Double feed detection device

Abstract

To provide a double feed detection device that is capable of handling various types of paper, where light-emitting and light-receiving elements detecting double feeds detect even the presence or absence of paper.SOLUTION: Double feed is detected by the difference in received light current on the side of a resistor array 31 between single-sheet feed and double-feed. The presence or absence of paper is detected by a Schottky barrier diode 38 such that when no paper is present in which an excessive light-receiving current flows to the side of the resistor array 31, light-receiving current flows to the side of a resistor array 34. The set values for the resistor arrays 31 and 34 are determined based on an emission gain and a reception gain adjusted so that the output of an operational amplifier 30 reaches a predetermined value in both paper-absent and paper-present states.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an optical double feed detection device that can accommodate a variety of paper types. [Background technology]

[0002] Mailing machines that separate loaded paper into sets and continuously transport them, and inkjet-print or label addresses and messages on the paper, may be fitted with a double-feed detection device to prevent unprocessed paper from leaking out due to multiple feeds. The paper handled by mailing equipment varies in print density, thickness, envelopes, gluing, labeling, size, etc., and the transport speed is also variable. As the conditions for detecting double feeds vary greatly, the detection conditions are adjusted when changing the paper.

[0003] As in Patent Documents 1 and 2, the double feed detection device may have different judgment values ​​for detecting double feed and detecting the presence or absence of paper, and the sensor that detects double feed may also detect the presence or absence of paper. If the sensor can be combined into one, it will be possible to reduce the space required for the device and reduce costs.

[0004] There are several methods for detecting double feed, including a method that detects thickness, an optical method that has a light-emitting element and a light-receiving element and detects the amount of transmitted or reflected light, and an ultrasonic method that has a transmitter and a receiver and detects the level of transmitted sound waves.The appropriate method is used depending on the application. A method that does not come into contact with the paper and is suitable for envelopes and paper that has gaps between sheets of paper that are stuck together is the optical transmission method, which is less affected by gaps.

[0005] Figure 7 shows paper with high-density printed cardboard pasted together and a label attached, as well as an explanatory diagram of the amount of light received optically. (a) shows the paper. 60 is glossy paper with a basis weight of over 200 g / m² folded in half. The outer edge of 60-1 is the pasting area, 60-3 is the address label area, 60-2 is the black halftone printing area, 60-4 and 60-6 are the solid black printing areas on the left and right sides of the spread, and 60-5 is the area where 60-4 and 60-6 overlap. (b) and (c) show the amount of light received while the paper is being transported. (b) is a graph with a vertical scale that shows the difference between the presence and absence of paper, and (c) is a graph with a vertical scale that shows the difference in the printing areas within the paper.

[0006] There is a very large difference in the amount of light received between areas where there is no paper before time t1 and after time t12 and areas where there is paper from time t1 to t12, and even within the paper there are large differences in the amount of light received due to differences in thickness and print density.

[0007] In actual devices, there is a limit to the light receiving range, and if the light emission amount and light receiving gain are set to a level that allows the presence or absence of paper to be distinguished, as in (b), the printed areas on the paper will saturate on the ground side, or if they are set to a level that does not saturate, there will be almost no voltage difference and it will be impossible to distinguish whether double feed has occurred, and if they are set to a level that allows the presence or absence of printed areas on the paper to be distinguished, as in (c), the absence of paper and the unprinted areas on the paper will saturate on the power supply side, making it impossible to distinguish whether paper is present or not.

[0008] Since the light intensity required for paper detection and double feed detection differs significantly, there are cases where multiple sets of sensors are provided for double feed detection and paper detection, as in Patent Document 3. In this case, it becomes difficult to reduce the space and cost of the device. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-172897 [Patent Document 2] Japanese Patent Application Publication No. 08-048439 [Patent Document 3] JP 2011-164952 Public Relations Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved is that in a multi-feed detection device that can handle a variety of paper types, the light-emitting element and light-receiving element that detect multi-feed cannot detect the presence or absence of paper with the same light emission amount and light-receiving gain as those used for multi-feed detection. [Means for solving the problem]

[0011] The present invention is characterized in that the device for inspecting double feed, which can handle a variety of paper types, has a means for detecting the presence or absence of paper using a gain different from that for detecting double feed, in order to detect the presence or absence of paper using a light-emitting element and a light-receiving element that detect double feed. [Effects of the Invention]

[0012] The double feed detection device of the present invention has a means for detecting the presence or absence of paper using a gain different from that for double feed detection, so it can detect double feed of various types of paper and can provide a space-saving, low-cost device that can detect the presence or absence of paper using a light-emitting element and a light-receiving element that detect double feed. [Brief explanation of the drawings]

[0013] [Figure 1] Mailing Device Block Diagram [Figure 2] Block diagram of the double feed detection device [Figure 3] External view of the double feed detection control unit [Figure 4] Circuit diagram of constant current control unit of light emitting element [Figure 5] Circuit diagram of the current-voltage conversion section of the light-receiving element (Examples 1, 3, and 4) [Figure 6] Circuit diagram of the current-voltage conversion unit of the light-receiving element (Example 2) [Figure 7] Illustration of paper and light reception amount [Figure 8] Illustrative diagram of paper and detection value (Examples 1, 3, and 4) [Figure 9] Illustrative diagram of paper, detection value, and gain (Examples 2 and 3) [Figure 10] Adjustment Mode Flowchart [Figure 11] Inspection mode flowchart (Examples 1, 3, and 4) [Figure 12] Inspection mode flowchart (Examples 2 and 3) DETAILED DESCRIPTION OF THE INVENTION [Example]

[0014] Figure 1 is a block diagram of a mailing device. Paper sheets 4 are supplied one set at a time from paper feed unit 2, which is loaded with paper, and are transported by paper transport unit 3 while inkjet printing unit 5 prints addresses and messages on the paper 4. Light transmitted through the paper is received by sensor unit 7, which has a light-emitting element and a light-receiving element, and the paper is ejected to an alignment unit (not shown). Main unit control unit 1 controls the operation of the entire device, and multi-feed detection control unit 6 controls the light emission and reception of the light-emitting element and light-receiving element of sensor unit 7, detects multi-feeds and the presence or absence of paper, notifies errors, and notifies main unit control unit 1 of the presence or absence of paper and errors. Main unit control unit 1 manages the number of sets that have been processed based on the paper presence / absence notification from multi-feed detection control unit 6, and stops paper feeding and transport based on a multi-feed notification. The inkjet printing unit 5 may be of a type that affixes a label with a printed address or individual message.

[0015] Figure 2 is a block diagram of the double feed detection device. The CPU 8 controls the entire device. The input unit 14 has a switch and sets the adjustment mode and inspection mode. The light emitting element 11 is an infrared LED, and the light receiving element 12 is an infrared photodiode; they emit light at a constant current in the constant current control unit 10, and the photocurrent is converted to voltage in the current-to-voltage conversion unit 13. The light emission and light reception conditions adjusted in the adjustment mode are saved in the non-volatile memory 9. The output unit 15 has an indicator LED and a buzzer and notifies the user of the mode and error status. The CPU 8 communicates with the main body control unit 1. The wavelength of the light-emitting element and the light-receiving element can be visible light. While the amount of visible light received changes depending on the printing color, infrared light is not affected by colors other than black, so infrared light is more suitable. If the power is not turned off between adjustment and inspection, the memory does not need to be non-volatile.

[0016] Figure 3 is an external view of the double feed detection control unit 6. Reference numeral 16 is a three-position toggle switch that sets the no-paper adjustment mode, paper-present adjustment mode, or inspection mode, and reference numeral 17 is a tactile switch that clears errors. Reference numeral 18 is a green LED that flashes at a long interval in no-paper adjustment mode, flashes at a short interval in paper-present adjustment mode, and is lit in inspection mode. Reference numeral 19 is a red LED that lights up in adjustment mode and goes out when adjustment is complete, and lights up in inspection mode when a double feed occurs. Reference numeral 20 is a buzzer that sounds a short sound when adjustment is complete in adjustment mode and a long sound when a double feed occurs in inspection mode.

[0017] Figure 4 is a circuit diagram of the constant current control unit 10 for the light-emitting element 11. The CPU 8 sets the voltage value of the non-inverting input terminal of the operational amplifier 43 in the D / A conversion unit 49, and the current value of the infrared LED 11 is controlled by the operational amplifier 43 and transistor 45 so that the voltage of resistor 46 remains constant. The light-emitting current value, which becomes the light-emitting gain, is determined in the adjustment mode. Resistors 44 and 47, and capacitor 48 are used for phase compensation of the operational amplifier 43.

[0018] FIG. 5 is a circuit diagram of the current-to-voltage converter 13 for the light-receiving element 12. The current value of the light-receiving element 12 is converted to a voltage value by the operational amplifier 30 and resistor array 31 on the resistor array 31 side, or the operational amplifier 33 and resistor array 34 on the resistor array 34 side. The voltage value is then converted from analog to digital by the A / D converter 36 or A / D converter 37, and detected by the CPU 8. The resistance values ​​of the resistor array 31 and resistor array 34 are adjustable by the CPU 8, and the light-receiving resistance value, which determines the light-receiving gain, is determined in the adjustment mode. Capacitor 32 is used for phase compensation of the operational amplifier 30, and capacitor 35 is used for phase compensation of the operational amplifier 33. The cathode of the light-receiving element 12 is connected to the inverting input terminal of the operational amplifier 30, and the cathode of the light-receiving element 12 is connected to the inverting input terminal of the operational amplifier 33 via a Schottky barrier diode 38 with a forward voltage of 0.2 V. A 0.2 V voltage source 39 is connected to the non-inverting input terminals of the operational amplifier 30 and the operational amplifier 33. The power supply voltage of the operational amplifiers 30 and 33 is 5V.

[0019] When the inverting input terminal of the operational amplifier 30 is at 0 V or higher, no current flows from the light-receiving element 12 to the resistor array 34 due to the forward voltage of the Schottky barrier diode 38. If the current in the light-receiving element 12 increases and the output of the operational amplifier 30 reaches the power supply voltage, and the current in the light-receiving element 12 increases further, the imaginary short between the inverting input terminal and the non-inverting input terminal can no longer be maintained, the voltage at the inverting input terminal drops below 0.2 V, and when the inverting input terminal falls below 0 V, current also flows to the resistor array 34.

[0020] Figure 10 is a flowchart of the adjustment mode. The light emission gain and the light receiving gain of the resistor array 31 are adjusted. When the toggle switch 16 is switched to the adjustment mode, the process starts with the minimum gain of 20 mA for the light emission gain and 20 kΩ for the light receiving gain (step 100). The target range for the amount of received light is set to an output value of 2.5 ± 0.1 V from the operational amplifier 30, and priority is given to increasing the light receiving gain to keep power consumption as low as possible. The gain is increased or decreased to fall within the target range (steps 101 and 102), and if the gain when it falls within the range is the maximum value up to that point, it is overwritten and saved in the non-volatile memory 9 (steps 103 and 104). Steps 101 to 104 are repeated, and the maximum value during the adjustment mode remains in the non-volatile memory 9. In the paper presence adjustment mode, the paper detection light receiving gain is calculated and saved (steps 105 and 106). When the toggle switch 16 is switched to the inspection mode at any step, the adjustment mode is terminated.

[0021] The no-paper adjustment is performed before the paper-present adjustment. The maximum values ​​are 20mA for the light-emitting gain and 40KΩ for the light-receiving gain, and these values ​​are saved in non-volatile memory 9 as the no-paper gains. The no-paper adjustment is completed in a short time because the conditions are constant. The no-paper adjustment should be performed at the time of installation and at a time that takes into account changes over time, and there is no need to perform it every time the paper is changed.

[0022] The paper presence adjustment is performed when changing the paper. Only one set of paper is passed through the inkjet printing unit 5 as the print content for adjustment. The paper shown in Figure 8 (described later) is passed through, and the gain is at its maximum value from time t8 to t9, which is the darkest part, with an emission gain of 500 mA and a reception gain of 500 kΩ. This value is saved in the non-volatile memory 9 as the paper presence gain. The light-receiving gain of resistor array 34 is calculated and saved based on the ratio of the total gain of light emission and light reception with and without paper. The ratio is 312.5 (500mA / 20mA x 500KΩ / 40KΩ), and when the light-receiving current on resistor array 31 increases 2.2 times (5V / (2.5V - 0.2V)), the inverting input terminal drops to 0V. Therefore, when there is no paper, a current of 310.3 times (312.5 times - 2.2 times) flows through resistor array 34. The light-receiving gain of resistor array 34 is set to 1.6KΩ (500KΩ / 310.3 times), which causes the output of operational amplifier 33 to be 2.5V when there is no paper. If the inkjet printing unit 5 affixes labels with printed destinations and individual messages, a sheet of paper with a label affixed with printing content for adjustment may be fed through the printer without operating the label affixing unit. If the darkest point is clearly identified, the paper may not be fed through the printer, and the darkest point of the paper may be placed on the sensor unit for adjustment.

[0023] Figure 8 is an explanatory diagram of paper and detection values. Since (a) is the same as Figure 7 explained in the background art, its explanation will be omitted. (b) is the detection value on the resistor array 31 side, (c) is the detection value on the resistor array 34 side, 63 is the output of the operational amplifier 30 when one set is being conveyed, 64 is the output of the operational amplifier 30 when double feed occurs, 65 is the double feed judgment value, which is 1.7 V, which is 2 / 3 times 2.5 V, 66 is the output of the operational amplifier 33, and 67 is the paper judgment value, which is 1.7 V, which is 2 / 3 times 2.5 V. 68 and 69 are not used in this embodiment (68 is used in embodiment 3, and 69 is used in embodiment 4).

[0024] Paper starts passing in inspection mode, and the paper-present gain is set. The output 66 of the operational amplifier 33 is higher than the paper threshold 67 before time t1 and after time t12 when there is no paper, but is lower than the paper threshold 67 from time t1 to t12 when there is paper. When one set is conveyed, the output 63 of the operational amplifier 30 saturates at the power supply voltage of 5V before time t1 and after time t12 because the light-receiving current is large compared to the light-receiving gain. From time t1 to t12, the output 63 fluctuates depending on the paper thickness and print content. Even within the paper, the output 63 saturates at 5V in areas where there is no printing. When multiple feeds occur, the output 64 of the operational amplifier 30 is less than half of the output when one set is conveyed, and falls below the multiple feed threshold 65 from time t7 to t10. Figure 8 shows the case where operation continues without the multiple feed error processing described later in Figure 11. When a double feed occurs, the two sheets do not necessarily overlap at the same position, so the output 64 of the operational amplifier 30 may be half or higher than when one set is being transported. In such cases, the double feed judgment value is set so that double feed can be detected appropriately. The sensitivity of the detection of multiple feeds and paper types may be made variable by a volume so that various paper types can be handled.

[0025] FIG. 11 is a flowchart of the inspection mode. Received light amount 1 indicates the amount of light received on the resistor array 31 side, and received light amount 2 indicates the amount of light received on the resistor array 34 side. Steps 114, 117, 118, 121, and 122 are not performed in this embodiment (they are performed in embodiment 4). When the toggle switch 16 switches to the inspection mode, light is emitted and received at the paper-present gain (step 110), the paper-present flag is set to 0 (step 111), and detection of paper presence or absence begins (step 112). When received light amount 2 falls below the paper presence threshold (timing t1 in FIG. 8), it is determined that paper is present, the paper-present flag is set to 1 (step 113), and the paper-present state is entered. During the paper-present state, a double feed is detected using received light amount 1 (step 115), and the presence or absence of paper is detected using received light amount 2 (step 119). When received light amount 1 is lower than the double feed threshold, a double feed error is detected (step 116, timing t7 in FIG. 8). The error can be cleared with the tactile switch 17 to resume processing. When the amount of received light 2 becomes higher than the paper determination value (timing t12 in Figure 8), it is determined that there is no paper, the paper presence flag is set to 0 (step 120), and the paper-out state is entered. During the paper-out state, the presence or absence of paper is detected using the amount of received light 2 (step 112). When the toggle switch 16 is switched to the adjustment mode at any step, the inspection mode is terminated.

[0026] The gain ratio between the presence and absence of paper is not limited to the range of this embodiment depending on the conditions of use of the device, and may be 1000 times or 2000 times. It is also possible to apply a configuration in which only one of the combinations of the light emission gain and the light reception gain on the side of the resistor array 31 for detecting double feed is variable.

[0027] In this embodiment, by having a resistor array 31 side which is a light receiving circuit for detecting double feed and a resistor array 34 side which is a light receiving circuit for detecting paper, the presence or absence of paper can be detected using the light emitting element and light receiving element that detect double feed, even in equipment that uses various types of paper and has significantly different conditions for detecting double feed, and further, the presence or absence of paper can be detected without affecting the detection of double feed, which has the effect of providing a space-saving, low-cost, and high-precision device. [Example]

[0028] The light receiving circuit, gain setting, and detection flow are different from those in the first embodiment. Figure 6 is a circuit diagram of the current-voltage converter for the photodetector. The current value of the photodetector 12 is converted to a voltage value by the operational amplifier 30 and resistor array 40, then converted from analog to digital by the A / D converter 36, and detected by the CPU 8. The resistance value of the resistor array 40 is adjustable by the CPU 8, and the photodetector resistance value, which determines the photodetector gain, is determined in the adjustment mode. Capacitor 41 is used for phase compensation of the operational amplifier 30. The cathode of the photodetector 12 is connected to the inverting input terminal of the operational amplifier 30, and the non-inverting input terminal is connected to ground. The Schottky barrier diode 42 with a forward voltage of 0.2V is used for protection against excessive negative voltages, as the output of the operational amplifier 30 may saturate at the power supply voltage and the inverting input terminal may become negative if the photodetector current is excessively high compared to the photodetector gain. The power supply voltage for the operational amplifier 30 is 5V. The constant current control section of the light emitting element is the same as that in the first embodiment shown in FIG.

[0029] The flow chart of the adjustment mode is the same as that of the first embodiment, shown in FIG. 10, except that steps 105 and 106 are not executed, and the gains with and without paper are also the same as those of the first embodiment.

[0030] 9 is an explanatory diagram of paper, detection values, and gains. The paper is the same as in Example 1. 70 is the output of operational amplifier 30 when one set is being conveyed, 71 is the paper determination value, which is 1.7V, which is 2 / 3 times 2.5V, Ta is the transition time to the no-paper gain (details will be described later), and 72 is the timing for setting the paper-present gain and no-paper gain for the light-emitting gain and light-receiving gain.

[0031] Paper begins to pass in inspection mode, and the no-paper gain is set. The output 70 of the operational amplifier 30 is 2.5V until time t1, when the paper reaches the sensor. When paper is present at time t1, the photocurrent drops significantly, causing the voltage to drop below the paper judgment value 71, so it is determined that paper is present and the amplifier switches to the paper-present gain. If paper is absent while in the paper-present gain, the photocurrent becomes excessively large compared to the photocurrent gain, causing the output of the operational amplifier 30 to saturate at 5V. Even if paper is present, differences in thickness and print density will cause the output 70 of the operational amplifier 30 to saturate at 5V in bright areas. If time Ta passes while the output remains at 5V, the gain switches to the no-paper gain. If paper is present at this time, the voltage drops significantly and becomes lower than the paper judgment value 71, so the amplifier switches back to the paper-present gain. If a similar area is found, the same operation is repeated. When the gain switches to the no-paper gain after time t12, there is no paper, so the light-receiving gain and light-receiving current match, and the output 70 of the operational amplifier 30 becomes 2.5V, which is higher than the paper judgment value 71, so it is determined that there is no paper, and the no-paper gain remains. In the case of multiple feeding, the output of the operational amplifier 30 becomes half or less of that in the case of single set feeding, as in the first embodiment, and therefore illustration and explanation thereof will be omitted.

[0032] FIG. 12 is a flowchart of the inspection mode. When the toggle switch 16 switches to the inspection mode, light is emitted and received at the no-paper gain (step 130), the paper-present flag is set to 0 (step 131), and detection of the presence of paper begins (step 132). When the amount of received light falls below the paper determination value (timing at time t1 in FIG. 9), it is determined that paper is present, the paper-present flag is set to 1 (step 133), and the gain is switched to the paper-present gain (step 134), establishing a paper-present state. During the paper-present state, multifeed is detected using the multifeed determination value (step 135), and the presence of paper is detected during the time at the upper limit of received light (5V) (step 137). If the upper limit of received light continues for more than Ta (timing at time t4 + Ta in FIG. 9), the gain is switched to the no-paper gain (step 138). At this point, no paper is detected, and the amount of received light at the no-paper gain is compared with the paper determination value (step 139). If the amount of received light is lower than the paper determination value, the gain is switched back to the paper-present gain. The same operation is repeated until it is determined that there is no paper. If the amount of received light is lower than the double feed judgment value, it is determined that there is a double feed error (step 136, timing t7 in Figure 9). The error can be cleared with the tactile switch 17 to resume processing. When the gain is switched to no paper and the amount of received light becomes equal to or greater than the paper judgment value (timing when the Ta period has elapsed after time t12 in Figure 9), it is determined that there is no paper, the paper presence flag is set to 0 (step 140), and the paper-out state is entered. When the toggle switch 16 is switched to the adjustment mode at any step, the inspection mode is terminated.

[0033] The voltage for determining the transition time Ta to the no-paper gain does not have to be the upper limit. Ta and the time to return from the gain without paper to the gain with paper are set to appropriate values ​​that will not overlook double feed or the presence or absence of paper. The gain ratio between the presence and absence of paper is not limited to the range of this embodiment, as in the embodiment. It is also possible to apply a configuration in which only one of the light emission gain and the light reception gain is variable.

[0034] In this embodiment, by switching between a paper-present gain and a paper-absent gain depending on the amount of light received during double feed detection, the presence or absence of paper can be detected using the light-emitting element and light-receiving element that detect double feed, even in devices that use a variety of paper formats and where the conditions for detecting double feed vary greatly.Furthermore, the light-receiving circuit for double feed and the presence or absence of paper is common, and the amount of light emitted can be reduced when there is no paper, so it is possible to provide a device that is small in space, low cost, and consumes low current. [Example]

[0035] The first and second embodiments are combined, and the second embodiment is performed for the transition from the paper-out state to the paper-present state, and the first embodiment is performed for the transition from the paper-present state to the paper-out state. The constant current control section of the light emitting element is the same as in the first and second embodiments shown in FIG. The current-voltage conversion section of the light receiving element is the same as that of the first embodiment shown in FIG. The flow chart of the adjustment mode is the same as in the first and second embodiments, FIG.

[0036] The explanation of paper, detection value, and gain combines the period up to time t1 in FIG. 9 of the second embodiment with the period from time t1 to t12 in FIG. 8 of the first embodiment. The output of operational amplifier 33 in FIG. 8 is 68, not 66. When the paper leaves the sensor at time t12, the output 68 of operational amplifier 30 becomes higher than the paper determination value, and it is determined that there is no paper. When it is determined that there is no paper, the gain switches to the no-paper gain, and the output 68 of operational amplifier 30 drops, returning to the state before time t1 in FIG. 9.

[0037] The inspection mode flowchart combines up to step 134 in Fig. 12 of embodiment 2 with steps 115 to 119 in Fig. 11 of embodiment 1. The amount of received light in Fig. 12 is the amount of received light 1 in Fig. 11. When N is reached in step 119 in Fig. 11, the process returns to step 130 in Fig. 12.

[0038] This embodiment has two light receiving circuits with different light receiving gains, and by changing the method of detecting whether paper is present and whether paper is absent, it is possible to detect the presence or absence of paper using the light emitting element and light receiving element that detect double feed, even in equipment that uses a variety of paper formats and has significantly different conditions for detecting double feed.It is also possible to detect the presence or absence of paper without affecting double feed detection, and the amount of light emitted can be reduced when paper is absent, so it has the effect of providing a space-saving, low-cost, high-precision, and low-power device. [Example]

[0039] If no adjustment is made when changing paper, the system will operate with the previous adjustment value. If the current paper is detected as darker than the previous paper, it will be a double feed, so the system will notice the unadjusted state and will not go uninspected. However, if the current paper is detected as lighter than the previous paper, the system may not be able to detect the double feed and the paper may go uninspected. Therefore, an embodiment will be shown in which uninspected paper is detected as being lighter than the adjusted paper, and a thin paper error is generated to prevent the paper from going uninspected.

[0040] Thin paper error detection is added to the first embodiment. Reference numeral 69 in Figure 8 indicates the output of the resistor array 34 when unadjusted paper, which is detected as brighter than the adjusted paper, is passed through. The gain of the adjusted paper is the same as in Example 1, with the unadjusted paper having a light-emitting gain of 20 mA and a light-receiving gain of 250 kΩ. The gain ratio between the adjusted and unadjusted paper is 50.0 (500 mA / 20 mA x 500 kΩ / 250 kΩ), so a current of 47.8 (50 - 2.2) flows through the resistor array 34, resulting in a detected value of 0.4 V (2.5 V x 48.7 / 310.3). Even without this significant brightness difference, the resistor array 31 reaches the power supply voltage when the light-receiving current exceeds 2.1 ((5 - 0.2 V) / (2.5 - 0.2 V)). Therefore, if the resistor array 31 is always saturated at 5 V during the paper-present period, a thin paper error is detected.

[0041] The flow of thin paper error detection is explained in Figure 11. If it is determined that paper is present, the thin paper flag is set to 1 (step 114). If, while paper is present, the received light amount 1 (resistor array 31 side) is lower than the thin paper determination value (5V) (step 117), the thin paper flag is set to 0 (step 118). If it is determined that paper is not present, the thin paper flag is checked (step 121), and if the thin paper flag is 1, the paper is detected as bright, with the resistor array 31 side always saturated at 5V through the paper, so a thin paper error is declared (step 122). The error can be cleared with the tactile switch 17 to resume processing. When a thin paper error occurs, the red LED 19 flashes and the buzzer 20 sounds twice briefly to distinguish it from a double feed error.

[0042] If it is more appropriate to determine that a thin paper error has occurred when the difference in brightness is greater, the output from the resistor array 34 may be used to make the determination. The same method can be used in the second and third embodiments. In the second embodiment, similar to this embodiment, it may be determined that the paper is thin if the gain is always 5V when there is paper. When the gain is set to no paper in the paper-present state, thin paper may be determined using a lower determination value than the paper determination value.

[0043] In this embodiment, by detecting paper that may go uninspected due to multiple feed if no paper-present adjustment is performed, in addition to the effects of Examples 1, 2, and 3, it is possible to provide an apparatus that can prevent uninspection.

Claims

1. A multi-feed detection device is attached to a paper transport device that separates stacked paper into sets and continuously transports them, the multi-feed detection device comprising: a light-emitting element; a light-receiving element that receives light from the light-emitting element; a light-emitting control means that controls the amount of light emitted by the light-emitting element; a light-receiving control means that controls the detection value of the light-receiving element; and the multi-feed detection device detects multi-feeding based on the detection value of the light-receiving control means, an adjusting means for adjusting a control value of at least one of the light-emitting control means and the light-receiving control means based on the detection value when there is no paper between the light-emitting element and the light-receiving element and when there is paper between the light-emitting element and the light-receiving element; A multi-feed detection device characterized in that a multi-feed detection gain and a paper presence / absence detection gain of the light-emitting control means and the light-receiving control means are calculated based on the control values ​​adjusted by the adjustment means, and multi-feed and the presence / absence of paper are detected using the light-emitting element, the light-receiving element, the multi-feed detection gain, and the paper presence / absence detection gain.

2. 2. The double feed detection device according to claim 1, wherein the control means comprises a light receiving means having a gain for detecting double feed, and a light receiving means having a gain for detecting the presence or absence of paper.

3. The double feed detection device according to claim 1, wherein the control means uses a light receiving means that is common to double feed detection and paper presence / absence detection, and switches between the double feed detection gain and the paper presence / absence detection gain in the common light receiving means.

4. 4. The double feed detection device according to claim 3, wherein the gain is switched based on the level and time of the detection value in the presence of paper.

5. The double feed detection device described in claim 1, characterized in that the control means has a first light receiving means that switches between a gain for detecting double feed and a gain for detecting first paper presence / absence, and a second light receiving means that has a gain for detecting second paper presence / absence, and detects the presence / absence of paper using the first light receiving means when there is no paper, and using the second light receiving means when there is paper.

6. A multi-feed inspection device as described in any one of claims 1 to 5, characterized in that it has a thin paper judgment value for judging thin paper for which the amount of light received by the light receiving element is greater than that of paper during adjustment when the paper is present, and detects the thin paper based on the detection value when the paper is present and the thin paper judgment value.

7. 7. The double feed inspection device according to claim 6, wherein the thin paper is detected based on a detection value of either one of the light receiving means according to claim 2 or a detection value of either one of the light receiving means according to claim 5.

8. 7. The double feed inspection device according to claim 6, wherein the thin paper is detected based on a detection value of one of the switching states according to claim 3.

9. 9. The double feed detection device according to claim 1, wherein the light emitting element and the light receiving element emit infrared light.

10. 9. The double feed detection device according to claim 1, further comprising a notification means for notifying the occurrence of double feed or the thin paper by using at least one of light and sound.

11. 9. The double feed detection device according to claim 1, further comprising a notification unit that notifies the paper transport device of at least one of double feed, the presence or absence of paper, and the thin paper.

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