DE102004053891A1 - Method for capacitive identification of error sheets in printing press entails moving of printed sheets through precision capacitor from which continuous or analogue measurement signal-data stream is made available - Google Patents

Abstract

The method is for the capacitive identification of error sheets, especially double sheets, in a printing press, whereby printed sheets (13) are moved in a shingle stream (12) through a precision capacitor (14) from which a continuous or analogue measurement signal-data stream is made available in such a way that per printing press revolution (17) a number of measurement signals is recorded and transmitted to an evaluating unit, whereby the continuous or analogue measurement signal-data stream is subjected to a signal evaluation in order to filter out high frequency unwanted signals from the low frequency wanted signals. An independent claim is included for a device for the capacitive identification of error sheets, especially double sheets, in a printing press, which has an evaluating unit (16) which senses error sheets in accordance with the aforesaid method.

Description

The The invention relates to a method for capacitive identification of false sheets, in particular of double sheets, on a printing machine according to the generic term of claim 1. Furthermore, the invention relates to a device for the capacitive identification of false bows, in particular double sheets, on a printing press according to the preamble of claim 11.

At Sheetfed presses are printed sheets in the form of a Plant stack kept in place, with sheets using suction devices individually lifted from the investment pile and placed on a feed table become. about The feed table is the printed sheet lifted from the investment pile one preferably arranged in the region of a first printing unit sheet feeder fed. The printed sheets lifted from the investment pile are transferred over the Anlegtisch usually in geschuppter sheet position as a scale flow the sheet feeder fed. To guarantee a proper printing operation is important that in the scale flow of the sheet no so-called False sheets occur. For example, a false-arch can be around a double arch of two superposed Trade sheet. Will such a double sheet of the printing press supplied this can cause damage lead a printing unit of the printing press. It may continue act on a false arch around a so-called oblique arch, so to one Arc, with an incorrect or oblique orientation of the sheet feeder supplied becomes. The detection of false bows is therefore important for the printing process.

Under The term false arch should all printed sheets in the scale flow be understood, with regard to at least one property from a proper sheet differ. In addition to double sheets and oblique sheets, this can also be missing sheets, multiple sheets, Early bow, Late bow, Thick bow or thin bow be. Missing bow and multiple bow soft as double bow in terms the number of sheets of a proper sheet in the scale flow from. At early bow and late bow gives way as with oblique bows the position of the sheet in the scale flow of a proper sheet from. Thick bow and thin bow differ in terms of the printing material thickness of a proper sheet in the shingled stream.

In practice come to sheet-fed presses for the identification of Double sheets usually mechanical devices used, the to be checked scale flow the Scan the printed sheet mechanically. Here, the mechanical double sheet control device rolls up the signature, causing run marks on the signature can be. running marks affect the printed sheet the print quality and are therefore disadvantageous. Furthermore come in practice double sheet control devices for use, either on the principle of optical transmission or the absorption or reflection of ultrasonic waves. optical Double sheet control devices or ultrasonic double sheet control devices However, double-sheet control requires the presence of a single sheet ahead. In a sheetfed press, this condition is only temporary and only immediately before any mechanical access to the sheet through the sheet feeder met the sheetfed press. It immediately follows that when using an optical Double sheet control device or an ultrasonic double sheet control device a double sheet is identified, only a short time to execute a Emergency stops the sheetfed press is available.

To avoid the above drawbacks of the double-sheet control devices hitherto used in practice, according to the prior art according to the DE 40 03 532 C2 as well as the EP 1 403 202 A1 capacitive double sheet control devices proposed. In these capacitive double-sheet control devices, the imbricated flow to be tested is moved through a measuring capacitor, wherein the measuring capacitor is formed by a measuring electrode and the feed table serving as counter-electrode. Since all printing materials invariably have a different dielectric than dielectric, the flow rate of the imbricated flow through the measuring capacitor changes as it does so, whereby, in principle, false bends or double sheets can be identified from the capacitance change.

In the practice has the capacitive double sheet control devices So far, however, has not yet made its entry, since the available Accuracy is insufficient to false-arch even with very thin substrates be able to identify or detect safely. So are from the state known in the art, capacitive double sheet control devices susceptible to mechanical vibrations and opposite Soiling, so they under real operating conditions a sheetfed press could not be used reliably so far. The known from the prior art, capacitive double sheet control devices feature only over an insufficient signal to noise ratio.

Of these, Based on the present invention, the problem is based a novel method for the capacitive identification of false sheets, in particular of double sheets, on a printing machine and a to create appropriate device.

This Problem is solved by a method for capacitive identification of false sheets, in particular of double sheets, on a printing machine according to the claim 1 solved.

According to the invention of the or each measuring capacitor, a continuous or analog measurement signal data stream provided such that per printing press revolution a plurality detected by measuring signals and forwarded to the evaluation is, wherein the continuous or analog measurement signal data stream in the Evaluation is subjected to a signal evaluation to high-frequency noise filter out from low frequency useful signals.

With The present invention is a novel signal acquisition as well as signal evaluation or signal analysis in the capacitive identification of Wrong bills suggested that over a sufficient signal to noise ratio has and therefore makes capacitive false-arc identification practically usable. For the purposes of the present invention is by the or each Measuring capacitor, a continuous or analog measurement signal data stream provided. One maybe Accordingly, existing double sheet will not, as in the prior art, only measured once per press revolution, but many times in Form of a continuous or analog measurement signal data stream. Therefore, a large number of measuring signals per press revolution detected. This multitude of measuring signals basically bears a statement about the Course of the scale flow, superimposed of interfering signals mechanical and electrical disturbances. Under knowledge of the process parameters Speed of the scale flow, format of the sheet and thickness The printed sheet can be used to establish signal evaluation or signal analysis be differentiated between useful signals and interfering signals. hereby can the signal to noise ratio in the capacitive identification of false arch compared to the stand Technique can be increased significantly, so also false arch in thin Printing materials can be reliably detected.

Preferably is the continuous or analog measurement signal data stream in the Evaluation device of a spectral analysis or spectral analysis subjected to high frequency noise filter out from low frequency useful signals.

The inventive device for the capacitive identification of false bows, in particular of Double sheet, on a printing machine is defined in claim 11.

preferred Further developments of the invention will become apparent from the dependent claims and the following description. An embodiment of the invention is without limitation to be closer to the drawing explained. Showing:

1 : A schematic representation of a moving on a feed table scale flow to illustrate the inventive method for the capacitive identification of false sheets, especially double sheets, on a printing press, and

2 : a highly schematized view of a measuring capacitor.

Hereinafter, the present invention will be described with reference to FIG 1 and 2 described in more detail.

1 shows a feed table 10 a printing press, over which in the direction of the arrow 11 a shingled stream 12 from several sheets 13 is moved in a shingled sheet position of a non-illustrated investment pile in the direction of a likewise not-shown printing unit of a sheet-fed press. The in 1 Shingled stream shown 12 is characterized in that apart from the beginning of the scale flow, the sheet 13 either with double or triple arc superposition in the scale flow 12 available. Depending on the format length of the printed sheets, more than double or triple sheet superimposition in the imbricated flow is also conceivable.

The shingled stream 12 is through at least one measuring capacitor 14 moves, in the preferred embodiment of a measuring electrode 15 and the feed table serving as the counter electrode 10 is formed. The measurement capacitor can also be formed by two discrete electrodes, one of these discrete electrodes then being preferably positioned in a recess of the application table.

From the measuring capacitor 14 detected measurement signals are sent to an evaluation device for evaluation 16 transmitted, which depends on the measuring capacitor 14 provided measurement signals a false sheet, in particular a double sheet, in the scale flow 12 identified or detected.

For the purposes of the present invention, it is proposed that the or each measuring capacitor 14 provides a continuous or analog measurement signal data stream, namely such that per printing press revolution detected a plurality of measurement signals and to the evaluation 16 be transmitted. In this case, based on machine-angle synchronous pulses, which are preferably provided by a non-illustrated angle sensor of the printing press, the or each measuring capacitor 14 queried. Each angle synchronous pulse is from each measuring capacitor 14 provided a reading. For example, if the angle encoder supplies 2048 pulses per machine revolution, then 2048 measured values per press revolution are sent to each evaluation capacitor by the measuring capacitor 16 forwarded. The number of measured signals recorded and relayed per printing press revolution accordingly corresponds to the number of pulses provided by the angle transmitter of the printing machine per press revolution. In this way, the scale flow 12 each printing press revolution measured several times and it is a continuous or analog measurement signal data stream of the evaluation 16 provided. In 1 are machine revolutions with double arrows 17 visualized 1 shows a total of seven press revolutions.

At this point it should be noted that the or each measuring capacitor 14 does not necessarily have to be queried on the basis of machine angle synchronous pulses. Rather, the continuous measurement signal data stream may also be provided based on one pulse per machine revolution in conjunction with a high rate free-running signal acquisition. A computer then determines the time duration of a machine revolution from the time interval between the pulses and interpolates a fixed number of measurement signals per machine revolution from the data stream recorded via the free-running signal acquisition so as to provide the continuous measurement signal data stream by way of resampling is cheaper, but somewhat inaccurate, as the provision of continuous or analog measurement signal data stream based on machine-angle synchronous pulses.

in the The meaning of the present invention is for a given number of press revolutions the same number of measuring signals per press revolution recorded and written to a shift register or pushed. The Size of the shift register, that is, the number of press rotations recorded in the shift register, determines a measurement window, which is used for capacitive false-arc identification becomes. The size of the measurement window is about the total capacitive false-arc identification constant and includes at least one signature length.

By the multiple or multiple measurement of the scale flow 12 per machine revolution, a continuous or analog measurement signal data stream is provided, which in the sense of the present invention in the evaluation device 16 is subjected to a signal analysis. As a result, high-frequency interference can be safely filtered out. As a result of the signal detection and signal processing according to the invention, the signal-to-noise ratio of the capacitive false-arc identification is markedly increased compared to the prior art, so that the capacitive false-arc identification is now accessible for practical use. The signal analysis can be carried out as a spectral analysis or spectral evaluation, preferably as a Fourier transformation. The Fourier transformation used is preferably the Fast Fourier Transformation (FFT) or the Discrete Fourier Transformation (DFT).

in the For the purposes of the present invention, before and / or during the capacitive false-arc identification automatic calibration Calculation of a setpoint course. So can in the sense of here present Invention from the predetermined format size of the printed sheets to be printed, from a given speed of the scale flow as well from a given scale length of the scale current, a setpoint curve for the measured signals is calculated become.

Furthermore, it is possible to generate a setpoint curve from measured values during a startup sequence of the scale flow. So visualized 1 with the curve 18 the time course of the measuring capacitor 14 provided, continuous or analog measurement signal data stream over a total of seven machine revolutions. Will be a first sheet 13 in the range of the measuring capacitor 14 moves, as it turns in the measurement signal data stream 18 a first signal swing 19 one. The height of the signal hub 19 corresponds to the condition of the printed sheet 13 , Get a second sheet 13 , which is partially covered by the first sheet, in the range of the measuring capacitor 14 , so turns a second signal 20 one. Already a comparison of these two Signalhube 19 and 20 can be used for plausibility checks. For example, would be the second signal swing 20 twice the size of the first signal swing 19 , so could already be concluded on a double sheet. At the in 1 Shingled stream shown 12 , which is characterized by a double or triple sheet overlay, turns after another machine revolution 17 a third signal swing 21 one. For a proper scale flow 12 corresponds to the Size as well as the temporal occurrence of the third signal stroke 21 the signal chicken 19 and 20 , Is the first sheet 13 completely through the measuring capacitor 14 has been moved through and leaves this area of the measuring capacitor 14 , so occurs a first signal drop 22 in the measurement signal data stream 18 on. Already from this, the further expected setpoint course for a proper scale flow can be used for the calibration 12 be derived or calculated. So have to follow the first signal drop 22 at additional predefined time intervals as well as with predefined level changes further signal envelope 23 as well as signal waste 24 to adjust. The amount of a signal swing changes 23 , it can be concluded on a false sheet, in particular a double sheet or triple sheet. If the time interval between the signal peaks and the signal drops changes, then an irregular scale current can change 12 getting closed. After the startup sequence of the scale flow, a signal deviation and a signal drop must be set within each machine revolution.

The Signal analysis of the continuous or analog measurement signal data stream is therefore preferably such that in particular by a spectral analysis high-frequency interference signals be filtered out of low frequency useful signals, the In this case obtained actual signal course with one of the parameters the shingled current calculated target signal waveform is compared. To be considered in the calculation of the desired signal curve Parameters are: format length and thickness of the printed sheet to be printed; Speed of the scale flow; shingle length of the shingled stream. The constant Comparison between desired signal course and actual signal course leads to a Adaptation of the theoretical waveform to the real waveform, giving the system a learning ability obtained. The above measurement can be anywhere within the scale flow performed become. The measurement is preferably made early, i. with clear Distance from mechanical access to the sheet by the sheet feeder, carried out.

It is also within the meaning of the present invention, to each side of the feed table 10 , and with it to each side of the Schuppenstrom 12 , at least one measuring capacitor 14 to position. By comparing the of these measuring capacitors 14 provided signals can then be identified, for example, a slanted arc, so an arc whose leading edge obliquely to the feed direction 11 of the shingled stream 12 runs. The number of measuring capacitors used 14 is freely selectable.

The described above, signal evaluation according to the invention can be done either within capacitive sensors or in a machine control. If the signal evaluation is to be carried out in the capacitive sensors, so must Machine synchronization signals are passed to the sensor. Should, however, the Signal processing in the machine control done so must be proportional to capacity Analog signals are passed from the sensors to the machine control. Since in addition to synchronization signals in the machine control a Variety of other relevant data is available, is the signal evaluation preferred in the machine control.

The or each measuring capacitor 14 can directly above a suction belt of the feed table 10 , Be positioned next to a suction belt or in the area of a bridge over a suction belt. The positioning of the measuring capacitor via a suction belt has the advantage that the scale flow to be measured 12 forming printed sheet 13 are sucked in the region of a suction belt and therefore an exact distance to the measuring electrode 15 the respective measuring capacitor can be maintained. The measurement next to a suction belt has the advantage that in this area of the feed table 10 has a homogenous or non-perforated surface, so that a modulation that occurs when measuring over a suction belt can be eliminated due to the suction belt perforation. Regardless of the specific positioning of the measuring capacitors 14 is a rigid support for the same desirable because rigid brackets have high natural frequencies and therefore due to the holders conditional vibrations of the measuring capacitors can be safely filtered out as high-frequency noise with sufficient signal to noise ratio of the low-frequency wanted signals.

As already mentioned, in the preferred embodiment, the or each measuring capacitor 14 from a measuring electrode 15 and the feed table serving as the counter electrode 10 educated. 2 shows a highly schematic of a preferred embodiment of the measuring capacitor 14 ,

So is according to 2 the measuring capacitor 14 from the measuring electrode 15 and the feed table serving as the counter electrode 10 formed, wherein the measuring electrode 15 in the preferred embodiment, a projection 25 having the distance between the measuring electrode 15 and the feed table 10 reduced locally. field lines 26 be in the area of the projection 25 bundled and caused by the scale flow change of the dielectric causes a strong signal change in this area. By using such a measuring electrode 15 the signal acquisition can be optimized. Furthermore, the position of the sheet in the Shingled stream can be detected more accurately. It should be noted that both electrodes of the measuring capacitor can have such a projection.

With The present invention can all non-conductive substrates be subjected to a secure and accurate false-arc identification. Likewise conductive Substrates are measured when an electrically insulating Distance between the substrate and the electrodes of the measuring capacitor is adjustable. This can, for example, via an air cushion or by spacer rollers respectively.

10

feed table

11

arrow

12

shingle stream

13

sheet

14

measuring capacitor

15

measuring electrode

16

evaluation

17

Druckmaschinen revolution

18

Curve

19

signal swing

20

signal swing

21

signal swing

22

signal drop

23

signal swing

24

signal swing

25

head Start

26

field line

Claims (11)

A method for the capacitive identification of false sheets, in particular of double sheets, on a printing press, wherein printed sheets are moved in a shingled sheet position as shingled stream through at least one measuring capacitor, and being forwarded by the or each measuring capacitor measuring signals to an evaluation, which from the measuring signals the occurrence of False sheets, in particular of double sheets, identified in the scale flow, characterized in that from the or each measuring capacitor, a continuous or analog measurement signal data stream is provided such that per printing press rotation a plurality of measurement signals is detected and forwarded to the evaluation, wherein the continuous or analog measurement signal data stream is subjected in the evaluation of a signal evaluation to filter out high frequency noise from low frequency useful signals. Method according to claim 1, characterized in that that the measuring signals are provided in an angle-synchronized manner, that in dependence of pulses provided by an angle transmitter of the printing press Measured signals from the or each measuring capacitor detected and sent to the Evaluation be forwarded. Method according to claim 2, characterized in that that the number of per press revolution detected and forwarded Measurement signals of the number of times by the angle encoder per press revolution provided pulses. Method according to one or more of claims 1 to 3, characterized in that for a predetermined number of Press revolutions per press revolution always the same number of measuring signals is detected. Method according to claim 4, characterized in that that for recorded a predetermined number of press revolutions Measuring signals for defining a measuring window of at least one Pressure arc length be pushed into a shift register, and that the measuring signals on the by the size of the shift register defined measuring window size for identification be evaluated by false-arch. Method according to one or more of claims 1 to 5, characterized in that the signal evaluation as spectral evaluation in the form of a Fourier transformation, in particular as a Fast Fourier transformation (FFT) or discrete Fourier transform (DFT). Method according to one or more of claims 1 to 6, characterized in that a calibration of the false-sheet identification automatically performed becomes. Method according to claim 7, characterized in that in that on the basis of a predetermined format size the printed sheet, a predetermined speed of the scale flow and a predetermined scale length of the scale current, a setpoint curve for the measured signals is calculated becomes. Method according to claim 7, characterized in that that on the basis of measured values, which during a startup sequence of Shingling current can be determined, a setpoint curve for the measurement signals is calculated. Method according to one or more of claims 1 to 9, characterized in that measurement signals from to both sides of the scale flow or the plant table positioned measuring electrodes for the identification of oblique sheets compared with each other. Device for the capacitive identification of false sheets, in particular of double sheets, on a printing press, with a feed table ( 10 ), on which sheet ( 13 ) in shingled sheet position as a shingled stream ( 12 ) are movable with at least one measuring capacitor ( 14 ), and with an evaluation device ( 16 ) to which the or each measuring capacitor ( 14 ) can be forwarded in order to determine from the measurement signals the occurrence of false bows, in particular of double sheets, in the scale flow ( 12 ), characterized in that the evaluation device ( 16 ) False bows in the sense of a method according to one or more of claims 1 to 10 determined.