Method and apparatus for measuring tubular strands

Abstract

The present invention relates to a method for measuring a tubular strand conveyed in a longitudinal direction discharged from an extrusion device, the method comprising the steps of: in a first measuring region, guiding terahertz radiation from at least one first radiation source from the inside onto the inner surface of the tubular strand, receiving the terahertz radiation reflected by the tubular strand by at least one first radiation receiver, and determining at least one geometric parameter of the tubular strand in the first measuring region from the received terahertz radiation; in a second measuring region downstream of the first measuring region in the conveying direction of the strand, guiding terahertz radiation from at least one second radiation source from the outside onto the outer surface of the tubular strand, receiving the terahertz radiation reflected by the tubular strand by at least one second radiation receiver, and determining at least one geometric parameter of the tubular strand in the second measuring region from the received terahertz radiation; determining a change in at least one geometric parameter of the tubular strand between the first measuring region and the second measuring region; and determining at least one adjustment indication for the extrusion device based on the determined change of the at least one geometric parameter. The present invention further relates to a corresponding device.

Description

Technical Field

[0001] The invention relates to a method and a device for measuring a tubular strand which emerges from an extrusion device and is conveyed in the longitudinal direction. Background Art

[0002] In the extruder, the plastic supplied, for example, in the form of granules, is melted and the flowable plastic emerges through the annular gap as a tubular strand. The tubular strand then enters a calibration device with a calibration sleeve, against the inner surface of which the tubular strand is pressed, for example, by applying a low pressure (vacuum tank). In the subsequent process, the tubular strand passes through one or more cooling sections, in which the outer surface of the strand is sprayed with a coolant (for example cooling water).

[0003] There is a desire to ascertain certain geometrical parameters of the tubular strand, such as diameter, wall thickness or deviations from a predefined shape, at an early stage in order to be able to intervene in a corrective manner in the extrusion process based on these parameters.

[0004] WO 2016 / 139155 A1 discloses a method and a device for measuring the diameter and / or wall thickness of a strand by means of terahertz radiation. The terahertz radiation is directed onto the strand to be measured by a radiation transmitter, and the terahertz radiation reflected by the strand is received by a radiation receiver. An analysis device can determine geometric parameters of the strand, such as the diameter or the wall thickness, for example based on the propagation time measurement.

[0005] DE 10 2016 109 087 A1 discloses a method for closed-loop and open-loop control of a pipe extrusion device, wherein the diameter, wall thickness, possible shape deviations and sag of the melt hose are determined at multiple locations between the extrusion tool and a subsequent calibration device, and these measured values ​​or data calculated therefrom are used for closed-loop and open-loop control of the extrusion device. For the measurement, a plurality of measuring sensors are arranged distributed over the circumference of the melt hose in an intermediate region between the extrusion device and the calibration device.

[0006] In addition to the aforementioned measuring methods, it is also known to measure geometrical parameters of tubular strands using ultrasonic sensors.

[0007] With the method described in DE 10 2016 109 087 A1, when an unexpected geometric deviation is detected, it should be possible to intervene quickly in the intervention of the extrusion device, in that the measuring sensor measures the tubular strand from the outside after it comes out of the extrusion device and before it enters the calibration device. However, in the known method, it is disadvantageous that the tubular strand may also be significantly different from the final geometry defined by the tubular strand in the calibration device before entering the calibration device. Therefore, the measured values ​​obtained by the known method may be subject to corresponding inaccuracies. Although the measurement performed by the known measuring method after the tubular strand is discharged from the calibration device (that is, when the tubular strand is accessible again for measurement from the outside) ensures that the measured geometric values ​​are now closer to the final geometry of the strand. However, the closed-loop control intervention of the extrusion device based on such later measured values ​​leads to defective products that are significantly produced in the interval time. Another problem of the known measuring method is the effect of defocusing of the outer surface of the strand. This can result in radiation directed onto the outer side of the strands only reaching the radiation sensor with a significantly reduced signal strength after reflection on the strands. This is a significant problem in particular in strands with thick walls or in strands with highly absorbing materials, since large wall thicknesses or highly absorbing materials are associated with correspondingly large radiation absorption.

[0008] In addition, between the annular gap and the calibration sleeve, the extrudate is typically not completely oriented orthogonally to the sensor, especially in the initial stage, where sagging occurs more. This may lead to signal loss or poor measurement signals, which in particular require vertical radiation incidence. Just in the initial stage of strand manufacturing, the wall thickness and its distribution still change, which leads to further measurement uncertainty. In addition, the later shape of the strand proposed in DE 10 2016 109 087 A1 is calculated by measurement, and in addition to the need to know the temperature and accurate measurement data, it is also necessary to accurately know the flow characteristics. Just the latter may be easily changed due to a mixture of additives or recycled materials.

[0009] DE 20 2019 102 002 U1 proposes measuring a tubular strand from the inside, in particular inside a calibration sleeve. In the calibration sleeve, the tubular strand is relatively round and is also kept oriented relative to the measuring device by the calibration sleeve. By measuring from the inside in the calibration sleeve, the measurement results for open-loop or closed-loop control of the extruder are still available very quickly, so that rejects can be minimized. It is also described here how the refractive index of the strand material can be determined in this case.

[0010] However, in some applications, it may be difficult to determine the refractive index. First of all, the distance between the measuring device and, for example, the calibration sleeve must be accurately determined in the circumferential direction in the absence of strands in the upstream air transport. This is done with the help of the measuring device itself. In the subsequent strand production, this relative position should not change during the measurement to avoid measurement errors. In practice, however, a significant heating of the calibration sleeve and thus a shift of the center point may occur, for example, the measuring device rotates around the center point during the measurement. In addition, there are adjustable calibration sleeves for producing strands of different diameters without having to restart the extrusion device. The adjustment of the inner diameter of the calibration sleeve is also partially carried out during production. These dimensional changes naturally make the determination of the refractive index more difficult.

[0011] Another problem is the so-called droop, i.e. the downward flow of the still flowable extrudate due to gravity. The droop leads to an inhomogeneous wall thickness distribution of the finished strand in the case of a circumferentially uniform wall thickness emerging from the extruder. Therefore, in anticipation of the droop, attempts are made to design the wall thickness distribution emerging from the extruder in a targeted inhomogeneous manner in order to achieve a wall thickness distribution that is as uniform as possible in the finished strand. However, the prediction of the droop is difficult, so that the described method is prone to errors. Summary of the invention

[0012] Starting from the prior art described above, the object of the present invention is to provide a method and a device of the type mentioned at the outset, with which a reliable strand production with a minimum of rejects can be achieved at any time.

[0013] The invention achieves this object by means of advantageous features.

[0014] For a method of the type mentioned at the outset, the present invention achieves the object by the following steps:

[0015] directing terahertz radiation from at least one first radiation source from the inside onto the inner surface of the tubular strand in a first measuring region, wherein the terahertz radiation reflected by the tubular strand is received by at least one first radiation receiver and at least one geometrical parameter of the tubular strand in the first measuring region is ascertained from the received terahertz radiation,

[0016] in a second measuring region located downstream of the first measuring region in the conveying direction of the strand, terahertz radiation from at least one second radiation source is externally guided onto the outer surface of the tubular strand, the terahertz radiation reflected by the tubular strand is received by at least one second radiation receiver, and at least one geometric parameter of the tubular strand in the second measuring region is determined from the received terahertz radiation,

[0017] determining a change in at least one geometric parameter of the tubular strand between a first measurement region and a second measurement region, and

[0018] Based on the ascertained change in the at least one geometric parameter, at least one adjustment instruction for the dispensing device is ascertained.

[0019] The invention further achieves the object by means of a device of the type mentioned at the outset, comprising:

[0020] at least one first radiation source for emitting terahertz radiation from the inside onto the inner surface of the tubular strand in a first measuring region; at least one first radiation receiver for receiving terahertz radiation reflected by the tubular strand in a second measuring region; and a first analysis device for determining at least one geometric parameter of the tubular strand in the first measuring region from the received terahertz radiation,

[0021] at least one second radiation source, the at least one second radiation source being used to emit terahertz radiation from the outside onto the outer surface of the tubular strand in a second measuring region, the second measuring region being located downstream of the first measuring region along the conveying direction of the strand; at least one second radiation receiver, the at least one second radiation receiver being used to receive terahertz radiation reflected by the tubular strand in the second measuring region; and a second analysis device, the second analysis device being used to determine at least one geometric parameter of the tubular strand in the second measuring region from the received terahertz radiation,

[0022] A third evaluation device for ascertaining a change in at least one geometric parameter of the tubular strand between the first measuring region and the second measuring region and for ascertaining at least one adjustment instruction for the extrusion device based on the ascertained change in the at least one geometric parameter.

[0023] The tubular strand measured according to the present invention is a strand, especially a hollow cylindrical strand, especially a plastic strand, discharged from an extrusion device. The tubular strand can have an outer diameter greater than 1m. This is followed by a correspondingly large wall thickness. The present invention is basically based on the measurement principle already described in the prior art, in which electromagnetic radiation from a radiation source is directed onto the tubular strand and the radiation reflected by the strand is received by a radiation receiver. Terahertz radiation is used here. The advantage of radiation in this frequency range is that, unlike laser radiation, for example, in the visible frequency range, the terahertz radiation is largely insensitive to external influences (such as those occurring during the extrusion process). Therefore, for example, geometric parameters such as diameter, wall thickness and / or deviations from a predetermined (for example, cylindrical) shape can be obtained in a manner known per se based on propagation time measurements. In order to obtain, for example, wall thickness, electromagnetic radiation in the following wavelength range can be used, for which the extruded strand is at least partially transparent.

[0024] In a particularly practical manner, the at least one first radiation source and the at least one first radiation receiver can be formed by at least one first transceiver. Correspondingly, the at least one second radiation source and the at least one second radiation receiver can be formed by at least one second transceiver.

[0025] According to the invention, the measurement of the tubular strand is carried out in two measuring areas spaced apart from each other. The first measuring area is located near the outlet of the extrusion device. The second measuring area is located downstream of the first measuring area in the conveying direction of the strand and is located in the area in which the shaping of the extruded strand is at least largely completed. The measurement is carried out from the inside in the first measuring area and from the outside in the second measuring area. In both measuring areas, at least one geometric parameter of the tubular strand in the respective measuring area is determined by means of the terahertz radiation directed onto the strand.

[0026] As described in DE 20 2019 102 002 Ul, the measurement from the inside in the first measuring area allows measurement in an area in which the outer surface of the tubular strand is covered (for example, covered by a calibration device) and is therefore on the one hand adjacent to the extrusion device and on the other hand there is already a relatively reliable shaping of the strand. In addition, measuring from the inside also brings other advantages, including the focusing effect of the curvature of the inner wall of the strand on the emitted radiation and reducing the required installation space. By measuring from the outside in the second measuring area, there is no need to provide measures for introducing the measuring device into the tubular strand in this area. At the same time, the second measuring area is arranged downstream of the first measuring area so that the outer surface of the tubular strand is accessible and therefore available for measurement. The second measuring area, based on its arrangement structure, also ensures that the strand has been further formed. In both measurement regions, geometrical parameters such as inner diameter, outer diameter, wall thickness and possibly deviations from a predetermined shape can be determined based on the terahertz radiation emitted and reflected by the boundary surfaces of the tubular strand, for example by means of propagation time measurements (as known per se).

[0027] At present, electromagnetic radiation in the frequency range from 0.001 THz to 6 THz, preferably in the frequency range from 0.02 to 3 THz is referred to as terahertz radiation. Preferably, the same geometric parameters are determined in the first and second measuring regions. As geometric parameters, for example, the (inner and / or outer) diameter and / or the wall thickness and / or the shape deviation from a predetermined, for example cylindrical shape can be determined. In the device according to the present invention, a first, second and third analysis device are provided. The first, second and third analysis devices can be separate analysis devices or formed by a common analysis device. The first, second and third analysis devices can also be combined with an open-loop and / or closed-loop control device. In addition, the device according to the present invention can include an extrusion device and / or a calibration device, in particular a calibration sleeve and / or at least one cooling section.

[0028] In the present invention, the measurement signals in the first and second measurement areas are correlated. The change of at least one geometric parameter of the tubular strand between the first measurement area and the second measurement area is obtained. Here, it is preferably related to the measured geometric parameter itself. However, it can also be related to a geometric parameter derived from the measured geometric parameter. In addition, at least one adjustment indication for the extrusion device is obtained based on the obtained change of the at least one geometric parameter. The adjustment indication can, for example, be related to the discharge efficiency of the extrusion device or the shape of the extrusion gap. Therefore, the at least one adjustment indication is obtained based on the at least one geometric parameter obtained in the first measurement area of ​​the tubular strand and based on the at least one geometric parameter obtained in the second measurement area of ​​the tubular strand.

[0029] As already explained, the second measuring area is located downstream of the first measuring area, especially downstream of the first measuring area, so that the forming of the tubular strand is basically finished. Therefore, the value obtained in the second measuring area basically reliably describes the final shape of the tubular strand. For example, the so-called sagging can be reliably identified by wall thickness measurement, especially the wall thickness measurement on multiple measuring points distributed on the circumference of the tubular strand. As is well known, sagging represents the downward flow of the extrudate that can still flow due to gravity. This usually leads to: for example, in the case of a completely uniform wall thickness on the circumference discharged from the extrusion device, the tubular strand made has a greater wall thickness in the area below it than in the area above it. This is overcome in the following way, that is, the wall thickness of the discharge of the extrusion device is slightly larger in the upper area than in the lower area. However, as explained at the beginning, it is difficult to reliably predict sagging in practice. Through the correlation according to the invention of the measurement signals from the two measuring areas, it is possible to achieve the association of the measurement data in the first measuring area obtained basically directly after the extrusion device with the measurement data in the second measuring area that is then located downstream. If, for example, a uniform wall thickness of the tubular strand in the circumferential direction is determined in the second measuring region, this can be correlated with the corresponding measured values ​​of the non-uniform wall thickness distribution in the first measuring region. Subsequently, a rapid closed-loop control of the extrusion device can then be performed based on the measured values ​​of the first measuring region identified as favorable. Thus, by correlating the measurement results, taking into account the measurement results in the second measuring region, in particular the changes in the measurement results between the first and second measuring regions, and also based on the measurement results in the first measuring region, and therefore the corresponding adjustment instructions can be determined very quickly, while minimizing rejects.

[0030] It is also possible to use the ascertained change of the at least one geometrical parameter for a subsequent production process following the current production process, in which the adjustment instruction is then ascertained, for example when production parameters of the subsequent production process do not otherwise change.

[0031] According to one embodiment, the extrusion device can be open-loop and / or closed-loop controlled based on the at least one adjustment indication obtained. For this purpose, the device according to the invention has an open-loop and / or closed-loop control device. In particular, automated open-loop control or closed-loop control is possible and thus highly automated operation with minimal errors is possible.

[0032] According to another design, in the first measuring area, the tubular strand can be located in a calibration device, especially a calibration sleeve, following the downstream of the extruder. Such a calibration device usually has a hollow cylindrical calibration sleeve, for example, by (vacuum tank) applying low pressure, the extruded strand is pressed against the calibration sleeve in a still soft state. Thus, on the one hand, the shrinkage (kollabieren) of the strand that can still flow is prevented. On the other hand, the desired outer diameter and the external shape of the strand are limitedly predetermined by the calibration sleeve. The calibration device, especially the calibration sleeve, can be directly connected to the extruder head of the extruder at this. Therefore, especially between the extruder head and the calibration device, there can be basically no spacing. When the extruded strand passes through the calibration device, by measuring in the calibration device, especially from the center of the calibration device, on the one hand, the geometry is determined basically immediately after extrusion and therefore at an early moment that is favorable for open-loop or closed-loop control. On the other hand, the tubular strand already has an external geometry close to the final shape of the strand in the calibration device.

[0033] According to another design, the second measuring area can be located downstream of the cooling section through which the tubular strand passes. In such a cooling section, the guided cooling of the tubular strand is carried out to obtain the final shape. In the cooling section, for example, a cooling liquid, such as water, can be applied to the strand from the outside. After passing through the cooling section, the shaping or sagging is largely completed. Therefore, the measured values ​​provided in the second measuring area give a particularly reliable description of the geometry of the tubular strand. The production equipment for such a tubular strand can include multiple cooling sections, for example three cooling sections. The second measuring area can be located, for example, between the first and second cooling sections.

[0034] In order to minimize or eliminate wavelength-dependent influences on the measurement, according to another design scheme, it can be provided that the wavelengths of the terahertz radiation emitted by the at least one first radiation source and from the at least one second radiation source differ by a maximum of 5 times, preferably by a maximum of 3 times, further preferably by a maximum of 1.5 times, and further preferably have no difference.

[0035] According to another design scheme, it can be provided that the terahertz radiation is guided onto the inner surface of the tubular strand at a plurality of measuring points distributed on the inner circumference of the tubular strand by the at least one first radiation source and / or the terahertz radiation is guided onto the outer surface of the tubular strand at a plurality of measuring points distributed on the outer circumference of the tubular strand by the at least one second radiation source.

[0036] In this case, it is particularly possible to direct the terahertz radiation emitted by the first and / or second radiation source onto the inner or outer surface of the tubular strand over a 360° measurement area. Thus, for example, a complete detection of the wall thickness distribution in the circumferential direction of the strand can be achieved. It is also possible to direct the terahertz radiation of the at least one first radiation source onto the inner surface of the tubular strand using at least one first radiation emitter arranged inside the tubular strand and rotating around the longitudinal axis of the tubular strand, and / or to direct the terahertz radiation of the at least one second radiation source onto the outer surface of the tubular strand using at least one second radiation emitter arranged outside the tubular strand and rotating around the longitudinal axis of the tubular strand. It is also possible that the at least one first radiation emitter is the at least one first radiation source and / or the at least one second radiation emitter is the at least one second radiation source. However, it is also conceivable that the radiation emitter is not a radiation source, but, for example, a mirror that reflects the terahertz radiation accordingly. For example, it is possible that the at least one first and / or second radiation emitter is at least one reflector which is irradiated by the at least one first and / or second radiation source and rotates about the longitudinal axis of the tubular strand. It is also conceivable that a plurality of first radiation sources and, if necessary, a plurality of first radiation receivers are provided, by which the terahertz radiation is guided to a plurality of measuring points distributed on the inner circumference of the tubular strand on the inner surface of the tubular strand and / or a plurality of second radiation sources and, if necessary, also a plurality of second radiation receivers are provided, by which the terahertz radiation is guided to a plurality of measuring points distributed on the outer circumference of the tubular strand on the outer surface of the tubular strand and / or

[0037] According to another design, the wall thickness of the tubular strand can be measured as at least one geometric parameter at a plurality of measuring points distributed on the circumference of the tubular strand in the first measuring region and at a plurality of measuring points distributed on the circumference of the tubular strand in the second measuring region. Here, the measuring points in the first measuring region and the measuring points in the second measuring region can correspond in particular to the same wall region, in particular the same circumferential region, of the tubular strand. The time correlation of the measurement can also be achieved in this way, so that the same wall region is also measured in the longitudinal direction. In this way, the optimized comparability of the measured values ​​is obtained. Detecting the wall thickness at a plurality of circumferential points provides conclusions about the wall thickness distribution and therefore about possible sagging. In this way, for example, it can be checked whether the wall thickness in the second measuring region (i.e., after the forming is largely completed) is the same on the circumference of the strand.

[0038] According to another design scheme, it can be provided that, in a first open-loop and / or closed-loop control process, open-loop and / or closed-loop control of the extrusion device is performed based on the measurement in the second measuring area in such a way that the measured value in the second measuring area corresponds to a predetermined theoretical measured value, and when the theoretical measured value in the second measuring area is reached, the corresponding measured value in the first measuring area is obtained, and in a subsequent open-loop and / or closed-loop control process, open-loop and / or closed-loop control of the extrusion device is performed based on the measurement in the first measuring area in such a way that the measured value in the first measuring area corresponds to the obtained corresponding measured value.

[0039] In this design, first in the first open-loop and / or closed-loop control process, based on the measurement in the second measuring area, the open-loop and / or closed-loop control of the extrusion device is carried out, so that the tubular strand has a predetermined shape, such as a wall thickness distribution, in the second measuring area after the shaping is at least largely completed. As long as this is achieved, the associated measured values, such as the wall thickness distribution, in the first measuring area are determined. In particular, when sagging occurs and in the case of the desired uniform wall thickness distribution in the second measuring area, the wall thickness distribution in the first measuring area is correspondingly uneven, as explained above. Then, that is, in the second open-loop and / or closed-loop control process, such an uneven wall thickness distribution can be open-loop and closed-loop controlled (only still) based on the measurement in the first measuring area. This process has the advantage that after the first open-loop and / or closed-loop control process is completed, an open-loop or closed-loop control is carried out based on the measured values ​​in the first measuring area and therefore, in particular, substantially immediately after the strand is discharged from the extrusion device. Therefore, a particularly fast open-loop or closed-loop control is achieved while minimizing defective products.

[0040] According to another particularly practical design, the refractive index of the tubular strand can be determined from the terahertz radiation received by the at least one second radiation receiver in the second measuring region. The refractive index determination can be performed, for example, as described in WO 2016 / 139155 A1. In particular, it is advantageous for the refractive index determination if, according to another design, at least one radiation reflector is provided on the side of the tubular strand opposite to the at least one second radiation source and / or the at least one second radiation receiver, the at least one radiation reflector reflecting the terahertz radiation emitted by the at least one second radiation source to the at least one second radiation receiver. In this way, the refractive index determination can be achieved based on the measurement of the propagation time of the terahertz radiation between the radiation transmitter or the radiation receiver (preferably a transceiver) and the reflector, in particular by comparing the propagation time of the terahertz radiation in the measuring region without the strand with the propagation time in the measuring region with the strand, as explained in WO 2016 / 139155 A1, when the wall thickness is known. For this purpose, in principle, only the wall of the strand needs to be irradiated. Only the positions of the fixed reflector and the radiation source must be known. It is also possible to provide two fixed, oppositely disposed reflectors, the spacing of which is known. It is also possible to determine the refractive index of the material at different positions in the circumferential direction. With the corresponding calibration, the average temperature of the strand material at the measuring point can be inferred from this. For example, when the PIR sensor measures the surface temperature of the strand, the temperature in the strand wall can be determined in this way. Naturally, the refractive index can also be additionally determined based on the measurement in the first area if necessary. For this purpose, for example, a metal calibration sleeve can be used as a reflector in a particularly simple manner.

[0041] According to another particularly advantageous design, the refractive index determined in the second measuring region can be used to determine the at least one geometric parameter in the first measuring region. As explained at the beginning, when the forming of the tubular strand is largely completed, it is more reliable and safer to determine the refractive index in the second measuring region than in the first measuring region, in which the strand material is still relatively flowable. In the above-mentioned design, this particularly reliably determined refractive index is then used to determine the geometric parameters in the first measuring region, for example, for determining the geometric wall thickness. Here, starting from this, the refractive index does not change between the first and second measuring regions. As is well known, the refractive index is only slightly temperature-dependent. It is then also possible that, when the temperature change of the strand between the first and second measuring regions is known, this temperature dependency can be taken into account when the refractive index determined in the second measuring region is used in the first measuring region. The temperature of the strand can be measured, for example, by a temperature sensor provided for this purpose. However, in principle, it is also possible to determine the change and adjustment indication without taking into account the refractive index, in the manner of, for example, only taking into account the visual wall thickness in the first and second measuring regions and therefore the relative change of the wall thickness.

[0042] As has already been explained in principle, particularly reliable measurements and simple analysis result when, according to another design, terahertz radiation is directed perpendicularly to the longitudinal axis of the tubular strand onto the inner surface of the tubular strand by the at least one first radiation source and / or terahertz radiation is directed perpendicularly to the longitudinal axis of the tubular strand onto the outer surface of the tubular strand by the at least one second radiation source.

[0043] The at least one first radiation source and / or the at least one first radiation receiver can be arranged inside the tubular strand. Thus, for example, the at least one first radiation source and / or the at least one first radiation receiver can be supplied with electrical energy, data and / or a coolant via at least one supply line leading from the extruder head of the extrusion device to the at least one first radiation source and / or the at least one first radiation receiver. However, it is also possible that the at least one first radiation source and / or the at least one first radiation receiver are arranged outside the tubular strand and that the terahertz radiation emitted by the at least one first radiation source is guided into the interior of the tubular strand via at least one radiation conductor, and that the terahertz radiation reflected by the tubular strand is guided from the interior of the tubular strand to the at least one first radiation receiver via at least one radiation conductor. Thus, the at least one radiation conductor can be guided, for example, from the extruder head of the extrusion device into the interior of the tubular strand.

[0044] The method according to the invention can be implemented using the device according to the invention. Accordingly, the device according to the invention can be designed to implement the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the present invention are described in more detail below with the aid of the drawings. In the drawings:

[0046] Figure 1 The device according to the invention is shown in a cross-sectional view,

[0047] Figure 2 Shown in Figure 1 A detailed view of a device according to a first embodiment is shown in FIG.

[0048] Figure 3 Shown in Figure 1 A detailed view of a device according to a second embodiment is shown in FIG.

[0049] Figure 4 Shown along Figure 3 A cross-sectional view of line AA in FIG.

[0050] Figure 5 Shown in Figure 1 Detailed view of a device according to a third embodiment is shown in FIG. DETAILED DESCRIPTION

[0051] Unless otherwise indicated, the same reference numerals in the various figures denote the same objects.

[0052] exist Figure 1 1 shows an extrusion device 10 for extruding a tubular strand 16. The extrusion device 10 has, in a manner known per se, for example, Figure 2 1 shows a supply device 11 for supplying plastic material to be processed. The plasticized plastic material is extruded from the annular gap 14 into a tubular strand 16 by means of the extruder screw 12. A rotationally driven central rod 18 extends inside the extruder screw 12. In the example shown, the calibration device 22 is connected in the vicinity of the extruder head 20 with a metal calibration sleeve 24, against which the extruded strand 16 is pressed by means of a negative pressure. In addition, a first cooling section 25 with a first cooling tube 27 is indicated by reference numeral 25, in which guided cooling of the tubular strand 16 takes place in such a way that the strand 16 is substantially completely formed after exiting the first cooling section 25. A second cooling section 29 with a second cooling tube 31 is arranged downstream of the first cooling section 25, which second cooling tube causes further cooling of the strand 16. In the example shown, a first measuring device 33 is present in the calibration sleeve 24 and inside the extruded strand 16, which is formed in Figure 1The first measuring region 35 is defined by the plane shown by the dashed line in FIG. For example, based on the propagation time measurement, the first measuring device 33 can determine geometric parameters of the strand 16 in the first measuring region 35, such as the outer diameter, the inner diameter and / or the wall thickness or the shape deviation from a predetermined shape. Figures 2 to 5 Different embodiments of the measuring device 33 are described. In addition, a second measuring device 37 is provided between the first cooling section 25 and the second cooling section 29, which is formed in Figure 1 39 is defined by the plane shown by the dashed line in FIG. In the example shown, the second measuring device 37 includes a plurality of transceivers 41, 43 which are arranged distributed in the circumference of the strand 16 and are used to transmit and receive terahertz radiation guided to the outer surface of the strand 16. Therefore, for example, based on the propagation time measurement, the second measuring device 37 can determine the geometric parameters of the strand 16 in the second measuring area 39, such as the outer diameter, the inner diameter and / or the wall thickness or the shape deviation from the predetermined shape. In this case, the transceivers 41, 43 can measure the geometric parameters distributed at different positions in the circumference of the strand 16. The transceivers 41, 43 can, for example, be rotated around the strand 16 and thus determine the geometric parameters in a circumferential range of up to 360°. The refractive index of the strand material can also be determined based on the measurement in the second measuring area 39. For this purpose, for example, a suitable reflector for the terahertz radiation can be arranged in the area outside the second measuring device 37.

[0053] Furthermore, the device according to the invention comprises a combined evaluation and closed-loop control device 45, which on the one hand determines the corresponding geometrical parameters and, if applicable, the refractive index from the measured values ​​of the measuring devices 33, 37, and on the other hand determines the change of the measured geometrical parameters between the first measuring region 35 and the second measuring region 39. Furthermore, the combined evaluation and closed-loop control device 45 determines at least one adjustment instruction for the extrusion device 10 based on the determined change of the geometrical parameters and controls the extrusion device 10 in a closed-loop manner on this basis. Thus, the evaluation and closed-loop control device 45 comprises the first, second and third evaluation devices according to the invention and an open-loop and / or closed-loop control device. In the first closed-loop control process, for example, the closed-loop control of the extrusion device 10 can be carried out based on the measurement in the second measuring region 39 in such a way that the measured value in the second measuring region 39 is equal to a predetermined theoretical measured value. When the theoretical measured value in the second measuring region 39 is reached, the corresponding measured value in the first measuring region 35 is determined. In the subsequent closed-loop control process, the extrusion device 10 is then closed-loop controlled based on the measurement in the first measuring region 35 so that the measured value in the first measuring region 35 is (in addition) equal to the measured value corresponding to the determined value. In addition, the refractive index determined in the second measuring region 39 by the second measuring device 37 can be used to determine the geometric parameters in the first measuring region 35 by the first measuring device 33. By means of the above-mentioned closed-loop control, for example, the droop of the strand material that is still flowing can be compensated so that the strand 16 has a predetermined wall thickness distribution that is as uniform as possible after the completion of its shaping, especially in the region of the second measuring region 39.

[0054] Various exemplary embodiments for measuring from the inside in first measuring region 35 are explained below.

[0055] exist Figure 2 In the example shown in , a reflector 26 is arranged inside the extruded strand 16 and essentially directly adjacent to the extruder head 20 and therefore in the calibration device 22. The reflector 26 is connected to the rod 18, which in turn is driven in rotation by the motor 28. As a result, the reflector 26 also rotates about the longitudinal axis of the tubular strand 16. In addition, a waveguide 30 extends in the rod 18, which guides the terahertz radiation emitted by a transceiver 32 (which in the example shown includes a radiation source and a radiation receiver) to the reflector 26, which deflects the radiation by 90° onto the inner surface of the strand 16, as shown in Figure 234. The terahertz radiation is reflected from the inner surface 36 of the extruded strand 16 back to the mirror 26 and is guided from the mirror via the waveguide 30 back to the transceiver 32. A further radiation portion enters the extruded strand 16 and is reflected at the boundary surface between the outer surface 38 of the strand 16 and the inner surface 40 of the calibration sleeve 24 and is guided from the mirror 26 and the waveguide 30 to the transceiver 32 again.

[0056] The measured values ​​received by the transceiver 32 are transmitted to the analysis and closed-loop control device 45 via the line 42. The analysis and closed-loop control device 45 determines the inner diameter and / or outer diameter and / or wall thickness and / or possible shape deviations of the extruded strand 16 from the measured values, for example based on a propagation time measurement. In addition, in the manner described above, the refractive index of the strand material can also be determined by means of the radiation reflected back on the boundary surface to the metal calibration sleeve 24. Based on the rotation of the reflector 26, the described measurements can be performed for multiple measurement areas distributed on the circumference of the tubular strand 16, for example, again on a 360° area. The analysis and closed-loop control device 45 can perform closed-loop control of the extrusion device based on the measured values ​​obtained.

[0057] exist Figure 3 A further embodiment is shown in FIG. 1 , which corresponds largely to the embodiment according to Figure 2 Embodiment of. Different from Figure 2 In the embodiment of Figure 3 1 shows an extrusion device 110 having two extruder screws 112 extending perpendicularly to the longitudinal axis of the annular gap 114. The extruder screws 112 are each driven in rotation by a motor 128. The supplied material is discharged through the annular gap 114 to form a tubular strand 116. Directly adjacent to the extrusion device 110, a calibration device 122 having a metal calibration sleeve 124 is provided. In addition, a first cooling pipe 127 of a first cooling section 125 is shown. Figure 2 Compared to the tubular strand 16 shown in Figure 3 The extruded tubular strands 116 may have a larger diameter. Figure 3 In the embodiment of the present invention, there is correspondingly more space in the interior space of the strand 116. Therefore, in this embodiment, the transceiver 132 is arranged inside the strand. The transceiver 132 is driven in rotation by means of a further motor 128 via the rod 118 guided through the extruder head 120, as in Figure 3146. The transceiver 132 can be connected to an external power supply device, not shown in detail, for example via slip ring contacts. The measured values ​​of the transceiver 132 can also be transmitted to the analysis device 45 via these slip ring contacts if necessary, as shown by the line 142 shown by the dashed line.

[0058] The transceiver 132 is rotated to Figure 2 The measured values ​​are recorded in essentially the same manner as described, so that the evaluation and closed-loop control device 45 can determine on this basis, in particular, the inner and / or outer diameter, the wall thickness and possible shape deviations of the tubular strand 116. On this basis, the extrusion device 110 can again be closed-loop controlled. In principle, it is also conceivable to arrange the rotary drive likewise inside the tubular strand 116. Figure 4 , radiation emitted by transceiver 132 and reflected back is shown at reference numeral 134. Figure 4 148 and a circular path 150 of the transceiver are shown. Reference numeral 152 shows the housing of the measuring head with the transceiver 132 .

[0059] exist Figure 5 A further exemplary embodiment is shown in FIG. , which in turn corresponds largely to the exemplary embodiment explained above. Figure 5 The extrusion device 210 shown in the figure discharges the plasticized plastic material supplied by the extruder screw not shown in detail into a tubular strand 216 through an annular gap 214. The calibration device 222 is connected to the extruder head 220 with a metal calibration sleeve 224, and the strand 216 is pressed against the calibration sleeve, for example by means of low pressure. The cooling tube of the cooling section 225 is shown in the reference numeral 227. In the example shown, inside the calibration device 222, a reflector 226 is located inside the strand, which deflects the terahertz radiation emitted by the transceiver 232 arranged in the extruder head 220 by 90° onto the inner surface of the strand 216, as shown in 234. By Figure 5 The motor shown at 228 rotates the transceiver 232 together with the reflector 226 about the longitudinal axis of the tubular strand 216, as shown by arrow 246. A supply line 248 serves to supply power to the transceiver and to supply a coolant, such as a cooling liquid.

[0060] Furthermore, the measured values ​​recorded by the transceiver 232 can be fed via the supply line 248 via the line 242 to the evaluation and closed-loop control device 45. Figure 5 In the exemplary embodiment shown in FIG. 1 , the recording of the measured values, the analysis by the analysis and closed-loop control device 45 and the closed-loop control of the extrusion device 210 based thereon correspond to the exemplary embodiment explained above. Figure 5 In the embodiment of the present invention, the reflector 226 and the transceiver 232 are located inside a housing 250, which can be inserted into the extruder head 220 as an insert for measurement. If desired, the measuring device can be removed in a simple manner by removing the housing 250.

[0061] Reference numerals list

[0062] 10, 110, 210 extrusion device

[0063] 11 Supply device

[0064] 12, 112 Extruder screw

[0065] 14, 114, 214 annular gap

[0066] 16, 116, 216 tubular strands

[0067] 18, 118

[0068] 20, 120, 220 extruder heads

[0069] 22, 122, 222 calibration device

[0070] 24, 124, 224 calibration sleeve

[0071] 25, 125, 225 first cooling section

[0072] 26, 226 reflector

[0073] 27, 127, 227 first cooling tube

[0074] 28, 128, 228 motors

[0075] 29 Second cooling section

[0076] 30 Waveguide

[0077] 31 Second cooling pipe

[0078] 32, 132, 232 transceivers

[0079] 33 First measuring device

[0080] 34, 134, 234 radiation

[0081] 35 First measurement area

[0082] 36 Inner surface of the strands

[0083] 37 Second measuring device

[0084] 38 Outer surface of the strands

[0085] 39 Second measurement area

[0086] 40 Inner surface of the calibration sleeve

[0087] 41, 43 Transceiver

[0088] Lines 42, 142, 242

[0089] 45 Analysis and closed-loop control device

[0090] 146, 246 Arrow

[0091] 148 Rotation midpoint

[0092] Circular track of 150 transceivers

[0093] 152 Measuring head housing

[0094] 248 Supply Line

[0095] 250 Shell

Claims

1. A method for measuring a tubular strand (16, 116, 216) discharged from an extrusion device (10, 110, 210) and conveyed in a longitudinal direction, the method comprising the steps of: In a first measurement region (35), terahertz radiation from at least one first radiation source is guided from the inside to the inner surface (36) of the tubular strand (16, 116, 216), the terahertz radiation reflected by the tubular strand (16, 116, 216) is received by at least one first radiation receiver, and at least one geometric parameter of the tubular strand (16, 116, 216) in the first measurement region (35) is determined from the received terahertz radiation, in a second measuring region (39) located downstream of the first measuring region (35) along the conveying direction of the strand (16, 116, 216), terahertz radiation from at least one second radiation source is externally directed onto the outer surface (38) of the tubular strand (16, 116, 216), the terahertz radiation reflected by the tubular strand (16, 116, 216) is received by at least one second radiation receiver, and at least one geometric parameter of the tubular strand (16, 116, 216) in the second measuring region (39) is determined from the received terahertz radiation, determining a change in at least one geometric parameter of the tubular strand (16, 116, 216) between the first measurement region (35) and the second measurement region (39), and Determining at least one adjustment indication for the extrusion device (10, 110, 210) based on the determined change of the at least one geometric parameter, determining the refractive index of the tubular strand (16, 116, 216) by terahertz radiation received by the at least one second radiation receiver in the second measuring area (39), and using the refractive index determined in the second measuring area (39) to determine the at least one geometric parameter in the first measuring area (35).

2. The method according to claim 1, characterized in that The extrusion device (10, 110, 210) is controlled in an open-loop and / or closed-loop manner based on the at least one control instruction determined.

3. The method according to claim 1, characterized in that In a first measuring region (35), the tubular strand (16, 116, 216) is located in a calibration device (22, 122, 222) downstream of the extrusion device (10, 110, 210).

4. The method according to any one of claims 1 to 3, characterized in that The second measuring region (39) is located downstream of a cooling section (25, 125, 225) passed through by the tubular strand (16, 116, 216).

5. The method according to any one of claims 1 to 3, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most 5.

6. The method according to any one of claims 1 to 3, characterized in that The terahertz radiation is guided to a plurality of measuring points distributed on the inner circumference of the tubular strand (16, 116, 216) on the inner surface (36) of the tubular strand (16, 116, 216) by the at least one first radiation source, and / or the terahertz radiation is guided to a plurality of measuring points distributed on the outer circumference of the tubular strand (16, 116, 216) on the outer surface (38) of the tubular strand (16, 116, 216) by the at least one second radiation source.

7. The method according to claim 6, characterized in that The wall thickness of the tubular strand (16, 116, 216) is measured as at least one geometric parameter in the first measuring area (35) at a plurality of measuring points distributed on the circumference of the tubular strand (16, 116, 216) and in the second measuring area (39) at a plurality of measuring points distributed on the circumference of the tubular strand (16, 116, 216).

8. The method according to any one of claims 1 to 3, characterized in that In a first open-loop and / or closed-loop control process, open-loop and / or closed-loop control of the extrusion device (10, 110, 210) is performed based on the measurement in the second measuring area (39), so that the measured value in the second measuring area (39) corresponds to a predetermined theoretical measured value, and when the theoretical measured value in the second measuring area (39) is reached, the corresponding measured value in the first measuring area (35) is obtained, and in a subsequent open-loop and / or closed-loop control process, open-loop and / or closed-loop control of the extrusion device (10, 110, 210) is performed based on the measurement in the first measuring area (35), so that the measured value in the first measuring area (35) corresponds to the obtained corresponding measured value.

9. The method according to claim 1, characterized in that: At least one radiation reflector is provided on the side of the tubular strand (16, 116, 216) opposite the at least one second radiation source and / or the at least one second radiation receiver, the at least one radiation reflector reflecting the terahertz radiation emitted by the at least one second radiation source to the at least one second radiation receiver.

10. The method according to any one of claims 1 to 3, characterized in that Terahertz radiation is directed perpendicularly to the longitudinal axis of the tubular strand (16, 116, 216) onto an inner surface (36) of the tubular strand (16, 116, 216) by the at least one first radiation source, and / or terahertz radiation is directed perpendicularly to the longitudinal axis of the tubular strand (16, 116, 216) onto an outer surface (38) of the tubular strand (16, 116, 216) by the at least one second radiation source.

11. The method according to claim 3, characterized in that The calibration device (22, 122, 222) is a calibration sleeve (24, 124, 224).

12. The method according to claim 5, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most 3.

13. The method according to claim 5, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most 1.

5.

14. The method according to claim 5, characterized in that The wavelength of the terahertz radiation emitted from the at least one first radiation source and from the at least one second radiation source does not differ.

15. A device for measuring a tubular strand (16, 116, 216) discharged from an extrusion device (10, 110, 210) and conveyed in a longitudinal direction, the device comprising: at least one first radiation source for emitting terahertz radiation from the inside in a first measurement region (35) onto an inner surface (36) of the tubular strand (16, 116, 216); at least one first radiation receiver for receiving terahertz radiation reflected by the tubular strand (16, 116, 216) in the second measurement region (39); and a first analysis device for determining at least one geometric parameter of the tubular strand (16, 116, 216) in the first measurement region (35) from the received terahertz radiation, at least one second radiation source for emitting terahertz radiation from the outside onto the outer surface (38) of the tubular strand (16, 116, 216) in a second measurement region (39), the second measurement region being located downstream of the first measurement region (35) in the transport direction of the strand (16, 116, 216); at least one second radiation receiver, the at least one second radiation receiver being used to receive terahertz radiation reflected by the tubular strand (16, 116, 216) in the second measurement area (39); and a second analysis device, the second analysis device being used to determine at least one geometric parameter of the tubular strand (16, 116, 216) in the second measurement area (39) from the received terahertz radiation, A third analysis device for determining a change in at least one geometric parameter of the tubular strand (16, 116, 216) between the first measuring region (35) and the second measuring region (39), and for determining at least one adjustment indication for the extrusion device (10, 110, 210) based on the determined change in the at least one geometric parameter, wherein the first, second and / or third analysis device and / or the open-loop and / or closed-loop control device for open-loop and / or closed-loop control of the extrusion device (10, 110, 210) based on the determined at least one adjustment indication are configured to determine a refractive index of the tubular strand (16, 116, 216) from terahertz radiation received by the at least one second radiation receiver in the second measuring region (39), and the first analysis device is configured to use the refractive index determined in the second measuring region (39) to determine at least one geometric parameter in the first measuring region (35).

16. The device according to claim 15, characterized in that Furthermore, a calibration device (22, 122, 222) is provided in the first measuring region (35) downstream of the extrusion device (10, 110, 210).

17. The device according to claim 15 or 16, characterized in that Furthermore, a cooling section (25, 125, 225) is provided through which the tubular strand (16, 116, 216) passes, and the second measuring region (39) is located downstream of the cooling section (25, 125, 225).

18. The device according to claim 15 or 16, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most 5.

19. The device according to claim 15 or 16, characterized in that The open-loop and / or closed-loop control device is configured to, in a first open-loop and / or closed-loop control process, implement open-loop and / or closed-loop control of the extrusion device (10, 110, 210) based on the measurement in the second measuring area (39), so that the measured value in the second measuring area (39) corresponds to a predetermined theoretical measured value, and further, when the theoretical measured value in the second measuring area (39) is reached, the corresponding measured value in the first measuring area (35) is determined, and further, in a subsequent open-loop and / or closed-loop control process, implement open-loop and / or closed-loop control of the extrusion device (10, 110, 210) based on the measurement in the first measuring area (35), so that the measured value in the first measuring area (35) corresponds to the determined corresponding measured value.

20. The device according to claim 15, characterized in that At least one radiation reflector is provided on the side of the tubular strand (16, 116, 216) opposite the at least one second radiation source and / or the at least one second radiation receiver, the at least one radiation reflector reflecting the terahertz radiation emitted by the at least one second radiation source to the at least one second radiation receiver.

21. The device according to claim 15 or 16, characterized in that The at least one first radiation source and / or the at least one first radiation receiver are arranged inside the tubular strand (16, 116, 216).

22. The device according to claim 15 or 16, characterized in that The at least one first radiation source and / or the at least one first radiation receiver are arranged outside the tubular strand (16, 116, 216), and the terahertz radiation emitted from the at least one first radiation source is guided into the interior of the tubular strand (16, 116, 216) through at least one radiation conductor, and the terahertz radiation reflected by the tubular strand (16, 116, 216) is guided from the interior of the tubular strand (16, 116, 216) to the at least one first radiation receiver through at least one radiation conductor.

23. The device according to claim 15 or 16, characterized in that The device is designed to carry out the method according to any one of claims 1 to 14 .

24. The device according to claim 16, characterized in that The calibration device (22, 122, 222) is a calibration sleeve (24, 124, 224).

25. The apparatus according to claim 18, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most three.

26. The device according to claim 18, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source differ by a factor of at most 1.

5.

27. The device according to claim 18, characterized in that The wavelengths of the terahertz radiation emitted by the at least one first radiation source and by the at least one second radiation source do not differ.

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