Device and method for determining the thickness of a surface of an elastomer article, preferably the profile depth of a tread of an air-filled tire

Abstract

The present invention relates to a device for determining the thickness (T) of a surface (4) of an elastomer article (2), preferably the profile depth (T) of a tread (4) of a pneumatic tire (2), with the elastomer article (2), which has at least one electrically conductive structure (8a) facing away from the surface (4), with a thickness sensor (12, 14, 16), preferably a profile depth sensor (12, 14, 16), which is arranged on the surface (4) of the elastomer article (2) aligned with the thickness (T) to be measured and is designed to generate, by means of electrical supply, an alternating magnetic field for exciting electrical eddy currents in the electrically conductive structure (8a) of the elastomer article (2) and to maintain a magnetic field generated by the eddy currents of the electrically conductive structure (8a) of the elastomer article (2), and with a control unit which is designed to control the thickness sensor (12, 14,16) for generating the alternating magnetic field and detecting the eddy current density of the magnetic field of the electrically conductive structure (8a) of the elastomer article (2) generated by the eddy currents, wherein the control unit is further configured to determine at least the thickness (T) of the surface (4) of the elastomer article (2) from the detected eddy current density of the elastomer article (2) in relation to a predetermined comparison value.

Description

The present invention relates to an apparatus and method for determining the thickness of a surface of an elastomeric article, preferably the tread depth of a tread of an air-filled tire.For measuring the thickness of elastomer layers, non-invasive measurements in the reactive electromagnetic near field of the products are known, for example. These measuring methods are applicable to sheet-like products such as printing cloths, conveyor belts, belts in general and the like as well as to three-dimensional structures such as hoses, air springs and air-filled tires.U.S. Pat. No. 11,060,841 B2 discloses a non-invasive method for measuring the layer thickness, in which an oscillating signal of constant frequency is applied to a first electrode, the signal propagating through the material to be measured to a second electrode. The measured variable for the layer thickness is the power which is transmitted back from the second electrode to the first.Tyrata has developed a similar system ("IntelliTread"TM) for tires: two electrodes on a flexible substrate are located below a tread on the inside of the tread. An oscillating electric voltage is applied between the electrodes. The electric field strength that is established is evaluated, which is dependent on the profile depth to be measured.Both solutions have the disadvantage that they must be integrated into each individual tire whose tread depth is to be measured. This results in additional effort for the complex electronics themselves and their integration into the tire. This also increases the cost of the tire.From a technical point of view, it is also disadvantageous that the electric field must penetrate all plies of the reinforcing members in the tire, including the belts made of conductive steel cord, before it reaches the elastomeric tread. This circumstance places high requirements on the selection of the materials for the sensor and on its design and operating mode.These disadvantages apply analogously to other elastomeric products, as already mentioned above.An object of the present invention is to provide an apparatus and or a method for improved determination of the thickness of a surface of an elastomer article, preferably the tread depth of a tread of an air-filled tire, of the type described at the beginning. At least, an alternative to the known possibilities is to be created.The object is achieved according to the invention by a device, by a thickness sensor, by a control unit and by a method having the features according to the independent claims. Advantageous refinements are described in the dependent claims.The present invention thus relates to a device for determining the thickness of a surface of an elastomer article, preferably the tread depth of a tread of an air-filled tire, having the elastomer article which has at least one electrically conductive structure facing away from the surface, having a thickness sensor, preferably a tread depth sensor, which is arranged on the surface of the elastomer article in a manner oriented with respect to the thickness to be measured and is designed to generate an alternating magnetic field for exciting electric eddy currents in the electrically conductive structure of the elastomer article by means of electrical feeding and to obtain a magnetic field generated by the eddy currents of the electrically conductive structure of the elastomer article, and having a control unit which is designed to feed the thickness sensor for generating the alternating magnetic field and to record the eddy current density of the magnetic field of the electrically conductive structure of the elastomer article generated by the eddy currents, wherein the control unit is further configured to determine at least the thickness of the surface of the elastomer article from the detected eddy current density of the elastomer article in relation to a predetermined comparison value.Thus, the method of eddy current testing as described above can be applied to elastomer articles such as in particular tires, conveyor belts, printing cloths and the like, which in any case have an electrically conductive structure which can be excited and the reaction of which can be detected in order to detect the thickness of the elastomer material lying therebetween. This detected thickness can be compared with a comparison value, which is known, as a reference in order to make a relative and absolute statement about the current thickness of the elastomer material. This can be used to infer the abrasion due to the past use, as a result of which statements can also be made about the further use of the elastomer product. It is also possible to determine other material properties from the measured values and evaluate these.According to one aspect of the invention, the control unit is configured to feed the thickness sensor for generating the alternating magnetic field at a frequency of at most 500 kHz. This can reduce the influence of the material properties of the detected elastomer material on the measurement result.According to a further aspect of the invention, the thickness sensor has a printed circuit board or a flexible conductor foil which is designed to be arranged on the surface of the elastomer article, wherein a loop antenna and a microstrip line are arranged on the printed circuit board or on the flexible conductor foil. This can represent a specific possibility of implementation.According to a further aspect of the invention, the predetermined comparison value is the thickness of the surface of the elastomer article in the new state of the elastomer article. This can allow information in relation to the new state and thus regarding the wear due to the current use.According to another aspect of the invention, the elastomeric article is an air-filled tire and the electrically conductive structure is a steel cord belt ply, preferably the outer steel cord belt ply. This can enable a concrete application of the invention in air-filled tires in order to use the outer steel cord belt ply present there in any case as an electrically conductive structure.According to a further aspect of the invention, the device further comprises a temperature sensor which is designed and arranged to detect the temperature of the surface of the elastomer article, wherein the control unit is designed to take into account the detected temperature of the surface of the elastomer article in determining the thickness of the surface of the elastomer article. This may allow for consideration of the current temperature of the surface of the elastomeric article, which may affect the determination of the thickness of the surface of the elastomeric article. This consideration can be effected by a mathematical relationship, by a value table or the like in order to make corresponding corrections of the thickness of the surface of the elastomer article as a function of the temperature.According to a further aspect of the invention, the device further comprises a moisture sensor which is designed and arranged to detect the moisture of the surface of the elastomer article, wherein the control unit is designed to take into account the detected moisture of the surface of the elastomer article in determining the thickness of the surface of the elastomer article. This can allow consideration of the current moisture of the surface of the elastomer article, which moisture can influence the determination of the thickness of the surface of the elastomer article. This consideration can be effected by a mathematical relationship, by a value table or the like in order to make corresponding corrections to the thickness of the surface of the elastomer article as a function of the moisture.The present invention also relates to a thickness sensor, preferably a profile depth sensor, for use in a device as described above. Thus, a thickness sensor as described above can be provided in order to implement a device according to the invention as described above and to realize the advantages and properties thereof.The present invention further relates to a control unit for use in a device as described above. Thus, a control unit as described above can be provided in order to implement a device according to the invention as described above and to realize the advantages and properties thereof.The present invention further relates to a method for determining the thickness of a surface of an elastomer article, preferably the tread depth of a tread of an air-filled tire, wherein the elastomer article has at least one electrically conductive structure facing away from the surface, comprising at least the steps:• generating an alternating magnetic field for exciting electric eddy currents in the electrically conductive structure of the elastomer article,• obtaining a magnetic field generated by the eddy currents of the electrically conductive structure of the elastomer article,• detecting the eddy current density of the magnetic field generated by the eddy currents of the electrically conductive structure of the elastomer article, and• Determining at least the thickness of the surface of the elastomer article from the detected eddy current density of the elastomer article in relation to a predetermined comparison value.A method can thus be provided to realize the previously described properties and advantages, which can preferably be effected by means of the previously described device.An exemplary embodiment and further advantages of the invention are explained below in conjunction with the following figures. The following shows: FIG. 1 is a perspective schematic sectional view of a portion of an air-filled tire; FIG. 2 shows a schematic plan view of the tire of FIG. 1 with a thickness sensor according to the invention; FIG. 3 shows a schematic cross section through one half of the tire with a thickness sensor according to the invention; and FIG. 4 is an enlarged view of the range of the thickness sensor of FIG. 3.FIG. 1 shows the structure of a tire 2. the tread 4 is located on the outer periphery of the tire 2. the winding bandages 6, the steel cord belt plies 8 a, 8 band the textile cord inserts 10 follow from the outside to the inside in the radial direction. As thickness T of the surface 4 of the elastomer article 2, the profile depth T of the air-filled tire 2 is determined or measured by measurement.The essential difference from the known devices and methods for measuring the tread depth T in air-filled tires is that the thickness sensor 12, 14, 16 or tread depth sensor 12, 14, 16 according to the invention is applied outside the tire 2.FIGS. 2 to 4 show the construction according to the invention for measuring the profile depth T.A loop antenna 14 and a microstrip line 16 are located on a printed circuit board 12 or on a flexible conductor foil 12, respectively. For the measurement, the printed circuit board 12 or the conductor foil 12 is placed on the outside of the tread 4 of the tire 2. The printed circuit board 12 or the flexible conductor foil 12, the loop antenna 14 and the microstrip line 16 together form the thickness sensor 12, 14, 16 or the profile depth sensor 12, 14, 16.A control unit or a measurement electronics (not shown) then uses the loop antenna 14 to determine the distance between the printed circuit board 12 or between the conductor foil 12 and the outer steel cord belt ply 8 aaccording to the principle of eddy current measurement. The frequency of the measurement current through the loop antenna 14 is adjusted by the control unit such that the influence of the material properties of the elastomeric tread 4 on the measurement result can be neglected, which is the case, for example, at frequencies below 500 kHz.Together with the outer steel cord belt ply 8 a, the microstrip line 16 on the printed circuit board 12 or on the conductor foil 12 forms an unsymmetrical strip line, the spectral transmission properties of which are likewise dependent on the distance from the steel cord belt ply 8 a, so that the profile depth T can be determined on the basis of two measurements. In this case, firstly the profile depth T is measured for a new tire 2 and secondly later during use, with the result that by comparing the two measured profile depths T or by ascertaining the difference between the two measured profile depths T, the wear which has taken place in the meantime can be detected and quantified.The present invention is based on the finding that the tread 4 of a tire 2 is exposed to high mechanical loads during operation of the tire 2, as a result of which the dielectric properties of the elastomeric material of the tread 4 of the tire 2 change over time. These changes are reflected in the frequency-dependent transmission function of the strip line formed by the microstrip line 16 and the outer steel cord belt ply 8a when the printed circuit board 12 or the conductor foil 12 rests on the tread 4 and is excited. By comparing it with the transmission behavior in the new state, it is possible to infer the wear or the aging of the tread 4 of the tire 2.In order to compensate for the influences of the environmental conditions on the measured variables (impedances), a temperature sensor and a humidity sensor can additionally be used and the measured values thereof can be taken into account by the control unit in order to calculate out these influences.List of Reference Numerals (part of the description)T Thickness of surface 4; tread depth 2 Elastomer article; air-filled tire 4 Surface; tread 6 Winding tapes 8a, 8b Electrically conductive structure; steel cord belt plies 10 Textile cord plies 12, 14, 16 Thickness sensor; tread depth sensor 12 Printed circuit board; flexible conductor film 14 Loop antenna 16 Micro-strip lineReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 11,060,841 B2

[0003]

Claims

Device for determining the thickness (T) of a surface (4) of an elastomer article (2), preferably the tread depth (T) of a tread (4) of an air-filled tire (2), with the elastomer article (2) which has at least one electrically conductive structure (8a) facing away from the surface (4), with a thickness sensor (12, 14, 16), preferably a tread depth sensor (12, 14, 16) which is arranged on the surface (4) of the elastomer article (2) in alignment with the thickness (T) to be measured and is designed to generate an alternating magnetic field by means of electrical supply for exciting electrical eddy currents in the electrically conductive structure (8a) of the elastomer article (2) and to obtain a magnetic field generated by the eddy currents of the electrically conductive structure (8a) of the elastomer article (2), and with a control unit, which is designed to feed the thickness sensor (12, 14, 16) for generating the alternating magnetic field and to detect the eddy current density of the magnetic field of the electrically conductive structure (8a) of the elastomer article (2) generated by the eddy currents, wherein the control unit is furthermore designed to determine at least the thickness (T) of the surface (4) of the elastomer article (2) from the detected eddy current density of the elastomer article (2) in relation to a predetermined comparison value.The device according to claim 1, wherein the control unit is configured to feed the thickness sensor (12, 14, 16) with a frequency of at most 500 kHz for generating the alternating magnetic field.Device according to claim 1 or 2, wherein the thickness sensor (12, 14, 16) comprises a printed circuit board (12) or a flexible conductor foil (12) which is configured to be arranged on the surface (4) of the elastomer article (2), wherein a loop antenna (14) and a microstrip line (16) are arranged on the printed circuit board (12) or on the flexible conductor foil (12).Device according to one of the preceding claims, wherein the predetermined comparison value is the thickness (T) of the surface (4) of the elastomer article (2) in the new state of the elastomer article (2).Device according to any of the preceding claims, wherein the elastomeric article (2) is an air-filled tyre (2) and the electrically conductive structure (8a) is a steel cord belt ply (8a), preferably the outer steel cord belt ply (8a).Device according to one of the preceding claims, further comprising a temperature sensor which is designed and arranged to detect the temperature of the surface (4) of the elastomer article (2), wherein the control unit is designed to take into account the detected temperature of the surface (4) of the elastomer article (2) when determining the thickness (T) of the surface (4) of the elastomer article (2).Device according to one of the preceding claims, further comprising a moisture sensor which is designed and arranged to detect the moisture of the surface (4) of the elastomer article (2), wherein the control unit is designed to take into account the detected moisture of the surface (4) of the elastomer article (2) when determining the thickness (T) of the surface (4) of the elastomer article (2).Thickness sensor (12, 14, 16), preferably profile depth sensor (12, 14, 16), for use in a device according to any one of claims 1 to 7.A control unit for use in a device according to any one of claims 1 to 7.Method for determining the thickness (T) of a surface (4) of an elastomer article (2), preferably the profile depth (T) of a tread (4) of an air-filled tire (2), wherein the elastomer article (2) has at least one electrically conductive structure (8a) facing away from the surface (4), comprising at least the steps of: • generating an alternating magnetic field for exciting electric eddy currents in the electrically conductive structure (8a) of the elastomer article (2), • obtaining a magnetic field generated by the eddy currents of the electrically conductive structure (8a) of the elastomer article (2), • detecting the eddy current density of the magnetic field generated by the eddy currents of the electrically conductive structure (8a) of the elastomer article (2), • Determining at least the thickness (T) of the surface (4) of the elastomer article (2) from the detected eddy current density of the elastomer article (2) in relation to a predetermined comparison value.

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