Patent ID: 12216050

FIG.1shows a THz sensor1in a sensor receptacle2. The THz sensor1may, in particular, be designed fully electronical, i.e. in particular as a dipole, with a THz chip3that emits THz radiation focused by a THz lens4so that the THz sensor1emits a transmitted THz beam12along a sensor axis B. The THz sensor1is received in the sensor receptacle2in a swivel axis C, extending, in particular, perpendicular through the sensor axis B, pivoting about a sensor correction angle α.

FIGS.2and3show the arrangement of a plurality of THz sensors1on a measuring receptacle6, designed, in particular, circular in shape, whereFIGS.2and3show different sensor correction angles α of the middle THz sensor1. Thus, the THz sensor1is pivoting in a measuring plane7defined by the plurality of THz sensors1and the measuring receptacle6, i.e. in particular, all THz sensors1pivot in the same measuring plane7, as will be further explained in the following.

Hereby, a sensor module27is formed by sensor1, sensor receptacle2, an adjustment device25which may be, in particular, an electrical micro motor and serves to swivel the sensor1in the sensor receptacle2, as well as a wire28and a plug29via which the sensor modules27are each replaceable received in the measuring receptacle6and, in the event of failure, can be replaced separately, even during operation. The plurality of THz sensors1put out their measurement signals as signal amplitudes Sa via the wired28to the central controller means30, the controller means30in turn controlling the sensor modules27for adjusting the adjustment devices25so as to set individual sensor correction angles α.

FIG.4shows a THz measuring apparatus8as a top view on the measuring plane7. The plurality of THz sensors1, eight THz sensors1according to this embodiment, are each directed in their sensor axis B onto an axis of symmetry A which is formed centrally in the measuring chamber9defined between the THz sensors1, i.e. in particular, in the geometric center of the circular measuring receptacle6. Thus, the axis of symmetry A extends perpendicular through the measuring plane7; thus, in particular, the swivel axes C each extend in parallel to the axis of symmetry A.

In the measuring chamber9a measurement object10is received, in this case a single-wall plastic pipe10, according to the embodiment shown here having an ideal cylindrical shape, i.e. having a cylindrical exterior surface10aand interior surface10b. When positioned ideally the measurement object10is received centrally or symmetrically respectively within the measuring chamber9so that a center of the pipe D or, respectively, the axis of symmetry of the measurement object10falls on the axis of symmetry A. As show already inFIG.4, however, the measurement object10will usually be positioned incorrectly so that the center of the pipe D or, respectively, center of the measurement object10does not coincide with the axis of symmetry A.

Thus, for one thing, the distance of the exterior surface10afrom the THz sensors1will be differing; however, this eccentricity as such is not problematic for layer thickness measuring because, subsequently the relative distances of the boundary surfaces of the pipe10, i.e. the exterior surface10aand interior surface10b, will be measured anyway. However, the sensor axes B will also usually extend not perpendicular to the exterior surface10aand the interior surface10bso that, accordingly, it will not be possible to measure the exact layer thicknesses as perpendicular layer thicknesses or, respectively, shortest distances between the surfaces10a,10bby measuring along the sensor axes B, and, moreover, the reflected THz beams reflected at the exterior surface10aand the interior surface10bwill not be reflected along the sensor axes B towards the THz sensors1.

Therefore, the THz sensors1are each swiveled about individual correction angles α in the measuring plane7so as to be aligned perpendicular towards the exterior surface10a. Hereby, it is recognized that, as a matter of principle, a calibration on a perpendicular path of the sensor axis B to the exterior surface10ais sufficient, and, in particular, also in such measurement objects like a pipe10, the interior surfaces10bmay exhibit changes of shape cause by various effects, such as e.g. curing or sagging respectively of the pipe material, which are non-ideal but nevertheless essentially to be determined.

Thus, according to the method for aligning the THz sensors1, neither the pipe10nor the measuring apparatus1is adjusted, but merely the THz sensors1are swiveled about individual sensor correction angles α allowing for a THz measurement with sufficient accuracy.

According toFIG.4, the THz sensors1are first divided into two sensor groups G1and G2allowing for a successive or, respectively, iterative correction of the individual groups. According to embodiment shown here, having eight THz sensors1, the groups G1, G2are formed by alternating division in circumferential direction; thus, in the first sensor group G1the sensor S1is at a starting position, hereinafter referred to as the 0° angular position in relation to the axis of symmetry A; further, the third sensor S3is at an angular position of 90°, the fifth sensor S5at an angular position of 180°, i.e. opposite the first sensor S1, and the seventh sensor S7at an angular position of 270°, i.e. opposite the third sensor S3. The second sensor group G2is formed by the other four THz sensors1, i.e. the sensors S2, S4, S6and S8at the corresponding angular positions of 45°, 135°, 215°, and 315°.

In a first calibration adjustment step KS1the first sensor group G1serves as the starting group and the second sensor group G2as adjustment group. Thus, in this starting position ofFIG.4, each THz sensor1of the first sensor group G1will each, in its starting position in which its sensor axis B is aligned towards the axis of symmetry A, measure the starting distance d0from the exterior surface10a, i.e. starting distances d0-S1, d0-S3, d0-S5, d0-S7are measured and stored. Thus, the so measured starting distance d0defines for each THz sensor S1, S3, S5, S7of the first sensor group G1also a spacing point P1, P3, P5, P7on the exterior surface10awhich is the result of the intersection point of its sensor axis B with the exterior surface10a. Sincere, therefore, the sensor axes B—here, in the starting position, still extending radially—are known, it is possible to determine the positions or coordinates respectively of the spacing points P1, P3, P5, P7on the basis of the known positions of the THz sensors S1, S3, S5, S7of the first sensor group G1, their swivel axes B and the measured starting distances d0-S1, d0-S2, . . . d0-S7. For e.g. the first THz sensor S1the first spacing point P1results from the position of the first THz sensor S1(on the measuring receptacle6), the starting distance d0-S1measured by it, and its sensor axis B_S1.

Generally, a measurement of the distance from the exterior surface10ais possible even in the event of a minor positioning error because the reflected beam will still exhibit sufficient intensity or signal amplitude respectively even with such an incorrect position.

In the following, the sensor correction angles α of the THz sensors1of the second sensor group G2are determined, i.e. the corrections in relation to initial orientation. Hereby, it is recognized that on the basis of a distance measurement of two not directly adjacent THz sensors1, in particular a THz sensor and next but one THz sensor, the angular position of the THz sensor1lying in-between, may already provide for a correction representing a very good approximation of a perpendicular orientation. Such a correction is quite effective already, in particular in the case of a round exterior surface10a, and will be further improved by an iterative course of action, in particular, successive repetition.

In particular in the embodiment shown here having eight THz sensors1, a circular arc is formed between a first THz sensor S1and a third THz sensor S3or, generally, its next but one THz sensor1, allowing for a highly precise positioning of the THz sensor1lying in-between, thus, in this case, of the second THz sensor S2, towards the exterior surface10a.

To that end, according to an advantageous embodiment shown, in particular, inFIGS.5,6and the diagram ofFIG.8, a straight base line L1is drawn in the measuring plane7between two next but one sensors in relation to the THz sensors1of the first group G1, in this case, therefore, the first sensor S1and the third sensor S3, preferably through the pivot points or, respectively, swivel axes C of the sensors S1and S3. Further, a straight balance line L2is drawn between the first spacing point P1of the first sensor S1and the third spacing point P3of the third sensor S3. Now, on the basis of these lines L1, L2and the position of the second sensor S2its sensor correction angle α_S2can be determined.

Thus, when a cylindrical pipe10is centrally aligned, as a matter of principle, the base line L1and the balance line L2are parallel; in case of deviations there will be an angle of intersection of the lines β between the lines L1, L2. The line intersection angle β is a direct indicator for the sensor correction angle α_S2, i.e. these angles α_S2, β may, in particular, be equated.

Hereby, the sensor correction angle α_S2can be determined directly as a function, e.g. by means of pre-stored tables of the spacing points P1, P3of the consecutive THz sensors S1, S3of each sensor group.

Furthermore, a geometric determination is also possible, as can be seen fromFIGS.5,7and8: Hereby, a line orthogonal L3starting from the balance line L2can be placed and this can be shifted or, respectively, positioned along the balance line L2such that the line orthogonal L3runs through the second sensor S2or, respectively, its pivot point C, as shown inFIG.8. Thus, this position will generally not lie centrally on the balance line L2. This orientation can be utilized directly as the new, corrected sensor axis B_S2of the second sensor S2.

This concludes the determination of the angular correction of the second sensor S2according to this procedure step. The sensor correction angles α_S4, α_S6and α_S8of the other THz sensors S4, S6and S8of the second sensor group S2are each determined accordingly by a similar computation or, respectively, geometric layout of the respective adjacent THz sensors1of the first group G1. Thus, the sensor correction angle α_S4is determined by means of the base line L1between the third sensor S3and the fifth sensor S5, as well as the corresponding balance line L2of the spacing points P3and P5on the exterior surface10a, and, similarly, the further sensor correction angles α_S6and α_S8.

Subsequently, the THz sensors S2, S4, S6and S8of the second sensor group S2are swiveled about their determined sensor correction angles α_S2, α_S4, α_S6and α_S8.

Thus, following this correction, ideally, the THz sensors S2, S4, S6and S8of the second sensor group G2are already aligned on the pipe center axis D or, respectively, the center point of the pipe10. This is followed by the calibration adjustment of the sensors of the first sensor group G1as adjustment group, in that the previously calibration adjusted THz sensors S2, S4, S6, S8of the second sensor group G2serves as starting group. Thus, distance measurements of the starting distances d0_S2, d0_S4, d0_S6and d0_S8are determined, and, derived from these, accordingly also the coordinates or vectors respectively of the spacing points P2, P4, P6and P8with the known corrected orientations of the sensor axes B_S2, B_S4, B_S6, B S8. Then, in turn, from these spacing points P2, P4, P6and P8the balance lines L2are determined, whereby the base lines L1through the sensor positions are unchanged. Thus, it is possible to determine for each sensor of the first sensor group G1, always from L1and L2, its sensor correction angle according to the above-described method.

Then, subsequently, the THz sensors S1, S3, S5and S7of the first sensor group G1are swiveled accordingly about their sensor correction angles α_1, α_3, α_5, α_7.

It is apparent that, in particular in the case of a pipe10having a completely or essentially circular exterior surface10aand relative minor displacement of its central axis D in relation to the axis of symmetry A, just a single cycle, i.e. two alternating calibrating steps, i.e. an adjustment of the THz sensors1of the second sensor group G2and subsequent according adjustment and correction of the THz sensors1in sensor group G1, will be sufficient to attain a very good alignment. In the event of more significant displacements and, in particular, also with other than round exterior surfaces10a, in particular, an iterative execution of this method may lead to successive further improvement. Thus, upon completion of one single execution of the procedure, a new correction procedure is carried out, wherein again initially, as described above, the THz sensors1of the second sensor group G2are adjusted depending on the measurements of the THz sensors1of the first sensor group G1, etc.

In the embodiment shown here, eight THz sensors1are arranged on the circular measuring receptacle, i.e. the circular circumference U, so that a sensor and its next but one sensor are aligned with one another at 90° and, by virtue of this alone, the circular arc between them, in which the second sensor S2is provided, is relatively small. In an embodiment having fewer THz sensors1, e.g. even only four THz sensors1, however, iterative repetition of the procedure, i.e. multiple cycles, are of particular advantage.

Hereby, it is apparent that such a swiveling adjustment can be carried out quickly and advantageously even compared to a translational adjustment of the entire pipe10, or even the measuring receptacle6or, respectively, the entire THz measuring apparatus1, because it is merely required to each pivot the THz sensor1about a small sensor correction angle α, with a low moment of inertia of the THz sensors1. Hereby, the corrections of the THz sensors1of the second sensor group G2and of the first sensor group G1may each be carried out simultaneously so that two adjustment operations for the sensor groups G1, G2are provided.

The calibration and, in particular, also computation of the sensor correction angle using the balance line L2can also be carried out in the event of flattening or ovality, irrespective of whether the pipe is present in the measuring apparatus centrically or eccentrically. It is always possible to adjust the determined sensor correction angle α_S2depending on the adjacent sensors S1, S3. This leads to sufficient accuracy while, owing to the geometric dependency of curvature and center of the sensor arrangement, a minor malposition will remain as a matter of principle. According to the invention, however, this is evaluated as negligible because the method of calibration allows for a quick and accurate determination and, generally, a direct and precise determination of a center point D is not possible in the case of a non-round eccentric measurement object10. In particular, it is recognized according to the invention that the method of calibration is so exact that it is possible to measure the wall thickness. Moreover, the quick adjustment of the THz sensors1allows for a faster adaptation to malposition and deformation than e.g. translational adjustment of the THz measuring apparatus, further increasing the accuracy compared to e.g. slower translational adjustment in the case of a measurement object10guided through the measuring chamber9which, consequently, cannot be stopped during the adjustment.

In addition to the angular correction by the sensor correction angle α, it is possible with all embodiments to carry out an amplitude correction further reducing the angular malposition.

Upon completion of the calibration adjustment of the THz sensors1a fine adjustment can be carried out by pivoting the individual THz sensors1, wherein these are adjusted, starting from their previously determined angular position, in both angular directions by small adjustment angles αv, and the non-adjusted measurement and the measurement including the two or more adjustment angles αv are compared to one another such that the position having the highest signal amplitude Sa_max is determined. Hereby, this measurement with the highest signal amplitude Sa_max generally represents the direct vertical or perpendicular respectively distance from the exterior surface. This fine adjustment by means of maximum value determination is also of advantage in the case of local and e.g. geometrically undefined flattenings and impurities.

Further, it is possible to additionally utilize the distance from the inner boundary surface, i.e. the interior surface10b, for the fine adjustment. Thus, it is possible to determine, starting from the starting position, the distances d of each THz sensor1from the exterior surface10aand the interior surface10b, then execute the small adjustment angles αv and compare the signals for each THz sensor1to determine and adjust the vertical position. In principle, this fine adjustment can be carried out by small successive angular corrections until a perpendicular position is determined for each THz sensor1, i.e. until a maximum is bounced back in the measurement signal.

The fine adjustment particularly complements the prior executed alternating calibration because the adjustment of the fine adjustment are merely small. Hereby, the angular position with the highest signal amplitude for each sensor may deviate from the von ideal perpendicular angular position referenced to the exterior surface10a; hereby, however, these corrected angles allow for a best possible measuring of the wall thickness.

FIGS.7a) andb) shows the measuring of a measured object10with a higher degree of or respectively a shape other than round, whereby, accordingly, there may also be a displacement of its central axis D in relation to the axis of symmetry A. Here, too, the method according to the invention can be carried out advantageously. Thus, e.g. the THz sensors1may be positioned with a deviation of 1.5° angular malposition, whereby an additional amplitude correction may reduce this to an angular malposition of almost 0°. Thus,FIG.7a) corresponds toFIG.6;FIG.7b) shows, for better illustration, a simplification including only a few relevant lines. Hereby, for clarity, only the sensors S1, S2, S3are provided with a few auxiliary lines. Thus, the two outermost sensors S3and S1lie in alignment with the axis of symmetry A, and, from the distances from the pipe10measured by them, the balance line L2and there with the line intersection angle β to the base line is formed, which is, therefore, the advised correction angle for the sensor S2in the middle.

Thus, the calibrating method according to the above-described embodiment may be represented according toFIG.10as including the following steps:start in step St0,step of providing St1the THz measuring apparatus8including the pivoting THz sensor1arranged around the measuring chamber9alignment step St2in the starting position,group forming step St3including allocating the THz sensors1to the two sensor groups G1, G2,thereafter, the two at least two calibration adjustment steps KS1, KS2following successively one after another, wherein always one of the sensor groups is the starting group and the other is the adjustment group,each including the following steps:St4-1determining the spacing points on the exterior surface10a, i.e., in the first calibration adjustment step KS1, of the first spacing points P1, P3, P5, P7,St4-2determining the sensor correction angles α of the THz sensors of the adjustment group using the spacing points determined by the starting group, i.e.in the first calibration adjustment step KS1, of the sensor correction angles α of the THz sensors S2, S4, S6, S8, St4-3adjusting the THz sensors (S2, S4, S6, S8) of the adjustment group by the determined sensor correction angles,this calibration adjustment being executed at least 2 times for mutual successive adjustment of both groups G1, G2, possibly, however, 4 times or 6 times, . . . ,and, preferably, subsequently the fine adjustment step St5with maximum value determination Sa_max of the signal amplitude Sa by small adjustment angles αv of the individual THz sensors, independent of each other, is carried out.

FIG.9shows an arrangement20of a manufacturing device21, e.g. an extruder, extruding and dispensing the pipe10, where, accordingly, this pipe10made of plastics or rubber is still soft and therefore susceptible to bending and sagging thus varying and fluctuating its central axis D. The pipe10is guided by the guide means20through the THz measuring apparatus8, with no translational adjustment of the THz measuring apparatus8being provided here but, rather, the above-described angular correction of the individual THz sensors1. Here, advantageously, no adjustment of the pipe10by the guide means22is required.

Thus the pipe10can be measured after the calibration, in particular, the layer thickness d_10as the distance between the exterior surface10aand the interior surface10bcan be measured in the circumferential direction, moreover, the interior diameter ID of the pipe10from the various measuring directions. Thus, this measuring method can be carried out, in particular, in order to inspect the pipe10as measurement object for meeting required tolerance values following the extrusion.

LIST OF REFERENCE NUMERALS

1THz sensor2sensor receptacle3THz chip4sensor lens6measuring receptacle7measuring plane8THz measuring apparatus9measuring chamber10measurement object, e.g. plastic pipe10aexterior surface of the measurement object1010binterior surface of the measurement object1012transmitted THz beam14reflected THz beam20arrangement21manufacturing device, extruder22guide means for guiding the pipe1025adjustment device, e.g. electric micro motor27sensor module made of sensor1, sensor receptacle2,28wire29plug30controller means, e.g. as central controller meansA axis of symmetry of the THz measuring apparatus8B sensor axis of the THz sensor1or, respectively, the plurality of sensors S1through S8C swivel axis of the THz sensor in the sensor receptacle2D center point of the measurement object10or, respectively, its exterior surface10a, e.g. axis of symmetry of the exterior surface10ad0starting distanceG1first sensor groupG2second sensor groupL1base lineL2balance lineL3line orthogonal on L2through sensor of the other groupS1bis S8sensors inFIG.6,7a,b)P1, . . . P8spacing pointsα sensor correction angleβ (L1, L2) line intersection angleU circular circumference of the measuring receptacle6D central axis of the pipe10L3line orthogonalID interior diameterd_10layer thickness