Instrumented crampon boots and corresponding measuring equipment

Abstract

TITLE: Instrumented Cleat Shoe and Corresponding Measuring Equipment The present invention relates to a cleat shoe (1), comprising at least one cleat (2) removably assembled to the sole (11), the cleat comprising at least one sensor sensitive to displacement and / or deformation of at least a portion of said cleat (2), the shoe comprising at least one electrical and / or electronic component located outside the cleat (2), and a wired electrical circuit between the sensor and the electrical and / or electronic component. According to the invention, the wired electrical circuit comprises at least one electrical connection between a first conductive track carried by a surface of the cleat (2) located opposite the sole (11) of the shoe, and a second conductive connection track carried by the sole (11), opposite the cleat (1). Abstract Figure: Figure 1

Description

Title of the invention: Instrumented crampon shoe and corresponding measuring equipment. Field of the invention

[0001] The present invention relates to the measurement of the forces exerted on a shoe with cleats.

[0002] It relates in particular to a shoe comprising a removable cleat carrying a deformation and / or displacement sensor. Previous art

[0003] In the field of sports, it can be useful to measure the forces exerted on athletes' footwear. In particular, document FR3086511A1 proposed providing shoes with removable cleats, which are instrumented with at least one deformation and / or displacement sensor. The signal measured by these sensors can be analyzed to deduce a value for the forces exerted on the cleat, and thus obtain valuable information about the athlete's actions.

[0004] However, the implementation of such a shoe with instrumented cleats has proven to be delicate. Indeed, in order to be processed usefully, the data from the sensors must be sent via wireless communication, for example using the technology known as "Bluetooth Low Energy", to a remote processing device, or be stored for processing by a remote processing device.

[0005] Radio or wireless communication means capable of sending such information, or storage means enabling the information to be stored for subsequent processing, are generally too large to allow integration into a crampon.

[0006] Furthermore, the sensors, radio communication means and / or storage means must be powered by electrical power sources. These power sources, generally consisting of cells or batteries, are themselves too bulky to be integrated into a crampon.

[0007] The shoe comprising a removable instrumented crampon must therefore include electrical and / or electronic equipment external to the crampon, but connected to it. This equipment, which may, for example, include means for recording and / or transmitting data and a power supply consisting of a battery, is associated with the shoe. It may, for example, be located in the heel of the shoe.

[0008] The shoe equipped with instrumented crampons must also have a wired connection between each instrumented crampon and this electrical and / or electronic equipment external to the crampon.

[0009] This wired communication system assumes that the instrumented crampons are equipped with wires exiting from them. Document FR3086511A1 proposes that the wires exit the crampon through a central passage located along the crampon's axis, in its threaded section which is screwed into the sole. This solution requires that the boot's sole be designed to accommodate the wires. Furthermore, it necessitates disassembling the boot each time the crampons are changed to ensure the wires are properly installed. This makes it difficult, in particular, to change the crampons on a boot to replace an instrumented crampon with a non-instrumented one, or vice versa. Description of the invention

[0010] The present invention aims to overcome these drawbacks of the prior art.

[0011] In particular, the invention aims to provide a shoe equipped with at least one instrumented crampon, carrying at least one displacement and / or force sensor, in which the mounting of the crampon on the shoe is facilitated.

[0012] Another objective of the invention, according to at least some of the embodiments, is to make it easy to equip a crampon boot with an instrumented crampon, without significant transformation of the boot.

[0013] These objectives, as well as others that will become clearer later, are achieved using a cramponed shoe comprising at least one crampon removably attached to the sole, the crampon comprising at least one sensor sensitive to displacement and / or deformation of at least a portion of the crampon, the shoe comprising at least one electrical and / or electronic component located outside the crampon, and a wired electrical circuit between the sensor and the electrical and / or electronic component. According to the invention, the wired electrical circuit comprises at least one electrical connection between: - a first conductive track carried by a surface of the cleat located opposite the sole of the shoe, and - a second conductive track carried by the sole, opposite the cleat.

[0014] In the present description, "deformation" of the cleat means any disturbance of the structure of the cleat under the effect of a mechanical stress.

[0015] Thus, the electrical connection is ensured as soon as the conductive track of the crampon and the conductive connection track of the sole are in contact or in close proximity to each other. Such a configuration allows the user to add or to easily remove the instrumented crampon from the sole of the shoe, without having to handle the electrical or electronic components associated with or included in the shoe or the connection cables associated with the shoe.

[0016] Preferably, the crampon can be assembled to the sole by screwing around an axis, and at least one of the conductive tracks can have an annular shape centered on the axis.

[0017] Screwing the crampon ensures its compression against the sole, and allows for a simple, quick and efficient electrical connection to be established between the conductive tracks of the crampon and the sole opposite the crampon.

[0018] Advantageously, the wired electrical circuit can have several distinct electrical connections between several first conductive tracks carried by a surface of the cleat located opposite the sole of the shoe, and several second tracks carried by the sole, opposite the cleat.

[0019] This arrangement offers the possibility of using each association of first and second conductive tracks for a distinct function. Therefore, a first association of a cleat conductive track and a corresponding sole conductive track can be used to supply electricity to the instrumented cleat, while the other conductive track associations can be reserved for transmitting signals from the sensors.

[0020] Preferably, the first several conductive tracks can be placed at different distances from the axis, and the second conductive tracks can be placed at different distances from the axis.

[0021] Preferably, the shoe may also have an annular seal positioned so as to be compressed between the sole and the cleat, so that the conductive tracks are located in the space closed by the sole, the cleat and the seal.

[0022] The present invention also relates to measuring equipment for cramponed footwear, the equipment comprising at least one crampon capable of being removably assembled to the sole of a shoe by inserting a portion of the crampon assembly into a recess in the sole, the crampon comprising at least one sensor sensitive to a displacement and / or deformation of at least a portion of the crampon, and a washer capable of surrounding the portion of the crampon assembly, to be tightened between the crampon and the sole when the crampon is assembled to the sole, the equipment comprising a wired electrical circuit capable of connecting the sensor(s) and at least one electrical and / or electronic component located outside the crampon, the wired electrical circuit comprising at least one electrical connection between: - a first conductive track carried by a surface of the cleat located opposite the puck, and - a second conductive connection track carried by the washer, opposite the stud.

[0023] Such measuring equipment advantageously allows for the very easy transformation of a non-instrumented shoe designed to receive crampons into a shoe, according to an embodiment described above, equipped with instrumented crampons. The wired electrical circuit of this equipment can, of course, have all the characteristics of the wired electrical circuit of the shoe described above. Description of the figures

[0024] The invention will be better understood upon reading the following description of preferred embodiments, given by way of simple figurative and non-limiting example, and accompanied by the figures, among which: - [Fig.1] is a schematic representation of a shoe comprising an instrumented crampon, according to one embodiment of the invention; - [Fig.2] is a perspective view of a removable instrumented crampon fixed to the sole of the shoe in [Fig.1]; - [Fig.3] is a side view of the instrumented crampon from [Fig.2] fixed to the sole of the shoe from [Fig.1]; - [Fig.4] is a cross-section of the instrumented crampon from [Fig.2] fixed to the sole of the shoe from [Fig.1]; - [Fig.5] is a perspective view of the instrumented crampon from [Fig.2], showing its face intended to be in contact with the sole of the shoe; - [Fig.6] is a perspective view of the portion of the sole of the shoe in [Fig.1], intended to receive the cleat of [Fig.5]; - [Fig.7] is a perspective view of a portion of a shoe sole according to another embodiment, intended to receive the cleat of [Fig.5]. Description of the implementation method

[0025] Figure 1 represents a shoe 1 intended for playing a sport such as, for example, football or rugby. This shoe 1 has a sole 11 onto which several studs 2 and 3 are conventionally fixed and removably mounted on the sole 11. The number and distribution of the studs on the sole may vary, and this description is not limited by these aspects.

[0026] Among these crampons, crampons 3 are of a classic design, without any sensors. In contrast, crampon 2 is an "instrumented" crampon which includes deformation and / or displacement sensors allowing the measurement of stresses exerted on the crampon. Of course, the shoe 1 can also, In one variant of the solution shown, be equipped with several instrumented crampons.

[0027] The shoe 1 is also equipped with a housing 12, which includes at least one electrical and / or electronic component intended to cooperate with the sensors of the instrumented crampon(s). This electrical and / or electronic component may include, but is not limited to: - a power source such as a battery, - radio communication means enabling real-time communication, to a remote processing unit, of information from the sensors installed in the instrumented crampons, and / or - digital recording means capable of recording data from these sensors, for subsequent processing.

[0028] In the embodiment shown in [Fig. 1], this housing 12 is integrated into the shoe 1, at the heel of the shoe 1. However, in other embodiments of the invention, it is also possible for this housing to be associated with the shoe without being integrated into it. For example, it can be attached to the shoelaces on the upper surface of the shoe, thus avoiding any modification to the shoe itself. Alternatively, the housing can be positioned at the back of the shoe, at the portion of the shoe that is intended to rest against the user's heel.

[0029] In other possible embodiments, this equipment can be distributed in several housings, which can be integrated into the shoe or associated with it.

[0030] The shoe 1 is also equipped with a wired connection 13 between the electrical and / or electronic equipment of the housing 12 and the sensor(s) installed in the instrumented crampon 2. In this description, "wired connection" means a physical electrical connection made by electrically conductive materials, or by a succession of electrically conductive materials in electrical contact with each other, in order to transmit an electrical current and / or signal.

[0031] Of course, if the shoe 1 is equipped with several instrumented crampons and / or several boxes, it may also include wired connections suitable for connecting each of these instrumented crampons to the electrical and / or electronic equipment distributed in each of the boxes.

[0032] Figure 2 shows in perspective the instrumented crampon 2 fixed to the sole 11 of the shoe 1. Figures 3 and 4 show the same instrumented crampon 2, respectively in side view and in section, fixed to the sole 11 of the shoe 1. Figure 5 shows in perspective the instrumented crampon 2, showing its face intended to be in contact with the sole 11 of the shoe 1.

[0033] This instrumented crampon 2 is advantageously made up of two main elements, assembled together: a rod 21 and a bell 22.

[0034] The shaft 21 of the crampon 2 extends along the entire height of the crampon 2, along the main axis 200 of this crampon 2, from its proximal end 201 assembled to the shoe 1 to its free distal end 202. From its proximal end 201 to its distal end 202, it comprises several successive portions: a portion of assembly 211, a base 212, a trunk 213, and a head 214.

[0035] The assembly portion 211 is a substantially cylindrical portion centered on the main axis 200 of the crampon 2, and forms the proximal end 201 of the crampon 2 and the stem 21. The peripheral surface of this assembly portion 211 is threaded, in order to be assembled by screwing into a housing 111 drilled in the sole 11 of the shoe, which has an internal thread corresponding to that of the assembly portion 211.

[0036] Preferably, the assembly portion 211 has the same dimensions as the assembly portion of a standard, uninstrumented crampon 3. The housing 111 can thus be dimensioned to receive, interchangeably, the assembly portion of an instrumented crampon 2 or of a standard, uninstrumented crampon 3.

[0037] The base 212 has the form of a thin plate which extends in a plane perpendicular to the main axis 200 of the cleat 2, and has a lower thickness than the sole 11. This base 212 advantageously has a surface substantially parallel to that of the sole 11 and facing this sole 11, when the cleat 2 is assembled to the shoe 1.

[0038] The plate forming this base 212 advantageously has a contour whose shape is chosen to serve as a grip for screwing. In the embodiment shown, this contour thus has a hexagonal shape, allowing the cleat shank 21 to be screwed into the sole 11 using a standard hexagonal key.

[0039] The trunk 213 is a cylindrical portion centered on the main axis 200 of the crampon 2. It is advantageously dimensioned such that the forces received by the head 214 cause a deformation of the trunk 213, preferentially to the other elements of the crampon 2. Thus, a measurement of the deformations undergone by this trunk 213 makes it possible to obtain information representative of the forces applied on the head 214 of the crampon 2.

[0040] This trunk 213 is advantageously equipped with strain gauges, capable of measuring the deformations of its surface. These sensors are not shown in the figures. They can conventionally consist of strain gauges, known per se, which are generally associated with amplifiers. The mounting of such sensors on the shaft of a crampon is known per se, in particular from document FR3086511A1.

[0041] According to variants of the invention, the crampon 2 may also include other types of deformation and / or displacement sensors, for example an accelerometer.

[0042] The head 214 is a substantially cylindrical portion of the stem 21, centered on the main axis 200 of the crampon 2, which forms the distal end 202 of the crampon 2 and of the stem 21. The peripheral surface of this head 214 is threaded, in order to allow the assembly, by screwing, of a crampon bell onto this head 214.

[0043] The end surface 2141 of this head, which forms the distal end 202 of the crampon 2 and the stem 21, advantageously has a marking 2142 enabling the installer fixing the crampon 2 onto the sole 11 to know the orientation of the crampon stem 21 relative to the orientation of the shoe 1. This marking facilitates correct installation of the crampon 2 onto the shoe 1, and / or the calibration of the sensors equipping this crampon 2 to take into account the orientation of the crampon stem 21 relative to the orientation of the shoe 1.

[0044] A crampon bell 22 is screwed to the head 214 of the crampon shank 21. This crampon bell 22 is designed to form the substantially frustoconical outer surface of the crampon 2. It has an internal thread for engaging with the external thread of the crampon head 214. It also has an external contour whose shape is chosen to provide a grip for screwing. In the illustrated embodiment, it thus has, near the distal end of the crampon 2, a gripping portion 221 with a hexagonal contour, allowing the crampon bell 22 to be screwed onto the crampon shank 21 using a standard hex key. This screwing can be done, for example, while another standard hex key of a larger diameter holds the base 212 of the shank 21 in rotation.

[0045] The crampon bell 22 also has a portion forming a substantially frustoconical skirt 222, covering the shaft 213 of the crampon shank 21, leaving a peripheral space around this shaft 213. The sensors equipping the shaft 213, and any electronic components accompanying these sensors, can be housed in this peripheral space and protected, by the skirt 222, from any contact with the ground.

[0046] Preferably, the bell 22 of the crampon 2 is connected to the rod 21 only at the head 214 of this rod 21. In particular, the edge of the skirt 222 which is close The base 212 remains advantageously distant from this base. Thus, any force applied to the bell 22 by contact with the ground is transmitted to the rod 21 via the head 214. It thus generates forces on the shaft 213 of the rod 21, which can be measured by the sensors.

[0047] According to the invention, the instrumented crampon 2 and the sole 11 on which this crampon 2 is fixed are configured to allow the establishment of an electrical circuit between the crampon 2 and the shoe 1. The expression "electrical circuit" designates, in the present description, at least two independent contacts each allowing the passage of an electric current, in order to ensure the circulation of a current and / or a signal between the crampon 2 and the shoe 1.

[0048] To ensure this electrical contact, in the embodiment shown in the figures, - the surface of the base 212 of the crampon shaft 21 which faces the sole 11 is equipped with at least one first electrical contact zone, and - the surface of the sole 11 which surrounds the housing 111 receiving the crampon fixing portion is equipped with at least one second electrical contact zone, the first electrical contact zones being brought into contact with the second electrical contact zones when the cleat 2 is fixed in the housing 111.

[0049] Figures 5 and 6 are perspective views showing respectively the face of the crampon 2 intended to be in contact with the sole 11, and the face of the sole 11 surrounding the housing 111.

[0050] As shown in [Fig. 5], the face of the base 212 of the crampon 2 that is intended to be in contact with the sole of the shoe is equipped with a printed circuit board 41 in the shape of a disc, surrounding the assembly portion 211. This printed circuit board 41 has, in the embodiment shown, three concentric circular conductive tracks 411, 412 and 413 of different diameters, centered on the main axis 200 of the crampon 2. These conductive tracks 411, 412 and 413 can, conventionally, be made up of deposits of conductive materials, such as tin or copper, on the insulating plate of the printed circuit board 41. They are therefore insulated from each other but are each connected, by a wire (not shown) passing through the printed circuit board 41 and the base 212, to the sensors equipping the shaft 213 of the crampon.

[0051] As shown in [Fig. 6], the surface of the base 11 equipped with a printed circuit board 51 has the shape of a disc surrounding the housing 111. This printed circuit board 51 has, in the embodiment shown, three concentric circular conductive tracks 511, 512, and 513 of different diameters, centered on the housing 111. The diameters of these conductive tracks 511, 512, and 513 are advantageously identical, respectively, to the diameters of the conductive tracks 411, 412 and 413 of the printed circuit 41.

[0052] These conductive tracks 511, 512 and 513 can, conventionally, be made up of deposits of conductive materials, such as tin or copper, on the insulating plate of the printed circuit 51. They are therefore insulated from each other but are each connected, by a wire (not shown) running in or on the shoe 1, to the electrical and / or electronic equipment contained in the housing 12.

[0053] Screwing the clip 2 into the housing 111 compresses the printed circuit board 41 against the printed circuit board 51, bringing the conductive tracks 411, 412, and 413 into contact with the conductive tracks 511, 512, and 513, respectively. Advantageously, a thin layer of solder can be deposited on some of the tracks prior to screwing. Screwing the clip 2 into the housing 111 compresses this solder upon contact, ensuring perfect contact between the facing tracks and compensating for any gaps that might exist between them.

[0054] Each of the pairs of conductive tracks in contact, respectively tracks 411 and 511, tracks 412 and 512 and tracks 413 and 513, then constitutes, with the wire connecting the conductive track of the printed circuit 41 to the sensors of the crampon 2 and the wire connecting the conductive track of the printed circuit 51 to the electrical and / or electronic equipment contained in the housing 12, an electrical connection between the electrical and / or electronic equipment of the housing 12 and the sensor(s) installed in the instrumented crampon 2.

[0055] These three electrical connections together form the wire connection 13, enabling an electrical circuit to be established between the sensors of the instrumented crampon 2 and the electrical and / or electronic equipment. In the embodiment shown, one of these electrical connections provides power to the sensors, another carries the signal from the sensor, and a third forms the ground. The number and function of each electrical connection may, however, differ in other embodiments. For example, the electrically conductive shaft 21 of the crampon may be used to form the ground. In this case, it is in electrical contact with the walls of the housing 111, which are themselves connected to a ground wire passing through the boot 1 to the electrical and / or electronic equipment contained in the housing 12, to form the ground wire connection.

[0056] The circular conductive tracks 411 and 511 have the advantage of ensuring the electrical connection independently of the orientation of the stud 2 with respect to the sole 11. In the embodiment described above, the circular conductive tracks in contact, respectively tracks 411 and 511, tracks 412 and 512 and tracks 413 and 513, can be in contact over their entire diameter.

[0057] It is also possible, in a variant of the invention described above, for a first of these conductive tracks to be circular, and for the second conductive track intended to come into contact with this first conductive track to have a different shape. This second conductive track may, for example, form a conductive pad that can come into contact with the first conductive track at any point on its diameter. This pad may, for example, be a retractable pin of the type known to those skilled in the art under the name "Pogo" (Registered Trademark).

[0058] In the embodiment shown, the crampon and the sole each have three circular conductive tracks. It is also possible, in variations of the embodiment shown, for the crampon and the sole to each have a greater number of distinct tracks, for example, arranged concentrically around each other. Some of the tracks may, for example, be dedicated to supplying power to the sensors of the instrumented crampon, and other tracks may be dedicated to carrying the signal from these sensors.

[0059] A person skilled in the art will be able to easily imagine other possible configurations for these conductive tracks, and in particular such configurations allowing the conductive tracks to be brought into contact independently of the orientation of the instrumented crampon relative to the shoe.

[0060] In other embodiments, it is also possible for the conductive tracks to have different shapes. For example, the various conductive tracks, insulated from one another, may form arcs of circles of the same diameter, centered on the axis of the crampon, and distributed angularly around this axis. In such a case, it is necessary that the angular position of the crampon relative to the boot, or at least the angular position of the facing tracks, be well defined to ensure the desired electrical connections.

[0061] Preferably, the underside of the base is equipped with a circular gasket 6, the diameter of which is larger than the outer diameter of the printed circuit boards 41 and 51. This gasket 6 is designed to be compressed between the base 212 and the sole 11 of the shoe 1 when the cleat 2 is attached to the shoe. It isolates the space between the underside of the base 212 and the sole 11 from the outside. This prevents moisture from entering the conductive tracks in contact.

[0062] According to possible embodiments of the invention, the conductive tracks carried by the cleat and the sole can be located in other positions. For example, the cleat may have conductive tracks, such as concentric circular tracks centered on the cleat axis, on the surface of the proximal end of the cleat, at the end of the cleat assembly portion. In this case, the sole of the shoe may be equipped with additional conductive tracks located at the bottom of the housing intended to receive this assembly portion.

[0063] In the embodiment shown in the figures, the shoe 1 is specially adapted to receive the instrumented crampon 2. Thus, its sole 11 has a bore around the opening of the housing 111, allowing the printed circuit board 51, carrying the conductive tracks 511, 512, and 513, to be received. This printed circuit board can be bonded to the sole 11 in this bore. Furthermore, the sole 11 may have a groove 112, designed to facilitate the passage of wires (not shown) connecting the conductive tracks of the printed circuit board 51 to the electrical and / or electronic equipment contained in the housing 12. This groove 112 can be filled, once the wires have been inserted, for example, with a plastic material similar to that of the sole 11, which protects these wires.

[0064] It is also possible, according to a particular embodiment represented by [Fig.7], to implement the invention without the shoe 1 undergoing any modification for the implementation of the instrumented crampon 2. In such a case, the printed circuit 51 associated with the sole 11 can be carried by a washer 7, which can be glued to the surface of the sole 11, around the opening of the housing 111, and / or be secured to this sole by screwing the crampon 2 into the housing 111.

[0065] The wires 71 connected to the conductive tracks of the printed circuit board 51 exit the washer 7 from one side thereof and can be held against the shoe 1, on the outside of the shoe, for example by adhesive tape. They can be used to connect the cleat 2 to electrical and / or electronic equipment associated with the shoe, but not necessarily integrated into it. For example, this equipment can be housed in a casing attached to the shoelaces.

[0066] The use of such a washer 7 makes it possible to use an instrumented crampon with any shoe designed to receive a removable crampon, without modification of the shoe, while maintaining a very high ease of mounting of the instrumented crampon.

[0067] Obviously, the conductive tracks present on such a washer are not necessarily circular, but can have any shape suitable for making a connection with the stud 2. As an example, the conductive tracks can be in the form of portions of rings, so that they cover part of a diameter of a circle, in particular a semicircle or a quarter circle.

Claims

Demands

1. Shoe with crampons (1), comprising at least one crampon (2) removably assembled to the sole (11), said crampon (2) comprising at least one sensor sensitive to a displacement and / or deformation of at least a part of said crampon (2), said shoe (1) comprising at least one electrical and / or electronic component placed outside said crampon (2), and a wired electrical circuit between said at least one sensor and said at least one electrical and / or electronic component, characterized in that said wired electrical circuit comprises at least one electrical connection between: - a first conductive track (411, 412, 413) carried by a surface of said crampon (2) located opposite said sole (11) of said shoe, and - a second conductive track (511, 512, 513) carried by said sole (11), opposite said crampon (2).

2. Shoe according to claim 1, wherein said cleat (2) is assembled to said sole (11) by screwing around an axis (200), and at least one of said conductive tracks (411, 412, 413, 511, 512, 513) has an annular shape centered on said axis (200).

3. Shoe according to any one of the preceding claims, wherein said wired electrical circuit has several distinct electrical connections between several first conductive tracks (411, 412, 413) carried by a surface of said cleat (2) located opposite said sole (11) of said shoe (1), and several second tracks (511, 512, 513) carried by said sole (11), opposite said cleat (2).

4. Shoe according to claims 2 and 3, wherein said several first conductive tracks (411, 412, 413) are placed at different distances from said axis, and said second conductive tracks (511, 512, 513) are placed at different distances from said axis (200).

5. Footwear according to any one of the preceding claims, said footwear further having an annular joint positioned to be compressed between said sole (11) and said cleat (2), such that said conductive tracks (411, 412, 413, 511, 512,

6. 513) are located in the space closed by said sole (11), said cleat (2) and said joint. Measuring equipment for crampon boots, said equipment comprising at least: - a cleat (2) capable of being removably assembled to the sole (11) of a shoe (1), by inserting an assembly portion (211) of the cleat (2) into a housing (111) of the sole (11), said cleat (2) comprising at least one sensor sensitive to a displacement and / or deformation of at least a part of said cleat (2), And - a washer (7) suitable for surrounding said assembly portion (211) of said cleat, to be tightened between said cleat (2) and said sole (11), when said cleat (2) is assembled to said sole (11), said equipment comprising a wired electrical circuit capable of connecting said or at least one of said sensors and at least one electrical and / or electronic component located outside said crampon (2), said wired electrical circuit comprising at least one electrical connection between - a first conductive track (411, 412, 413) carried by a surface of said stud (2) located opposite said washer (7), and - a second conductive track (511,512, 513) carried by said washer (7), opposite said stud (2).