DEVICE AND METHOD FOR DETERMINING THE LAYER THICKNESS OF A COATING OF A ROTATING MEASURING OBJECT

Abstract

A device and a method for the non-contact measurement of a rotating object (50) are provided. During the rotation of the object (50), the thickness (d) of a coating (51) of the object (50) is determined, taking into account the current rotational position of the object (50), by identifying a circumferential region (52) of the object (50) that is positioned essentially perpendicular to the axis of a measuring beam (S). By continuously or stepwise rotating the object (50), a complete profile of the thickness (d) of the object (50) can be obtained in this way.

Description

Technical field

[0001] The present invention relates generally to the testing and measurement of a test object. More specifically, the present invention relates to a device and a method for the interferometric determination of the layer thickness of a sheathing of a rotating test object, such as a cable section. background

[0002] In the electrical and electronics industry, wires are frequently used to transmit electricity and / or signals. For reliable and safe transmission of electricity and / or signals, the wires are typically insulated from the environment with a sheath. A wire with an insulating sheath is also called a cable. Wires can be made of metals such as iron, copper, brass, aluminum, silver, gold, or stainless steel and can have various cross-sectional shapes (round, rectangular, etc.). Insulating sheaths can consist of coatings made of plastics such as PEEK (polyetheretherketone) or PAI (polyamide-imide), lacquers, or powder coatings.

[0003] Cables are used, for example, in electric motors (hairpins, coils, connectors, etc.). For the reliable and safe operation of these electric motors, the dimensional accuracy of the insulation is crucial. Regardless of the wire's shape, the coating should, for instance, have a minimum thickness that does not cause damage and maintains consistent electrical properties. Potential defects that could affect reliable wire insulation include variations in coating thickness around the circumference (edge ​​drift, dogbone effect) or longitudinal variations in coating thickness (in the wire direction). These variations can be caused by fluctuations in the coating or drying process, such as die wear, uneven material application, or surface contamination.Other potential defects that could affect the reliable insulation of the wire include air inclusions in the insulation, microcracks, or delamination of the insulation from the wire. Furthermore, the dimensional accuracy of the coating is also of great importance for the automated processing of the wire in winding machines, bending machines, or other coating systems.

[0004] To verify whether a cable is reliably insulated and suitable for further processing, the thickness of the cable's insulating sheath is determined. One currently used technology for measuring layer thickness is eddy current measurement, which offers high accuracy but low spatial resolution. Another currently used technology is radiometry, which is complex and expensive due to the handling of radioactive material. Cross-sectional analysis is also used to measure layer thickness, but this method is time-consuming and poses health and environmental hazards due to the use of epoxy resin.

[0005] For further processing of a cable, it may be necessary to remove sections of the insulation and check the dimensional accuracy of the underlying wire. Insulation removal is required, for example, if the wire is to be welded, soldered, or mechanically contacted. The insulation can be removed mechanically by milling or peeling, or by pulsed lasers. Complete removal of the insulation is crucial for the quality of the contact. Any remaining insulation material can cause voids, fissures (volcanoes), porosity, or inclusions during soldering or welding due to vaporization.

[0006] Devices and methods in this technical field are described in the publications US 2007 / 0 146 691 A1, US 2011 / 0 128 552 A1 and WO 2017 / 101 906 A1.

[0007] The present invention is based on the technical problem of providing an improved measuring system and an improved measuring method. Description of the invention

[0008] According to a first aspect, the technical problem underlying the invention is solved by a device having the features of claim 1.

[0009] According to a second aspect, the technical problem underlying the invention is solved by a method with the features of claim 15.

[0010] The invention is based on the concept of measuring an object (the object being measured) without contact using a measuring beam over a measuring range extending along the longitudinal axis of the object, while simultaneously rotating it automatically about its longitudinal axis. The object being measured could, for example, be a section of cable that is checked for dimensional accuracy before being processed into components for the electrical and electronics industry, such as coils in electric motors. The automatic rotation of the object allows it to be measured along the measuring range over a section of its circumference or its entire circumference.The invention enables fast and highly accurate measurement of the object being measured and the determination of parameters such as the dimensional accuracy of the insulation of a cable section and / or the surface quality of stripped surfaces of a cable section.

[0011] The control unit is designed to control the radiation source and the drive unit in such a way that the rotatably mounted measuring object is irradiated with the measuring beam of the radiation source in the measuring range and is automatically rotated around its longitudinal axis during irradiation.

[0012] The control of the radiation source and the drive unit by the control unit allows a high degree of automation in the execution of the measurement, since, for example, manual rotation of the object being measured is not necessary during the measurement process.

[0013] By simultaneously rotating the object being measured and illuminating it with the measuring beam, reliable measurements can be obtained even of the object's edges, such as the corner radii of rectangular cable sections. If, for example, the four sides of a rectangular cable section are measured sequentially (frontally) while stationary (with the cable section rotated 90° between each measurement and not illuminated), it can be technically challenging to accurately detect and measure the corner radii. However, by simultaneously rotating and illuminating the object, it is possible to rotate the corner radii into the measuring beam's field of view and obtain reliable measurements of the cable section's corner radii.

[0014] Since the measurement is based on the reflection of rays at the surface of the object being measured, or at the interface between the core of the object and its outer layer, and since the rotation of the object constantly changes the angular position, particularly of the layer thickness to be measured, relative to the sensor, leading to changes in the reflection behavior, a reliable measurement is only possible if the beam strikes the object essentially perpendicularly. If the cross-section of the object is known, and given the angular position of the object relative to the sensor, it is possible to calculate the angle that the surface of the object currently forms with respect to the sensor, or which part of the object's circumference forms an angle of essentially 90° with the sensor.Using suitable evaluation sensors, particularly the control unit with integrated processing unit, the areas around the object being measured can be selected for which reflections are to be evaluated to determine the layer thickness. Additionally, the intensity of the detected reflections can be used to filter the acquired data, as the intensity of the reflected radiation correlates with the angle of incidence. In other words, the intensity of the detected radiation is highest at an angle of approximately 90° and decreases at smaller and larger angles. This further improves the accuracy of the layer thickness measurement.

[0015] The control unit can be designed to control the radiation source and the drive unit in such a way that the rotatably mounted object being irradiated with the measuring beam of the radiation source in the measuring range and being continuously rotated, preferably at a constant speed, during the irradiation and / or being rotated at least once completely around its longitudinal axis during the irradiation.

[0016] Continuous rotation means that there are no interruptions (no standstill) during the process. Continuous rotation, especially rotation at a constant speed, has the advantage that precise measurements are possible even in areas such as the corner radii of rectangular cable sections. Rotating the object at least once completely around its longitudinal axis allows for measurements along the entire circumference of the object within the measurement range. This enables measurements of, for example, coating thickness across the entire circumference. Measuring coated round wire is also possible in this way.

[0017] The measuring range, over which the object is irradiated along its longitudinal axis, extends, for example, from 0.1 to 5 cm. The radiation source can be equipped with an optical system that allows the measuring beam to be deflected so that it can irradiate the entire measuring range. The radiation source itself then does not need to be moved.

[0018] Using a sensor, measurement data from points distributed along the length and circumference of the object are collected by rotating the object being measured and by moving the measuring beam in the longitudinal direction of the object being measured.

[0019] The radiation source and the sensor can, in particular, be part of an interferometric measuring system. Interferometric measuring systems utilize the effects that occur when two or more beams from the same radiation source with different path lengths are superimposed. For example, the Flying Spot from Precitec GmbH & Co. KG, as it was available at the filing date of the present invention, can be used as a radiation source and sensor.

[0020] The radiation source and the sensor can be designed in such a way that a highly accurate scan of the surface of the object being measured can be created, for example with a resolution in the range of 1 to 10 µm.

[0021] The device comprises a first support and a second support spaced apart from the first, both rotatably mounted about a common axis of rotation. The first and second supports allow the object being measured to be held securely in place so that it rotates about its longitudinal axis during measurement and does not slip, thus enabling highly accurate measurement results.

[0022] According to an exemplary embodiment, the first and / or the second holder has clamping jaws. The clamping jaws are movably arranged and designed to move towards each other in such a way as to clamp the object being measured. At least one clamping jaw can be pre-tensioned by a spring element such that the clamping jaws move towards each other.

[0023] Clamping jaws provide a fixture for the object being measured, allowing for quick and easy clamping and unclamping. Different object geometries and dimensions may require different fixtures, which can be accommodated using suitable workpiece-specific clamping jaws. For example, the clamping jaws can be designed to securely clamp an object with a rectangular cross-section. Alternatively, they can be designed to securely clamp an object with a round cross-section. Clamping jaws allow for the object to be clamped without additional preparatory steps such as grinding or embedding it in epoxy resin or similar materials, while simultaneously providing a sufficiently accurate fixture for measurement.

[0024] According to an exemplary embodiment, the first and / or the second holder, in addition to the clamping jaws described above, has a rotatably mounted outer clamping ring, which is in drive connection with the drive unit, and an inner clamping ring, which is arranged coaxially and rotatably with respect to the outer clamping ring. The outer clamping ring and the inner clamping ring are coupled to the clamping jaws in such a way that the clamping jaws move away from each other in a first direction and towards each other in a second direction when the outer clamping ring is rotated relative to the inner clamping ring.

[0025] With the embodiment described here, it is possible to open the clamping jaws by rotating the outer clamping ring relative to the inner clamping ring. By rotating the outer clamping ring relative to the inner clamping ring in a first direction, the fixture can be opened and the workpiece inserted. By rotating the outer clamping ring relative to the inner clamping ring in a second direction, opposite to the first, the fixture can be closed again. This relative rotation of the outer and inner clamping rings represents a practical and easily repeatable (automatable) method for opening and closing the fixture (clamping jaws) of the first and second holders, respectively.

[0026] The rotation of the outer clamping ring relative to the inner clamping ring can be achieved by the inner clamping ring having a projection extending axially in the direction of the inner clamping ring, such as a pin or similar element. Furthermore, the device includes a locking mechanism designed to allow the projection of the inner clamping ring to pass in a first direction of rotation but to prevent it from passing in a second direction of rotation. The locking mechanism can, for example, be designed like a door catch and include a wedge element beveled on one side, which is slidably mounted and can be displaced by the projection of the inner clamping ring, which presses against the bevel of the wedge element, thus clearing the path for the projection of the inner clamping ring.The device can be designed such that the inner clamping ring is coupled to the outer clamping ring in such a way that when the outer clamping ring, which is connected to the drive unit, rotates, the inner clamping ring also rotates. The spring element exerts a force on the inner clamping ring, causing it to rotate together with the outer clamping ring. The locking device can stop the rotation of only the inner clamping ring in one of the two directions, thereby preventing the outer clamping ring from rotating relative to the inner clamping ring. By changing the drive direction of the outer clamping ring, the receptacle formed by the clamping jaws can be opened and closed.

[0027] According to an exemplary embodiment, the drive unit comprises a motor, such as an electric motor, and at least one belt. The motor is connected to the first and / or second rotatably mounted bracket via the at least one belt.

[0028] The drive unit can be designed to rotate the first and / or the second rotatably mounted bracket in both directions of rotation.

[0029] This allows the object being measured to be rotated in either the first or second direction during irradiation. Furthermore, in conjunction with the embodiment described above, in which the first and second holders each have clamping jaws, an outer clamping ring, an inner clamping ring, a projection, and a locking device, this enables the clamping jaws to open by rotating the outer clamping ring in the first direction and close by rotating it in the second direction. The drive unit thus has a dual function: firstly, it rotates the object being measured during the measurement process, and secondly, it opens and closes the clamping jaws forming the receptacle of the first and second holders.With this embodiment, a high degree of automation can be achieved in carrying out the measurement, since the opening and closing of the recording is possible using the control unit, which controls the drive unit.

[0030] According to an exemplary embodiment, the first and second supports for changing their distance to the radiation source are arranged on a movable slide.

[0031] The first and second supports are adjustable, allowing the object being measured to be conveniently secured in a first position, away from the radiation source. By moving them to a second position, closer to the radiation source, the first and second supports can be positioned at the correct distance from the radiation source (focus area) for measurement. The device may include a spring element that pushes or preloads the movable carriage towards the radiation source.

[0032] According to an exemplary embodiment, the device further comprises a stop with a stop surface designed to allow the object being measured to slide along the stop surface while rotating about its longitudinal axis during irradiation.

[0033] The stop surface can be positioned so that it projects into the area between the first and second supports, allowing the object being measured, held by the first and second supports, to slide (rotate) past the stop surface as it rotates during irradiation. By striking the object against the stop surface, optimal positioning of the object relative to the radiation source (distance between the surface of the object and the radiation source) can be ensured. Multiple stops, each with a stop surface, can be provided, distributed along the longitudinal axis of the object. This ensures that the object is guided along its length by the stop surfaces, preventing bulging. For example, two stops can be arranged so that the measuring area lies between them.In a device where it is possible to move the first and second supports into a second position shifted towards the radiation source, the second position can be determined by pressing the first and second supports towards the radiation source and against at least one stop surface by a spring force.

[0034] According to an exemplary embodiment, the control unit of the device has a computing unit which is designed to determine the course of measured quantities such as layer thickness or surface condition for the irradiated area of ​​the measured object from the rays reflected by the object being measured and detected by the sensor.

[0035] It was observed that with the device using the mounts described above, or when the object is shifted towards the sensor so that its surface rests against the stop, the object's center point can wobble. This is a consequence of a fluctuating spring force during rotation, which, in particular, preloads the carriage against the stop. As a result, during measurement, the object's center point shifts not only in a direction perpendicular to the stop, as expected, but also in a direction parallel to it. The center point can, for example, describe an epicycloid, which, as is known, can be defined by two parameters. If the parameters of this epicycloid are known, the calculated position of the surface for which a measurement is taken can be corrected for the deviation caused by the wobble.

[0036] The parameters of the epicycloid can be determined by measuring a calibration part whose layer thickness profile has been previously determined using another measurement method, such as micrographs, eddy current analysis, or similar techniques. When this calibration part is then measured in the device disclosed herein, suitable measurement software can determine the deviation from the expected measured value for each position and thus ascertain the parameters of the epicycloid. For subsequent measurements, the measurement position on the circumference of the object being measured is then corrected accordingly to improve the measurement accuracy of the device. It is understood that, depending on the precise design of the device, particularly the supports and the unit for preloading the carriage against the stop surface, the center point of the object being measured does not necessarily have to describe an epicycloid, but may also follow another suitable curve or positional shift.However, even in this case, a relationship between, in particular, the angular position or rotational position of the object being measured and the displacement of its center point, especially in a direction parallel to the stop surface, can be determined by first measuring a calibration part using a different method and then measuring the calibration part using the device disclosed herein. For example, corresponding curves can be approximated or otherwise described based on a plurality of recorded measurements and associated deviations. If the same discrete measurement positions are always used, it is sufficient to determine the displacement for each of these measurement positions using the calibration part. Brief description of the drawings

[0037] Exemplary embodiments of the present invention are described and explained in more detail below with reference to the accompanying drawings. Fig. Figure 1 shows an exemplary embodiment of the invention in a perspective view from an oblique angle above. Fig. Figure 2 shows the first and second brackets 15, 16 and the drive unit 20 of the in Fig. 1 Exemplary embodiment of the device 1 shown in perspective view from obliquely above. Fig. Figure 3 shows the first and second brackets 15, 16 and the drive unit 20 of the in Fig. 1 Exemplary embodiment shown in a side view. Fig. 4 shows the one in the Fig. 1 Exemplary embodiment shown in simplified representation in a top view at a first position. Fig. 5 shows the one in the Fig. 1 Exemplary embodiment shown in simplified representation in a top view at a second position. Fig. 6 shows the one in the Fig. 1 Exemplary second bracket 16 shown in an enlarged side view in closed position. Fig. 7 shows the one in the Fig. 6 Second bracket 16 shown in open position. Fig. Figure 8 shows individual components of the assembly to illustrate the coupling of the outer clamping ring with the discs. Fig. 6 and Fig. 7 shown second bracket 16. Fig. Figure 9 shows a schematic view to illustrate a device or method for the interferometric determination of the layer thickness of a coating of a rotating measuring object. Fig. Figure 10 shows an enlarged schematic representation of a cross-section of the object to be measured. Fig. Figure 11 schematically shows a change in the position of the object to be measured in relation to the stop surface 81 when the object is rotated. Fig. Figure 12 schematically shows a relationship between the intensities of measured values ​​captured by the sensor and the angular position of the object being measured relative to the sensor. Fig. Figure 13 illustrates a wobbling motion of the center of the measured object during a complete rotation of the same. Fig. Figure 14 schematically shows an example of a curve traversed by the center of the object being measured during a complete rotation of the same. Detailed description of exemplary embodiments of the invention

[0038] Fig. Figure 1 shows an exemplary embodiment of the invention in a perspective view from an oblique angle above. The device 1 is positioned on a work surface 3.

[0039] In the front left area of ​​the worktop 3, a first bracket 15 and a second bracket 16, spaced apart from the first bracket 15, are shown. The first and second brackets 15, 16 are rotatably mounted on the worktop 3. The first and second brackets 15, 16 are designed to allow a measuring object 50 to be attached to them. The measuring object 50 (see Fig. 4) In the fixed state, it extends between the first and second brackets 15, 16. A drive unit 20 is arranged next to the first and second brackets 15, 16. The drive unit 20 has belts that are coupled to the first and second brackets 15, 16 to drive the respective brackets. The drive unit 20 and the first and second brackets 15, 16 are arranged on guide rails 71 via a carriage.

[0040] In the front right area of ​​the work surface 3, a radiation source 10 and a sensor 11 are arranged. The radiation source 10 and the sensor 11 are housed in a common unit. This unit is also arranged on the work surface 3 and is oriented such that a measuring beam S, which can be emitted by the radiation source 10, shines in the direction of the area located between the first and second supports 15, 16. The measuring beam S can thus irradiate the object 50, which is secured by the first and second supports 15, 16. By sliding it on the guide rails 71, the drive unit 20 as well as the first and second supports 15, 16 can be moved towards and away from the radiation source 10 and the sensor 11.

[0041] A control unit 30 is arranged next to the radiation source 10 and the sensor 11. The control unit is designed to control the radiation source 10 and the drive unit 20. Signal and / or data transmission between the control unit 30, the radiation source 10, and the drive unit 20 can be wireless or wired. Integrated with the control unit 30 is a processing unit 40, which is designed to calculate the progression of measured quantities, such as a layer thickness d (see [reference]), from data transmitted by the sensor 11. Fig. 10) or a surface finish for the irradiated area of ​​the object being measured 50.

[0042] Fig. Figure 2 shows the first and second brackets 15, 16 and the drive unit 20 of the in Fig. Figure 1 shows an exemplary embodiment of the device 1 in a perspective view from an oblique angle above. The drive unit 20 comprises a motor 22 and two belts 21. One of the two belts 21 is connected to the motor 22 and the first support 15 for driving. The other of the two belts 21 is connected to the motor 22 and the second support 16 for driving. The drive unit 20, as well as the first and second supports 15 and 16, are each arranged on two guide rails 71 via a slide 70 such that they move in the direction of the direction shown in the Fig. The guide rails 71, indicated by the arrow 2, can be moved back and forth along the guide rail. The guide rails 71 are mounted on a base plate 85. The base plate 85, in turn, is mounted on the worktop 3 (see Figure 2). Fig. 1) attached. Stops 80 are firmly attached to the base plate 3. One stop 80 is in Fig. 2 is concealed by the bracket 16 and therefore not visible. The stop 80 has a stop surface 81. The stop surface 81 is arranged such that it projects into the area between the first and the second bracket.

[0043] Fig. Figure 3 shows the first and second brackets 15, 16 and the drive unit 20 of the in Fig. Figure 1 shows an exemplary embodiment in a side view. The drive unit 20 and the first and second supports 15, 16 are slidably arranged on two guide rails 71 via the carriage 70. The guide rails 71 are mounted on a base plate 85. The second support 16 has a rotatably mounted outer clamping ring 62. The rotatably mounted outer clamping ring 62 is connected to the motor 22 via a belt 21. The second support 16 also has an inner clamping ring 63. The inner clamping ring 63 is arranged coaxially and rotatably with respect to the outer clamping ring 62. The second support 16 also has clamping jaws 61 and spring elements 64. The clamping jaws 61 are movably arranged and designed to move towards each other so that they clamp the measuring object 50 between them.By rotating the outer clamping ring 62 with the inner clamping ring 63 locked, the clamping jaws 61 move away from or towards the axis of rotation D of the first and second holders. The spring elements 64 are arranged such that they pre-tension the clamping jaws into the closed position. The in the . Fig. The three clamping jaws 61 shown are designed for a measuring object 50 with a substantially rectangular cross-section. The outer clamping ring 62 and the inner clamping ring 63 are coupled to the clamping jaws 61 such that the clamping jaws 61 move away from each other (open) in a first direction and towards each other (close) in a second direction when the outer clamping ring 62 is rotated relative to the inner clamping ring 63. More precisely, the clamping jaws 61 open when the outer clamping ring 62 rotates counterclockwise while the inner clamping ring 63 is stationary. The clamping jaws 61 close when the outer clamping ring 62 rotates clockwise while the inner clamping ring 63 is stationary.

[0044] The one in Fig. The exemplary device 1 shown in Figure 3 also has a projection 65 and a locking device 66. The projection 65 is arranged on the inner clamping ring 63 and extends forward in the direction of rotation of the inner clamping ring in the opposite direction to the first support 15 (forward out of the plane of the drawing). The locking device 66 is designed such that it allows the projection 65 of the inner clamping ring 63 to pass in a first direction of rotation of the inner clamping ring 63 and stops it in a second direction of rotation of the inner clamping ring 63. In this way, the inner clamping ring 63 can be held in place by the locking device 66 when the belt 21 rotates the outer clamping ring 62 counterclockwise. This causes the outer clamping ring 62 to rotate relative to the inner clamping ring 63, and the clamping jaws 61 open.When the belt 21 rotates the outer tension ring 62 clockwise, the locking device 66 will be displaced by the projection 65 of the inner tension ring 63 such that it allows the projection 65 to pass.

[0045] Fig. 4 shows the one in the Fig. Figure 1 shows an exemplary embodiment in a simplified top view at a first position. Additionally, the Fig. 4 a measuring object 50, which is secured by the first and second supports 15, 16. The drive unit (motor 22 and belt 21), the first and second supports 15, 16, and the locking devices 66 are slidably arranged on the guide rails 71. The guide rails 71 are arranged on a base plate 85. On the guide rails 71, the aforementioned components can be moved towards and away from the radiation source 10. In the Fig. In the first position shown in Figure 4, the aforementioned components are in a state moved away from the radiation source 10. It can be seen that the projection 65 rests on the locking device 66. The clamping jaws 61 are in the open position. Two stops 80 are arranged on the right side of the base plate 85. Each stop 80 has a stop surface 81. The stop surface is directed towards the measuring object 50, which is clamped by the first and second supports 15, 16.

[0046] Fig. 5 shows the one in the Fig. 1 Exemplary embodiment shown in simplified representation in a top view at a second position. In the Fig. In the second position shown in Figure 5, the drive unit (motor 22 and belt 21), the first and second supports 15, 16, and the locking devices 66 are in a state moving towards the radiation source 10. It can be seen that the projection 65 is not resting on the locking device 66. The clamping jaws 61 are in the closed position. The object being measured 50 is in contact with the stop surfaces 81 of the two stops 80 arranged on the right side of the base plate 85.

[0047] Fig. Figure 6 shows the second holder 16 in a side view. The second holder 16 has an inner clamping ring 63 and an outer clamping ring 62. The inner clamping ring 63 is arranged coaxially and rotatably with respect to the outer clamping ring 62. The second holder 16 also has four clamping jaws 61, which are designed so that the object to be measured can be clamped between them. Two clamping jaws are rotatably connected at one end to a first disk 67 and at the other end to a second disk 67 such that rotation of the first and second disks 67 causes the two clamping jaws 61 to move towards or away from each other.Two further clamping jaws are rotatably connected at one end to a third disc 67 and at the other end to a fourth disc 67 such that rotation of the third and fourth discs 67 causes the two clamping jaws 61 to move towards or away from each other. The four discs are connected to the inner clamping ring 63, being evenly distributed around the circumference of the inner clamping ring 63. The four discs 67 are each rotatably connected to the inner clamping ring 63 and coupled to the outer clamping ring 62 via a pin-and-groove connection such that a relative rotation of the outer clamping ring 62 with respect to the inner clamping ring 63 causes the four discs 67 to rotate about their axis of rotation, thereby moving the clamping jaws 61 attached to the discs 67 towards or away from each other.Spring elements 64 (coil springs) are connected to the inner clamping ring 63 and the clamping jaws 61 such that they pre-tension the clamping jaws 61 into the closed position. The inner clamping ring 63 is prevented from rotating counterclockwise by the projection 65, which abuts the locking device 66 (catch). In the . Fig. 6 the clamping jaws 61 are in the closed position.

[0048] Fig. 7 shows the one in the Fig. 6. The second bracket 16 shown is in the open position. As in the Fig. As can be seen in Figure 7, the position of the inner clamping ring 63 is unchanged, but the washers 67 and the outer clamping ring 62 have changed compared to the Fig. 6 turned counterclockwise. This opened the clamping jaws 61.

[0049] Fig. Figure 8 shows individual components of the assembly to illustrate the coupling of the outer clamping ring 62 with the disks 67. Fig. 6 and Fig. The second bracket 16 shown in Figure 7 is connected to two clamping jaws 61. Each jaw is rotatably connected at one end to a first disc 67 and at the other end to a second disc 67 such that rotation of the first and second discs 67 causes the two clamping jaws 61 to move towards or away from each other. The first and second discs 67 are each attached to the inner clamping ring 63 (not shown) such that they are rotatably mounted about their axis of rotation 75. The first and second discs 67 are coupled to the outer clamping ring 62 (only partially shown) via a pin 68 that projects into a groove 69 in the outer clamping ring 62, such that relative rotation of the outer clamping ring 62 with respect to the inner clamping ring 63 causes the discs 67 to rotate about their respective axis of rotation 75. Commercial applicability

[0050] The operation of the device according to the invention is described below with reference to the exemplary embodiments shown in the figures.

[0051] For non-contact measurement, a measuring object 50 is provided. This can be, for example, a cut-to-length section of cable or wire.

[0052] To secure the measuring object 50 in the first and second holders 15, 16 of the device 1, the first and second holders 15, 16 are moved away from the radiation source 10 on the guide rails 71 and into a position in the Fig. The first position shown in Figure 4 is brought into position 4. The guide rails 71 are mounted on the base plate 85. In the first position, the object 50 is attached to the first and second supports 15, 16 such that the object 50 can be rotated about its longitudinal axis L.

[0053] To secure the workpiece, the measuring object 50 is clamped between the clamping jaws of the first and second holders 15, 16. To open the clamping jaws, the outer clamping ring is rotated relative to the inner clamping ring of the first or second holder. For this purpose, the outer clamping ring is turned counterclockwise with the drive unit (with reference to the in Fig. 3 (view shown) rotated until the projection 65 of the inner clamping ring rests on the (non-chamfered side) of the locking device from above (see Fig. 3) This blocks the movement of the inner clamping ring, and the outer clamping ring continues to rotate counterclockwise, thus opening the clamping jaws. As described in the Fig. As can be seen in Figure 4, the projection 65 sits on the locking device 66. The clamping device is in the open position. By turning the outer clamping ring clockwise (with reference to the one shown in Figure 4), the clamping device can be opened. Fig. (3 shown view) the clamping jaws can be closed again and the object being measured can thus be clamped in the clamping jaws.

[0054] When the object being measured 50 is attached to the first and second supports 15, 16, the first and second supports 15, 16 are moved on the guide rails 71 towards the radiation source 10 and into a position in the Fig. The second position shown in Figure 5 is brought into this position. In this second position, the object 50 can be irradiated with the measuring beam S of the radiation source 10 over a measuring range M extending between the first and second supports 15, 16 and in the direction of the longitudinal axis L of the object 50. For non-contact measurement, the object 50 is irradiated with the measuring beam S of the radiation source 10 in the second position. During irradiation, the object 50 is rotated, for example clockwise, by means of the motor 22 (via the belts and the first and second supports 15, 16), and the beams reflected by the object 50 are detected by the sensor 11. The object 50 can be rotated continuously or stepwise, preferably at a constant speed. The object 50 can be rotated at least once completely around its longitudinal axis L.

[0055] The device 1 has a stop 80 with a stop surface 81, the stop 80 being positioned such that the object 50 being measured is in contact with the stop surface 81 of the stop 80 in the second position. The second position can be determined by moving the first and second supports 15, 16 with the clamped object 50 towards the radiation source 10 until the object 50 abuts the stop surface 81 of the supports 80. During rotation of the object 50, it slides along the stop surface 81 and is thus held in position by the stop surface 81.

[0056] Fig. Figure 9 schematically shows the measuring object 50 positioned on the stop surface 81 and the sensor 11 with the radiation source 10. As in Fig. As shown in Figure 9, the sensor 11 is positioned with respect to the stop surface 81 such that one of its central axis is substantially perpendicular to the stop surface 81. As already described, the sensor 11, or rather the radiation source 10, is designed such that the emitted beam can be moved back and forth within a measuring range M on the circumference of the object 50 in a plane parallel to the stop surface 81. At corresponding measuring positions, the sensor 11 acquires measured values ​​that indicate the measured layer thickness of the coating of the object 50, or the acquired measured values ​​are forwarded to the control unit 30 and the layer thickness is calculated by the processing unit 40. In the following, it is assumed that the measured values ​​acquired by the sensor 11 are specified in a coordinate system defined by the sensor 11. A Z-axis indicates the direction from the sensor 11 to the object 50, i.e.,The X and Y axes indicate directions perpendicular to the stop surface 81, and the X and Y axes indicate directions orthogonal to each other in a plane parallel to the stop surface 81. Based on the coordinates in the X and Y directions, and given the known position of, in particular, the center point or the longitudinal axis L of the object 50, the layer thickness can then be measured at any point on the surface of the object 50 facing the sensor 11.

[0057] In general, the control unit 30 is designed to take a plurality of measured values ​​M1, M2, M3 for the layer thickness d at a plurality of measuring positions P1, P2, P3 (see) when the object being measured is in a given rotational position 50 about the axis of rotation D or longitudinal axis L of the same. Fig. 10) in a first direction (in particular the direction X perpendicular to the longitudinal axis L and parallel to the stop surface 81) based on the rays detected by the sensor 11. The following description only describes the measurement of the layer thickness in a cross-section perpendicular to the longitudinal axis L, i.e., for a fixed value of the coordinate of the measurement positions in the Y-direction (along the longitudinal direction L of the object 50). It is understood that the measurement procedure described below can be carried out analogously for any number of successive cross-sections in the Y-direction within the measurement range M.

[0058] Fig. Figure 10 illustrates a measurement of the layer thickness d at a given position along the Y-direction using the measuring beam S. In the Fig. At the position shown in Figure 10, the measuring beam S strikes a side surface of the object 50 essentially perpendicularly, which rests against the stop surface 81 (not shown). In the case shown in Fig. In the example shown in Figure 10, the long side of the essentially rectangular cross-section of the object being measured is the measuring beam. As already mentioned, the measuring beam S strikes the object 50 at the majority of measuring positions P1, P2, P3 and is reflected by it. This reflection occurs not only at the outer surface of the object 50, i.e., a sheath 51 thereof, but also at the interface between the sheath 51 and a core 50a of the object, for example, a wire surrounded by the sheath 51. The sensor 11 can then determine the layer thickness d at the respective measuring position using interferometric measurement based on the two reflections in a known manner. In practice, the measuring beam S is moved back and forth in the X-direction so that, apart from the central position, it strikes the respective surfaces at an angle other than 90° in the X-direction. This can, however, be compensated for by the sensor 11, if necessary.in conjunction with the control unit 30 or computing unit 40, can be taken into account in a known manner, so that a measured value for the layer thickness d can be obtained at each measuring position P1, P2, P3.

[0059] However, as explained at the beginning, the quality of the measurement depends on the surfaces from which the measuring beam S is reflected being essentially perpendicular to the beam axis of the measuring beam S. Therefore, it is evident that, for example, at the in Fig. At measurement position P3 shown in Figure 10, a measured value M3 is obtained that may not accurately represent the layer thickness, particularly at a rounded edge of the object 50. Furthermore, it is evident that the intensity of measured value M3 may also be significantly lower than the intensities of measured values ​​M1 and M2, which are located near the center of the circumference of the object 50 in the X direction.

[0060] Therefore, the control unit 30 is further configured to select a portion of the majority of measured values ​​based on the given rotational position of the object 50 and to assign the selected measured values ​​to a circumferential area 52 of the object 50, which corresponds to a part of the object 50 in its circumferential direction. For the in Fig. In the case shown in Figure 10, these are the measured values ​​M1 and M2 at the measuring positions P1 and P2. Based on the selected measured values, the control unit determines at least one layer thickness value for the layer thickness d for the circumferential range 52. For example, the control unit can determine the layer thickness d for the area shown in Figure 10. Fig. In the case shown in Figure 10, where a side surface of the object 50 is essentially perpendicular to the (central) beam axis of the measuring beam S, an arbitrary desired number of discrete measurement positions or measured values ​​in the X-direction are traversed in order to determine a profile of the layer thickness d for the essentially straight part of the circumference of the object 50. It is understood that, for example, more than one measured value M1 can be recorded at the measurement position P1, and that an average value can be calculated from the multiple measured values ​​at a measurement position to obtain a reliable result for the layer thickness d at the measurement position.

[0061] To obtain a layer thickness profile along the entire circumference of the object 50, it is necessary to rotate the object 50 as described herein. As in Fig. As shown in Figure 11, the device 1 described herein can therefore be controlled by the control unit 30 such that the object 50 is rotated by an angle α from a starting position, which can, for example, be a position in which a predetermined side surface of the object 50 is parallel to the stop surface 81, and then the layer thickness is measured again at this angular position or in this angular position of the object 50. In the case shown in Fig. In the example shown in Figure 11, the rotation is clockwise. The rotation can be continuous, provided the deflection of the measuring beam S and the calculation / evaluation by the computing unit 30 or control unit 40 are fast enough, or it can be performed in steps, i.e., the object being measured can be moved at the point shown in Figure 11. Fig. The angle shown in 11 is recorded before it is rotated further by an additional angle in a further step.

[0062] Due to the rotation, the measuring beam S now strikes the object 50 at a different point on its circumference, essentially perpendicular to it. This means that the area of ​​the object 50's circumference for which the layer thickness can be reliably determined changes during the rotation. This area essentially corresponds to the portion of the object 50's outer circumference that rests against the stop surface 81. Because the object 50 is mounted so that it can be moved in the Z-direction, a portion of its circumference is always in contact with the stop surface 81. This portion corresponds to the area for which reliable and relevant measurements of the layer thickness d can be obtained.

[0063] In particular, reliable measurements can also be taken in this way for the area of ​​the object 50 that corresponds to the rounded corners of its cross-section. Fig. For example, in step 11, the object 50 has been rotated such that a radius of a corner region of the otherwise essentially rectangular cross-section of the object 50 rests against the stop surface 81. Thus, for a measurement position P1 in this corner region, the layer thickness d can be reliably determined in the manner described above. It is understood that, on the other hand, the measured values ​​obtained for measurement positions P2 and P3 along the straight sides of the object 50 are not selected, as they do not lie within the range for which reliable measurements can be recorded.

[0064] In other words, even though the sensor 11 can generate measured values ​​for the layer thickness d over a large area X1 where the measuring beam S is reflected by the object 50, only a sub-area X2 in the X-direction is selected for the measured values, depending on the angular position of the object 50. This is possible because it is known which part of the contour 54 of the object 50 is in contact with the stop surface 81 at a given rotational position or angle α. Based on this, for example, an area with a given extent in the X-direction around a contact point of the object 50 on the stop surface 81 can be selected as the area X2 for which measured values ​​for the layer thickness d are reliably acquired and can therefore be used to calculate the layer thickness d.

[0065] In the manner described above, it is possible to determine a layer thickness d at each of the desired circumferential positions of the measuring object 50 during a complete rotation of the measuring object 50 and thus to record a complete profile of the layer thickness d in the circumferential direction.

[0066] In some embodiments, the control unit 30 is configured to obtain the contour 54 of the object 50 in a plane perpendicular to its longitudinal axis L, and, based on the contour 54, an initial position of the object 50, and the given rotational position, to select the portion of the plurality of measured values ​​to be considered and assign these to the circumferential area 52 as a part of the contour 54. That is, the control unit 30 can obtain the shape of the contour 54 of the object 50 in a plane perpendicular to its longitudinal axis L either through user input or from its memory. The contour 54 can, for example, be a rectangle with rounded corners, i.e.,A rectangle whose corners are represented by segments of circles c with a specific radius, while the sections between the circle segments are approximated by straight lines corresponding to a long side a and a short side b of the rectangle. It is readily apparent to a person skilled in the art how, for example, the associated contour 54 can be mathematically represented. Alternatively, contour 54 can be specified as a contour based on a superellipse, the parametric representation of which is also known to a person skilled in the art. An example of such a contour is a contour called a squircle (see, for example, https: / / en.wikipedia.org / wiki / squircle). Of course, the object being measured can have any other contour, so that, for example, an object with a circular cross-section can also be measured.However, regardless of the specific parameterization of contour 54, it is evident that, given contour 54, initial position and current rotation position, the control unit 30 can easily calculate the point at which contour 54 or the measuring object 50 is in contact with the stop surface 81.

[0067] The area X2, in which the measured values ​​are to be recorded or selected, can be selected by the control unit 30 such that a tangent to the contour 54 in area X2 must form an angle with the stop surface 81 that is less than or equal to a predetermined angle. The reason for this is that, as already mentioned, for a reliable measurement, the measuring beam S should strike the respective surfaces essentially perpendicularly. Strictly speaking, this is the case when, at the point where the measuring beam S strikes the surface, this tangent is parallel to the stop surface 81. However, in order to be able to record more than one measured value, a certain small angular range can be specified within which the quality of the measured values ​​is assumed to be sufficiently good. For example, the angular range could be between ±5°.Alternatively, if contour 54 is known, the control unit 30 could predefine not only a position of area X2, but also its size, for each rotation angle α. It is evident that for the in . Fig. The rotation position shown in section 10, where the X2 range can of course be much larger than for example in... Fig. Figure 11 shows the rotational position. However, it is also possible that in some embodiments only the measured values ​​are taken into account where the predetermined angle is essentially 0°, i.e., the measuring beam S is essentially perpendicular to the measuring position.

[0068] As mentioned at the beginning, the accuracy of the measurement can be further increased by only considering measured values ​​for which the rays detected by sensor 11 have an intensity I that exceeds a predetermined threshold T. This is the case, for example, in Fig. 12 are shown for two different rotation positions. It should be noted that in the illustration in Fig. 12 the measuring beam S from the left hits the measuring object 50. Also from Fig. However, as shown in Figure 12, the intensity profile varies considerably in the X-direction depending on the rotational position, i.e., the given angle α. By comparing this with the threshold T, only those measurements for which the intensity is high enough to reliably calculate the layer thickness d can be considered. It should be noted that the intensity does not necessarily vary exclusively depending on the position along the X-direction, but can also vary, at least to some extent, between different measurements at the same position along the X-direction. Therefore, in the case of multiple measurements at the same position, only those measurements with a sufficiently high intensity I can be considered.Furthermore, it is evident that in this way, for example, the area X2, which is determined based on the given rotation position, can be chosen to be comparatively larger, since additional filtering is carried out based on the detected intensities.

[0069] It was also mentioned at the beginning that, due to the preload from the various springs, a wobbling motion of the center point or the longitudinal axis L of the measuring object 50 can occur when the measuring object 50 is rotated about the longitudinal axis L or the axis of rotation D. This is in Fig. Figure 13 is shown schematically. In other words, ideally, the center point or longitudinal axis L of the object 50 would only move back and forth in the Z-direction while the object 50 is rotated. In reality, however, the center point or axis of rotation D also shifts in the X-direction. The measurement by sensor 11, however, is based on the assumption that the center point or axis of rotation L of the object 50 remains in the same position in the X-direction during rotation. Therefore, deviations may occur when calculating the layer thickness d by sensor 11 in conjunction with the control unit 30.

[0070] According to some embodiments, these deviations can be corrected by the control unit 30 taking into account a displacement of the longitudinal axis L of the object 50 in the first direction X with respect to an initial position at the given rotational position when selecting and assigning the measured values ​​to the circumferential range 52. The displacement is determined as a function of the rotational position by a relationship stored in a memory of the control unit 30. In some embodiments, the control unit 30 is configured to derive the displacement from a parameterized curve 55 stored in the memory, which, for example, is defined in Fig. Figure 14 shows that the parameterized curve 55 represents a movement of the longitudinal axis L in a plane perpendicular to the longitudinal axis during a rotation of the measured object 50. In some embodiments, the curve 55 can be an epicycloid or a Pascal's worm, which can be parameterized in a known manner.

[0071] The relationship stored in the memory of the control unit 30 can be determined in advance by measuring a reference object with the device 1. This reference object has the same geometry as the measurement object 50 and its layer thickness is known, for example, through a previous measurement using another method. Based on a comparison of the layer thicknesses d of the reference object measured for several rotational positions with the known layer thicknesses, the control unit 30 can determine the relationship stored in its memory, in particular the parameters of the curve 55. Subsequently, when the measurement object 50 is measured, the control unit 30 can determine the displacement of the axis of rotation L in the X-direction for a given rotational position and, based on this, determine, for example, the region X2 in which the layer thickness is to be measured.This means that if the displacement of the axis of rotation L in the X direction were not taken into account, the control unit would assume that, for example, in the in . Fig. In the case shown in Figure 11, the area X2' in the X-direction is the area for which the measured values ​​are evaluated or the layer thickness d is calculated. However, due to a shift of the rotation axis L in the +X direction, the area X2 is actually located elsewhere. This shift can be taken into account when selecting the area X2 or calculating the layer thickness values, as described above, thus further improving the quality of the measurement and, in particular, the accuracy of the layer thickness d along the circumference of the object 50.

[0072] As mentioned above, in some embodiments the control unit 30 can be configured to control the radiation source 10 and the drive unit 20 such that the rotatably mounted measuring object 50 is continuously rotated during irradiation, preferably at a constant speed, whereby the majority of measured values ​​M1, M2, M3 can be recorded at the given rotational position during several rotations of the measuring object 50. This is advantageous when, due to the speed of the continuous rotation, not all measured values ​​M1, M2, M3 can be recorded at the given rotational position, or not enough measured values ​​can be recorded at the individual measuring positions for averaging during one rotation.

[0073] Alternatively, the control unit 30 can be configured to control the radiation source 10 and the drive unit 20 such that the rotatably mounted measuring object 50 is rotated stepwise during irradiation, preferably with between 10 and 1000, more preferably between 100 and 400, more preferably between 200 and 300, and in particular 240, steps per revolution, wherein at each given rotational position several, preferably between 3 and 5, measurements are taken at the plurality of measuring positions P1, P2, P3. Thus, it is only necessary to rotate the measuring object once completely around the axis of rotation L to determine a profile for the layer thickness d.

[0074] As explained above, this document discloses a method for the interferometric determination of the layer thickness d of a sheath 51 of a rotating object 50, such as a cable section. The method comprises the following steps: providing a radiation source 10 configured to emit a measuring beam S to irradiate the object 50; providing a sensor 11 configured to detect the beams reflected by the sheath 51 and a core 50a of the object 50 surrounded by the sheath; and fixing the object 50 such that it is rotatable about its longitudinal axis L and can be irradiated with the measuring beam S of the radiation source 10 over a measuring range M.Irradiating the object 50 with the measuring beam S of the radiation source 10 and rotating the object 50 during irradiation, wherein the object 50, while rotating about its longitudinal axis L during irradiation, slides along a stop surface 81 of a stop 80, wherein the fixed object 50 is mounted displaceably in a direction Z perpendicular to the stop surface and is preloaded against the stop surface;and the detection of the rays reflected by the object 50 with the sensor 11. For a given rotational position of the object 50 about the axis of rotation D, a plurality of measured values ​​M1, M2, M3 for the layer thickness d are determined at a plurality of measuring positions P1, P2, P3 in a first direction X perpendicular to the longitudinal direction L and parallel to the stop surface 81 based on the rays detected by the sensor 11. Based on the given rotational position, a portion M1, M2 of the plurality of measured values ​​is selected and assigned to a circumferential region 52, which corresponds to a portion of the object 50 in the circumferential direction. At least one layer thickness value of the layer thickness d is determined from the selected measured values ​​for the circumferential region 52.

[0075] With the device or method described above, a reliable measurement of the layer thickness d along the entire circumference of the object 50 is possible.

[0076] Once the measurement is complete, the first and second supports 15, 16 can be moved back to their initial positions on the guide rails 71, and the object being measured can be removed from the clamping jaws. To open the clamping jaws, refer to the procedure described above for clamping the object being measured.

[0077] The control unit is designed to control both the drive unit and the radiation source. Furthermore, the control unit can have a function that allows the first and second supports 15, 16 to be moved from the first position to the second position and vice versa. This further increases the level of automation of the device.

[0078] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently of one another, both for the purpose of the original disclosure and for the purpose of limiting the claimed invention, irrespective of the combination of features in the embodiments and / or the claims. It is explicitly stated that all ranges of values ​​or specifications of groups of objects disclose every possible intermediate value or every possible object in between, both for the purpose of the original disclosure and for the purpose of limiting the claimed invention, in particular for determining the limits of value ranges. Reference symbol list 1 Device 3 Worktop 10 Radiation source 11 Sensor 15 first bracket 16 second bracket 20 drive unit 21 belts 22 Engine 30 Control unit 40 computing units 50 measuring objects 50a Core 51 Sheathing 52 Scope 54 contour 55 Curve 61 clamping jaws 62 outer clamping ring 63 inner clamping ring 64 Spring element 65 lead 66 Locking device 67 disc 68 pens 69 Nut 70 sliding carriages 71 Running rail 75 Axis of rotation of the disc 80 stops 81 Stop surface 85 Base plate d layer thickness M1, M2, M3 measured values P1, P2, P3 measuring positions X first direction α Rotation angle I Intensity T threshold The axis of rotation of the first and second brackets L Longitudinal axis of the object being measured M measuring range S measuring beam

Claims

Device (1) for interferometric determination of a layer thickness (d) of a sheath (51) of a rotating object (50) such as a cable section, comprising: - a radiation source (10) configured to emit a measuring beam (S) to irradiate the object (50); - a sensor (11) configured to detect the beams reflected by the sheath (51) and a core (50a) of the object (50) surrounded by the sheath;- a first support (15) and a second support (16) spaced apart from the first support (15), which are rotatably mounted about a common axis of rotation (D) and are designed to secure the object being measured (50) in such a way that the object being measured (50) can be rotated about its longitudinal axis (L) and can be irradiated with the measuring beam (S) of the radiation source (10) over a measuring range (M) extending between the first and the second support (15, 16) and in the direction of the longitudinal axis (L) of the object being measured (50); - a drive unit (20) which is in drive connection with the first and / or second support (15, 16) and is designed to rotate the first and / or second support (15, 16) and the object being measured (50) held therein;- a stop (80) having a stop surface (81) designed to allow the object being measured (50) to slide along the stop surface while rotating about its longitudinal axis (L) during irradiation, wherein the first and second supports (15, 16) are mounted to be displaceable in a direction (Z) perpendicular to the stop surface and are preloaded against the stop surface;and a control unit (30) configured to control the radiation source (10) and the drive unit (20) such that the rotatably mounted measuring object (50) is irradiated with the measuring beam (S) of the radiation source (10) in the measuring range (M) and is rotated about its longitudinal axis (L) during irradiation, wherein the control unit (30) is further configured to: at a given rotational position of the measuring object (50) about the axis of rotation (D), determine a plurality of measured values ​​(M1, M2, M3) for the layer thickness (d) at a plurality of measuring positions (P1, P2, P3) in a first direction (X) perpendicular to the longitudinal axis (L) and parallel to the stop surface (81) based on the beams detected by the sensor (11); based on the given rotational position, select a portion (M1, M2) of the plurality of measured values ​​and assign the selected measured values ​​to a Circumferential area (52) corresponding to a part of the object being measured (50) in its circumferential direction;and determine at least one layer thickness value of the layer thickness (d) for the circumferential area (52) based on the selected measured values.; Device (1) according to claim 1, wherein the control unit (30) is configured to obtain a contour (54) of the object being measured in a plane perpendicular to the longitudinal axis (L) and, based on the contour (54), an initial position of the object being measured (50) and the given rotational position, to select the part (M1, M2) of the plurality of measured values ​​and to assign it to the circumferential area (52) as a part of the contour (54). Device according to claim 2, wherein the control unit (30) is configured to select the measured values ​​that are assigned to a part of the contour (54) in which a tangent to the contour (54) has an angle to the stop surface (81) that is less than or equal to a predetermined angle. Device according to claim 3, wherein the predetermined angle is essentially 0 degrees. Device according to one of claims 2 to 4, wherein the control unit (30) is configured to obtain the contour (54) as a contour based on a superellipse or a rectangle with rounded corners and, based thereon, to calculate the part of the contour (54) to which the selected measured values ​​are to be assigned. Device according to one of claims 1 to 5, wherein the control unit (30) is configured to consider only measured values ​​for which the rays detected by the sensor (11) have an intensity (I) that exceeds a predetermined threshold (T) when selecting the measured values. Device according to one of claims 1 to 6, wherein the control unit (30) is configured to take into account, when selecting and assigning the measured values ​​to the circumferential area (52), a displacement of the longitudinal axis (L) of the object being measured (50) in the first direction (X) with respect to an initial position at the given rotational position, wherein the displacement is determined as a function of the rotational position on the basis of a relationship stored in a memory of the control unit (30). Device according to claim 7, wherein the control unit (30) is configured to derive the displacement on the basis of a parameterized curve (55) stored in the memory, which indicates a movement of the longitudinal axis (L) in a plane perpendicular to the longitudinal axis during a rotation of the measuring object (50). Device according to claim 8, wherein the curve (55) is an epicicloid or Pascal's spiral. Device according to one of claims 7 to 9, wherein the control unit (30) is configured to measure a reference object which has the same geometry as the measuring object (50) and whose layer thickness is known, and to determine, based on a comparison of the layer thicknesses (d) measured for several rotational positions with the known layer thickness, the relationship which is stored in the memory of the control unit (30), in particular the parameters of the curve (55). Device according to one of claims 1 to 10, wherein the control unit (30) is configured to control the radiation source (10) and the drive unit (20) in such a way that the rotatably mounted measuring object (50) is continuously rotated during irradiation, preferably at a constant speed, wherein the majority of measured values ​​(M1, M2, M3) are recorded at the given rotational position during several rotations of the measuring object (50). Device according to one of claims 1 to 11, wherein the control unit (30) is configured to control the radiation source (10) and the drive unit (20) such that the rotatably mounted measuring object (50) is rotated stepwise during irradiation, preferably with between 10 and 1000, preferably between 100 and 400, more preferably between 200 and 300, in particular 240, steps per revolution, wherein at each given rotational position several, preferably between 3 and 5, measurements are taken at the majority of the measuring positions (P1, P2, P3). Device (1) according to one of the preceding claims, wherein the first and / or the second holder (15, 16) comprises: clamping jaws (61) which are movably arranged and designed to be moved towards each other in such a way as to clamp the object being measured (50). Device (1) according to claim 13, wherein the first and / or second support (15, 16) comprises: - a rotatably mounted outer clamping ring (62) which is in drive connection with the drive unit (20), and - an inner clamping ring (63) which is arranged coaxially and rotatably to the outer clamping ring (62), wherein the outer clamping ring (62) and the inner clamping ring (63) are coupled to the clamping jaws (61) in such a way that the clamping jaws (61) move away from each other in a first direction by rotating the outer clamping ring (62) relative to the inner clamping ring (63) and move towards each other in a second direction opposite to the first direction by rotating it. Method for the interferometric determination of a layer thickness (d) of a sheath (51) of a rotating object (50), such as a cable section, comprising the following steps: - Providing a radiation source (10) configured to emit a measuring beam (S) to irradiate the object (50); - Providing a sensor (11) configured to detect the beams reflected by the sheath (51) and a core (50a) of the object (50) surrounded by the sheath; - Fixing the object (50) such that the object (50) is rotatable about its longitudinal axis (L) and can be irradiated with the measuring beam (S) of the radiation source (10) over a measuring range (M);- Irradiating the object (50) with the measuring beam (S) of the radiation source (10) and rotating the object (50) during irradiation, wherein the object (50), while rotating about its longitudinal axis (L) during irradiation, slides along a stop surface (81) of a stop (80), wherein the fixed object (50) is displaceably mounted in a direction (Z) perpendicular to the stop surface and is preloaded against the stop surface; - Detecting the beams reflected by the object (50) with the sensor (11); - at a given rotational position of the object (50) about the axis of rotation (D), determining a plurality of measured values ​​(M1, M2, M3) for the layer thickness (d) at a plurality of measuring positions (P1, P2, P3) in a first direction (X) perpendicular to the longitudinal axis (L) and parallel to the stop surface (81) based on the the rays detected by the sensor (11);- based on the given rotational position, selecting a part (M1, M2) of the plurality of measured values ​​and assigning the selected measured values ​​to a circumferential region (52) that corresponds to a part of the object being measured (50) in its circumferential direction; and - determining at least one layer thickness value of the layer thickness (d) for the circumferential region (52) based on the selected measured values.;

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