Device and method for detecting a defect in an object containing wire ropes

Abstract

The invention relates to a device (1) for detecting, inside an object containing a plurality of wire ropes, a positioning defect of one of the wire ropes with respect to another of the wire ropes, which device comprises: - a magnetic field generator (10) arranged to generate a magnetic field referred to as an "inspection magnetic field", and to be positioned facing the object in such a way that the plurality of wire ropes causes the inspection magnetic field to deform, - a magnetic sensor (12), referred to as the "primary magnetic sensor", which is provided to measure the intensity of the inspection magnetic field, the device (1) being characterised in that the inspection magnetic field has, before being deformed by the plurality of wire ropes, at least one neutral point where the intensity of the inspection magnetic field is zero, and in that the primary magnetic sensor (12) is arranged relative to the magnetic field generator (10) in a chosen position which corresponds to a position of that neutral point.

Description

[0001] Device and method for detecting defects in an object containing metal cables

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of defect detection in an object containing metal cables, more precisely of defect in the positioning of a metal cable relative to another metal cable, and, more particularly still, of defect detection in an object constituting a tire such as a reinforcing ply containing a plurality of reinforcing metal cables embedded in a rubber-based matrix.

[0004] STATE OF THE ART

[0005] When manufacturing a tire, the metal carcass ply is wrapped around a thin rubber and two edges of the carcass ply are welded together so as to give the carcass ply a cylindrical shape.

[0006] However, the weld may have defects that cause irreversible quality problems once the tire has been cured. A poor weld of the carcass ply can cause the tire to be destroyed during driving or, to a lesser extent, premature tire wear or discomfort during driving. Therefore, it is necessary to check the weld after the carcass ply has been installed.

[0007] Currently, this verification can be carried out using different methods:

[0008] - a metal comb is used to determine the position and spacing of the edges at the weld. This method is not necessarily reliable and requires the intervention of an operator to handle the comb;

[0009] - a laser profilometer is used to scan the carcass ply before and after welding. This method is expensive due to the hardware and IT dedicated to analyzing the defects required.

[0010] There is therefore currently no solution for checking the welding of carcass plies, and more generally of reinforcement plies, during tire manufacturing that is inexpensive and easy to use.

[0011] STATEMENT OF THE INVENTION

[0012] An aim of the invention is to provide a solution for detecting defects within an object which contains a plurality of metal cables, such as a metal carcass ply of a tire, which is inexpensive, easy to implement, reliable and preferably automated.

[0013] According to a first aspect, a detection device is provided for detecting, within an object which contains a plurality of metal cables, such as a reinforcing sheet containing a plurality of reinforcing metal cables embedded in a rubber-based matrix, a positioning defect of one of the metal cables relative to another of said metal cables, said device comprising:

[0014] - a magnetic field generator, preferably consisting of a magnet or a coil, which is arranged to generate a magnetic field called an “inspection magnetic field”, and to be positioned opposite the object in such a way that the plurality of metal cables causes a deformation of said inspection magnetic field,

[0015] - a magnetic sensor called a "primary magnetic sensor" which is provided for measuring the intensity of the inspection magnetic field, said device being characterized in that the inspection magnetic field has, before being deformed by the plurality of metal cables, at least one neutral point where the intensity of said inspection magnetic field is zero, and in that the primary magnetic sensor is arranged relative to the magnetic field generator in a chosen position which corresponds to a position of this neutral point.

[0016] According to advantageous and non-limiting characteristics, taken alone or in any combination: the magnetic field generator has a toroidal shape which is centered on an axis called the "central axis of the generator" and which delimits a free internal space, and in that the adjustment system comprises a support part which carries the primary magnetic sensor and which is engaged in said free internal space so as to be able to be moved along the central axis of the generator in order to modify the position of the primary magnetic sensor along said central axis of the generator; the device comprises at least one stabilizing element, such as a roller, adapted to come into contact with the object in order to maintain a constant distance between the primary magnetic sensor and an external surface of the object; the device comprises at least one suspension member, such as a spring, adapted to elastically press the stabilizing element against the object;the device comprises a secondary magnetic sensor which is distinct from the primary magnetic sensor, which is not subjected to the inspection magnetic field and which is arranged to be placed opposite an area of ​​the object in order to measure the intensity of the magnetic field called the "background magnetic field" which is representative of a magnetic field which prevails in the object in the absence of an inspection magnetic field; the device comprises a sub-assembly forming a train of three carriages which are arranged in a row in a direction called the "longitudinal direction" and which are articulated two by two, one with respect to the other so as to be able to fit an external surface of the object, each bearing on said external surface in order to provide at least three corresponding distinct bearing areas along the longitudinal direction, said carriages being formed respectively by:;

[0017] - a primary carriage which carries the magnetic field generator and the primary magnetic sensor, as well as at least one primary stabilizing element, preferably a primary roller whose axis of rotation is perpendicular to the longitudinal direction, which allows said primary carriage to roll on the external surface of the object while maintaining the magnetic field generator and the primary magnetic sensor at a predefined, constant distance from the external surface,

[0018] - a secondary carriage which carries the secondary magnetic sensor and at least one secondary stabilizing element, preferably a secondary roller whose axis of rotation is perpendicular to the longitudinal direction, which allows said secondary carriage to roll on the external surface while maintaining the secondary magnetic sensor at a predefined, constant distance from the external surface,

[0019] - a tertiary carriage which carries at least one tertiary stabilizing element, preferably a tertiary roller whose axis of rotation is perpendicular to the longitudinal direction, which allows said tertiary carriage to roll on the external surface of the object.

[0020] According to another aspect, a detection assembly is proposed, characterized in that it comprises a detection device presented previously as well as a drive system making it possible to generate a relative movement of scrolling of an external surface of the object with respect to the magnetic field generator and the primary magnetic sensor in a predetermined direction called "scanning direction", and in that the secondary magnetic sensor is arranged so as to precede the primary magnetic sensor in consideration of said scanning direction, so that the same zone of the external surface of the object is successively traversed by the secondary magnetic sensor, which measures the background magnetic field, then by the primary magnetic sensor, which measures the inspection magnetic field as deformed by the plurality of metal cables of the object.

[0021] According to another aspect, there is provided a method for detecting, within an object which contains a plurality of metal cables, such as a reinforcing ply containing a plurality of reinforcing metal cables embedded in a rubber-based matrix, a positioning defect of one of the metal cables relative to another of said metal cables, the method comprising the following steps: a) providing a magnetic field generator and a primary magnetic sensor, in order to form a detection device, the primary magnetic sensor being arranged relative to the magnetic field generator in a chosen position which corresponds to the position of a neutral point, the neutral point corresponding to a point of an inspection magnetic field generated by the magnetic field generator, before it is deformed by the plurality of metal cables, where the intensity of said inspection magnetic field is zero;b) positioning the detection device relative to the object so that the magnetic field generator and the primary magnetic sensor are arranged opposite the object; c) relative movement of the detection device relative to the object and continuous acquisition of a primary signal received by the primary magnetic sensor; d) detecting, in the primary signal, a signature representative of a positioning defect of a metal cable of the object.;

[0022] According to advantageous and non-limiting characteristics, taken alone or in any combination: step a) comprises a step a0) of adjusting the detection device by positioning the primary magnetic sensor relative to the magnetic field generator in the chosen position; in step a0), the primary magnetic sensor (12) is positioned using an adjustment system (143) making it possible to adjust, for example by screwing, the position of the primary magnetic sensor (12) relative to the magnetic field generator (10) and to maintain the primary magnetic sensor (12) in the chosen position, fixed relative to the magnetic field generator (10), the adjustment system (143) being included in a support (14), called the “primary support”,which carries the magnetic field generator (10) and the primary magnetic sensor (12) and which is provided with the adjustment system (143); the magnetic field generator (10) has a toroidal shape which is centered on an axis (A) called the "central axis of the generator" and which delimits a free internal space (101), and the adjustment system (143) comprises a support part (142) which carries the primary magnetic sensor (12) and which is engaged in said free internal space (101) and in step a0), the support part (142) which carries the primary magnetic sensor (12) is moved along the central axis of the generator (A) in order to modify the position of the primary magnetic sensor (12) along said central axis of the generator (A). in step b), at least one stabilizing element (18), such as a roller, is placed in contact with the object (2) in order to maintain a constant distance between the primary magnetic sensor (12) and an external surface (22) of the object (2); in step b),the stabilizing element (18) is elastically pressed against the object (2) by means of a suspension member (19), such as a spring; during step c), the detection device is moved relative to the object so that the primary magnetic sensor is successively arranged in different positions relative to the object, the different positions comprising at least one position of interest in which the magnetic sensor is arranged opposite a zone of interest of the object, in which a possible defect is to be detected, and a nominal position in which the magnetic sensor is arranged opposite a zone of the object free of defect, different from the zone of interest, so that a nominal magnetic field intensity of the primary signal is measured; the signature representative of a positioning defect of a metal cable of the object is a local extremum relative to the nominal magnetic field intensity,the local extremum having a magnetic field intensity greater than a first threshold value or a magnetic field intensity less than a second threshold value; in step d), if the presence of a local extremum is determined and, if this extremum has a magnetic field intensity greater than the first threshold value, it is concluded that there is a defect corresponding to a superposition of two metal cables, whereas, if this extremum has a magnetic field intensity less than the second threshold value,the presence of a defect is concluded to be present corresponding to the existence of a gap between two consecutive metal cables which is greater than a nominal gap; the method comprises a step prior to the acquisition of the primary signal of acquiring a secondary signal corresponding to the evolution during the movement of a magnetic field called "background magnetic field" which is representative of a magnetic field which prevails in the object in the absence of an inspection magnetic field and in which step d) comprises processing of the primary signal including subtraction of the secondary signal from the primary signal; the prior step of acquiring a secondary signal is implemented by a secondary magnetic sensor (16) which is separate from the primary magnetic sensor (12), which is not subjected to the inspection magnetic field and, during the implementation of the prior step of acquiring a secondary signal,the secondary magnetic sensor (16) is placed opposite an area of ​​the object (2). in step b), a subassembly (13) is placed in contact with an external surface (22) of the object (2), the subassembly (13) forming a train of three carriages (130a, 130b, 130c) which are arranged in a row in a direction (D) called the "longitudinal direction" and which are articulated two by two, one with respect to the other so as to be able to fit an external surface (22) of the object (2) while each resting on said external surface (22) in order to provide at least three corresponding distinct support areas along the longitudinal direction (D), said carriages (130a, 130b, 130c) being formed respectively by:,

[0023] - a primary carriage (130a) which carries the magnetic field generator (10) and the primary magnetic sensor (12), as well as at least one primary stabilizing element (18a), preferably a primary roller whose axis of rotation (Xa) is perpendicular to the longitudinal direction (D), which allows said primary carriage (130a) to roll on the external surface (22) of the object (2) while maintaining the magnetic field generator (10) and the primary magnetic sensor (12) at a predefined, constant distance from the external surface (22),

[0024] - a secondary carriage (130b) which carries the secondary magnetic sensor (16) and at least one secondary stabilizing element (18b), preferably a secondary roller whose axis of rotation (Xb) is perpendicular to the longitudinal direction (D), which allows said secondary carriage (130b) to roll on the external surface (22) while maintaining the secondary magnetic sensor (16) at a predefined, constant distance from the external surface (22),

[0025] - a tertiary carriage (130c) which carries at least one tertiary stabilizing element (18c), preferably a tertiary roller whose axis of rotation (Xc) is perpendicular to the longitudinal direction (D), which allows said tertiary carriage (130c) to roll on the external surface (22) of the object (2), and to implement the prior step of acquiring a secondary signal and step c) of relative movement of the detection device (1) with respect to the object (2) and continuous acquisition of a primary signal received by the primary magnetic sensor (12), the carriages (130a, 130b, 130c) are rolled on the external surface (22) of the object (2) so that the same area of ​​the object (2) is first opposite the primary carriage (130a), then the secondary carriage (130b) and finally the carriage tertiary (130c);step d) comprises processing the primary signal, the processing comprising at least one processing operation from among the following processing operations: filtering with a low-pass filter, calculating the absolute value of the signal, normalizing, thresholding and a combination of these processing operations; the method is implemented to detect, within a reinforcing ply containing metal cables extending non-parallel to an edge of the reinforcing ply, a positioning defect of one of the metal cables relative to another of said metal cables.;

[0026] DESCRIPTION OF FIGURES

[0027] Other features and advantages of the present invention will become apparent upon reading the following description of a preferred embodiment. This description will be given with reference to the appended figures, including: Figure 1 shows a defect detection device in use on an object; Figure 2 shows a part of an object free of defects; Figure 3 shows a part of an object having a cable gap type defect; Figure 4 shows a part of an object having a cable superposition type defect; Figure 5 shows a support carrying a primary magnetic sensor and a magnetic field generator; Figure 6 shows a magnetic field generator; Figure 7 shows a magnetic field generator and the inspection magnetic field; Figure 8 is a sectional view of a support carrying a primary magnetic sensor and a magnetic field generator;Figure 9 represents the device comprising three carriages including a primary carriage carrying a magnetic field generator and a primary magnetic sensor; Figure 10 represents the steps of a fault detection method; Figure 11 represents a signal received by the primary magnetic sensor.;

[0028] DETAILED DESCRIPTION OF THE INVENTION Device

[0029] With reference to Figure 1, there is provided a detection device 1 intended to detect, within an object 2 which contains a plurality of metal cables 20, a positioning defect of one of the metal cables relative to another of the metal cables. Said metal cables 20 are preferably arranged in a non-metallic matrix 21, preferably an elastomer matrix, for example a rubber-based matrix.

[0030] The object 2 is for example a reinforcing ply containing a plurality of metal reinforcing cables embedded in a rubber-based matrix 21, such as a carcass ply or a crown ply of a tire. The object 2 can therefore be a composite object comprising metal and rubber.

[0031] Object 2 may also be a rod intended to hold a tire in position on a rim.

[0032] Referring to Figure 2, the object 2 contains a plurality of metal cables 20 arranged in a theoretical arrangement. For example, the cables 20 may be arranged in a regular pattern, for example being placed at equal distances from each other and parallel to each other. More specifically, as illustrated in Figure 2, the cables 20 may be arranged according to a predefined nominal distribution pitch E1, the pitch being the center-to-center distance between neighboring cable sections. The cables may also be placed at different distances from each other. The cables 20 may be, for example, straight or corrugated.

[0033] The cables 20 preferably extend in a direction not parallel to the edges of the object 2. In the case of a tire ply, the edges of the ply usually designate the width limits, i.e. the edges which axially limit the ply, and which run parallel to each other and in the circumferential direction of the tire. In the case of a carcass ply, the cables 20 are generally perpendicular to the edges of the ply. In the case of a crown ply, the cables 20 are generally oriented obliquely relative to the edges.

[0034] The object 2 may have a defect. More specifically, there may be a positioning defect of one of the metal cables 20 relative to another of the metal cables 20 of the object 2. As illustrated in FIG. 3, the defect may for example consist of a spacing E2 between two consecutive metal cables 20 greater than a nominal spacing expected between two consecutive metal cables 20. The defect may also consist of a superposition of two metal cables 20, as illustrated in FIG. 4.

[0035] More particularly, the object 2 may have a defect at the weld 23 between two edges of the object 2. The edges of the object 2 are sides of the object 2 which each connect the edges of the object 2 together. The edges of the object 2 therefore extend in a direction not parallel to the edges of the object 2. The edges preferably extend parallel to the cables 20 and, thus, the weld 23 typically extends parallel to the cables 20. In the case of a carcass ply, the edges, and thus the weld 23, are generally perpendicular to the edges of the ply. In the case of a crown ply, the edges, and thus the weld 23, are generally oriented obliquely relative to the edges. Weld 23 is an area of ​​object 2 that may particularly exhibit defects if weld 23 is poorly performed. Weld 23 generally constitutes an area of ​​interest in the defect detection of object 2.

[0036] With reference to Figure 5, the detection device 1 comprises a magnetic field generator 10. The magnetic field generator 10 is for example a magnet, an electromagnet or a coil.

[0037] Advantageously, the magnetic field generator 10 is a single element, i.e., a single magnet, a single electromagnet or a single coil. In other words, the magnetic field generator 10 is not formed from a combination of elements such as a combination of magnets.

[0038] The magnetic field generator 10 generates a magnetic field called an “inspection magnetic field”. The coil has the advantage of allowing better adjustment of the magnetic field parameters.

[0039] As illustrated in Figure 5, the magnetic field generator 10 preferably has a toroidal shape which is centered on an axis A called the “central axis of the generator” and which delimits a free internal space 101. It is understood that the central axis of the generator A is the axis of revolution of the magnetic field generator 10. Preferably, the magnetic field generator 10 has a toroidal shape with a rectangular section.

[0040] Preferably, the central axis of the generator A corresponds to the axis connecting the north pole and the south pole of the magnetic field generator 10.

[0041] The magnetic field generator 10 may have other shapes, preferably shapes of revolution centered on a central axis A. The magnetic field generator 10 may for example be a hollow, annular or toric cylinder with a circular section.

[0042] Referring to Figure 6, the magnetic field generator 10 is designed so that the north and south poles are arranged one on top of the other. The magnetic field generator 10 therefore comprises a north portion 102 and a south portion 104 and, in the example of a magnetic field generator 10 having a toroidal shape centered on a central axis A, each of the north portion 102 and south portion 104 has a toroidal shape centered on the central axis A. When the inspection magnetic field is not subject to magnetic disturbances linked to metallic elements (therefore, for example, when the magnetic field generator 10 is sufficiently far from the metal cables 20 of the object 2 so that the inspection magnetic field is not deformed by said metal cables 20 of the object 2), the inspection magnetic field has at least one neutral point where its intensity is zero.By "zero" is meant a magnetic field intensity whose absolute value is preferably equal to 0 Tesla. It is understood that a neutral point is a point intrinsic to the magnetic field of the magnetic field generator 10.

[0043] Preferably, the neutral point(s) of the magnetic field of the magnetic field generator 10 are positioned on the axis connecting the north pole and the south pole of the magnetic field generator 10.

[0044] As illustrated in Figure 7, at the neutral points P1 and P2, the inspection magnetic field lines substantially cancel each other out and the inspection field has a substantially zero intensity value. Thus, at a neutral point, the deformations of the inspection magnetic field lines are easily detectable because it is sufficient to detect that the magnetic field intensity is no longer zero, or at least separated by a certain difference from a zero intensity value, at a neutral point to deduce that the inspection magnetic field lines are deformed.

[0045] As illustrated in Figure 5, the detection device 1 also comprises a magnetic sensor 12, called the “primary magnetic sensor”. The primary magnetic sensor 12 is configured to acquire magnetic signals and therefore to measure magnetic field intensity values. More specifically, the primary magnetic sensor 12 is provided to measure the intensity of the inspection magnetic field.

[0046] Preferably, the primary magnetic sensor 12 is a Hall effect sensor.

[0047] The primary magnetic sensor 12 is arranged relative to the magnetic field generator 10 in a selected position which corresponds to the position of a neutral point of the inspection magnetic field. Therefore, in the absence of magnetic disturbance which can cause the deformation of the inspection magnetic field, the primary magnetic sensor 12 is assumed to measure a magnetic field intensity which is not influenced by the inspection magnetic field.

[0048] The primary magnetic sensor 12 is therefore arranged to measure a magnetic field intensity at a neutral point. Thus, the primary magnetic sensor 12 is arranged to detect variations in the intensity of the inspection magnetic field at a neutral point and therefore to detect deformations of the inspection magnetic field. Preferably, with reference to FIGS. 5 and 8, the device 1 comprises a support 14 called the “primary support”. The primary support 14 carries the magnetic field generator 10 and the primary magnetic sensor 12.

[0049] According to a certain embodiment, the primary support 14 comprises a first support portion 141 to which the magnetic field generator 10 is attached and a second support portion 142 to which the primary magnetic sensor 12 is attached.

[0050] The primary support 14 is preferably provided with an adjustment system 143 which makes it possible to adjust the position of the primary magnetic sensor 12 relative to the magnetic field generator 10.

[0051] For example, as illustrated in Figure 8, the first support portion 141 comprises a first thread 1411 and the second support portion 142 comprises a second thread 1421 complementary to the first thread 1411. The second support portion 142 is adapted to be screwed through the first support portion 141 so that the position of the primary magnetic sensor 12 relative to the magnetic field generator 10 can be adjusted by screwing or unscrewing the second support portion 142 screwed through the first support portion 141. In this example, it is considered that the adjustment system 143 comprises the first support portion 141 and the second support portion 142.

[0052] According to the embodiment illustrated in figure 8, according to which the magnetic field generator 10 has a toroidal shape, it is understood that the second support part 142 is engaged in the free internal space 101 delimited by the magnetic field generator 10 so as to be able to be moved along the central axis of the generator A, by screwing or unscrewing.

[0053] Preferably, as illustrated in Figure 9, the device 1 comprises a secondary magnetic sensor 16 which is distinct from the primary magnetic sensor 12. The secondary magnetic sensor 16 is intended to be arranged so as not to be subjected to the inspection magnetic field. In other words, the secondary magnetic sensor 16 is sufficiently far from the magnetic field generator 10 so that the intensity of the inspection magnetic field to which the secondary magnetic sensor 16 is subjected is zero. Thus, the secondary magnetic sensor 16 is arranged so that, when the device 1 is arranged facing the object 2, the area of ​​the object 2 which is facing the secondary magnetic sensor 16 is not subjected to the inspection magnetic field.

[0054] The secondary magnetic sensor 16 is arranged to measure the intensity of a magnetic field called the “background magnetic field” representative of a remanent magnetic field of the object 2, that is to say the magnetic field which prevails in the object 2 in the absence of the inspection magnetic field. This remanent magnetic field may be due to a magnetization of the object 2, more precisely a magnetization of the metal cables of the object 2, for example following the arrangement of a magnet in the vicinity of the object 2 for a certain duration. The background magnetic field may also be representative of a magnetic field of the environment of the device 1 and of the object 2, namely for example the industrial environment which may include different magnetized tools.

[0055] Preferably, as illustrated in Figure 9, the device 1 comprises at least one stabilizing element 18 adapted to come into contact with the object 2 in order to maintain a predefined and constant distance between the magnetic field generator 10 and the object 2 and between the primary magnetic sensor 12 and the object 2 when the device 1 is in use. The predefined distance depends in particular on the size and density of the cables 20. It may for example be of the order of a few millimeters, for example 4 millimeters.

[0056] More specifically, as illustrated in Figure 1, the stabilizing element 18 is adapted to come into contact with an external surface 22 of the object 2 when the device 1 is in use. By "in use" is meant that the device 1 is used to detect a defect in an object 2. In use, it is desired to maintain a predefined distance between the magnetic field generator 10 and the object 2 so that the object 2 is subjected to the inspection magnetic field in a similar manner in any area of ​​the object 2 opposite which the magnetic field generator 10 will be positioned during use. Similarly, in use, it is desired to maintain a predefined distance between the primary magnetic sensor 12 and the object 2 so that the primary magnetic sensor 12 performs measurements under similar conditions with respect to the object 2 during use.According to the embodiment in which the device 1 comprises a secondary magnetic sensor 16, a stabilizing element 18 can also make it possible to maintain a predefined and constant distance between the secondary magnetic sensor 16 and the object 2 when the device 1 is in use.

[0057] The stabilizing element 18 is preferably adapted to allow the relative movement of the object 2 with respect to the device 1 while being in contact with the object 2. More particularly, preferably, the stabilizing element 18 is adapted to roll on the object 2.

[0058] The stabilizing element 18 may take the form of a roller as in the example illustrated in Figures 1 and 9. A roller makes it possible to control the direction of movement of the device 1 relative to the object 2. The roller also makes it possible to distribute the contact surface between the device 1 and the object 2 and to control the distance between the primary magnetic sensor 12 and the object 2 (and possibly also between the secondary magnetic sensor 16 and the object 2). The stabilizing element 18 may also be, for example, a carrier ball. The diameter of the rollers or balls may depend on the diameter of a drum around which the object 2 is extended. The diameter of the rollers or balls may for example be a few centimeters, for example 2 centimeters.

[0059] Advantageously, with reference to Figure 9, the device 1 comprises at least one suspension member 19 adapted to elastically press the stabilizing element(s) 18 against the object 2 when the device 1 is in use. The suspension member 19 may for example comprise a spring.

[0060] The stabilizing element(s) 18 and the suspension member 19 can also make it possible to compensate for an inaccuracy in the positioning of the device 1 relative to the object 2 by a robotic arm.

[0061] According to a preferred embodiment illustrated in Figure 9, the device 1 comprises a subassembly 13 forming a train of three carriages 130a, 130b, 130c arranged in a row in a direction D called the “longitudinal direction”. According to this embodiment, the device comprises at least three stabilizing elements 18a, 18b, 18c.

[0062] As illustrated in Figure 1, the three carriages 130a, 130b, 130c are articulated two by two with respect to each other so that they are adapted to fit the external surface 22 of the object 2, each bearing on the external surface 22. Thus, when the device 1 is in use and each carriage 130a, 130b, 130c bears on the external surface 122 of the object 2, the device 1 has at least three distinct bearing zones (respectively corresponding to the three carriages 130a, 130b, 130c) along the longitudinal direction D. The device 1 is therefore positioned in a stable manner with respect to the object 2 and the distance between the primary magnetic sensor 12 and the object 2 remains constant during use of the device 1.

[0063] The three carriages 130a, 130b, 130c include a primary carriage 130a, a secondary carriage 130b and a tertiary carriage 130c.

[0064] The primary carriage 130a carries the magnetic field generator 10 and the primary magnetic sensor 12. The primary carriage 130a also preferably carries at least one stabilizing element 18a, called the “primary stabilizing element”.

[0065] Preferably, as illustrated in Figure 9, the primary stabilizing element 18a is a roller, called “primary roller” whose axis of rotation Xa is perpendicular to the longitudinal direction D. Consequently, the primary stabilizing element 18a allows the primary carriage 130a to roll on the external surface 22 of the object 2 while maintaining the magnetic field generator 10 and the primary magnetic sensor 12 at a predefined and constant distance from the external surface 22.

[0066] The secondary carriage 130b carries the secondary magnetic sensor 16 and at least one secondary stabilizing element 18b. The secondary stabilizing element 18b is preferably a roller called a “secondary roller” whose axis of rotation Xb is perpendicular to the longitudinal direction D. The secondary roller 18b allows the secondary carriage 130b to roll on the external surface 22 while maintaining the secondary magnetic sensor 16 at a predefined and constant distance from the external surface 22.

[0067] The tertiary carriage 130c carries at least one tertiary stabilizing element 19c. The tertiary stabilizing element 19c is preferably a roller called a “tertiary roller” whose axis of rotation Xc is perpendicular to the longitudinal direction D. The tertiary roller 19c allows the tertiary carriage 130c to roll on the external surface 22.

[0068] Preferably, the carriages 130a, 130b, 130c are linked together by pivot links, typically in pitch.

[0069] As illustrated in Figure 9, the device 1 comprises at least one suspension member 19 for constraining at least one carriage 130a, 130b, 130c (in Figure 9, the primary carriage 130a) so as to press at least one carriage 130a, 130b, 130c against the object 2 when the device 1 is in use.

[0070] As explained previously, the carriages 130a, 130b, 130c are arranged in a row. The carriages 130a, 130b, 130c therefore comprise a head carriage, a central carriage and a tail carriage, the head carriage being the first in the row of carriages 130a, 130b, 130c in a primary direction S along the longitudinal direction D as illustrated in FIG. 9. In use, during a relative movement of the device 1 with respect to the object 2, the same zone of the object 2 is first opposite the head carriage, then the central carriage and finally the tail carriage.

[0071] Preferably, the head carriage corresponds to the secondary carriage 130b, the center carriage corresponds to the primary carriage 130a and the tail carriage corresponds to the tertiary carriage 130c.

[0072] The head carriage, the center carriage and / or the tail carriage may be constrained by a suspension member 19.

[0073] The device 1 also comprises a processing unit such as a processor. The processing unit is adapted to acquire and analyze signals received by the primary magnetic sensor 12 and the secondary magnetic sensor 16.

[0074] Together

[0075] As explained previously, the device 1 is adapted to be moved relative to the object 2. A detection assembly is thus proposed comprising the device 1 and at least one movement system adapted to allow relative movement of the device 1 relative to the object 2.

[0076] According to a preferred embodiment, the movement system makes it possible to scroll the external surface 22 of the object 2 opposite the magnetic field generator 10 and the primary magnetic sensor 12 in a predetermined direction B called “scanning direction” as illustrated in FIG. 1. Here, by “scroll”, we mean a relative scrolling of the external surface 22 with respect to the device 1 and we are not limited to the movement of the external surface. The scrolling can be enabled by the movement of the device 1 with respect to the external surface 22 of the object 2.

[0077] The movement system may be a robotic arm. Indeed, preferably, the device 1 is adapted to be attached to a robotic arm. The robotic arm is adapted to move the device 1 and to hold it stably in a certain position opposite the object 2.

[0078] According to a preferred embodiment, the object 2, which is typically a ply of a tire, is extended around a drum and the movement system is a drive system which rotates the drum so that the object 2 is rotated and its external surface 22 moves opposite the device 1. Conversely, the drum can be fixed and the drive system can rotate the device 1 relative to the drum.

[0079] Preferably, the scanning direction B is such that the secondary magnetic sensor 16 is arranged so as to precede the primary magnetic sensor 14 in consideration of the scanning direction. In other words, the secondary carriage 130b is arranged so as to precede the primary carriage 130a in consideration of the scanning direction. Thus, the movement system is designed so that, in use, the same area of ​​the external surface 22 of the object 2 is successively traversed by the secondary magnetic sensor 16 then by the primary magnetic sensor 12.

[0080] Process

[0081] With reference to Figure 10, a method is proposed for detecting, within an object which contains a plurality of metal cables 20, a positioning defect of one of the metal cables 20 relative to another of the metal cables 20 from the device 1.

[0082] Advantageously, the method is implemented to detect, within a reinforcing ply, for example a carcass ply of a tire, containing metal cables 20 extending non-parallel to an edge of the reinforcing ply, a positioning defect of one of the metal cables 20 relative to another of the metal cables 20.

[0083] The method preferably comprises a step aO) of positioning the primary magnetic sensor 12 relative to the magnetic field generator 10 so that the primary magnetic sensor 12 is arranged in a chosen position which corresponds to the position of a neutral point of the inspection magnetic field, i.e. the magnetic field emitted by the magnetic field generator 10. Step aO) is a step of adjusting the device 1.

[0084] For this, step a0) preferably comprises a step a01) of acquisition, by the processing unit, of an off-load signal received by the primary magnetic sensor 12 when it is not subjected to a magnetic field, in particular to the inspection magnetic field. In other words, the magnetic field intensity, called the "off-load magnetic field", is measured when the primary magnetic sensor 12 is not in the vicinity of magnetic disturbance. Then, step a0) preferably comprises a step a02) of arrangement of the primary magnetic sensor 12 relative to the magnetic field generator 10 so that the signal received by the primary magnetic sensor 12 is equal to the off-load signal. Thus, it is assumed that the primary magnetic sensor 12 is arranged at a neutral point of the inspection magnetic field when it measures an off-load signal while being in the inspection magnetic field.

[0085] Step a02) comprises the relative displacement of the primary magnetic sensor 12 with respect to the current generator 10. In particular, according to a certain embodiment, the second primary support part 142 which carries the primary magnetic sensor 12 is translated along the central axis of the generator A with respect to the first primary support part 141 which carries the magnetic field generator 10, for example by screwing / unscrewing.

[0086] Preferably, as explained previously, the central axis of the generator A corresponds to the axis connecting the north pole and the south pole of the magnetic field generator 10. Consequently, it is understood that translating the second primary support part 142 along the central axis of the generator A makes it possible to easily position the primary magnetic sensor 12 at a neutral point of the inspection magnetic field.

[0087] The method comprises a step a) of providing the device 1 thus adjusted.

[0088] The method then comprises a step b) of positioning the device 1 relative to the object 2 so that the magnetic field generator 10 and the primary magnetic sensor 12 are positioned opposite the object 2, more precisely opposite the external surface of the object 2.

[0089] Preferably, the device 1 is positioned relative to the object 2 so that the axis connecting the north pole and the south pole of the magnetic field generator 10 is perpendicular to a plane tangent to the external surface 22 of the object 2.

[0090] It is understood that the magnetic field is free. In other words, the magnetic field is not guided as it could be for example by branches adapted to allow the circulation of the magnetic field. The device 1 is preferably arranged so that the stabilizing element(s) 18 of the device 1 are in contact with the object 2. Consequently, the distance between the object 2 and the magnetic field generator 10 and between the object 2 and the primary magnetic sensor 12 is known and is considered constant as long as the stabilizing elements 18 of the device 1 are in contact with the object 2.

[0091] When the device 1 is thus positioned, the magnetic inspection field undergoes a deformation due to the metal cables 20 of the object 2. It is considered here that the device 1 is not positioned opposite a defect of the object 2. In other words, the device 1 is not positioned opposite an area of ​​the object 2 likely to have a defect, such as for example a weld area between two edges of a metal reinforcement ply of a tire, which is called the “area of ​​interest”.

[0092] Thus, preferably, initially, and therefore during the implementation of step b), the device 1 is positioned so as not to be opposite a defect in the object 2.

[0093] In this position, the primary magnetic sensor 12 is considered to be in a position called the “nominal position” and receives a signal called the “nominal signal” which has a magnetic field intensity called the “nominal intensity”. In other words, when the primary magnetic sensor 12 is positioned opposite the object 2 while not being positioned opposite a defect, it receives a nominal signal which results from the deformations of the inspection magnetic field due to the sole interference between the inspection magnetic field and the metal cables 20 of the object 2. This nominal signal is in fact a basic signal and indicates the signal which is supposed to be received by the primary magnetic sensor 12 when no defect is detected in the object 2.

[0094] According to one embodiment, step b) also comprises the positioning of the secondary magnetic sensor 16 opposite the object 2. This comprises, for example, bringing into contact the stabilizing element 18b of the secondary carriage 130b carrying the secondary magnetic sensor 16 so that the magnetic sensor is arranged at a known distance from the object 2.

[0095] According to one embodiment, step b) comprises the arrangement of the subassembly 13 comprising the train of three carriages 130a, 130b, 130c arranged in a row along the longitudinal direction D. The carriages 130a, 130b, 130c are positioned so that the longitudinal direction D is collinear with the intended direction of relative movement of the device 1 relative to the object 2. Advantageously, carriages 130a, 130b, 130c are positioned so that the longitudinal direction D is collinear with the intended scanning direction of the external surface 22 of the object 2. In other words, the carriages 130a, 130b, 130c are positioned to be in a row along the scanning direction. Preferably, they are positioned so that the head carriage is the secondary carriage 130b, the central carriage is the primary carriage 130a and the tail carriage is the tertiary carriage 130c.

[0096] Step b) can for example be implemented using the robotic arm 3 which operates the device 1.

[0097] Then, the method comprises a step c) of relative movement of the device 1 with respect to the object 2. According to one embodiment, the device 1 is moved, for example by the robotic arm, while the object 2 remains stationary. According to another embodiment, the object 2 is set in motion with respect to the device 1, while the device 1 is for example kept stationary by the robotic arm.

[0098] Preferably, the object 2 is wound around a drum and is adapted to be driven in rotation around its axis of revolution by the movement system which is a drive system. In such a way, the external surface 22 of the object 2 scrolls opposite the magnetic field generator 10 and the primary magnetic sensor 12 in the scanning direction. Preferably, the drive system drives the object 2 so that the object 2 only makes one complete rotation. Conversely, the drive system can drive the magnetic field generator and the primary magnetic sensor in scrolling opposite the drum.

[0099] It is therefore understood that, during the relative movement, each zone of the object 2 which passes opposite the magnetic field generator 10 is subjected to the inspection magnetic field.

[0100] According to a certain embodiment, as explained, preferably, during the relative movement, the same zone of the external surface 22 of the object 2 is successively traversed by the secondary magnetic sensor 16 then by the primary magnetic sensor 12. Thus, when a zone of the object 2 is opposite the secondary magnetic sensor 16, said zone has advantageously not been magnetized by the magnetic field generator 10. In such a way, the secondary magnetic sensor 16 receives a secondary signal which corresponds to the background magnetic field, i.e. to a remanent magnetic field of the object 2 and / or to a magnetic field of the environment, and this secondary signal is advantageously independent of any magnetization of the object 2 due to the magnetic field generator 10.

[0101] According to the embodiment in which the device 1 comprises a secondary magnetic sensor 16, step c) comprises the continuous acquisition by the processing unit of a secondary signal received by the secondary magnetic sensor 16. The secondary signal corresponds to the change in the intensity of the background magnetic field during the relative movement. Step c) further comprises the continuous acquisition by the processing unit of a primary signal received by the primary magnetic sensor 12. The primary signal varies in particular as a function of the variations in the intensity of the inspection magnetic field during the relative movement.

[0102] Preferably, during the relative movement, the primary magnetic sensor 12 is arranged successively in different positions relative to the object 2 and the different positions comprise at least one position of interest in which the primary magnetic sensor 12 is arranged opposite an area of ​​interest of the object 2 and a nominal position. As explained previously, the area of ​​interest corresponds to an area of ​​the object 2 likely to have a defect, i.e. an area in which a possible defect is to be detected. The nominal position corresponds to a position in which the primary magnetic sensor 12 is not arranged opposite a defect of the object 2. In other words, it is desired that the device 1 be moved opposite the object 2 so that it is positioned opposite at least one area of ​​interest and at least one area free of defect.Being positioned opposite at least one area free of defects makes it possible to determine a nominal magnetic field intensity of the primary signal in order to be able to detect a variation in intensity of the primary signal compared to the nominal intensity. Being positioned opposite at least one area of ​​interest makes it possible to acquire a primary signal in order to detect the presence or absence of a defect in this area of ​​interest.

[0103] The method comprises a step d) of detecting, in the primary signal, a signature representative of a positioning defect of a metal cable 20 of the object 2. Step d) is preferably implemented by the processing unit. Step d) preferably comprises the analysis and processing of the primary signal by the processing unit.

[0104] Preferably, step d) comprises processing of the primary signal which includes subtraction of the secondary signal received by the secondary magnetic sensor 16 from the primary signal received by the primary magnetic sensor 12. This makes it possible to clean the primary signal by subtracting from it the variations in magnetic field intensity linked to the background magnetic field.

[0105] Step d) may comprise different processing operations to facilitate the analysis of the primary signal. Step d) may therefore comprise at least one processing operation from, for example, the following processing operations: filtering with a low-pass filter, calculating the absolute value of the signal, normalization, and thresholding. These different operations may, for example, make it possible to remove background noise or flatten the signal and thus clarify the signal and make it easily interpretable. A combination of these operations may also be implemented to process the primary signal.

[0106] The signature representative of a positioning defect of a metal cable of the object is a local extremum of the primary signal. The local extremum corresponds to a local maximum of the primary signal which is greater than a first threshold value or to a local minimum of the primary signal which is less than a second threshold value. For example, Figure 11, which represents a primary signal, i.e. the evolution of the magnetic field intensity measured by the primary magnetic sensor 12 as a function of time, illustrates a local extremum E1 corresponding to a local maximum of the primary signal. The first and second threshold values ​​are defined relative to the nominal signal. For example, the measured magnetic field intensity corresponding to the first threshold value may correspond to an intensity greater than a certain deviation from the nominal intensity.Likewise, for example, the measured magnetic field intensity corresponding to the second threshold value may correspond to an intensity lower than the nominal intensity by a certain deviation. It is understood that the first threshold value is higher than the nominal intensity and that the second threshold value is lower than the nominal intensity.

[0107] The presence of a local extremum indicates a variation between the magnetic field intensity of the primary signal and the nominal intensity, i.e. the magnetic field intensity of the primary signal which corresponds to the magnetic field intensity when the magnetic field generator 10 is not positioned opposite a defect of the object 2. This indicates a deformation of the inspection magnetic field. A deformation of the inspection magnetic field indicates a potential defect of the object 2.

[0108] Advantageously, if the presence of a local extremum is determined and if this local extremum has a magnetic field intensity greater than the first threshold value, it is concluded that there is a fault corresponding to a superposition of two metal cables 20. On the other hand, if the presence of a local extremum is determined and if this local extremum has a magnetic field intensity less than the second threshold value, it is concluded that there is a fault corresponding to the existence of a gap between two consecutive metal cables 20 which is greater than a nominal gap.

[0109] According to a certain embodiment, the reasoning is based on the absolute value of the magnetic field intensity of the primary signal (it is assumed that a processing allowing the calculation of the absolute value of the signal is implemented) which can facilitate the analysis of the primary signal. In this case, it is understood that all the values ​​of the processed primary signal are positive. In the case where a defect is detected, different actions can be implemented. For example, object 2 can be replaced correctly or modified so as to remove the defect.

[0110] The invention is not limited to the embodiment described and shown in the attached figures. Modifications remain possible, in particular from the point of view of the constitution of the various technical characteristics or by substitution of technical equivalents, without departing from the general teaching.

Claims

CLAIMS 1. Detection device (1) intended to detect, within an object (2) which contains a plurality of metal cables (20), such as a reinforcing sheet containing a plurality of reinforcing metal cables (20) embedded in a rubber-based matrix (21), a positioning defect of one of the metal cables (20) relative to another of said metal cables (20), said device (1) comprising: - a magnetic field generator (10), consisting of a magnet or a coil, which is arranged to generate a magnetic field called an “inspection magnetic field”, and to be positioned opposite the object (2) in such a way that the plurality of metal cables (20) causes a deformation of said inspection magnetic field, - a magnetic sensor (12) called "primary magnetic sensor" which is provided for measuring the intensity of the inspection magnetic field, said device (1) being characterized in that the inspection magnetic field has, before being deformed by the plurality of metal cables (20), at least one neutral point where the intensity of said inspection magnetic field is zero, and in that the primary magnetic sensor (12) is arranged relative to the magnetic field generator (10) in a chosen position which corresponds to a position of this neutral point.

2. Device (1) according to claim 1 characterized in that it comprises a support (14), called "primary support", which carries the magnetic field generator (10) and the primary magnetic sensor (12) and which is provided with an adjustment system (143) making it possible to adjust, for example by screwing, the position of the primary magnetic sensor (12) relative to the magnetic field generator (10), in order to reach the chosen position, and to maintain said primary magnetic sensor (12) in said chosen position, fixed relative to the magnetic field generator (10).

3. Device (1) according to claim 2 characterized in that the magnetic field generator (10) has a toroidal shape which is centered on an axis (A) called "central axis of the generator" and which delimits a free internal space (101), and in that the adjustment system (143) comprises a support part (142) which carries the primary magnetic sensor (12) and which is engaged in said free internal space (101) so as to be able to be moved along the central axis of the generator (A) in order to modify the position of the primary magnetic sensor (12) along said central axis of the generator (A).

4. Device (1) according to one of the preceding claims, characterized in that it comprises at least one stabilizing element (18), such as a roller, adapted to come in contact with the object (2) in order to maintain a constant distance between the primary magnetic sensor (12) and an external surface (22) of the object (2).

5. Device (1) according to claim 4 characterized in that it comprises at least one suspension member (19), such as a spring, adapted to elastically press the stabilizing element (18) against the object (2).

6. Device (1) according to one of the preceding claims, characterized in that it comprises a secondary magnetic sensor (16) which is distinct from the primary magnetic sensor (12), which is not subjected to the inspection magnetic field and which is arranged to be placed opposite an area of ​​the object (2) in order to measure the intensity of the magnetic field called the “background magnetic field” which is representative of a magnetic field which prevails in the object (2) in the absence of an inspection magnetic field.

7. Device (1) according to claim 6 characterized in that it comprises a sub-assembly (13) forming a train of three carriages (130a, 130b, 130c) which are arranged in a row in a direction (D) called the “longitudinal direction” and which are articulated two by two, one with respect to the other so as to be able to fit an external surface (22) of the object (2) while each resting on said external surface (22) in order to provide at least three corresponding distinct support zones along the longitudinal direction (D), said carriages (130a, 130b, 130c) being formed respectively by: - a primary carriage (130a) which carries the magnetic field generator (10) and the primary magnetic sensor (12), as well as at least one primary stabilizing element (18a), preferably a primary roller whose axis of rotation (Xa) is perpendicular to the longitudinal direction (D), which allows said primary carriage (130a) to roll on the external surface (22) of the object (2) while maintaining the magnetic field generator (10) and the primary magnetic sensor (12) at a predefined, constant distance from the external surface (22), - a secondary carriage (10b) which carries the secondary magnetic sensor (16) and at least one secondary stabilizing element (18b), preferably a secondary roller whose axis of rotation (Xb) is perpendicular to the longitudinal direction (D), which allows said secondary carriage (130b) to roll on the external surface (22) while maintaining the secondary magnetic sensor (16) at a predefined, constant distance from the external surface (22), - a tertiary carriage (130c) which carries at least one tertiary stabilizing element (18c), preferably a tertiary roller whose axis of rotation (Xc) is perpendicular to the longitudinal direction (D), which allows said tertiary carriage (130c) to roll on the external surface (22) of the object (2).

8. Detection assembly characterized in that it comprises a detection device (1) according to any one of claims 6 and 7 as well as a drive system enabling a relative scrolling movement of an external surface (22) of the object (2) to be generated relative to the magnetic field generator (10) and to the primary magnetic sensor (12) in a direction (B) called the predetermined "scanning direction", and in that the secondary magnetic sensor (16) is arranged so as to precede the primary magnetic sensor (12) in consideration of said scanning direction (B), so that the same area of ​​the external surface (22) of the object (2) is successively traversed by the secondary magnetic sensor (16), which measures the background magnetic field, then by the primary magnetic sensor (12), which measures the inspection magnetic field as deformed by the plurality of metal cables (20) of the object (2).

9. A method of detecting, within an object (2) which contains a plurality of metal cables (20), such as a reinforcing ply containing a plurality of reinforcing metal cables (20) embedded in a rubber-based matrix (21), a positioning defect of one of the metal cables (20) relative to another of said metal cables (20), the method comprising the following steps: a) providing a magnetic field generator (10) and a primary magnetic sensor (12), in order to form a detection device (1), the primary magnetic sensor (12) being arranged relative to the magnetic field generator (10) in a chosen position which corresponds to the position of a neutral point, the neutral point corresponding to a point of an inspection magnetic field generated by the magnetic field generator (10), before it is deformed by the plurality of metal cables (20), where the intensity of said inspection magnetic field is zero;b) positioning the detection device (1) relative to the object (2) so that the magnetic field generator (10) and the primary magnetic sensor (12) are arranged opposite the object (2); c) relative movement of the detection device (1) relative to the object (2) and continuous acquisition of a primary signal received by the primary magnetic sensor (12); d) detecting, in the primary signal, a signature representative of a positioning defect of a metal cable of the object (2).; 10. Method according to claim 9, in which step a) comprises a step a0) of adjusting the detection device (1) by positioning the primary magnetic sensor (12) relative to the magnetic field generator (10) in the chosen position.

11. Method according to claim 10, in which, in step a0), the primary magnetic sensor (12) is positioned using an adjustment system (143) making it possible to adjust, for example by screwing, the position of the primary magnetic sensor (12) relative to the magnetic field generator (10) and to maintain the primary magnetic sensor (12) in the chosen position, fixed relative to the magnetic field generator (10), the adjustment system (143) being included in a support (14), called “primary support”, which carries the magnetic field generator (10) and the primary magnetic sensor (12) and which is provided with the adjustment system (143).

12. Method according to claim 11, in which the magnetic field generator (10) has a toroidal shape which is centered on an axis (A) called "central axis of the generator" and which delimits a free internal space (101), and the adjustment system (143) comprises a support part (142) which carries the primary magnetic sensor (12) and which is engaged in said free internal space (101) and in which, in step a0), the support part (142) which carries the primary magnetic sensor (12) is moved along the central axis of the generator (A) in order to modify the position of the primary magnetic sensor (12) along said central axis of the generator (A).

13. Method according to any one of claims 9 to 12, in which, in step b), at least one stabilizing element (18), such as a roller, is placed in contact with the object (2) in order to maintain a constant distance between the primary magnetic sensor (12) and an external surface (22) of the object (2).

14. Method according to claim 13, in which, in step b), the stabilizing element (18) is elastically pressed against the object (2) by means of a suspension member (19), such as a spring.

15. Method according to any one of claims 9 to 14, wherein, during step c), the detection device (1) is moved relative to the object (2) so that the primary magnetic sensor (12) is arranged successively in different positions relative to the object (2), the different positions comprising at least one position of interest in which the magnetic sensor is arranged opposite an area of ​​interest of the object (2), in which a possible defect is to be detected, and a nominal position in which the magnetic sensor is arranged opposite an area of ​​the object (2) free of defect, different from the area of ​​interest, so that a nominal magnetic field intensity of the primary signal is measured.

16. Method according to claim 15, in which the signature representative of a positioning defect of a metal cable of the object (2) is a local extremum relative to the nominal magnetic field intensity, the local extremum (E1) having a magnetic field intensity greater than a first threshold value or a magnetic field intensity less than a second threshold value.

17. Method according to claim 16, in which, in step d), if the presence of a local extremum is determined and, if this extremum has a magnetic field intensity greater than the first threshold value, it is concluded that there is a defect corresponding to a superposition of two metal cables (20), while, if this extremum has a magnetic field intensity less than the second threshold value, it is concluded that there is a defect corresponding to the existence of a gap between two consecutive metal cables (20) which is greater than a nominal gap.

18. Method according to any one of claims 9 to 17, comprising a step prior to the acquisition of the primary signal of acquiring a secondary signal corresponding to the evolution during the movement of a magnetic field called "background magnetic field" which is representative of a magnetic field which prevails in the object (2) in the absence of an inspection magnetic field and in which step d) comprises a processing of the primary signal including a subtraction of the secondary signal from the primary signal.

19. Method according to claim 18, in which the prior step of acquiring a secondary signal is implemented by a secondary magnetic sensor (16) which is distinct from the primary magnetic sensor (12), which is not subjected to the inspection magnetic field and, during the implementation of the prior step of acquiring a secondary signal, the secondary magnetic sensor (16) is placed opposite an area of ​​the object (2).

20. Method according to claim 19, in which, in step b), a subassembly (13) is placed in contact with an external surface (22) of the object (2), the subassembly (13) forming a train of three carriages (130a, 130b, 130c) which are arranged in a row in a direction (D) called the “longitudinal direction” and which are articulated two by two, one with respect to the other so as to be able to fit an external surface (22) of the object (2) while each resting on said external surface (22) in order to provide at least three corresponding distinct support zones along the longitudinal direction (D), said carriages (130a, 130b, 130c) being formed respectively by: - a primary carriage (130a) which carries the magnetic field generator (10) and the primary magnetic sensor (12), as well as at least one primary stabilizing element (18a), preferably a primary roller whose axis of rotation (Xa) is perpendicular to the longitudinal direction (D), which allows said primary carriage (130a) to roll on the external surface (22) of the object (2) while maintaining the magnetic field generator (10) and the primary magnetic sensor (12) at a predefined, constant distance from the external surface (22), - a secondary carriage (130b) which carries the secondary magnetic sensor (16) and at least one secondary stabilizing element (18b), preferably a secondary roller whose axis Tl of rotation (Xb) is perpendicular to the longitudinal direction (D), which allows said secondary carriage (130b) to roll on the external surface (22) while maintaining the secondary magnetic sensor (16) at a predefined, constant distance from the external surface (22), - a tertiary carriage (130c) which carries at least one tertiary stabilizing element (18c), preferably a tertiary roller whose axis of rotation (Xc) is perpendicular to the longitudinal direction (D), which allows said tertiary carriage (130c) to roll on the external surface (22) of the object (2), and in which, to implement the preliminary step of acquiring a secondary signal and step c) of relative movement of the detection device (1) with respect to the object (2) and continuous acquisition of a primary signal received by the primary magnetic sensor (12), the carriages (130a, 130b, 130c) are rolled on the external surface (22) of the object (2) so that the same area of ​​the object (2) is first opposite the primary carriage (130a), then the secondary carriage (130b) and finally the carriage tertiary (130c).

21. Method according to any one of claims 9 to 20, wherein step d) comprises processing the primary signal, the processing comprising at least one processing operation from among the following processing operations: filtering with a low-pass filter, calculating the absolute value of the signal, normalization, thresholding and a combination of these processing operations.

22. Method according to any one of claims 9 to 21, said method being implemented to detect, within a reinforcing ply containing metal cables (20) extending non-parallel to an edge of the reinforcing ply, a positioning defect of one of the metal cables (20) relative to another of said metal cables (20).

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