Method for monitoring a print on a substrate

Abstract

Method for monitoring a print on a substrate, in which ultrasonic waves (25) are sent through the substrate (7) in transmission mode, in which an attenuation measurement of the received sound level (I E ) is carried out, where a signal for the quality of the print (18-21) is derived from the damping measurement and where a measurement location (29) is selected depending on the color saturation in the print (18-21).

Description

[0001] The invention relates to a method for monitoring a print on a substrate according to the preamble of claim 1.

[0002] From DE 43 21 179 A1, a device for controlling or regulating the operating processes of a printing press is known, comprising an image acquisition device directed at the surface of a printed product. The signals representing a printed image are processed in a computer. As a result of this processing, control signals for an ink metering device are generated, and the substrate is inspected for material defects such as spots or holes. A program also runs in the computer that identifies suitable measurement locations. The speed of the image signal processing is limited. The camera optics used for image acquisition are susceptible to contamination.

[0003] It is also known from DE 198 52 719 A1 to use ultrasonic detectors to monitor whether sheets are being fed to a printing press double or multiple times and whether the sheets are damaged. A transmitter and several receivers are arranged on both sides of the sheet transport path. If a double sheet occurs, the power of the sound waves at the receivers is significantly attenuated. The interface attenuation can be locally eliminated by printing ink or dampening solution between the sheets. However, it is assumed that adhesion between the sheets, which are usually unprinted, does not occur simultaneously at multiple locations.

[0004] DE 692 16 043 T2 describes a device for ultrasonic testing of composite materials, in which a multitude of focused ultrasonic beams emanating from a transducer have essentially the same angle of incidence on the surface of the material being tested. If the composite material, which is stationary in water, exhibits delamination, additional characteristic echoes of the ultrasonic waves are generated. The arrangement of a multitude of ultrasonic sensor pairs is structurally complex. The signal processing is designed for testing stationary objects. For mapping material defects, the transducer can only be moved towards the object at low speed.

[0005] German patent DE 10 2005 026 200 A1 describes a method for detecting layered, planar objects in which ultrasound waves are transmitted through at least one object. The ultrasound waves are attenuated as they pass through the object. For a flat recording medium of any thickness, the same signal level is always obtained at an ultrasound receiver. To monitor the quality of an object, several ultrasound transmitter-receiver arrangements can be positioned across its width. This method can be used, for example, to detect voids or delamination in paper webs. The measurement locations on the object are fixed by the spacing of the transmitter-receiver arrangements.

[0006] In a device for feeding sheets according to US 6,540,222 B2, a double feed in transmission mode is monitored by an ultrasonic detector. Sheets lying in pairs are separated by a conveyor element. The air between the sheets causes strong attenuation of the emitted sound waves, so that the signal level at an ultrasonic receiver is significantly reduced.

[0007] US 7 404 559 B2 shows an ultrasonic double-arc control in transmission mode. The reception characteristics of an ultrasonic receiver change depending on the ambient temperature.

[0008] German patent application DE 44 46 367 A1 discloses a method and a device for the dynamic determination of the thickness or basis weight of moving material. The material is exposed to a focused ultrasonic field of high sound intensity, whereby the sound component emanating from the material is directly detected in the near field and evaluated to determine the thickness or basis weight. Preferably, the near-field measurement is carried out with continuous sound and in transmission.

[0009] German patent application DE 101 37 389 A1 discloses a method and a device for testing thin materials, wherein the material is exposed to ultrasound waves, at least in certain areas, and the transmission of the ultrasound waves through the material is determined and evaluated. The transmission of ultrasound waves at different frequencies is measured. Based on the differences in transmission at the various frequencies, a criterion for assessing the quality of the treated material is then determined.

[0010] German patent application DE 10 2007 015 365 A1 describes a method for determining the degree of hardening or drying of printing inks or varnish layers on a printing substrate. The degree of hardening or drying is determined indirectly by measuring the change in the mechanical or viscoelastic properties of the printing inks or varnish layers on the printing substrate during the hardening or drying process. An ultrasonic measurement method is used. Measurements are taken both before and after passing through a dryer, and the recorded and analyzed values ​​are then compared.

[0011] German patent application DE 10 2005 018 855 A1 discloses a device for inspecting printed products manufactured on a printing press. The device is equipped with a first camera which is directed at an inspection area on the printed product to be checked, and at least one further camera is provided which is directed at least partially at the same inspection area already monitored by the first camera.

[0012] In the German trade journal DE-Z: Deutscher Drucker No. 38 / 22.11.2007, page 15 describes how blistering in web offset printing with high ink layer thicknesses can be avoided by using measuring devices to record and store moisture levels in the paper rolls, the printed product, and the pressroom online. If blistering occurs, the paper moisture can be adjusted to predefined levels.

[0013] The object of the invention is to develop a method for monitoring a print on a substrate which makes it possible to avoid bubble formation with minimal effort.

[0014] The problem is solved by a method which has the features of claim 1. Advantageous embodiments are described in the dependent claims.

[0015] According to the invention, a print on a substrate is monitored by sending sound waves through the substrate in transmission mode and by measuring the attenuation of the sound waves as they pass through the substrate at at least one measuring point depending on the color saturation in the print.

[0016] It is particularly advantageous to perform the attenuation measurement at a measurement location with maximum color saturation. The probability of bubble formation is greatest at this measurement location.

[0017] If the damping at the selected measuring point exceeds a limit value, a signal can be generated to control an operating process of the printing machine. In particular, a warning signal or control signals for a dryer and / or a printing speed actuator can be derived. The invention will be explained in more detail with reference to an exemplary embodiment.

[0018] They show: Fig. 1: A printing press with an ultrasonic detector in transmission mode, Fig. 2: a diagram of an ultrasound detector on an arc with bubble formation, Fig. 3: Level diagrams from absorption measurements with an ultrasonic detector, and Fig. 4: A diagram for positioning an ultrasound detector.

[0019] Fig. Figure 1 shows a schematic of an offset printing press with a feeder 1, four printing units 2 to 5, and a delivery unit 6. The sheet-feeding cylinders or drums 7 are connected by a common gear drive. A motor 8 and a gearbox 9 drive the machine. A rotary encoder 11 is mounted on the drive shaft of the printing cylinder 10 of printing unit 3. A chain conveyor 12 is located in the delivery unit 6 for transferring the sheets 7 from the last printing unit 5 to a stack 13. A dryer 14 and an ultrasonic detector 15 are arranged in the conveying path between the printing unit 5 and the stack 13. The motor 8, the encoder 11, the dryer 14, and the detector 15 are connected to a control unit 16.

[0020] The sheets 7 are separated from a stack 17 in feeder 1 and printed in printing units 2-5 with four partial color images 18-21 ( Fig. 2) Printed. While the sheets 7 are conveyed past dryer 14, the partial color images 18-21 are dried. The dryer capacity is matched to the conveying speed of the sheets 7.

[0021] The detector 15 consists of an ultrasonic sensor 22 and an ultrasonic receiver 23, which are described in more detail in Fig. Figure 2 shows the detector 15, which can be positioned transversely to the conveying direction 24. Depending on the printed image, the detector 15 is set to a position where a printed image area with maximum color saturation is detected. Sound waves 25 are emitted from the ultrasonic transmitter 22 at a predetermined intensity, penetrating the sheet 7 to a greater or lesser extent. The sound waves 25 are attenuated by the printing ink of the partial color images 18-21 and by the material of the sheet 7. The portion of the sound waves 25 that is still present on the side of a sheet 7 facing away from the ultrasonic transmitter 22 is detected by the ultrasonic receiver 23 and evaluated in the control unit 16.

[0022] In the Fig. In diagram 3, two different receiver intensities, IE1 and IE2, are shown, which occur in the specified print image area with maximum color saturation for an OK sheet 7 and a sheet 7 with blisters 26. On the OK sheet 7, the printing ink of the partial color images 18-21 is firmly bonded to the material of the sheet 7. The intensity I E1 The sound wave intensity at the ultrasonic receiver 23 is high and normalized to 100% in the diagram. If the dryer 14's power is incorrectly set, the printing ink detaches from the sheets in the areas of maximum color saturation, resulting in blisters 26. The intensity I E2 At ultrasound receiver 23, in this case, the intensity is I E1 greatly reduced. If the intensity I EIf a predefined threshold value IES is undershot, then control signals for the dryer 14 and / or the motor 8 are generated in the control unit 16. These control signals cause the dryer output and / or the machine speed to be reduced when blisters 26 appear. If a dryer 14 with individually controllable jets is used, it is possible to reduce the dryer output automatically or manually only where blisters 26 appear. The appearance of blisters 26 can be indicated to the machine operator visually or audibly by a warning signal.

[0023] Fig.Figure 4 shows a diagram for positioning an ultrasonic detector 15. The detector 15 is attached to a holder 27. The holder 27 can be positioned transversely to the conveying direction 24 on a frame-mounted crossbeam 28 by means of a motor. The motor is connected to the control unit 16. The data for the partial color images 18-21 are available from the prepress stage. Using this data, the control unit 16 calculates the coordinates (X1, Y1) of a suitable measuring location 29 and generates control signals for the motor. The motor automatically moves the holder 27 to the y-coordinate y1 of the measuring location 29. The ultrasonic receiver 23 of the detector 15 is activated by the signals from the rotary encoder 11 precisely when the measuring location 29 is within the detection range of the receiver 23. Reference symbol list 1 investor 2-5 printing unit 6 outriggers 7 sheets 8 engine 9 gearboxes 10 pressure cylinders 11 rotary encoders 12 chain conveyors 13 stacks 14 dryers 15 Detector 16 Control unit 17 stacks 18-21 Partial color image 22 ultrasound transmitters 23 ultrasound receivers 24 Direction of conveyance 25 sound wave 26 blisters 27 holders 28 traverse 29 Measurement location

Claims

[1] Method for monitoring a print on a substrate, in which ultrasonic waves (25) are sent through the substrate (7) in transmission mode, in which an attenuation measurement of the received sound level (I E ) is carried out, where a signal for the quality of the print (18-21) is derived from the damping measurement and where a measurement location (29) is selected depending on the color saturation in the print (18-21). [2] Method according to claim 1, characterized by , that a measurement location (29) with maximum color saturation is selected. [3] Method according to claim 1, characterized by , that the signal is used to control an operating process of a machine producing the imprint (18-21). [4] Method according to claim 3, characterized by , that the signal is used to generate a warning signal. [5] Method according to claim 3, characterized by, that the signal is used to generate a control signal for a dryer (14). [6] Method according to claim 3, characterized by , that the signal is used to generate a pressure speed control signal. [7] Method according to claim 1, characterized by , that the measurement location (29) is calculated from the data reproduced in the imprint (18-21).

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