JP2000095391A - Duplicate feed detecting device in printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duplicate feed detection device capable of detecting the lapping of sheet from the transmitted light quantity through the sheet even when the sheet which is not constant in concentration by an image formed thereon is used. SOLUTION: Stacked sheets are separated at a specified timing and carried by a sheet feeding means 4, and the transmitted light quantity is measured at a plurality of positions along the carrying direction on the sheets by a transmitted light quantity measuring means 8 comprising a light-flooding part 81 and a light-receiving part 82 which are provided across a carrying path of the sheet. A duplicate feed detection device measures the reference sheet in advance, a plurality of transmitted light quantities are stored as the reference values in relation to the positions on the sheet, and the value of the stored transmitted light quantity is compared with the measured value of the transmitted light quantity for each position on the sheet. The duplicate feed of the sheets is discriminated based on the result of comparison of a comparing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double feed detecting device for detecting the overlap of two or more sheets when separating sheets such as stacked printing paper one by one and feeding the separated sheets to a printing apparatus. The present invention relates to a double feed detection device in the case of using a sheet having an image or the like and having a density difference at each part on the sheet surface.

[0002]

2. Description of the Related Art In a printing apparatus or the like using sheet-fed printing paper, printing is performed by separating sheets such as stacked printing paper one by one, but the separation of the sheets is incomplete and two or more sheets are printed. A double feed detecting device is provided for detecting a double feed of sheets in order to stop the printing apparatus or to issue an error alarm when the sheets are supplied in an overlapping manner. Note that the double feeding of sheets means that the sheets are conveyed in a state where at least a part of two or more sheets are overlapped.

As a conventional general double feed detecting device, there is a device which mechanically detects the thickness of a sheet by using an actuator which is driven in contact with a passing sheet. That is, if the thickness of the sheet is equal to or greater than a predetermined value, it is determined that the sheets are overlapping. In such a double feed detection device, since the position adjustment of the actuator is delicate, there is a disadvantage that it takes a long time to adjust the position when replacing sheets having different thicknesses.

Some of the above-described double feed detecting devices detect the double feed of a sheet by measuring the amount of light transmitted through the sheet. In this double feed detecting device, the light emitting portion and the light receiving portion are arranged above and below the conveyed sheet so as to face each other, and the amount of transmitted light passing through the sheet is measured to detect the overlap of the sheets.
For example, the amount of transmitted light passing through one sheet and the amount of transmitted light passing through two overlapping sheets are obtained in advance, and a threshold value is set for an intermediate value between both transmitted light amounts. Each time the sheet is conveyed, it is determined whether or not the amount of transmitted light passing through the sheet exceeds the threshold value, thereby detecting whether or not the sheets are overlapped.

[0005]

In a general printing apparatus, the printing is not stable at the beginning of the first printing, and often causes a waste paper (a sheet with poor printing). For example, the case where the print density is not stable or the case where there is no multi-color registration is considered. In such a case, at the beginning of printing of the printing press, a waste paper or the like generated in the previous printing may be used as a test so that a printing failure may occur in advance.

When using the above-mentioned waste paper, for example, when printing is performed on the back surface of the sheet, the density of the entire sheet is not constant. It is difficult to accurately determine whether they overlap. For example, even if the sheets are accurately separated, the density at the measurement point is high, so that erroneous detection may be made as a double feed. Also, if the measurement location overlaps the low density area on the sheet,
In some cases, double feeds were not detected correctly.

[0007] On the other hand, there is a similar problem when performing double-sided printing using a printing apparatus that can only perform single-sided printing. That is, there is a case where only one side of a sheet is printed by a printing apparatus, and after this printing is completed, the sheet is turned over and the other side is printed. In such a case, at the time of the second printing, the density of the entire sheet is not constant and the transmitted light amount is not constant due to the previously printed image, so that it is difficult to perform an accurate operation with the double feed detection device that detects the transmitted light amount. Met. In addition, the same problem occurs when multi-color printing is sequentially performed by a single-color or two-color printing machine or when the density of the entire area of the sheet is not constant because some mark or watermark is previously included in the sheet. Could occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to detect the overlap of sheets from the amount of transmitted light of a sheet even when a sheet containing an image or the like and having a non-constant density is used. It is an object to provide a double feed detection device.

[0009]

According to a first aspect of the present invention, there is provided a double feed detecting apparatus for detecting the overlap of sheets when separating stacked sheets one by one and supplying the separated sheets to a printing apparatus. A sheet feeding unit that separates and conveys the sheet at a predetermined timing, and a light projecting unit and a light receiving unit that are opposed to each other so as to sandwich the sheet conveyed by the sheet feeding unit, and measures the amount of transmitted light passing through the sheet Measuring means for measuring the amount of transmitted light based on the timing of the sheet supply means so as to measure the amount of transmitted light at a plurality of positions on the sheet in the transport direction. Storage means for measuring a reference sheet in advance and storing a plurality of transmitted light amounts in association with positions on the sheet; Comparing means for comparing the amount of light transmitted through the measurement for each position on the sheet, determining means for determining the double feed of the sheets based on the comparison result of the comparing means consists of.

In the double feed detecting device according to the first aspect, since the amount of light transmitted through the sheet is detected and compared at each of a plurality of locations along the sheet conveying direction, the density is reduced over the entire area of the sheet. Even if it is not constant, double feed of sheets can be detected.

According to a second aspect of the present invention, in the first aspect of the present invention, there is provided a feature point extracting means for extracting a predetermined feature point from a distribution of the amount of transmitted light to the reference sheet obtained in advance by measuring the sheet. The storage unit stores a position on the sheet with respect to the feature point as a measurement position, and the measurement control unit controls a measurement timing of the transmitted light amount measurement unit in accordance with the measurement position.

In the double feed detecting device according to the second aspect, a characteristic point suitable for judging double feed is extracted from the distribution of the transmitted light amount with respect to the reference sheet, and the position corresponding thereto is set as the transmitted light amount measurement position. Therefore, the accuracy of double feed detection can be improved.

[0013]

FIG. 1 is a schematic diagram showing an offset printing apparatus provided with a double feed detecting device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a control form thereof.

As shown in FIGS. 1 and 2, this offset printing apparatus holds a plate cylinder 1 holding a printing plate, a blanket cylinder 2 rotating in contact with the plate cylinder, and a sheet such as printing paper. An impression cylinder 3 rotating in contact with the blanket cylinder 2; and sheet feeding means 4 for supplying a sheet to the impression cylinder 3
Sheet discharging means 5 for discharging a sheet from the impression cylinder 3,
A control device 6 for controlling each part of the printing apparatus; a storage means 7 connected to the control device 6; and a transmitted light quantity measuring means 8 provided in the sheet supply means 4 for measuring the transmitted light quantity of the conveyed sheet. Having.

The plate cylinder 1 holds a printing plate on which an image is recorded on its peripheral surface by a gripping means (not shown). A fountain solution supply means and an ink supply means (not shown) are arranged around the plate cylinder 1, and fountain solution and ink are supplied to the printing plate from both devices, so that an image area on the printing plate is provided. To form an ink image. The blanket cylinder 2 has the same diameter as the plate cylinder 1, and rotates synchronously with the plate cylinder 1 in contact with the plate cylinder 1. A rubber blanket for transferring an ink image on the printing plate is wound around the peripheral surface of the blanket cylinder 2, and transfers the ink image.

The impression cylinder 3 is provided with a holding means 31 for holding and holding the leading end of the sheet. This impression cylinder 3 abuts on a blanket cylinder while holding a sheet on its peripheral surface,
The ink image on the blanket is configured to be retransferred onto the sheet. In the example shown in FIG. 1, the impression cylinder has a diameter twice as large as that of the plate cylinder 1, and is provided with two sets of gripping means 31 so that two sheets can be held on the peripheral surface of the impression cylinder.

The sheet supply means 4 includes a supply table 41 on which a plurality of sheets are stacked, separation means 42 for separating and extracting sheets one by one from the supply table, and And supply means 43 for supplying.

The supply table 41 is a table on which a plurality of sheets can be positioned and placed, and is moved up and down by means (not shown) so that the height of the uppermost sheet can be kept at a constant position. It is configured as follows. The separating means 42
It comprises a suction means for sucking and taking out the uppermost sheet on the supply table 41, and a not-shown two-sheet pick-up preventing means for separating and dropping the second and subsequent sheets by air or a peeling claw. The feeding unit 43 includes a conveying roller and a guide member for conveying the sheet, and conveys the sheet so that the sheet separated by the separating unit 42 is transferred to the holding unit 31 of the impression cylinder 3. Further, a transmission light amount measuring means 8 described later is provided in the sheet conveying path in the feeding means 43.

The sheet discharge means 5 is provided between two discharge cylinders 51, one of which is disposed close to the impression cylinder 3 and the other is provided at a predetermined interval. Two sets of wound loop-shaped chains 52 and a chain 5
It comprises a claw means 53 arranged between the two, and a discharge table 54 for storing discharged sheets. The discharge cylinder 51 rotates in synchronization with the impression cylinder 3, and the claw means 53
The sheet is arranged to be delivered from the upper holding means 31. The claw means 53 receives the leading edge of the sheet from the gripping means 31 of the impression cylinder 3, releases the gripping of the sheet on the discharge tray 54, and discharges the sheet.

As shown in FIG. 2, the control device 6 is connected to a transmitted light amount measuring means 8 described later, the sheet feeding means 4 and other components 9 constituting the offset printing apparatus to control each part. And a microcomputer provided with various input / output means. The control device 6 also performs data processing, comparison operation, and the like, which will be described later, as the double feed detection device in the present invention. The storage means 7 is for storing the transmitted light quantity obtained by the transmitted light quantity measuring means 8 to be described later, and comprises an external memory or the like connected to the control device 6. The storage means 7 may be a memory provided in the control device 6.

The transmitted light quantity measuring means 8 is provided with a light projecting section 81 provided with the sheet conveying path of the feeding means 42 interposed therebetween.
And a light receiving section 82. The light projecting unit 81 includes, for example, a light emitting diode, a semiconductor laser, or the like, and emits light at a predetermined timing or continuously according to a command from the control device 6.
The light receiving unit 82 is formed of a photoelectric conversion element such as a CCD, and receives light at a timing synchronized with the light projecting operation of the light projecting unit 81 according to a command from the control device 6 to detect a current value corresponding to the light amount. Note that two or more sets of the light projecting unit 81 and the light receiving unit 82 may be provided in the sheet width direction (the direction perpendicular to the sheet of FIG. 1), or may be configured to be movable in the sheet width direction. Is also good.

Next, the operation principle of double feed detection in the above embodiment will be described with reference to FIGS. Here, FIG. 3 is a diagram showing a distribution example of the transmitted light amount on the sheet serving as a reference, and FIGS. 4 and 5 are diagrams showing distribution examples of the transmitted light amount when double feeding occurs.

The lower part of FIG. 3 is a graph showing an example of the distribution of the transmitted light amount measured at a plurality of locations in the transport direction while the reference sheet is being transported.
The horizontal axis indicates the position on the sheet in the transport direction. In this example, the values of the transmitted light amounts at the positions P1 to P6 on the sheet are represented as T1 to T6 for simplification.

FIG. 4 is a view showing the distribution of the amount of transmitted light of a sheet when two sheets are completely overlapped and conveyed. In this example, since the sheets are completely overlapped with each other, at positions P1 to P6 on the sheets, the values Q1
To Q6 are substantially half the values of the transmitted light amounts T1 to T6 of the reference sheet. Therefore, double feed can be detected from a mismatch between the two transmitted light amounts.

FIG. 5 is a diagram showing an example of the distribution of the amount of transmitted light of a sheet when the sheets are conveyed overlapping one another. In this example, since the sheets are overlapped from the middle, the values R1 and R2 of the transmitted light amounts from the positions P1 and P2 on the sheet substantially coincide with the transmitted light amounts T1 and T2 of the reference sheet. Transmitted light amount R3 after P3
R6 to R6 have different values from the transmitted light amounts T3 to T6 of the reference sheet. Therefore, also in this case, double feed can be detected from a mismatch between the two transmitted light amounts.

When sheets overlap one another as shown in FIG. 5, double feed can be detected also in sheet length detection. For example, when there is no sheet, the detection value of the light receiving unit becomes almost maximum, so that it can be easily detected whether or not the sheet exists even if the density of the sheet is slightly different. Therefore, if the amount of transmitted light is continuously measured during conveyance, the length of the conveyed sheet can be obtained. Here, when the sheets are overlapped in the middle as shown in FIG. 5, the apparent length of the sheet is longer than usual, so that it can be determined that the double feed has occurred.

However, as described above, when judging double feed simply by the length of the sheet, the double feed cannot be detected until the entire length of the sheet is detected. That is, if the conveying length of the sheet feeding means 4 is not increased, there is a possibility that a problem such as that the leading end of the sheet has already been fed into the impression cylinder when double feed is detected. This is a factor that hinders space saving of the printing apparatus. In the present invention, since double feed can be detected at the time when the values of the transmitted light amount differ, there is an advantage that double feed can be detected earlier without detecting the entire length of the sheet.

Next, the operation of the double feed detecting apparatus according to the present embodiment will be described with reference to the operation flowchart of FIG. In the figure, first, in step S1, initial settings of each section of the printing apparatus and setting of conditions of the multifeed detecting apparatus are performed. For example, as the condition setting of the double feed detecting device, for example, the measurement position, the measurement interval, the number of times of measurement of the transmitted light amount on the sheet, and the like are determined.

In step S2, it is determined whether or not a reference value is set by measuring the amount of transmitted light of a reference sheet. Here, when the same sheet as that used in the previous printing is used, the stored reference value may be used, so that steps S3 to S5 are skipped and the process proceeds to step S6. When a new sheet is used, the process proceeds to the subsequent step S3 to obtain a reference value from the reference sheet.

In step S 3, a reference sheet is selected from the waste paper used at the start of printing, for example, and conveyed by the sheet supply means 4. In a succeeding step S4, the transmitted light amount of the conveyed reference sheet is measured for each position set in the step S1. Note that this step S3 to S4
Then, the actual printing need not be performed. And step S
In step 5, the read value of the transmitted light amount is stored corresponding to the position on the sheet. For example, in FIG. 3, the values T1 to T6 of the transmitted light amounts corresponding to the positions P1 to P6 are stored as the reference values at each position. The measurement position of the sheet is determined by the passage time from the transport timing based on the transport speed of the sheet.

In step S6, an instruction for printing is awaited. Scrap paper containing the same image as the reference sheet is set on the predetermined number supply table 41 for test printing, and when printing starts, the process proceeds to step S7 and subsequent steps. In step S7, the sheets are conveyed one by one from the sheet supply means 4 and sent to the impression cylinder 3. In step S8, the transmitted light amount of the conveyed sheet is measured. This measurement position is controlled so as to coincide with the position measured on the reference sheet.

In step S9, it is determined whether or not the amount of transmitted light measured in step S8 matches a reference value stored in advance. This determination is sequentially performed for each measurement position as the sheet is conveyed. If they do not match, it is determined that the sheet is multi-feed, and the process proceeds to step S10. Here, since the density of the waste paper varies, if the value of the transmitted light amount is within a predetermined error range with respect to the reference value, it is determined that they match. In order to prevent malfunction due to local dirt or dust on the sheet, multiple measured values are compared and compared.
If the number of mismatches among them is equal to or greater than a predetermined number, it may be determined that the sheets are multi-fed.

In step S10, an error process is performed when sheets are multi-fed. For example, a stop of the printing apparatus or an error warning is performed. If it is determined that there is no double feed of sheets, the process proceeds to step S11, and it is determined whether printing has been completed for a predetermined number of sheets. When the printing is continued without reaching the predetermined number of prints, the process returns to step S7, and the sheets are sequentially conveyed. When the printing is completed, the operation is stopped.

[Other Embodiments (1)] In the above-described embodiment, the value of each transmitted light amount is compared with each reference value. However, when using a waste paper having an extremely different density, the amount of transmitted light may greatly differ from the reference value and deviate from the error range. For example, in the early stage of printing, the ink density is not increased, and the printed matter is often thin overall. It is conceivable that the image may be the same between the initial waste paper and the later waste paper, but the overall density may be different. In such a case, the error is smaller when comparing a plurality of transmitted light amount patterns on the sheet, instead of individually comparing the respective transmitted light amount values. Hereinafter, this embodiment will be described.

FIG. 7 is a view for explaining the measurement position on the sheet and the amount of transmitted light. In the figure, measurement positions P1 to P6
, T1 to T6, and the average value T0 of the transmitted light amounts is used as a threshold for binarization.
The values T1 to T6 of the transmitted light amounts are the average transmitted light amount T.
It is determined whether the value is larger or smaller than 0, and the result of the determination is represented by a binary value. In this example, since the large case is “1” and the small case is “0”, the binary data to be obtained is “011”.
001 ”. Thus, the distribution pattern of the transmitted light amount of the sheet can be represented by binary values.

In the comparison in step S9, the double feed of sheets can be detected based on whether or not the arrangement of the binary data matches. That is, if the sheets have the same image, the relative density change pattern in each part on the sheet is approximately constant even if the absolute shading is different. Therefore, in this embodiment, even if the relative density fluctuation between the sheets is large, the double feed can be detected with high accuracy. In order to eliminate the error fluctuation in the example of FIG. 7, it is conceivable that data in the case where the transmitted light amount value T5 is close to the average transmitted light amount T0, such as the measurement position P5, is not used for comparison.

[Other Embodiment (2)] In the above-described embodiment (1), it is possible to use even a waste paper having a large density variation between sheets. However, when the image position between the sheets is displaced, particularly when the density change on the sheet is steep, the double feed detection may not be accurately performed due to the displaced measurement position. In such a case,
When the transmitted light amount of a reference sheet is measured in advance, it is conceivable to determine a measurement position where a change in density is small even if a slight displacement occurs based on the measurement data.
Hereinafter, a measurement position suitable for such a double feed determination will be described as a feature point.

FIG. 8 is a diagram for explaining the transmitted light amount distribution on the sheet and the setting of the measurement position based on the distribution. As shown in the figure, first, the amount of transmitted light is measured over the entire area on the reference sheet, and the distribution state is obtained. Then, a portion where the change amount of the transmitted light amount is relatively small over a predetermined length, in other words, a portion where the density change on the sheet is small is extracted as a feature point. This can be determined based on whether or not the difference between the transmitted light amounts at a plurality of consecutive measurement positions is within a certain range. For example, in this example, it is assumed that there is relatively little change in the amount of transmitted light near each of the points X, Y, and Z in the figure, and this is set as a feature point. The values of the transmitted light amounts of the characteristic points X to Z and the measurement positions Px to Pz on the sheet for the characteristic points are stored. Then, the measurement position in step S8 is based on the measurement positions Px to Pz at this feature point. As a result, since a portion on the sheet where the density change is relatively small is set as the measurement position, even if the position of the image on the sheet is slightly shifted, it can be handled.

[Other Embodiment (3)] In the above-described embodiment (2), even if the position of the image between the sheets is slightly displaced, the measurement position where the density change is small is determined. Thus, double feed detection can be performed with high accuracy. On the other hand, depending on the sheet to be used, a case is conceivable in which a sheet having a small image displacement between the sheets is used.
This is because, for example, in the case of printing on the back side using the sheet after the normal one-sided printing is completed instead of the waste paper, the image registration is performed accurately. In such a case, as described in the above-described embodiment (2), it is not necessary to consider the position where the density change is small in consideration of the positional deviation of the image as a feature point. Alternatively, a point that becomes a maximum point or a minimum point on the distribution of the transmitted light amount may be set as the feature point.

[0040]

According to the double feed detecting device of the present invention, the amount of transmitted light passing through the sheet is detected and compared at each of a plurality of locations along the sheet conveying direction. Can be detected even if is not constant.

In the double feed detecting device according to the second aspect, a characteristic point suitable for judging double feed is extracted from the distribution of the transmitted light amount with respect to the reference sheet, and the position corresponding thereto is set as the transmitted light amount measurement position. In addition, the accuracy of double feed detection can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a printing apparatus including a double feed detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control form of the double feed detecting device.

FIG. 3 is a diagram for explaining the principle of double feed detection according to the present invention, and is an explanatory diagram showing an example of a distribution of transmitted light amount on a reference sheet.

FIG. 4 is a diagram for explaining the principle of double feed detection according to the present invention, and is an explanatory diagram showing an example of the distribution of the amount of transmitted light on a sheet when the sheets are completely overlapped and conveyed.

FIG. 5 is a diagram for explaining the principle of double feed detection according to the present invention, and is an explanatory diagram showing an example of the distribution of the amount of transmitted light on a sheet when the sheets are partially overlapped and conveyed;

FIG. 6 is a flowchart showing an operation procedure of the double feed detection device according to the embodiment of the present invention.

FIG. 7 is a diagram for explaining the principle of double feed detection according to another embodiment of the present invention, and is a diagram for explaining binarization of the amount of transmitted light on a sheet.

FIG. 8 is a diagram for explaining the principle of double feed detection according to another embodiment of the present invention, and is a diagram for explaining a characteristic point of a sheet on which a change in transmitted light amount is small.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Plate cylinder 2 Blanket cylinder 3 Impression cylinder 4 Sheet supply means 5 Sheet discharge means 6 Control device (measurement control means, comparison means, judgment means,
Feature point extraction means) 7 storage means 8 transmitted light quantity measurement means

Claims (2)

[Claims] 1. A multi-feed detecting device for detecting an overlap of sheets when separating stacked sheets one by one and supplying the separated sheets to a printing apparatus, wherein the sheets are separated and conveyed at a predetermined timing. Supplying means; a transmitting light amount measuring means for measuring a transmitting light amount transmitted through the sheet, comprising a light projecting unit and a light receiving unit which are arranged opposite to each other so as to sandwich the sheet conveyed by the sheet supplying means; Measuring control means for controlling the transmitted light quantity measuring means based on the timing of the sheet supply means so as to measure the transmitted light quantity at a plurality of positions on the sheet in the direction, and measuring a reference sheet in advance; A storage unit for storing a plurality of transmitted light amounts in association with positions on the sheet, and a transmitted light amount stored in the storage unit and a transmitted light amount of a current measurement on the sheet. Comparing means for comparing for each position, and determining means for determining double feed of sheets based on the comparison result of the comparing means, double feed detection device consists. 2. A method according to claim 1, further comprising: a feature point extracting unit configured to extract a predetermined feature point from a distribution of the amount of transmitted light to the sheet obtained by measuring a reference sheet in advance. 2. The measurement control means controls the measurement timing of the transmitted light amount measurement means in accordance with the measurement position, while storing the position as a measurement position.
2. The double feed detection device according to 1.