Radar method and radar measuring device for measuring a dimension between two spaced-apart, opposing side surfaces of a measuring object.

Abstract

A radar measuring device (1) for measuring the thickness (D) or width of a measurement object (4) comprises two opposing radars (5, 6). The radar measuring device (1) measures distance signals (R1, R2) for the distances to the opposite side surfaces (2, 3) of the measurement object (4) and calculates the thickness (D) or width of the measurement object (4) from these measurements. The radars (5, 6) each have a retroreflector (15, 20) with three reflective surfaces (16, 17, 18) arranged such that the intersection of the planes spanned by the first three reflective surfaces (16, 17, 18) lies at the virtual emission point of the radar antenna (8, 10) of the other radar. The thickness (D) or width is calculated from the distance (A) between the radars (5, 6), which is measured using the radars (5, 6) when there is no object (4) in the measuring section, and the distance signals (R1, R2) to the surfaces.The distance drift of the radars (5, 6) to each other can thus be monitored precisely and continuously corrected.

Description

[0001] The invention relates to a radar method for measuring a dimension between two spaced-apart, opposite side surfaces of a measurement object, wherein at least a first radar having a first radar antenna and a second radar having a second radar antenna are provided, wherein the first and second radar antennas are arranged facing each other and at a distance from each other, wherein the measurement object is arranged between the radar antennas such that a first side surface of the measurement object faces the first radar antenna and a second side surface of the measurement object faces the second radar antenna, wherein a first radar signal is transmitted from the first radar antenna to the first side surface and a second radar signal is transmitted from the second radar antenna to the second side surface,wherein the radar signals reflected at the side surfaces are received by the respective radar antennas, and according to the principle of time-of-flight measurement, a first distance signal for the distance between the first radar antenna and the first side surface and a second distance signal for the distance between the second radar antenna and the second side surface are generated, and wherein the dimension of the measurement object between the side surfaces is determined from the distance between the radar antennas and the first and second distance signals. Furthermore, the invention relates to a radar measuring device for measuring a dimension between two spaced-apart, opposite side surfaces of a measurement object, - wherein the radar measuring device comprises a first radar with a first radar electronics and a first radar antenna connected thereto for transmitting and receiving a first radar signal, - wherein the radar measuring device comprises a second radar with a second radar electronics and a second radar antenna connected thereto for transmitting and receiving a second radar signal, wherein the first and second radar antennas are arranged facing each other and at a distance from each other, wherein the radar electronics are designed such that when the measuring object is arranged between the radar antennas and faces a first side surface of the first radar antenna and a second side surface of the second radar antenna according to the principle of time of flight measurement - a first distance signal for the distance between the first radar antenna and the first side surface of the measuring object and - a second distance signal for the distance between the second radar antenna and the second side surface of the measurement object can be generated, and wherein the radar electronics are connected to an evaluation device which is designed to determine the dimension which the measurement object has between the side surfaces from the distance between the radar antennas and the first and second distance signals.

[0002] Such a radar method and such a radar measuring device for measuring the thickness of a cast strand in a continuous casting plant used to produce a metallic product are known from EP 3 628 416 B1. In the method, a strand of a metallic product continuously emerges vertically downwards from an outlet opening arranged in the base of a mold in the continuous casting plant. The cast strand is then transported along a supporting strand guide in a conveying direction. At a measuring position at which the cast strand emerges from the supporting strand guide, the thickness of the cast strand is measured by a radar measuring device. The measured strand thickness is compared with a predetermined reference value. If the measured strand thickness is greater than the reference value, at least one casting parameter is changed such that the stump tip of the cast strand migrates towards the mold.

[0003] The radar measuring device known from EP 3 628 416 B1 comprises a first radar with a first radar antenna and a second radar with a second radar antenna facing the first. The radar antennas are located at a predetermined distance from each other, and the cast strand is arranged on a straight line between the radar antennas that connects the virtual emission points of the radar antennas.

[0004] A radar signal is transmitted to the cast strand in front of the first and second radar antennas, and the radar signal reflected by the cast strand is measured using the respective radar antenna. Based on the time-of-flight measurement principle, a first distance signal is generated for the distance between the first radar antenna and the cast strand, and a second distance signal is generated for the distance between the second radar antenna and the cast strand. The thickness of the cast strand is determined from the previously known distance between the radar antennas and the first and second distance signals.

[0005] As can be seen from the 2014 annual report of the Fraunhofer FHR, page 74, “Precision Measurement in Steelworks”, it is also known to use radar sensors to determine the width or material thickness of a strip passing between radar antennas in steel and rolling mills.

[0006] The previously known radar method and radar measuring device have the disadvantage that the measurement accuracy depends on the accuracy with which the distance between the radar antennas is known. In real industrial environments, however, this distance is not constant; it changes due to environmental influences, such as thermal expansion of the radar mounting points, vibrations, or other drifts. Therefore, the distance must be checked at specified maintenance intervals to ensure measurement accuracy. This involves additional effort and expense. If one of the mounting points changes, incorrect measurements will occur.

[0007] The objective is therefore to create a radar method and a radar measuring device of the type mentioned above that enable high measurement accuracy despite low maintenance requirements. Furthermore, the radar method should be simple to implement, and the radar measuring device should enable low operating costs.

[0008] This object is achieved with regard to the radar method of the type mentioned at the outset in that a first retroreflector is provided for the first radar signal, which first retroreflector has three mutually orthogonal first reflection surfaces, that the first retroreflector is arranged on the second radar antenna in such a way that the intersection point of the planes spanned by the three first reflection surfaces lies in the virtual emission point of the second radar antenna or has an offset to this emission point which is a maximum of 20 times the mean wavelength of the first radar signal, that when the measurement object is removed between the radar antennas, the first radar signal is sent to the first retroreflector and from there reflected back to the first radar antenna,to record at least one first distance value for the distance between the radar antennas according to the principle of time-of-flight measurement and to determine the dimension of the measuring object between the side surfaces from the at least one first distance value and the first and second distance signals.

[0009] According to the invention, the distance between the first and second radar antennas is measured using the first radar and a retroreflector arranged on the radar antenna of the second radar. This allows the distance between the radar antennas to be determined precisely and easily. From this distance, the dimension D (e.g., thickness or width) between the two opposite side surfaces of the measurement object is determined using the first and second distance signals measured by the radars, according to the following equation: D=A−R1−R2

[0010] Here, R1 is the distance measured by the first radar to the first side surface of the target, R2 is the distance measured by the second radar to the opposite second side surface of the target, and A is the distance between the first radar antenna and the second radar antenna. The accuracy of the measurement of D is therefore the sum of the accuracies of A, R1, and R2 and is described by Equation 2: ΔD=ΔA+2ΔR

[0011] In equation 2, ΔD is the expected measurement uncertainty of the dimension, ΔA is the inaccuracy of the distance between the two radars and ΔR is the accuracy of the radar distance measurements, since to a good approximation ΔR1 = ΔR2 applies for identically constructed radars.

[0012] Since in the radar method according to the invention changes in the distance A between the radar antennas are measured with the aid of the first radar, the radar method is self-calibrating.

[0013] With regard to the radar measuring device, the above-mentioned object is achieved in that - when the measurement object is located between the first radar antenna and the second radar antenna - a first retroreflector is arranged on the second radar antenna for reflecting the radar signal emitted by the first radar antenna back to the first radar antenna, and in that the first retroreflector has three mutually orthogonal first reflection surfaces which are arranged such that the intersection point of the planes spanned by the three first reflection surfaces lies in the virtual emission point of the second radar antenna or has a predetermined offset from the emission point which is a maximum of 20 times the wavelength of the radar signal of the first radar.

[0014] This makes it possible to measure the distance between the first and second radar antennas using the radar measuring device itself, even when there is no object or obstacle between the first and second radar antennas. It is even possible for the radar measuring device to be self-calibrating. This can be achieved, for example, by the radar measuring device having a data memory with a storage location in which the measured value for the distance between the first radar antenna and the second radar antenna can be stored, in order to use this measured value to determine the dimension between the side surfaces of the measuring object when the measuring object is located between the first and second radar antennas.

[0015] However, it is also possible to provide storage locations for the first and second distance signals in the data storage device, in order to store the first and second distance signals when the measurement object is positioned between the first and second radar antennas. When the distance between the radar antennas is subsequently measured with the measurement object positioned between the first and second radar antennas, the distance signals can be read from the data storage device to determine the dimensions between the side surfaces of the measurement object.

[0016] In order to measure the distance between the first and second radar antennas with the highest precision, the radar measuring system is designed so that the virtual reflection point lies at the isocenter of the second radar antenna. The isocenter is the virtual emission point of the radar antenna. In the far field, electromagnetic waves propagate spherically around the antenna. The center of the spheres is the isocenter or the virtual emission point. The virtual reflection point is realized by a retroreflector with three orthogonal metal surfaces. The radars are constructed so that the virtual emission point and virtual reflection point are at the same location or have a known constant offset from one another. The virtual reflection point is located at the intersection of the planes spanned by the first three reflection surfaces.

[0017] In a preferred embodiment of the invention, a second retroreflector is provided for the second radar signal, which has three mutually orthogonal second reflection surfaces, wherein the second retroreflector is arranged on the first radar antenna in such a way that the intersection point of the planes spanned by the three second reflection surfaces lies in the virtual emission point of the first radar antenna or has an offset to this emission point which is a maximum of 20 times the mean wavelength of the second radar signal, that when the measurement object is located between the radar antennas, the second radar signal is sent to the second retroreflector and from there is reflected back to the second radar antenna in order to detect at least one second distance value, the distance between the radar antennas, according to the principle of time of flight measurement, and to determine the dimension from the at least one first and second distance value as well as the first and second distance signal,the distance between the side surfaces of the object being measured. This allows the dimensions of the object to be measured with even greater accuracy.

[0018] It is advantageous if the travel time measurement for generating the first distance signal and the travel time measurement for generating the second distance signal are performed simultaneously. This can be achieved using a radar measuring device in which the evaluation device has a trigger output connected via a trigger line to trigger inputs of the first and second radars for simultaneously performing the travel time measurements of the first and second radars. This allows the dimensions of the measurement object to be measured very precisely, even when the object is moving relative to the radar antennas. This is particularly advantageous for measurement objects that are subject to oscillations and / or vibrations and / or are moved along a conveyor line during the measurement.

[0019] In a suitable embodiment of the invention, the arithmetic mean is calculated from the first distance value and the second distance value, with the measurement object's dimensions between the side surfaces being determined from the arithmetic mean and the first and second distance signals. This procedure is preferably used when the first and second radars have the same measurement accuracy for radar distance measurements and, in particular, are of identical design: A=(A12+A21) / 2

[0020] Where A is the distance between the first and the second radar antenna, A 12 the first distance value and A 21 the second distance value.

[0021] In an advantageous embodiment of the invention, the difference between the first distance value and the second distance value is determined in absolute terms and compared with a tolerance value or a tolerance value range. If a difference occurs that is greater than the tolerance value or outside the tolerance value range, an error is indicated. The radar method then enables a plausibility check of the distance values. If the deviations between the distance values ​​become too large, an alarm can be triggered.

[0022] In order to prevent the radars from interfering with each other, a preferred embodiment of the invention provides that the frequency of the first radar signal differs from the frequency of the second radar signal or that the frequency range of the first radar signal differs from the frequency range of the second radar signal.

[0023] It is advantageous if the first radar and the second radar each operate according to the FMCW principle. The transmission frequency of the radars is preferably modulated linearly according to a frequency ramp, and to determine the propagation time of the radar signals, the frequency difference between the transmitted radar signal and the received radar signal is measured for each radar.

[0024] In a preferred embodiment of the invention, it is provided that during the runtime measurement - the radar frequency of the first radar signal, starting from a first start frequency, passes through a first frequency ramp, and - the radar frequency of the second radar signal, starting from a second starting frequency, passes through a second frequency ramp, - that the first radar signal emitted by the first radar antenna and the reflected first radar signal received by the first radar antenna are mixed to generate a first intermediate frequency, - that the second radar signal emitted by the second radar antenna and the reflected second radar signal received by the second radar antenna are mixed to generate a second intermediate frequency, - and that the frequency difference between the first and the second starting frequency is greater in magnitude than the first intermediate frequency and greater in magnitude than the second intermediate frequency when the measurement object is located between the radar antennas.

[0025] The radar procedure can therefore be carried out largely without interference.

[0026] In a further development of the invention, the first retroreflector has a first recess for the second radar antenna at the intersection point of the three first reflection surfaces, and / or the second retroreflector has a second recess for the first radar antenna at the intersection point of the three second reflection surfaces. As a result, the intersection point of the planes spanned by the three first reflection surfaces can be arranged exactly at the virtual emission point of the second radar antenna, or the intersection point of the planes spanned by the three second reflection surfaces can be arranged exactly at the virtual emission point of the second radar antenna. This ensures that the first radar measures the distance to the radar antenna of the second radar and / or the second radar measures the distance to the radar antenna of the first radar as soon as there is no measuring object and no obstacle in the measuring section.

[0027] In an advantageous embodiment of the radar measuring device - the first radar antenna comprises a first transmitting antenna and a first receiving antenna, which are spaced apart from each other by less than a mean radar wavelength of the first radar, wherein the first transmitting antenna is designed to emit a first radar beam lobe, wherein a first dielectric lens is arranged in the beam path of the first radar beam lobe for focusing the first radar beam lobe, and / or - the second radar antenna comprises a second transmitting antenna and a second receiving antenna which are spaced apart from each other by less than a mean radar wavelength of the second radar, wherein the second transmitting antenna is designed to emit a second radar beam lobe, and wherein a second dielectric lens is arranged in the beam path of the second radar beam lobe for concentrating the second radar beam lobe.

[0028] This enables precise measurement of the distance between the radar antennas and the distance between the radar antenna in question and the side surface of the measuring object assigned to it.

[0029] Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. It shows: Fig. 1 a radar measuring device with two radars for measuring the width of a measuring object, which is arranged between the radar antennas of the radars on a roller conveyor, Fig. 2 is a graphical representation of the frequency responses of a first radar signal transmitted by a first radar and a second radar signal transmitted by a second radar, with the time t being plotted on the abscissa and the transmission frequency being plotted on the ordinate, and with the frequency response of the first radar being shown as a solid line and that of the second radar being shown as a dashed line, Fig. 3 a retroreflector (corner cube) at which a radar beam is reflected, which is shown schematically in dashed lines, Fig. 4 the radar measuring device Fig. 1 without measuring object, Fig. 5 a radar measuring device for thickness measurement, with a C-arm, at the ends of which two radars are arranged, and Fig. 6 a radar antenna having a transmitting antenna and a receiving antenna closely adjacent thereto.

[0030] One in Fig. 1 Radar measuring device, designated as a whole by 1, for measuring a dimension D between two spaced-apart, opposite side surfaces 2, 3 of a measuring object 4, has a first radar 5 and a second radar 6.

[0031] For transmitting and receiving a first radar signal, the first radar 5 has a first radar electronics unit 7, which is connected to a first radar antenna 8 via a first radio-frequency line. For transmitting and receiving a second radar signal, the second radar 6 has a second radar electronics unit 9, which is connected to a second radar antenna 10 via a second radio-frequency line. The second radar antenna 10 faces the first radar antenna 8 and is arranged at a distance A from it.

[0032] As in Fig. 1, the measurement object 4 is arranged between the radar antennas such that a first side surface 2 of the measurement object 4 faces the first radar antenna 8 and a second side surface 3 of the measurement object 4 faces the second radar antenna 10. The measurement object 4, which can be a metal plate or a slab, for example, is arranged on a roller conveyor having a plurality of adjacently arranged rollers 11 on which the measurement object 4 rests. During the measurement, the measurement object 4 is moved on the rollers 11 between the first radar antenna 8 and the second radar antenna 10 in a direction of movement indicated by the arrow 12.

[0033] While the measurement object 4 is located between the first radar antenna 8 and the second radar antenna 10, a first FMCW radar signal is sent from the first radar antenna 8 to the first side surface 2 and a second FMCW radar signal is sent from the second radar antenna 10 to the second side surface 3.

[0034] As in Fig. As can be seen in Figure 2, the first radar signal undergoes a first frequency ramp 13 or a first chirp, and the second radar signal undergoes a second frequency ramp 14 or a second chirp. Starting from a first starting frequency f u1 the first frequency ramp 13 increases linearly up to a first upper frequency f o1 After that, the frequency of the first radar signal jumps back to the first start frequency f u1 .

[0035] The second frequency ramp 14 increases linearly from a first starting frequency f u1 up to its second upper frequency f o2After that, the frequency of the second radar signal jumps back to the second start frequency f u2 . As in Fig. As can be seen in Figure 2, there is a constant frequency difference Δf between the frequency of the first radar signal and the frequency of the second radar signal. This difference is chosen to be large enough so that the radars 5 and 6 do not interfere with each other.

[0036] The radar signals reflected at the side surfaces 2, 3 are each received by the radar antenna 8, 10 from which they were emitted, and according to the time-of-flight measurement principle, a first distance signal R1 for the distance between the first radar antenna 8 and the first side surface 2 and a second distance signal R2 for the distance between the second radar antenna 10 and the second side surface 3 are generated.

[0037] Due to the propagation time required by the radar signals to travel from the radar antenna 8, 10 to the associated side surface 2, 3 of the measurement object 4 and from the side surface 2, 3 back to the radar antenna 8, 10, a frequency difference arises between the transmitted and received signals due to the frequency ramps 13, 14. In each radar electronics unit 7, 9, the transmitted and received signals of the respective radar are mixed in a mixer to form an intermediate frequency whose frequency corresponds to the frequency difference. From the two intermediate frequencies of the radars 5, 6, the distance signals R1 and R2 are determined in a manner known per se and stored in a data memory of the respective radar 5, 6 (not shown in detail in the drawing).

[0038] To determine a first distance value for the distance between the first and second radar antennas 8, 10, a first retroreflector 15 is arranged on the second radar antenna 10 such that the radar signal emitted by the first radar antenna 8 is reflected back to the first radar antenna 8 by the first retroreflector 15 when there is no object between the first and second radar antennas 8, 10.

[0039] The first retroreflector 15 has three mutually orthogonal first reflection surfaces 16, 17, 18 made of metal, which are arranged such that the intersection of the planes spanned by the three first reflection surfaces 16, 17, 18 lies at the virtual emission point of the second radar antenna 10. At the intersection of the three planes spanned by the first reflection surfaces 16, 17, 18, the first retroreflector 15 has a first recess 19 for the second radar antenna 10.

[0040] Fig. Figure 3 illustrates in perspective the first retroreflector 5 with the three orthogonal reflection surfaces 16, 17, 18. The orthogonality of the reflection surfaces 16, 17, 18 ensures that every radar beam striking an inner surface of the first retroreflector 5 is reflected back in the same direction. This reflects spherical waves back to their origin.

[0041] Determining the first distance value A 12 is carried out as with the first distance signal R1, but with the difference that the first radar signal does not run from the first radar antenna 8 to the first side surface 2 and then back to the first radar antenna 8, but with the measuring object removed between the first and second radar antennas 8, 10 from the first radar antenna 8 to the first retroreflector 15 and from there back to the first radar antenna 8 ( Fig. 4). The first distance value A 12is stored in the data memory of the first radar 5.

[0042] Similarly, to determine a second distance value A 21 for the distance between the first and second radar antennas 8, 10, a second retroreflector 20 is arranged on the first radar antenna 8 such that the radar signal emitted by the second radar antenna 10 is reflected back to the second radar antenna 10 at the second retroreflector 20 when there is no object between the first and second radar antennas 8, 10.

[0043] The second retroreflector 20 has three mutually orthogonal second reflection surfaces 21, 22 made of metal, only two of which are shown in the drawing. The second reflection surfaces 21, 22 are arranged such that the intersection of the planes spanned by the three second reflection surfaces 21, 22 lies at the virtual emission point of the first radar antenna 8. At the intersection of the three second reflection surfaces 21, 22, the second retroreflector 16 has a second recess 23 for the first radar antenna 8.

[0044] Also when determining the second distance value A 21 The measurement object 4 is located between the radar antennas 8, 10. The second radar signal travels from the second radar antenna 10 to the second retroreflector 20 and from there back to the second radar antenna 10.

[0045] Determining the second distance value A 21is carried out as with the second distance signal R2, but with the difference that the second radar signal does not run from the second radar antenna 10 to the second side surface 3 and then back to the second radar antenna 10, but with the measuring object removed between the first and second radar antennas 8, 10 from the second radar antenna 10 to the second retroreflector 20 and from there back to the second radar antenna 10 ( Fig. 4). The second distance value A 21 is stored in the data memory of the second radar 6.

[0046] The first radar 5 and the second radar 6 are connected to an evaluation device 24, which calculates the distance values ​​A by averaging the first distance value A 12 and the second distance value A 21 the distance A between the first radar antenna 8 and the second radar antenna 10 is determined as follows: A=(A12+A21) / 2

[0047] In the evaluation device 24, the dimension D between the first and second side surfaces 2, 3 of the measuring object 4 is determined from the distance A and the distance signals R1 and R2 as follows: D=A−R1−R2

[0048] Furthermore, in the evaluation device 24, the difference between the first distance value A 12 and the second distance value A 21 The value is determined in absolute terms and compared with a tolerance range. If a difference occurs that lies outside the tolerance range, an error is displayed. Radar system 1 can thus calibrate and monitor itself.

[0049] In order to avoid measurement errors in the event that relative movements occur between the measurement object 4 and the radar antennas 8, 10 during the measurement of the dimension D of the measurement object 4 in the measurement direction, the evaluation device 24 has a trigger output 25, which is connected via a trigger line 26 to a trigger input of the first radar 5 and a trigger input of the second radar 6 for simultaneously performing the runtime measurements of the first and second radars 5, 6. Such relative movements can occur, for example, if the measurement object 4 is exposed to vibrations and / or shocks during the measurement that have a component pointing in the measurement direction. When a trigger occurs, the frequency ramps 13, 14 of the radar signals are run through simultaneously, and the measurements of the first and second distance signals R1 and R2 are performed synchronously. The measurements of the first and second distance values ​​A12 , A 21 are also synchronized via trigger output 25.

[0050] Fig. Figure 5 shows an embodiment of the radar measuring device 1' according to the invention for measuring the thickness of a measurement object 4 arranged on a roller conveyor 27. The measurement object 4 is designed as a metal plate having a first side surface 2 and a second side surface 3 opposite and facing away from the first side surface 3, which is arranged substantially parallel to the first side surface 3.

[0051] The radar measuring device 1' has a C-shaped support member comprising an upper boom 28, a lower boom 29, and a connecting support 30. A first radar 5 is attached to the upper boom 28, and a second radar 6 is attached to the lower boom 29. The first radar 5 has a first radar antenna 8, and the second radar has a second radar antenna 10, which faces the first radar antenna 8 and is arranged at a distance A from it.

[0052] A first retroreflector 15 is arranged on the second radar antenna 10, which has three mutually orthogonal first reflection surfaces 16, 17, of which Fig. 5, only two are visible. The intersection point of the planes spanned by the first three reflection surfaces 16, 17 lies at the virtual emission point of the second radar antenna 10.

[0053] In a corresponding manner, a second retroreflector 20 is arranged on the first radar antenna 8, which has three mutually orthogonal second reflection surfaces 21, 22, of which Fig. 5, only two are visible. The intersection point of the planes spanned by the three second reflection surfaces 21, 22 lies at the virtual emission point of the first radar antenna 8.

[0054] If no object is located between the radar antennas 8, 10, a first distance value for the distance between the first radar antenna 8 and the first retroreflector 15 is determined using the first radar 5. A second distance value for the distance between the second radar antenna 10 and the second retroreflector 20 is determined using the second radar 6. The distance A between the first and second radar antennas 8, 10 is determined from the arithmetic mean of the two distance values.

[0055] When the measurement object 4 is arranged between the first and second radar antennas 8, 10, a first distance signal R1 for the distance between the first radar antenna 8 and the first side surface 2 of the measurement object 4 is measured using the first radar 5. A second distance signal R2 for the distance between the second radar antenna 10 and the second side surface 3 of the measurement object 4 is measured using the second radar 6. The thickness D of the measurement object 4 is determined by equation 1 from the distance A and the distance signals R1, R2.

[0056] As in Fig. As can be seen in Figure 6, the first and / or second radar antenna 8, 10 can comprise a transmitting antenna Tx and a receiving antenna Rx, which are arranged closely adjacent to one another and are designed as dipole antennas. These are located in a semiconductor chip housing 31 with an edge length c = 2 λ, where λ is the mean wavelength of the radar frequency of the respective radar 4, 5.

[0057] The length b of the dipole antennas is derived from the known calculations for dipole antennas. The distance a between the receiving antenna Tx and the transmitting antenna Rx has a value between 0.5 λ and 1.5 λ. In a specific embodiment, the wavelength λ is 2.5 mm. As a result, the transmitting and receiving antennas Tx and Rx are so closely spaced that, in a first approximation for the calculation, they are located in the isocenter of the first and second radars 5 and 6. Fig. 1. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] EP 3 628 416 B1 [0002, 0003]

Claims

[1] Radar method for measuring a dimension (D) between two spaced-apart, opposite side surfaces (2, 3) of a measurement object (4), wherein at least a first radar 5 with a first radar antenna (8) and a second radar (6) with a second radar antenna (10) are provided, wherein the first and second radar antennas (8, 10) are arranged facing each other and at a distance from each other, wherein the measurement object (4) is arranged between the radar antennas (8, 10) in such a way that a first side surface (2) of the measurement object (4) faces the first radar antenna (8) and a second side surface (3) of the measurement object (4) faces the second radar antenna (10), wherein a first radar signal is transmitted from the first radar antenna (8) to the first side surface (2) and a second radar signal is transmitted from the second radar antenna (10) to the second side surface (3), wherein the signals transmitted on the side surfaces (2,3) reflected radar signals from the respective radar antennas (8, 10) are received and, according to the principle of time-of-flight measurement, a first distance signal (R1) for the distance between the first radar antenna (8) and the first side surface (2) and a second distance signal (R2) for the distance between the second radar antenna (10) and the second side surface (3) are generated, and wherein the dimension of the measurement object 4 between the side surfaces (2, 3) is determined from the distance (A) between the radar antennas (8, 10) and the first and second distance signals (R1, R2), characterized bythat a first retroreflector (15) is provided for the first radar signal, which has three mutually orthogonal first reflection surfaces (16, 17, 18), that the first retroreflector (15) is arranged on the second radar antenna (10) in such a way that the intersection point of the planes spanned by the three first reflection surfaces (16, 17, 18) lies in the virtual emission point of the second radar antenna (10) or has an offset to this emission point which is at most 20 times the mean wavelength of the first radar signal, that when the measurement object (4) is removed between the radar antennas (8, 10), the first radar signal is sent to the first retroreflector (15) and reflected from there back to the first radar antenna (8) in order to determine at least a first distance value A according to the principle of time-of-flight measurement 12 for the distance between the radar antennas (8, 10) and from which at least one first distance value (A 12) and the first and second distance signals (R1, R2), the dimension (D) which the measuring object (4) has between the side surfaces (2, 3) is determined. [2] Radar method according to claim 1, characterized bythat a second retroreflector (20) is provided for the second radar signal, which second retroreflector has three mutually orthogonal second reflection surfaces (21, 22), that the second retroreflector (20) is arranged on the first radar antenna (8) in such a way that the intersection point of the planes spanned by the three second reflection surfaces (21, 22) lies in the virtual emission point of the first radar antenna (8) or has an offset to this emission point which is at most 20 times the mean wavelength of the second radar signal, that when the measurement object (4) is removed between the radar antennas (8, 10), the second radar signal is sent to the second retroreflector (20) and is reflected from there back to the second radar antenna (10) in order to determine at least a second distance value (A 21 ) to detect the distance between the radar antennas (8, 10) and from the at least one first and second distance value (A 12 , A21 ) and the first and second distance signals (R1, R2) to determine the dimension (D) which the measuring object (4) has between the side surfaces (2, 3). [3] Radar method according to claim 2, characterized by that the runtime measurement for generating the first distance signal (R1) and the runtime measurement for generating the second distance signal (R2) are carried out simultaneously. [4] Radar method according to claim 2 or 3, characterized by that from the first distance value (A 12 ) and the second distance value (A 21 ) the arithmetic mean is formed, and that the dimension (D) which the measuring object (4) has between the side surfaces (3, 4) is determined from the arithmetic mean and the first and second distance signals (R1, R2). [5] Radar method according to one of claims 2 to 4, characterized by that the difference between the first distance value (A 12) and the second distance value (A 21 ) is determined in terms of amount and compared with a tolerance value or a tolerance value range, and that if a difference occurs which is greater than the tolerance value or lies outside the tolerance value range, an error is indicated. [6] Radar method according to one of claims 1 to 5, characterized by that the frequency of the first radar signal differs from the frequency of the second radar signal or that the frequency range of the first radar signal differs from the frequency range of the second radar signal. [7] Radar method according to one of claims 1 to 6, characterized by that the first radar (5) and the second radar (6) each operate according to the FMCW principle. [8] Radar method according to claims 2 and 7, characterized by that during the runtime measurement - the radar frequency of the first radar signal, starting from a first start frequency, passes through a first frequency ramp (13), and - the radar frequency of the second radar signal, starting from a second starting frequency, passes through a second frequency ramp (14), - that the first radar signal emitted by the first radar antenna (8) and the reflected first radar signal received by the antenna are mixed to generate a first intermediate frequency, - that the second radar signal emitted by the second radar antenna (10) and the reflected second radar signal received by the latter are mixed to generate a second intermediate frequency, - and that the frequency difference (Δf) between the first and the second starting frequency is greater in magnitude than the first intermediate frequency and greater in magnitude than the second intermediate frequency when the measurement object (4) is removed between the radar antennas (8, 10). [9] Radar measuring device (1, 1') for measuring a dimension (D) between two spaced-apart, opposite side surfaces (2, 3) of a measuring object (4), - wherein the radar measuring device (1, 1') comprises a first radar (5) with a first radar electronics (7) and a first radar antenna (8) connected thereto for transmitting and receiving a first radar signal, - wherein the radar measuring device (1, 1') comprises a second radar (6) with a second radar electronics unit (9) and a second radar antenna (10) connected thereto for transmitting and receiving a second radar signal, wherein the first and second radar antennas (8, 10) are arranged facing each other and at a distance (A) from each other, wherein the radar electronics units (7, 9) are designed such that when the measuring object (4) is arranged between the radar antennas (8, 10) and faces a first side surface (2) of the first radar antenna (8) and a second side surface (3) of the second radar antenna (10), according to the principle of time-of-flight measurement - a first distance signal (R1) for the distance between the first radar antenna (8) and the first side surface (2) of the measuring object (4) and - a second distance signal (R2) for the distance between the second radar antenna (10) and the second side surface (3) of the measurement object (4) can be generated, and wherein the radar electronics (7, 9) are connected to an evaluation device (24) which is designed to determine the dimension (D) that the measurement object (4) has between the side surfaces (2, 3) from the distance (A) between the radar antennas (8, 10) and the first and second distance signals (R1, R2), characterized bythat - when the measurement object (4) is located between the first radar antenna (8) and the second radar antenna (10) - a first retroreflector (15) is arranged on the second radar antenna (10) for reflecting the radar signal emitted by the first radar antenna (8) back to the first radar antenna (8), and that the first retroreflector (15) has three mutually orthogonal first reflection surfaces (16, 17, 18) which are arranged such that the intersection point of the planes spanned by the three first reflection surfaces lies in the virtual emission point of the second radar antenna or has a predetermined offset from the emission point which is a maximum of 20 times the wavelength of the radar signal of the first radar (5). [10] Radar measuring device (1, 1') according to claim 9, characterized bythat - when the measurement object (4) is located between the radar antennas (8, 10) - a second retroreflector (20) is arranged on the first radar antenna (8) for reflecting the radar signal emitted by the second radar antenna (10) back to the second radar antenna (10), and that the second retroreflector (20) has three mutually orthogonal second reflection surfaces (21, 22) which are arranged such that the intersection point of the planes spanned by the three second reflection surfaces (21, 22) lies in the virtual emission point of the first radar antenna (8) or has a predetermined offset from the emission point which is at most 20 times the wavelength of the radar signal of the second radar (5). [11] Radar measuring device (1, 1') according to claim 9 to or 10, characterized bythat the first retroreflector (15) has a first recess (19) for the second radar antenna (10) at the intersection point of the three first reflection surfaces (16, 17, 18), and / or that the second retroreflector (20) has a second recess (23) for the first radar antenna (8) at the intersection point of the three second reflection surfaces (21, 22). [12] Radar measuring device (1, 1') according to one of claims 9 to 11, characterized by that the evaluation device (24) has a trigger output (25) which is connected to trigger inputs of the first and second radars (5, 6) via a trigger line (26) for simultaneously carrying out the transit time measurements of the first and second radars (5, 6). [13] Radar measuring device (1, 1') according to one of claims 9 to 12, characterized by , - that the first radar antenna (8) comprises a first transmitting antenna (Tx) and a first receiving antenna (Rx), which are spaced apart from each other by less than a mean radar wavelength of the first radar (5), that the first transmitting antenna (Tx) is designed to emit a first radar beam lobe, that a first dielectric lens is arranged in the beam path of the first radar beam lobe to focus the first radar beam lobe, and / or - that the second radar antenna (10) comprises a second transmitting antenna and a second receiving antenna which are spaced apart from each other by less than a mean radar wavelength of the second radar (6), that the second transmitting antenna is designed to emit a second radar beam lobe, and that a second dielectric lens is arranged in the beam path of the second radar beam lobe to focus the second radar beam lobe. [14] Radar measuring device according to one of claims 9 to 13, characterized bythat the first radar and / or the second radar is designed as an FMCW radar. [15] Radar measuring device (1, 1') according to claim 14, characterized by that the radar electronics (7) of the first radar (5) are integrated into a first semiconductor chip and the radar electronics (9) of the second radar (6) are integrated into a second semiconductor chip, and that these semiconductor chips are designed differently to reduce mutual interference of the radar electronics (7, 9).

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