DE202016008433U1 - Terahertz measuring device for measuring test objects using terahertz radiation - Google Patents

Abstract

A terahertz measuring device for measuring test objects, comprising at least: a) a transmitter-receiver unit (3) with a transmitter (9) for emitting radiation (S) in the terahertz range and an associated receiver (10) for detecting a b) an elliptical first mirror (7;) having a first elliptical focal point in a first xy plane (Exy) (B1) and a second elliptical focal point (B2) is formed, and which is at least partially elliptical curved for deflecting the radiation (S, R) between the focal points (B1, B2) in the first xy plane (Exy), - b2) a second mirror (8) arranged in the region of the first elliptical focal point (B1) for deflecting the radiation (S, R) between a z-direction running transversely to the first xy plane (Exy) and the first xy plane (Exy) , c) a parabolic second mirror arrangement (4 ') with - c1) a first parabolic mirror (7 ') forming a first parabolic focal point (B1') in a second xy plane (Exy '), and - c2) a second parabolic mirror (19') operating in the second xy plane (Exy ') is parabolic and forms a second parabolic focal point (B2') and is arranged opposite to the first parabolic mirror (7 '), wherein the first parabolic mirror (7') and the second parabolic mirror ( 19 ') for deflecting the radiation (S, R) between the parabolic focal points (B1', B2 ') are parabolically curved, and c3) a in the region of the first focal point (B1') arranged third mirror (8 ') for deflecting the Radiation (S, R) between a transverse to the second xy plane (Exy ') extending z-direction and the second xy plane (Exy'), d) a Prüfobjekthalter (5) for placing the test object (2) in the area the second foci (B2, B2 ') of both XY planes, and e) a control unit (6 ) for evaluating the detected radiation (R) and determining at least one layer thickness of the test object, wherein the second xy plane (Exy ') of the second mirror arrangement (4') in the z-direction offset from the first xy plane (Exy ') of the first mirror arrangement (4) is provided.

Description

The invention relates to a terahertz measuring device for measuring test objects by means of terahertz radiation. The test objects to be measured have, in particular at least in sections, at least one hollow cylindrical material layer.

From the DE 102008046988 A 1, a reflectometer for characterizing materials with respect to at least one optical reflection property is known. The reflectometer comprises an ellipsoidal mirror, in the first focal point of which a sample to be characterized is held by means of a sample holder. The sample is rotatable about a rotation axis by means of the sample holder. The irradiation of the sample takes place through an opening in the ellipsoidal mirror by means of a radiation source. The ellipsoid mirror images the radiation reflected by the sample illuminated in the first focal point through a diaphragm positioned in the second focal point onto a detector located behind it. The measurement data of the reflectometer are then evaluated to characterize the sample.

The invention has for its object to provide a terahertz measuring device that allows the measurement of test objects in a simple and flexible manner. The terahertz measuring device is intended in particular to enable the measurement of test objects which have at least in sections at least one hollow cylindrical material layer.

This object is achieved by a terahertz measuring device according to claim 1. Advantageous embodiments of the invention emerge from the subclaims. The terahertz measuring device or terahertz reflection measuring device is preferably used for carrying out reflection measurements on the test object to be measured. It is preferably provided a transit time measurement for determining wall thicknesses of pipes, in particular plastic pipes or layers of plastic pipes.

In the context of the invention, "elliptical mirror" denotes a mirror which is elliptical at least in sections and forms two focal points; Preferably, an "elliptical mirror" is completely elliptical in its xy plane

In the context of the invention, "parabolic mirror" denotes a mirror which is at least partially parabolic and forms a focal point; Preferably, a "parabolic mirror" is completely parabolic in its xy plane, especially as a parabolic trough or a rotational paraboloid.

A "pair of parabolic mirrors" means first and second parabolic mirrors facing each other with their openings and having a common optical axis; Thus, in particular, the two focal points are on the common optical axis.

The first mirror of the at least one mirror arrangement is elliptically curved at least in sections and forms a first focal point and an associated second focal point in an x-y plane. In the region of the first focal point, a second mirror is arranged which extends through the first focal point and is arranged inclined relative to the xy plane, that is with this an angle not equal to 0 °. The test object to be measured is arranged by means of the test object holder in the region of the second focal point. The at least one transmitter-receiver unit is arranged outside the x-y plane, that is to say in a z-direction at a distance from the x-y plane. This is possible due to the deflection by means of the second mirror. The second mirror encloses an angle α with the x-y plane, where α = 30 ° ≦ α ≦ 60 °, in particular 35 ° ≦ α ≦ 55 °, and in particular 40 ° ≦ α ≦ 50 °. Preferably, the angle α = 45 °.

The measurement of the test object is preferably carried out independently of one another in both mirror arrangements. First of all, the transmitter of the transmitter-receiver unit emits radiation in the direction of the deflecting mirror or second mirror. In the elliptic mirror arrangement, the emitted radiation is deflected by means of the second mirror in the xy plane and then strikes the first mirror. Due to the elliptical curvature of the first mirror, the radiation is reflected in the direction of the second focal point. Due to the arrangement of the test object in the region of the second focal point, the radiation impinges on the test object and is reflected from there again. The test object is preferably arranged such that a central longitudinal axis of the test object extends through the second focal point, so that the radiation or the beam impinges radially on the test object and the angle of incidence of the radiation corresponds to the reflection angle. The radiation reflected on the test object has the same beam path, but in the opposite direction, as the incident radiation. The reflected radiation is reflected by the first mirror due to its elliptical curvature in the direction of the first focus and meets there on the second mirror. Of the second mirror deflects the reflected radiation transversely, in particular perpendicular, to the xy plane in the direction of the transceiver unit. The receiver detects the reflected radiation and forwards the measured values to the control unit, which evaluates the detected radiation or the measured values.

In the parabolic mirror arrangement, the transmitter of the transmitter-receiver unit first emits radiation in the direction of the third mirror. The emitted radiation is deflected by means of the third mirror in the x-y plane and then strikes the first parabolic mirror. The radiation is then deflected by the first parabolic mirror and then hits the second parabolic mirror due to its parabolic curvature. The parabolic curvature of the second mirror reflects the radiation from the second mirror in the direction of the second focal point. Due to the arrangement of the test object in the region of the second focal point, the radiation impinges on the test object and is reflected from there again. The test object is preferably arranged such that a central longitudinal axis of the test object extends through the second focal point, so that the radiation or the beam impinges radially on the test object and the angle of incidence of the radiation corresponds to the reflection angle. Due to the arrangement of the test object in the region of the second focal point by means of the test object holder and the second mirror in the region of the first focal point, the test object can be measured in a flexible manner.

The measuring device according to the invention has a comparatively simple design, since the at least one transmitter-receiver unit can be positioned outside the x-y planes of the mirror arrangements, because of the associated mirror arrangement outside, that is to say in the z-direction.

By means of the two mirror arrangements, a test object, in particular a thickness of at least one hollow cylindrical material layer, can be measured over the entire circumference.

The test object is in particular designed as a hollow cylinder, ie as a tube with a circular cross section. The test object is formed in particular of plastic. In particular, the test object has a hollow cylindrical material layer or a plurality of hollow cylindrical material layers. Preferably, the thickness of the at least one material layer can be determined, in particular to check that a homogeneous wall thickness is present over the circumference.

Thus, in particular a tube of z. B. plastic are guided by a measuring device and examined over its entire circumference. The investigation can thus already after production, for. As the extrusion of the plastic tube done.

A mechanical adjustment, i. Turning or pivoting of the test object or the measuring device is thus not required.

The at least one transmitter-receiver unit is designed such that electromagnetic terahertz radiation having a frequency in the range from 0.01 THz to 50 THz, in particular from 0.05 THz to 20 THz, and in particular from 0.1 THz to 10 THz emits or detects. This allows in particular the measurement of test objects made of plastic. The measurement of the test object by means of the radiation or THz radiation is based on the measurement of a transit time difference of the radiation which is reflected at the boundary layers. Boundary layers are the surfaces of the test object, for example, the tube outer wall and the tube inner wall, and contiguous material layers within the test object. The at least one transmitter-receiver unit is in particular designed such that THz pulses can be emitted or detected.

By the at least one transmitter-receiver unit along the z-axis, that is arranged perpendicularly spaced from the xy plane of the first and second mirror arrangement, the limited by the elliptical first mirror or the two parabolic mirrors space or Interior is not unnecessarily affected by the transmitter-receiver unit, with a deflection of the radiation takes place in a simple manner. The second mirror or third mirror provided for deflecting from the respective x-y plane requires a comparatively small space requirement, so that the first and second mirror arrangement is constructed in a comparatively compact manner. The size of the mirror arrangement is determined only by the size of the largest test object to be measured. The z-axis is perpendicular to the x-y plane. Accordingly, the second mirror or third mirror for deflecting the radiation is inclined by preferably 45 ° to the respective x-y plane.

The mirror arrangements are aligned with one another such that the area shaded by the first mirror arrangement can be measured by means of the second mirror arrangement and vice versa, thus By each mirror arrangement, in each case the area shaded by the other mirror arrangement can be detected, ie in different z positions, wherein in particular the test object is guided in the z direction by both mirror arrangements. In this case, the two mirror arrangements are offset in the z-direction, so that they do not interfere. In principle, more than two mirror arrangements can be provided, if this is advantageous. The further mirror arrangements are then parabolic and / or elliptical.

The invention will be explained in more detail below with reference to embodiments. In the accompanying drawing shows:

1 a side view of a portion of a terahertz measuring device according to an embodiment,

2 a plan view of the elliptical first mirror assembly in 1 .

3 a side view of the first or second mirror arrangement according to another embodiment,

4 a plan view of the parabolic second mirror arrangement in 1 .

5 a plan view of the measuring device with two mirror assemblies 2 and 4 , and

6 a first side view of a measuring device according to another embodiment, and

7 a second and rotated by 90 ° side view of the measuring device in 6 ,

8th a time course of a radiation emitted as THz pulses radiation.

A terahertz measuring device 1 for measuring a test object 2 has two transceiver units 3 and 3 ' , two associated mirror arrangements 4 and 4' , a test object holder 5 and a control unit 6 on. Here, in a first xy plane E _{xy is} a first elliptical mirror arrangement 4 and in a second xy plane E _'xy is a second parabolic mirror assembly 4' provided, which are spaced in the z-direction.

The following is based on the 2 First, the first, elliptical mirror arrangement 4 described.

The first mirror arrangement 4 includes an elliptical first elliptical mirror 7 which is formed and arranged symmetrically to an xy plane E _xy . The xy plane E _xy is defined by an x-direction and a perpendicular y-direction. The first elliptical mirror 7 is curved in the xy plane E _xy and parallel to it elliptically. The first elliptical mirror 7 Thus, in the xy plane E _{xy, it forms} a mirror surface S ₁ in the form of an ellipse. Due to the elliptical curvature, the first elliptical mirror points 7 in the xy-plane E _xy two foci B ₁ and B ₂ . The foci B ₁ and B ₂ each have a distance e from a center M of the ellipse in the x direction.

The ellipse or ellipse shape of the first elliptical mirror 7 is defined by a first half-axis A with an associated length a and a shorter compared to the first half-axis A second half-axis B with a length b. For a ratio of the lengths a / b: a / b ≦ 1.3, in particular a / b ≦ 1.2, and in particular a / b ≦ 1.1.

The first mirror arrangement 4 further comprises a second mirror 8th which is arranged in the region of the first focal point B ₁ . The second mirror 8th is planar, thus has a plane mirror surface S ₂ . The second mirror 8th closes with the xy plane E _xy an angle α, where for α - depending on the arrangement of the transmitter-receiver unit 3 applies: 30 ° ≤ α ≤ 60 °, in particular 35 ° ≤ α ≤ 55 °, and in particular 40 ° ≤ α ≤ 50 °. Preferably, the angle α = 45 °. The second mirror 8th is preferably arranged such that the first focal point B _{1 is} located substantially centrally on the mirror surface S ₂ .

The first transceiver unit 3 includes a first transmitter 9 for emitting radiation S. The emitted radiation is emitted by the transmitter 9 up to the test object 2 hereinafter referred to as S The on the test object 2 reflected radiation is subsequently from the test object 2 up to a receiver 10 With R denotes. The recipient 10 serves to detect the on the test object 2 reflected radiation R. For measuring the test object 2 is by means of the control unit 6 the detected radiation R evaluated.

Due to the elliptical curvature of the first elliptical mirror 7 occurs a deflection of the radiation S, R between the focal points B ₁ and _B2. In contrast, the second mirror is used 8th for deflecting the radiation S, R between a transverse or perpendicular to the xy plane E _xy extending z-direction and the xy plane E _xy . The z-direction is perpendicular to the x-direction and the y-direction, so that the x-, y- and z-directions form a Cartesian coordinate system.

The first transceiver unit 3 is arranged in the z-direction at a distance from the first xy plane E _xy . The first transceiver unit 3 is arranged along a first z-axis Z ₁ , which runs parallel to the z-direction through the first focal point B ₁ .

The transceiver unit 3 , the mirror arrangement 4 , the test object holder 5 and the control unit 6 are on a base frame 11 the terahertz measuring device 1 attached. The second z-axis Z ₂ extends parallel to the z-direction through the second focal point B ₂ . For this purpose, the test object holder 5 for example, two retaining shots 12 . 13 which are arranged on both sides of the xy plane E _xy and concentric with the second z-axis Z ₂ .

The test object 2 is hollow cylindrical and has a circular or annular cross-section. The test object 2 is by means of the test object holder 5 arranged such that a central longitudinal axis L is congruent with the second z-axis Z ₂ . The test object 2 is formed in two layers and has two hollow cylindrical material layers K ₁ and K ₂ . The test object 2 is made of plastic, wherein in particular the two material layers K ₁ and K _{2 are} made of different plastic materials. For measuring the test object 2 is the transceiver unit 3 such that the electromagnetic radiation S, R can be emitted or detected at a frequency in the range from 0.01 THz to 50 THz, in particular from 0.05 THz to 20 THz, and in particular from 0.1 THz to 10 THz. The radiation S is preferably emitted in pulsed form, that is to say generates THz pulses.

For focusing the radiation S, R in the z-direction is according to one embodiment, the first mirror 7 concavely curved in the z-direction. As in 1 is illustrated has the mirror surface S _{1 of} the first mirror 7 in the z-direction z. B. an elliptical curvature.

The operation of the terahertz measuring device 1 is as follows:
The transmitter 9 emits radiation S in the form of THz pulses. The generation of THz pulses is basically known. THz pulses are generated, for example, optically by means of femtosecond laser pulses and photoconductive switches. The radiation S is emitted substantially in the z-direction and focused on the first focal point B ₁ .

Through the second mirror 8th the radiation S is deflected from the z-direction into the xy-plane E _xy and impinges on the mirror surface S _{1 of} the first mirror 7 , Due to the elliptical curvature, the radiation S coming from the direction of the first focal point B _{1 is} reflected at the mirror surface S ₁ in the direction of the second focal point B ₂ . Since in the beam path between the mirror surface S ₁ and the second focal point B _2, the test object 2 is located, the radiation S hits radially on the test object 2 and will be at the different boundary layers of the test object 2 reflected. The individual boundary layers are the outer surface and the inner surface of the test object 2 as well as the intermediate boundary layer of the material layers K ₁ and K ₂ . The THz pulses are from the transceiver unit 3 thus radially on the test object 2 or the pipe 2 irradiated.

The reflected radiation R or the reflected THz pulses travel along the same beam path back to the transceiver unit 3 and be there by the receiver 10 detected. The structure of the receiver 10 is known in principle. THz pulses are detected, for example, by optical sampling with femtosecond laser pulses.

When measuring the test object 2 In particular, a wall thickness d _{W of} the test object 2 and layer thicknesses d ₁ and d _{2 of} the material layers K ₁ and K _{2 are} determined. The measurement of the wall thickness d _W and the layer thicknesses d ₁ and d ₂ are based on the measurement of propagation time differences of the THz pulses reflected at the individual boundary layers. By means of the control unit 6 the propagation time differences are evaluated and the thicknesses d _W , d ₁ and d _{2 are} determined.

In the 1 and 2 is drawn with solid lines an ideal beam. The radiation S hits the test object punctiform as an ideal beam 2 so that the test object 2 is measured in a measuring point.

By means of a drive unit 15 is the test object holder 5 also along the z-direction linearly movable, so that the test object 2 is completely measured along its length.

Here, the drive unit 15 also z. B. in a device for producing the designed as a plastic tube test object 2 be involved; thus can a plastic pipe 2 in particular after its extrusion are measured directly, so that the terahertz measuring device 1 remains stationary and the plastic tube 2 through the terahertz measuring device 1 is passed linearly in the z-direction.

In the 1 and 2 Furthermore, a real beam propagation of the radiation S, R is shown with dashed lines. The emitted radiation S is transmitted by means of the transmitter-receiver unit 3 initially focused in the first focus B ₁ . For this purpose, the transmitter-receiver unit 3 for example, a lens. The at the second mirror 8th reflected radiation S has a beam divergence. The radiation S, R has, on the one hand, a divergence angle Δφ _R in the xy plane E _xy and a divergence angle Δφ _Z in the z direction. Due to the elliptical curvature of the first mirror 7 in the xy-plane E _xy the radiation S, R is focused on the respective focal point B ₁ and B ₂ . The radiation S does not hit the test object punctiformly during a real beam propagation 2 but in a measuring range, wherein the individual beams or partial beams in each case radially to the test object 2 to meet. The size of the measuring range depends on the divergence angle Δφ _R and a radius r of the test object 2 from.

The second mirror 8th is arranged such that the radiation S is ideally at an angle φ _R to the x-direction to the first mirror 7 is reflected, wherein the radiation S due to the real beam propagation divergence angle Δφ _R has. Due to the fixed arrangement of the second mirror 8th applies to the angle φ _R : φ _R = 90 °. With ideal beam propagation, the radiation S strikes the test object at an angle φ _L relative to the z direction 2 , wherein the radiation S when hitting the test object 2 has a divergence angle Δφ _L. For the divergence angle or opening angle Δφ _L , equation (1) applies.

For a dimension d of the measuring range in the xy-plane E _xy approximately equation (2) applies:

The dimension d of the measuring range at a certain angle is thus directly proportional to the radius r of the test object 2 , For the smallest possible measuring range Δφ _L should be as small as possible. The opening angle Δφ _L depends on the angle φ _R. The angle Δφ _L is smaller, the smaller φ _R.

In addition, the angle Δφ _L of the lengths a and b of the semi-axes A and B depends.

By means of a single transmitter-receiver unit 3 and the associated mirror arrangement 4 can the test object 2 Thus - without rotation of the test object or the measuring device - are measured to a shaded area D. Despite the divergent beam propagation, the radiation S or the respective THz pulse impinges radially on the boundary layers of the test object 2 , ie perpendicular to the boundary layers and also at the same time points. This ensures that the reflected radiation R has a high signal quality and in particular the reflected THz pulses are not washed out and are attenuated in their amplitude.

Since the mirror surface S _{1 is} also elliptically curved in the z-direction, the radiation S, R is also focused in the z-direction. The first mirror 7 is preferably elliptically curved in the z-direction such that a first focal point coincides with the first focal point B ₁ and a second focal point on the outer surface of the test object 2 lies. This is in 1 illustrated. The radiation S thus also has an optimized, ie the smallest possible measuring range in the z-direction.

Preferably, the second mirror 8th around the first z-axis Z ₁ by means of a mirror drive unit 16 pivotable, in particular rotatable through 360 °. The angle φ _R is thus variable by the rotation. This is the test object 2 even if it is fixed about the second z-axis Z ₂ , it can be measured over a wide circumferential range. In 2 additional radiation patterns of the radiation S are drawn, which is a measurement of the test object 2 illustrate. Regardless of the angle φ _R , the radiation S by means of the first mirror 7 deflected between the focal points B ₁ and B ₂ . When measuring the test object 2 Irrespective of the angle φ _R , the radiation S always impinges radially or perpendicularly on the test object 2 ,

At an angle φ _{R, max} affects the to the test object 2 extending radiation S the test object 2 so that the test object 2 at angles greater than φ _{R, max} at one of the second mirrors 8th is shaded away from the opposite side. The shaded area D of the test object 2 is in 2 shown by dashed lines and denoted by D. For the angle φ _{R, max} equation 3 applies: φ _{R, max} = π-arcsin (r / 2e)

The radiation S strikes the test object at an angle φ _{R, max} at an angle φ _{L, max} 2 , so that the maximum measurable angular range of the test object 2 if this is fixed around the second z-axis Z ₂ , 2φ _{L, max} is.

According to equation (1), the divergence angle Δφ _{L is} dependent on the angle φ _R. The change of Δφ _L as a function of the angle φ _R , however, is the smaller, the closer the lengths a of the large half-axis A and b of the small half-axis B are closer to each other. The measuring accuracy of the measuring device 1 is thus less dependent on the angle φ _R , the closer the ratio a / b is 1.

According to the embodiment of the 3 is the first mirror 7 is parabolically curved in the z-direction, wherein the first focus B ₁ at all angles φ _R coincides with the focus of the parabola. By reflection of the radiation S, the radiation S is collimated in the z-direction. This is in 3 illustrated by the parabolic curvature of the first mirror 7 the radiation S is collimated in the z-direction so that all rays or partial rays are independent of the radius r of the test object 2 always perpendicular to the test object 2 come to mind. The extension of the measuring range in the z-direction is the diameter of the collimated radiation S, which is given by the divergence angle Δφ _Z or is adjustable.

Hereinafter, with reference to 4 the parabolic second mirror arrangement 4' described. The parabolic second mirror arrangement 4' has a first parabolic mirror 7' formed symmetrically to an xz plane Exz. The xz-plane Exz is defined by an x-direction and a perpendicular z-direction. The first mirror 7' is in a second xy plane E _xy ', which is perpendicular to the xz plane and parallel parabolic curved. The second xy plane E _xy 'is spaced from the first xy plane E _xy in the z-direction. The first mirror 7' Thus, in the second xy plane E _{xy '} forms a mirror surface S ₁ in the form of a parabola. Due to the parabolic curvature, the first mirror points 7 in the second xy plane E _xy 'a first focus B ₁ ' on.

The mirror arrangement 4 also includes a second parabolic mirror 19 which is formed symmetrically to the xz-plane Exz. The second mirror 19 is in the second xy plane E _xy 'and parallel parabolically curved. The second mirror 19 thus forms in the second xy plane E _xy 'a mirror surface S ₂ in the form of a parabola. Due to the parabolic curvature, the second mirror points 19 in the second xy plane E _xy 'a second parabolic focal point B ₂ ' on. The focal points B ₁ 'and B ₂ ' each have a distance e from a center M of the mirror arrangement in the x direction 4' , The openings of the mirrors 7' . 19' are facing each other. The mirror 7' . 19' are arranged directly opposite one another and are mirror-symmetrical with respect to a yz-plane E _yz . The yz plane E _yz is perpendicular to the second xy plane E _xy '.

The second mirror arrangement 4' further comprises a third mirror 8th which is arranged in the region of the first focal point B ₁ '. The third mirror 8th is planar, thus has a plane mirror surface S ₃ . The third mirror 8th closes with the second xy plane E _xy 'an angle α, where for α - depending on the arrangement of the second transceiver unit 3 ' applies: 30 ° ≤ α ≤ 60 °, in particular 35 ° ≤ α ≤ 55 °, and in particular 40 ° ≤ α ≤ 50 °. Preferably, the angle α = 45 °. The third mirror 8th is preferably arranged such that the first focal point B _{1 is} located substantially centrally on the mirror surface S ₃ .

The second transceiver unit 3 ' is preferably separate from the first transceiver unit 3 formed and according to the first transmitter-receiver unit 3 educated. Here, the two transmitter-receiver units radiate 3 . 3 ' - As described below - offset in the x direction. Basically, however, also THZ radiation S from a single transmitter-receiver unit 3 on both mirror arrangements 4 and 4' be split.

Due to the parabolic curvature of the first and second mirror 7 respectively. 19 there is a deflection of the radiation S, R between the focal points B ₁ 'and B ₂ '. In contrast, the third mirror is used 8th for deflecting the radiation S, R between a transverse or perpendicular to the xy plane E _xy 'extending z-direction and the xy plane E _xy '. The z-direction is perpendicular to the x-direction and the y-direction, so that the x-, y- and z-directions form a Cartesian coordinate system.

The transceiver unit 3 ' is arranged in the z-direction at a distance from the xy plane E _xy '. The transceiver unit 3 ' is arranged along the z-axis and thus radiates to the first focal point B ₁ 'a. The z-axis Z ₁ 'is from the z-axis Z _{1 of} the first mirror arrangement 4 spaced, especially in the x direction.

The transceiver unit 3 ' and the mirror arrangement 4' are also on the base frame 11 the measuring device 1 attached.

For focusing the radiation S, R in the z-direction, according to one embodiment, the first parabolic mirror 7' and the second parabolic mirror 19' concavely curved in the z-direction. The mirror surface S _{1 of} the first mirror 7 and the mirror surface S _{2 of} the second mirror 19 have an elliptical curvature in the z-direction together according to one embodiment.

The operation of the second mirror arrangement 4' corresponds essentially to the first mirror arrangement:
The radiation S is emitted substantially in the z-direction along the axis Z ₂ and focused on the first parabolic focal point B ₁ '.

Through the third mirror 8th the radiation S is deflected from the z-direction into the xy-plane E _xy 'and strikes the mirror surface S _{1 of} the first parabolic mirror 7' , Through the first parabolic mirror 7 the radiation S is deflected and then strikes the mirror surface S _{2 of} the second parabolic mirror 19 , Due to the parabolic curvature of the second parabolic mirror 19 becomes that of the first parabolic mirror 7 incoming radiation S in the direction of the second parabolic focal point B ₂ reflected. Since in the beam path between the mirror surface S ₂ and the second parabolic focal point B _2, the test object 2 is located, the radiation S hits radially on the test object 2 and will be at the different boundary layers of the test object 2 reflected. The individual boundary layers are the outer surface and the inner surface of the test object 2 as well as the intermediate boundary layer of the material layers K ₁ and K ₂ . The THz pulses of the transceiver unit 3 ' are also from the second parabolic mirror arrangement 4' from thus again - as above in the first mirror arrangement 4 described - radially on the test object 2 or the pipe 2 irradiated.

The reflected radiation R or the reflected THz pulses travel along the same beam path back to the transceiver unit 3 ' and be there by the receiver 10' detected.

Even with the second parabolic mirror arrangement 4' can as above with the first mirror arrangement 4 described one or more lenses may be provided for bundling; Furthermore, the curvature of the first and second parabolic mirrors 7' and 19' and the third mirror (deflecting mirror) 8th according to the embodiments of the first mirror arrangement 4 be different.

Thus, in turn z. B. in the real beam propagation of the radiation S, R according to 1 the emitted radiation S is first focused by means of a lens in the first focal point B _1. The at the third mirror 8th reflected radiation S has a beam divergence. The radiation S, R has, on the one hand, a divergence angle Δφ _R in the xy plane E _xy 'and a divergence angle Δφ _Z in the z direction. Due to the parabolic curvature of the first parabolic mirror 7' and second parabolic mirror 19' in the xy-plane E _xy 'the radiation S, R is focused on the respective focal point B ₁ ' and B ₂ '. The radiation S does not hit the test object point-like with a real beam propagation 2 but in a measuring range, wherein the individual beams or partial beams in each case radially to the test object 2 to meet. The size of the measuring range depends on the divergence angle Δφ _R and a radius r of the test object 2 from.

The third mirror 8th again, it is arranged such that the radiation S is ideally at an angle φ _R to the x-direction to the first parabolic mirror 7' is reflected, wherein the radiation S due to the real beam propagation divergence angle Δφ _R has. Due to the fixed arrangement of the third mirror 8th applies to the angle φ _R : φ _R = 90 °. With ideal beam propagation, the radiation S strikes the test object at an angle φ _L relative to the z direction 2 , wherein the radiation S when hitting the test object 2 has a divergence angle Δφ _L.

The dimension d of the measuring range at a certain angle φ _L is directly proportional to the radius r of the test object 2 , For the smallest possible measuring range Δφ _L must be as small as possible. The opening angle Δφ _L depends on the angle φ _R. The angle Δφ _L is smaller, the smaller φ _R.

By the mirror surface S ₁ and S _{2 is} elliptically curved in the z-direction, the radiation S, R is also focused in the z-direction. The first and second mirrors 7' respectively. 19' are preferably elliptically curved in the z-direction together so that a first focus coincides with the first focus B ₁ 'and a second focus on the outer surface of the test object 2 lies. This is in 1 illustrated. The radiation S thus also has an optimized, ie the smallest possible measuring range in the z-direction.

Preferably, in turn, the third mirror 8th around the z-axis Z ₁ 'by means of a third drive unit 160 pivotable, in particular rotatable through 360 °. The angle φ _R is thus variable by the rotation. This is the test object 2 even if it is fixed about the second z-axis Z ₂ , it can be measured over a wide circumferential range. In this case, additional beam paths of the radiation S are shown, which is a measurement of the test object 2 illustrate. Regardless of the angle φ _R , the radiation S by means of the first parabolic mirror 7' and second parabolic mirror 19' deflected between the focal points B ₁ 'and B ₂ '. When measuring the test object 2 Irrespective of the angle φ _R , the radiation S always impinges radially or perpendicularly on the test object 2 ,

At an angle φ _{R, max} affects the to the test object 2 extending radiation S the test object 2 so that the test object 2 at angles greater than φ _{R, max} at one of the third mirrors 8th is shaded away from the opposite side. The shaded area of the test object 2 is in 4 shown by dashed lines and denoted by D.

In this case, the first and second mirror arrangement complement each other 4 and 4' by placing the shaded areas D of the other mirror arrangement respectively 4 and 4' to capture.

Furthermore, even in the second parabolic mirror arrangement 4' the first parabolic mirror 7' and the second parabolic mirror 19' be parabolically curved in the z-direction, wherein the first focus B ₁ 'at all angles φ _R coincides with the focus of the parabola. By reflection of the radiation S, the radiation S is collimated in the z-direction.

According to 5 Thus, the two mirror arrangements complement each other 4 and 4' , wherein they are spaced apart in the z-direction and are rotated relative to each other, that the second focal points B ₂ and B ₂ 'spaced from each other on the second z-axis Z ₂ and the first focal points B ₁ and B ₁ ' in a through the second foci B ₂ and B ₂ 'extending xz plane Exz. The foci B ₁ and B ₁ 'are thus maximally spaced from a yz plane E _yz passing through the second foci B ₂ and B ₂ '. The second mirror 8th . 8th' are about their associated and through the respective first focus B ₁ , B ₁ 'extending first z-axis Z ₁ and Z ₁ ' rotatable. The test object 2 is measured inline in the manufacturing process and is accordingly about its own central longitudinal axis L, ie about the second z-axis Z ₂ or Z ₂ 'not pivotable. As already explained for the second exemplary embodiment, the test object has 2 in the measurement by the respective mirror arrangement 4 . 4 ' and the associated transceiver unit 3 . 3 ' a shaded area D, D '. By positioning the mirror assemblies 4 . 4 ' However, the mirror arrangement can 4 ' the shaded area D of the mirror arrangement 4 measured and according to the mirror arrangement 4 the shaded area D 'of the mirror arrangement 4 ' , Thus, the test object 2 fully vermessbar, although this is not pivotable or rotatable. The test object 2 has an extrusion direction due to the manufacturing process, which runs in the z-direction so that the test object 2 also measurable or measured along its length. The test object holder 5 that must be UUT 2 Thus, neither actively pivot nor move linearly and accordingly may have a simplified structure such that only a guide of the test object 2 is guaranteed.

According to the invention it is also recognized that different from 5 the first and second mirror arrangement 4 and 4' according to another embodiment z. B. each need only detect an angular range slightly above 180 °, since they overlap.

Furthermore, different from 5 the two mirror arrangements 4 and 4' also not in the x-direction, but be deviating relative to each other. In principle, initially only a congruent position of the second focal points B ₂ and B ₂ 'is provided; Thus, the first focal points with respect to the xy plane can also be provided to other positions relative to each other.

An application of the measuring device 1 is thus the in-line full test of the wall thickness d _W and the layer thicknesses d ₁ and d _{2 of} the test object designed as a plastic pipe 2 in the extrusion process. The measurement of the test object 2 takes place according to the preceding embodiments without contact and without any coupling medium. Thereby, that for the complete or complete measurement of the test object 2 only two transceiver units 3 . 3 ' are required, the structure remains relatively simple, causing the measuring device 1 ensures an acceptable cost-benefit ratio. If more than two mirror assemblies 4 and corresponding transmitter-receiver units 3 are needed, this is the measuring device 1 of course possible. The transmitter-receiver units 3 . 3 ' are also fixed to the associated first mirrors 7 . 7 ' arranged, which also ensures a simple structure.

With regard to the further structure and further operation, reference is made to the preceding embodiments.

The features of the described embodiments can be combined with each other as desired. In particular, the focusing or collimation of the radiation S in the z-direction can be done as needed and arbitrarily with other features of the measuring device 1 be combined. In addition, the mirror surface S _{1 of} the respective first mirror 7 respectively. 7 ' be optimized in the z-direction such that for a predefined radius range of the test object 2 a measuring range or measuring point with acceptable focus size is achieved. For this purpose, the mirror surface S _{1 may be formed} in the z-direction as a free-form surface.

The preferred application of the measuring device according to the invention 1 is the full test or inline full test of wall and / or layer thicknesses of plastic pipes, especially in the manufacturing or extrusion process.

The emitted radiation is designed in particular as pulsed THz radiation, as CW-THz radiation (CW: Continuous Wave) and / or as FMCW-THz radiation (FMCW: Frequency Modulated Continuous Wave). A time course of a pulsed THz radiation is in 8th shown. The successive THz pulses T ₁ and T ₂ and corresponding further THz pulses each have a frequency spectrum which lies in the mentioned THz range. By means of the THz radiation, the measurements are made without contact and without coupling medium.

In addition, with the terahertz measuring device according to the invention 1 further evaluations or measurements are made. For example, the position of the central longitudinal axis L of the test object 2 be determined relative to the second focal point B ₂ . Due to the elliptical curvature of the first mirror 7 respectively. 7 ' is the distance of an optical path, which passes from one focal point by reflection on the mirror surface S ₁ in the other focal point, always constant. In a test object arranged concentrically to the second focal point B ₂ 2 Accordingly, all beam paths have the exact same distance. Thus, the transit time of the reflected radiation R and THz pulses does not change and the detected time position remains when scanning the test object 2 constant. If the central longitudinal axis L and the second focal point B ₂ do not coincide, the temporal position of the THz pulses changes during scanning of the test object 2 , The THz pulses incident along the straight line defined by the central longitudinal axis L and the second focal point B ₂ have the maximum pulse displacements. Thus, the direction of the shift and the size of the shift from the maximum transit time difference is given and can be determined in the evaluation. The position of the central longitudinal axis L relative to the second focal point B ₂ can thus be determined. For example, this information can be used for automatic adjustment of the test object 2 when starting the extrusion process or for any necessary readjustment of the measuring device 1 be used. A reference measurement is not required.

The duration of the THz pulses can also be used to determine the diameter or radius r of the test object 2 and any deviations from the circular shape, such as eccentricity or ovality are determined. The diameter of the test object 2 results from known parameters of the elliptical mirror 7 respectively. 7 ' directly from the duration of the respective THz pulse. Shape parameters, such as eccentricity and ovality, can be calculated from the deviations of the transit time of individual THz pulses.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008046988 A [0002]

Claims (17)

Terahertz measuring device for measuring test objects, comprising at least: a) a transceiver unit ( 3 ) with a transmitter ( 9 ) for emitting radiation (S) in the terahertz range and an associated receiver ( 10 ) for detecting a test object ( 2 ) rekflektierten radiation (R), b) an elliptical first mirror arrangement ( 4 ) with - b1) an elliptical first mirror ( 7 ;) forming a first elliptical focal point (B ₁ ) and a second elliptical focal point (B ₂ ) in a first xy plane (E _xy ), and for deflecting the radiation (S, R) between the focal points (B ₁ , B ₂ ) in the first xy plane (E _xy ) is elliptically curved at least in sections, - b2) a second mirror arranged in the region of the first elliptical focal point (B ₁ ) ( 8th ) for deflecting the radiation (S, R) between a z-direction running transversely to the first xy plane (E _xy ) and the first xy plane (E _xy ), c) a parabolic second mirror arrangement ( 4 ' ) with - c1) a first parabolic mirror ( 7 ' ), which forms a first parabolic focal point (B ₁ ') in a second xy plane (E _xy '), and - c2) a second parabolic mirror ( 19 ' ) which is parabolic in the second xy plane (E _xy ') and forms a second parabolic focal point (B ₂ ') and opposite to the first parabolic mirror ( 7 ' ), the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ) for deflecting the radiation (S, R) between the parabolic focal points (B ₁ ', B ₂ ') are parabolically curved, and c3) a in the region of the first focal point (B ₁ ') arranged third mirror ( 8th' ) for deflecting the radiation (S, R) between a transverse to the second xy plane (E _xy ') extending z-direction and the second xy plane (E _xy '), d) a Prüfobjekthalter ( 5 ) for the arrangement of the test object ( 2 ) in the region of the second focal points (B ₂ , B ₂ ') of both XY planes, and e) a control unit ( 6 ) for evaluating the detected radiation (R) and determining at least one layer thickness of the test object, wherein the second xy plane (Exy ') of the second mirror arrangement ( 4' ) in the z-direction offset from the first xy plane (Exy ') of the first mirror arrangement ( 4 ) is provided. Terahertz measuring device according to claim 1, characterized in that the control unit ( 6 ) for determining at least one layer thickness of the test object ( 2 ) is formed by propagation time measurement of the radiation (S) in the terahertz range under reflection at boundary layers. Terahertz measuring device according to claim 1 or 2, characterized in that the first and / or second transceiver unit ( 3 . 3 ' ) is arranged along a z-axis (Z ₁ , Z ₁ ') running parallel to the z-direction through the first focal point (B ₁ , B ₁ '). Terahertz measuring device according to one of the preceding claims, characterized in that the respective second focal points (B ₂ , B ₂ ') of the two mirror arrangements ( 4 . 4 ' ) lie on a straight line (Z ₂ ), which runs parallel to the z-direction. Terahertz measuring device according to one of the preceding claims, characterized in that the respective first focal points (B ₁ , B ₁ ') of the two mirror arrangements ( 4 . 4 ' ) are spaced transversely or perpendicularly to the z-direction, preferably in the x-direction. Terahertz measuring device according to claim 5, characterized in that the respective first focal points (B ₁ , B ₁ ') of the two mirror arrangements ( 4 . 4 ' ) lie on different sides of a yz plane (E _yz ) passing through the second foci (B ₂ , B ₂ '). Terahertz measuring device according to one of the preceding claims, characterized in that each mirror arrangement ( 4 . 4 ' ) own transmitter-receiver unit ( 3 . 3 ' ) assigned. Terahertz measuring device according to one of the preceding claims, characterized in that the first elliptical mirror ( 7 . 7 ' ) is curved along an ellipse which is defined by a first semiaxis (A) having a length a and a shorter second semiaxis (B) having a length b compared to the first semiaxis (A), where the ratio of the lengths is : a / b ≦ 1.3, in particular: a / b ≦ 1.2, and in particular a / b ≦ 1.1. Terahertz measuring device according to one of the preceding claims, characterized in that the first mirror ( 7 . 7 ' ) of the first and / or second mirror arrangement ( 4 . 4 ' ) in the z-direction has a concave curvature, wherein the curvature is selected in particular from the group parabolic, elliptical and spherical. Terahertz measuring device according to one of the preceding claims, characterized in that the first mirror ( 7 . 7 ' ) of the first and / or second mirror arrangement ( 4 . 4 ' ) is planar in the z-direction and at least one focusing element ( 18 ) is provided for focusing the radiation (S) in the z-direction. Terahertz measuring device according to one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ), in particular in the form and / or size, are identical. Terahertz measuring device according to one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) has a first opening and the second parabolic mirror ( 19 ' ) has a second opening, wherein the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ) are arranged such that the first opening and the second opening facing each other. Terahertz measuring device according to one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) and the second mirror ( 19 ' ) are arranged and formed mirror-symmetrically to each other. Terahertz measuring apparatus according to any one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ) are arranged spaced from each other. Terahertz measuring device according to one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ) are each designed as a parabolic trough or rotationally symmetrical parabolic mirror. Terahertz measuring device according to one of the preceding claims, characterized in that the third mirror ( 8th' ) the radiation (S) on the first parabolic mirror (, 7 ' ) and the first parabolic mirror ( 7 ' ) the radiation (S) on the second parabolic mirror ( 19 ' ), the second parabolic mirror ( 19 ' ) redirects the radiation (S) to the second parabolic focal point (B ₂ '). Terahertz measuring device according to one of the preceding claims, characterized in that the first parabolic mirror ( 7 ' ) the radiation (S) impinging at different angles on the second parabolic mirror ( 19 ' ) deflects the radiation (S) between the first parabolic mirror ( 7 ' ) and the second parabolic mirror ( 19 ' ) is always parallel but spaced from each other.

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