JP2007313766A - Printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer which can highly precisely detect an existence of a printing paper even in double-side printing. <P>SOLUTION: The printer prints a second image on the back surface of the printing paper on the surface of which a first image is printed. The printer scans image data of the first image to determine the position of a detecting point P2 of the printing paper S by a sensor from a low density region, and sets the detecting threshold value by the sensor by the density of the detecting point P2. Then, based on the position of the detecting point determined and the position of the angle of rotation of a delivering body, a detecting timing of the printing paper S by the sensor is set, to detect the existence of the printing paper S based on the set threshold value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a printing machine that prints a second image on the back surface of a printing paper on which the first image is printed.

In general, in a printing machine, in order to prevent the impression cylinder from being contaminated with ink due to a mistake in conveying the printing paper, a configuration in which the presence or absence of the printing paper is detected at the outer periphery of the cylinder that conveys the printing paper by a sensor. Is adopted. As a sensor for detecting printing paper, a reflective sensor as described in Patent Document 1 is used.
JP-A-2004-277071

  However, in the case of double-sided printing, there arises a problem that the printing paper is not accurately detected. That is, in the case where the second image is printed on the back surface of the printing paper on which the first image is printed, the sensor irradiates light on the surface of the printing paper on which the first image is printed. The presence or absence of paper is detected. For this reason, when detecting the presence or absence of printing paper by irradiating light to a relatively high density area on the surface of the printing paper, the difference in reflected light amount between when there is no printing paper and when there is no printing paper is small. Become. For this reason, it becomes difficult to accurately detect the printing paper.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a printing machine capable of accurately detecting the presence or absence of printing paper even in the case of double-sided printing.

  The invention according to claim 1 is a printing machine for printing the second image on the back surface of the printing paper on which the first image is printed, the printing paper on the outer peripheral surface, and the surface of the printing paper. Mounted in a state facing outward, a cylinder for transporting the printing paper, detection means for detecting the rotational angle position of the cylinder, and irradiating light on the surface of the printing paper mounted on the cylinder and reflecting the light The position of the detection point of the print paper by the sensor is determined from the sensor for detecting the presence or absence of the print paper by the amount of light and the image data of the first image, and the detection threshold value by the sensor is set by the density of the detection point And a detection timing of the printing paper by the sensor is set based on the position of the detection point determined by the control unit and the rotational angle position of the cylinder detected by the detection means, and the detection At the timing That on the basis of the output detection threshold set by the control unit of the sensor, and detects the presence or absence of the printing paper.

  According to a second aspect of the present invention, in the first aspect of the present invention, an antireflection region in which reflection of light is prevented or reduced is formed in the body, and the control unit is provided in the antireflection region. The detection point is determined from the corresponding region.

  According to a third aspect of the present invention, in the invention of the second aspect, the cylinder has a hollow cylindrical shape, and the antireflection region has a hole formed in a surface of the cylindrical cylinder. Is formed.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, a plurality of the hole portions are arranged in a circumferential direction of the trunk.

  According to a fifth aspect of the present invention, in the third aspect of the present invention, the hole has a slit-like shape extending in a circumferential direction of the trunk.

  A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, wherein the cylinder is a transfer cylinder disposed between printing units that perform printing with different color inks. .

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, when the detection point is determined, a point having a low density in the first image is determined as a detection point.

The invention according to claim 8 is the printing press according to any one of claims 1 to 7,
When the detection threshold value is set, paper is detected at the detection point calculated from the detection value to be output by the sensor when no paper is loaded at the determined detection point and the density value at the determined detection point. The detection threshold value is determined between detection values to be output by the sensor when the sensor is attached.

The invention according to claim 9 is the printing press according to any one of claims 2 to 5,
At the time of determining the detection point, a point having a low density in the first image is determined as a detection point, and the detection threshold value is set when the printing paper is not attached to the determined detection point. The detection threshold is determined in a range that is greater than or equal to a detection value to be output by the sensor and less than the detection value to be output by the sensor when printing paper is mounted at the determined detection point.

  According to the first aspect of the present invention, it is possible to accurately detect the presence or absence of printing paper even in the case of duplex printing.

  According to the second to fifth aspects of the present invention, it is possible to detect the presence or absence of printing paper with higher accuracy.

  According to the sixth aspect of the present invention, it is possible to effectively prevent contamination of the impression cylinder in the next printing unit due to a printing paper conveyance error.

  According to the seventh to ninth aspects of the present invention, it is possible to more accurately detect the presence or absence of printing paper.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a printing press according to the present invention.

  The printing machine records an image on a printing plate on which images held on the first and second plate cylinders 11 and 12 are not recorded, and then makes the ink supplied to the printing plate first, Printing on four colors is performed by transferring to the printing paper held by the first and second impression cylinders 15 and 16 via the second blanket cylinders 13 and 14.

  The printing press includes a first plate cylinder 11, a second plate cylinder 12, a first blanket cylinder 13 provided in contact with the first plate cylinder 11, and a second plate cylinder 12. A second blanket cylinder 14 provided so as to be able to contact, a first pressure cylinder 15 provided so as to be able to contact the first blanket cylinder 13, and a contact with the second blanket cylinder 14 The second impression cylinder 16 provided in a possible manner, the feed cylinder 17 for passing the printing paper supplied from the paper feeding unit 31 to the first impression cylinder 15, and the print received from the first impression cylinder 15. A transfer cylinder 18 for passing the sheet to the second impression cylinder 16 and a chain 23 for discharging the printing sheet received from the second impression cylinder 16 to the sheet discharge unit 32 are wound around the sprocket 22. A paper discharge cylinder 19 and an image pickup unit 60 for picking up an image printed on the printing paper are provided.

  The first plate cylinder 11 and the second plate cylinder 12 are so-called double cylinders that hold printing plates for two different colors on the outer periphery thereof. The first blanket cylinder 13 and the second blanket cylinder 14 have the same diameter as the first plate cylinder 11 and the second plate cylinder 12, and each has a blanket surface on which images of two colors can be transferred. .

  A first impression cylinder 15 and a second impression cylinder 16 provided so as to be able to contact the first blanket cylinder 13 and the second blanket cylinder 14, respectively, 1. It has a diameter that is ½ of the diameter of the second blanket cylinder 13, 14. The first and second impression cylinders 15 and 16 have grippers (not shown) for holding and conveying the leading edge of the printing paper.

  A sheet feeding cylinder 17 disposed adjacent to the impression cylinder 15 has the same diameter as the first and second impression cylinders 15 and 16. The sheet feeding cylinder 17 holds and conveys the leading end portion of the printing paper supplied one by one from the sheet feeding unit 31 with a gripper (not shown) for each rotation of the sheet feeding cylinder 17. The leading end of the printing paper held by the gripper is held by the gripper of the first pressure drum 15 when the printing paper is transferred from the paper feeding drum 17 to the first pressure drum 15.

  A transfer cylinder 18 disposed between the first impression cylinder 15 and the second impression cylinder 16 includes first and second plate cylinders 11 and 12 and first and second blanket cylinders 13 and 14. It has the same diameter as the diameter. The transfer cylinder 18 holds and conveys the leading end of the printing paper received from the first impression cylinder 15 by a gripper (not shown), and delivers the leading end of the printing paper to the gripper of the second impression cylinder 16.

  A paper discharge cylinder 19 disposed adjacent to the second impression cylinder 16 has the same diameter as that of the first and second plate cylinders 11 and 12 and the first and second blanket cylinders 13 and 14. Have. The discharge drum 19 has a structure in which a pair of chains 23 are wound around both ends thereof, and a gripper is disposed on a connecting member (not shown) that connects the pair of chains 23. The leading end portion of the printing paper held by the gripper of the second impression cylinder 16 is held by any of the grippers of the discharge cylinder 19 when the printing paper is transferred from the second impression cylinder 16 to the discharge cylinder 19. The The printing paper is discharged onto the paper discharge unit 32 as the chain 23 moves.

  A gear attached to the end of the paper feed cylinder 17 is connected to a gear 26 that is disposed concentrically with the driven pulley 25. A belt 29 is wound between a driving pulley 28 and a driven pulley 25 that are rotated by driving the motor 27. For this reason, the paper feed cylinder 17 is rotated by the drive of the drive motor 27. On the other hand, the first and second plate cylinders 11 and 12, the first and second blanket cylinders 13 and 14, the first and second impression cylinders 15 and 16, the paper feed cylinder 17, the transfer cylinder 18 and the paper discharge cylinder 19 are connected by the gear attached to the edge part, respectively. For this reason, when the motor 27 is driven, the feed cylinder 17, the first and second impression cylinders 15 and 16, the discharge cylinder 19, the first and second blanket cylinders 13, 14, the first and second cylinders. The plate cylinders 11 and 12 and the transfer cylinder 18 rotate in synchronization with each other.

  Around the first plate cylinder 11, an ink supply device 20a for supplying, for example, black (K) ink to the printing plate, and an ink supply device for supplying, for example, cyan (C) ink to the printing plate 20b and dampening water supply devices 21a and 21b for supplying dampening water to the printing plate are arranged. Further, around the second plate cylinder 12, an ink supply device 20c for supplying, for example, magenta (M) ink to the printing plate, and an ink for supplying, for example, yellow (Y) ink to the printing plate. A supply device 20d and dampening water supply devices 21c and 21d for supplying dampening water to the printing plate are arranged.

  Further, around the first plate cylinder 11 or the second plate cylinder 12, a plate feeding section 33 for supplying a printing plate to the outer peripheral portion of the first plate cylinder 11, and a second plate cylinder, respectively. A plate supply unit 34 for supplying a printing plate to the outer periphery of the first plate cylinder, an image recording device 35 for recording an image on the printing plate mounted on the outer periphery of the first plate cylinder 11, and a second plate cylinder An image recording device 36 for recording an image on a printing plate mounted on the outer peripheral portion of 12 is disposed.

  The transfer cylinder 18 includes a printing unit including a first plate cylinder 11, a first blanket cylinder 13, a first impression cylinder 15 and the like for printing with black and cyan inks, and magenta and yellow inks. A printing unit comprising a second plate cylinder 12, a second blanket cylinder 14, a second impression cylinder 16 and the like for printing is disposed. The outer periphery of the transfer cylinder 18 is provided with a sensor 10 that irradiates light onto the surface of the printing paper mounted on the outer periphery of the transfer cylinder 18 and detects the presence or absence of the printing paper by the amount of reflected light. Yes.

  FIG. 2 is a block diagram showing the main electrical configuration of the printing press.

  The printing machine includes a control unit 80 including a ROM 81 that stores an operation program necessary for controlling the apparatus, a RAM 82 that temporarily stores data and the like during control, and a CPU 83 that executes a logical operation.

  The control unit 80 is connected to the above-described sensor 10 via the interface 84. The control unit 80 is connected to an encoder 87 for detecting the rotational angle position of the transfer cylinder 18 via the interface 84. The control unit 80 is connected via an interface 84 to an image data supply unit 86 that stores image data to be subjected to plate making and printing. Further, the control unit 80 is driven through the interface 84 to generate a drive signal for the drive unit in the ink supply device 20, the dampening water supply device 21, the paper feed unit 21, the image recording devices 35 and 36, and the like. A circuit 85 is also connected.

  The printing machine is controlled by the control unit 80, and executes a plate making operation and a printing operation which will be described later. In addition, as will be described later, the control unit 80 performs a detection point position determination operation and a detection threshold setting operation by the sensor 10.

  In the printing machine having the above-described configuration, the printing plate drawn from the supply cassette 41 in the plate supply unit 33 is cut into a predetermined size by the cutter 42. Then, the leading end portion of the cut sheet-like printing plate is guided by a guide roller and a guide member (not shown), and is held by a holding claw of the first plate cylinder 11. Then, the first plate cylinder 11 is rotated at a low speed by driving a motor (not shown), the printing plate is wound around the outer peripheral portion of the first plate cylinder 11, and the rear end portion of the printing plate is held by the other holding nail. . In this state, while rotating the first plate cylinder 11 at a high speed, the image recording device 35 irradiates the surface of the printing plate held on the outer periphery of the first plate cylinder 11 with a modulated laser beam, Record.

  Similarly, the printing plate drawn out from the supply cassette 43 in the plate supply unit 34 is cut into a predetermined size by the cutter 44. Then, the leading end portion of the cut sheet-like printing plate is guided by a guide roller and a guide member (not shown), and is held by a holding claw of the second plate cylinder 12. Then, the second plate cylinder 12 is rotated at a low speed by driving a motor (not shown), the printing plate is wound around the outer periphery of the second plate cylinder 12, and the rear end portion of the printing plate is held by the other holding nail. . In this state, while rotating the second plate cylinder 12 at a high speed, the image recording device 36 irradiates the surface of the printing plate held on the outer periphery of the second plate cylinder 12 with a modulated laser beam, Record.

  A printing plate for printing with black ink and a printing plate for printing with cyan ink are mounted on the outer periphery of the first plate cylinder 11. These two printing plates are arranged at positions where they are evenly distributed (that is, separated from each other by 180 degrees), and the image recording device 35 records an image on these printing plates. Similarly, a printing plate for printing with magenta ink and a printing plate for printing with yellow ink are mounted on the outer periphery of the second plate cylinder 12. These two printing plates are also arranged at positions where they are equally distributed, and the image recording device 36 records an image on these printing plates, and the plate making process is completed.

  When the plate making process is completed, a printing process is performed in which printing is performed on printing paper using the printing plates on the first and second plate cylinders 11 and 12. This printing process is performed as follows.

  That is, first, each fountain solution supply device 21 and each ink supply device 20 are brought into contact only with the corresponding printing plates among the printing plates held on the first and second plate cylinders 11 and 12. Accordingly, the dampening water and the ink are supplied to each printing plate from the corresponding dampening water supply device 21 and the corresponding ink supply device 20. The ink supplied to the printing plate is transferred to corresponding areas of the first and second blanket cylinders 13 and 14.

  Then, the printing paper is supplied from the paper feeding unit 31 to the paper feeding cylinder 17. This printing paper is delivered from the paper feed cylinder 17 to the first impression cylinder 15. When the first impression cylinder 15 that has received the printing paper continues to rotate, the first impression cylinder 15 has a diameter that is ½ that of the first plate cylinder 11 and the first blanket cylinder 13. On the printing paper held on the outer peripheral portion of one impression cylinder 15, black ink is transferred in the first rotation, and cyan ink is transferred in the second rotation.

  If the first impression cylinder 15 rotates twice, the printing paper is transferred from the first impression cylinder 15 to the second impression cylinder 16 via the transfer cylinder 18. When the second impression cylinder 16 that has received the printing paper continues to rotate, the second impression cylinder 16 has a diameter that is ½ that of the second plate cylinder 12 and the second blanket cylinder 14. On the printing paper held on the outer periphery of the second impression cylinder 16, magenta ink is transferred in the first rotation, and yellow ink is transferred in the second rotation.

  In this way, the leading end portion of the printing paper on which the printing of four colors has been completed is transferred from the second impression cylinder 16 to the discharge cylinder 19. Then, the printing paper on which the printing of the four colors has been completed is conveyed toward the paper discharge unit 32 by the drive of the pair of chains 23 and is discharged. At this time, the printing paper being conveyed is measured by the imaging unit 60, and the ink supply amount is controlled based on the measurement result, and the color tone is adjusted.

  When the printing process is completed, the printing plate used for printing is discharged. Then, the first and second blanket cylinders 13 and 14 are cleaned by a blanket cylinder cleaning device (not shown), and the printing process is completed.

  In the above-described printing machine, when the second image is printed on the back surface of the printing paper on which the first image is printed, the surface of the printing paper on which the first image is printed is directed downward. In the state, it is placed on the paper feeding unit 31. The printing paper is conveyed to the transfer cylinder 18 via the paper supply cylinder 17 and the first impression cylinder 15. At this time, the printing paper is conveyed with its surface on which the first image is printed facing outward (sensor 10 side).

  In this transfer cylinder 18, the sensor 10 detects the presence or absence of printing paper, thereby confirming a printing paper feed error, and the second plate cylinder 12 and the second printing cylinder 12 for printing with magenta and yellow inks. In the printing unit including the blanket cylinder 14 and the second impression cylinder 16, the second impression cylinder 16 and the like are prevented from being contaminated.

  Hereinafter, an operation for detecting a printing paper according to the present invention will be described. FIG. 3 is an explanatory diagram for explaining a detection operation for detecting the printing paper S. FIG. FIG. 4 is a perspective view showing a main part of the transfer drum 18 having a hole H formed on the surface thereof.

  As shown in FIG. 4A, the transfer drum 18 has a hollow cylindrical shape. In addition, three holes H1, H2, and H3 (referred to as “holes H” when the holes are collectively referred to in this specification) are formed in the surface of the cylindrical transfer cylinder 18. The hole portions H1, H2, and H3 function as an antireflection region for preventing or reducing light reflection on the outer peripheral surface of the transfer drum 18. That is, when the reflectance of the surface of the transfer cylinder 18 is high, the sensor 10 receives the light reflected by the surface of the transfer cylinder 10, so that the presence or absence of the printing paper S cannot be detected. For this reason, when there is no printing paper S, such an antireflection region is formed so that light emitted from the sensor 10 does not enter the sensor 10 again.

  FIG. 3 shows the surface of the printing paper S on which the first image is formed. In the printing machine described above, the second image is printed on the back surface of the printing paper S. In this figure, L indicates a detection line of the printing paper S by the sensor 10. Reference numeral 51 indicates the position of the horizontal needle in the paper feeding unit 31. The position 51 of the horizontal needle is used for correcting the detection line L and the like. As shown in this figure, it is assumed that an image having two regions E1 and E2 having high density as the first image of the present invention is printed on the surface of the printing paper S.

  In such a case, the presence / absence of the printing paper S is detected at points P1, P2, P3 where the detection line L by the sensor 10 and the three holes H1, H2, H3 formed in the transfer cylinder 18 overlap. Need to do it either. However, when the presence or absence of the printing paper S is detected by using the points P1 and P3 on the two high density areas E1 and E2, the intensity of the reflected light from the printing paper S becomes weak. The presence or absence of the paper S cannot be accurately detected. For this reason, in the present invention, in order to detect the presence or absence of the printing paper S, the point P2 that does not overlap with the two regions E1, E2 having high density among the regions corresponding to the three holes H1, H2, H3. This is the detection point.

  Even when the point P2 that does not overlap with the two regions E1 and E2 with high density is set as the detection point, the intensity of the reflected light from the printing paper S changes depending on the density of the detection point P2. Therefore, in the present invention, the detection threshold value by the sensor 10 is set based on the density of the detection point P2, and the presence or absence of the printing paper S is detected based on the set threshold value.

  Note that the image data of the first image supplied from the image data supply unit 86 and stored in the RAM 82 of the control unit 80 is used for determining the position of the detection point P2 and setting the detection threshold value by the sensor 10 described above. The

  FIG. 5 is a flowchart showing a detection operation for detecting the presence or absence of the printing paper S.

  In order to detect the presence or absence of the printing paper S during printing, first, a threshold value for detection by the sensor 10 is provisionally set (step S1). The threshold value at this time is the detection value of the sensor 10 when the printing paper S is not on the transfer cylinder 18 and the light irradiated from the sensor 10 irradiates the hole H, and the blank printing paper S on the transfer cylinder 18. Is set to an intermediate value between the detected value of the sensor 10 when the sensor is mounted.

  Next, the control unit 80 scans the position on the detection line L in the first image data, finds a low-density region among the regions corresponding to the three holes H1, H2, and H3, and detects the detection point P2. Is determined (step S2). At this time, the detection point may be determined from a region having the lowest density among the three regions, or the detection point may be determined from a point equal to or less than a preset set value.

  Next, the control unit 80 stores the density value and position of the detection point P2 (step S3), and the sensor 10 outputs when the sensor point 10 reads the detection point P2 from the density value at this time. A detection value to be calculated is calculated (step S4).

  Next, the threshold value for detection by the previously set sensor 10 is changed (step S5). The threshold value at this time is the detected value of the light of the sensor 10 when the printing paper S is not on the transfer cylinder 18 and the light irradiated from the sensor 10 irradiates the hole H, and the sensor 10 calculated in step S4. Set to an intermediate value from the detected value.

  When the above preparation process is completed, printing is started (step S6). After the start of printing, the control unit 80 detects the printing paper S by the sensor 10 based on the position information of the detection point P2 previously determined and stored and the rotational angle position of the transfer cylinder 18 detected by the encoder 87. Set the timing. Then, the presence or absence of the printing paper S is detected based on the threshold value previously changed by the control unit 80 (step S7). That is, the control unit 80 acquires the detection value output from the sensor 10 at the set detection timing, and compares the detection value with the detection threshold set in step S5. If the detected value is equal to or greater than the detection threshold, it is determined that the printing paper S is mounted on the transfer cylinder 18. On the other hand, if the detection is less than the detection threshold, it is determined that the printing paper S is not loaded on the transfer cylinder 18. This operation is executed twice while the transfer cylinder 18 makes one rotation until printing is completed (step S8). When it is detected in step S7 that the printing paper S is not loaded on the peripheral surface of the transfer cylinder 18, the control unit 80 supplies a required drive signal from the drive circuit 85 to supply the impression cylinder 16 from the transfer cylinder 18. Error processing including prohibition of delivery of the printing paper S to the printer is performed.

  In the above-described embodiment, three holes H1, H2, and H3 as shown in FIG. 4A are used as an antireflection region for preventing or reducing light reflection on the surface of the transfer cylinder 18. is doing. Instead of the three holes H1, H2, and H3, a single hole H4 having a slit-like shape extending in the circumferential direction of the transfer drum 18 as shown in FIG. Good.

  In the above-described embodiment, the sensor 10 is fixed and the detection point P2 is determined on the detection line L by the sensor 10, but the sensor 10 may be configured to be movable.

  FIG. 5 is a perspective view showing the sensor 10 and the transfer cylinder 18 according to such an embodiment.

  In this embodiment, the sensor 10 is driven by a screw 52 that is rotated by driving a motor (not shown), and is movable in a direction parallel to the axis of the transfer cylinder 18. Further, the transfer cylinder 18 has a hollow cylindrical shape as in the first embodiment, and the hole H is formed on the surface of the transfer cylinder 18 in a state of 3 rows and 3 columns. When such a configuration is adopted, the degree of freedom increases when selecting a detection point.

  Further, in the above-described embodiment, various hole portions H are used as an antireflection region for preventing or reducing the reflection of light on the surface of the transfer cylinder 18. You may make it perform the surface treatment which reduces reflection. Further, in the above-described embodiment, it is detected whether or not the printing paper S is mounted on the peripheral surface of the transfer cylinder 18. However, it is also possible to detect whether or not the printing paper S is mounted on the peripheral surface of the paper feed cylinder 17 by arranging a sensor around the paper feed cylinder 17. In this case, when it is detected that the printing paper S is not mounted on the peripheral surface of the paper feed cylinder 17, error processing including prohibition of delivery of the printing paper S from the paper feed cylinder 17 to the first impression cylinder 15 is performed. Is done.

  Further, in the above-described embodiment, the hole H that is an antireflection region is formed on the surface of the transfer cylinder 18, and the reflected light from the detection point is detected by the sensor when the printing paper S is not mounted on the surface of the transfer cylinder 18. 10 so as not to enter as much as possible. Further, a point having the lowest image density is selected from a plurality of candidates corresponding to the plurality of holes H based on the image data, and the point is determined as a detection point. Further, the detection threshold is equal to or higher than the detection value to be output when the sensor 10 reads the set detection point when the printing paper S is not mounted on the peripheral surface of the transfer cylinder 18, When the printing paper S is mounted on the peripheral surface, the sensor 10 is set in a range less than the detection value to be output when the set detection point is read.

  However, a reflection region may be formed on the surface of the transfer cylinder 18 so that as much reflected light as possible is incident on the sensor 10 when the printing paper S is not mounted on the surface of the transfer cylinder 18. In this case, a point having the highest image density is selected from a plurality of candidates corresponding to the reflection region based on the image data, and the point is determined as a detection point. Further, the detection threshold is not less than a detection value to be output when the sensor 10 reads the determined detection point when the printing paper S is mounted on the surface of the transfer cylinder 18, What is necessary is just to set in the range below the detection value which should be output when the sensor 10 reads the determined detection point when the printing paper S is not mounted on the surface.

1 is a schematic diagram of a printing press according to the present invention. It is a block diagram which shows the main electrical structures of a printing machine. FIG. 6 is an explanatory diagram for explaining a detection operation for detecting the printing paper S. FIG. 6 is a perspective view showing a main part of a transfer drum 18. 4 is a flowchart showing an operation for detecting the presence or absence of printing paper S. It is a perspective view which shows the sensor 10 and the transfer cylinder 18 which concern on other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sensor 11 1st printing cylinder 12 2nd printing cylinder 13 1st blanket cylinder 14 2nd blanket cylinder 15 1st impression cylinder 16 2nd impression cylinder 17 Paper feed cylinder 18 Transfer cylinder 19 Paper discharge cylinder 20 Ink supply device 21 Dampening water supply device 31 Paper feed portion 32 Paper discharge portion 33 Plate feed portion 34 Plate feed portion 35 Image recording device 36 Image recording device 60 Imaging portion 80 Control portion 86 Image data supply portion 87 Encoder H Hole portion H1 Hole H2 Hole H3 Hole H4 Hole P2 Detection point S Printing paper

Claims (9)

A printing machine for printing a second image on the back surface of a printing paper having a first image printed on the front surface,
A printing paper is mounted on the outer peripheral surface of the printing paper with the surface facing outward, and a cylinder for conveying the printing paper;
Detecting means for detecting a rotational angle position of the barrel;
A sensor for irradiating light on the surface of the printing paper mounted on the cylinder and detecting the presence or absence of the printing paper by the amount of reflected light;
A control unit that determines the position of the detection point of the printing paper by the sensor from the image data of the first image, and sets a detection threshold value by the sensor according to the density of the detection point;
Based on the position of the detection point determined by the control unit and the rotation angle position of the cylinder detected by the detection unit, the detection timing of the printing paper by the sensor is set, and the output of the sensor at the detection timing and the A printing machine that detects the presence or absence of printing paper based on a detection threshold set by a control unit. The printing press according to claim 1, wherein
The cylinder is formed with an antireflection region that prevents or reduces light reflection,
The control unit determines the detection point from an area corresponding to the antireflection area. The printing press according to claim 2,
The barrel has a hollow cylindrical shape,
The antireflection region is a printing press formed by drilling a hole in the surface of a cylindrical body.   4. The printing press according to claim 3, wherein a plurality of the hole portions are arranged in a circumferential direction of the cylinder.   4. The printing press according to claim 3, wherein the hole has a slit-like shape extending in a circumferential direction of the cylinder. The printing press according to any one of claims 1 to 5,
The cylinder is a printing machine that is a transfer cylinder disposed between printing units that perform printing with inks of different colors. The printing press according to any one of claims 1 to 6,
A printing press that determines a detection point as a detection point in the first image when determining the detection point. The printing press according to any one of claims 1 to 7,
When setting the detection threshold,
Calculated from the detection value to be output by the sensor when paper is not loaded at the determined detection point and the density value at the determined detection point, when the paper is loaded at the detection point. A printing press that determines the detection threshold value with a detection value to be output by a sensor. The printing press according to any one of claims 2 to 5,
At the time of determining the detection point, a point having a low density in the first image is determined as a detection point,
For the detection threshold setting,
Detection value to be output by the sensor when printing paper is loaded at the determined detection point, which is equal to or greater than a detection value to be output by the sensor when printing paper is not loaded at the determined detection point A printing press that determines the detection threshold within a range of less than.

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