Method and apparatus for determining at least one geometric parameter of an elongated object having a periodic structure

Abstract

The present invention relates to a method for determining at least one geometric parameter of an elongated object having a periodic structure, specifically a corrugated tube having a corrugated layer having a periodic waveform, wherein the object is irradiated with X-ray radiation diverging transversely to the longitudinal direction of the object, and after the X-ray radiation has passed through the object, the X-ray radiation is detected by an X-ray detector having spatial resolution as a measurement signal spatially resolved transversely to the longitudinal direction of the object, wherein the X-ray radiation is used to irradiate a measurement portion of the object extending in the longitudinal direction of the object, the X-ray detector detects a plurality of measurement signals spatially resolved transversely to the longitudinal direction of the object with respect to the X-ray radiation passing through the measurement portion, the measurement signals are combined to form an evaluation signal spatially resolved transversely to the longitudinal direction of the object, layer transitions within the object and / or layer transitions between the object and a medium surrounding the object at multiple positions of the object and the measurement portion, and the method for determining at least one geometric parameter of the object based on the identified layer transitions. The present invention also relates to a corresponding apparatus.

Description

Technical Field

[0001] The present invention relates to a method for determining at least one geometric parameter of an elongated object having a periodic structure, specifically a corrugated tube having a corrugated layer with a periodic waveform, the method comprising irradiating the object with X-ray radiation that diverges laterally with respect to the longitudinal direction of the object, and after the X-ray radiation has passed through the object, detecting the X-ray radiation as a measurement signal spatially resolved laterally with respect to the longitudinal direction of the object by means of an X-ray detector having spatial resolution.

[0002] Furthermore, the present invention relates to an apparatus for determining at least one geometric parameter of an elongated object having a periodic structure, specifically a corrugated tube having a corrugated layer with a periodic waveform, the apparatus comprising an X-ray source designed to irradiate the object with X-ray radiation that diverges laterally with respect to the longitudinal direction of the object, and an X-ray detector having spatial resolution designed to detect the X-ray radiation as a measurement signal spatially resolved laterally with respect to the longitudinal direction of the object after the X-ray radiation has passed through the object.

Background Art

[0003] For example, corrugated tubes are available in various variations, shapes, and sizes. The corrugated tube has a corrugated layer with a periodic waveform, such as a sine wave, or other periodic structures, such as a box profile or a trapezoidal profile. The corrugated tube may consist of a corrugated layer. Further, the corrugated tube may, with respect to its shape, for example, have an inner layer corresponding to the shape of a smooth tube in which a corrugated layer with a periodic waveform is arranged. Corrugated tubes are often made of plastic material. However, conductive and / or magnetic materials are also possible.

[0004] For example, in the case of a corrugated tube having an inner layer and a corrugated layer placed on top of the inner layer, the inner layer and the corrugated layer are separated from each other by air or another medium within the peak regions of the periodic waveform, so the material layers of the inner layer and the corrugated layer can be differentiated within the peak regions of the periodic waveform. However, in the valleys, the inner layer and the corrugated layer overlap almost directly, and only a composite layer exists. In particular, when the inner layer and the corrugated layer are made of the same material, it is almost impossible to divide the wall thickness between the corrugated layer and the inner layer in the valleys.

[0005] Metametrically recording geometric parameters such as layer thickness of elongated objects with periodic structures is fundamentally important. For example, when measuring a corrugated tube, layer transitions between multiple corrugated layers, between corrugated layers and air, and / or between inner layers and air can be recorded. The radius and center point position of each layer can be described by trigonometry through the layer transitions. This then allows for the determination of the thickness (wall thickness) of each layer. In practice, to technically determine layer transitions, it is known that X-ray radiation is emitted into the corrugated tube, and after the X-ray radiation passes through the corrugated tube, the X-ray radiation is detected using an X-ray detector. The X-ray radiation diverges perpendicular to the longitudinal direction of the corrugated tube, and the X-ray detector captures an absorption image of the X-ray radiation that is spatially resolved perpendicular to the longitudinal direction of the corrugated tube. From the measured signal curve, the layer transitions of the corrugated tube to air can be inferred, and then geometric parameters such as the layer thickness of the corrugated tube can be inferred from these layer transitions.

[0006] For example, corrugated tubes are often transported along their longitudinal axis through the measurement area during measurement. This is desirable, especially when measurements are taken immediately after the corrugated tube is manufactured, from the standpoint of early detection of manufacturing defects and, consequently, minimizing defective products. Typically, the relatively low sampling rate of X-ray sensors leads to motion blur problems, particularly during X-ray measurements. Therefore, the X-ray detector records the measurement signal of X-ray radiation that has passed through different parts of the corrugated tube, and consequently regions with different waveform periods. This makes conventional evaluation of the measurement signal for determining layer transitions difficult. To address this problem, attempts have been made to minimize blurring of the X-ray image by ideally ensuring that only the cross-section of the corrugated tube is captured by the X-ray detector. Next, as a result, it is necessary to be able to precisely evaluate the measurement signal of the X-ray detector using standard methods. For example, attempts have been made to operate the X-ray detector in so-called TDI (Time Delay Integral) mode. For instance, the readout speed of an X-ray detector designed as a line sensor is synchronized with the transport speed of the corrugated tube. Ideally, this would produce a clear image of the absorption signal across one line of the X-ray detector. However, this synchronization is technically complex and requires readjustment every time the production conditions for the corrugated tube change. It has also been proposed to place a detector, such as a terahertz radiation detector, on a platform movable along the longitudinal direction of the corrugated tube and move it in synchronization with the transport speed of the corrugated tube. Here again, the goal is to generate the clearest possible image from the detector. However, this method is also very complex from a design standpoint and prone to errors in practice. Each time the production speed changes, time-consuming adjustments are required again. [Overview of the project] [Problems that the invention aims to solve]

[0007] Building upon the prior art described above, the object of the present invention is to provide a method and apparatus of the type mentioned at the beginning that can reliably and precisely determine at least one geometric parameter of an elongated object having a periodic structure using a simple design. [Means for solving the problem]

[0008] The present invention solves the problem as described by independent claims 1 and 15. Advantageous embodiments can be found in the dependent claims, specification, and drawings.

[0009] Regarding the type of method mentioned at the beginning, the present invention solves the problem in that it uses X-ray radiation to irradiate a measurement portion of an object extending in the longitudinal direction of the object, an X-ray detector detects multiple measurement signals spatially resolved laterally with respect to the longitudinal direction of the object with respect to the X-ray radiation passing through the measurement portion, combines the measurement signals to form an evaluation signal spatially resolved laterally with respect to the longitudinal direction of the object, identifies layer transitions within the object and / or layer transitions between the object and a medium, such as air surrounding the object at multiple locations of the measurement portion, and determines at least one geometric parameter of the object based on the identified layer transitions.

[0010] With respect to the type of apparatus mentioned at the beginning, the present invention solves the problem by further comprising an evaluation device, the X-ray source being designed to irradiate a portion of an object to be measured with respect to the longitudinal direction of the object with respect to the X-ray radiation passing through the portion to be measured, the X-ray detector being designed to detect a plurality of measurement signals spatially resolved laterally with respect to the longitudinal direction of the object with respect to the X-ray radiation passing through the portion to be measured, the apparatus being designed to combine the measurement signals to form an evaluation signal spatially resolved laterally with respect to the longitudinal direction of the object, and in the evaluation signal to identify layer transitions within the object and / or layer transitions between the object and a medium, such as air surrounding the object at multiple locations of the portion to be measured, and to determine at least one geometric parameter of the object based on the identified layer transitions.

[0011] According to the present invention, at least one geometric parameter of an object, specifically a corrugated tube, such as the radii and center points of two layers, and thus the layer thickness, is determined. The object has a periodic structure. If the object is a corrugated tube, the corrugated tube has at least one corrugated layer having a periodic waveform. The periodic waveform may be designed, for example, sinusoidal, or box-shaped profile, or trapezoidal, or another periodic shape. For example, in the case of a box-shaped profile structure, flat regions may exist in the peaks and troughs of the waveform. The object may be strand-shaped, specifically tubular. The object may be made of, for example, a plastic material. However, other materials, such as conductive and / or magnetic materials, are also possible. If the object is a corrugated tube, the corrugated tube may consist of corrugated layers. However, the corrugated tube may have an inner layer on which the corrugated layers are arranged. The inner layer may be, for example, cylindrical, or designed in another way. The inner layer may be, for example, cylindrical or circular. The inner layer may be in the form of a smooth tube. The periodic shape of an object consists of alternating peaks and valleys, where ascending and descending slopes are arranged. If an inner layer exists in a corrugated tube, the corrugated layer is often in direct contact with the inner layer within the valley regions. The inner layer and the corrugated layer can be made of the same material, although different materials are also possible.

[0012] According to the present invention, in order to determine at least one geometric parameter, layer transitions within an object, for example, layer transitions between multiple corrugated layers of a corrugated tube, and / or layer transitions between an object and a surrounding medium, specifically layer transitions between the corrugated layers of a corrugated tube and the surrounding medium, and / or layer transitions between the inner layer of a corrugated tube and the surrounding medium are determined. The surrounding medium is generally a gaseous medium, specifically air. However, the surrounding medium may also be a liquid medium. Furthermore, the surrounding medium may be located, for example, at the peaks of the corrugated layers of a corrugated tube between the inner layer and the corrugated layers.

[0013] First, in a manner similar to the prior art, an object is irradiated with X-ray radiation that diverges at least transversely to the longitudinal direction of the object, preferably in a direction transverse to the longitudinal direction of the object (primary radiation). After the X-ray radiation passes through the object, it is detected as a spatially resolved measurement signal by an X-ray detector having spatial resolution at least transversely to the longitudinal direction of the object. As explained at the beginning, the prior art has attempted to prevent position or motion blur of the measurement signal captured by the X-ray detector using complex methods. Deviating from the teachings of the prior art, the present invention not only considers the position and / or motion blur of the measurement signal of the X-ray detector, but also utilizes it for measurement and evaluation. For this purpose, X-ray radiation is used to irradiate a measurement portion of an object extending in the longitudinal direction of the object, and the X-ray detector detects multiple measurement signals that are spatially resolved at least transversely to the longitudinal direction of the object with respect to the X-ray radiation passing through the measurement portion. These measurement signals, resulting from position and / or motion blur, are combined to form an evaluation signal that is spatially resolved at least transversely to the longitudinal direction of the object. This evaluation signal identifies layer transitions within the object and / or layer transitions between the object and the surrounding medium at multiple locations on the measurement portion. Based on the identified layer transitions, at least one geometric parameter of the object is determined, for example, at multiple locations on the measurement portion. The measurement portion has a range in the longitudinal direction of the object. This range may be, for example, at least 10% of the period of the periodic structure of the object, for example, the period of the waveform of the corrugated layer of a corrugated tube.

[0014] In this specification, when referring to the direction perpendicular to the longitudinal direction of an object, this includes both the direction perpendicular to the longitudinal direction of the object and the direction oblique to the longitudinal direction of the object. According to the present invention, the evaluation of the measurement signal is simplified when the X-ray radiation is irradiated in a primary radiation direction perpendicular to the longitudinal direction of the object, and the measurement signal is spatially resolved perpendicular to the longitudinal direction of the object.

[0015] According to the present invention, extending the field of view of the X-ray detector to the measurement portion extending in the longitudinal direction of the object can be achieved by moving the object along its longitudinal axis during measurement, and / or by having the X-ray detector have spatial resolution in the direction of the object's longitudinal axis, and / or by adjusting the exposure time of the X-ray detector. There is a duality between positional and temporal blurring. X-ray radiation diverges at least transversely to the longitudinal direction of the object. X-ray radiation may also diverge in the longitudinal direction of the object, i.e., it may have a conical beam pattern. In this case, the measurement portion extending in the longitudinal direction of the object can be simultaneously irradiated with X-ray radiation. However, the measurement portion can be sequentially irradiated with X-ray radiation, especially when the object is transported in the same transport direction as the longitudinal direction of the object during measurement. It is also possible to combine measurement using X-ray radiation diverging in the longitudinal direction of the object, more precisely, in the transport direction of the object, with transport of the object along its longitudinal axis, more precisely, in the transport direction through the measurement area.

[0016] An X-ray detector has spatial resolution at least in the transverse direction with respect to the longitudinal direction of the object. Alternatively, an X-ray detector may have spatial resolution in the longitudinal direction of the object. An X-ray detector may comprise a scintillator and at least one optical sensor array, such as a one-dimensional or two-dimensional CCD array. If the X-ray detector has spatial resolution in the longitudinal direction of the object, it can directly and, if necessary, simultaneously detect X-ray radiation passing through different regions of the measurement area. However, if the X-ray detector has spatial resolution only in the transverse direction with respect to the longitudinal direction of the object, i.e., if the X-ray detector is a line sensor with only one sensor line, it is also conceivable to sequentially detect X-ray radiation passing through different regions of the measurement area.

[0017] In contrast to the prior art described at the beginning, the present invention is based on the discovery that the blurring of the X-ray detector image itself, where various regions of an object overlap along the measurement area in the absorption image, facilitates, or even enables, the identification of geometric parameters of specific features. By allowing blurring of the X-ray detector image along the longitudinal direction of the object, the requirements on the sensor are significantly reduced and simplified compared to the prior art. At the same time, by combining the measurement signals from various regions along the measurement area, the evaluation signal formed by the present invention provides more overall information about the geometric shape of the object than a sharp image of only a single region of the object. Therefore, the geometric parameters of the object can also be determined more reliably and accurately compared to the prior art. The blurring of the X-ray detector image intentionally utilized by the present invention allows the X-ray detector to record significantly more components from the vibration period. As a result, the proportion of the tube containing evaluated information can increase. Therefore, regions of the vibration period that are not visible in a sharp detector image can also be recorded. This is particularly important when considering the typical low sampling rates of such X-ray systems, for example, 1 to 10 Hz, as it increases the number of possible measurement points. Furthermore, according to the present invention, the specific characteristics of the determination of geometric parameters can be expressed more clearly in the evaluation signal. Specifically, blurring enhances the contribution of various regions of the periodic structure, such as the waveform of the waveform layer of a corrugated tube, such as the peaks and troughs, and the corresponding characteristics become more prominent in the absorption curve of the evaluation signal.

[0018] As already described, according to one embodiment, an object, such as a corrugated tube, may be transported in a transport direction while X-ray radiation passes through the object. The transport direction may correspond to the longitudinal axis of the object. Furthermore, according to the present invention, the apparatus may include a transport device designed for this purpose.

[0019] Similarly, as already explained, X-ray radiation irradiating an object can also diverge in the longitudinal direction of the object. X-ray detectors can also have spatial resolution in the longitudinal direction of the object. For example, an X-ray detector may include a scintillator, specifically a two-dimensional scintillator layer, in addition to a two-dimensional sensor array, such as a two-dimensional CCD array. The scintillator, more precisely the scintillator layer, converts the received X-ray radiation into electromagnetic radiation, such as visible or invisible wavelength light, which can be detected by an optical sensor, such as a CCD sensor.

[0020] To elaborate further, the amount of information in the evaluation signal for determining at least one geometric parameter is increased by metrologically recording the waveforms of multiple regions of an object, such as the waveforms of the waveform layers of a corrugated tube, along the measurement portion. Thus, according to one embodiment, the measurement portion may extend to at least 20%, preferably at least 40%, of the period of a periodic structure, such as the waveform of the waveform layers of a corrugated tube. According to the present invention, recording different portions of the period is particularly preferable for evaluation. Thus, according to a further embodiment, it is possible to provide that the measurement portion extends to a periodic structure, such as at least a portion of the wave crests and wave troughs of the waveform of the waveform layers of a corrugated tube, as well as the slopes between the wave crests and wave troughs. The above embodiments of the field of view of the X-ray detector allow, firstly, to identify layer transitions within an object and / or between the object and the surrounding medium at more locations in the measurement portion. Secondly, the characteristic features indicating layer transitions become more prominent in the evaluation signal.

[0021] It is further recognized that, according to the present invention, the evaluation signal for evaluation according to the present invention may be further impaired by covering an excessively large measurement area, specifically an excessively wide area of ​​the periodic structure. For example, if not only the peaks of the periodic structure covered by the measurement area but also adjacent peaks are recorded, the characteristics of the evaluation signal specific to the layer transition will be degraded, and consequently, the determination of geometric parameters may be distorted. Furthermore, if the measurement area, more precisely the field of view of the X-ray detector, is extended by more than one period, it is assumed that the perfect characteristics of the features in the evaluation signal characteristic of the layer transition will be significantly impaired. Therefore, according to further embodiments, it is possible to provide that the measurement area extends to 100% or less, preferably 75% or less, of one period of the waveform of the waveform layer of a corrugated tube, for example. Furthermore, it is possible to provide that the measurement area does not extend beyond one wave peak and one wave trough of the periodic structure, as well as one slope between the wave peaks and wave troughs of the periodic structure.

[0022] In particular, according to practical embodiments, the average value of the measurement signals detected across the measurement area can be formed in order to combine the measurement signals and form an evaluation signal that is spatially resolved laterally with respect to the longitudinal direction of the object. Thus, the individual measurement signals recorded across the measurement area and spatially resolved laterally with respect to the longitudinal direction of the object are averaged to form an evaluation signal. This evaluation signal is then spatially resolved laterally with respect to the longitudinal direction of the object. The spatial resolution laterally with respect to the longitudinal direction of the object is not lost during averaging. Averaging is performed only in the direction of the measurement area. For example, if an X-ray detector with spatial resolution in the longitudinal direction of the object is used, averaging can be formed in a simple manner on the sensor pixels in the longitudinal direction of the object. Thus, integration is performed on the line of the X-ray detector in the longitudinal direction of the object.

[0023] According to further embodiments, layer transitions within an object, and / or between the object and the surrounding medium, specifically layer transitions between multiple waveform layers of a corrugated tube, and / or between the waveform layers of a corrugated tube and the surrounding medium, and / or between the inner layers of a corrugated tube and the surrounding medium, can be identified based on minimum and / or maximum values, and / or changes in slope, and / or irregularities in the evaluation signal. In particular, features specific to and readily identifiable for the identified layer transitions are identified in the spatially resolved curve of the evaluation signal. According to the present invention, in order to determine layer transitions, at least two, preferably at least three, more preferably at least four, for example, five minimum and / or maximum values, and / or changes in slope, and / or irregularities can be identified in the evaluation signal by selecting an appropriate measurement portion that is sufficiently large and not excessively large. The identified layer transitions are located at different positions along the measurement portion of the object, as described above.

[0024] In a further embodiment, layer transitions can be identified using a machine learning algorithm, preferably an artificial neural network, based on minimum and / or maximum values, and / or changes in slope and / or irregularities in the evaluation signal. Such so-called artificial intelligence algorithms can clearly and reliably identify the above-mentioned specific features even in evaluation signals that actually exhibit disturbances.

[0025] As already explained, the thickness of the corrugated layer and / or inner layer of an object, specifically a corrugated tube, can be determined as at least one geometric parameter, for example, at multiple locations on the measurement section. The layer thickness is particularly important for evaluating the production quality of the manufactured object. If an unacceptable deviation from the target value is observed in the layer thickness, this can be indicated by the evaluation device, for example, in the form of a warning message. Intervention in the production equipment for manufacturing the object, such as an extruder, is also possible.

[0026] As a principle, for example, it is also conceivable to provide an object with a plurality of X-ray sources and an X-ray detector that irradiate the object with X-ray radiation from two directions orthogonal to each other. Therefore, the object is irradiated with X-ray radiation that diverges in at least the lateral direction with respect to the longitudinal direction of the object, preferably in the main radiation direction in the lateral direction with respect to the longitudinal direction of the object, from two directions. After the X-ray radiation passes through the object, it can be detected by an X-ray detector having at least two spatial resolutions as a measurement signal spatially resolved at least in the lateral direction with respect to the longitudinal direction of the object. The measurement portion extending in the longitudinal direction of the object is irradiated with X-ray radiation from two directions respectively. With respect to the X-ray radiation passing through the measurement portion, the X-ray detector detects a plurality of measurement signals spatially resolved at least in the lateral direction with respect to the longitudinal direction of the object respectively. The measurement signals detected by the X-ray detector are combined respectively to form an evaluation signal spatially resolved at least in the lateral direction with respect to the longitudinal direction of the object. In the evaluation signal, layer transitions within the object and / or layer transitions between the object and the medium surrounding the object at a plurality of positions of the measurement portion are identified, and based on the identified layer transitions, at least one geometric parameter of the object is determined.

[0027] In this case, a further measurement axis of the X-ray system becomes available in this way. The X-ray source and the X-ray detector are designed as described above and below and the measurement signals can be evaluated. As a result, further information regarding the geometric shape of the layer becomes available. In particular, by this method, geometric parameters such as radius and center point position can be determined in a simple way, and as will be described in more detail later, the wall thickness can be determined based on this. For example, using two measurement axes, the center point position of each layer can be determined. Thereby, when at least two layer transitions are determined, the radius can be derived and based on this, the wall thickness can be derived. Of course, according to the method of the present invention, it is also possible to form more than two measurement axes. In the case of more than two measurement axes, an elliptical shape, that is, for example, when the layers have different radii on the outer periphery of the tube, can be determined more accurately.

[0028] By diverging X-ray radiation and arranging the X-ray source, object, and X-ray detector at a distance from each other, the layer transitions identified in the evaluation signal need to be converted into corresponding geometric parameters, such as layer thickness, using trigonometry, taking into account known distances, specifically the distance between the X-ray source and the X-ray detector, and, if applicable, the distance to the object. This is itself a known technique. For this purpose, according to one embodiment, the center point position and radius of the layer associated with the identified layer transition can be calculated, and at least one geometric parameter, such as the layer thickness of the layer, can be determined. After extracting the specific features of the layer transition in the evaluation signal, target values such as the center point position, radius, and subsequently the layer thickness of the corresponding layer can be calculated. The center point position and radius are confirmed for each layer transition. For each layer transition, it is necessary to find two positions for each measurement axis of the X-ray measurement system. For example, in the case of two measurement axes perpendicular to each other, it is necessary to find two positions on both sides of the object, such as a corrugated tube, respectively. For this purpose, first, the angle between the measurement axis and the direct connection from the point-like X-ray source to the corresponding detector value of the specific feature on the X-ray detector can be confirmed. The center of the object, such as a corrugated tube, is located on the beam between the X-ray source and the X-ray detector, and this beam may be angled with respect to the measurement axis. Considering the geometric design of the measurement axis, specifically the distance between the X-ray source and the X-ray detector, the center point position of the relevant layer is calculated. For the radius of the layer, a semi-opening angle is determined. This semi-opening angle is measured by the connection from the point-like X-ray source to the position of the specific feature on the X-ray detector. Once the center point positions and radii of both layer transitions of the relevant layer are determined, the layer thickness, more precisely the wall thickness, can be calculated. For this purpose, it is necessary to subtract only the radii from each other, considering the possibility of eccentricity.

[0029] The device according to the invention can be designed to implement the method according to the invention. Therefore, the method according to the invention may also be implemented by the device according to the invention.

[0030] Exemplary embodiments of the invention are explained in more detail below with reference to the figures. The drawings are shown schematically.

Brief Description of the Drawings

[0031] [Figure 1] The apparatus according to the present invention as shown in Figure 1. [Figure 2] A partial cross-sectional view of a corrugated tube showing the sensor area of ​​the X-ray detector of the apparatus according to the present invention. [Figure 3] A magnified view of a portion of Figure 1. [Figure 4] A graph showing the measurement signal from the X-ray detector. [Figure 5] Further graphs showing the measurement signals from the X-ray detector. [Figure 6] A graph showing how an evaluation signal is generated according to the method of the present invention. [Figure 7] Apparatus of the present invention according to a further exemplary embodiment shown in Figure 1.

[0032] Unless otherwise specified, identical reference numerals in drawings refer to the same thing. [Modes for carrying out the invention]

[0033] An apparatus for determining at least one geometric parameter of the corrugated tube 10 shown in Figure 1 comprises a substantially point-shaped X-ray source 12. In Figure 1, this X-ray source 12 emits X-ray radiation that diverges at least in a plane extending along the X and Y axes of the illustrated Cartesian coordinate system, as shown by the dashed lines in Figure 1. The X-ray source can also emit X-ray radiation that diverges in the longitudinal direction of the corrugated tube 10, i.e., in Figure 1, in a plane extending along the x and z axes. In Figure 1, the longitudinal axis of the corrugated tube 10 extends in the direction of the z axis, i.e., in the direction of the drawing plane. During measurement, the corrugated tube 10 may be transported in a transport direction through the measurement area of ​​the apparatus. The transport direction corresponds to the longitudinal axis of the corrugated tube 10, i.e., the z direction in Figure 1. For this purpose, the apparatus may be equipped with a corresponding transport device.

[0034] In the illustrated embodiment, the corrugated tube 10 is irradiated divergently in the xy plane perpendicular to the longitudinal direction of the tube by X-ray radiation emitted by the X-ray source 12. Also, in Figure 1, when the X-ray radiation diverges in the xz plane, the corrugated tube 10 is irradiated in the longitudinal direction of the corrugated tube 10. The X-ray radiation passes through the corrugated tube 10 and, after passing through the corrugated tube 10, is detected by the spatially-resolution X-ray detector 14 as a measurement signal spatially resolved perpendicular to the longitudinal direction of the corrugated tube 10, in this example in the y-axis direction. In this embodiment, the spatially-resolution X-ray detector 14 has spatial resolution in at least the y-direction. The X-ray detector 14 may also have spatial resolution in the z-direction, i.e., along the longitudinal axis of the corrugated tube 10. The X-ray detector 14 may include a two-dimensional scintillator layer with a downstream two-dimensional sensor array, for example, a CCD array. The measurement signal from the X-ray detector 14 is applied to the evaluation device 16, which processes the signal in a manner described in more detail later to determine the geometric parameters of the corrugated tube 10.

[0035] In the illustrated embodiment, the corrugated tube 10 comprises an inner layer 18 in the form of a smooth tube and a corrugated layer 20 having a periodic waveform arranged on the inner layer 18. In Figure 2, a portion of the corrugated tube 10 is shown in a longitudinal cross-sectional view. Here, the waveform of the corrugated layer 20 with approximately two periods can be seen. In particular, it can be seen that in the region of the wave trough 22, the corrugated layer 20 is in direct contact with the inner layer 18, whereas in the region of the wave crest 24, there is a gap filled with air between the corrugated layer 20 and the inner layer 18. As a result, in the region of the wave trough 22, two interlayer transitions occur with respect to the air, namely between the outer surface of the corrugated layer 20 and the air, and on the other hand, two interlayer transitions occur between the inner surface of the inner layer 18 and the air. In contrast, in the region of the wave crest 24, there are four layer transitions, namely two between the corrugated layer 20 and the air, and two between the inner layer 18 and the air. According to the present invention, the layer transitions are intended to be confirmed so that geometric parameters such as the layer thickness (wall thickness) of the inner layer 18 and / or the corrugated layer 20 can be determined from the layer transitions in a manner well known to those skilled in the art. Furthermore, Figure 2 shows a two-dimensional sensor array of the X-ray detector 14. In the illustrated embodiment, 2000 pixels of the array are shown in the Y direction and 128 pixels are shown in the Z direction. Therefore, when the corrugated tube 10 is transported along its longitudinal axis, i.e., the z direction, during operation, the sensor array of the X-ray detector 14 alternately detects the X-ray radiation after it has passed through the troughs 22 and crests 24 of the wave and the intermediate slopes. In Figure 1, the crests 24 of the wave can be seen in the cross-sectional view of the corrugated tube 10, and a gap exists between the inner layer 18 and the corrugated layer 20.

[0036] Based on an enlarged detail view of Figure 1 derived from Figure 3, and with reference to Figure 4, the absorption signal generated on the X-ray detector 14 and spatially resolved perpendicular to the longitudinal axis of the corrugated tube 10 will be described in more detail. In Figure 4, the absorption signals obtained at three positional states of the corrugated tube 10 relative to the X-ray detector 14 are shown in the form of three graphs. A still image of the stationary corrugated tube 10 is shown in each graph. Therefore, especially when averaging in the z direction across the line of the X-ray detector 14, only positional blurring due to the two-dimensional spread of the X-ray detector 14 exists. Similar to Figure 2, the axis information of the top graph in Figure 4 relates to the X-ray detector 14 as shown in Figure 1. In the three lower graphs of Figure 4, the intensity in arbitrary units is plotted across the pixels of the sensor array of the X-ray detector 14 in the y direction, i.e., perpendicular to the longitudinal axis of the corrugated tube 10.

[0037] The bottom graph in Figure 4 corresponds to the position state shown in the upper right of Figure 4, in which state the X-ray detector 14 receives only X-ray radiation that has passed through the trough 22 of the wave. The second-to-last graph in Figure 4 shows the position state shown in the upper center of Figure 4, in which state the X-ray detector 14 receives X-ray radiation that has passed through the slope between the trough 22 and the crest 24 of the wave, as well as the short portions of the trough 22 and the crest 24 of the wave. The second-to-last graph in Figure 4 shows the position state shown in the upper left of Figure 4, in which state the X-ray detector 14 receives only X-ray radiation that has passed through the crest 24 of the wave. This position state is also shown in Figure 3. In the ideal state shown in the upper left and upper right of Figure 4, the corrugated tube 10 does not deform in the region under consideration, so positional blurring does not affect the signal.

[0038] In Figure 3, for illustrative purposes, the six beams 0 through 5 of diverging X-ray radiation emitted by the X-ray source 12 are depicted as dashed lines. The X-ray radiation passes through the corrugated tube 10 unobstructed between beams 0 and 1. Therefore, no absorption occurs, and in the second graph from the top in Figure 4, it is reflected in the form of a constant maximum intensity in region A. Each layer transition between the air and the corrugated tube 10 layers results in an initial decrease in intensity, as depicted at B in the second graph from the top in Figure 4. Between beams 1 and 2 in Figure 3, the chord length through the plastic material of the corrugated layer 20 increases, and consequently, the absorption of X-ray radiation increases. This results in a decrease in intensity between points B and C in the second graph from the top in Figure 4. The maximum chord length of the corrugated layer 20 is achieved at point C in Figure 4, corresponding to beam 2 in Figure 3. This results in a local minimum of the intensity curve depicted at C in the second graph from the top in Figure 4. Subsequently, the intensity increases between beam 2 and beam 3 in Figure 3 because the proportion of the two strings of the irradiated waveform layer 20 decreases until beam 3 is reached. From this point onward, in addition to the absorption contribution of the two strings of the waveform layer 20, the material of the inner layer 18 also contributes to the absorption of X-ray radiation. Therefore, from beam 3 onward, the received intensity decreases again, as depicted by D in the second graph from the top in Figure 4. As the length of the irradiated inner layer 18 strings increases, the intensity level decreases up to beam 4 in Figure 3, where the absolute minimum of the intensity curve depicted by E in the second graph from the top in Figure 4 occurs. From beam 4 onward, absorption increases again up to beam 5 in Figure 3. This is because the length of the strings of the inner layer 18 and waveform layer 20 decreases as a local maximum is reached, as depicted by F in the second graph from the top in Figure 4. Subsequently, an ideal symmetrical intensity curve is generated for the remaining half of the waveform tube 10, which is not shown in Figure 3.

[0039] In the example shown in the bottom graph of Figure 4, the X-ray detector 14 receives only X-ray radiation that has passed through the trough 22 of the wave, and the intensity curve clearly has fewer distinctive features compared to the previous example. In particular, as mentioned above, only two layer transitions exist here. The absolute intensity maximum value E depicted in the second graph from the top of Figure 4 can also be identified in the intensity curve at the position state shown in the bottom graph of Figure 4. However, in particular, distinctive features B, C, and D cannot be identified in the curve of the bottom graph of Figure 4. Instead, a further distinctive feature G can be identified. That is, a distinctive feature when X-ray radiation is irradiated to the layer transition between the outer surface of the waveform layer 20 and the air, which is in direct contact with the inner layer 18. Therefore, the aforementioned distinctive feature G cannot be identified in the second graph from the top of Figure 4.

[0040] The second-to-last graph in Figure 4 shows the intensity curve for the positional state shown in the center of the top graph in Figure 4, in which the X-ray detector 14 receives X-ray radiation that has passed through the slope between the wave trough 22 and the wave crest 24, as well as parts of the wave trough 22 and the wave crest 24. In this intensity curve, it can be seen that all of the characteristic features A through G of the other two intensity curves plotted in Figure 4 are included in the signal detected by the X-ray detector 14. Compared to the other two intensity curves in Figure 4, some features, specifically features C, G, and D, are relatively difficult to identify due to the influence of the slope between the wave trough 22 and the wave crest 24. Therefore, these features are relatively inconspicuous, but still identifiable.

[0041] Building upon the results described above, the present invention is based on the idea that blurring in the longitudinal direction of the corrugated tube 10 within the intensity image of the X-ray detector 14, specifically positional blurring and / or motion blurring, i.e., superposition of X-ray radiation passing through various regions of the corrugated tube 10, can improve the detection of features specific to layer transitions of a particular object in the intensity signal of the X-ray detector 14. Figure 5 shows the change in the intensity curve captured by the X-ray detector 14 as the measured portion showing blurring increases, which in this case is expressed as the percentage of the recorded period of the waveform of the corrugated layer 20. In this measured portion, the X-ray detector 14 receives X-ray radiation after it has passed through the corrugated tube 10. Here, the intensity is in all cases represented in arbitrary units on the sensor pixels of the sensor array in the direction perpendicular to the longitudinal axis of the corrugated tube 10, i.e., the y-direction. It can be confirmed that the number of evaluable specific features for layer transitions increases in the intensity signal as the field of view of the X-ray detector 14, i.e., the size of the measured portion, increases. In the illustrated embodiment, this specifically applies to a measurement portion extending 25% of the period of the waveform layer 20. Once the wave crests 24 and troughs 22, along with the intermediate slopes, are sufficiently extended, five features characteristic of the layer transition between the air and the waveform layer 20, or between the air and the inner layer 18, namely features B, C, D, E, and G, as depicted in Figure 4, can be identified as minimums and / or maximums and / or changes in slope and / or irregularities in the intensity curve. Further increasing the size of the measurement portion beyond 25% of the period of the waveform layer 20 improves the manifestation of these characteristic features and further improves the evaluation. However, if other adjacent slopes of the waveform of the waveform layer 20 are included in the measurement portion, the manifestation of these features may deteriorate. If the measurement portion extends beyond one period of the waveform of the waveform layer 20, the features are assumed to no longer be perfectly characteristic.

[0042] As shown in Figure 2, the X-ray detector 14 has spatial resolution in the longitudinal direction of the corrugated tube 10, i.e., the z-direction in Figure 1. For example, the sensor may have 128 lines in this direction. In Figure 6, the measured values ​​are represented as a series of gray intensity curves spatially resolved perpendicular to the longitudinal direction of the corrugated tube 10, for example, as the measurement signals 26 of the X-ray detector 14 across 128 lines in the longitudinal direction of the corrugated tube 10. These measurement signals 26 received by the X-ray detector 14 are combined by the evaluation device 16 to form an evaluation signal 28. In this embodiment, the measurement signals are spatially resolved perpendicular to the longitudinal direction of the corrugated tube 10 by averaging across the set 26, and are shown as solid black lines in Figure 6. The distinctive features described above, specifically the five minimum and / or maximum values, and / or changes in slope, and / or irregularities B, C, D, E, and G, can be identified by the evaluation device 16 in the evaluation signal 28 as layer transitions between the corrugated tube 10, specifically between the inner layer 18 and the corrugated layer 20, and between the corrugated tube and air. Identifying these features, and thus the layer transitions, can be simplified by using machine learning algorithms, specifically artificial neural networks. The layer thicknesses of the inner layer 18 and the corrugated layer 20, i.e., the wall thicknesses, can be calculated as geometric parameters by trigonometry based on the layer transitions identified above, using knowledge of geometric conditions, specifically the distance between the X-ray source 12 and the X-ray detector 14, and, where applicable, the position of the corrugated tube 10, as geometric parameters that are basically well known to those skilled in the art and by the method described above.

[0043] Figure 7 shows an apparatus of the present invention according to a further exemplary embodiment. In this apparatus, a second X-ray source 12' and a second X-ray detector 14' form an additional measurement axis, which is oriented perpendicular to the measurement axis formed by the first X-ray source 12 and the first X-ray detector 14. The second X-ray source 12' and the second X-ray detector 14' may, in particular, be designed identically to the first X-ray source 12 and the first X-ray detector 14, respectively. Furthermore, the evaluation of the measurement signal received by the second X-ray detector 14' may be performed by an evaluation device 16, similar to the evaluation of the measurement signal from the first X-ray detector 14. As described above, for example, the center point position of individual layers can be determined using the two measurement axes. This allows for the derivation of the radius, and based on this, the wall thickness can be derived when at least two layer transitions have been determined.

[0044] Although the present invention has been described based on exemplary embodiments of a corrugated tube, other elongated objects having a periodic structure may be used instead of a corrugated tube. Of course, as mentioned above, the corrugated tube may have further corrugated layers. [Explanation of Symbols]

[0045] 10 corrugated tube 12 X-ray source 12' X-ray source 14 X-ray detectors 14' X-ray detector 16 Evaluation device 18 Inner Layer 20 corrugated layers 22. The Valley of the Waves 24 Wave Mountains 26 Measurement signal 28 Evaluation signal

Claims

1. A method for determining at least one geometric parameter of an elongated object (10) having a periodic structure, specifically a corrugated tube (10) having a corrugated layer (20) having a periodic waveform, In a method in which an object (10) is irradiated with X-ray radiation diverging laterally with respect to the longitudinal direction of the object, and after the X-ray radiation has passed through the object (10), the X-ray radiation is detected by an X-ray detector (14) having spatial resolution as a measurement signal spatially resolved laterally with respect to the longitudinal direction of the object (10), Using the aforementioned X-ray radiation, the measurement portion of the object (10) extending in the longitudinal direction of the object (10) is irradiated. With respect to the X-ray radiation passing through the measurement portion, the X-ray detector (14) detects a plurality of measurement signals (26) that are spatially resolved laterally with respect to the longitudinal direction of the object (10). The measurement signals (26) are combined to form an evaluation signal (28) that is spatially decomposed laterally with respect to the longitudinal direction of the object (10). In the evaluation signal (28), layer transitions within the object and / or layer transitions between the object (10) and the medium surrounding the object (10) at multiple locations of the measurement portion are identified. A method characterized by determining at least one geometric parameter of the object (10) based on the identified layer transitions.

2. The method according to claim 1, characterized in that the object (10) is transported in the transport direction while the X-ray radiation passes through the object (10).

3. The method according to any one of claims 1 or 2, characterized in that the X-ray radiation irradiating the object (10) also diverges in the longitudinal direction of the object (10), and / or the X-ray detector (14) has spatial resolution in the longitudinal direction of the object (10).

4. The method according to any one of claims 1 to 3, characterized in that the X-ray detector (14) comprises a scintillator and a sensor array, specifically a CCD array.

5. The method according to any one of claims 1 to 4, characterized in that the measuring portion extends to at least 20%, preferably at least 40%, of the period of the periodic structure of the object (10).

6. The method according to any one of claims 1 to 5, characterized in that the measuring portion extends to at least a portion of the wave crests (24) and wave troughs (22) of the periodic structure of the object (10), and the slope between the wave crests (24) and wave troughs (22) of the periodic structure of the object (10).

7. The method according to any one of claims 1 to 6, characterized in that the measurement portion extends to 100% or less, preferably 75% or less, of the period of the periodic structure of the object (10).

8. The method according to any one of claims 1 to 7, characterized in that the measuring portion does not extend beyond the crest (24) and trough (22) of one wave of the periodic structure of the object (10), and the slope between the crest (24) and trough (22) of the wave of the periodic structure of the object (10).

9. The method according to any one of claims 1 to 8, characterized in that an average value of the measurement signals (26) detected over the measurement portion is formed, and the measurement signals (26) are combined to form the evaluation signal (28) which is spatially decomposed laterally with respect to the longitudinal direction of the object (10).

10. The method according to any one of claims 1 to 9, characterized in that the layer transition is identified based on the minimum value and / or maximum value and / or change in slope and / or irregularity in the evaluation signal (28).

11. The method according to claim 10, characterized in that the layer transition is identified based on at least two, preferably at least three, more preferably at least four minimum values ​​and / or maximum values ​​and / or changes in slope and / or irregularities in the evaluation signal (28).

12. The method according to any one of claims 1 to 11, characterized in that the layer transitions are identified using a machine learning algorithm, preferably an artificial neural network, based on the minimum value and / or maximum value and / or change in slope and / or irregularity in the evaluation signal (28).

13. The method according to any one of claims 1 to 12, characterized in that the thickness of the corrugated layer (20) and / or inner layer (18) of the object (10), specifically the corrugated tube (10), is determined as at least one geometric parameter.

14. The object (10) is irradiated from two directions with X-ray radiation diverging laterally with respect to the longitudinal direction of the object, and after the X-ray radiation has passed through the object (10), the X-ray radiation is detected by at least two X-ray detectors (14, 14') having spatial resolution as a measurement signal spatially resolved laterally with respect to the longitudinal direction of the object (10). The X-ray radiation is irradiated from two directions onto the measuring portion of the object (10) that extends in the longitudinal direction of the object (10), With respect to the X-ray radiation passing through the measurement portion, the X-ray detectors (14, 14') each detect a plurality of measurement signals (26) that are spatially resolved laterally with respect to the longitudinal direction of the object (10). The measurement signals (26) detected by the X-ray detectors (14, 14') are combined to form an evaluation signal (28) that is spatially resolved laterally with respect to the longitudinal direction of the object (10). In the evaluation signal (28), layer transitions within the object (10) and / or layer transitions between the object (10) and the medium surrounding the object (10) at multiple locations of the measurement portion are identified. The method according to any one of claims 1 to 13, characterized in that at least one geometric parameter of the object (10) is determined based on the identified layer transition.

15. An apparatus for determining at least one geometric parameter of an elongated object (10) having a periodic structure, specifically a corrugated tube (10) having a corrugated layer (20) having a periodic waveform, The aforementioned device is An X-ray source (12) is designed to irradiate the object (10) with X-ray radiation that diverges laterally with respect to the longitudinal direction of the object (10), An X-ray detector (14) having spatial resolution is provided, which is designed to detect the X-ray radiation after it has passed through the object (10) as a measurement signal that is spatially resolved in the direction laterally with respect to the longitudinal direction of the object (10). Equipped with, The X-ray source (12) is further designed to irradiate the measurement portion of the object (10) that extends in the longitudinal direction of the object (10), With respect to the X-ray radiation passing through the measurement portion, the X-ray detector (14) is further designed to detect a plurality of measurement signals (26) that are spatially resolved laterally with respect to the longitudinal direction of the object (10). The apparatus further comprises an evaluation device (16) designed to combine the measurement signals (26) to form an evaluation signal (28) that is spatially resolved laterally with respect to the longitudinal direction of the object (10), and to identify layer transitions within the object and / or layer transitions between the object (10) and a medium surrounding the object (10) at multiple locations of the measurement portion in the evaluation signal (28), and to determine at least one geometric parameter of the object (10) based on the identified layer transitions.

16. The apparatus comprises two X-ray sources (12, 12') designed to irradiate the object (10) with X-ray radiation diverging laterally with respect to the longitudinal direction of the object (10) from various directions. The apparatus comprises two X-ray detectors (14, 14') designed to detect the X-ray radiation as a measurement signal that is spatially resolved laterally with respect to the longitudinal direction of the object (10) after the X-ray radiation has passed through the object (10). Each of the X-ray sources (12, 12') is designed to irradiate the measurement portion of the object (10) that extends in the longitudinal direction of the object (10), With respect to the X-ray radiation passing through the measurement portion, the X-ray detectors (14, 14') are designed to detect a plurality of measurement signals (26) that are spatially resolved laterally with respect to the longitudinal direction of the object (10). The apparatus according to claim 15, wherein the evaluation device (16) is designed to combine the measurement signals (26) to form evaluation signals (28) that are spatially resolved laterally with respect to the longitudinal direction of the object (10), and to identify layer transitions within the object and / or layer transitions between the object (10) and the medium surrounding the object (10) at multiple locations of the measurement portion in the evaluation signals (28), and to determine at least one geometric parameter of the object (10) based on the identified layer transitions.

17. The apparatus according to any one of claims 15 or 16, characterized in that the apparatus is designed to carry out the method described in any one of claims 1 to 14.

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