WO2005066050A1 - Method and device for the contactless detection of flat objects - Google Patents

Abstract

The invention relates to a method and a device for the contactless detection of flat objects, especially in the form of sheets, such as paper, films, sheet metal, labels, splices, stub cards, tear strips, and similar flat materials or packagings. Said method and devices require, e.g. in the printing industry, a reliable and precise identification of single sheets, missing sheets or multiple sheets, special double sheets, flat objects and labels. To this end, the invention provides a very flexible solution that can be applied to a very large spread or mass per unit area range, whereby the evaluation device arranged downstream from the sensor device, especially the receiver, receives at least one correction characteristic curve, by which means the characteristic curve of the input voltage of the measuring signal in the receiver is reproduced as a target characteristic curve according to the spread or the mass per unit area of the flat objects, in such a way that a linear or approximately linear dependence or a characteristic curve close to the ideal characteristic curve for identifying the single sheet is achieved as a target characteristic curve.

Description

Method and device for the contactless detection of flat objects.

The invention relates to methods for the contactless detection of flat objects according to the preamble of claims 1 and 6 and devices according to the preamble of claims 37 and 41.

Methods and devices of this type are e.g. used in the printing industry to determine whether a single sheet or multiple sheets or a missing sheet is present in the printing and manufacturing process for paper, foils or similar flat materials. Usually the requirement is to have a single sheet during the printing process, while when determining a multiple sheet, e.g. of a double sheet, such a double sheet is normally required to protect the printing press. Similarly, when it is determined that there is no single sheet, so to speak a "missing sheet", the normal printing process is changed or interrupted until a single sheet is detected again.

In a comparable manner, these methods and devices are also used in the packaging industry, in which, for example, labels applied to the base or carrier material are counted or checked for the presence or absence of them. Another area of application is the detection of tear threads or tear points, particularly in the case of thin foils used as wrapping, such as cigarette packs. However, metal-clad papers, flat plastic eyes or foils and sheets can also be detected in manufacturing processes without contact using such methods and devices.

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 is based on the fact that the ultrasound wave emitted by the transmitter penetrates the paper and the transmitted portion of the ultrasound wave is received by the receiver as a measurement signal and its amplitude is evaluated. If a multiple or double sheet is present, the receiver has a significantly smaller amplitude than if a single sheet was present.

The subsequent evaluation of the received measurement signal has so far been carried out in practice with approximately linearly operating amplifiers or similarly designed amplification circuits and downstream filters. Due to the relatively small dynamic range, in particular of linear amplifiers, thick paper, 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 foils, whereby this means a movement of the thin, flexible sheet during the detection between the transmitter and receiver in the direction of the sheet normal, was insufficiently controllable with such amplifiers. A comparable behavior is revealed by strongly inhomogeneous materials.

With regard to a better control of the previously mentioned problems, especially in greatly differing material-specific attenuation of the transmitted signal, where in this regard in addition in accordance with the practice only ^'nor Grammages and grammages are spoken, a learning process or a teach-in step was carried out. Before the actual detection process begins, the flat object to be detected, such as a sheet of paper, is detected with regard to its grammage or its sound absorption characteristics and entered into the evaluation device in the sense of teaching.

A considerable part of the fact is that a corresponding teach-in step has to be carried out and taught in again for other flat objects with different grammages, which on the one hand is complex and on the other hand usually leads to considerable downtimes in the corresponding systems.

With regard to the material specifications for paper, reference is made to the present standards, for example DIN pocket book 118 (edition 2003-06), DIN pocket book 213 (edition 2002-12), DIN pocket book 274 (edition 2003-06), DIN-Taschenbuch 275 (edition 1996-08), or with regard to corrugated cardboard to DIN 55468-1.

A device for the detection of single sheets or multiple sheets is known from DE 200 18 193 Ul and EP 1 201 582 A. To detect these arcs, this known device has at least one capacitive sensor and at least one ultrasonic sensor. Here is an evaluation unit for deriving a signal for determining the simple or Multiple sheets provided. This signal is derived from a logical combination of the output signals of the sensors, the relevant detection signal being determined in an adjustment phase.

Another device is known as a capacitive sensor from DE 195 21 129 Cl. This device, which is primarily aimed at the contactless detection of labels on a carrier material, works with two capacitor elements and an oscillator influencing them. The dielectric properties ten of the paper or other flat objects therefore influence the oscillating circuit of the oscillator with regard to the frequency, which is evaluated for detection. The disadvantage here, however, is that relatively thin papers can only be detected with difficulty or not at all, just like metal-coated papers. Even very thin foils are difficult to detect due to their small thickness and the dielectric constant, which in some cases differs only slightly from one.

Other detection methods with ultrasonic proximity switches are e.g. in EP 0 997 747 A2 and EP 0 981 202 B1. With these scanning sensors, an automatic frequency adjustment takes place, in which after the transmission of an ultrasound pulse and subsequent reflection on the object to be detected, the optimal transmission frequency is evaluated as a function of the level of the received ultrasound echo amplitude.

Another device of the type mentioned is known from DE 203 12 388 U1. This device, which works with ultrasound, determines the presence and strength of the corresponding objects via the transmission and reflection of the radiation. However, this device also uses reference reflectors, so that the device has a relatively complex structure.

Furthermore, DE 297 22 715 U1 discloses an inductively operating device for measuring the thickness of metal sheets, which can consist of non-ferrous metals or ferrous metals. The thickness of the sheets is measured by evaluating the working frequency of a frequency generator or by evaluating its amplitude. To set this device, a teach-in step is first required, in which a calibration plate is introduced into the measuring space and the working frequency or the amplitude of the frequency generator is set according to a standard thickness curve. A distinction can be made between single, faulty and multiple sheets using this device, but different standard thickness curves must be saved and evaluated for this decision. This device is also suitable for the detection of sheet thicknesses up to approx. 6 mm. The detection of thin sheets or foils is not very reliable due to the small change in damping.

DE 44 03 011 Cl describes a device for separating non-magnetic sheets. For this purpose, it is provided that a traveling field inductor, when a double sheet is present, exerts a force which is provided opposite to the conveying direction of the sheet stack, so that the present double sheet is separated into two sheets. This device is completely unsuitable for non-metallic flat objects or foils.

DE 42 33 855 C2 describes a method for checking and recognizing inhomogeneities in sheets. This method works optically and on the basis of a transmission measurement. However, especially when checking paper sheets with regard to single and multiple sheets, there is the problem that, due to the material properties of the sheets, very large fluctuations are caused due to inhomogeneities or the reflection behavior and the fluttering of the sheets. In order to overcome this problem, this document provides for a measurement evaluation using the fuzzy logic rules.

From US 2003/0006550 a method is known which carries out a digital evaluation on the basis of ultrasound waves and the phase difference between a reference phase and the received phase, and on this basis determines a signal for the determination of missing sheet, single or multiple sheets , However, the evaluation of the phase difference alone can be inadequate for special papers or foils and lead to incorrect information, which should be ruled out in the case of reliable detection. A method that can be used in particular for counting banknotes, but also for other papers and foils, is known from DE 30 48 710 C2. This method, which is based on the determination of the weight per unit area or the thickness of the materials to be detected, works with pulsed ultrasound waves, with the evaluation of the integration of the phase shift being used in particular for the detection of a double sheet, ie the presence of two overlapping or overlapping bank notes. The field of application of this method is therefore primarily aimed at counting banknotes or comparable papers and foils, taking into account the basis weights of such materials. This method therefore appears unsuitable for use with packaging materials or counting labels.

Another method based on acoustics or ultrasound is known from DE 40 22 325 C2. This method, which is based on the control of incorrect or multiple sheets of sheet or film-like objects, requires a first run of the corresponding flat object with a calibration and adjustment process, which is carried out automatically by a microprocessor. This method therefore requires a type of teach-in first of all on the thickness of the object in relation to an optimal measurement and frequency range, and furthermore, in the case of such a first run, the detection and storage of a corresponding threshold value.

Comparable methods and devices are known in the field of application for the detection or counting of labels. The difference in a label can be seen here first, since it is provided on a base or carrier material as an applied material layer. This layered material behaves towards the outside in terms of opacity, the dielectric, the electromagnetic conductivity or the sound propagation time as a connected piece of material, so that with these detection possibilities there is only a comparably low attenuation, which is, however, still evaluable.

DE 199 21 217 AI, together with DE 199 27 865 AI and EP 1 067 053 B1, discloses a device for detecting labels or flat objects. This device uses ultrasonic waves with a modulation frequency, with a threshold value being determined during an adjustment process or a teach-in step in order to distinguish between single and multiple bends. Using the teach-in step, the detection can be set on the special flat object in the sense of a label. However, this teach-in step makes the device more complex and requires longer setting times when changing to another flat object. This shows that a larger range of materials cannot be detected per se, but only in line with the specific individual material.

Taking this state of the art into account, the object of the invention is therefore to design a generic method and a device for the contactless detection of flat objects, which is very flexible and reliable detection of simple, faulty and over a wide range of materials. or multiple sheets with different flat materials on the one hand, in particular with papers, foils, sheets and the like, on the other hand with labels and similarly layered materials, which can be done without a teach-in step and different beams or waves such as optical, acoustic, inductive Type or the like can be used.

According to the invention, this object is achieved in the case of methods by the features of claim 1 or claim 6 and in the case of apparatuses. tions solved by the features of claim 37 or claim 41.

An essential core idea of the invention can therefore be seen in specifying a correction characteristic curve for the evaluation of the measurement signal over a grammage and basis weight range in order to achieve a target characteristic curve with a largely linear or almost linear course over the intended material range or also one of the papers and similar materials to achieve an ideal characteristic curve for the detection of the single sheet, which enables a clear distinction when analyzing the amplitude of the amplified measurement signal, in particular as compared to a corresponding threshold value for air, as a threshold for a missing sheet or as a threshold value for a double sheet.

To achieve this, a further important core idea of the invention is that when the received measurement signal is amplified, the correction characteristic of the corresponding signal amplification is specified statically or dynamically in order to achieve a target characteristic that can be easily evaluated.

However, the invention also takes into account that an immediate conversion of the measurement signal can be carried out as part of an A / D conversion, the digital values obtained in this way being subjected to the measurement signal characteristic curve to the corresponding purely digital correction characteristic curve, so to speak, so to speak, the evaluable target characteristic curve to reach.

This principle of using a correction characteristic curve also has the great advantage that different sensor devices, in particular as a barrier or barrier arrangement, for example in the form of a fork, can be used, it being possible advantageously to use ultrasonic sensors, optical, capacitive or inductive sensors, the same method can equally be used for these sensors. The corresponding correction characteristic for papers and the like. Materials are achieved in particular by mirroring the measured value characteristic at the ideal target characteristic for single sheet detection, possibly with a special transformation of the Cartesian coordinate system.

The correction characteristic can also be selected inversely or almost inversely to the characteristic of the input voltage U _{E of} the measurement signal. In this way it is possible to achieve a good approximation of a target characteristic curve that runs ideally for single sheet detection over a relatively large grammage or basis weight range of the objects to be detected, in particular between 8 g / m ² and 4000 g / m ² . Inverse is seen as an inverse function.

The method according to the invention is therefore not only suitable for the detection of single sheets, multiple sheets or missing sheets of thin to thick papers which are in the above-mentioned grammage range. Rather, stackable, box-shaped packaging made of paper or plastic or labels applied to carrier material, or adhesive, tear-off or tear-open points of paper or foils can also be detected.

If the measurement signal obtained at the output of the receiver or of the measurement signal converter is subjected to a signal amplification for further evaluation, the corresponding correction characteristic, which can also consist of a combination of several correction characteristics, is preferably impressed on the output side to obtain an easily evaluable target characteristic curve over the entire basis weight range for further evaluation. Using this target characteristic, the corresponding flat object can then be detected with regard to certain threshold values in a subsequent method step, which can be implemented, for example, in a microprocessor, so that a clear detection signal for single sheets, missing sheets or multiple sheets is obtained. As an alternative, the method also provides that the measurement signal or its measurement signal characteristic curve received in the receiver is subjected directly to an analog-digital conversion, these digital values taking into account a corresponding purely digital correction characteristic curve to a target characteristic curve with generation of a corresponding one Detection signals are processed.

According to the invention, the advantage of these measures is 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 system downtimes. In addition, the dynamic range of the evaluation device is expanded considerably, so that the detection of very thin or very inhomogeneous materials, which tend to flutter behavior, can be implemented with good certainty. The method according to the invention therefore makes it possible, on the basis of the amplitude evaluation of the measurement signal received in the receiver, by means of a correction characteristic and target characteristic, to reliably distinguish single sheets, missing sheets and multiple or double sheets, and this for very thin or very sound-transmissive objects, for example with a basis weight of 8 g / m ² or approx. 10 μm thickness, up to relatively thick and strongly sound-transmissive objects up to 4000 g / m ² , e.g. with a thickness of 4 mm, without a prior teach-in process differ.

With a view to a high degree of flexibility, not only with regard to the most varied of materials such as corrugated cardboard or plastic packaging, the invention also provides for correction characteristic curves to be taken into account, which represent a combination of different correction characteristic curves, these combined correction characteristic curves also only in sections over partial areas of the entire grammage range can be applied. This makes it possible to achieve the target characteristic curves with improved approximation to the ideal characteristic curve for the 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 be used in sections as a linear or non-linear characteristic, as a single or multiple logarithmic characteristic, as an exponential characteristic, as a hyperbolic characteristic, as Polygon course, be designed as a function of any degree or as an empirically determined or calculated characteristic curve or as a combination of several of these characteristic curves.

With regard to the combined detection of labels and single, missing and multiple sheets, it is preferred here to specify the correction characteristic as an approximately linearly increasing and weighting or exponentially or similarly increasing characteristic or as a logarithmic, multiple-logarithmic or similarly running nonlinear characteristic, also designed in combination with the first mentioned correction characteristics.

According to the invention, it is therefore possible both in a method and by means of a device to detect labels, adhesive, tear-off or tear-off points and similarly constructed materials well even without a teach-in step. It should be taken into account here that the basis weight range for labels and similar materials can be set from approximately 40 g / m ² to approximately 300 g / m ² , that is to say is relatively narrow.

It should also be taken into account that in the case of labels, where there are possibly slight grammage differences between the base or carrier material and the multi-layer materials, such as labels, which are applied in an adhesive manner, there is a relatively small difference in the damping, for example the ultrasound waves, so that there is an effort to in the target characteristic never achieve the largest possible voltage swing of the target characteristic ZK with a small voltage swing of the measured value characteristic MK.

The correction characteristic curve for the detection of labels is therefore preferably at least linear, this linear correction characteristic curve KK having a weighting function, or is chosen to increase exponentially.

As a largely ideal target characteristic for labels and similar materials, the function of the output voltage U _A or U _z depending on the grammage g / m ² as a curve or straight line is aimed in an optimal way, with a large and constant negative slope (ΔU _z = maximum and constant) and thus maximum voltage difference. That is, the highest possible voltage swing (ΔU _z = max.) With regard to the base or carrier material and the adherently applied, multi-layered materials, such as labels, even with slight changes in grammage, depending on the entire grammage or basis weight range.

Such an ideal target characteristic for the detection of labels therefore makes it possible to generate a clear detection signal for detecting labels and similar materials even with small to very small differences in grammage.

In the case of labels and the like materials, evaluation is primarily carried out for the presence or absence of, or for multiple layers reduced by at least one layer.

The invention also makes it possible to implement such a combination of correction characteristic curves, for example also in separate paths or channels. Here, the logarithmic and / or double logarithmic correction characteristic to be stamped on the first channel, for example, to thereby primarily the double sheet detection ^• reliably achieved. The second channel can then, for example, be subjected to an exponentially or linearly increasing correction characteristic, in order to optimally implement the detection of labels, glue points or thread detection in this path. This combination of the two opposing methods with a logarithmic correction characteristic in combination with an exponentially increasing correction characteristic therefore creates an optimal detection possibility for labels and materials such as tear or tear points and / or tear threads and simple, faulty - and multiple sheets.

In label recognition, it is therefore the goal to achieve the largest possible and constant signal swing through the target characteristic over the entire material range with the aforementioned design of the correction characteristic, ie dU _z should be maximum or constant.

In contrast to this, the method of the correction characteristic curve for the detection of single, missing and multiple sheets is based on an embodiment of the target characteristic curve in which the smallest possible change in the amplitude values or dU _z = 0 is achieved over the entire grammage range for single sheet detection , ideally a constant size or a target characteristic with a gradient of approximately 0.

The combination of a logarithmic and a linear correction characteristic appears to be important for practical purposes. The advantage of a signal amplifier with an impressed logarithmic correction characteristic, or a similar correction characteristic, is above all that the signal amplifier has a very large dynamic range, so that a large ratio of the voltage signals from the largest to the smallest signal can be processed. A linear signal amplifier can, for example, achieve a voltage-signal ratio on the order of 50: 1, which corresponds to approximately 34 dB. A logarithmic signal amplifier, on the other hand, achieves a voltage-signal ratio of 3 × 10 ⁴ : 1, which corresponds to approximately 90 dB. When using a logarithmic signal amplifier, which is understood here as an impressed logarithmic correction characteristic curve, signal overdriving at high signal amplitudes can therefore be counteracted. This property is invented used in an advantageous manner in order to realize the single, missing sheet or multiple sheet detection as well as the detection of stackable packaging without performing a teach-in process over a very wide range of materials.

In an advantageous manner, logarithmic and / or multiple logarithmic signal amplifiers can also be used in the method according to the invention and the corresponding device, so that the possible spectrum of materials is expanded to thin or very light arcs. This is due to the fact that with an increasing signal level in these signal amplifiers, the characteristic of the signal amplification saturates and there is practically no signal swing anymore. With decreasing signal amplification for large signals, even with the slightest changes, such as, for example, very thin sheets of paper between the transmitter and receiver, signals that can still be easily evaluated can still be obtained.

Another advantage of using nonlinear, in particular logarithmic and / or multiple logarithmic signal amplifiers is that the detectable material spectrum is expanded to thicker or heavier arcs. This results from the fact that with a low signal level the amplification is very high and even the weakest signals, which still penetrate a heavy or thick single sheet, are amplified sufficiently and can be evaluated. This property is used in particular for the detection of stacked packaging or also for the detection of single sheets, missing or multiple sheets.

A further expedient development of the invention consists in that the correction characteristic curve is determined or calculated empirically, in particular empirically. For this purpose, for example, the transmission attenuation or the resulting measurement signal voltage can be plotted as a function of the grammage or the basis weight of the object or objects to be detected, and in this way the Characteristic curves of the measurement signal of a plurality of different objects are determined and the optimal inverse or almost inverse correction characteristic curve is arithmetically or empirically generated in order to achieve a target characteristic curve which is at least approximated to the ideal target characteristic curve for the detection of single sheets.

In terms of the method, there is also the possibility of permanently impressing the correction characteristic curve or actively controlling or regulating it, so that the materials to be examined can be even closer to the ideal target characteristic curve.

I

For this control or regulation, e.g. a microprocessor, a corresponding electrical network for adjusting the correction characteristic, an application-specific component or a resistance network can be used.

According to a further embodiment of the invention, the target characteristic for different material spectra is divided into several sections, in particular three sections or five sections.

In three areas, for example, a partial target characteristic curve for the grammage range above 1200 g / m ² for very thick papers and another section below 20 g / m ² for a very thin paper spectrum can be formed. The introduction of sections of the target characteristic curve therefore enables improved reliability with regard to single, missing or multiple sheet detection.

For labels, adhesive and tear-off points or tear threads, it is expedient to specify at least one detection threshold, this being evaluated as a “multiple system” when the detection threshold is undershot and as a “carrier material or as a multiple system reduced by at least one layer” if this is exceeded. With a view to clear detection of single sheets, missing sheets or multiple sheets, in particular double sheets, the amplitude value is compared with threshold values on the basis of 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 sheet". A received measurement signal lower than the lower threshold value means a "multiple or double sheet". In the case of a received measurement signal with the corresponding value on the target characteristic between the threshold values, this is detected as a "single sheet".

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

In this sense, a dynamic double sheet threshold can be used to further expand the measurable grammages. For this, e.g. the single sheet value measured and with the associated multiple sheet value e.g. be evaluated as a polygon function if it is a simple function, e.g. a falling straight line or a constant value for the single arc.

The method and the device can be implemented particularly well by means of at least one ultrasound sensor device. In this case, the sensor device preferably has at least one pair of coordinated and coaxially aligned ultrasound transducers.

However, the method and device according to the invention can also be used with optical, capacitive or inductive sensors.

In the case of ultrasound sensors, it has been shown in particular that even flat objects with printing, color printing or reflecting surfaces can be easily detected. Is too it is possible to attach the pair of sensors, particularly in the case of barriers and when mounting in a fork shape, perpendicular or inclined to the plane of the curve.

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

In the case of continuous operation, it is preferable to mount the pair of sensors at an angle to avoid interference or standing waves using this measure. The continuous operation is expediently designed as a quasi-continuous operation, for example by periodically, compared to the evaluation time short periods, the signal is switched off and on again. To avoid standing waves, phase jumps can also be provided in the transmission signal.

The inclined mounting of the pair of sensor elements is particularly suitable for the detection of thicker materials, e.g. single-wall or multi-wall, in particular double-wall corrugated cardboard, in order to achieve better material penetration and to avoid interference.

It has also proven to be advantageous to modulate the transmission signal with at least one modulation frequency. With this, tolerances of the transducers can be corrected or compensated, in particular in the case of ultrasonic sensors. Although the sensor elements are matched to one another, they generally have different resonance frequencies. If a frequency sweep f _s with a frequency significantly lower than the exciting frequency is used for frequency modulation, the resonance maximum of the sensor elements is periodically exceeded. If the response time of the sensor is significantly less than l / f _{S /} , the transducer properties of each individual sensor element or sensor pair can be optimally used for ultrasound transmission in this way. The frequency sweep will normally be up to some 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 transducers are made worse. A correction factor is necessary to compensate for this. According to the method, this can be done by using a straight line which is stored or calculated as value pairs in the microprocessor uP, since the measurement signal is already with 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 distance. That the input signal at the microprocessor of an evaluation device drops linearly with the transducer distance to a good approximation. Therefore, the correction of the values is easy even with a variable distance, since when a corresponding device is switched on, only a straight line function for the correct initial value has to be calculated or stored as a pair of values. The correct determination of the sensor head distance is carried out by a run time measurement.

A particular advantage of the method using ultrasound can be seen in the fact that the distance between transmitter and receiver in the sensor device can be configured variably for this teach-in-free method. In other words, the sensor device can be adapted to different applications relatively quickly with regard to its distance, without the measuring precision of the method being impaired thereby. A further improvement of the method can be brought about by monitoring the distance between transmitter and receiver and determining it. This determination of the distance between the transmitter and receiver can be realized on the one hand by reflection of the radiation between the transmitter and receiver and on the other hand by means of reflection between see transmitter and receiver despite a flat material in the space in between, even a thick sheet. If it is determined that the permissible maximum sensor distance has been exceeded, the evaluation device, for example a microprocessor, can carry out a corresponding correction of the determined amplitude values of the measurement signal depending on the distance between the transmitter and receiver.

The transmitter and receiver are aligned with one another in the main radiation direction, in particular coaxially, with one another, with almost any angle of inclination to the plane of the arc being able to be provided.

When single-wall or multi-wall corrugated board is detected, this is expediently carried out approximately orthogonally to the widest surface of the corrugated board shaft.

In terms of optimal detection, a method can also be used to provide feedback between the transmitter and the evaluation device, in particular a microprocessor, in order to obtain a maximum amplitude at the output, taking into account the material specification of the flat objects to be examined and other operating conditions. It is also possible to regulate the optimum transmission frequency. With this measure, aging effects of the sensor elements can also be compensated for and a product test of the device according to the invention, in a particularly advantageous embodiment of the invention, can be fully automated during series production.

In order to achieve even better detection security for recognizing labels, adhesive and tear-off points and tear threads, these objects can be moved between the transmitter and receiver so that, depending on the specific measurement signal of the object received, the corresponding switching threshold for the object is automatically or externally triggered Target characteristic is determinable.

Since the label recognition is expediently carried out by means of a second channel in terms of method and device, there remains a teach-in-free detection for single or multiple Subject sheet, which is realized with a first channel of the evaluation device, is not affected.

In an advantageous development, a feedback is provided between the evaluation device and the transmitter, by means of which the amplitude of the received measurement signal can be maximized. 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 defined pause times or also via a separate input provided externally on the sensor device.

With regard to optimal process control for systems in which the method and the device are used, it is suitable to provide at least one A / D converter or a threshold value generator for digitizing the analog measurement signal in order to be able to carry out the further processing of the values digitally ,

In particular when processing and selecting various signals from 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.

For better detection of elongated objects and materials laminated onto carrier material, in particular by means of ultrasound or optical sensors, it is advisable to provide at least one pinhole and / or slit diaphragm between the transmitter and the elongate object to be detected, and to improve the spatial resolution Detect presence of the object continuously.

The diaphragms, and in particular the slit diaphragms in particular, are arranged in the thread running direction to improve the detection of material threads adhering to a base or carrier material, for example tear threads in packaging foils for cigarettes. This is usually an arrangement of the diaphragm for the direction of travel of the elongated objects. When monitoring scaled sheets lying next to each other, slit or perforated diaphragms are aligned by 90 ° to the direction of movement of the sheets.

When using diaphragms, the elongated object guided between the transmitter, receiver and diaphragm, e.g. a thread laminated onto a carrier material, hovering as close as possible over the screen or slidingly touching it. The arrangement of the transmitter, especially in the case of ultrasound sensors, is advantageously carried out below the sheet to be detected, since in this case the maximum transmission energy can be coupled out and self-cleaning effects on the sensor head can be used. However, it is also possible to reverse the arrangement with the receiver, provided that the loss of signal strength can be accepted.

The invention is explained in more detail below with the aid of schematic representations and diagrams and with reference to the underlying measurement principles. Show it:

Fig. 1 shows the principle of a method according to the invention and block-like a corresponding device including voltage diagrams according to Figures la, lb, lc, which illustrate the structure of the characteristic curves in the detection of sheets of paper, foils or similar materials.

FIG. 2 shows the principle of a method according to the invention and a corresponding device in block diagram form, including voltage diagrams according to FIGS. 2a, 2b, 2c, 2d, which illustrate the structure of the characteristic curves in the detection of labels, tear-open points and similar materials;

3a shows a curve diagram which shows the schematic dependency of the output voltage of an amplifier, as shown in FIG. 1 by way of example, as a function of the grammage or the basis weight of the tectating materials, including idealized target characteristics;

Fig. 3b is 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 examined, with several target characteristics together with corresponding threshold values, e.g. Air threshold, double arch threshold are shown;

4a shows a schematic representation of how the correction characteristic curve can be determined in the Cartesian coordinate system in the case of a known measured value characteristic curve and ideal target characteristic curve for single or double sheet detection;

4b shows a schematic illustration, based on the label recognition with ideal target characteristic curve, known measured value characteristic curve and a correction characteristic curve required for transformation;

Fig. 4c is a schematic representation of the characteristics

Double sheet detection if there is no ideal target characteristic;

4d shows characteristic curves for double sheet detection with reflection on an imaginary axis, including the transformation according to FIG. 4f;

4e shows a schematic illustration of characteristic curves for label recognition with reflection on the imaginary axis, taking into account FIG. 4f; 4f schematically shows a transformation of the Cartesian coordinate system by an angle α with a reference axis of the new ^' coordinate system;

4g shows a schematic representation of the ideal target characteristic and real drawing characteristics in double sheet detection;

4h shows a schematic representation of an ideal target characteristic and a realistic target characteristic for label recognition;

4i schematic representations of a measured value characteristic and correction characteristic in single or double sheet detection, the correction characteristic representing a characteristic derived from an e-function and a reversing function, with target characteristics determined therefrom;

4j shows a schematic representation of a measured value characteristic derived from a weighted hyperbola and a correction characteristic derived from a logarithmic function with the target characteristic determined therefrom for single or double sheet detection;

5a is a schematic illustration of the principle of the measurement criteria present as an example in the detection of a double sheet of material by means of ultrasound waves;

FIG. 5b in a manner comparable to that in FIG. 5a, the schematic representation of an adhesive point between a double sheet of material and the measurement criteria that arise in this case when recorded by means of ultrasound; 5c shows the schematic representation of materials adhered to a base or carrier material, partly as single-layered and partly as multi-layered materials, this structure showing the structure of a label;

6 shows the method and a device in the form of a block diagram using the example of a combination of different correction characteristic curves;

FIG. 7 shows a schematic illustration similar to FIG. 6, the principle for setting a correction characteristic curve and calculating a correction characteristic curve with feedback on the circuit blocks being illustrated;

8 shows a schematic illustration for the empirical determination of a measured value characteristic over a large grammage or basis weight range;

Fig. 9 is a schematic block diagram representation of a method or the corresponding device with the combination e.g. the multiple sheet detection with the detection of material layers or labels adhered to the carrier material;

10 schematically shows a diagram of the standardized output

Voltage U _A over the grammage range with constant or dynamic double arc thresholds,

11 shows a target characteristic curve with the upper and lower flutter region shown, and

12 with the representations of FIGS. 12a and 12b the arrangement of a sensor with optimal alignment in a single-wall corrugated cardboard and corresponding to FIG. 12b, the analog alignment of a sensor with corrugated cardboard.

The diagram according to FIG. 1 schematically shows the method according to the invention and a device with a block-type structure and the voltage curves that can be achieved at certain points in the sense of characteristic curves over a grammage or basis weight range g / m ^{2 of} a material spectrum to be detected.

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

A corresponding sensor device 10 in this case 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 in the form of an arc, are moved without contact.

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

Since the amplitude evaluation of the measurement signal U _M for the detection of a single sheet, a missed sheet, ie no sheet, or a double or multiple sheet, is assumed for this basic example, a possible voltage curve U _{M is} dependent on the grammage or the basis weight g / m ² for the measurement characteristic MK shown in FIG.

With regard to a clear, reliable decision as to whether a single sheet, a double sheet or a missing sheet is present, it is the aim of the invention, taking into account threshold values, such as for the air threshold or as a double sheet threshold, to unambiguously intersect with these threshold values or as large a voltage gap as possible to get these thresholds. The knowledge on which the invention is based assumes that in the case of generic methods and devices in the prior art, in the case of multiple sheet detection and an assumed, subsequent approximately linear amplification, if appropriate with further filtering and evaluation, depending on the grammage or Weight per unit area, a characteristic curve for the amplified measurement signal, which is essentially strongly non-linear, in particular exponential, multiple exponential or hyperbolic or similar, whereby an uncertain and error-prone detection is frequently present over a large desired range of use of the material spectrum, this to change with a simple principle.

The principle according to the invention is therefore to take into account a correction characteristic and e.g. to impress the evaluation circuit following the receiver, for which purpose the following amplifier device is particularly suitable in order to achieve a target characteristic which can be easily evaluated over the desired grammage range for reliable detection by deciding whether a single sheet, no sheet or a multiple, in particular double sheet, is present.

Such a correction characteristic KK is shown schematically in FIG. 1b. This correction characteristic curve, which only shows in principle the dependence between the output voltage U _{A and} the input voltage U _E in FIG. 1b, illustrates in comparison with the measurement characteristic curve MK according to FIG. 1 a, which likewise only shows the course of the measurement signal U _M only schematically shows that relatively high voltage values U _{M seen} over the grammage range experience no or only a slight gain, while smaller voltage values, for example with relatively large basis weights (g / m ² ), experience a significantly higher, possibly exponential gain.

The resulting target characteristic curve ZK with the voltage U _z as a function of the grammage (g / m ² ) is also only shown schematically in FIG. 1c. The desired ZK can can also be transformed from a point-by-point mapping (implicit KK) of the measurement signal U _M to the desired output signal U _z and thus the desired target characteristic ZK can be achieved. For this, a variable gain amplifier is necessary ^■ which then receives the correction characteristic of a uP.

The mapping of the measurement signal U _M to the desired output signal U _z on the basis of the KK can also be done point-by-point instead of value-discretely, also continuously.

This target characteristic curve shown in FIG. 1 c could have, for example, the curve shown by the solid line, which has three areas. A first and a third relatively steeply sloping area and a middle area, which is inclined only relatively slightly to the abscissa and which comprises a large grammage area.

Since the first and the third area could show a more optimal course with regard to a reliable detection display or unambiguous switching behavior of the device, a linearly decreasing target characteristic ZK2 going through the end points of the first target characteristic ZK1 is shown with an interrupted line as an improved target characteristic.

With regard to the device 1 for the detection of single sheets, missing sheets or multiple sheets shown in principle in block diagram form in FIG. 1, the measurement signal U _{M received} at the receiver R. is fed to an evaluation device 4. The evaluation device 4 is shown in a simplified manner with the amplifier device 5 and downstream of a microprocessor 6.

In the example, the correction characteristic KK is specified or impressed in the amplifier device 5, so that the target characteristic ZK1 or ZK2 is obtained at the output for further evaluation in the microprocessor 6. The microprocessor 6- can then generate a corresponding detection signal with regard to single sheets, missing sheets or multiple sheets, in particular double sheets, taking into account stored or dynamically calculated data, such as threshold values. 2 and the associated FIGS. 2a, 2b, 2c, 2d schematically show the method and a device for the detection of labels and similar materials without a teach-in step having to be carried out. The reference symbols here correspond to the reference symbols from FIG. 1.

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

The measurement signal U _M or U _E obtained when a label is present in the receiver R can, for example, have the schematically indicated curve of the characteristic curve over the grammage, with a curve that drops approximately linearly, non-linearly, exponentially or the like.

The following evaluation device, which e.g. can have an amplifier device 5 and a microprocessor 6 connected downstream, receives a correction characteristic in the amplifier 5, which e.g. linearly increasing (I.) or exponentially increasing (II.) as shown in FIG. 2b. At the output of amplifier 5, taking into account the correction characteristic, e.g. a target characteristic over the grammage range as shown in FIG. 2c by the curve shape I or II.

An ideal course of the target characteristic curve for label recognition is shown in principle in the diagram according to FIG. 2.

This target characteristic ZKi has the course of a negative falling straight line, from smaller grammages to larger grammages, optimally a constant slope and a maximum voltage difference for the output voltage U _z small differences in grammage should be achieved over the entire grammage or basis weight range intended for the detection of labels.

As will be explained below, the correction characteristic curve KK can also be a combination of individual different characteristic curves. Other correction characteristic curves, such as logarithmic or multiple logarithmic, can also be used depending on the characteristic curve profile of the measurement signal U _M and the gain characteristic curve. The aim here is to achieve an ideal characteristic curve ZKi, as shown in FIG. 2, if possible.

The curve profiles according to FIGS. 2a, 2b, 2c show two examples of different characteristic curves. On the one hand for the measurement signal U _M according to FIG. 2a with the characteristic curve MK of a first characteristic I and a characteristic II with an interrupted line.

These different characteristic curves for the measurement signals MK I and MK II are then transformed via exemplary correction characteristic curves KK shown in FIG. 2b in such a way that a characteristic curve course for the target characteristic curve ZK according to FIG. 2c can be achieved at the output of the evaluation.

For further clarification, the output voltage U _{A of} an amplifier device over the grammage range is shown in a schematic representation in FIG. 2 d with an exemplary course of a measured value characteristic MK _E for a label and the target characteristic ZK _E , as is taken into account with a correction impressed on the amplifier. Characteristic curve KK can be reached. The illustration applies to the recognition of labels or glue points. To achieve the desired target characteristic ZK _E , the measured value characteristic MK _{E is transformed} by means of a suitable correction characteristic KK. Here, so to speak, every point of the measured value characteristic MK _{E is transformed} continuously or value-discretely in digital systems into a corresponding value on the target characteristic ZK _E mized. This is illustrated by the arrows for clarification.

In the input range for very thin materials, for example with 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 foils for labels can also quickly reach the limit range of the amplifier for noise, since foils vaporize very strongly.

This can be seen in the diagram in the grammage range from 100 to 300 g / m ² .

The method of characteristic curve correction can be used particularly advantageously in the case of such measurement value characteristic curves MK _E , so that saturation of the measurement signal is avoided in the case of very thin and strongly damping materials, which ultimately ensures flawless detection of the presence or absence of labels.

For comparison with the label detection in FIG. 2d, a possible course of the measured value characteristic MK _DB for a single sheet for double sheet detection of preferably paper materials is shown as an example, which approaches the double sheet threshold DBS approximately asymptotically in the upper grammage range.

The diagram according to FIG. 3a shows a schematic representation of the basic dependency of a standardized output voltage signal U _A / pu of a signal amplifier as a function of the basis weight or the grammage (g / m ² ) in the case of differently designed signal amplifiers for single and multiple sheets, especially double sheets.

The line I in FIG. 3a symbolizes a largely idealized course in the output voltage of single sheets as a function of the grammage when using an approximately linear signal amplifier 5, with an approximately exponential drop in the voltage line. This voltage characteristic I does not take into account any correction characteristic KK. From this approximately exponentially decreasing voltage characteristic curve I, by using the nonlinear, in particular logarithmic and / or double logarithmic correction characteristic curve KK inherent or impressed in the corresponding signal amplifier, a desired target characteristic curve II for single sheets over a ^' very large grammage range, that is to say various materials.

• The target characteristic curve II thus symbolizes a characteristic curve for the output signal in the case of single arcs when using a logarithmic signal amplifier, the target characteristic curve II exhibiting an approximately linear drop.

3a, the air threshold and, on the other hand, the double arc threshold are entered as examples in the diagram according to FIG. 3a. The intersection points of the target characteristic curve II according to FIG. 3a with the air threshold or the double arch threshold show a sufficiently high steepness around a defined, relatively small material area.

The largely asymptotic course of curve I in the vicinity of the double-arch threshold is transformed into a target characteristic II by the transformation of a curve I with a correction characteristic curve KK, whereby a greater distance of the tension value for single sheets compared to the double-arch threshold for heavier grammages or basis weights is achieved ,

This example illustrates that the detection as "missing sheet" or air "or as" multiple or double sheet "over a large grammage and basis weight range can be easily achieved without a teach-in process according to the invention.

A signal transformation from the measurement signal U _M to a constant output signal U _{A of} the single sheet over the entire grammage range with ideally a central voltage value between the two threshold values, namely the upper threshold value for missing sheets or air and the lower threshold values for multiple sheets or double sheets, would be the ideal to be achieved , ie corresponds to the ideal target characteristic ZK for the single curve. This ideal target characteristic is marked I in Fig. 3b. 3a also shows a curve la which shows a multiple-arc signal, in particular a double-arc signal when using an approximately linear signal amplifier, the curve la having an approximately double-exponential drop in the multiple-curve characteristic.

The curve Ila further exemplified symbolizes a multiple sheet signal, in particular a double sheet signal, with logarithmic correction characteristic, whereby näherungswei- ^■ se a simple exponential decay of Mehrfachbogen- characteristic Ila is achieved.

3b shows several target characteristic curves of single sheets with the representation of the standardized 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 amplifiers.

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

The horizontal line I in Fig. 3b indicates an ideal target characteristic for single sheets. This ideal target characteristic shows no saturation for thin materials and is at a high distance from the noise threshold or the double-arc threshold. This ideal target characteristic curve means that the output voltage U _{A of} the signal amplification would ideally result in a constant signal if a wide variety of grammages or grammages were entered.

Since there are high signal-to-noise ratios for this ideal target curve for single sheets compared to the threshold values shown. safe switching and detection of single sheets, missing sheets or double sheets can be assumed.

Curve II shows a non-linear target characteristic with two branches Ila and Ilb, which is relatively difficult to implement due to the turning point, but can be regarded as a characteristic approximating the ideal target characteristic I for single sheets.

The relatively flat partial areas of Ila and Ilb could be realized, the area Ila for lighter grammages advantageously being able to be realized via an almost linear signal amplification. The area Ilb for heavier grammages can e.g. can be realized by means of a double logarithmic signal amplification, the steeply falling kink proving to be too complex in technical implementation due to the damping properties of papers with a very high grammage.

Curve III represents a target characteristic curve which approximates the end points of curve II in the simplest way by means of a 2-point straight line connection to an ideal course as shown in curve I. For example, This can be achieved by using a minimum of simple logarithmic signal amplifiers and shows the linearization of the measured values for single sheets 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 sheet, so that clear shift points and detection criteria are present in ^'relation to these thresholds.

Target characteristic curves according to curves I, II and III therefore allow unambiguous detections over a material spectrum that is broadened compared to the prior art. Curve IV, which is also shown, shows an unsuitable target characteristic for single sheets. On the one hand there is an asymptotic course of curve IV to the saturation limit in the upper area and on the other hand to the threshold value of the noise in the lower area. Such an asymptotic course should also be avoided with respect to the switching thresholds for air or for double arcs, since a clear distinction of the states, missing arcs or double arcs, would then be problematic because of the small signal differences to these thresholds.

The steep drop of the curve IV in the central region detected ogen to Fehlb ^'or double sheets only a small gram weight range, with a clear distinction in this example.

Since, according to the invention, the target characteristic curve is to allow unambiguous detection for single sheets, missing sheets or double sheets over a very large material spectrum, a course according to curve IV should be avoided.

The principles of the invention shown in FIGS. 1, 2, 3a and 3b therefore show that when evaluating the received measurement signal, a signal amplification is used, which is given a correction characteristic curve, which is the characteristic curve of the output voltage U _A / pu depending on the Grammage of the flat objects over a large grammage range inversely or almost inversely or the target characteristic curve approximated to the ideal characteristic curve for single sheet detection in a suitable manner. In this way, a linear or almost linear dependency is achieved between the measurement signal U _E received by the receiver and the signal voltage U _A at the output of the signal amplifier.

4a schematically shows 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 sheets.

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

The example according to FIG. B shows corresponding courses 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 high stroke.

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

4c schematically shows the course of the characteristic curves for single or double sheet detection 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 that is greater than 0. In this case, the drawn-in measured value characteristic curve MK _DB could be transformed into the target characteristic curve ZK _DBr by impressing, for example, the correction characteristic curve KK _DB as an upper, continuous line. This transformation is indicated by the arrows P.

The diagram according to FIG. 4d schematically shows the transformation of a measured value characteristic MK _DB for single or double sheet detection to the desired target characteristic ZK _DB . The abscissa marks the material _spectrum g / m ² , the realistic measuring range M _{DBr being} indicated.

The signal output voltage U _{A of} the measured value is indicated as a percentage on the ordinate. This corresponds approximately to the attenuation measure dB. Furthermore, the virtual endpoints El and E2 as shown ge ^'covered intersections of the measuring value characteristic MK _DB with the target characteristic ZK _DB.

Therefore, in known measuring value characteristic MK _DB in the double sheet detection of a linear target characteristic ZK _DB is a correction characteristic KK _DB necessary to achieve, as in broken line between the end points El and E2 shown. In theory, therefore, the measured value characteristic MK _{DB is transformed} in the direction of the arrows to the real target characteristic ZK _DB . This is achieved, so to speak, by mirroring the measured value characteristic MK _DB on the ZK _DB axis after coordinate transformation.

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

The further representation according to FIG. 4e schematically shows the transformation of the measured value characteristic MK _E for labels into the desired, ideal target characteristic ZK _E by means of the required correction characteristic KK _E.

If the measured value characteristic MK _{E is known} , the correction characteristic KK _{E can be achieved} by mirroring MK _E on the axis of the target characteristic ZK _E after the coordinate transformation (see FIG. 4f). The coordinate transformation shown in FIG. 4f shows, in a simplified manner, the shift for a rectilinear coordinate system x, y by an angle α. X, y are, for example, the axes of the Cartesian rectilinear coordinate system.

The new coordinate reference system is specified by the imaginary reference axis of the target characteristic curves ZK _DB or ZK _E through the coordinate transformation.

While maintaining the Cartesian coordinate system, the following applies to the transformation:

x '= x- cosθ (+ y sin (X; y' = - x- cos (X + y sin (X. With regard to the required correction characteristic curve KK, this applies only after the coordinate transformation in relation to the realignment by the desired target characteristic curve ZK _DB or ZK _E , by mirroring at the corresponding target characteristic curve ZK _DB or ZK _E.

4g and 4h the basic difference between the ideal and real target characteristic for the single or double sheet (FIG. 4g) and the label recognition (FIG. 4h) is shown schematically.

4g for the single curve shows the ideal target characteristic ZKi, which ideally runs in a straight line, without a slope, that is to say is constant. The stroke would be Hi = 0 over the entire ideal range over the material spectrum Mi. In single sheet detection, one would therefore achieve a maximum distance to the upper air threshold as well as a maximum distance to the double sheet threshold displayed below with such an ideal target characteristic ZKi.

The arrow in the diagram indicates the transition from the ideal target characteristic ZKi to real target characteristics, e.g. ZK _X or ZK ₂ .

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

4h shows a comparable diagram for target characteristic curves ZK for label recognition.

The ideal target characteristic ZKi for label recognition has a maximum stroke Hi over a relatively large range of the material spectrum, which is characterized as the ideal material spectrum Mi.

Real target characteristics ZK _X in label recognition, however, deviate from the ideal target characteristic ZKi in the direction of the arrow read off. Accordingly, the more realistic target characteristic ZK _{X has} a smaller stroke Hi and also a smaller material spectrum Mi.

The steeper the real target characteristic is and the ideal target characteristic Ki approaches, the more stroke is available for a given range of materials.

4i and 4j exemplarily show measured value characteristic curves and correction characteristic curves and target characteristic curves derived therefrom.

4i shows a measured value characteristic MK, which could be used for single or double sheet detection in a specific material spectrum. The correction characteristic KK has the function

y = -ln (l / x) +3.

The correction characteristic curve is derived from an e-function and an inverse or inverse function x = ln (l / y). The target curves ZK _{3 shown} . and ZK ₂ can therefore be derived from the measured value characteristic MK and the correction characteristic KK essentially by the difference.

The example according to FIG. 4j also schematically shows characteristic curves for single or double sheet detection.

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

5a, 5b and 5c, some basic principles of the method according to the invention and the corresponding device are described below using the example of a sensor device operating with ultrasound and the ones used for clear detection. significant physical differences using a double sheet, a double sheet with glue and briefly explained using the example of labels.

Some of these fundamental considerations also apply to other sensor devices, e.g. optical, inductive capacitive type.

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

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

In a more general view, a double sheet or multiple sheet can therefore be regarded as a material structure which has a sheet stratification or a box stratification and in one of the spaces between the sheet stratification there is at least one medium, in particular air, which differs from the different sheet materials and which is related to the sheet materials has a clearly different acoustic resistance in the case of an ultrasound measurement method 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 disproportionately damped. With other measurement methods, this concerns the opacity and the surface texture and color and thickness, another dielectric, another electro-magnetic conductivity or other magnetic damping.

Such a double sheet also includes a connection of sheets that is not designed to be adhesive, e.g. by means of mechanical gearing or knurling of arches, 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 one another.

In Fig. 5b, a double sheet 12 with adhesive 13 is shown schematically.

The direction of action of the measuring method used, again using ultrasound, is indicated by arrows.

In the context of this consideration, the point of glue is considered to be blunt, more or less overlapping or such connections of sheets, in particular sheets of paper, plastics, foils and fabrics (nonwovens). The connection takes place predominantly by means of at least one partial or full surface adhesive medium, in particular by means of adhesive and adhesive strips or adhesive provided on one or two sides.

In physical terms, therefore, an adhesive point for a method using ultrasound means an "acoustic short circuit" through which the space between the upper sheet Zi and lower sheet Z ₂ fills and intimately connects the adhesive material layer, air above and below the single sheet being assumed to be Z ₀ becomes.

A glue spot could therefore be detected in the detection method using ultrasound essentially as a single sheet with a high grammage. 5c schematically shows two embodiments of labels 15, 17.

In the context of this application, label is understood to mean at least one or more layers of material or layers of material adhering to a base or carrier material. The layered material behaves e.g. with respect to the sound transmission to the outside like a connected piece of material, so that there is sometimes no significant damping of the respective physical quantities, but only a comparatively low, but still evaluable damping. Possible inhomogeneities in the carrier material or applied material are not taken into account in this consideration, since a faultless material can be assumed in particular for labels.

In the example according to FIG. 5c, label 15 has an upper material with the parameter Z ₂ applied to a carrier material by means of an intimate adhesive connection. There is air with parameter Z ₀ on both sides of the label. As a result of this intimate adhesive connection, there is an acoustic short circuit between the materials in a detection method by means of ultrasound, so that there is an analogy to glue points according to FIG. 5b.

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

These basic considerations within the scope of the invention for the detection of double sheets, glue point, label and the like therefore also make it possible to use the method and the device according to the invention to detect and differentiate single sheets or materials with multiple layers. In particular, this also enables the detection or counting of materials applied to flat materials Labels with an object gap in between are possible.

6 schematically and in block-like fashion shows a device for missing, single and multiple sheet detection, the correction characteristic being generated as a combination of individual characteristics.

The flat materials or sheets to be detected are guided between the transmitter T and the receiver R. The correction characteristic curve resulting after the amplifiers is implemented in the example with a first correction characteristic curve in the amplifier device 21 and at least one second correction characteristic curve in the amplifier device 22, which is connected in parallel. The measurement signal present at the output of the receiver R or its characteristic curve over the grammage is therefore subjected to a combined correction characteristic curve in order to obtain an easily evaluable target characteristic curve 23 which is further evaluated in a microprocessor 6.

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

7 shows the schematic and block-circuit-like structure of a modified device for realizing the invention. The measurement signal of the receiver R is subsequently passed to an amplifier device 24, the signal output of which is directed to a microprocessor 6.

In this example, the microprocessor 6 allows a predetermined correction characteristic to be set via the symbolized potentiometer 25 via the feedback in the path A. In an alternative circuit, a corresponding correction characteristic curve is calculated by means of the microprocessor 6 and the data received or stored, and is fed back and impressed via the path B to the amplifier device 24.

It is also possible to determine a correction characteristic curve empirically or by measuring a representative material spectrum that is to be detected, and to input it to the evaluation unit including the microprocessor 6. In this case, the determined correction characteristic curve C can be impressed discreetly or continuously 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.

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

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

In Fig. 9 an apparatus according to the invention is schematically 40 for beruhrungslosen detection of multiple sheets A, without the ^• implementation of a teach-in step and the detecting on a carrier material adhesively applied layers of material B, as labels shown.

An important idea here is to route the measurement signal evaluation for multiple sheets to a separate channel A with the corresponding correction characteristic curve and, in parallel, the measurement Feed signal evaluation for labels B to a separate channel B with an adjusted 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 an optimal design for multiple sheet detection. The signal amplification 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, to the downstream microprocessor 6 for further evaluation and detection of multiple sheets or labels.

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

10 schematically shows a diagram of the normalized output voltage U _A in% as a function of the grammage. The target characteristic curve 42 of a single sheet is entered with logarithmic amplification over the grammage range. The air threshold LS is shown in the upper area with a solid line and the double arch threshold DBS in the lower area with a broken line.

It is essential, however, that the double-arch threshold can be provided dynamically, and this can take place 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 arc threshold can also be adjusted linearly or as a polynomial train of any degree, as is shown, for example, between points P1, P2, P3 and P4. With this dynamic setting of the double-arch threshold, an additional expansion of the measurable grammages or basis weights can be achieved, so that the detectable range of materials can be enlarged even further.

FIG. 11 relates to a diagram which is largely similar to that of FIG. 10, the course of the target characteristic curve 42 for the single sheet largely coinciding over the entire grammage range. The dynamic threshold MBS for the multiple sheet and its course between the points Pia, P2a and P3a are shown on the one hand.

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

FIGS. 12a, 12b schematically show the basic arrangement for the detection of single-wall corrugated cardboard 51 or double-wall corrugated cardboard 60 and the running direction L, taking into account two sensors 61, 62, in particular ultrasonic sensors.

The corrugated cardboard 51 according to FIG. 12a is single-corrugated and has at its adhesion points with a lower bottom layer 52 or an upper cover layer 53 adhesive areas 54 and webs connecting the bottom and top layers, which span a corrugated surface 55. These webs 55 between the cardboard shaft and the corresponding, e.g. horizontally running floor or top layers represent, so to speak, an "acoustic short circuit" when using ultrasound.

The sensor used in the example according to FIG. 12a has on the one hand the transmitter T and the receiver R, which are aligned coaxially to one another in their main axis. The alignment of transmitter T and receiver R is preferably carried out wa perpendicular to the largest corrugated surface 55 or at an angle βi to the perpendicular of the single-corrugated cardboard. The angle ß ₂ also indicated marks the angle between the perpendicular to the corrugated cardboard and the surface direction of the main surface of the shaft.

The optimum angle J3χ for sound coupling in an ultrasonic sensor onto a single-wall corrugated cardboard, which has a required acoustic short circuit AK between bottom layer 52 and top layer 53, is determined by the slope t / 2h. Here t is the distance between two wave crests and h is the height of the wave or the distance between the bottom layer and the top layer.

With an optimal arrangement of the sensor one tries to align with

to achieve, these angles would then be 45 ° in the example. The coincidence of the angles ß ₁ and ß ₂ is not necessarily necessary for the detection of incorrect, single or multiple layers of corrugated cardboard.

12b shows a two-ply corrugated cardboard 60 with the lower first shaft 58 and the upper second shaft 59; The arrangement of an ultrasonic sensor T, R corresponds to that according to FIG. 12a.

Here, too, the acoustic short circuit AK1 and AK2 between the individual layers is essential for detection in the case of double-walled or multi-walled corrugated cardboard, ie a material connection in the sense of a web adhering to the layers for connecting the individual cover layers. In this way, it is possible to transmit a high sound energy to the multi-corrugated corrugated cardboard in an ultrasonic sensor, so that a maximum force effect is achieved approximately perpendicular to the spanned surface of the shaft. Taking into account the preceding description, the method and device provides a solution for the reliable detection of single sheets, false sheets and multiple sheets, especially double sheets, this not only applying over a very wide grammage and basis weight range, but also with regard to flexible possible uses and different material spectra.

Claims

Method for the contactless detection of flat objects, in particular in sheet form, such as paper, foils, sheets and similar flat materials or packaging, in relation to single sheets, missing sheets or multiple sheets of the flat objects, the flat objects in the radiation path of at least one transmitter and one assigned receiver be arranged in a sensor device and wherein the radiation transmitted through the flat objects or the radiation received by the receiver in the case of a missing sheet is received as a measurement signal (U _M ) and the measurement signal (U _M ) is fed to a subsequent evaluation for generating a corresponding detection signal, thereby characterized in that the evaluation is given at least one correction characteristic (KK), that the correction characteristic (KK) is the characteristic of the input voltage (U _E , U _M ) of the measurement signal (U _M ) from the receiver (R) depending on the Grammage or basis weight of the area Objects (2) transformed into the target characteristic (ZK) in such a way that for papers and the like. Materials a linear, almost linear or a curve approximating the ideal characteristic curve of the single sheet, as the target curve between the output voltage (U _A , U _z ) at the output of the evaluation and the grammage or weight per unit area, in order to generate the corresponding detection signal.

, Method according to claim 1, characterized in that the correction characteristic (KK) for papers and the like.

Materials from a target curve (ZK) mirrored to the ideal or approximated target curve for single sheet detection

Characteristic curve of the input voltage (UE, UM) of the measurement signal is derived.

3. The method according to claim 1, characterized in that the correction characteristic for papers and the like. Materials from a target characteristic approximated to the ideal target characteristic of the single sheet after Cartesian coordinate transformation with respect to the connecting straight line of the two end points of the measured value characteristic for the material spectrum to be detected mirrored characteristic of the input voltage (U _E , U _M ) of the measurement signal is derived.

Method according to one of claims 1 to 3, characterized in that a constant target characteristic curve with an incline of approximately 0 is selected as the ideal target characteristic curve (ZK).

Method according to one of claims 1 to 4, characterized in that by means of the correction characteristic, the characteristic of the input voltage (U _E , U _M ) of the measurement signal over a large grammage or basis weight range, in particular between 8 g / m ² and 4,000 g / m ^{2 is} transformed into the target characteristic. Method for non-contact detection of flat objects, in particular in the form of an arch, such as multi-layered materials adhering to the base or carrier material, e.g. labels, adhesive, tear-off or tear-off points and similar flat materials, with regard to their presence or absence, the flat objects be arranged in the radiation path of at least one transmitter and an assigned receiver of a sensor device and the radiation transmitted through the flat objects or the radiation received by the receiver in the absence of the receiver is received as a measurement signal (U _M ) and the measurement signal (U _M ) for subsequent evaluation Generation of a corresponding detection signal is supplied, characterized in that the evaluation has at least one correction characteristic

(KK) it is specified that the correction characteristic (KK) is the characteristic of the input voltage (U _E , U _M ) of the measurement signal (U _M ) from the receiver

(R) as a function of the grammage or the weight per unit area of the flat objects (2), such as the target characteristic

(ZK) transforms that a linear or almost linear characteristic curve with a finite slope, in particular a curve provided with a maximum slope in the grammage range to be detected, as the ideal target curve (ZK) or a target curve approximating this ideal target curve between the output voltage (U _A , U ₂ ) at the output of the evaluation and the grammage or the basis weight, for generating the corresponding detection signal.

, A method according to claim 6, characterized in that the correction characteristic (KK) for labels and the like materials from the characteristic of the input voltage (U _E , U _M ) of the measurement signal, the ideal characteristic in the grammage or basis weight range to be detected (ZK) is mirrored for label recognition, is derived.

8. The method according to claim 6, characterized in that the correction characteristic (KK) for labels and the like. Materials from the characteristic of the input voltage (U _E , U _M ) of the measurement signal, which in the grammage or basis weight range to be detected ideal target characteristic (ZK) for label recognition after Cartesian coordinate transformation with respect to the connecting straight line of the two end points of the measured value characteristic for the material spectrum to be detected is mirrored.

9. The method according to any one of claims 6 to 8, characterized in that by means of the correction characteristic (KK) for labels, the characteristic of the input voltage (U _E , U _M ) of the measurement signal to the target characteristic (ZK) over the grammage or to be detected Basis weight range, 'for example from about 40 ^• g / m ² to 300 g / m ² , is transformed.

10. The method according to any one of claims 6 to 9, characterized in that the correction characteristic (KK) is selected so that a target characteristic (ZK) with the maximum and constant negative slope and maximum voltage difference over the grammage or basis weight range to be detected , for example from about 40 g / m ² to 300 g / m ² .

11. The method according to any one of claims 1 to 10, characterized in that the evaluation, in particular the amplitude of the measurement signal, is carried out via at least one signal amplification, that the signal amplification is given at least one correction characteristic curve such that at the output of the signal amplification Target characteristic curve for generating the detection signal is reached.

12. The method according to any one of claims 1 to 11, characterized in that the analog measurement signal received in the receiver is subjected to an analog-digital conversion with subsequent or direct digital evaluation by means of at least one correction characteristic curve for generating the corresponding detection signal.

13. The method according to any one of claims 1 to 12, characterized in that cardboard in sheet form, corrugated cardboard or stackable packaging are also used as flat objects in the radiation path between the transmitter and receiver.

14. The method according to one of claims 1 to 13, characterized in that the correction characteristic is impressed as a single characteristic or as a continuous or section-wise combination of several different correction characteristics over the entire grammage or basis weight range or over partial ranges.

15. The method according to any one of claims 1 to 14, characterized in that the correction characteristic as a linear or non-linear characteristic, as a single or multiple logarithmic characteristic, as an exponential characteristic, as a hyperbolic characteristic, as a polygon, as a function of any degree, or as an empirically determined or calculated characteristic, or as a combination of several of these characteristics.

16. The method according to any one of claims 1 to 14, characterized in that the correction characteristic is impressed as a combination of linear and logarithmic, linear and two- or multiple-logarithmic, or non-linear and logarithmic or multiple-logarithmic characteristic or amplification.

17. The method according to any one of claims 1 to 15, characterized in that the correction characteristic is specified as a logarithmic or multiple-logarithmic or similarly running nonlinear characteristic in combination with an approximately linear or exponential or similarly increasing characteristic or gain.

18. The method according to claim 1, characterized in that a suitable characteristic curve for achieving the ideal or approximately ideal target characteristic curve, in particular an inverse or almost inverse characteristic curve for the characteristic curve of the input voltage (U _E , U _M ) of the measurement signal is used.

19. The method according to any one of claims 1 to 18, characterized in that the respective correction characteristic is permanently impressed or actively controlled or regulated.

0 .. The method according to any one of claims 1 to 19, characterized in that in relation to single sheet, missing sheet or multiple sheet, at least two thresholds are specified as the upper and lower threshold, with a received measurement signal greater than the upper threshold, this as "missing sheet "is evaluated, if the measurement signal between the thresholds is received, this is evaluated as a" single sheet "and if the measurement signal is received it is smaller than the lower threshold, this is evaluated as a" multiple sheet ".

21. The method according to any one of claims 1 to 19, characterized in that at least one detection threshold is provided in relation to labels, adhesive and tear-off points and tear threads, this being evaluated as a "multiple layer" when the detection threshold is undershot and this is exceeded when the detection threshold is exceeded is evaluated as "carrier material or multiple layers reduced by at least one layer".

22. The method according to any one of claims 1 to 21, characterized in that the thresholds, in particular the detection threshold or the threshold for multiple sheets, are set permanently or are designed to be dynamically adaptable.

23. The method according to any one of claims 1 to 22, characterized in that the correction characteristic curve is determined as a function of the object and material-specific transmission damping and / or the resulting measurement signal voltage as a function of the grammage or the basis weight, and that the optimal correction characteristic or the optimal correction characteristic for the ideal target characteristic of the material-specific single sheet is determined mathematically and / or empirically.

24. The method according to any one of claims 1 to 23, characterized in that the correction characteristic for larger areas of material spectra is divided into several sections or several different section correction characteristics.

25. The method according to claim 16, characterized in that three or more sections are provided which are assigned to different grammage or basis weight ranges.

26. The method according to any one of claims 1 to 25, characterized in that at least one ultrasonic sensor or one or more optical, capacitive or inductive sensors are used as the sensor device.

27. The method according to any one of claims 1 to 26, characterized in that the transmitter (T) and receiver (R) of the sensor device (10) are aligned with one another in the main radiation axis of the radiation used, in particular coaxially, and that the main radiation axis is largely perpendicular or is aligned at an angle to the plane of the flat objects (2) arranged between the transmitter (T) and the receiver (R) or moved relative thereto.

28. The method according to any one of claims 1 to 27, characterized in that the sensor device (10), in particular switchable, is operated in pulse mode or continuous mode.

29. The method according to claim 28, characterized in that continuous operation of the sensor device (10) is provided to avoid standing waves and / or interference, phase jumps and / or short interruptions in the transmission signal.

30. The method according to any one of claims 1 to 28, characterized in that the transmission signal of the transmitter (T) is frequency-modulated.

31. The method according to any one of claims 1 to 30, characterized in that, in particular for ultrasound, transmitter (T) and receiver (R) are normalized in pairs to an optimal mounting distance, and that tolerances of transmitter and receiver at the beginning and / or during of ongoing operations are automatically corrected.

32. The method according to any one of claims 1 to 31, characterized in that, depending on application and arrangement criteria, transmitters and receivers for ultrasonic sensors are installed with a variable spacing.

33. The method according to any one of claims 1 to 32, characterized in that the distance between the transmitter and receiver by reflection of the radiation used between the transmitter and Receiver, in particular also in the case of damping sheet material arranged in between, and that an error message, in particular by LED, is generated when the permissible distances are exceeded or undershot.

34. The method according to any one of claims 1 to 33, characterized in that for the detection of single-shaft or multi-shaft corrugated cardboard and / or their direction of transport, the sensor axis between the transmitter and receiver of at least one sensor inclined to the perpendicular of the corrugated cardboard sheet, in particular orthogonal to widest surface of the corrugated cardboard shaft.

35. Method according to one of claims 1 to 34, characterized in that feedback is carried out between the evaluation device and the transmitter in order to maximize the amplitude of the received measurement signal.

36. The method according to any one of claims 1 to 35, characterized in that at least one A / D converter and / or a threshold value generator are used for the digitization of the analog measurement signal, and / or that a time-division multiplex method for selecting the different signals of the Signal amplification devices is used.

37.Device for the contactless detection of flat objects, in particular in sheet form such as paper, foils, sheets and similar flat materials or packaging, in relation to single sheets, missing sheets or multiple sheets of the flat objects, with at least one sensor device (10) with at least one transmitter ( T) and assigned recipient (R), wherein the flat objects to be detected are arranged in the radiation path between the transmitter (T) and the receiver (R), the receiver (R) receiving the radiation transmitted through the flat objects or the radiation obtained in the case of a missing sheet as a measurement signal, and with a downstream evaluation device (4) to which the measurement signal (U _M , U _E ) is fed in order to generate a detection signal, in particular to carry out the method according to one of claims 1 to 36, characterized in that the evaluation device (4) connected to the receiver (R) at least one correction characteristic (KK) is predetermined such that the correction characteristic (KK) is the characteristic of the input voltage (U _E , U _M ) of the measurement signal from the receiver (R) as a function of the grammage or weight per unit area of the flat objects transformed to the target characteristic curve (ZK), that a linear, almost linear or one of the ideal characteristics for papers and similar materials Characteristic curve approximated to the single curve of the single sheet, can be generated as a target characteristic (ZK) between the output voltage (U _A , U _z ) at the output of the evaluation device (4) and the grammage or basis weight, for the detection of single sheets, missing sheets or multiple sheets.

Device according to claim 37, characterized in that the evaluation device (4) acts as a correction characteristic

(KK) for papers and the like materials one with the ideal or approximate target characteristic

(ZK) for single sheet detection is a mirrored characteristic of the input voltage (U _E , U _M ) of the measurement signal.

9. The device according to claim 37, characterized in that the evaluation device (4) as a correction characteristic for papers and the like materials has an ideal or approximate target characteristic for single sheet detection, after Cartesian coordinate transformation with respect to the connecting straight line of the two End points of the measured value characteristic for the material spectrum to be detected, mirrored characteristic of the input voltage (U _E , U _M ) of the measurement signal.

40. Device according to one of claims 37 to 39, characterized in that the correction characteristic is selected such that the characteristic of the input voltage (U _E , U _M ) of the measurement signal over a large grammage or basis weight range, in particular between 8 g / m ² to 4,000 g / m ² , can be transformed into the target characteristic.

41.Device for the contactless detection of flat objects, in particular in the form of an arch, such as multi-layered materials adhering to the base or carrier material, e.g. labels, adhesive, tear or tear points and similar flat materials, in relation to their presence or absence, with at least a sensor device (10) with at least one transmitter (T) and associated receiver (R), the flat objects to be detected being arranged in the radiation path between the transmitter (T) and the receiver (R), the receiver (R) being through the flat surface Objects transmitted radiation or the radiation received if none is present as a measurement signal, and with a downstream evaluation device (4) to which the measurement signal (U _M , U _E ) is fed to generate a detection signal, In particular for carrying out the method according to one of claims 1 to 36, characterized in that the evaluation device (4) connected to the receiver (R) is predefined at least one correction characteristic (KK) such that the correction characteristic (KK) is the characteristic the input voltage (U _E , U _M ) of the measurement signal from the receiver (R) in dependence on the grammage or the basis weight of the flat objects is transformed into the target characteristic curve (ZK) in such a way that a linear or almost linear characteristic curve with a finite slope, in particular one with a maximum slope Slope in the grammage range to be detected, as an ideal target characteristic (ZK) or a target characteristic approximating this ideal target characteristic between output voltage (U _A , Zu) at the output of the evaluation and the grammage or basis weight, for detecting the presence or absence of flat materials, can be generated.

42. Device according to claim 41, characterized in that the correction characteristic (KK) for labels and the like. Materials by mirroring the characteristic of the input voltage (U _E , U _M ) of the measurement signal on the grammage or to be detected in Basis weight range ideal target characteristic (ZK) can be generated for label recognition.

43. Device according to claim 41, characterized in that the correction characteristic (KK) for labels and the like. Materials by mirroring the characteristic of the input voltage (U _E , U _M ) of the measurement signal on the grammage or to be detected in Basis weight range ideal target characteristic (ZK) for label recognition according to Kartesi- shear coordinate transformation with respect to the connecting straight line of the two end points of the measured value characteristic for the material spectrum to be detected.

44. Device according to one of claims 41 to 43, characterized in that the correction characteristic for labels or the like. Materials is selected so that the characteristic of the input voltage (U _E , U _M ) of the measurement signal can be transformed into the target characteristic over a grammage or basis weight range of approximately 40 g / m ² to 300 g / m ² .

45. Device according to one of claims 41 to 44, characterized in that the target characteristic curve (ZK) for labels and the like. Materials a maximum and constant negative slope gradient and a maximum voltage difference with respect to changes in grammage, in particular over the basis weight range of about 40 g / m ² to 300 g / m ² .

46. Device according to one of claims 37 to 45, characterized in that the evaluation device (4) has at least one amplification device (5), that the amplification device (5) has the at least one correction characteristic (KK) for generating the target characteristic (ZK) at the output of the amplification device.

47. Device according to one of claims 37 to 46, characterized in that the evaluation device (4) has an analog-digital converter device for converting the measurement signal of the receiver, and that an evaluation device (6) for the subsequent one or direct digital evaluation of the converted measurement signal by means of a correction characteristic curve (KK) is provided for generating a detection signal.

48. Device according to one of claims 37 to 47, characterized in that the correction characteristic is constructed as a single characteristic or as a continuous or section-wise combination of several different correction characteristics over the entire grammage or basis weight range or over partial ranges.

49. Device according to one of claims 37 to 48, characterized in that the correction characteristic as a linear or non-linear characteristic, as a single or multiple logarithmic characteristic, as an exponential characteristic, as a hyperbolic characteristic, as a polygon, as a function of any degree , or is designed as an empirically determined or calculated characteristic curve, or as a combination of several of these characteristic curves.

50. Device according to one of claims 37 to 49, characterized in that the correction characteristic is designed as a logarithmic or multiple-logarithmic or similarly running non-linear characteristic in combination with an approximately linear or exponential or similarly increasing characteristic or amplification.

51. Device according to claim 37, characterized in that a suitable characteristic curve for achieving the ideal or approximately ideal target characteristic curve, in particular a, is used as the correction characteristic for papers and the like materials inverse or nearly inverse characteristic to the characteristic of the input voltage (U _E , U _M ) of the measurement signal.

52. Device according to one of claims 37 to 51, characterized in that the correction characteristic curve (KK, 23) is permanently impressed, predetermined in a material-specific manner or dynamically, in particular controlled by a microprocessor.

53. Device according to one of claims 37 to 52, characterized in that the evaluation device (4) with respect to single sheet, missing sheet or multiple sheet, at least two thresholds are specified as the upper and lower threshold, wherein when the measurement signal received is greater than the upper threshold, this is detected as a "missing sheet", when a measurement signal between the thresholds is received this as a "single sheet" and when a measurement signal is received smaller than the lower threshold, this is detected as a "multiple sheet".

54. Apparatus according to claim 53, characterized in that the thresholds, in particular the detection threshold or threshold for multiple sheets, are designed to be permanently adjustable or can be designed to be dynamic.

55. Apparatus triggered automatically or externally to one of claims 37 to 54, characterized in that, in particular for labels, adhesive and demolition ^'represent and tear-off threads, these objects are passed between the transmitter and receiver, and depending on the received specific measuring signal of the object that object-specific switching threshold can be determined in relation to the target characteristic.

56. Device according to one of claims 37 to 55, characterized in that the sensor device (10) has at least one ultrasonic sensor or one or more optical, capacitive or inductive sensors.

57. Device according to one of claims 37 to 56, characterized in that the transmitter (T) and receiver (R) of the sensor device (10) are aligned with one another in the main radiation axis of the radiation used, in particular coaxially, and that the main radiation axis is largely perpendicular or is oriented at an angle to the plane of the flat objects (2) arranged between the transmitter (T) and receiver (R) or moved relative thereto.

58. Device according to one of claims 37 to 57, characterized in that the evaluation device (4) has a plurality of amplification devices (21, 22), in particular connected in parallel, whose output signals are combined to form the target characteristic curve (23).

59. Device according to one of claims 37 to 58, characterized in that the operating mode of the sensor device (10) can be changed from pulse operation to continuous operation and vice versa.

60. Device according to one of claims 37 to 59, characterized in that the transmission signal has phase jumps in continuous operation or short interruptions of the transmission signal are provided.

61. Device according to one of claims 37 to 60, characterized in that the transmission signal is frequency-modulated.

62. Device according to one of claims 37 to 61, characterized in that a device is provided for self-alignment or for setting the transmission frequency and / or the transmission amplitude to the receiver signal.

63. Device according to claim 62, characterized in that the self-adjustment can be carried out in times synchronized with the transmission frequency or in defined pause times.

64. Device according to one of claims 37 to 63, characterized in that the distance between transmitter (T) and receiver (R), in particular the sensor heads, can be varied depending on the application.

65. Device according to one of claims 37 to 64, characterized in that a feedback device is provided between the evaluation device (4), in particular a microprocessor (6), and the sensor device (10).

66. Device according to one of claims 37 to 65, characterized in that the evaluation device (4) has a plurality of specific channels for detecting different flat objects, such as double sheets or labels, that different correction characteristic curves are impressed on the channels, and that multiplexers (34, 35) are provided for controlling the inputs and outputs of the channels in order to generate an overall target characteristic.

67. Device according to one of claims 37 to 66, characterized in that the transmitter is provided below the sheets or flat objects to be detected and the receiver is provided above, and that the transmitter head is arranged at a short distance from the sheet.

68. Device according to one of claims 37 to 67, characterized in that between the transmitter (T) and the elongated object to be detected (2) at least one pinhole and / or slit diaphragm and / or lens to improve the spatial resolution in ultrasonic or optical sensors is provided.

69. Apparatus according to claim 68, characterized in that the arrangement of the diaphragms and / or lenses takes place transversely to the direction of movement of the flaky flat objects, or that the arrangement of the diaphragms and / or lenses is applied longitudinally to the direction of movement of the adhesively attached to a base or carrier material Multiple layers occur, or in particular slit diaphragms and / or lenses for the detection of elongated objects adhering to a base or carrier material, such as material threads, tear threads, are arranged in the thread running direction.

0. Device according to one of claims 68 or 69, characterized in that elongated objects (2) introduced between the transmitter (T), receiver (R) and diaphragm hover as close as possible above the diaphragm or touch it in a sliding manner.