Test method and test apparatus for testing the leakage flux of cables

Abstract

The invention relates to a test method for testing the leakage flux of a cable in order to detect defects, wherein a test apparatus (100) and the cable (200) are moved relative to one another in the longitudinal direction of the cable. In the method, portions of the cable are successively magnetised by means of a magnetising device (120) of the test apparatus such that magnetisation field lines in the cable are oriented substantially in the longitudinal direction of the cable. The circumference of the magnetised portion of the cable is scanned by means of sensors (140) of a sensor array (130) which are sensitive to magnetic fields, in order to sense stray magnetic fields caused by defects. This sensor array has a plurality of sensors (140) which are sensitive to magnetic fields and are arranged offset from one another in the circumferential direction and at a test distance (142) from the surface of the test object during the test. Electrical sensor signals from the sensors are evaluated to assess the defects. Each sensor of the sensor array is arranged in a movably mounted test shoe (150), which has a sliding face (146) for sliding on the circumferential face of the cable, wherein the sensor (140) is set back from the sliding face by a sensor distance (145). In a first test configuration, the test shoe (150) is pressed against the circumferential face such that the sliding face (146) is in contact with the circumferential face, and the sensor is kept at a finite first test distance, which corresponds substantially to the sensor distance, from the surface of the test object.

Description

[0001] Test method and test device for flux leakage testing of wire ropes

[0002] FIELD OF APPLICATION AND STATE OF THE ART

[0003] The invention relates to a test method for flux leakage testing of wire ropes to detect defects and to a test device suitable for carrying out the test method.

[0004] A typical wire rope, such as those used in cable cars, elevators, or bridge construction, consists of numerous individual wires that are twisted together. A wire rope can consist of individual wires or of a few strands, which in turn consist of numerous individual wires. The starting material for wire ropes is usually ferromagnetic steel wire.

[0005] A wire rope achieves its flexibility by twisting the individual wires or strands over one another, a process known as lay. Strands and individual wires can have the same or opposite lay direction. The distance at which an individual wire or strand returns to the same circumferential position is called the lay length.

[0006] Wire ropes are frequently used in locations where ropes, such as plastic ones, are not strong enough and rods or pipes are not flexible enough. These locations are often outdoors, where the wire ropes can be exposed to harsh weather conditions, such as heat and cold, rain, snow and ice, storms and thunderstorms. Cable cars, in particular, subject the wire rope to additional stresses due to normal use. These include, for example, continuous or frequently repeated bending or clamping by cabins.

[0007] Minor damage to the surface of the rope or even breakage of individual wires within the wire rope may be tolerable or even repairable in certain cases. Nevertheless, wire ropes must not break under any circumstances, as they are usually a safety-critical part of a system. Typical types of damage that occur in wire ropes include wire breakage, crushing or deformation due to clamping, imprints from wires, damage caused by the rope jumping out of its guide, superficial damage caused by lightning, and corrosion. To ensure the operational safety of wire ropes, e.g., on cable cars, bridges, elevators, etc., regular inspections of the wire ropes are mandatory.

[0008] A proven method for testing a wire rope for defects is the magnetic flux leakage test. This involves successively magnetizing sections of the wire rope using a magnetizing device in a testing device with a magnetic field whose magnetization field lines are oriented essentially in the longitudinal direction of the wire rope. Simultaneously, the circumference of the magnetized section is scanned by magnetic-field-sensitive probes in a probe array to detect magnetic stray fields caused by defects.

[0009] Permanent magnets are often used as magnets. By means of a folding mechanism, they can enclose the wire rope and magnetize the part of the rope lying between the poles of the magnetization device as evenly as possible. The document DE 38 21 070 A1 shows an example of such a testing device. This includes a sensor arrangement with inductive probes. The sensor arrangement consists of two coils, so-called half-shells, which span 180° of the rope and whose signals can be added together to form a fault signal. Such probe arrangements are cost-effective and efficient, especially for locating wire breaks, since the distance of the probes from the rope and the integration of the changes in the magnetic flux over the entire circumference allow damage inside the rope to be easily detected. A disadvantage of this arrangement is that superficial defects are difficult or not at all to detect. These may then have to be replaced.can be found through regular visual inspection of the rope, which can often take several days for kilometers of rope and is therefore costly.

[0010] Trained personnel are required for visual inspections. Patent EP 2 383 566 B1 discloses a testing method for computer-assisted optical testing of a rope comprising multiple wires or fibers, based on image data sets of at least one section of the rope using image processing.

[0011] In some testing systems, the probe arrangement comprises more than two magnetic-field-sensitive probes, which are arranged offset from one another in the circumferential direction and, during testing, are arranged at a finite test distance from the surface of the test material. Electrical probe signals from the probes are evaluated to qualify the defects. Patent EP 1 995 589 B1 discloses a relatively complex leakage flux testing device that is said to be capable of detecting defects in the wires of a wire rope, even when the defects are located inside the wire rope. The testing device comprises a magnetization device and magnetic detection means. These include a first magnetic detection means for detecting a magnetic flux around the entire circumference of the steel rope; several second magnetic detection means; and several third magnetic detection means.The second and third detection means are arranged circumferentially "spaced" from each other. Furthermore, there is a total measuring device, to which an output of the first magnetic detection means is supplied and in which a total value of the leakage magnetic flux is measured, and a differential measuring device, to which the outputs of the second and third magnetic detection means are supplied.Furthermore, there is a memory, a first CPU configured to receive signals from the differential measuring device and the total measuring device, and configured to calculate a ratio between signals from the differential measuring device and the total measuring device, and configured to output a signal indicating a depth of damage based on the relationship between the depth of damage and the signal ratios previously stored in the memory; a second CPU configured to calculate a degree of damage from the signal from the differential measuring device and from threshold value data stored in the memory.

[0012] The probes are spaced far enough from the wire rope that the eccentric position of the rope in the testing device and / or serious defects on the rope surface, such as protruding wires, cannot damage the sensors (see e.g. US 5 198 765 A).

[0013] TASK AND SOLUTION

[0014] It is an object of the invention to provide a testing method and a testing device for flux leakage testing of wire ropes which enable reliable, highly selective testing for defects of different types.

[0015] To achieve this object, the invention provides a testing method having the features of claim 1 and a testing device having the features of claim 13. Advantageous further developments are specified in the dependent claims. The wording of all claims is incorporated into the description by reference. The testing method and the testing device serve to detect defects in a wire rope by means of a flux leakage test. The testing device and the wire rope are moved relative to one another in the longitudinal direction of the wire rope. This can be achieved by keeping the wire rope stationary, i.e. not moving, while the testing device is moved longitudinally along the wire rope. It is also possible to hold the testing device stationary and move the wire rope longitudinally through the testing device.In principle, both the test fixture and the wire rope can be moved, but at different speeds and / or directions, so that the wire rope can be scanned along its length.

[0016] In the test method, sections of the wire rope are successively magnetized using a magnetization device of the test apparatus such that the field lines of the magnetization field, i.e., the magnetization field lines, within the wire rope are oriented essentially in its longitudinal direction. The magnetization device is preferably designed to encompass the entire circumference of the wire rope in order to achieve flux introduction across the entire circumference and generate a uniformly high magnetization field in the area of ​​the test volume.

[0017] To detect stray magnetic fields caused by defects in the wire rope, the circumference of the magnetized section of the wire rope is scanned using magnetic-field-sensitive probes in a probe array. A probe array consists of a plurality of magnetic-field-sensitive probes that are circumferentially offset from one another and arranged at a test distance from the surface of the test piece during testing. The probes generate electrical probe signals that are evaluated to qualify the defects.

[0018] In the test method and device, each probe of the probe assembly is mounted in a movably mounted test shoe, which has a sliding surface for sliding along the circumferential surface of the wire rope. The probe is positioned within the test shoe, offset from the sliding surface by one probe spacing.

[0019] In a first test configuration, the test shoe is pressed against the circumferential surface during the relative movement between the test fixture and the wire rope in such a way that the sliding surface is in contact with the circumferential surface and the probe is accordingly held at a finite first test distance from the surface of the test material, which essentially corresponds to the probe distance. The term "circumferential surface of the wire rope" here refers to the envelope of the wire rope, i.e. a minimal surface that touches the outermost parts of the wire rope and bridges the depressions or valleys between individual wires or strands. This envelope can, for example, be the surface of a circular cylinder, or possibly even the surface of an oval cylinder. The sliding surface of a test shoe is so large that the envelope is traversed without significantly dipping into the "valleys" between wires or strands. This allows wire ropes to be tested without causing massive damage (e.g.protruding ends of broken individual wires) ensures a relatively smooth running or gentle sliding.

[0020] This approach differs significantly from previously known procedures for wire rope testing. To the inventors' knowledge, in conventional systems, the probes are spaced far enough from the wire rope that an eccentric position of the wire rope in the testing device and / or serious defects on the rope surface, such as protruding wires, cannot damage the probes. This inevitably results in a relatively large testing distance, which can also vary over time if the position of the wire rope within the probe arrangement changes during the test.

[0021] In contrast, the procedure proposed here offers the possibility of testing at a largely constant test distance from the surface of the wire rope. This largely eliminates distance-dependent fluctuations in the signal amplitude, allowing changes in the signal amplitude to be reliably attributed to potential defects. A constant test distance contributes significantly to high reproducibility and thus reliability of the test results, which can then be compared with each other. Since the probe is set back from the sliding surface within the test shoe, the probes of a test shoe are nevertheless protected against mechanical contact with the surface.If the surface of the wire rope is damaged, for example, because a wire has broken and is protruding outwards, the movable mounting of the test shoe allows the shoe to deflect at the damaged area, allowing it to pass over it without causing damage. Lifting of the test shoe, for example, due to a wire protruding outwards, leads to a loss of test sensitivity, especially for defects close to the surface. However, this lifting can be detected in various ways, allowing these areas of the rope to be classified as defective.

[0022] The arrangement of the probes within a test shoe offers the further advantage that the probes can be arranged at a very short test distance from the circumferential surface of the wire rope if required. In preferred embodiments, the test distance in the first test configuration is in the range of 0.5 mm to 5 mm, in particular in the range of 1 mm to 3 mm. In other words, the probe distance from the sliding surface is preferably within these ranges. This achieves high sensitivity for defects close to the surface, which would not be detectable in the probe signal if a magnetic field-sensitive probe were arranged at a greater distance from the surface. The short distance thus leads to a very favorable signal-to-noise ratio for defects close to the surface. This allows defects to be detected that could also be noticed during a visual surface inspection.In addition, however, the flux leakage test can also detect defects close to the surface that would otherwise be impossible to visualize because they do not change the appearance of the surface.

[0023] The probes of the probe assembly are preferably designed and arranged in such a way that a continuous circumferential inspection of the wire rope is possible in a single pass. A single probe sweeps a test track running essentially in the longitudinal direction of the wire rope, the width of which (test width) is determined by the effective width of the probe transverse to the scanning direction. The test tracks of all probes partially or completely overlap with the test tracks of other probes, so that no sensitivity gaps arise between test tracks.

[0024] In order to achieve, on the one hand, a continuous inspection in the circumferential direction and, on the other hand, a fine spatial resolution in the circumferential direction for the detection of near-surface defects, in preferred embodiments, e.g., those with common cable diameters of 30 mm to 70 mm, the probe arrangement comprises more than 20 probes distributed over the circumference, wherein the probe arrangement preferably comprises 30 or more probes, in particular 60 or more probes. The number of probes in the probe arrangement can even be in the order of magnitude of 100, for example, between 80 and 120. In addition to the achievable spatial resolution in the circumferential direction, such a fine division in the circumferential direction has further advantages, which will be explained in connection with further aspects.

[0025] In order to achieve high spatial resolution in the circumferential direction, it is further preferably provided that each of the probes has a test width measured in the circumferential direction which corresponds to an arc length in the range of 1 mm to 5 mm, in particular 2 mm to 3 mm. The term “test width” refers to the effective width of the test track of a probe, but not the width of the probe itself. This can be significantly smaller than the width of the test track. Preferably, the test width can be approximately a factor of 0.5 to 2 of the nominal sensor spacing. Preferably, the testing device has three or four or more test shoes distributed over the circumference and movable relative to one another. This allows the testing device to be easily adapted to different cross-sectional dimensions of wire ropes and wire ropes from a certain diameter spectrum can be tested with one and the same testing device.According to the inventors' experience, three or four individually movable test shoes are sufficient for this purpose. While more test shoes could be provided, this could potentially make the design of the test device unnecessarily complex.

[0026] Preferably, each test shoe is movably mounted on the base body of the test device by means of a single-piece or multi-piece joint arrangement. A joint arrangement is a movable connecting structure. This should preferably be designed so that degrees of freedom of movement are provided in the radial plane containing the test shoe relative to the passage axis, while degrees of freedom of movement transverse to this (e.g., an inclined position or greater lateral deflection) are not provided or are only provided to a limited extent and may be subject to greater resistance. This can, among other things, prevent collisions between adjacent test shoes. The joint arrangement can, for example, comprise a parallelogram guide and / or one or more flexure joints.

[0027] Preferably, each test shoe has a plurality of probes arranged offset from one another in the circumferential direction, which, preferably at least in the first test configuration, collectively cover a circumferential angular range greater than 360° divided by the number of test shoes. This ensures that the edge regions of test shoes adjacent to one another in the circumferential direction partially overlap, allowing for continuous testing even in the transition region between adjacent test shoes with different diameters or ovality. The test shoes can be constructed essentially identically to one another, thereby keeping the costs of providing the test device moderate.

[0028] According to a further development, the testing device comprises a controllable switching device for switching the testing device between the first test configuration and a lift-off configuration, in which a test shoe is held in a lift-off position such that the sliding surface is arranged at a predeterminable distance from the surface or circumferential surface of the wire rope. The switching device can be operated remotely, for example.

[0029] If necessary, a protective device can also be provided to detect or recognize structural defects in the wire rope. This device can generate control signals to then activate the switching device and cause a switchover from the first test configuration to the lifting configuration. For example, it is possible to perform the evaluation in such a way that the test shoe is lifted by actuating the switching mechanism if an excessively high signal is detected, or that the test shoe or the magnetization device is equipped with at least one additional sensor that measures a force parallel to the transport direction and triggers the lifting mechanism when a limit is exceeded. In some cases, a mechanical sliding bevel on the test shoe is sufficient.

[0030] A controlled switching option offers the further advantage that a test can be carried out in the lift-off configuration, with the probe arranged at a second test distance from the surface, wherein the second test distance is greater than the test distance in the first test configuration. The distance difference between the first test distance and the second test distance can be a multiple of the first test distance, for example in the range of at least 5 mm, for example in the range of 10 mm to 25 mm. When testing with the second test configuration, the probes are thus arranged at a greater distance from the wire rope surface. This reduces the sensitivity for defects close to the surface and the probe signals can largely only provide information about deeper-lying defects. The test depth can therefore be changed by switching between the first test configuration and the second test configuration.More specifically, the array is sensitive to near-surface defects at short spacing, and deep defects can also be detected. As the spacing increases, the sensitivity for near-surface defects decreases progressively, approaching the sensitivity for deep defects.

[0031] In some wire rope testing variants, at least one pass is performed with the first test configuration and at least one pass with the second test configuration. This allows reliable information about larger defects at any depth to be obtained using a single testing device, although the significance of the probe signals regarding the depth of the defects decreases with increasing distance. If necessary, additional information about smaller defects on the wire rope surface can be obtained.

[0032] Some variants include a contact monitoring system that automatically detects whether a test head has lost contact with the wire rope surface, e.g., due to a loose wire. If the distance to the test head becomes too great due to a loss of contact, the test is no longer reliable. The wire rope sections passed through during a loss of contact phase can then be marked as untested or faulty. Some embodiments provide for the continuous determination of the signal frequencies of all sensors in a test head. If at least one sensor fails to detect the high-frequency signals that are always generated due to wire gaps, this is an indication that the test head has lost contact with the rope surface.

[0033] One goal of wire rope testing is to obtain the most precise information possible about the presence of defects on and in the wire rope, and to determine the location of a defect. According to a further development, special steps are performed for this purpose when evaluating the probe signals. The evaluation of the probe signals comprises several coordinated operations that are specifically adapted to the properties of the probe arrangement, with the potential for high spatial resolution in the circumferential direction (in the first test configuration), and to the requirements for detecting defects at different depths.According to a further development, the evaluation of the probe signals comprises a mapping operation in which, for each probe signal, signal information representing the probe signal is linked with location information representing the location of origin of a probe signal in order to form location-dependent signal data, a matrix formation operation in which the location-dependent signal data or signal data derived therefrom are stored in correctly assigned fields of a base matrix, and at least one evaluation operation in which location-dependent signal data from at least two fields of the base matrix that are adjacent in an evaluation direction are linked to one another using at least one evaluation algorithm.

[0034] In a mapping operation, for each probe signal, signal information representing the probe signal is linked with location information representing the location of the probe signal within a scanned area. This creates location-dependent signal data. The mapping operation creates a clear association between signal information and location information and can then serve as the basis for generating a "map" of the respective scanned area.

[0035] In a matrix formation operation, the location-dependent signal data (or signal data derived from it) is then stored in correctly assigned fields or elements of a base matrix. In contrast to the usual definition of a matrix in mathematics (a two-dimensional rectangular arrangement of elements in rows and columns), the term "matrix" refers to an n-dimensional arrangement of elements, where n is greater than or equal to 2. A matrix as defined in the application can therefore have more than two dimensions, for example, three or four. In the broadest sense, the matrix creates a mapping between location information, signal information, and possibly further information on parameters that influence the test method and its results. In one embodiment, the mapping is as follows:

[0036] A first dimension of the base matrix represents the signal information, which contains information about the leakage flux measured at a specific location on the wire rope surface. This signal information can be given as a scalar quantity (e.g., signal amplitude or a selected component of the leakage flux) or as a vector quantity. A second dimension of the base matrix represents the position in the longitudinal direction of the wire rope. A third dimension of the base matrix can represent a position in the circumferential direction of the wire rope. If each probe in the probe array is assigned its own channel, the position in the third dimension can also be given by the channel number.

[0037] The method variant then comprises at least one evaluation operation in which location-dependent signal data from at least two fields of the base matrix that are adjacent in an evaluation direction are linked using at least one evaluation algorithm. Specific features of this will be explained in more detail in connection with the exemplary embodiments.

[0038] Preferably, bipolar signal information is used to form the base matrix, i.e., "raw" signal information from non-rectified probe signals. This allows information that would otherwise be lost through rectification to be utilized for evaluation.

[0039] There are various ways to determine the position of a defect in the longitudinal direction of the wire rope. This requires a known travel cycle. For example, a timing wheel or measuring wheel can be used, which is fixedly mounted in relation to the testing device and which runs along the wire rope. It is also possible to use a proximity sensor which is oriented so that it can detect the individual lays of the passing wire rope. According to one embodiment, however, the travel cycle is calculated from the probe signals themselves. For this purpose, a periodically varying signal component of a probe signal that correlates with the lay length of the wire rope is determined during evaluation, and an associated periodicity length of this signal component is used to determine the axial spatial coordinate of the location of origin of a probe signal. This eliminates the need for a separate measuring device for measuring the travel cycle.In a wire rope, defects can occur for various reasons at different depths, i.e., on the surface or near the surface, as well as within the wire rope, for example, near the center of the wire rope. Preferred advanced training allows for the specific depth(s) to be examined. The inspection can therefore include the detection of defects at a single depth or at several different depths of the wire rope.

[0040] For this purpose, according to a further development, pre-filtering of probe signals is carried out, wherein the pre-filtering comprises depth-specific bandpass filtering for each depth, preferably with adjustable cutoff frequencies. A lower cutoff frequency should be set to a lowest and an upper cutoff frequency to a highest frequency of the probe signals expected for a depth. This takes advantage of the fact that defects near the surface, as they pass the probe arrangement, cause a relatively short signal on the time axis, which contains frequency components with relatively high frequencies. In contrast, a central defect, i.e. a defect in the middle of the wire rope, would lead to a signal that is longer on the time axis and contains correspondingly lower frequencies.Depth levels located radially between the center of the wire rope and the surface would generate corresponding error signals with signal components of a medium frequency. Depth-specific bandpass filtering can thus be used to precisely specify the focus of the test.

[0041] A further possibility for specifically limiting the test to one or more specific depths and determining depth-specific signal information is used in a preferred embodiment by jointly evaluating probe signals from a predeterminable probe group comprising two or more probes arranged offset from one another in the circumferential direction with directly adjacent or partially overlapping test tracks, so that the probe group forms an effective probe having an effective test width in the circumferential direction that can be predetermined by the number of probes in the probe group. In other words, integration can be carried out using the probe signals from several adjacent test tracks; the resulting signal then belongs to the virtual probe length, which results from the effective length of the group of adjacent probes.

[0042] For example, to detect near-surface defects, i.e. defects located on or near the surface, probe signals from a probe group comprising no more than 10% of all probes in the probe array, in particular only two, three, or four of the probes, can be evaluated. Such an effective probe has a relatively narrow effective test width. On the one hand, this means that the circumferential position of a defect can be determined relatively precisely, since the effective test width covers only a small part of the circumference. With regard to depth resolution, it is crucial that probe groups with a relatively short virtual probe length are particularly suitable for detecting the short, high-frequency signals typical of near-surface defects, the signal amplitude of which stands out sufficiently clearly from the background signal.

[0043] If, on the other hand, defects are to be found that are located in the middle of the wire rope or in its vicinity, probe signals from a probe group that includes 90% or more of all probes in the probe arrangement, if necessary all probes, are preferably evaluated, so that an effective probe is created that completely encloses the circumference and, by integrating the signals from the individual probes, provides a similar overall signal to a single coil enclosing the wire rope.

[0044] For the detection of defects at medium depths, i.e. those that are at a certain distance from both the wire surface and the wire rope center, the probe signals of a probe group comprising more than 10% and less than 90% of all probes in the probe arrangement are evaluated.

[0045] An additional analysis can determine how many neighboring probes have detected the defect. If only one or a few probes detect high-frequency signals, the defect is near the surface. If all probes detect increased low-frequency stray flux at the same longitudinal position along the wire, the defect is located in or near the center of the wire rope. This allows for depth information to be determined. Depth information can thus be determined by evaluating how many immediately adjacent probes simultaneously detect a stray flux signal corresponding to a specific defect that exceeds a signal threshold.

[0046] According to a further development, further improvements in the significance of the test results can be achieved by carrying out a difference formation operation in which a difference between location-dependent signal information data of two fields of the matrix located in a difference formation direction and at a difference distance from one another is determined.

[0047] Preferably, the difference formation direction is set so that it essentially corresponds to the lay angle of a strand or a single wire of the wire rope. This allows the stray fluxes caused by the rope structure to be eliminated through spiral or helical difference formation with a suitable difference base. The signals of the defects being sought then exhibit an even more reliably detectable difference from the background signal.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further advantages and aspects of the invention emerge from the claims and from the description of embodiments of the invention, which are explained below with reference to the figures.

[0050] Fig. 1 shows a schematic section through an embodiment of a testing device for the leakage flux test of a continuous wire rope;

[0051] Fig. 2 shows components of a probe assembly of the test device in an oblique perspective;

[0052] Fig. 3 shows components of a probe arrangement of the testing device in an axial view and illustrates relationships in the detection of defects at different depths;

[0053] Fig. 4 illustrates different waveforms of the probe signals and corresponding frequency spectra as well as adapted bandpass filtering;

[0054] Fig. 5 illustrates the relationships to the difference formation operation.

[0055] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] The following examples describe various test methods and test devices for flux leakage testing of wire ropes. The flux leakage test is used to detect defects on and / or in the wire rope. A defect can be, for example, a broken wire, a crack in a wire, an unusual change in shape, or even a more superficial damage that may be accompanied by structural changes. A defect can be located near the surface or inside the wire rope.

[0057] The test is carried out in a continuous motion, i.e., in such a way that a testing device 100 and the wire rope 200 are moved relative to one another in the longitudinal direction of the wire rope, so that the entire length of the wire rope to be tested can be successively tested using the leakage flux test. The schematic Fig. 1 shows a section of a wire rope 200 consisting of a large number of individual wires that are stranded together. In the example case, the wire rope consists of several strands 210, which in turn are composed of a large number of individual wires 205, which in the example case consist of a ferromagnetic steel. The wire rope can be intended, for example, for use in a cable car, in an elevator, or in the construction of bridges. It derives its flexibility from its multi-stranded structure. The wire rope center 202, which runs in the longitudinal direction of the wire rope, is straight in the section shown, since the wire rope is under axial tension.Wire ropes of this type can be several hundred meters or even several kilometers long. The lay lengths of the strands and individual wires can be as shown or different. The lay length 214 of the strands corresponds, in the longitudinal direction of the wire rope, to the distance at which a strand is again at the same circumferential position. Accordingly, the individual wires also have a (smaller) lay length. Accordingly, the angle between the central direction of the wire rope (direction of the wire rope center 202) and the course of a strand is referred to as the lay angle 212 of the strand; the same applies to the lay angle of individual wires in a strand.

[0058] For most wire ropes used on cable cars, bridges, elevators, or the like, regular inspections for potentially safety-relevant defects are required for operational safety reasons. In the example case, a testing device 100 is provided for this purpose, only some components of which are shown schematically in Fig. 1. In the example case, the testing device 100 is stationary and mounted at a station of a cable car; the wire rope does not need to be removed from the system and is moved in its longitudinal direction relative to the testing device 100. Alternatively, it is also possible for the wire rope to remain stationary while the testing device is moved along the wire rope.

[0059] The testing device 100 has a base body 110, which can also be referred to as a housing, and which carries the functional components shown on its inside. The base body has a passage opening 105 for the wire rope and can, for example, be in the form of a sleeve that can be opened and closed to insert the wire rope from the side into the interior of the housing or into the passage opening, or to remove the testing device.

[0060] In an ideal test configuration, the wire rope center 202 or the neutral axis of the wire rope runs more or less coaxially to the passage axis 115 of the test device defined by the base body, which here runs centrally in the axially continuous passage opening. The base body carries on its inner side components of a magnetization device 120 for magnetizing sections of the wire rope as they pass through the passage opening. In the example, the magnetization device 120 is equipped with permanent magnets 122-1, 122-2, which have north poles (N) and south poles (S) and are arranged such that field lines 125 of the magnetization field, i.e., the magnetization field lines 125, are oriented, at least in the central region between the front end and rear end of the test device, essentially in the longitudinal direction of the wire rope or parallel to the passage axis.The magnetization device is designed to encompass the entire circumference of the wire rope and introduce magnetic field lines, or magnetic flux, from all radial directions. This allows a uniformly high magnetization field to be generated within the test volume. The base body contributes to the magnetic return. In this example, the continuous wire rope is magnetized with an axially directed DC field. Electromagnets are usually impractical for mobile magnetization devices due to the necessary power supply cables, but can be used in stationary systems.

[0061] Components of a probe assembly 130 are arranged in the central region between the front and rear ends of the testing device. Components of the probe assembly are shown schematically in an oblique perspective in Fig. 2 and in an axial view in Fig. 3. The probe assembly has a plurality of magnetic field-sensitive probes 140 for detecting magnetic stray fields caused by defects. These can be Hall probes, for example. The probes are arranged offset from one another in the circumferential direction UR of the probe assembly around the passage opening at a radial distance from the passage axis 115. The schematic Fig. 3 shows a section through the probe assembly perpendicular to the passage axis.It can be seen that the probe arrangement encloses the wire rope in such a way that the test tracks on the outer surface of the wire rope scanned by the individual probes are so wide that they overlap each other in the circumferential direction and thus ensure a continuous test over the entire circumference.

[0062] Furthermore, the design allows the probe arrangement to reliably detect even small defects on or near the surface. For this purpose, the individual probes are relatively narrow in the circumferential direction (e.g., coverage only in the arc length range of 1 mm to 5 mm), and many individual probes are provided around the circumference, for example, 30 or more (in the example case, there are 32), but if necessary, twice as many, three times as many, or even more than 100 individual probes. In addition to the achievable spatial resolution in the circumferential direction, such fine division in the circumferential direction has other advantages, which will be explained in detail later.

[0063] To perform the flux leakage test, the individual probes should be in a defined position with a (radial) distance from the surface of the test object (here the wire rope). This radial distance between the surface of the test object and the respective probe is also referred to as the test distance 142. Typical test distances are usually in the range of around 2 mm, for example in the range from 0.5 mm to 5 mm, in particular in the range from 1 mm to 3 mm. In order to be able to maintain these relatively short test distances without risking a collision between the wire rope and probe with possible destruction of the wire rope and / or probe, each of the probes in the probe arrangement is arranged or installed in a movably mounted test shoe 150.

[0064] Fig. 1 shows a test shoe 150 schematically in longitudinal section. A diametrically opposed test shoe is only indicated by dashed lines. Fig. 2 shows an oblique perspective with four circularly curved test shoes 150-1 to 150-4, each carrying several probes of the probe arrangement. Each of the four test shoes extends over a circumferential angular range of approximately 100° to 110°. The test shoes are arranged diametrically opposite one another in pairs, the pairs being arranged axially offset from one another in two planes. Viewed in the circumferential direction UR, the covered areas of the test shoes each overlap in an overlap area 155. This overlap area is dimensioned such that even when the test shoes are positioned radially further outwards, mutual overlap at the ends is ensured in such a way that no test gaps arise in the transition area between test shoes adjacent in the circumferential direction.

[0065] Each test shoe has, on the side facing the wire rope, a more or less flat or slightly convex, cylindrically curved sliding surface 146, which is intended to slide during the test on the outer surface of the continuous wire rope 200, which is moved relative to the test arrangement. For this purpose, the test shoe is made of a mechanically hard metallic or ceramic material, at least on the side facing the wire rope. In the direction of travel, in front of and behind the central region with the probes, so-called run-up slopes are formed on the test shoe. The axial ends of these slopes, in the test configuration shown in Fig. 1, are set back significantly behind the magnets 122 of the magnetization device 120 in the radial direction, so that a passing wire will always strike part of an inclined surface, but not the end face of a test shoe.The probes 140 are set back from the corresponding sliding surfaces 146 of their pole pieces in the radial direction by a so-called probe spacing 145. When the sliding surface slides on the surface of the wire rope in a test configuration, the probe spacing 145 precisely determines the test spacing 142, which can be maintained with high accuracy during the test, at least with respect to the outwardly projecting vertices of the strands 210.

[0066] The test configuration in which the sliding surfaces of the test shoes slide along the surface and the probes are therefore arranged at the minimum possible distance from the wire rope surface is also referred to here as the first test configuration. Here, test distance 142 essentially corresponds to probe distance 145.

[0067] The test shoes 150 are not fixedly or rigidly mounted to the base body, but rather have limited mobility in the radial direction. This is achieved by each of the test shoes 150 being mounted movably relative to the base body by means of a movable suspension or a joint arrangement 160 such that the test shoe can be positioned at different distances from the passage axis 115. In the example, a schematically illustrated joint arrangement 160 is provided, as well as a spring device 170, with which the test shoe 150 can be reliably pressed against the outside of the wire rope for the test.The joint arrangement may, for example, comprise a parallelogram guide, i.e. a mechanism by means of which the test shoe can be attached to a double arm and is held during the radial movement at the original angle (sliding surface parallel to the surface line of the wire rope) of a plane running through the passage axis 115.

[0068] The test device is equipped with a lifting mechanism (not shown in detail), which allows signal-controlled switching between the first test configuration shown and a lifting configuration in which a test shoe is in a lifting position with the sliding surface 146 arranged at a predefined distance from the surface of the wire rope. This then provides a second test distance for the test, which is greater than the aforementioned first test distance, which corresponds to the probe distance. Thus, testing with at least two different test distances is possible. The advantages of this feature will be explained later.

[0069] In the second test configuration, the test spacing can be at least twice as large as in the first test configuration; for example, it can be at least 10 mm, for example, in the range from 10 mm to 25 mm. It may be expedient to perform at least one pass with the first test configuration and at least one pass with the second test configuration during a wire rope test. This allows significantly more significant information to be obtained about the defect condition of the wire rope, including with regard to the depth distribution of the defects.

[0070] During normal operation, a continuous inspection can be performed in the second position. At regular intervals or after events with an increased probability of surface defects, such as thunderstorms, an inspection can be performed in the first position, e.g., as a support or supplement to a visual inspection. The inspection can also be designed to replace a visual inspection by operating personnel.

[0071] The ability to switch between the first test configuration and the second test configuration via signals not only improves the informative value of the entire test, but also improves operational reliability. In principle, it is possible for a single wire in the outer region of the wire rope to break and protrude above the surface. A collision with such protruding ends could disrupt the test and possibly damage or destroy a test shoe or the entire test device. In some embodiments, a protective device is provided that can detect such structural defects, generates a signal upon detection, and the control system is configured so that upon receipt of the signal, a switch from the first test configuration to the lift-off configuration is automatically initiated. This makes a significant contribution to improved operational reliability.

[0072] The test shoe can be placed on the test object (the wire rope) using a remote-controlled mechanism, for example, and automatically lifted off in the event of danger, for example if several wires break off from the surface of the wire rope. The danger can be detected visually or in another way, and a corresponding lift-off signal can be triggered. There are several ways to generate such lift-off signals. In one case, the control unit or evaluation unit is configured so that the test system detects an excessively high signal and then a lift-off signal is sent to the test shoe. It is also possible for the test shoe to contain an additional sensor that measures a force parallel to the direction of transport and triggers the lift-off mechanism when a limit is exceeded. However, a mechanical bevel on the test shoe may also be sufficient to protect it.The probes 140 are connected to the evaluation unit 180 in a signal-conducting manner, allowing the evaluation unit to process the probe signals. In this exemplary embodiment, the evaluation of the probe signal by the evaluation unit is specifically adapted to the properties of the probe arrangement in order to achieve high spatial resolution in the circumferential direction, on the one hand, and to enable defect signals to be assigned to a defect at a specific radial depth, on the other.

[0073] For this purpose, the evaluation device is configured to perform a mapping operation, with which, for each probe signal, signal information representing the probe signal is linked with location information representing the location of the probe signal. This creates location-dependent signal data. The signal data is further processed in a matrix formation operation, which is designed such that the location-dependent signal data or signal data derived therefrom are stored in correctly assigned fields of a base matrix. The subsequent evaluation steps can then access the contents of the base matrix and use it for a wide variety of analyses. At least one evaluation operation is performed, in which location-dependent signal data from at least two fields of the base matrix that are adjacent in an evaluation direction are linked using at least one evaluation algorithm.

[0074] Some basic principles of matrix-based signal analysis are described in patent US 10 082 485 B2. This technique can also be used for wire rope testing with appropriate modifications and adaptations.

[0075] The base matrix can have three or more dimensions. According to a convenient definition, the first dimension of the base matrix represents the signal information, i.e., the information about the leakage flux measured at a specific location. Preferably, bipolar signal information is used here, i.e., raw signal information from non-rectified probe signals, so that the full information content of the local measurement result is available. For example, the second dimension can be the position in the longitudinal direction of the wire rope (x-value), and the third dimension can be the position in the circumferential direction (of the corresponding signal) (y-value). Thus, in the broadest sense, the base matrix creates a relationship between signal information and location information, and it can also contain additional information if necessary.

[0076] In order to be able to write the signals from the individual probes into a position-accurate base matrix (x-value corresponding to the axial position of the test object, y-value corresponding to the circumferential position), a displacement clock is determined from the leakage flux signals themselves. This is possible if the impacts, among other things, are clearly visible in the leakage flux signal. Separate devices such as a timing wheel or similar can be dispensed with. For some wire ropes, e.g., those without strands, there may not be a periodic signal with a sufficiently high amplitude. In this case, a timing wheel or another device suitable for the purpose can be used.

[0077] The base matrix, or rather the signal information it contains, is then filtered using different bandpass filters. The number of different bandpass filters depends on how many different depths in the wire rope are to be evaluated. An evaluation track is introduced for each depth. If, for example, three evaluation tracks are required—one for the outer third of the wire rope (including the surface), one for the middle third, and one for the innermost third (including the center of the wire rope), the base matrix is ​​filtered using a bandpass that allows high frequencies to pass through for the outer third, and a bandpass for low frequencies for the innermost third. The middle third is filtered using a medium frequency.The filtering of the signal information with bandpass filters is based on the knowledge that the leakage flux signals generate a broader signal in the overflow direction (usually also with a smaller amplitude) with increasing distance from a detected discontinuity to the probe and thus have smaller frequencies at the same overflow speed.

[0078] Fig. 4 illustrates this effect. Fig. 4 shows three superimposed sub-figures, each showing a bipolar signal waveform plotting the signal amplitude A over time t on the left and the corresponding representation in frequency domain (amplitude versus frequency t) on the right. The corresponding bandpass filters are symbolized by the trapezoids. The bandpass filtering results in three differently bandpass-filtered matrices for three evaluation tracks.

[0079] For the next step, an integration length can be set on the evaluation device for each evaluation track. The integration length specifies the number of adjacent probes in the circumferential direction over which the signal is to be summed. During this integration, a moving sum or moving average is calculated for a specific number of y values ​​(corresponding to the individual probes included in the integration) in the matrix, assuming the same x-value (same axial position). Fig. 3 shows three different integration lengths IL1, IL2, and IL3. The integration length IL1 represents the integration over the entire circumference, i.e., the signals from all probes are summed.The integration length IL3 represents the shortest integration length in the example (only three adjacent probes), while the integration length IL2 represents an intermediate, relatively long integration length covering less than half and more than a quarter of the entire circumference. In the maximum case (IL1), the totals are summed over the entire circumference, i.e., over all y-values ​​at an x-position of the matrix, to detect a discontinuity in the central wire (DR1) of the wire rope. An advantage of integration over the entire circumference is that periodically occurring flux changes, which generally occur between individual strands, cancel each other out, thus producing a relatively low-noise sum signal, also called the base signal.

[0080] For discontinuities on or near the outer surface (e.g. surface wire DR3), the integration length should be chosen to be relatively short, e.g. only three adjacent probes (see IL3). By filtering at high frequencies, it can be ensured that more distant probes cannot detect a signal from a surface defect that is not directly beneath them. In addition, signals from deeper defects are suppressed in this evaluation channel. When filtering with a high-frequency bandpass, it can also be useful to adapt the angle of the integration direction to the lay direction of the wire in order to better detect the narrow defect maximum. For internal defects, the maximum of the defect signal is so broad over the circumference that optimizing the integration direction offers no advantage.The mean integration length IL2 is used to find defects on internal wires DR2 that are located between the wire rope center and the circumferential surface of the wire rope.

[0081] Furthermore, in preferred embodiments, differentiation can be applied in a difference formation operation prior to integration. During differentiation, differences between adjacent values ​​at a defined distance (difference basis) are formed. This leaves only those signal changes that either deviate in the differentiation direction or have a shorter spatial extent than the difference basis. In wire ropes, there are lay directions of the strands and wires, which also generate stray flux. The differentiation directions should therefore match the lay angles of the strands and wires in order to suppress the oblique stripe patterns that occur in the ropes. For illustration, Fig. 5 shows a schematic plan view of a wire rope with the differentiation directions DF1 for the strands and DF2 for the individual wires. The symbol OD stands for a small surface defect.The thick black line ZD with two thick white lines next to it represents the signal of a central wire break, which is detectable over the entire circumference.

[0082] Subtraction is particularly important when the integration length does not encompass the entire circumference of the rope. Due to the rope's symmetrical structure across its circumference, all stray fluxes caused by the rope's structure can cancel each other out during integration over the entire circumference, at least if the rope's structure is exactly uniform and all sensors on the circumference are at the same distance from the rope. With a shorter integration length, which is chosen for the detection of near-surface defects with high sensitivity, the stray fluxes caused by the rope's structure can be eliminated beforehand using spiral subtraction with a suitable difference base (-> width of the stray flux in the direction of travel, depending on the depth).

[0083] With the three operations (depth-specific bandpass filtering, integration, and difference calculation) and the associated algorithms (bandpass filter, integration length and direction, and difference base and direction), the signal-to-noise ratio of discontinuities can be improved depending on the depth by suppressing periodic signals caused by the individual strands and wires. Furthermore, the depth-dependent signal level of a wire break can be compensated for by detecting the depth.

[0084] Below, some special features of exemplary embodiments for wire rope testing are summarized. These can be useful individually or in combination. The test device has a magnetization device which, when ready for operation, surrounds the wire rope completely in the circumferential direction in order to generate a homogeneous, longitudinally oriented magnetic field in the test volume. The test device has test shoes that slide on the test specimen (wire rope), so that a significantly reduced and consistent probe spacing is achieved compared to conventional wire rope tests. A plurality of magnetic field-sensitive sensors are installed in each of the test shoes so that the stray flux can be scanned continuously around the entire circumference of the test specimen with high resolution and accuracy. A variety of bandpass filters can be used that correlate with the depth of the defect.The integration length can be selected depending on the depth of the defect. The integration and differentiation directions can be adapted to the wire lays. The difference base can be adapted to the depth of the defect. Compensation for the depth-dependent signal level of a wire break is possible. The displacement rate can be calculated from the leakage flux signal, e.g., via the lay length, and / or via the correlation function of probes in the overlap area of ​​the test heads. An automatic lifting device can be provided.

Claims

Patent claims 1. Test method for flux leakage testing of a wire rope to detect defects, in which a test device and the wire rope are moved relative to each other in the longitudinal direction of the wire rope, Sections of the wire rope are successively magnetized by means of a magnetization device of the testing device such that magnetization field lines in the wire rope are oriented substantially in the longitudinal direction of the wire rope; a circumference of the magnetized section of the wire rope is scanned to detect magnetic stray fields caused by defects using magnetic field-sensitive probes of a probe arrangement comprising a plurality of magnetic field-sensitive probes arranged offset from one another in the circumferential direction and, during testing, at a test distance from the surface of the test material, and electrical probe signals from the probes are evaluated to qualify the defects, characterized in that each probe of the probe arrangement is arranged in a movably mounted test shoe having a sliding surface for sliding on the circumferential surface of the wire rope,wherein the probe is arranged offset from the sliding surface by a probe distance and the test shoe is pressed against the peripheral surface in a first test configuration such that the sliding surface is in contact with the peripheral surface and the probe is held at a finite first test distance from the surface of the test material that substantially corresponds to the probe distance.

2. Test method according to claim 1, characterized in that the test distance in the first test configuration is in the range from 0.5 mm to 5 mm, in particular in the range from 1 mm to 3 mm.

3. Testing method according to claim 1 or 2, characterized in that the testing device has three or four or more test shoes distributed over the circumference and movable relative to one another, wherein preferably each test shoe has a plurality of probes arranged offset from one another in the circumferential direction, which probes preferably at least in the first test configuration together cover a circumferential angular range which is greater than 360° divided by the number of test shoes and / or that magnetic flux is coupled into the wire rope from all radial directions and / or that a test is carried out which is continuous in the circumferential direction and / or that the magnetization device is designed such that in the operating state it encompasses the entire circumference of the wire rope without gaps.

4. Testing method according to one of the preceding claims, characterized by a controlled switching between the first test configuration and a lifting configuration, wherein a test shoe is held in a lifting position such that the sliding surface is arranged at a predeterminable distance from the circumferential surface of the wire rope, wherein preferably a protective device is provided for detecting structural defects on the wire rope and for generating a control signal for automatically initiating a switching from the first test configuration to the lifting configuration.

5. Testing method according to one of the preceding claims, characterized by a test in the lift-off configuration, wherein the probe is arranged at a second test distance from the surface, wherein the second test distance is preferably at least 5 mm greater than the test distance in the first test configuration, wherein preferably in a wire rope test at least one pass is carried out with the first test configuration and at least one pass is carried out in the second test configuration.

6. Testing method according to one of the preceding claims, characterized by automatic contact monitoring, which automatically detects whether a test head has lost contact with the wire rope surface, wherein preferably for contact monitoring the frequencies of the signals of all sensors of a test head are continuously determined and a contact loss signal is generated if at least one sensor does not detect the high frequency signals which always arise due to wire gaps on the wire rope surface, wherein preferably wire rope sections which have passed through during a contact loss phase are marked as untested or faulty.

7. Test method according to one of the preceding claims, characterized in that an evaluation of the probe signals comprises the following steps: a mapping operation in which, for each probe signal, signal information representing the probe signal is linked with location information representing the location of origin of a probe signal in order to form location-dependent signal data, a matrix formation operation in which the location-dependent signal data or signal data derived therefrom are stored in correctly assigned fields of a base matrix, and at least one evaluation operation in which location-dependent signal data from at least two fields of the base matrix that are adjacent in an evaluation direction are linked to one another using at least one evaluation algorithm wherein bipolar signal information is preferably used in the formation of the base matrix.

8. Test method according to one of the preceding claims, characterized in that during the evaluation a periodically varying signal component of a probe signal correlated with the lay length of the wire rope is determined and an associated periodicity length of this signal component is used to determine an axial location coordinate of the location of origin of a probe signal.

9. Testing method according to one of the preceding claims, characterized in that the test comprises a detection of defects in a single depth or in several different depths of the wire rope and that a pre-filtering of probe signals is carried out, wherein the pre-filtering for each depth comprises a depth-specific bandpass filtering with preferably adjustable cut-off frequencies, wherein in particular a lower cut-off frequency is set to a smallest and an upper cut-off frequency is set to a largest frequency of the probe signals to be expected for a depth.

10. Testing method according to one of the preceding claims, characterized in that during the evaluation, probe signals of a predeterminable probe group with two or more probes arranged offset from one another in the circumferential direction with directly adjacent or partially overlapping test tracks are evaluated together, so that the probe group forms an effective probe which has an effective test width in the circumferential direction which can be predetermined by the number of probes in the probe group.

11. Testing method according to one of the preceding claims, characterized in that for the detection of defects located at or near the surface, probe signals from a probe group are evaluated which comprises at most 10% of all probes, in particular only two or three or four probes and / or that for the detection of defects located in or near the middle of the wire rope, probe signals from a probe group are evaluated which comprises 90% or more, in particular all probes of the probe arrangement and / or that for the detection of defects at medium depths, the probe signals from a probe group are evaluated which comprises more than 10% and less than 90% of all probes of the probe arrangement and / or that it is determined how many immediately adjacent probes simultaneously detect a leakage flux signal belonging to a specific defect which exceeds a signal threshold and that depth information for the defect is determined therefrom.

12. Test method according to one of the preceding claims, characterized by a difference formation operation in which a difference of location-dependent signal information data of two fields lying in a difference formation direction and at a difference distance from one another is determined, wherein preferably the difference formation direction is set such that it substantially corresponds to a lay angle of a stranded wire or a single wire.

13. A testing device (100) for flux leakage testing of a wire rope (200) to detect defects, wherein the testing device has a passage opening (105) for the wire rope, and the wire rope and the testing device are movable relative to one another in the longitudinal direction of the wire rope, comprising: a base body (110) forming the passage opening (105) and defining a passage axis (115) located in the passage opening; a magnetization device (120) carried by the base body for magnetizing sections of the wire rope (200) as they pass through the passage opening (105) such that magnetization field lines (125) in the wire rope are oriented substantially in the longitudinal direction of the wire rope; a probe arrangement (130) with a plurality of magnetic-field-sensitive probes (140) for detecting magnetic stray fields caused by defects,wherein the probes are arranged offset from one another in a circumferential direction around the passage opening (105), and an evaluation unit (180) for evaluating electrical probe signals from the probes to qualify the defects, characterized in that each probe of the probe arrangement is arranged in a test shoe (150) and the testing device has three or more test shoes, wherein each of the test shoes is movably mounted relative to the base body (110) such that the test shoe can be positioned at different distances from the passage axis (115), has a sliding surface (146) for sliding on the circumferential surface of the wire rope (200), wherein each probe of the test shoe is arranged offset from the sliding surface by a probe distance (145), and in a first test configuration can be pressed against the circumferential surface of a wire rope (200) passing through the passage opening in such a way,that the sliding surface (146) is in contact with the peripheral surface and the probe (140) is held at a finite first test distance (142) from the surface of the wire rope substantially corresponding to the probe distance., 14. Testing device according to claim 13, characterized in that at least one, preferably several or all of the following conditions are met: the probe arrangement (130) has more than 20 probes distributed over the circumference, wherein the probe arrangement preferably has 30 or more or 60 or more probes; each of the probes (140) has a test width measured in the circumferential direction which corresponds to a circumferential angle in the range of 5° to 10°; the magnetization device (120) is designed such that it encompasses the entire circumference of the wire rope in the operating state; the probes (140) of the probe arrangement (130) are designed and arranged such that a gapless testing of the wire rope in the circumferential direction is possible in a single pass.

15. Testing device according to claim 13 or 14, characterized by at least one of the following features: a test shoe (150) is movably mounted on the base body (110) by means of a joint arrangement (160), wherein the joint arrangement preferably comprises a parallelogram guide and / or a solid-state joint; a pressing device is provided which preloads the test shoe in the direction of the passage axis, wherein the pressing device preferably comprises a spring arrangement (170) with at least one spring.

16. Testing device according to one of claims 13 to 155, characterized in that the evaluation device (180) is configured to carry out an evaluation of the probe signals according to the features of the characteristics of one of claims 6 to 12

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