Device for holding sheets using suction air

Abstract

Pneumatically acting holding device for a sheet (3) transported on a support surface (26) in a sheet (3) processing machine (1), wherein the support surface (26) has a plurality of suction openings (24), wherein at least one sensor (29) is assigned to each of the suction openings (24) for controlling the suction force of the suction air provided through the suction opening (24) depending on the coverage of the suction opening (24) by the sheet (3), characterized in that at least three sensors (29a, 29b, 29c) are assigned to each of the suction openings (24) for controlling the suction force, wherein the sensors (29a, 29b, 29c) are arranged adjacent to the suction openings (24).

Description

[0001] The invention relates to a device for holding sheets on a cylinder or a tray by means of suction air, in particular in a printing machine, e.g., an inkjet printing machine.

[0002] The cylinder or tray each has a number of suction openings, which are arranged, for example, in a grid pattern next to each other and one behind the other. By shutting off the suction air, especially at suction openings located outside the sheet format to be processed, the effective suction area can be adapted to the sheet format being processed.

[0003] DE 100 02 094 B4 already discloses suction openings that are activated when covered by a sheet.

[0004] DE 20 2011 107 531 U1 discloses a suction air generating impeller which can be activated or deactivated by means of a slide or a diaphragm.

[0005] DE 698 21 120 T2 describes a suction drum whose drum wall has radial passages. Each passage has an air pressure sensor located therein and a valve flap associated with it. A mechanical or electrical arrangement connects the respective air pressure sensor to its valve flap, so that the valve flap is closed when the air pressure detected by the air pressure sensor is relatively high and the valve flap is open when the detected air pressure is relatively low.

[0006] Further state of the art is provided by DE 10 2009 048 928 A1 and DE 10 2011 003 962 A1.

[0007] The invention is based on the object of creating a sensor-controlled suction air holding device.

[0008] The object is achieved according to the invention by the features of claim 1.

[0009] It is a particular advantage of the invention that sensors are provided for activating the suction openings, which also detect sheet corners or edges if, for example, they are raised and thus do not seal a suction opening tightly.

[0010] This measure allows sheets, especially in their edge areas, to be securely sucked in and fixed flat on a cylinder surface or a tray surface.

[0011] In order to control the suction intensity of a suction opening, it is advantageous to assign several sensors to each individual suction opening.

[0012] The number of covered sensors determines the level of suction power.

[0013] Covering only one sensor means that the detected sheet area is far from the support surface, requiring a high suction force to draw it onto the support surface. Covering two sensors assumes that the sheet edge is raised and requires medium suction force. If all sensors are covered, this means that the sheet is lying flat and is being well suctioned, so the suction force can be reduced.

[0014] No sensor cover means that the suction opening is outside the sheet format and therefore should not generate any suction power.

[0015] Further advantageous embodiments are described in the subclaims.

[0016] Embodiments of the invention are illustrated in the drawings and are described below.

[0017] They show: Fig. 1 a sheet-fed rotary printing press in section in a schematic representation, Fig. 2 a plan view of a developed surface of a printing cylinder or a tray with a suction air control by means of solenoid valves, Fig. 3 a suction opening of the pressure cylinder or tray with an impeller as a suction air generator, Fig. 4 the suction openings of the printing cylinder or tray with a suction air control by means of impellers, Fig. 5 a section of a support surface with suction openings, each of which is assigned four sensors, Fig. 6 a plan view of a surface not according to the invention with suction air control, Fig. 7 shows a section of a support surface not according to the invention with suction openings, wherein a smaller number of sensors is used.

[0018] A sheet-fed printing press 1, in particular a digital printing press, has a feeder 2 for feeding sheets to the sheet-fed printing press 1 and a delivery 4 for removing the printed sheets from the digital printing press 1. At least one printing station 6 is provided for printing the sheets 3. The sheet is transferred from the feeder 2 by means of a feed table 7 to a feed cylinder 8, which preferably transfers the sheet to a double-sized transfer drum 9. From here, the sheet 3 is transferred by means of a transfer cylinder 11, for example, of single size, to a printing cylinder 12, for example, of triple size, on which the sheet is printed by means of an inkjet printing unit 13. The printed sheet 3 is transferred from the printing cylinder 12 to a transfer drum 14, in particular of double size, from where it is transferred via a transfer drum 16, for example, of single size, to a chain gripper system 17 of the delivery 4.In turning operation, the transfer drum 14 operates as a storage drum and transfers the sheet at its rear edge to a downstream turning drum 18, from where the sheet 3 is returned to the transfer drum 9 by means of a transfer drum 19 for printing on its back side so that it can be printed on the back side in the printing unit 6.

[0019] The printing cylinder 12 is designed, in particular, as an inkjet printing cylinder and has mechanical and / or pneumatic gripper devices 22 for holding a sheet in order to fix the sheet at its leading edge. To improve the holding force acting on the sheet and ensure a smooth, wrinkle-free position of the sheet on the printing cylinder 12, the support surface 26 for the sheet, e.g., the outer surface of the printing cylinder 12, is provided with additional suction grippers, e.g., in the form of suction openings 24.

[0020] The support surface 26 for the sheet 3 according to Fig. In a preferred embodiment, 2 is a cylinder surface or the surface of a tray for transporting sheets through a printing press. The support surface 26 has suction openings 24 arranged in a uniform grid, which are arranged evenly one behind the other in the sheet transport direction B and next to each other transversely to the sheet transport direction Q.

[0021] Each suction opening 24 is assigned a solenoid valve 27, which controls the suction air supply from a common suction air source 28. Activation of the solenoid valves 27 is effected by sensors 29, which are assigned to each suction air opening 24.

[0022] In an embodiment according to Fig. 3, each suction opening 24 is provided with its own suction air generator 31, e.g., in the form of an impeller. The suction force of an impeller 31 can be controlled by baffles, slides, or disruptive air.

[0023] For controlling the suction air, three sensors 29a, 29b, 29c are assigned to the impeller 31 or the solenoid valve 27, for example, which react to being covered by a sheet and thus control the suction air accordingly.

[0024] If none of the sensors 29a, b, c is covered, the impeller 31 or the solenoid valve 27 is ineffective and does not generate any suction air. If only one of the sensors 29a; 29b; 29c is covered, it is assumed that a raised bend corner is present, and the impeller 31 or the solenoid valve 27 is operated with maximum suction force generation (p max ) so that the raised corner of the sheet is sucked down onto the suction opening 24.

[0025] When two sensors 29 are covered, it is assumed that there is a raised arc edge, whereby the impeller 31 or the solenoid valve 27 is operated with a medium suction force generation (e.g. ½ p max ) is operated.

[0026] When all three sensors 29 are covered, it is assumed that the suction opening 24 is completely covered by the sheet, so that only a small suction force (e.g. ¼ p max ) is needed to keep the bow in the suctioned state.

[0027] To save sensors 29 on a support surface 26, it is according to Fig. 4, it is provided that suction openings 24, which are within the smallest sheet format to be processed (B min ), have no sensors 29 and are constantly operated with a small suction force (p min ) are operated.

[0028] According to Fig. 5, it is provided that each suction opening 24 is assigned four sensors 29a, 29b, 29c, 29d. This measure eliminates the orientation dependence of the suction opening 24 on the position of the sheet relative to the suction opening 24. In this case, the three offset sensors must be evaluated to detect a sheet corner or edge (see, for example, Fig. 7), i.e., from adjacent suction openings 24, in order to determine the position of sheet edges and corners. Alternatively, it could be provided that only one sensor 29 is assigned to each suction opening 24.

[0029] As an alternative to the embodiment according to the invention, in which the suction units are independent of each other, the information about the sheet edges or sheet corners can be evaluated centrally in order to avoid incorrect control, e.g. due to the malfunction of a sensor, via the redundant knowledge about the relationship between sheet edges and sheet corners.

[0030] If redundant information is to be avoided, a minimum number of sensors is sufficient to clearly determine the sheet edges and corners (see in particular Fig. 6).

[0031] If data about the format and position of the substrate is also transmitted to the suction system, targeted control can be achieved purely via preset values, even without sensors on the suction surface. Instead of a suction cylinder, the suction surface can also be a tray or chain segment. Alternatively, it may be required that the suction element be completely covered in order to be able to suction at all (e.g., to prevent air currents under jetting nozzles). List of reference symbols 1 sheet-fed printing press 2 investors 3 sheets 4 booms 5 . / . 6 printing stations 7 Feed table 8 feed cylinders 9 Transfer drum 10 . / . 11 transfer cylinders 12 printing cylinders 13 printing unit 14 Transfer drum 15 . / . 16 transfer drum 17 chain grippers 18 Turning drum 19 Transfer drum 20 - 22 . / . 23 Gripper device 24 Suction opening 25 . / . 26 support surface (12) 27 Solenoid valve 28 Suction air source 29 Sensor 29a Sensor 29b Sensor 29c Sensor 29d Sensor 30 . / . 31 suction air generators (impellers) p max maximum suction power ½ p max half suction power ¼ p max low suction power B max maximum sheet format B min minimum sheet format B Sheet transport direction Q transverse direction

Claims

[1] Pneumatically acting holding device for a sheet (3) transported on a support surface (26) in a sheet (3) processing machine (1), wherein the support surface (26) has a plurality of suction openings (24), wherein at least one sensor (29) is assigned to each of the suction openings (24) for controlling the suction force of the suction air provided through the suction opening (24) depending on the coverage of the suction opening (24) by the sheet (3), characterized by that at least three sensors (29a, 29b, 29c) are assigned to each of the suction openings (24) for controlling the suction force, wherein the sensors (29a, 29b, 29c) are arranged adjacent to the suction openings (24). [2] Pneumatically acting holding device according to claim 1, characterized by that a controllable switching valve (27) is provided for each suction opening (24). [3] Pneumatically acting holding device according to claim 1, characterized bythat a controllable suction air generator (31) generating suction air is provided for each suction opening (24). [4] Pneumatically acting holding device according to one of the preceding claims 1 to 3, characterized by that each suction opening (24) is assigned four sensors (29a, 29b, 29c, 29d), wherein the sensors (29a, 29b, 29c) are arranged adjacent to the suction openings (24). [5] Pneumatically acting holding device according to one of the preceding claims, characterized by that the support surface (26) has a plurality of suction openings (24) arranged in rows one behind the other and in rows next to one another. [6] Pneumatically acting holding device according to one of the preceding claims, characterized by that the level of suction force of a suction opening (24) is determined depending on the number of covered sensors (29a, 29b, 29c, 29d) of the suction opening (24). [7] Pneumatically acting holding device according to one of the preceding claims, characterized by that the support surface (26) is a lateral surface of a cylinder (12). [8] Pneumatically acting holding device according to one of claims 1 to 6, characterized by that the support surface is the surface of a tray. [9] Digital printing machine with a pneumatically acting holding device according to one of claims 1 to 8.

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