double feeding from a thin sheet to a thick sheet, an optical signal obtained by amplifying a signal proportional to the transmitted light amount of the sheet obtained by the light receiving element must be a relatively small value when the thick sheet is conveyed. I don't get it.
[0006]
In the double feed detection device described in the above-mentioned Japanese Patent Application Laid-Open No. 58-212539, the small optical signal is held by the sample hold circuit, and the held voltage is used for comparison with the optical signal by the comparator. It is easily affected by offset voltage error, and erroneous paper double feeding is detected (detected as double feeding when paper is not double fed, or missed even though paper is double feeding) There is a high possibility of malfunction.
[0007]
Further, the voltage held in the capacitor by the sample and hold circuit is charged and discharged by a leak current having a small but substantially constant characteristic, and the voltage value gradually changes. For example, even if there is the same change of 0.1V in the voltage held in the capacitor by the sample hold circuit, the voltage of 10V only changes to 9.9V, but the voltage of 1V changes to 0.9V. . Therefore, particularly when the paper is a thick paper, the reference voltage changes, and the possibility of performing erroneous double feed detection is further increased.
[0008]
An object of the present invention is to provide a double feed detection device and an image forming apparatus that can reliably detect double feed from a sheet material having a high light transmittance to a sheet material having a low light transmittance.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is provided with a sheet material detection sensor that detects a sheet material that has a light emitting element and a light receiving element and is conveyed through a passage, and outputs an optical signal from the light receiving element. In a double feed detection device that detects double feed of the sheet material in comparison with a threshold value, a first comparator that compares an optical signal from the light receiving element with a reference voltage, and a signal from the first comparator An integration unit that performs charging / discharging according to the magnitude of the optical signal and the reference voltage, and a voltage-current conversion unit that causes a current proportional to the output voltage of the integration unit to flow through the light emitting element are provided.
[0010]
According to a second aspect of the present invention, in the double feed detection device according to the first aspect of the present invention, a switching unit is provided in front of the first comparator to switch a charging / discharging current of the integrating unit.
[0011]
According to a third aspect of the present invention, in the double feed detection device according to the first aspect, a peak hold circuit that holds a peak value of the optical signal, a voltage dividing circuit that divides an output voltage of the peak hold circuit, A second comparator that compares the output voltage of the pressure circuit with the optical signal and outputs a sheet material detection signal, generates a predetermined timing signal based on the sheet material detection signal, and operates according to the timing signal To do.
[0012]
The invention according to claim 4 includes the double feed detection device according to claim 1, 2, or 3, and detects double feed of the sheet material by the double feed detection means.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 shows an outline of an embodiment of the present invention. This embodiment is an example of an image forming apparatus comprising a stencil printing machine. A sheet feeding device 1 as a sheet material supply device calls a printing sheet 2 by a calling roller 3 and feeds the printing sheet 2 to a feed roller pair 6 one by one by a separation roller 4 and a separation pad 5. The original plate is made by a plate making apparatus (not shown) and mounted on the outer peripheral surface of the printing drum 7. The printing drum 7 is rotated clockwise by a driving unit (not shown) and the impression cylinder 8 is rotated counterclockwise.
[0014]
The printing paper is supplied to the original on the printing drum 7 by the feed roller 6, and the leading end is held by an openable / closable paper clamper provided on the impression cylinder 7. The ink supply device in the printing drum 7 supplies ink to the original plate on the printing drum 7 through the printing drum 7, and the original image is printed on the printing paper on the impression cylinder 8 at the nip portion between the printing drum 7 and the impression cylinder 8. The This printing paper is separated from the impression cylinder 8 by the release of the paper clamper by the cam and discharged to a paper discharge device (not shown).
[0015]
Further, a light emitting element 9 and a light receiving element 10 constituting a print sheet detection sensor as a sheet material detection sensor are arranged in front of the feed roller 6 in the path through which the print sheet is conveyed, with the path interposed therebetween. The light emitting element 9 emits light to the light receiving element 10 through the path, and the light receiving element 10 receives light incident from the light emitting element 9 through the path or light incident from the light emitting element 9 through the printing paper. To do. For example, a light emitting diode is used as the light emitting element 9, and a phototransistor is used as the light receiving element 10, for example.
[0016]
FIG. 1 shows a double feed detection device of this embodiment.
The phototransistor as the light receiving element 10 generates a photocurrent proportional to the amount of incident light, and this photocurrent is converted into a voltage by the resistor 11. This voltage is amplified with a predetermined gain by the non-inverting amplifier 12 to become an optical signal 13. The optical signal 13 is compared with a first reference voltage 16 (8.0 V in this embodiment) selected by the analog switch (analog SW) 15 in the comparator 14 at a predetermined timing in the print standby state. At this time, the D flip-flop 22 is off, and the analog switch 15 selects the first reference voltage 16 by the low signal FF3 from the D flip-flop 22. Here, the analog switch 15 constitutes switching means for switching the charging / discharging current of the CR integration circuit 18 by switching the reference voltage.
[0017]
The comparison result voltage (high or low voltage) of the comparator 14 passes through the analog switch 17 in the ON state and is input to a CR integration circuit 18 constituted by a resistor and a capacitor as integration means. When the optical signal 13 is lower than the first reference voltage 16, a high voltage is output from the comparator 14, and the capacitor of the CR integration circuit 18 is charged. Conversely, when the optical signal 13 is higher than the first reference voltage 16, a low voltage is output from the comparator 14, and the capacitor of the CR integration circuit 18 is discharged. Here, the analog switch 17 is turned on by the SH timing signal 32 from the timing generation circuit 31 at a predetermined timing in the print standby state.
[0018]
The output voltage of the CR integration circuit 18 is inputted as a SH voltage 21 to a voltage / current conversion (V / I conversion) circuit 20 including a field effect transistor 19 as a voltage / current conversion means, and a current corresponding to the SH voltage 21 is a light emitting element 9. As a light emitting diode flows. The light emission amount of the light emitting element 9 is substantially proportional to the current flowing through the light emitting element 9.
[0019]
As described above, when the optical signal 13 is lower than the first reference voltage 16, the capacitor of the CR integration circuit 18 is charged, and the SH voltage 21 gradually increases. For this reason, the light emission quantity of the light emitting element 9 increases, and the optical signal 13 becomes large. As a result, the optical signal 13 becomes higher than the first reference voltage 16, the capacitor of the CR integration circuit 18 is discharged, and the SH voltage 21 gradually decreases. By repeating such an operation, the optical signal 13 is balanced at a voltage substantially equal to the first reference voltage 16. Therefore, the comparator 14, the analog switch 17, the CR integration circuit 18, and the voltage-current conversion circuit 20 constitute a negative feedback circuit as an auto gain control circuit (AGC circuit) that controls the optical signal 13 to a constant voltage.
[0020]
In this embodiment, the print signal 23 is input from the control system (CPU) of the printing press main body to the D flip-flop 22 and the D flip-flop 22 is set, so that the double feed detection circuit is set in an operable state. . Along with this, the analog switch 15 is turned off by the high output signal of the D flip-flop 22, and charging / discharging of the capacitor of the CR integration circuit 18 is stopped. Since the leakage current from the CR integration circuit 18 to the peripheral circuit is very small, the SH voltage 21 is kept constant. Therefore, the amount of light emitted from the light emitting element 9 does not change, and as a result, the optical signal 13 does not change near the first reference voltage 16.
[0021]
With this paper feeding operation, the printing paper passes through the gap between the light emitting element 9 and the light receiving element 10. At this time, the amount of light emitted from the light emitting element 9 does not change, but the amount of light transmitted from the light emitting element 9 through the printing paper to the light receiving element 10 decreases, and the optical signal 13 decreases. The voltage obtained by dividing the voltage of the optical signal 13 held in the peak hold circuit 24 by the voltage dividing circuit including the resistors 25 and 26 and the optical signal 13 are compared by the comparator 27, and the voltage of the optical signal 13 is divided by the voltage dividing circuit. When the voltage becomes lower than the voltage, the comparator 27 outputs a paper signal 28 as a sheet material detection signal. The paper signal 28 is a signal indicating a state in which the printing paper is passing between the light emitting element 9 and the light receiving element 10.
[0022]
The timer 29 is triggered by the leading edge of the paper signal 28 to start a time measuring operation, and generates a first timer signal having a certain time width (20 ms in this embodiment). Next, the timer 30 is triggered at the trailing edge (falling edge) of the first timer signal from the timer 29 to start a time measuring operation, and generates a second timer signal having a certain time width (20 ms in this embodiment). The first timer signal from the timer 29 and the second timer signal from the timer 30 are input to the timing generation circuit 31.
[0023]
The timing generation circuit 31 sets the SH timing signal 32 to high at a predetermined timing in the print standby state, sets the SH timing signal 32 to low during the input by the print signal 23, and inputs it by the second timer signal from the timer 30. The SH timing signal 32 is once set high. Accordingly, the analog switch 17 which has been once turned off by the print signal 23 is turned on only during the period of the second timer signal.
[0024]
The timing generation circuit 31 generates a signal CK03 from the paper signal 28, and the D flip-flop 22 latches the print signal 23 by the signal CK03 from the timing generation circuit 31 and outputs a signal FF3. The analog switch 15 selects the second reference voltage 33 by the high signal FF 3 from the D flip-flop 22, and the optical signal 13 is compared with the second reference voltage 33 selected by the analog switch 15 in the comparator 14. Therefore, negative feedback control is performed so that the optical signal 13 is in the vicinity of the second reference voltage 33.
[0025]
Specifically, when the light from the light emitting element 9 passes through the printing paper and enters the light receiving element 10, the amount of light received by the light receiving element 10 is greatly reduced, and light emission is performed to compensate for the decrease in the amount of received light. The amount of light emitted from the element 9 is greatly shifted in the increasing direction. This is that the SH voltage 21 is increased. Although the light transmittance of the printing paper differs depending on the weighing and color of the printing paper, the SH voltage 21 is increased or decreased, and the optical signal 13 is controlled in the vicinity of the second reference voltage 33.
[0026]
When the period of the second timer signal from the timer 30 elapses, the SH timing signal 32 from the timing generation circuit 31 goes low, the analog switch 17 is turned off, and the SH voltage 21 is held in the CR integration circuit 18. That is, the light emitting element 9 continues to emit light with a constant light amount even after the printing paper passes between the light emitting element 9 and the light receiving element 10.
[0027]
When the second printing paper (the printing paper that has been passed through second) passes between the light emitting element 9 and the light receiving element 10, the operation of the peak hold circuit 24, the resistors 25 and 36, and the comparator 27 as described above. As a result, a paper signal 28 is generated. As described above, since the amount of light emitted from the light emitting element 9 does not change, the second printing paper is not double-fed (a state where only one printing paper passes between the light emitting element 9 and the light receiving element 10). If so, the optical signal 13 is controlled in the vicinity of the second reference voltage 33. If the second printing paper is in a double feed state (a state where two or more printing papers overlap and pass between the light emitting element 9 and the light receiving element 10), the optical signal 13 is the second reference. The voltage is controlled to be lower than the voltage 33 (a low voltage corresponding to the light transmittance of the double-fed printing paper).
[0028]
The optical signal 13 is compared with a low threshold voltage (low threshold voltage) by a comparator 34, and the comparison result is based on a signal CK <b> 02 from the timing generation circuit 31, and the leading edge of the printing paper is between the light emitting element 9 and the light receiving element 10. Is held in the D flip-flop 35 at the timing when 20 ms elapses from the timing of passing through, that is, at the rear end of the first timer signal from the timer 29. The signal held in the D flip-flop 35 becomes the double feed detection signal 36. FIG. 3 shows each signal at the time of detecting the double feed of the second printing paper.
[0029]
Next, it is assumed that the first printing paper (the first printing paper passed) is double-fed and only the second printing paper is passed. When the second printing paper is passed, the amount of light transmitted through the printing paper is larger than when the first printing paper is passed, so that the optical signal 13 has a voltage higher than the second reference voltage 33. . The optical signal 13 is compared with a high threshold voltage (threshold voltage high) by a comparator 37, and the comparison result is a signal CK <b> 02 from the timing generation circuit 31, and the leading edge of the printing paper passes between the light emitting element 9 and the light receiving element 10. It is held in the D flip-flop 35 at the timing when 20 ms elapses from the passing timing, that is, at the rear end of the first timer signal from the timer 29. The signal held in the D flip-flop 35 becomes the front double feed detection signal 38. This is a signal for detecting that the first printing paper that has been passed through the previous time is being double-fed.
[0030]
When the front multi-feed detection signal 38 is held in the D flip-flop 35, the SH voltage 21 held in the CR integration circuit 18 causes the two or more print sheets fed double as the first print sheet. Therefore, it is necessary to reset the voltage to reflect the light transmittance of one print sheet.
[0031]
As described above, the analog switch 17 that was once turned off by the print signal 23 is turned on only during the second timer signal when the second printing paper is passed, and the optical signal 13 is selected by the analog switch 15. The negative feedback control is applied so that the optical signal 13 is in the vicinity of the second reference voltage 33 as compared with the second reference voltage 33 and the comparator 14, so that the two SH voltages 21 held in the CR integration circuit 18 are obtained. The voltage is reset (stored) to a voltage corresponding to the light transmittance of one printing sheet when the sheet is passed.
[0032]
Since the SH voltage 21 is held in an analog manner by the CR integration circuit 18, it gradually changes although the leakage current of its peripheral circuit is very small. In this case, since the judgment criteria for the double feed detection and the front multi-layer detection are shifted, the SH voltage 21 is reset (stored) in the ON period of the second timer signal every time a sheet is passed. Can be reset to a voltage reflecting the light transmittance of one sheet of printing paper. However, since an incorrect SH voltage 21 is set when double feed is detected, the timing generation circuit 1 gates the analog switch control signal (SH timing signal 32) with the double feed detection signal and turns on the analog switch 17. Is blocking. FIG. 4 shows each signal at the time of detecting such a double feed.
[0033]
The SH voltage 21 from the CR integration circuit 18 is compared with the adjustment voltage in the comparator 39, and the comparison result of the comparator 39 is held in the D flip-flop 40 by the signal CK01 from the timing generation circuit 31. The signal held in the D flip-flop 40 is a signal (paper thickness 1) indicating that the printing paper is a printing paper weighing 100 kg or more thicker than a printing paper weighing 60 kg that is usually used.
[0034]
According to this embodiment, there is provided a sheet material detection sensor which has a light emitting element 9 and a light receiving element 10 and detects printing paper as a sheet material conveyed through a passage, and the optical signal from the light receiving element 10 is a threshold value. In the double feed detection device for detecting the double feed of the printing paper as compared with the first comparator 14, the first comparator 14 for comparing the optical signal from the light receiving element 10 with the reference voltage, and the light from the first comparator 14 by the signal from the first comparator 14 A CR integration circuit 18 as an integration means for charging / discharging according to the magnitude of the signal and the reference voltage, and a voltage as a voltage / current conversion means for passing a current proportional to the output voltage of the CR integration circuit 18 to the light emitting element 9 With the configuration including the current conversion circuit 20, a negative feedback circuit (AGC circuit) that controls the optical signal to a voltage substantially equal to the reference voltage can be configured. This allows the optical signal to be maintained at a level substantially equal to the reference voltage even when printing through a thick paper having a very low light transmittance such as a 180 kg printing paper. It is less susceptible to noise and offset voltage errors, which are problematic, and is also less susceptible to leakage current in the sample-and-hold circuit, which was also problematic in the prior art. Accordingly, the possibility of erroneously detecting double feed can be greatly reduced, and double feed detection can be reliably performed from a printing paper having a high light transmittance to a printing paper having a low light transmittance. In addition, it is generally predicted that paper powder accumulates in the path of the printing paper, or that the amount of transmitted light of the printing paper becomes weak due to deterioration of the light emitting element and the light receiving element itself. Since the change with time is automatically corrected by the AGC circuit, it becomes strong against the change with time.
[0035]
In addition, according to the present embodiment, the first printing paper is allowed to pass through the configuration including the analog switch 15 provided as a switching means for switching the charging / discharging current of the CR integration circuit 18 provided before the first comparator 14. When the paper is fed, the optical signal is controlled to be constant by turning on the analog switch and operating the AGC circuit at a predetermined timing from the leading edge, and the analog switch is turned off after a certain time to hold the SH voltage in the AGC circuit. be able to. Since the amount of light emitted from the light emitting element is determined and held by the SH voltage, an optical signal voltage having the same magnitude is generated if the second print sheet is not fed and is not fed double. By holding the SH voltage in this way, the amount of transmitted light of the first printing paper can be held, and double feed detection can be performed more reliably.
[0036]
Furthermore, according to the present embodiment, the peak hold circuit 24 that holds the peak value of the optical signal, the voltage dividing circuit that includes the resistors 25 and 26 that divide the output voltage of the peak hold circuit 24, and the voltage dividing circuit A second comparator 27 that compares the output voltage and the optical signal and outputs a sheet material detection signal, generates a predetermined timing signal based on the sheet material detection signal, and operates according to the timing signal; From the signals from the light emitting element 9 and the light receiving element 10 used for double feed detection, a signal indicating the transmission of light through the printing paper is generated, and the circuit system is operated from this signal at a predetermined timing to control the printing press main body. The signal received by the double feed detection device from the control system (CPU) is not required except for a print signal with a slow timing to notify the start of printing. This reduces the load on the printer main body control system.
[0037]
The present invention is not limited to the above-described embodiments, and can be applied to image forming apparatuses such as copying machines other than printing machines, printers, facsimiles, and the like. The present invention can be applied to a double feed detection device that detects multiple feeds.
[0038]
【The invention's effect】
As described above, according to the first aspect of the invention, it is possible to reliably detect double feed from a sheet material having a high light transmittance to a sheet material having a low light transmittance.
According to the second aspect of the present invention, it is possible not only to reliably detect double feed from a sheet material having a high light transmittance to a sheet material having a low light transmittance, but also to maintain the amount of transmitted light of the sheet material. This makes it possible to detect double feed more reliably.
[0039]
According to the third aspect of the invention, it is possible not only to reliably detect double feed from a sheet material having a high light transmittance to a sheet material having a low light transmittance, but also to reduce signals received from the outside.
According to the fourth aspect of the invention, it is possible to reliably detect double feed from a sheet material having a high light transmittance to a sheet material having a low light transmittance.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a double feed detection device according to an embodiment of the present invention.
FIG. 2 is a schematic view showing the same embodiment.
FIG. 3 is a timing chart showing signals at the time of detecting double feeding of the second printing paper in the embodiment.
FIG. 4 is a timing chart showing signals at the time of detecting a front double feed in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 9 Light emitting element 10 Light receiving element 11, 25, 26 Resistance 12 Non-inverting amplifier 14, 27, 34, 37 Comparator 15, 17 Analog switch 18 CR integration circuit 20 Voltage current conversion circuit 22, 35, 40 D flip-flop 24 Peak hold circuit 29, 30 Timer 31 Timing generation circuit

Claims (4)

A sheet material detection sensor that detects a sheet material that has a light emitting element and a light receiving element and that is conveyed through the passage is provided, and an optical signal from the light receiving element is compared with a threshold value to detect double feeding of the sheet material. In the double feed detection device, a first comparator that compares an optical signal from the light receiving element with a reference voltage, and charging and discharging are performed according to the magnitude of the optical signal and the reference voltage by a signal from the first comparator. A double feed detection device comprising: integrating means for performing; and voltage-current converting means for passing a current proportional to an output voltage of the integrating means to the light emitting element. 2. The double feed detection device according to claim 1, further comprising a switching unit provided in a preceding stage of the first comparator for switching charge / discharge current of the integration unit. 2. The multifeed detection device according to claim 1, wherein a peak hold circuit that holds a peak value of the optical signal, a voltage dividing circuit that divides an output voltage of the peak hold circuit, an output voltage of the voltage dividing circuit, and the light And a second comparator that compares the signal and outputs a sheet material detection signal, generates a predetermined timing signal based on the sheet material detection signal, and operates based on the timing signal. Detection device. An image forming apparatus comprising the double feed detection device according to claim 1, wherein the double feed detection unit detects double feed of a sheet material.

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