Method and device for calibrating a sensor for measuring material thickness or basis weight

Abstract

Method for calibrating an ultrasonic sensor (8, 10) operating by means of transmission measurement and used for measuring the basis weight and / or thickness of a material web (100), wherein the method comprises the steps: Providing a planar calibration pattern (18) with a known basis weight; Acquiring the transmission values ​​of the calibration pattern (18) using the ultrasonic sensor (8, 10) at a multitude of different positions distributed over the area of ​​the calibration pattern (18); and Determining the calibration value for the ultrasonic sensor (8, 10) by averaging the large number of recorded transmission values ​​and linking the mean transmission value with the known basis weight of the calibration pattern (18).

Description

[0001] The invention relates to a method for calibrating a sensor used in the thickness measurement or basis weight measurement of a material web.

[0002] German patent DE 42 36 436 A1 discloses a method for the non-contact determination of the basis weight of thin material webs using ultrasound. In this method, the transmission absorption of an ultrasound beam as it passes through a material film is determined non-contact using an ultrasound transmitter and an ultrasound receiver. The basis weight is then calculated based on the absorption and a calibration factor.

[0003] From DE 201 09 119 U1, another device for measuring the thickness of material webs is known. In this device, the material web is drawn over a roller, and a sensor is arranged on a trolley that moves back and forth across the roller for thickness measurement.

[0004] DE 10 2009 011 122 A1 relates to a method for calibrating a thickness measuring device, wherein the thickness measuring device measures the thickness of a measuring object in a predefinable measuring direction with a displacement measuring sensor, wherein a reference object with known thickness and shape is placed in at least a partial area of ​​the measuring field of the at least one displacement measuring sensor.

[0005] JP 2000-155 022 A discloses a frame-shaped main body with an opening through which a sheet metal plate is to be passed, and a sheet metal thickness measuring sensor at the top. The sheet metal thickness measuring sensor is approached and removed from the upper and lower surfaces of the passing sheet metal plate by the approach and separation device. It is equipped with a pair of upper and lower measuring heads and a movement mechanism that synchronizes the pair of upper and lower measuring heads and moves them in the width direction orthogonal to the direction of passage of the sheet metal plate.

[0006] US 5,327,770 A relates to a scanning system with a plurality of scanning elements mounted on one or more carriers that move back and forth over a moving web of material. The scanning zones of adjacent scanning elements define scanning paths that periodically overlap within a scanning area. One of the scanning elements (primary) scans a known reference to periodically or continuously update its calibration, and this is effectively transferred (due to the overlap) to the other scanning element (secondary) via the moving material.

[0007] The object of the invention is to provide a method for improved calibration of a sensor. Furthermore, it is an object to make the measurement of the layer thickness and / or the basis weight of a material web more reliable by means of an improved method or device.

[0008] This problem is solved by the features of claim 1, 5 or 7.

[0009] Advantageous embodiments are the subject of dependent claims.

[0010] According to claim 1, a method for calibrating an ultrasonic sensor is provided. The ultrasonic sensor is used to determine the basis weight and / or the material thickness of a web or film (hereinafter, reference is generally made to webs, which also includes films). The measurement of the layer thickness or basis weight can be implemented exclusively via transmission measurement, in which a measurement signal is emitted through the web by a transmitter of the sensor and received by a receiver of the sensor on the side of the web opposite the transmitter. The layer thickness or basis weight can be determined from the attenuation of the signal during transmission through the web. In an unclaimed example, the layer thickness is determined based on the signal reflected by the web.The sensor's signal transmitter and receiver are located on the same side of the material web. In one embodiment, the sensor has a transmitter on the first side of the material web, a first receiver on the first side of the material web, and a second receiver on the second side of the material web, with the transmission being measured by the second receiver and the reflection by the first receiver.

[0011] In the calibration procedure, the ultrasonic sensor to be calibrated (which, as mentioned, is used in normal measurement operation for material thickness and / or basis weight measurement) is calibrated using a planar calibration pattern. For this purpose, a large number of transmission values ​​(and preferably reflection values) are recorded with the sensor on the planar calibration pattern, with the values ​​being recorded at various positions distributed across the surface of the calibration pattern.

[0012] Preferably, the calibration sample is a reference material with a known basis weight, determined, for example, by calibrated measuring methods, which is then used as a comparison standard for the ongoing monitoring of the layer thickness and / or the basis weight of the material web. A further advantage is that the calibration sample is a round stamped blank with an area of ​​one square decimeter, the basis weight of which has been determined by weighing on a precision balance.

[0013] From the multitude of values ​​recorded at the various positions of the calibration pattern, an average of the recorded transmission values ​​(and preferably reflection values) is calculated. This average is mathematically linked to the known basis weight of the calibration pattern, so that this calibration value can be used to calibrate the thickness and / or basis weight measurement of the sensor on the material web to be measured. Preferably, a calibration curve of the signal transmission (the course of the transmission intensity as a function of the layer thickness and / or basis weight, if measurement is taken in transmission or in combined transmission and reflection) is calibrated using the determined calibration value.Or a calibration curve of the signal reflection (course of the reflection intensity as a function of the thickness and / or the basis weight, if measured in reflection or in combined reflection / transmission) is calibrated.

[0014] By measuring transmission values ​​at distributed positions across the calibration pattern rather than at a single point, variations in layer thickness or basis weight are averaged out, thus reducing the sensor calibration error through averaging. Consequently, the higher precision of the sensor calibration also leads to more accurate determination of the layer thickness and / or basis weight of the material web.

[0015] In an advantageous embodiment, the spatially distributed positions on the calibration pattern are accessed by rotating the calibration pattern relative to the sensor. This rotation can be implemented with a mechanically simple setup, and during the rotation of the calibration pattern, positions lying on a circular path are accessed.

[0016] Alternatively or additionally, the positions on the calibration pattern are approached by translationally shifting the sensor relative to the calibration pattern and / or by translationally shifting the calibration pattern relative to the sensor. For example, a rotation of the calibration pattern can be combined with a translational shift of the sensor. With such a combination, positions that are helically offset or that lie on different circle diameters can be approached.

[0017] Both when rotating the calibration pattern and when moving it via translation, the approach to the spatially distributed positions can be performed either sequentially or continuously. When approaching the positions sequentially, the positions are approached and the measurement is taken, and then the next position is approached and the measurement is taken. When approaching or traversing the spatially distributed positions continuously, the measurement is taken while the rotation or translation is being performed.

[0018] Preferably, the transmission values ​​(and preferably reflection values) are measured continuously or quasi-continuously, either during continuous movement of the calibration pattern relative to the sensor and / or during continuous movement of the sensor relative to the calibration pattern. Quasi-continuous in this context means that the sensor acquires the measured values ​​at measurement intervals, such as those determined by the digital evaluation rate of the sequence signal pulse - signal reception - signal processing of the received signal. Continuous acquisition is achieved, for example, by analog or digital integration of the continuously transmitted and received measurement signal.

[0019] In the method for measuring the layer thickness and / or basis weight of a material web, the sensor is calibrated as described above before, during, and / or after determining the layer thickness and / or basis weight. The measurement of the layer thickness and / or basis weight of the material web is preferably carried out by moving the (calibrated or uncalibrated) sensor transversely to a longitudinally moving material web. During the transverse movement of the sensor, the transmission (and preferably the reflection) of the material web is recorded. The layer thickness and / or basis weight of the material web is determined by calculation based on the recorded transmission value(s) (and preferably the reflection values) using a calibration value or a calibration curve, which itself has been or is being calibrated based on the calibration of the sensor.

[0020] In an advantageous embodiment of the measuring method, the sensor is calibrated using the calibration pattern, preferably at predetermined time intervals. However, calibration can also be triggered by other events, for example, upon detection of a temperature drift in the production environment or the measurement environment of the material web, upon batch change of the starting material for the material web, or the like.

[0021] In the device for determining the layer thickness and / or basis weight of a material web according to claim 7, a sensor unit is associated with a material web transport device. The sensor unit includes a sensor for detecting transmission values ​​(and preferably reflection values) of the material web, which is movable in the transverse direction of the longitudinally transported material web. The sensor can be moved back and forth along the sensor unit, for example, between the outer longitudinal edges of the material web. This allows, for example, monitoring of the transverse distribution of the layer thickness and / or basis weight during a production process for the material web.

[0022] The device has a sensor calibration position in which the sensor is moved out of the material web measuring section and placed next to a holding device with a calibration pattern located at the sensor calibration position. In the sensor calibration position, the sensor is moved relative to the calibration pattern and / or the calibration pattern is moved relative to the sensor by means of a drive.

[0023] In this embodiment, a rotational and / or linear movement is achieved by means of a rotational and / or linear drive, which moves the calibration measurement pattern held in the holding device relative to the sensor. Additionally or alternatively, the sensor can be moved across the surface or at least in a linear direction, preferably in the transverse direction of the material web, over the calibration pattern held in the holding device in the sensor calibration position.

[0024] The sensor is an ultrasonic sensor where the measurement signal for determining layer thickness and / or basis weight is an ultrasonic pulse. In an unclaimed example, an optical sensor is used, employing, for instance, a laser beam or a light-emitting diode beam. Alternatively, the sensor is a radiation sensor that emits and receives gamma or beta rays.

[0025] In one embodiment, and as described above, the sensor can be configured solely as a transmission unit, where only the absorption during transmission of the sensor signal through the material web is determined. In another embodiment, the sensor unit is a combined transmission and reflection measurement unit, where both the attenuation of the sensor signal in reflection and in transmission are determined. With such a transmission and reflection measurement, one of the values ​​can be used to verify the plausibility of the other value and / or to calculate an average value for determining layer thickness and / or basis weight.

[0026] Exemplary embodiments of the invention are explained with reference to the figures. These show: Fig. 1 a schematic representation of an area weight measuring unit with calibration stations, Fig. 2 a schematic representation of the measuring and control arrangement when the sensor is positioned in the calibration station, and Fig. 3 the intensity / area weight or layer thickness curve and its recalibration.

[0027] Fig. Figure 1 schematically shows a planar view of a basis weight measuring unit 2, which is arranged on a material web 100 moving in the longitudinal direction x. For the sake of simplicity, the transport device for the forward movement of the material web 100 is not shown.

[0028] The figures do not show the proportions and distances to scale, but are presented in such a way as to illustrate the invention.

[0029] The area weight measuring unit 2 has as its basic component a transverse portal 4, which extends above and below the material web 100 across its full width and beyond. The transverse portal 4 leaves a slot-like opening through which the material web 100 is moved in the longitudinal direction x. At the upper crossbeam of the transverse portal 4 (in Fig. (as can be seen from above as a beam running in the y-direction) a carriage arm 6 is mounted on a carriage which is not visible in the illustration, the carriage being able to be moved in a reversing direction transversely (i.e. in the y-direction) to the material track 100 by means of a linear drive.

[0030] The carriage arm 6 carries a transmitter head 8, which can be moved across the full width of the material web 100 by means of the carriage arm 6. The transmitter head 8 emits an ultrasonic pulse onto the top side of the material web, and the ultrasonic signal propagates, attenuated, through the material web 100 to its underside, where the attenuated ultrasonic signal emerges and strikes a receiver head 10 located opposite the transmitter head 8.

[0031] In the schematic cross-sectional view of Fig. Figure 2 shows the arrangement of the transmitting head 8 and the receiving head 10 in a side view, where in the side view the y-direction is perpendicular to the plane of the drawing. Fig. Figure 2 is shown. Figure 32 illustrates the ultrasonic transmission beam emanating from the transmitter head 8. In the depicted parked position 14 of the transmitter head 8, the transmission beam 32 passes through a calibration pattern 18 and strikes the receiver head 10.

[0032] The receiving head 10 is also mounted on a slide on the lower crossbeam of the cross portal 4 (not shown) and is moved synchronously with the transmitting head 8 in the y-direction. The synchronous movement of the transmitting head 8 and the receiving head 10 is such that they are always positioned collinearly to each other on an axis in the z-direction.

[0033] Fig. Figure 1 further shows a standby and calibration station 12 of the basis weight measuring unit 2. The standby and calibration station 12 is offset laterally to the material web, i.e., offset in the y-direction or transverse direction to the material web 100. The standby and calibration station 12 has a parking position 14 in which both the transmitting head 8 and the opposite receiving head 10 are parked during measurement interruptions or for calibration of the transmitting / receiving unit 8, 10.

[0034] In the standby and calibration station 12, a clamping ring 16 is rotatably mounted, which is set in rotation on its outer side by means of a pinion 22. As from Fig. As can be seen in Figure 2, the pinion or gear 22 is driven by a drive motor 20. The pinion 22 engages with a toothed ring formed on the outside of the clamping ring 16, so that the rotational speed or angular position of the clamping ring 16 can be controlled by the motor 20. A calibration sample 18 is clamped in the clamping ring 16. The calibration sample 18 is a round stamped piece of a standard material used for calibration. The stamped piece has an area of ​​one square decimeter, so that the basis weight of the standard can be easily determined by weighing the stamped piece on a precision scale. The calibration standard in the form of the calibration sample 18 represents a target value for the thickness and / or basis weight of the material web 100 and is used for the repeated calibration of the transmitting unit consisting of the transmitting and receiving heads 8, 10.

[0035] Fig. Figure 2 shows a schematic side view of the transmitting and receiving heads 8 and 10, as well as the relative position of the calibration pattern 18. The control electronics for the basis weight measuring unit 2 are also shown in block diagram form. A position sensor 24 detects whether the transmitting head 8 and the receiving head 10 have reached the correct parking position 14, for example, to perform calibration. The position sensor 24 sends its signal to a control unit 26 of the basis weight measuring unit 2.

[0036] The control unit 26 controls a transmitter controller 28. For example, the transmitter controller 28 receives the supply voltage and a gain setting signal from the control unit 26 to adjust the signal amplification. A pulse signal, also received by the control unit 26, is amplified at the specified signal amplification for the transmitter head 8. The transmitter controller 28 outputs the amplified pulse signal to the transmitter head 8, which converts the voltage signal into the ultrasonic signal 32.

[0037] The ultrasound signal received at the receiver head 10 is converted into an electrical signal and fed to a receiver controller 30. The receiver controller performs signal processing and forwards the processed received signal to the control unit 26. For example, the receiver controller 30 includes a digital signal processor which, through appropriate programming via the control unit 26, provides a signal processing algorithm to perform the computationally intensive signal evaluation directly at the receiver controller 30 level.

[0038] Fig. Figure 2 further shows the intensity distribution of the transmitted signal over the diameter of the active ultrasound emitting surface of the transmitter head 8 at 34. The approximately Gaussian intensity distribution can be seen, with its intensity maximum located in the middle area.

[0039] To compensate for effects such as thermal drift, aging processes, impurities on the transmission / reception path of the ultrasonic signal 32, and similar effects, the measurement of the basis weight or layer thickness of the material web 100 is interrupted at predefined time intervals for calibration. For this purpose, the transmitting and receiving head 8, 10 moves laterally out of the measuring section (width of the material web 100) into the parking position 14. If the correct position of the transmitting and receiving head 8, 10 is detected by the position sensor 24, the control unit 26 activates the motor 20, so that the calibration pattern 18, clamped in the clamping ring 16, is rotated between the transmitting and receiving heads. The center of the transmit / receive surface of the transmit / receive head 8, 10 is offset radially to the center of the calibration pattern 18, so that the center of the transmit / receive head is moved on a circular path relative to the calibration pattern.

[0040] During the rotation of the calibration pattern 18, ultrasonic transmission pulses are continuously sent from the transmitter head 8 and detected by the receiver head 10. This allows the transmission values ​​of the calibration pattern 18 to be measured from various positions distributed across its surface. The measured values ​​are recorded by the control unit 26. After one or more rotations of the calibration pattern 18, the control unit 26 calculates an average of the measured transmission values ​​and uses this average to calibrate the calibration curve for determining the basis weight or layer thickness.

[0041] Fig. Figure 3 shows an exemplary and schematic calibration curve for the intensity I of the transmission T of the ultrasonic signal 32 as a function of the thickness d (the same applies to the basis weight) of the material web 100. The solid line shows the dependence of the intensity I on the layer thickness d with the last calibration value. If the averaging of the previously described transmission measurement yields a different calibration value for the layer thickness d or the basis weight, the calibration curve is corrected accordingly upwards or downwards, as indicated by the corresponding dashed curves. Thus, after calibration, a newly calibrated calibration curve is available ( Fig. 3) available and the layer thickness measurement perpendicular to the material web 100 can be continued with the new calibration curve, so that the basis weight or layer thickness determinations can be carried out with higher reliability. Reference symbol list 2 Area weight unit 4 Cross portal 6 sled arms 8 Transmitter head 10 receiver head 12 Standby and calibration stations 14 Parking positions 16 clamping ring 18 calibration patterns 20 Drive motor 22 gear 24 position sensor 26 Control unit 28 transmitter controllers 30 receiver controllers 32 Transmission beam 34 Intensity distribution 100 material conveyor

Claims

[1] Method for calibrating an ultrasonic sensor (8, 10) operating by means of transmission measurement and used for basis weight measurement and / or thickness measurement of a material web (100), wherein the method comprises the steps: Providing a planar calibration pattern (18) with a known areal weight; Acquiring the transmission values ​​of the calibration pattern (18) using the ultrasonic sensor (8, 10) at a multitude of different positions distributed over the area of ​​the calibration pattern (18); and Determining the calibration value for the ultrasonic sensor (8, 10) by averaging the large number of recorded transmission values ​​and linking the mean transmission value with the known basis weight of the calibration pattern (18). [2] Method according to claim 1, wherein the plurality of planar distributed positions on the calibration pattern (18) is approached by rotating the calibration pattern (18). [3] Method according to claim 1 or 2, wherein the plurality of planar distributed positions on the calibration pattern (18) is approached by translational displacement of the ultrasonic sensor (8, 10) relative to the calibration pattern (18) and / or by translational displacement of the calibration pattern (18) relative to the ultrasonic sensor (8, 10). [4] Method according to claim 1, 2 or 3, wherein the plurality of transmission values ​​is detected by continuous or quasi-continuous detection during a continuous movement of the calibration pattern (18) relative to the ultrasonic sensor (8, 10) and / or during a continuous movement of the ultrasonic sensor (8, 10) relative to the calibration pattern (18). [5] Method for measuring the layer thickness and / or basis weight of a material web (100) and for calibrating an ultrasonic sensor (8, 10) comprising the steps: Method of an ultrasonic sensor (8, 10) transversely (y) to a material web (100) moving in the longitudinal direction (x) and recording transmission values ​​of the material web (100), Determination of the layer thickness and / or the basis weight of the material web (100) or its distribution over the material web (100) by calculation from the recorded transmission values ​​and a calibration value or a calibration curve, and Calibrating the ultrasonic sensor (8, 10) according to one of claims 1 to 4, wherein the mean calibration value determined on the basis of the calibration pattern (18) is provided for determining the layer thickness and / or the basis weight or is used for recalibrating the calibration curve. [6] Method according to claim 5, wherein the calibration measurement is carried out after preferably predetermined time intervals of measuring the layer thickness and / or the basis weight of the material web (100). [7] Device for determining the layer thickness and / or basis weight of a material web (100), in particular for carrying out the method according to one of the preceding claims, wherein the device comprises: a material web transport device for transporting a material web (100) in the longitudinal direction (x); and a sensor unit (2) arranged on the material web transport device, wherein the sensor unit (2) comprises: an ultrasonic sensor (8, 10) for detecting transmission and / or reflection values ​​of the material web (100), a sensor movement device (6) for moving the ultrasonic sensor (8, 10) in the transverse direction (y) to the material web (100), preferably for moving over the entire width of the material web (100); a sensor calibration station (12) in which the ultrasonic sensor (8, 10) has been moved out of the material web measuring section, wherein preferably in the sensor calibration position the ultrasonic sensor (8, 10) is arranged offset in the extension of the transverse direction (y) of the material web (100) to the material web (100) to be measured; a holding device (16) for holding a planar calibration pattern (18), wherein in the sensor calibration station (12) the ultrasonic sensor (8, 10) is movable relative to the calibration pattern (18) held in the holding device (16) and / or the calibration pattern (18) is movable relative to the ultrasonic sensor (8, 10), wherein the calibration pattern (18) is a calibration pattern with a known basis weight; and a control unit (26) designed to to detect transmission and / or reflection values ​​of the calibration pattern (18) using the ultrasonic sensor (8, 10) at a variety of different positions distributed over the area of ​​the calibration pattern (18); to determine a calibration value for the ultrasonic sensor (8, 10) by averaging the multitude of recorded transmission and / or reflection values, and to link the mean value of the transmission and / or reflection with the known areal weight of the calibration pattern (18). [8] Device according to claim 7, wherein the holding device (16) has a rotational and / or linear drive (20, 22) for rotating and / or translationally moving the held calibration pattern (18) relative to the ultrasonic sensor (8, 10) located in the sensor calibration station (12). [9] Device according to claim 7 or 8, wherein the ultrasonic sensor (8, 10) has a signal source (8) for emitting an ultrasonic pulse directed at one of the surfaces of the planar calibration pattern (18), and the ultrasonic sensor (8, 10) has a receiver (10) for receiving, wherein the receiver (10) is located on the same side of the calibration pattern (18) as the signal source (8) and receives the signal reflected from the calibration pattern (18), or is located on the side of the calibration pattern (18) opposite the signal source (8) and receives the signal transmitted by the calibration pattern (18); or the ultrasonic sensor (8, 10) a first receiver which is located on the same side of the calibration pattern (18) as the signal source (8) and receives the signal reflected from the calibration pattern (18), and a second receiver which is located on the side of the calibration pattern (18) opposite the signal source (8) and receives the signal transmitted by the calibration pattern (18). [10] Device according to one of claims 7 to 9, wherein the calibration pattern (18) is arranged at a parking and / or maintenance position (12) for the ultrasonic sensor (8, 10). [11] Device according to one of claims 7 to 10, wherein the calibration pattern (18) is arranged in the extension of the transverse direction (y) of the material web (100) to be measured, which is moved in the longitudinal direction (x).

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