EP1701901B1 - Method and device for the contactless detection of flat objects - Google Patents

Description

The invention relates to methods for non-contact detection of flat objects according to the preamble of claim 1 and to a device according to the preamble of claim 3.

Methods and devices of this kind are described e.g. Used in the printing industry to determine whether a single sheet or multiple sheets or a missing sheet exists for paper, film or similar sheet materials in the printing and manufacturing process. Usually, the need to have a single sheet in the printing process, while in determining a multiple sheet, e.g. a double sheet is a separation of such a double sheet to protect the printing press normally required. In an analogous manner, even when determining that there is no single sheet, so to speak a "missing sheet" is present, the normal printing process is modified or interrupted until a single sheet is detected again.

Likewise, these methods and devices are also used in the packaging industry, in which, for example, labels applied to base material or carrier material are counted or checked for the presence or absence. Another area of use is the detection of tear threads or tear points, especially in thin, used as wrapping films, such as cigarette packs. But even metal-clad papers, sheet-like plastic sheets or films and sheets can be detected by means of such methods and devices without contact in manufacturing operations.

The measuring principle used in a generic method and a device when using e.g. Ultrasound and the detection of paper in sheet-like form, based on the fact that the ultrasonic wave emitted by the transmitter penetrates the paper and the transmitted portion of the ultrasonic wave is received by the receiver as a measurement signal and is evaluated in terms of its amplitude. In the presence of a multiple or double arc therefore sets in the receiver a much smaller amplitude, as in the presence of a single arc.

The subsequent evaluation of the received measurement signal was previously in practice with approximately linear amplifiers or similarly designed amplification circuits and downstream filters. Due to the relatively low dynamic range, in particular of linear amplifiers, thick papers, cardboard or even corrugated cardboard were often difficult or impossible to detect. In addition, the flutter behavior, which often occurs especially with very thin papers or films, which is understood as a movement of the thin, flexible sheet during the detection between the transmitter and receiver in the direction of the bow normal, insufficient to master with such amplifiers. A comparable behavior reveals strongly inhomogeneous materials.

With regard to a better mastery of the above-mentioned problems, especially with very different material-specific attenuation of the transmitted signal, which further in accordance with the practice in this regard only from Basis weights and grammages is spoken, a teaching process or a teach-in step was performed. In this case, the flat object to be detected, such as a paper sheet, for example, is detected with regard to its grammage or its sound absorption characteristic and entered into the evaluation device in the sense of teaching in before the actual detection process begins.

A significant disadvantage is that in other flat objects with different weights again a corresponding teach-in step must be performed and taught, which on the one hand is complex and on the other hand usually leads to significant downtime in the corresponding facilities.

With regard to the material specifications for papers, reference is made to the present standards, which can be exemplified by DIN-Taschenbuch 118 (Edition 2003-06), DIN-Taschenbuch 213 (Edition 2002-12), DIN-Taschenbuch 274 (Edition 2003-06), DIN-Taschenbuch 275 (1996-08 edition), or regarding corrugated cardboard refer to DIN 55468-1.

From the DE 200 18 193 U1 respectively. EP 1 201 582 A An apparatus for detecting single sheets or multiple sheets is known. For the detection of these sheets, this known device has at least one capacitive sensor and at least one ultrasonic sensor. Here, an evaluation unit for deriving a signal for the detection of the single or multiple sheet is provided. This signal is derived from a logical combination of the output signals of the sensors, wherein the appropriate detection signal is determined in an adjustment phase.

Another device is as a capacitive sensor from the DE 195 21 129 C1 known. This primarily aimed at the non-contact detection of labels on a substrate device works with two capacitor elements and an oscillator influencing them. The dielectric properties of the paper or other planar objects therefore influence the resonant circuit of the oscillator with respect to the frequency, which is evaluated for detection.

The disadvantage here, however, that relatively thin papers are difficult or impossible to detect, as well as metal-laminated papers. Even very thin films are difficult to detect due to their small thickness and sometimes only slightly different from one different dielectric constant.

Further detection methods with ultrasonic proximity switches are eg in the EP 0 997 747 A2 respectively. EP 0 981 202 B1 described. In these probing sensors, an automatic frequency adjustment takes place, in which, after the emission of an ultrasonic pulse and subsequent reflection on the object to be detected, the optimum transmission frequency is evaluated as a function of the height of the received ultrasonic echo amplitude.

Another device of the type mentioned is from the DE 203 12 388 U1 known. This ultrasonic device uses the transmission and reflection of the radiation to determine the presence and strength of the corresponding objects. However, this device also uses reference reflectors, so that a relatively complex structure of the device is present.

Furthermore, from the DE 297 22 715 U1 an inductively operating device for measuring the thickness of sheets known, which may consist of non-ferrous metals or ferrous metals. The measurement of the thickness of the sheets takes place here via the evaluation of the operating frequency of a frequency generator or via the evaluation of its amplitude. To set this device, it first requires a teach-in step in which a calibration plate is introduced into the measuring chamber and the operating frequency or the amplitude of the frequency generator is set according to a standard thickness curve.

Although a distinction between single, false and multiple sheets can be carried out by means of this device, but for this purpose different standard thickness curves must be stored and evaluated for this decision. In addition, this device is suitable for detecting sheet thicknesses up to about 6 mm. The detection of thin sheets or films is not very safe due to the small change in damping.

In the DE 44 03 011 C1 a device for separating non-magnetic sheets is described. For this purpose, it is provided that, in the presence of a double sheet, a traveling-field inductor exerts a force provided opposite to the conveying direction of the laminated core, so that the present double sheet is separated into two sheets. For non-metallic sheet objects or films, this device is completely unsuitable.

The DE 42 33 855 C2 describes a method for controlling and detecting bump inhomogeneities. This method works optically and on the basis of a transmission measurement. However, especially in the control of paper sheets with respect to single sheets and multiple sheets there is the problem that due to the material nature of the sheets very strong fluctuations due to inhomogeneities or the reflection behavior and the flutter of the sheets are caused. To overcome this problem, this document provides a measured value evaluation using the fuzzy logic rules.

From the US 2003/0006550 For example, a method is known which performs a digital evaluation on the basis of ultrasonic waves and the phase difference between a reference phase and the received phase, and on this basis determines a signal for the determination of false-arc, single or multiple-arc. However, the sole evaluation of the phase difference may be insufficient for special papers or films and lead to misinformation, which should be excluded in a secure detection.

A particularly useful for counting banknotes, but also in other papers and films usable method is from the DE 30 48 710 C2 known. This method, which is based on the determination of the basis weight or the thickness of the materials to be detected, works with pulsed ultrasound waves, wherein for the detection of a double sheet, ie the presence of two overlapping or overlapping banknotes, in particular the evaluation of the integration of the phase shift is used. The field of application of this method is therefore primarily geared to the counting of banknotes or of comparable papers and foils taking into account the basis weights of such materials. For use in packaging materials or the counting of labels, therefore, this method seems unsuitable.

Another method on acoustic or ultrasonic basis is from the DE 40 22 325 C2 known. This method, which is based on the control of faulty or multiple sheets of sheet or foil-like objects, requires a first pass of the corresponding flat object with a calibration and adjustment process, which is carried out automatically by microprocessor controlled. It is therefore in this method, a kind of teaching first on the thickness of the object with respect to an optimal measurement and frequency range required and continue in such a first pass the detection and storage of a corresponding threshold.

In the field of application of the detection or the counting of labels, comparable methods and devices are known. In this case, the difference in a label is initially to be seen, since this is provided on a base or carrier material as an applied material layer. This layered material behaves outwardly in terms of opacity, dielectric, electromagnetic conductivity, or the sound propagation time as a connected piece of material, so that there is only a comparatively low attenuation in these detection options, which is still evaluable.

From the DE 199 21 217 A1 is together with the DE 199 27 865 A1 and EP 1 067 053 B1 a device for the detection of labels or flat objects known. This device uses ultrasonic waves with a modulation frequency, wherein a threshold value during a calibration process or a teach-in step is determined to distinguish between single and multiple sheets. By means of the teach-in step, the detection can indeed be set to the special flat object in the sense of a label. However, this teach-in step makes the device more complex and requires longer setup times when switching to another planar object. This shows that a larger material spectrum can not be detected per se, but only tuned to the specific individual material.

In consideration of this prior art, the invention has for its object to design a generic method and apparatus for non-contact detection of flat objects, or very flexible and has a large range of materials, a reliable detection of single, missing or Multiple sheets with different sheet materials, especially papers, allows, can be done without teach-in step and different rays or waves as optical or acoustic type can be used.

This object is achieved according to the method by the features of claim 1 and in devices solved by the features of claim 3.

The invention takes into account that an immediate conversion of the measurement signal can be carried out in the context of an A / D conversion, whereby the digital values obtained are subjected to the measurement signal characteristic of the corresponding purely digital correction characteristic in order to achieve, as it were, directly the evaluable target characteristic ,

This principle of the application of a correction characteristic also has the great advantage that different sensor devices, in particular as a barrier or barrier arrangement, eg in a fork shape, can be used, whereby advantageously ultrasonic sensors or optical sensors can be used, wherein for these sensors the same procedure can be used equally. If, procedurally, the measurement signal obtained at the output of the receiver or the measurement signal converter is subjected to further amplification, the corresponding correction characteristic, which may also consist of a combination of several correction characteristics, is impressed on the output side for the further amplification device Evaluation to obtain a well-evaluated target characteristic over the entire basis weight range. By means of this target characteristic, the detection of the corresponding planar object with respect to certain threshold values can then take place in a subsequent method step, which can be implemented, for example, in a microprocessor, so that a clear detection signal is obtained in single-sheet, missing-sheet or multiple-sheet.

As an alternative, the method also provides that the measurement signal obtained in the receiver or its measurement signal characteristic is subjected directly to an analog-to-digital conversion, these digital values, taking into account a corresponding purely digital correction characteristic, to a target characteristic with generation of a corresponding Detection signals are processed.

According to the invention, these measures provide the advantage that reliable detection of the corresponding flat objects over a very large grammage and basis weight range is achieved without the need for a teach-in process, which would lead to downtimes of the system. In addition, the dynamic range of the evaluation is considerably expanded, so that the detection of very thin or very inhomogeneous materials that tend to flutter behavior, with good security is feasible. On the basis of the amplitude evaluation of the measurement signal obtained in the receiver, by means of the correction characteristic curve and the target characteristic curve, the method according to the invention therefore makes it possible to reliably distinguish between single sheet, missing sheet and multiple sheet or double sheet, and this for very thin or very sound-transmissive objects, eg with a basis weight From 8 g / m ² or about 10 microns thick, up to relatively thick and strong Schallintransmissiven objects up to 4000 g / m ² , for example, with a thickness of 4 mm, without a previous teach-in process sure to distinguish.

With regard to a high degree of flexibility, not only with regard to a wide variety of materials, such as corrugated cardboard or plastic packaging, the invention also envisages taking account of correction characteristic curves which represent a combination of different correction characteristics, whereby these combined correction characteristics also only partially over partial areas of the entire grammage range can be applied.

This makes it possible to achieve the target characteristics with improved approximation to the ideal curve for detection of single sheets.

Depending on the circumstances of the circuit design of the evaluation device, the sensor device used and / or the examined material spectrum, the correction characteristic can also sections as a linear or non-linear characteristic, as a single or multiple logarithmic curve, as an exponential curve, as a hyperbolic curve, as a polygon, be designed as a function of any degree or empirically determined or calculated characteristic or as a combination of several of these characteristics.

According to the invention, the target characteristic for different material spectra is divided into three sections.

In three areas a partial target characteristic for the gram weight range above 1200 g / m ² for very thick papers and another portion below 20 g / m ² can be formed for a very thin paper, for example, spectrum. The introduction of portions of the target characteristic thus allows for improved reliability in terms of single, false or multiple arc detection.

With regard to a clear detection of single sheet, missing sheet or multiple sheet, in particular double sheets, the amplitude value is compared with threshold values based on the target characteristic. These are in particular an upper threshold for air and a lower threshold for double or multiple sheets.

Therefore, if the received measurement signal with the corresponding value of the target characteristic is greater than the upper threshold value, this is evaluated as a "missing signature". A received measuring signal smaller than the lower threshold value means a "multiple or double sheet". For a received measurement signal with the corresponding value on the target characteristic between the threshold values, this is detected as a "single arc".

In order to improve the detection possibilities, in particular with regard to a more precise adjustment to the material spectrum to be detected, the threshold values, in particular for multiple sheets, can be permanently or continuously defined or designed to be carried dynamically.

A dynamic double arch threshold can be used in this sense to an additional extension of the measurable grammages. For this, e.g. the single-sheet value is measured and compared with the associated multiple sheet value e.g. be evaluated as a polygon function, if it is a simple function, such as a descending straight line or a constant value for the single sheet.

Method and device can be realized well in particular by means of at least one ultrasonic sensor device. The sensor device preferably has at least one coordinated and coaxially aligned ultrasound transducer pair.

However, the method and apparatus according to the invention are also applicable to optical sensors.

In the case of ultrasonic sensors, it has been found, in particular, that even flat objects with printing, color printing or reflecting surfaces can be detected well. Also is it is possible to mount the pair of sensors, in particular for barriers and when mounted in a fork shape, perpendicular or inclined to the sheet plane.

Appropriately, the operating mode of the sensor device is selectable or switchable depending on the material spectra to be detected and the operating conditions as pulse operation or continuous operation.

In continuous operation, an inclined mounting of the sensor pair is preferable in order to avoid interference or standing waves by means of this measure. Conveniently, the continuous operation is, so to speak, designed as quasi-continuous operation, e.g. periodically, in comparison to the evaluation time short periods, the signal is switched off and turned on again. To avoid standing waves and phase jumps can be provided in the transmission signal.

It has also proved to be advantageous to modulate the transmission signal with at least one modulation frequency. In this way tolerances of the transducers can be corrected or compensated in particular for ultrasonic sensors. Although the sensor elements are tuned to each other, they usually have different resonance frequencies. If a frequency sweep f _s with a frequency significantly lower than the exciting frequency is used for a frequency modulation, the resonance maximum of the sensor elements is periodically exceeded. If the response time of the sensor is significantly less than 1 / f _s , the transducer properties of each individual sensor element or pair of sensors can be used optimally for ultrasonic transmission in this way.

The frequency sweep will normally be up to several 10 kHz.

The tolerances of the sensor elements are expediently corrected automatically before or during operation. This is done by normalizing the sensor element pairs to a fixed value at a predetermined fixed distance, in particular the optimal mounting distance. As a result, bad sensor elements are made better and good sensor elements or converters made worse. To compensate for this, a correction factor is necessary. According to the method, this can be done by the use of a straight line stored or calculated in the microprocessor μP as value pairs, since the measurement signal is already connected to e.g. a simple-logarithmic correction characteristic is evaluated and the correction characteristic generates an approximately linearly falling target characteristic over the transducer or sensor element spacing. That the input signal at the microprocessor of an evaluation device falls to a good approximation linearly with the transducer distance. Therefore, the correction of the values is easy even with variable distance, since when turning on a corresponding device only a straight line function for the correct initial value has to be calculated or stored as a value pair. The correct determination of sensor head spacing is made by a transit time measurement.

A particular advantage of the method by means of ultrasound can be seen in the fact that the distance between transmitter and receiver in the sensor device for this teach-in-free method can be designed variably. In other words, the sensor device can be adapted relatively quickly to different applications with regard to their distance, without this affecting the precision of the measurement of the method. A further improvement of the method can be brought about by the monitoring of the distance between transmitter and receiver and its determination. This determination of the distance between transmitter and receiver can be realized on the one hand by reflection of the radiation between transmitter and receiver and on the other hand also by means of reflection between Transmitter and receiver despite a present in the space flat material, even a thick bow. If an exceeding of the permissible maximum sensor distance is determined, then the evaluation device, eg a microprocessor, can carry out a corresponding correction of the ascertained amplitude values of the measurement signal as a function of the distance between transmitter and receiver.

The orientation of the transmitter and receiver to each other in the main radiation direction, in particular coaxially to each other, with almost any inclination angle can be provided to the sheet plane.

With regard to an optimal detection, a feedback between the transmitter and the evaluation device, in particular a microprocessor, can be provided, in order to obtain a maximum amplitude at the output taking into account the material specification of the planar objects to be examined and further operating conditions. It is also possible to control the optimum transmission frequency. With this measure, aging effects of the sensor elements can be compensated and a product test of the device according to the invention, in a particularly advantageous embodiment of the invention in series production fully automated.

In an advantageous development, a feedback is provided between the evaluation device and the transmitter, by means of which a maximization of the amplitude of the received measurement signal can be carried out. It is also preferred to provide a self-alignment between transmitter and receiver with regard to an optimal transmission frequency and / or amplitude.

This self-adjustment can be carried out in times synchronized with the transmission frequency, in fixedly defined pause times or else via a separate input provided externally to the sensor device.

With a view to optimal process control for installations in which the method and the apparatus are used, it is suitable to provide at least one A / D converter or a threshold generator for digitizing the analog measuring signal in order to be able to digitally process the further processing of the values ,

In particular, in the processing and selection of various signals of a plurality of signal amplification devices, the activation and selection of the corresponding channels and signals is preferably carried out via time-division multiplexing devices.

Fig. 1

das Prinzip eines erfindungsgemäßen Verfahrens sowie blockschaltartig eine entsprechende Vorrichtung unter Einbeziehung von Spannungsdiagrammen nach den Fig. 1a, 1b, 1c, welche die Struktur der Kennlinien bei der Detektion von Bögen aus Papier, Folien oder dergleichen Materialien verdeutlichen;

Fig. 2

das Prinzip eines Verfahrens sowie blockschaltartig eine entsprechende Vorrichtung unter Einbeziehung von Spannungsdiagrammen nach den Fig. 2a, 2b, 2c, 2d welche die Struktur der Kennlinien bei der Detektion von Etiketten, Aufreißstellen und dergleichen Materialien verdeutlichen;

Fig. 3a

ein Kurvendiagramm, welches die schematische Abhängigkeit der Ausgangsspannung eines Verstärkers, wie in Fig. 1 beispielhaft aufgezeigt, in Abhängigkeit von der Grammatur bzw. dem Flächengewicht von zu detektierenden Materialien zeigt, wobei idealisierte Zielkennlinien miteinbezogen sind;

Fig. 3b

ein schematisches Diagramm analog zu Fig. 3a mit der Ausgangsspannung eines Verstärkers in Abhängigkeit von der Grammatur bzw. dem Flächengewicht der zu untersuchenden Materialien, wobei mehrere Zielkennlinien zusammen mit entsprechenden Schwellwerten, z.B. Luftschwelle, Doppelbogenschwelle, dargestellt sind;

Fig. 4a

eine schematische Darstellung, wie bei bekannter Messwert-Kennlinie und idealer Zielkennlinie für Einfach- bzw. Doppelbogenerkennung im kartesischen Koordinatensystem die Korrektur-Kennlinie ermittelt werden kann;

Fig. 4b

eine schematische Darstellung, bezogen auf die Etikettenerkennung mit idealer Zielkennlinie, bekannter Messwert-Kennlinie und einer zur Transformation erforderlichen Korrektur-Kennlinie;

Fig. 4c

eine schematische Darstellung der Kennlinien bei Doppelbogenerkennung, sofern keine ideale Zielkennlinie vorliegt;

Fig. 4d

eine Darstellung von Kennlinien zur Doppelbogenerkennung mit Spiegelung an einer gedachten Achse unter Einbeziehung der Transformation nach Fig. 4f;

Fig. 4e

eine schematische Darstellung von Kennlinien für die Etikettenerkennung mit Spiegelung an der gedachten Achse unter Berücksichtigung Fig. 4f;

Fig. 4f

schematisch eine Transformation des kartesischen Koordinatensystems um einen Winkel a mit Darstellung einer Bezugsachse des neuen Koordinatensystems;

Fig. 4g

eine schematische Darstellungen von idealer Zielkennlinie und realen Zielkennlinien bei der Doppelbogenerkennung;

Fig. 4h

eine schematische Darstellung einer idealen Zielkennlinie und einer realistischen Zielkennlinie für die Etikettenerkennung;

Fig. 4i

schematische Darstellungen einer Messwert-Kennlinie und Korrektur-Kennlinie bei der Einfach- bzw. Doppelbogenerkennung, wobei die Korrektur-Kennlinie eine aus einer e-Funktion und einer Umkehrfunktion abgeleitete Kennlinie darstellt, mit daraus ermittelten Zielkennlinien;

Fig. 4j

schematische Darstellung einer aus einer gewichteten Hyperbel abgeleiteten Messwert-Kennlinie sowie eine aus einer logarithmischen Funktion abgeleiteten Korrektur-Kennlinie mit daraus ermittelter Zielkennlinie für die Einfach- bzw. Doppelbogenerkennung;

Fig. 5a

eine schematische Prinzipdarstellung der bei der Detektion eines Doppelbogens von Material mittels Ultraschallwellen beispielhaft vorliegenden Messkriterien;

Fig. 5b

in vergleichbarer Weise wie in Fig. 5a die schematische Darstellung einer Klebestelle zwischen einem Material-Doppelbogen und die sich hierbei erhebenden Messkriterien bei Erfassung mittels Ultraschall;

Fig. 5c

die schematische Darstellung von auf einem Grund- oder Trägermaterial haftend aufgebrachte Materialien, teils als einfach geschichtete und teils als mehrfach geschichtete Materialien, wobei dieser Aufbau die Struktur einer Etikette zeigt;

Fig. 6

in blockschaltartiger Darstellung das Verfahren und eine Vorrichtung am Beispiel einer Kombination von verschiedenen Korrektur-Kennlinien;

Fig. 7

eine schematische Darstellung ähnlich Fig. 6, wobei das Prinzip für das Einstellen einer Korrektur-Kennlinie und das Berechnen einer Korrektur-Kennlinie mit Rückwirkung auf die Schaltungsblöcke dargestellt ist;

Fig. 8

eine schematische Darstellung für die empirische Bestimmung einer Messwert-Kennlinie über einen großen Grammatur- bzw. Flächengewichtsbereich;

Fig. 9

eine schematische blockschaltartige Darstellung eines Verfahrens bzw. der entsprechenden Vorrichtung mit der Kombination z.B. der Mehrfachbogenerkennung mit der Erkennung von auf Trägermaterial haftend aufgebrachten Materialschichten bzw. Etiketten;

Fig. 10

schematisch ein Diagramm der normierten Ausgangsspannung U_A über den Grammaturbereich mit konstanter bzw. dynamischen Doppelbogenschwellen,

Fig. 11

eine Zielkennlinie mit eingezeichnetem oberen und unteren Flatterbereich, und

Fig. 12

mit den Darstellungen zu Fig. 12a und 12b die Anordnung eines Sensors mit optimaler Ausrichtung bei einer einwelligen Wellpappe und entsprechend Fig. 12b, die analoge Ausrichtung eines Sensors bei zweiwelliger Wellpappe.

The invention will be explained in more detail below with reference to schematic illustrations and diagrams as well as with reference to underlying measuring principles. Show it:

Fig. 1

the principle of a method according to the invention as well as block-like a corresponding device including voltage diagrams according to the Fig. 1a, 1b, 1c which illustrate the structure of the characteristics in the detection of sheets of paper, foil or the like materials;

Fig. 2

the principle of a method and block like a corresponding device including voltage diagrams according to the Fig. 2a, 2b, 2c . 2d which illustrate the structure of the characteristics in the detection of labels, tear points and the like materials;

Fig. 3a

a graph showing the schematic dependence of the output voltage of an amplifier, as in Fig. 1 exemplified, depending on the grammage or the basis weight of detected Shows materials, with idealized target characteristics included;

Fig. 3b

a schematic diagram analogous to Fig. 3a with the output voltage of an amplifier as a function of the grammage or the basis weight of the materials to be investigated, wherein a plurality of target characteristics are shown together with corresponding threshold values, eg air threshold, double arch threshold;

Fig. 4a

a schematic representation of how with known measured value characteristic and ideal target characteristic for single or double sheet detection in the Cartesian coordinate system, the correction characteristic can be determined;

Fig. 4b

a schematic representation, based on the label recognition with ideal target characteristic, known measured value characteristic and required for transformation correction characteristic;

Fig. 4c

a schematic representation of the characteristics in double sheet detection, if no ideal target characteristic exists;

Fig. 4d

a representation of characteristics for double-sheet recognition with reflection on an imaginary axis, including the transformation to Fig. 4f ;

Fig. 4e

a schematic representation of characteristics for the label recognition with reflection at the imaginary axis under consideration Fig. 4f ;

Fig. 4f

schematically a transformation of the Cartesian coordinate system by an angle a with representation of a reference axis of the new coordinate system;

Fig. 4g

a schematic representations of ideal target characteristic and real target characteristics in the double-sheet detection;

Fig. 4h

a schematic representation of an ideal target characteristic and a realistic target characteristic for the label recognition;

Fig. 4i

schematic representations of a measured value characteristic and correction characteristic curve in the single or double sheet detection, wherein the correction characteristic is a derived from an e-function and an inverse curve characteristic, with determined target characteristics;

Fig. 4j

schematic representation of a derived from a weighted hyperbola measurement curve and a derived from a logarithmic correction curve with derived therefrom target characteristic for single or double sheet detection;

Fig. 5a

a schematic diagram of the present in the detection of a double sheet of material by means of ultrasonic waves by way of example measuring criteria;

Fig. 5b

in a similar way as in Fig. 5a the schematic representation of a splice between a material double sheet and the thereby raising measurement criteria when detected by ultrasound;

Fig. 5c

the schematic representation of adhesively applied to a base or substrate materials, partly as a single-layered and partly as a multi-layered materials, this structure shows the structure of a label;

Fig. 6

in Blockschartiger representation of the method and an apparatus using the example of a combination of different correction characteristics;

Fig. 7

a schematic representation similar Fig. 6 showing the principle for setting a correction characteristic and calculating a correction characteristic with effect on the circuit blocks;

Fig. 8

a schematic representation for the empirical determination of a measured value characteristic over a large grammage or area weight area;

Fig. 9

a schematic block diagram-like representation of a method or the corresponding device with the combination, for example, the multiple sheet recognition with the recognition of adhesive on carrier material applied material layers or labels;

Fig. 10

schematically a diagram of the normalized output voltage U _A over the grammage range with constant or dynamic double arch thresholds,

Fig. 11

a target characteristic with marked upper and lower flutter area, and

Fig. 12

with the illustrations too Fig. 12a and 12b the arrangement of a sensor with optimal alignment in a single-wall corrugated board and accordingly Fig. 12b . the analog alignment of a sensor with two-shaft corrugated board.

The in the Fig. 2-5 and 9-12 contents shown are not part of the invention.

The representation after Fig. 1 schematically shows the inventive method and a device with Blockschaltartigem structure and achievable at certain points voltage curves in the sense of characteristics over a grammage or basis weight range g / m ^{2 of} a material to be detected spectrum.

The further discussion is based on an ultrasonic sensor device, but in principle also other sensor devices of optical, capacitive or inductive nature can be used.

In this case, a corresponding sensor device 10 has, on the one hand, a transmitter T and an opposing receiver R aligned therewith, between which the flat objects to be detected, in the example, are moved without contact in an arc shape.

In Fig. 1 For example, a multiple arc is shown as double sheet 2.

Since the amplitude evaluation of the measuring signal UM for detecting a single sheet, a missing sheet, ie no sheet, or a double or multiple sheet is assumed for this basic example, a possible stress curve UM is dependent on the grammage or grammage g / m ² for the measuring characteristic MK in Fig. 1a shown.

With regard to an unambiguous reliable decision as to whether a single sheet, a double sheet or a missing sheet is present, it is an object of the invention, taking into account threshold values, such as for the air threshold or as a double-arch threshold, to have clear intersections with these threshold values or the greatest possible stress separation to get these thresholds.

The knowledge underlying the invention assumes that in generic methods and devices in the prior art, in the multiple arc detection and an assumed, subsequent approximately linear amplification, optionally with further filtering and evaluation, depending on the grammage or the Basis weight, a characteristic curve for the amplified measurement signal is obtained, which is substantially highly nonlinear, in particular exponential, multiply exponential or hyperbolic or similar, over a large desired range of application of the material spectrum an uncertain and error-prone detection is often present, with a simple Change the principle.

The principle according to the invention therefore is to take into account a correction characteristic curve and to apply this e.g. memorize the evaluation circuit subsequent to the receiver, for which purpose the following amplifier device is suitable, in particular, for achieving a well evaluable target characteristic for reliable detection with the decision as to whether a single sheet, no sheet or a multiple sheet is present over the desired grammage range.

Such a correction characteristic KK is in Fig. 1b shown schematically. This correction characteristic, which is in Fig. 1b the dependence between the output voltage U _A of the input voltage U _E only shows in principle, illustrates in comparison with the characteristic curve MK after Fig. 1a , which also shows only schematically the course of the measuring signal UM, that relatively high voltage values U _{M seen} over the grammage range, little or no gain, while smaller voltage values, eg at relatively large basis weights (g / m ² ) a much higher, possibly exponential gain experienced.

The resulting target characteristic ZK with the voltage U _Z as a function of the grammage (g / m ² ) is in Fig. 1c also shown only schematically. The desired ZK can also from a pointwise mapping (implicit KK) of the measurement signal UM to the desired output signal U _{Z are} transformed and thus the desired target characteristic ZK can be achieved. This requires an amplifier with adjustable gain _, which then receives the correction characteristic from a μP.

The mapping of the measurement signal UM to the desired output signal U _Z based on the KK can also be done instead of value discrete, so pointwise, also continuous value.

This in Fig. 1c The target characteristic shown has the solid line trace having three regions. A first and a third relatively steeply sloping region and a middle, only slightly inclined to the abscissa region comprising a large grammage range.

Since the first and the third region could show a more optimal course with regard to a reliable detection indication or clear switching behavior of the device, a linearly descending target characteristic ZK2 passing through the end points of the first target characteristic ZK1 is shown with an interrupted polyline as an improved target characteristic. However, this does not fall under the invention.

With regard to in Fig. 1 In principle and Blockschaltmäßig shown device 1 for the detection of single sheet, missing sheet or multiple sheet, the received at the receiver R measuring signal UM is fed to an evaluation device 4. The evaluation device 4 is shown in simplified form with the amplifier device 5 and downstream of a microprocessor 6.

The amplifier device 5 is given or impressed in the example, the correction characteristic KK, so that at the output the target characteristic ZK1 and ZK2 is obtained for further evaluation in the microprocessor 6. The microprocessor 6 can then generate a corresponding detection signal with respect to single, missing or multiple sheets, in particular double sheets, taking into account stored or dynamically calculated data, such as threshold values.

In Fig. 2 and the associated one Fig. 2a, 2b, 2c . 2d schematically shows the method and an apparatus for the detection of labels and similar materials, without a teach-in step would have to be performed.

The reference numerals correspond to the reference numerals Fig. 1 ,

The block-type structure shows a transmitter T, e.g. for the emission of ultrasonic waves, and an associated receiver R as a sensor device 10. Between transmitter T and receiver R labels 7 are passed. The aim of the device is therefore to recognize on the one hand, whether labels or no labels are present. On the other hand, it is also possible to determine the number of labels guided by the sensor device.

The measurement signal U _M or U _E obtained in the presence of a label in the receiver R can, for example, have the characteristic curve progression over the grammage with approximately linear, non-linear, exponential or the like slope that drops as indicated schematically.

The subsequent evaluation device, which may have, for example, an amplifier device 5 and a microprocessor 6 connected downstream, receives a correction characteristic curve in the amplifier 5 which, for example, increases linearly (I.) or exponentially (II.) As in FIG Fig. 2b shown, can be designed. At the output of the amplifier 5, taking into account the correction characteristic, for example after Fig. 2b reaches a target characteristic over the grammage range, as in Fig. 2c is represented by the curve I or II.

An ideal course of the target characteristic for label recognition is shown in the diagram Fig. 2 shown in principle.

This target characteristic ZK _I has the course of a negative falling line, from smaller grammages to larger grammages, optimally a constant slope and a maximum voltage difference for the output voltage U _Z at small grammage differences should be achieved across the entire grammage or basis weight range provided for label detection.

As explained below, the correction characteristic KK can also be a combination of individual different characteristics. Other correction characteristics, such as logarithmic or multiple logarithmic, can also be used depending on the characteristic curve variation of the measurement signal U _M and the gain characteristic curve. Here it is the goal, if possible, an ideal characteristic ZK _I , as in Fig. 2 shown to reach.

The curves according to the Fig. 2a, 2b, 2c show two examples of different characteristics. On the one hand for the measuring signal UM after Fig. 2a with the characteristic curve MK of a first characteristic I and a characteristic II with an interrupted polyline.

These different characteristic curves for the measurement signal MK I and MK II are then shown by way of example illustrated schematic correction characteristics KK in Fig. 2b so transformed that at the output of the evaluation, a characteristic curve for the target characteristic ZK according to Fig. 2c can be achieved.

For further clarification is in Fig. 2d a schematic representation of the output voltage U _A amplifier means over the grammage range with an exemplary course of a measured characteristic curve MK _E for a label and the target characteristic ZK _E shown how this is achievable taking into account the amplifier impressed correction characteristic KK. The illustration is exemplary for the detection of labels or splices. To achieve the desired target characteristic ZK _E , the measured value characteristic MK _{E is transformed} by means of a suitable correction characteristic KK. In this case, so to speak, each point of the measured value characteristic MK _{E is transformed} continuously or discretely in digital systems, into a corresponding value on the target characteristic ZK _E. This is shown for clarity by the arrows.

In the input area with very thin materials, for example at a grammage between 1 to 8 g / m ² , the amplifier voltage can very easily be in the saturation range. On the other hand, the use of films in labels can also quickly reach the noise amplifier's borderline, since films damp very heavily.

In the diagram, this can be seen approximately in the range of the grammage of 100 to 300 g / m ² .

Especially with such measured value characteristics MK _E , the method of characteristic correction can be used particularly advantageously, so that saturation of the measurement signal is avoided in the case of very thin and strongly attenuating materials, which ultimately ensures perfect detection of the presence or absence of labels.

For comparison with the label detection in the Fig. 2d nor a possible course of the measured value characteristic MK _DB for a single sheet for double sheet detection of preferably paper materials shown, which approximates in the upper grammage area asymptotically the double arch threshold DBS.

The diagram according to Fig. 3a shows a schematic representation of the principal dependence of a normalized output voltage signal U _A / pu of a signal amplifier as a function of basis weight or grammage (g / m ² ) with differently designed signal amplifiers for single and multiple arc, especially double sheet.

The line I in Fig. 3a symbolizes a largely idealized curve in the output voltage of single arcs as a function of the grammage when using an approximately linear signal amplifier 5, wherein there is an approximate exponential decay of the voltage line. This voltage characteristic I still does not take into account a correction characteristic KK.

From this approximately exponential decaying voltage characteristic I, by using the non-linear, in particular logarithmic and / or double logarithmic correction characteristic KK inherent to the corresponding signal amplifier, a desired target characteristic II for single arcs over a very large grammage range, i. various materials.

The target characteristic II thus symbolizes a characteristic curve for the output signal in single sheets when using a logarithmic signal amplifier, wherein the target characteristic II has an approximately linear drop.

As switching thresholds are in the diagram after Fig. 3a on the one hand the air threshold and on the other hand the double arch threshold entered as an example. The intersections of the target characteristic II after Fig. 3a with the air threshold or the double arch threshold show a sufficiently large steepness, around a defined relatively small material area around.

The largely asymptotic course of the curve I in the vicinity of the double-arched threshold is achieved by the intended transformation of a curve I with a correction characteristic KK to the target characteristic II, whereby a larger distance of the voltage value for single sheets compared to the double-sheet threshold for heavier grammages or area weights is achieved.

This example illustrates that the detection as a "missing sheet" or "air" or as "multiple or double sheet" over a large grammage and basis weight range without a teach-in process is very easy to reach.

A signal transformation from the measurement signal UM to a constant output signal U _{A of} the single arc over the entire grammage range with ideally central voltage value between the two thresholds, namely upper threshold for missing arc or air and lower threshold for multiple arc or double arc, would be the ideal to be achieved ie would correspond to the ideal target characteristic ZK for the single arc. This ideal target characteristic is in Fig. 3b marked with I. Furthermore, in Fig. 3a a curve Ia showing a multi-bow signal, in particular a double-bow signal using an approximately linear signal amplifier, wherein the curve Ia has an approximately double-exponential drop in the multiple-arc characteristic.

The further illustrated by way of example curve IIa symbolizes a multiple arc signal, in particular a double-sheet signal, with logarithmic correction characteristic, whereby approximately a single exponential drop of the multiple arc characteristic IIa is achieved.

Fig. 3b shows several target characteristics of single sheet with the representation of the normalized output voltage U _A / pu of the signal amplifier as a function of the grammage or the basis weight (g / m ² ) when using different signal amplifier.

Various thresholds and thresholds are shown. For example, the top horizontal line with broken lines indicates the saturation limit or maximum supply voltage for a signal amplifier used as an example. Furthermore, the threshold value for air or a missing sheet is shown as an example at approximately 0.7 U _A / pu. At a value of U _{A of} about 0.125, the double-arc threshold and, below it, the threshold for the noise of electrical signal amplifiers is shown by way of example.

The horizontal line I in Fig. 3b identifies an ideal target characteristic for single sheets. This ideal target characteristic shows no saturation for thin materials and has a high distance to the threshold of the noise or the double arch threshold. This ideal target characteristic means that the output voltage U _{A of} the signal amplification would ideally result in a constant signal when various grammages or area weights are input.

Since there are high residual disturbances with this ideal target curve for single curves compared to the threshold values shown, It can be assumed that the switching is secure and the detection of single-sheet, missing-sheet or double-sheet detection is secure.

Curve II shows a non-linear target characteristic with two branches IIa and IIb, which is relatively difficult to realize because of the inflection point, but can be considered as a characteristic approximating the ideal target characteristic I for single-arc curves.

The relatively shallow portions of IIa and IIb could be realized, the range IIa for lighter grammages can be conveniently realized via a nearly linear signal amplification. The area IIb for heavier grammages may e.g. be realized by means of a double-logarithmic signal amplification, the strong downward sloping kink proves to be too expensive in the technical realization due to the damping properties of papers with very high grammage.

The curve III represents a target characteristic which approximates the end points of the curve II in the simplest manner by means of a 2-point straight line connection to an ideal course as shown in the curve I. For example, this can be achieved by using a least single-logarithmic signal amplifier and shows the linearization of the measured values for single arcs over a large grammage range taking into account a corresponding correction characteristic.

The curve III has clear passages for the threshold values for air or for a double arc, so that clear switching points and detection criteria with respect to these threshold values are present.

Target curves according to the curves I, II and III therefore allow unambiguous detections over a widened compared to the prior art material spectrum.

The curve IV shown further shows an unsuitable target characteristic for single sheets. On the one hand, there is an asymptotic curve of the curve IV to the saturation limit in the upper region and, on the other hand, in the lower region to the threshold value of the noise. Such an asymptotic course should also be avoided with respect to the switching thresholds to air or to the double bow, because a clear differentiation of the states, missing sheets or double sheets would then be problematic due to small signal differences to these thresholds.

The steep drop of Curve IV in the middle region in this example only covers a small grammage range with a clear distinction to missing sheets or double sheets. Since the target characteristic over a very large material spectrum should allow a clear detection for single sheet, missing sheet or double sheet, a course according to curve IV should be avoided.

The in the Fig. 1 . 2 . 3a and 3b shown principles therefore show, in the evaluation of the received measurement signal to use a signal amplification, which is given a correction characteristic curve, the characteristic of the output voltage U _A / pu depending on the grammage of the flat objects over a large grammage range inverse or nearly inverse or the Ideal characteristic for single arc detection approximates the target characteristic curve in a suitable manner. In this way, a linear or almost linear dependence between the measurement signal U _E received by the receiver and the signal voltage U _A at the output of the signal amplifier is achieved.

Fig. 4a shows schematically in the Cartesian coordinate system with the material spectrum g / m ² on the abscissa and the percentage signal output voltage U _A on the ordinate an exemplary course of a measured value characteristic MK _DB for the detection of single or double sheet.

The ideal target characteristic ZK _i for the detection of single, false or double sheets is a constant with slope 0 (H _DB = 0). The required correction characteristic KK _DB is also shown for this example. From this, it can be seen that, initially, a transformation of the points of the measured value characteristic curve MK in the direction of the arrows P downwards and then for larger grammages, an upward transformation, in order to achieve the ideal target characteristic ZK _i for single-sheet detection.

The example after 4b shows corresponding curves of the characteristic curves for labels.

The measured value characteristic MK _E is shown as an example with a solid line.

The ideal target characteristic ZK _E represents a straight line with a negative slope or a high lift.

The correction characteristic curve KK _E required for the transformation is shown with an interrupted polyline and, in this case, has a point of discontinuity at the intersection between measured value characteristic curve MK _E and target characteristic curve ZK _E.

The Fig. 4c schematically shows the profile of the characteristics for the single or double sheet recognition for a case in which not the ideal target characteristic, but a real target characteristic ZK _{DBr is} achieved. The real target characteristic ZK _DBr therefore has a stroke H _DBr which is greater than 0. In this case, the plotted measured characteristic curve MK _DB could be transformed into the target characteristic ZK _DBr by impressing, for example, the correction characteristic KK _DB , as an upper, solid line _trace . This transformation is indicated by the arrows P.

The diagram after Fig. 4d schematically shows the transformation of a measured value characteristic MK _DB for single or double sheet recognition to the desired target characteristic ZK _DB .

The abscissa denotes the material _spectrum g / m ² , wherein the realistic measuring range M _{DBr is} indicated.

The ordinate indicates the signal output voltage U _{A of} the measured value as a percentage. This corresponds approximately to the attenuation dB.

Furthermore, the virtual end points E1 and E2 are shown as imaginary intersections of the measured value characteristic MK _DB with the target characteristic ZK _DB .

Therefore, in known measuring value characteristic MK _DB in the double-sheet detection, a correction characteristic KK _DB is necessary to obtain a linear target characteristic ZK _DB, as shown in broken line between the end points E1 and E2. The idea is therefore to transform the measured value characteristic curve MK _DB in the direction of the arrows to the real target characteristic ZK _DB . This is achieved, so to speak, by a reflection of the measured value characteristic MK _DB on the axis ZK _DB after coordinate transformation.

This coordinate transformation from the Cartesian coordinate system into a new coordinate system x ', y' is simplified in Fig.4f shown.

The further illustration after Fig. 4e schematically shows the transformation of the measured value characteristic MK _E for labels in the desired, ideal target characteristic ZK _E by means of the required correction characteristic KK _E.

If the measured characteristic curve MK _{E is known} , the correction characteristic KK _{E can be obtained} by mirroring MK _E at the axis of the target characteristic ZK _E after the coordinate transformation (see Fig. 4f ) can be achieved. In the Fig. 4f represented coordinate transformation shows simplifying the displacement for a rectilinear coordinate system x, y by an angle α. X, y are eg the axes of the Cartesian rectilinear coordinate system.

Due to the coordinate transformation, the new coordinate reference system is given by the imaginary reference axis of the target characteristics ZK _DB or ZK _E.

$$\mathrm{yʹ}=-\mathrm{x}\cdot \mathrm{cos\alpha }+\mathrm{y}\cdot \mathrm{sin\alpha }\mathrm{.}$$

Maintaining the Cartesian coordinate system, the following applies to the transformation: $$\mathrm{x\; \text{'}}=\mathrm{x}\cdot \cos +\mathrm{y}\cdot \mathrm{sin\; .alpha};$$

$$\mathrm{y\; \text{'}}=-\mathrm{x}\cdot \cos +\mathrm{y}\cdot \mathrm{sin\; .alpha}\mathrm{,}$$

With regard to the required correction characteristic KK, this applies only after the coordinate transformation with respect to the realignment by the desired target characteristic ZK _DB or ZK _E , by mirroring at the corresponding target characteristic ZK _DB or ZK _E.

In the Fig. 4g and 4h the basic difference between the ideal and the real target characteristic for the single or double sheet ( Fig. 4g ) and the label recognition ( Fig. 4h ).

The Fig. 4g for the single bow shows the ideal target characteristic ZK _i , which ideally runs in a straight line, without incline, ie is constant. Here, the stroke H _i = 0 over the entire ideal range over the material spectrum M _i .

In single-sheet detection, therefore, with such an ideal target characteristic ZK _i, one would achieve a maximum distance to the upper air threshold as well as a maximum distance to the double-sheet threshold displayed below.

The arrow in the diagram indicates the transition from the ideal target characteristic ZK _i to real target characteristics, eg ZK ₁ or ZK ₂ .

It can be seen here that the flatter the real target characteristic, the wider the detectable material spectrum M1 or M2.

The Fig. 4h shows a comparable diagram to target characteristics ZK for the label recognition.

The ideal target characteristic ZK _i for the label recognition in this case has a maximum stroke H _i over a relatively large area of the material spectrum, which is characterized as an ideal material spectrum M _i .

However, real target characteristics ZK ₁ in label recognition deviate from the ideal target characteristic ZK _i in the direction of the arrow from. Accordingly, the more real target characteristic ZK _{1 has} a smaller stroke H ₁ and also a smaller material spectrum M ₁ .

Therefore, the steeper the real target characteristic is and approaches the ideal target characteristic ZK _i , the more stroke is available for a given material spectrum.

In the 4i and 4j For example, measured value characteristic curves and correction characteristic curves and derived target characteristics are shown.

So is in Fig. 4i a measured value characteristic MK shown, which could be used for a specific material spectrum for single or double sheet detection. The correction characteristic KK has the function $$\mathrm{y}=-\mathrm{<figure-callout\; id="1"\; label="ln"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">ln</figure-callout>}\left(\mathrm{1}/\mathrm{x}\right)+\mathrm{Third}$$

The correction characteristic here is derived from an e-function and an inverse or inverse function x = ln (1 / y). The illustrated target characteristic curves ZK ₁ and ZK ₂ can therefore be derived from the measured value characteristic MK and the correction characteristic KK essentially by the difference.

The example after Fig. 4j also shows schematically characteristic curves for single or double sheet recognition.

The measured value characteristic curve MK is derived in this example approximately from a weighted hyperbola. The correction characteristic KK is a correction characteristic derived from a logarithmic function. The measured value characteristic MK can be transformed in this example, taking into account the correction characteristic KK to a target characteristic ZK, which corresponds approximately to an ideal target characteristic for the single and a double sheet recognition.

Based on Fig. 5a, 5b and 5c In the following, some basic principles of the method and the corresponding device will be explained using the example of an ultrasonic sensor device and that for clear detection physical differences on the basis of a double sheet, a double sheet with splice and the example of labels briefly outlined.

These basic considerations are at least partially applicable to other sensor devices, e.g. optical, inductive capacitive type.

In Fig. 5a schematically the overlap of two single sheets is shown, so that in the overlap region of a double sheet 11 can be spoken. This double sheet 11 is to consist of two sheets of paper, wherein the space between the two single sheets is a different material from their material. Since a non-contact detection is provided, it can be assumed that on both sides of the double arc air with the parameter Z _{0 is} present and also the intermediate medium in the overlap region of the single sheets of air with Z ₀ , which as air cushion by the surface roughness of the materials in this Double sheet is present.

The direction of action of the measuring method, e.g. By means of ultrasound, in the example, is perpendicular to the double-arched region, so that a transmitted ultrasonic signal in such a "true double-bow" becomes very small due to the multiple refraction over at least three interfaces, i. the transmission factor over three layers ideally approaches zero.

More generally, therefore, a double sheet may be considered as a material structure having a lamination or a nesting layer and in one of the spaces between the lamination, at least one of the various sheet materials different medium, in particular air, is present, which is the sheet materials in the case of an ultrasonic measuring method has a significantly different acoustic resistance and thus leads to signal reflections. When two or more sheets are inserted, the signal attenuation due to signal refraction and reflection is so great that the emitted signal is strongly disproportionately damped. In other measurement methods, this affects the opacity and the surface finish and color and thickness, another dielectric, other electro-magnetic conductivity or other magnetic damping.

Under such a double sheet also falls a compound of sheets, which is not designed adhesive, e.g. by means of a mechanical toothing or knurling of sheets, since the corresponding intermediate medium would also be air.

This consideration also applies to multiple sheets in which three or more individual layers of sheet materials are stacked on top of each other.

In the Fig. 5b schematically a double sheet 12 is shown with splice 13.

The direction of action of the measuring method used, which in turn is assumed to be ultrasound, is indicated by arrows.

As a splice in the context of this consideration blunt, more or less overlapping or so executed compounds of sheets, especially sheets of paper, plastics, films and fabrics (nonwovens) considered. The connection is done predominantly by means of at least one part of the surface or the entire surface adhering medium, in particular by means of one or two sides provided adhesive and adhesive tape or adhesive.

In physical terms, therefore, a splice for a method by ultrasound means an "acoustic short circuit" by the gap between the upper arch Z ₁ and lower arch Z ₂ filling and intimately bonding adhesive layer, above and below the single arc air with Z _{0 is} assumed ,

A splice could therefore be detected in the detection method by means of ultrasound essentially as a single sheet with a high grammage.

In Fig. 5c schematically two embodiments of labels 15, 17 are shown.

In the context of this application, the term "label" is understood to mean at least one or more material layers or material layers adhesively applied to a base or carrier material. The layered material behaves e.g. With respect to the sound transmission to the outside as a connected piece of material, so that in some cases no significant attenuation of the respective physical quantities is present, but only a comparatively low, but still well evaluable damping. Possible inhomogeneities in the carrier material or applied material are not taken into account in this consideration, since in particular labels can be assumed to be of a defect-free material.

The label 15 follows in the example Fig. 5c an upper material with the parameter Z ₂ applied to a carrier material by means of an intimate adhesive bond. There is air with parameter Z ₀ on both sides of the label. As a result of this intimate adhesive bond, an acoustic short circuit exists between the materials in a detection method by means of ultrasound, so that an analogy to splices can follow Fig. 5b is available.

The same applies to the label 17 after Fig. 5c , which differs from the label 15 only by a second upper layer of material applied. In this case too, an acoustic short circuit between the materials can be assumed.

These basic considerations for the detection of double sheet, splice, label and the like, therefore, also allows the method and the device to detect and distinguish differently layered single sheets or multi-layered materials. In particular, this is also the detection or counting of applied to flat materials Labels that have an intermediate object gap possible.

In Fig. 6 is shown schematically and block-like a device for false, single and multiple sheet detection, the correction characteristic is generated as a combination of individual characteristics.

Between the transmitter T and the receiver R to be detected sheet materials or sheets are performed. The correction characteristic resulting after the amplifiers is realized in the example with a first correction characteristic in the amplifier device 21 and at least a second correction characteristic in the amplifier device 22, which is connected in parallel. The present at the output of the receiver R measurement signal or its characteristic curve over the grammage is therefore subjected to a combined correction characteristic to obtain a well-evaluated target characteristic 23, which is further evaluated in a microprocessor 6.

With regard to the combination of correction characteristics, this can also be realized in a signal amplifier or in a plurality of individual signal amplifiers connected in series or in parallel to produce the overall amplification. The realization of the correction characteristic curve can therefore be carried out in many different ways, since the essential basic idea of the invention to carry out detection of single sheet, missing sheet or multiple sheet, and this over a large grammage range, without having to integrate a teach-in process, is maintained ,

In Fig. 7 the schematic and block diagram like structure of a modified device for implementing the invention is shown. The measurement signal of the receiver R is subsequently fed to an amplifier device 24 whose signal output is routed to a microprocessor 6.

The microprocessor 6 allows in this example via the feedback in the path A set a predetermined correction characteristic over the symbolized potentiometer 25.

In an alternative circuit, a corresponding correction characteristic is calculated by means of the microprocessor 6 and the obtained or stored data and fed back via the path B to the amplifier means 24 and impressed.

It is also possible to determine a correction characteristic curve empirically or via the measurement of a representative material spectrum which is to be detected, and to enter the evaluation unit including the microprocessor 6. In this case, the determined correction characteristic curve C can be impressed in a discrete-value or continuous-value manner over the path B of the amplifier device 24 or the evaluation of the amplified output signal can be carried out directly in the microprocessor 6 on the basis of the correction characteristic curve C.

In Fig. 8 is shown in a schematic representation of the empirical determination of a measurement signal characteristic. For this purpose, a large number of materials customary in the market are passed between the transmitter T and the receiver R, and the corresponding measurement signal characteristic is determined via this. Usually in this case the measuring range is determined by the introduction of the thinnest available sheet material A and the thickest sheet material B to be detected.

The measurement signal characteristic thus determined can then be sent to the further processing system, e.g. a microprocessor, are supplied in order to determine a largely optimal correction characteristic for this measurement signal characteristic in order to achieve the required target characteristic.

In Fig. 9 schematically a device 40 for non-contact detection of multiple sheets A, without the implementation of a teach-in step, and the detection of adhesively applied to a substrate material layers B, for example, labels shown.

An important idea here is to transmit the measurement signal evaluation for multiple arcs to a separate channel A with the corresponding correction characteristic and parallel to this the measurement signal evaluation for labels B to supply a separate channel B with adapted correction characteristic.

The measurement signal obtained at the output of the receiver R is therefore switched to the corresponding channel A or channel B via a multiplexer 34 controlled by the microprocessor 6. The signal amplification in channel A is subject to a separate correction characteristic with optimum design for multiple arc detection. The signal gain in channel B is subject to a correction characteristic for the label measurement signal. Both channels A, B are fed via a subsequent multiplexer 35, which is also microprocessor-controlled, the downstream microprocessor 6 for further evaluation and detection of multiple sheet or label.

This device 40 is suitable both for the detection by means of ultrasonic waves. The essential advantage is the targeted possibility of including the respectively most suitable correction characteristic curves for fundamentally different measuring tasks, namely for the most diverse types of material, such as in the present case multiple sheets and labels, for evaluation.

Fig. 10 schematically shows a graph of the normalized output voltage U _A in% as a function of the grammage. The target characteristic curve 42 of a single arc with logarithmic amplification over the grammage range is entered. Also shown are the air threshold LS in the upper area with a solid line and the double arch threshold DBS in the lower area with an interrupted polyline.

It is essential, however, that the double arched threshold can be provided dynamically, whereby this can be done constantly over sections of the grammage range. This is illustrated by the lines B1, B2 and B3.

On the other hand, the dynamic setting of the double-bowed threshold is also linear or as a polynomial of arbitrary degree running adjustable, as shown for example between the points P1, P2, P3 and P4.

With this dynamic adjustment of the double arched threshold, an additional extension of the measurable grammages or basis weights can be achieved, so that the detectable material spectrum can be increased even further.

The Fig. 11 concerns a largely similar diagram as the Fig. 10 , wherein the course of the target curve 42 for the single bow over the entire grammage range largely matches. On the one hand, the dynamic threshold MBS is plotted for the multiple arc and its course between the points P1a, P2a and P3a.

The curve 44 marks the upper value of the flutter area for a single arc and the curve 45 the lower value of the flutter area for a single arc.

In the Fig. 12a, 12b schematically shows the basic arrangement for the detection of single-walled corrugated board 51 and two-wave corrugated board 60 and the running direction L, taking into account two sensors 61, 62, in particular ultrasonic sensors shown.

The corrugated cardboard 51 after Fig. 12a is single-walled and has at its Adhäsionspunkten with a lower bottom layer 52 and an upper cover layer 53 adhesive regions 54 and bottom and top layer connecting webs that span a wave surface 55. These webs 55 between Pappwelle and the corresponding, eg horizontally extending ground or Cover layers, so to speak constitute an "acoustic short circuit" when using ultrasound.

The example in the example Fig. 12a used sensor has on the one hand the transmitter T and the receiver R, which are aligned coaxially with each other in their main axis. The alignment of transmitter T and receiver R is preferably about perpendicular to the largest wave surface 55 or at an angle β ₁ to the perpendicular of the single-walled corrugated board.

The further stated angle β ₂ marks the angle between the perpendicular to the corrugated board and the surface direction of the main surface of the shaft.

The optimum angle β ₁ for sound coupling in an ultrasonic sensor on a single-walled corrugated board, which has a required acoustic short AK between ground layer 52 and cover layer 53, is determined by the slope t / 2h. Here, t is the distance between two wave crests and h the height of the shaft or the distance between the bottom layer and top layer.

With an optimal arrangement of the sensor, one endeavors to achieve an alignment with β ₁ = β ₂ , these angles then being 45 ° in the example. However, the conformity of the angles β ₁ and β ₂ is not necessarily required for the detection of faulty, single or multiple layers of corrugated cardboard.

In Fig. 12b For example, a two-ply corrugated board 60 having the lower first shaft 58 and the upper second shaft 59 is shown. The arrangement of an ultrasonic sensor T, R corresponds to the Fig. 12a ,

The acoustic short circuit AK1 and AK2 between the individual layers, ie a material connection in the sense of a web connected to the layers for joining the individual cover layers, is also essential for the detection in the case of twin-wave or multi-corrugated corrugated boards. In this way, it is possible to transmit a high acoustic energy to the multiwell corrugated cardboard in an ultrasonic sensor, so that a maximum force is achieved approximately perpendicular to the spanned surface of the shaft.

In view of the foregoing description, the invention provides a device-to-device solution for the reliable detection of single sheets, false sheets and multiple sheets, especially double sheets, not only over a very broad grammage and basis weight range, but also in terms of flexible uses and different material spectra.

Claims (7)

1. Method for the contactless detection of a single sheet, a missing sheet and multiple sheets of objects (2) in sheet form, in particular paper,

   a) wherein the objects (2) are arranged in the beam path between at least one transmitter (T) and an associated receiver (R) of a sensor unit (10),

   b) wherein the radiation transmitted through the objects (2) or the radiation received by the receiver (R) in the event of a missing sheet is received as a measuring signal (U_M),

   c) wherein the measuring signal (U_M) is supplied to a downstream evaluation unit (4) to generate a detection signal,

   d) wherein a measurement curve (MK) is formed by an input voltage (U_E) of the measuring signal (U_M) in dependence upon a weight per unit area of the objects (2),

   e) wherein a target curve (ZK) for single sheets is formed by an output voltage (U_A) at an outlet of the evaluation unit (4) in dependence upon the weight per unit area of the objects (2),

   f) wherein at least one correction curve (KK) is predefined for the evaluation unit (4),

   g) wherein the measurement curve (MK), in order to generate the detection signal, is transformed with the correction curve (KK) to the target curve (ZK) for the objects (2),
   characterised in that

   h) the target curve (ZK) descends monotonously with increasing weight per unit area of the objects (2),

   i) the target curve (ZK) has a first, a middle and a third region of the weight per unit area, wherein the middle region lies between the first region and the third region, and

   k) the target curve descends more steeply in the first region and in the third region with increasing weight per unit area than in the middle region, wherein the target curve descends linearly in all three regions.
2. Method according to claim 1,
   characterised in that
   at least two thresholds, as an upper threshold and a lower threshold, are predefined in relation to single sheets, missing sheets or multiple sheets,
   wherein if an output voltage is greater than the upper threshold this is evaluated as a "missing sheet",
   if an output voltage lies between the thresholds this is evaluated as a "single sheet" and
   if an output voltage is lower than the lower threshold this is evaluated as "multiple sheets".
3. Device for the contactless detection of a single sheet, a missing sheet and multiple sheets of objects in sheet form (2), in particular paper, in particular to carry out the method according to one of the claims 1 or 2,

   a) having at least one sensor unit (10) which has at least one transmitter (T) and an associated receiver (R),

   b) wherein the objects (2) can be positioned in the beam path between the transmitter (T) and the receiver (R),

   c) wherein the receiver (R) serves to receive the radiation transmitted through the objects (2) or the radiation received in the event of a missing sheet of the objects (2) as a measuring signal (U_M), and

   d) having a downstream evaluation unit (4, 5, 6) which is connected to the receiver (R) to supply the measuring signal (U_M) and is adapted to generate a detection signal,

   e) wherein a correction curve (KK) for a measurement curve (MK) is predefined for the evaluation unit (4), wherein the measurement curve (MK) is the input voltage (U_E) of the measuring signal (U_M) for the objects (2) in dependence upon a weight per unit area of the objects (2),

   f) wherein a target curve (ZK) for single sheets is formed through the output voltage (U_A) at an output of the evaluation unit (4, 5, 6) in dependence upon the weight per unit area of the objects (2),
   characterised in that

   g) the evaluation unit (4, 5, 6) is adapted to transform the measurement curve (MK) with the correction curve (KK) to the target curve (ZK) in such a way that

   h) the target curve (ZK) descends monotonously with increasing weight per unit area of the objects (2),

   i) the target curve (ZK) has a first, a middle and a third region of the weight per unit area, wherein the middle region lies between the first region and the third region,

   k) the target curve descends more steeply in the first region and in the third region with increasing weight per unit area than in the middle region, and

   I) the target curve descends linearly in all three regions.
4. Device according to claim 3,
   characterised in that
   the sensor unit (10) has at least one ultrasound sensor or one or more optical sensors.
5. Device according to claim 3 or 4,
   characterised in that
   a unit is provided for automatic calibration or for adjusting the transmission frequency and / or the transmission amplitude to the receiver signal.
6. Device according to claim 5,
   characterised in that
   the automatic calibration can be carried out in periods synchronised with the transmission frequency or in defined pause periods.
7. Device according to one of the claims 3 to 6,
   characterised in that
   a feedback unit is provided between the evaluation unit (4), in particular a microprocessor (6), and the sensor unit (10).

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