Improved detection head for a handheld metal detector and associated manufacturing process

Abstract

A detection head (1) configured to be fixed to a handle (110) of a metal detector (100), the detection head (1) comprising: - a chassis (2) including a first face (2a) and supports (3) extending from the first face (2a); and - an inductive sensor (4), mounted on the supports (3) of the chassis (2); the inductive sensor (4) and the chassis (2) being overmolded with a plastic material such that the inductive sensor (4) and the chassis (2) are embedded in the plastic material. Figure for the abbreviation: Fig. 1

Description

Title of the invention: Improved detection head for a handheld metal detector and associated manufacturing method. Technical field

[0001] The present exposition relates to the field of target object detection, and more particularly to the detection of explosive charges such as landmines buried in the ground. STATE OF THE ART

[0002] A handheld metal detector generally includes a handle for gripping the device by an operator, a detection head including an inductive sensor and a body fixed on the handle, opposite the detection head, and including processing means.

[0003] The inductive sensor may include one or more coils configured to generate a magnetic field and measure a change in its inductance and / or parasitic currents induced by objects placed nearby. The processing means include a microprocessor, such as an electronic board, to detect the presence of metallic parts and send an alert command to an alarm of the detector.

[0004] The detection head generally comprises a base, configured to be positioned opposite an area to be inspected (for example, the ground), and a cover, configured to be mounted on the base and, together with the base, defining a housing for the inductive sensor. The inductive sensor is also connected to the processing means, for example, via electrical cables. To protect the inductive sensor from impacts and moisture, the housing is generally filled with expanding foam. For this purpose, the inductive sensor is placed in the housing, and then the base and cover are bonded together. The assembly is then placed under pressure to hold the cover and base in position during the pressure injection and drying of the expanding foam.

[0005] However, this manufacturing process is lengthy (several tens of minutes) due to the application and drying time of the adhesive, and the duration of the pressure injection step of the expanding foam. Furthermore, the application of the adhesive, generally carried out using a robot and requiring precise control of the adhesive's condition and positioning, is a delicate step necessitating bulky tooling. In addition, the base and lid, while offering a certain level of rigidity, do not guarantee optimal stability of the inductive sensor against vibrations or shocks, which can cause the coils to move. likely to cause false alarms and affect detector performance. EXPOSED

[0006] One aim of the present application is to remedy the aforementioned drawbacks and in particular to propose a solution enabling the production of a metal detector comprising a detection head which is simpler and faster to produce, while ensuring good resistance to shocks and external agents of the detector (humidity, dust, etc.).

[0007] For this purpose, a detection head configured to be fixed to the handle of a metal detector is proposed, the detection head comprising: - a chassis comprising a first face and supports extending from the first face; and - an inductive sensor, mounted on the chassis supports.

[0008] The inductive sensor and the chassis are also overmolded with a plastic material so that the inductive sensor and the chassis are embedded in the plastic material.

[0009] Some preferred but non-limiting features of the detection head according to the first aspect are the following, taken individually or in combination: - the detection head further comprises an electronic board, the inductive sensor being carried by the electronic board and the electronic board being overmolded with the inductive sensor and the chassis in the plastic material so that the electronic board is also embedded in the plastic material; - the inductive sensor is mounted on the chassis supports via the electronic board; - the inductive sensor is printed on the electronic board; - the detection head further includes an electrical cable with a connector electrically connected to the electronic board, part of the electrical cable also being overmolded with the plastic material; - the electrical cable includes a sheath mounted near the connector, the sheath being positioned in a corresponding hole formed in the chassis, and a portion of cable extending between the sheath and the connector being overmolded with the plastic material; and / or - the chassis also includes walls extending from the first face positioned so as to delimit chambers around electronic components of the electronic board.

[0010] According to a second aspect, a metal detector is proposed comprising: - a detection head according to the first aspect; and - a handle mounted on the detection head.

[0011] According to a third aspect, a method for manufacturing a detection head according to the first aspect is proposed, comprising the following steps IF: provide a chassis comprising a first face and supports extending from the first face; S2: mount an inductive sensor on the chassis supports; S4: Place the assembly consisting of the chassis and the inductive sensor in a mold; and S5: Injecting a plastic material under pressure into the mold so as to embed the chassis and the inductive sensor in the plastic to obtain the sensing head.

[0012] Some preferred but non-limiting features of the manufacturing process according to the third aspect are the following, taken individually or in combination: - during step S2, the process further includes mounting an electronic board on the chassis supports, the inductive sensor being carried by the electronic board; - the inductive sensor is printed on the electronic board; - the manufacturing process also includes, prior to step S4, a step S3 of electrical connection of a connector of an electrical cable with the electronic board; - the electrical cable includes a sheath fixed to the electrical cable near the connector, and the chassis includes an opening configured to receive the sheath, the method further comprising, during step S3, the mechanical fixing of the sheath in the opening; - the chassis includes walls extending from the first face, positioned to delimit chambers around electronic components of the circuit board, the walls being positioned relative to a plastic injection orifice in the mold so as to reduce the flow of plastic entering the chambers; and / or - A plastic injection orifice opens into a central area of ​​the inductive sensor, away from the electronic components of the circuit board. DESCRIPTION OF FIGURES

[0013] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0014] The [Fig. 1] is a perspective view of an example embodiment of a detection head according to an embodiment;

[0015] The [Fig.2] is a transparent view of the chassis and electronic board of the detection head of the [Fig.1];

[0016] [Fig.3] is a detailed view of [Fig.2];

[0017] Fig. 4 is a cross-sectional view of Fig. 2; and

[0018] Fig. 5 is a perspective view of a first face of the chassis including a partial zoom on a part of the chassis delimiting a chamber for the flow of plastic material;

[0019] Fig. 6 illustrates an injection step of an example embodiment of a manufacturing process for a detection head according to an embodiment illustrating the propagation speed of the plastic material flow during the injection step (in seconds);

[0020] Fig. 7 schematically illustrates an example of the realization of an electronic board;

[0021] Figure 8 is a flowchart of steps in a manufacturing process for a detection head according to an embodiment; and

[0022] Fig. 9 is an example of an embodiment of a metal detector comprising the detection head of Fig. 1.

[0023] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0024] A metal detector 100 according to the invention comprises a detection head 1 and a handle 110 for gripping the device by an operator.

[0025] The detection head 1 corresponds to the part designed to come close to the ground in order to detect target objects, in particular metallic objects. It comprises, for this purpose: - a chassis 2 comprising a first face 2a and supports 3 extending from the first face 2a; and - an inductive sensor 4, mounted on chassis 2.

[0026] To simplify the manufacturing process of the sensing head 1 while ensuring good shock resistance and optimal environmental resistance of the sensing head 1, the inductive sensor 4 and the chassis 2 are overmolded with a plastic material so that the inductive sensor 4 and the chassis 2 are embedded in the plastic. The inductive sensor 4 and the chassis 2 are therefore monolithic and form a single molded part of the plastic. Securing the inductive sensor 4 to the chassis 2 ensures that, when the plastic is injected, the inductive sensor 4 does not move within the mold despite the injection pressure. Furthermore, overmolding the inductive sensor 4 onto the chassis 2 eliminates the step of injecting the expanding foam and thus significantly reduces the time and stresses of the manufacturing process.Furthermore, overmolding improves the mechanical rigidity of the detection head 1, thus reducing the . risks of deformation of the head 1 (and in particular of the inductive sensor 4). Finally, the overmolding of the inductive sensor 4 reduces the risks of movement or vibration of the coils that compose it, thus avoiding false alarms.

[0027] The detection head 1 can be obtained in accordance with the following steps: SI: provide a chassis 2 comprising supports 3 extending from a first face 2a of the chassis 2; S2: mount an inductive sensor 4 on the supports 3 of the first face 2a; S4: place the assembly consisting of the chassis 2 and the inductive sensor 4 in a mold; and S5: inject under pressure a plastic material into the mold so as to embed the chassis 2 and the inductive sensor 4 in the plastic material to obtain the detection head 1. The inductive sensor 4

[0028] The inductive sensor 4 comprises either a single coil forming both emitter and receiver, or a separate emitter coil 5 and a separate receiver coil 6. The emitter coil 5 and the receiver coil 6 then each form a loop and are configured such that the loop of the emitter coil 5 at least partially overlaps the loop of the receiver coil 6 so as to form a coupling zone 7. This configuration makes it possible to obtain an inductive sensor 4 in which the mutual inductance is minimal.

[0029] By way of comparison, with respect to an inductive sensor 4 comprising a single coil constituting the transmitter and receiver and formed of two loops in series of reversed direction in order to neutralize the effects of external interference, the use of two separate coils 5, 7 for the transmitter coil 5 and the receiver coil 6 makes it possible to amplify the signal, and therefore does not require lowering the detection threshold to avoid the risk of false alarms.

[0030] In what follows, the invention will be described more particularly in the case where the inductive sensor 4 comprises at least one separate transmitting coil 5 and at least one separate receiving coil 6. For example, one, two, or more transmitting coils 5 and receiving coils 6. This is not, however, limiting, as the invention also applies in the case of an inductive sensor 4 comprising a single coil.

[0031] The transmitting coil 5 and the receiving coil 6 are homopolar windings. They can be fixed directly onto the chassis 2. The loop of the transmitting coil 5, the coupling area 7 and the loop of the receiving coil 6 extend side by side.

[0032] In a manner known per se, the transmitting coil 5 and the receiving coil 6 are configured to transmit and receive waves having a frequency between 300 Hz and 180 kHz.

[0033] The transmitting coil 5 and the receiving coil 6 may include wound wires and be attached and fixed to the first face 2a chassis 2, the transmitting coil 5 then having a greater number of turns than the receiving coil 6.

[0034] The transmitting coil 5 and the receiving coil 6 can each be fixed on the corresponding supports 3 of the chassis 2.

[0035] Alternatively, the detection head 1 may further comprise an electronic board 8 including a substrate 9 on which electronic components 10 are mounted. The inductive sensor 4 is then supported by the substrate 9 of the electronic board 8. In this embodiment, the inductive sensor 4 may include wound wires that are attached to and fixed on the substrate 9. Alternatively, the transmitting coil 5 and the receiving coil 6 of the inductive sensor 4 may be integrated directly into the electronic board 8. For this purpose, the transmitting coil 5 and the receiving coil 6 may, for example, be printed on the substrate 9 of the electronic board 8. The electronic board 8 and the transmitting and receiving coils 5, 6 thus together form a printed circuit board.This embodiment has the advantage of reducing the size of the inductive sensor 4 and the number of separate components in the detection head 1, which simplifies manufacturing and further reduces the overall weight of the detector 100. Moreover, the integration of the inductive sensor 4 into the electronic board 8 improves the mechanical stability and the positioning accuracy of the coils 5, 6, which is advantageous here as it prevents the coils 5, 6 from moving in the mold (described below) during the S5 injection molding stage of the plastic material under pressure.

[0036] In this embodiment, the electronic board 8 is then overmolded with the inductive sensor 4 and the chassis 2 in the plastic material so that the electronic board 8 is also embedded in the plastic material. The inductive sensor 4 is further mounted on the supports 3 of the chassis 2 via the electronic board 8.

[0037] Since the electronic board 8 and the inductive sensor 4 are embedded in the plastic material, they are better protected against moisture, dust (IP 68) and external agents in general than when they are surrounded by expanding foam.

[0038] The chassis 2, thanks to its supports 3, allows (among other things) the electronic board 8 and the inductive sensor 4 to be held in position during the overmolding stage, thus guaranteeing the position of the electronic board 8 and the inductive sensor 4 in the finished product.

[0039] Such a detection head 1 can in particular be obtained by placing, during step S2, the electronic board 8 comprising the inductive sensor 4 against the first face 2a of the chassis 2, resting on the supports 3, and by placing the assembly formed of the chassis 2 and the electronic board 8 comprising the inductive sensor 4 in the mold during step S4. During injection step S5, the plastic material then embeds the electronic board 8 within the plastic material, along with the chassis 2 and the inductive sensor 4. The chassis 2

[0040] The chassis 2 comprises a substantially flat plate 11 having a first face 2a and a second face 2b. The supports 3 project from the first face 2a of the plate 11. In one embodiment, the first face 2a is opposite the second face 2b of the plate 11 and is configured to face the inspected ground (e.g., the soil) during use. In this embodiment, the inductive sensor 4 and, where applicable, the electronic board 8, therefore extend between the ground and the plate 11 when the detection head 1 is in use.

[0041] The plate 11 may, for example, have a substantially elongated shape so as to follow the shape of the coils 5, 6. In particular, the plate 11 may be perforated or have areas of reduced thickness and follow the shape of the coils, which makes it possible to reduce the amount of plastic material to be injected and thus limit the weight of the sensing head 1. For example, when the inductive sensor 4 may comprise two coils 5, 6 each forming an overlapping loop, the second portion may follow the shape of the coils 5, 6 and in particular the shape of the two loops and the coupling area 7. It then comprises a reduced thickness or through-windows (as illustrated in the figures) at the center of each loop 5, 6 and of the coupling area 7.

[0042] When the detection head 1 further comprises an electronic board 8, which carries the inductive sensor 4, the plate 11 may in particular have: - a first portion 9a configured to be fixed on the handle 110 of the detector 100 and to support the part of the electronic board 8 which carries the electronic components 10; - a second portion 9b, monolithic with the first portion 9a, which is configured to support the part of the electronic board 8 which carries the inductive sensor 4.

[0043] The first portion 9a can be solid. The second portion 9b, on the other hand, can be perforated or have areas of reduced thickness corresponding to the center of the coils 5, 6 and the coupling zone 7 as described above.

[0044] Furthermore, the face 8a of the electronic board 8 which is in contact with the supports 3 of the chassis 2 corresponds to the face 8a carrying the electronic components 10 and the inductive sensor 4. The electronic components 10 and the inductive sensor 4 are therefore located between the substrate 10 of the electronic board 8 and the first face 2a of the chassis 2.

[0045] In one embodiment, the frame 2 further comprises stiffeners 12 configured to make the frame 2 rigid and stable. The stiffeners 12 may, in particular, comprise ribs extending radially from the second face 2b of the plate 11, for example according to the extension direction of the plate 11. For example, the chassis 2 may include three ribs 12 of variable height extending from the first portion 9a of the plate 11 towards the second portion 9b of the plate 11. A first and a second rib 12 each run along a respective lateral edge of the plate 11, stopping near the coupling zone 7 of the coils 5, 6. A third rib 12 is placed in a plane of symmetry of the plate 11, between the first and second ribs 12, and extends beyond the coupling zone 7, to the center of the loop. The three ribs 12 have a decreasing height from the first portion 9a to the second portion 9b and a thickness (in the X, Y plane of the plate 11) less than their height, for example on the order of 1 to 3 millimeters so as not to weigh down the detection head 1.

[0046] Where appropriate, the chassis 2 may also include all or part of the means for attaching the detection head 1 to the handle 110 of the metal detector 100. For example, the chassis 2 may include two monolithic hinges 13 with the plate 11 extending radially from the second face 2b of the plate 11, in its first portion 9a. The hinges 13 may, in particular, each be positioned along a lateral edge of the plate 11, at the end of the first portion 9a.

[0047] If necessary, the hinges 13 are press-fitted into the mold during the injection molding step S5. However, they are not necessarily overmolded with the plastic material. For example, only one base of the hinge 13 may be overmolded with the plastic material.

[0048] The frame 2 may further include reference studs 14 distributed on the first face 2a and / or the second face 2b of the plate 11 in order to ensure precise positioning of the frame 2 in the mold. The studs 14 may, for example, be configured to fit into corresponding holes in the injection mold.

[0049] Alternatively, the reference pads can be formed on the mold, the chassis then comprising corresponding holes.

[0050] The chassis 2 is made of a plastic material having a very high elastic modulus, preferably greater than or equal to 5,000 MPa, exhibiting high impact resistance, even at low temperatures (below 0°C), low post-molding shrinkage (and therefore optimal dimensional stability), and chemical compatibility (adhesion) with the material used for overmolding. Indeed, in the absence of such chemical compatibility, external agents, and in particular water or dust, could penetrate the detection head 1 at the interface between the two materials.

[0051] For example, the chassis 2 can be made of glass fiber reinforced polyurethane. The plastic material of the overmolding can then comprise polyurethane Thermoplastic. Advantageously, these two materials have good chemical compatibility because they can mix at their interface, creating a zone where both materials are present (an "interdiffuse" interface). Thermoplastic polyurethane has the advantage of being chemically compatible with glass fiber reinforced polyurethane, exhibiting high resistance to hydrolysis and atmospheric agents, high flexibility at low temperatures, and good durability under mechanical and chemical stresses.

[0052] Preferably, the melting temperature of the glass fiber reinforced polyurethane of the chassis 2 is higher than the melting temperature of the thermoplastic polyurethane of the plastic material, to avoid any softening of the constitutive material of the chassis 2 during step S5. A difference between the melting temperatures of these two materials is preferably at least equal to 50°C.

[0053] The thickness of the plate 11 (i.e., the distance between its two faces 2a, 2b) of the chassis 2 is substantially constant (except, of course, in areas containing stiffeners 13 or supports 3), so as to limit dimensional shrinkage and post-molding deformation. Similarly, the thickness of the overmolding material is substantially constant to minimize mechanical stress on the internal components of the detection head 1.

[0054] First embodiment of the supports 3 (inductive sensor 4 mounted directly on supports 3)

[0055] In a first embodiment, the supports 3 are configured to anchor the coils of the inductive sensor 4 directly onto the plate 11 of the chassis 2. For this purpose, the supports 3 may in particular include hoops configured to surround the coils 5, 6 and press them against the chassis 2. The hoops may be attached and fixed to the plate 11 of the chassis 2, for example by inserting the ends of the hoops into dedicated holes formed in the plate 11, or be monolithic with the plate 11, in which case the wires of the coils 5, 6 are threaded into the hoops. Alternatively, the supports 3 may include one or more ribs, continuous or discontinuous, configured to run laterally along the coils 5, 6 when mounted on the plate 11 of the frame 2 so as to form lateral stops for the coils 5, 6 and prevent their movement in the (X, Y) plane of the plate 11 during the injection step S5.According to yet another variant, through holes can be formed in the chassis 2, and the coils 5, 6 can be fixed to the chassis by insertion into the through holes and winding electrically insulating wires around the coils 5, 6. The insulating wires can be wound so as to form several spiral turns.

[0056] Second embodiment of the supports 3 (inductive sensor mounted on the supports 3 via an electronic card 8)

[0057] In this second embodiment, the supports 3 are configured to fix the electronic board 8 relative to the chassis 2, the inductive sensor 4 being fixed (or printed) onto the substrate 9 of the electronic board 8. The supports 3 then cooperate with the electronic board 8 to hold it in position with the inductive sensor 4 in the mold during the S5 injection molding step of the plastic material. By "hold in position," it is understood here that the supports 3 are configured to ensure spacing (Z-positioning) between the plate 11 and the electronic board 8 and thus act as spacers to prevent the electronic board 8 from coming into surface contact with the plate 11 and to allow the passage of the plastic material between the electronic board 8 and the first face 2a of the plate 11 during the S5 injection molding step.In addition, the supports 3 ensure the positioning of the electronic board 8 in the plane of the plate 11 (positioning in X, Y) in order to control the placement of the electronic board 8 inside the mold, by forming lateral stops for the electronic board 8.

[0058] In one embodiment, the supports 3 comprise spans 3a and lateral stops 3b.

[0059] The bearing surfaces 3 are configured to ensure spacing between the plate 11 and the electronic board 8: the face of the electronic board 8 opposite the components is therefore configured to bear against the bearing surfaces 3. For example, the bearing surfaces 3 may include cylindrical pads protruding from the first face 2a of the plate 9.

[0060] The lateral stops 3 are configured to bear laterally (i.e., in the X, Y plane of the plate 11) against the electronic board 8 and hold it in position in this plane. Optionally, the lateral stops 3 can be configured to hold the electronic board 8 relative to the plate 11 by friction and / or lateral clamping. Alternatively or in addition, the lateral stops 3 can be configured to fix the electronic board 8 by snap-fit, i.e., by engagement and temporary elastic deformation, in order to lock the electronic board 8 in the plane of the plate 11. When the supports 3 and the electronic board 8 are snapped into place, the supports 3 have then returned to their initial shape or an intermediate shape due to the effect of elastic rebound and no longer exhibit elastic deformation.They therefore cooperate with each other in such a way as to remain assembled together and their relative movements along the click direction (here, in Z) are limited. For this purpose, the lateral stops 3 may, for example, have a foot extending from the first face 2a of the plate 11 and a head extending at a distance from the plate 11. The head protrudes laterally from the foot in order to cooperate. with the substrate 9 of the electronic board 8. The foot is also elastically deformable, so that when the electronic board 8 is placed against the chassis 2, the substrate 9 of the electronic board 8 presses and slides on the head of the lateral stop 3, which elastically deforms the foot of the lateral stop 3 and moves the head away in the opposite direction to the substrate 9. Then, when the substrate 9 passes the underside of the head of the lateral stop (and comes into contact with the bearing surfaces 3), the foot of the lateral stop returns to its initial shape and rests against the substrate 9 of the electronic board 8. Furthermore, the underside of the head of the lateral stop 3 also acts as a stop along the Z-axis and prevents any unintentional separation of the electronic board 8 from the chassis 2.

[0061] Of course, the lateral stop 3 can cooperate with the edge of the substrate 9, or alternatively with the wall delimiting a through-hole formed in the electronic board and configured to receive the lateral stop 3.

[0062] Furthermore, the same support 3 can serve as a lateral stop and a bearing surface for the electronic board 8.

[0063] For example, the chassis 2 may include a peripheral lateral stop 3 configured to contact all or part of the edge of the electronic board 8, and where appropriate to hold the electronic board 8 by friction or snap-fit, and several bearing surfaces 3 distributed on the first face 2a of the plate 11 configured to maintain the spacing between the electronic board 8 and the plate 11. Where appropriate, the chassis 2 may further include a perimeter rim 3 extending radially from the first face 2a and surrounding the portion of the electronic board 8 carrying the electronic components 10, in order to protect the electronic board 8 and to reinforce the structure of the detection head 1 at the level of the first portion 9a of the plate 11

[0064] In one embodiment, the chassis 2 further comprises walls 15 extending from the first face 2a of the plate 11, which are configured to protect all or part of the electronic components 10 of the electronic board 8 from direct flows of plastic material during the injection step S5. To this end, the walls 15 are positioned to delimit chambers 20 around all or part of the electronic components 10 so that, during the injection step S5, the plastic material is at least partially blocked by the walls 15 before entering the chambers 20, thus locally reducing its flow rate and consequently the risk of damage to the components housed in the chambers 20.

[0065] For this purpose, the walls 15 can be positioned so as to surround one or more electronic components 10 to define a chamber 20 receiving the electronic component(s) 10 in question.

[0066] For example, the walls 15 are positioned on the plate 11 so that, when the electronic board 8 is placed on the supports 3, they define a small opening (compared to the size of the electronic component(s) 10 received in the chamber 20) for the entry of the plastic material into the chamber 20. In this position, the top of the walls 15 can come into contact with the electronic board 8. Since the plastic material can only enter the chamber 20 through the small opening, its flow rate is locally reduced, thus protecting the electronic component(s) 10 received in this chamber 20.

[0067] In another example, the top of the walls 15 is configured to contact the electronic board 8, and the walls 15 are positioned on the plate 11 relative to the plastic injection orifice 19 in the mold so that, during the injection step S5, the plastic is forced to bypass the walls 15 before entering the chamber 20. In other words, the position of the walls 15 is chosen so that the plastic cannot enter the chamber 20 directly but is forced to bypass the walls 15 before it can enter the chamber 20. This configuration of the walls 15 therefore reduces the flow rate of the plastic before it reaches the electronic components 10 housed in the chamber 20.

[0068] Of course, the walls 15 can both delimit a small opening and be positioned so that this opening is opposite the injection orifice 19 with respect to the chamber 20.

[0069] In another example, the top of the walls 15 extends a short distance from the electronic board 8, thus providing a small cross-sectional gap (compared to the gap between the first face 2a of the plate 11 and the electronic board 8) between the walls 15 and the electronic board 8 for the introduction of the plastic material into the chamber 20. Here again, this configuration makes it possible to reduce the flow rate of the injected material entering the chamber 20. The electronic card 8

[0070] The electronic board 8 includes a driver amplifier connected to the transmitting coil 5 in order to amplify the signal and adapt its impedance, an impedance amplifier / adapter connected to a first receiver stage of the receiving coil 6 in order to amplify the induced signal.

[0071] Optionally, the electronic board 8 may further include processing means which may include, in particular, a computer such as a processor, microprocessor, microcontroller, etc., for example, a field-programmable gate array (FPGA) connected to the inductive sensor 4 so as to send instructions for generating a transmission signal to the transmitting coil 5 and to receive an electrical signal of the transmitting coil 7. The processing means are further configured to process the signal in order to detect a target object. For this purpose, the processing means include, in particular, analog-to-digital converters whose input is connected to the output of the amplifier / impedance matching network and whose output is connected to the computer (typically, the FPGA). If necessary, the processing means are further configured to send instructions to generate an alert to an alarm, which can be located in the detection head 1 or on the joystick 110.

[0072] The electronic card 8 further includes a control circuit (“driver” in English) configured to drive the transmitting coil 5, the amplifiers and the control circuit being controlled by the processing means.

[0073] The electronic card 8 finally includes a memory in which, in particular, the calibration factors of the inductive sensor 4 can be stored.

[0074] The electronic card 8 can comprise a single printed circuit board carrying all the electronic components 10 (the processing means, the memory and the inductive sensor 4) which is mounted on the chassis 2. The detection head 1 is then analog and digital, the logic part taking place directly in the head (and not remotely, for example at the handle 110 or the grip 120).

[0075] Alternatively (not illustrated in the figures), the electronic board 8 could comprise two printed circuits: a first one mounted in the detection head 1 and comprising the inductive sensor 4 and optionally the memory and / or an alarm, and a second one located remotely on the handle 110 or in the grip 120 and comprising the processing means and optionally an alarm, the first and second electronic boards 8 then being electrically connected, either by wire or wireless means.

[0076] The inductive sensor 4 can be mounted on the face 8b of the substrate 9 of the electronic board 8 which is opposite the face 8a on which the electronic components 10 are mounted. When the inductive sensor 4 is integrated into the electronic board 8, the coils 5, 6 are therefore printed (or integrated) on the face 8b of the substrate 9 which is opposite the electronic components 10.

[0077] Alternatively, the inductive sensor 4 can be mounted on the same face 8a as the components of the electronic board 8, or according to yet another alternative on both faces 8a, 8b of the electronic board 8.

[0078] The electronic board 8 is electrically connected to the metal detector 100 (typically, to an autonomous power supply such as a battery and / or to an electronic board configured to control a human-device interface (power button, programming buttons, message displays, audible and visual alarms, etc.) mounted on the handle 110 or the grip 120 of the detector 100) via an electrical cable 16.

[0079] In one embodiment, the electrical cable 16 comprises a connector 17 configured to be electrically connected to a complementary connector on the electronic board 8, and a sheath 18, mounted near the connector 17. The sheath 18 is configured to be attached to and fixed onto the chassis 2, in the first portion 9a of the plate 11. The sheath 18 is preferably overmolded onto the electrical cable 16, then attached and fixed in a dedicated opening in the chassis 2. It is preferably made of a deformable elastic material such as rubber to reduce the risk of damage to the cable 16 in the area adjacent to the chassis 2. For example, the sheath 18 has a flared or conical shape, the wider base of which is configured to rest against the chassis 2. In this position, the connector 17 of the electrical cable 16 protrudes from the base of the sheath 18 to allow its connection to the board electronic 8.

[0080] The chassis 2 further includes a passage connecting the dedicated opening of the chassis 2 and the electronic board 8 which is configured to receive the portion of the electrical cable 16 extending between the sheath 18 and the connector 17 of the electrical cable 16 and guide it to the complementary connector of the electronic board 8.

[0081] This portion of the electrical cable 16 and the sheath 18 are preferably placed in the chassis 2, and the connector 17 is electrically connected to the complementary connector of the electronic board 8 before the S4 step of placement in the mold so as to be overmolded with the plastic material. Overmolding the electrical cable 16 with the plastic material makes it possible to limit the risk of damage to the electrical cable 16 at the level of the detection head 1 and to improve the sealing of the detection head 1 compared to a removable electrical cable 16.

[0082] Here again, the constituent material of the electrical cable 16 and the sheath 18 are chosen to ensure chemical compatibility with the constituent material of the plastic material and the chassis 2 and to avoid the risk of penetration of external agent into the detection head 1. For example, the electrical cable 16 can be made of at least one of the following materials: rubber, a thermoplastic polyurethane. Manufacturing process for the detection head 1

[0083] During a step SI, the chassis 2 is provided. The chassis 2 comprises monolithic supports 3 with the plate 11, and optionally stiffeners 12 and / or hinges 13. The supports 3, the plate 11 and where applicable the stiffeners 12 and the hinges are formed integrally and in one piece, for example by molding.

[0084] When the detection head 1 receives the electronic board 8, the chassis 2 further includes the walls 15 configured to delimit the chambers 20, which are also monolithic with the plate 11.

[0085] During step S2, the inductive sensor 4 is mounted on the chassis 2.

[0086] In the embodiment in which the mounting of the inductive sensor 4 is direct, the inductive sensor 4 is fixed directly onto the supports 3 of the chassis 2. In this case, the coils of the inductive sensor 4 can be wired and are assembled with the supports 3.

[0087] In the embodiment in which the inductive sensor 4 is carried by an electronic board 8, step S2 includes mounting or printing the inductive sensor 4 on the electronic board 8 and then fixing the electronic board 8 onto the supports 3 of the chassis 2.

[0088] For example, the chassis 2 may include supports and lateral stops. The electronic board 8 is then placed in contact (along the Z-axis) with the supports 3 of the chassis 2 and in simple lateral contact or clipped into the lateral stops. Mounting the electronic board 8 on the supports 3 of the chassis 2 also secures the inductive sensor 4 to the chassis 2.

[0089] The placement of the electronic card 8 can be carried out manually by an operator, or automatically by a machine.

[0090] During a step S3, the cable 16 is positioned on the chassis 2. For this, the end of the cable 16 is inserted into the dedicated hole and pushed into the passage extending immediately downstream of it, then the connector 17 is electrically connected to the corresponding connector of the electronic board 8. Simultaneously or successively, the sheath 18 is placed against the dedicated hole formed in the chassis 2. For example, the base of the sheath 18 can be inserted into the dedicated hole and placed against the wall in which this hole is formed.

[0091] During step S4, the assembly consisting of the chassis 2, the inductive sensor 4 (mounted where appropriate on the electronic board 8) and the cable 16 is placed in a mold.

[0092] The position of the chassis 2 in the mold can in particular be adjusted by taking into account the position of the reference studs distributed on the first face 2a and / or the second face 2b of the plate 11 (and / or in the mold).

[0093] Optionally, when the chassis 2 includes the hinges 13, these are mounted tightly in the mold in order to hold the chassis 2 in position in the mold during the injection step S5.

[0094] When the mold is closed, it forms a sealed enclosure. It also includes an injection port 19, positioned relative to the frame 2 to optimize the flow of plastic material within the mold enclosure. As mentioned above, when the detection head 1 includes the electronic board 8, the position of the injection port 19 is further chosen to reduce the risk of damage to the electronic components 10 of the electronic board 8.

[0095] During step S5, plastic material is heated to its melting temperature and introduced under pressure into the mold.

[0096] In one embodiment, the injection orifice 19 is positioned at the level of the second portion 9b of the plate 11, at a distance from the electronic board 8. For example, the injection orifice 19 may open onto the coupling area 7 of the inductive sensor 4 (as illustrated, for example, in [Fig. 6]). The plastic material under pressure therefore first fills the volume of the mold receiving the second portion 9b of the electronic board 8, and thus the inductive sensor 4, and only then the volume of the mold receiving the first portion 9a of the electronic board 8, which includes the electronic components 10, the cable portion 16, the connector 17, and, where applicable, the hinge base 13.In this way, the flow rate and temperature of the plastic material, when it reaches the part of the mold comprising the first portion 9a of the plate 11 and the electronic components 10 of the electronic board 8, are lower than those of the plastic material in the second portion 9b of the plate 11. Where appropriate, the walls 15 further modify the flow of the plastic material in the mold in order to protect the electronic components 10.

[0097] The injection pressure of the plastic material can, for example, be on the order of 250 MPa.

[0098] The duration of the S5 injection step is on the order of a few minutes, for example between two and three minutes.

[0099] The detection head 1 can then be mounted on a handle 110 of a metal detector 100 and the electrical cable 16 can be electrically connected to an independent power supply.

Claims

Demands

1. A detection head (1) configured to be fixed on a handle (110) of a metal detector (100), the detection head (1) comprising: - a chassis (2) comprising a first face (2a) and supports (3) extending from the first face (2a); and - an inductive sensor (4), mounted on the supports (3) of the chassis (2); the inductive sensor (4) and the chassis (2) being overmolded with a plastic material so that the inductive sensor (4) and the chassis (2) are embedded in the plastic material.

2. Sensing head (1) according to claim 1, further comprising an electronic board (8), the inductive sensor (4) being carried by the electronic board (8) and the electronic board (8) being overmolded with the inductive sensor (4) and the chassis (2) in the plastic material so that the electronic board (8) is also embedded in the plastic material.

3. Sensing head (1) according to claim 2, wherein the inductive sensor (4) is mounted on the supports (3) of the chassis (2) via the electronic board (8).

4. Sensing head (1) according to any one of claims 2 and 3, wherein the inductive sensor (4) is printed on the electronic board (8).

5. Detection head (1) according to any one of claims 2 and 4, further comprising an electrical cable (16) having a connector (17) electrically connected to the electronic board (8), a portion of the electrical cable (16) also being overmolded with the plastic material.

6. Detection head (1) according to claim 5, wherein the electrical cable (16) comprises a sheath (18) mounted near the connector (17), the sheath (18) being positioned in a corresponding hole formed in the chassis (2) and a portion of cable extending between the sheath (8) and the connector (17) being overmolded with the plastic material.

7. Detection head (1) according to any one of claims 2 to 6, wherein the chassis (2) further comprises walls (15) extending from the first face (2a) positioned so as to delimit chambers (20) around electronic components (10) of the electronic board (8).

8. Metal detector (100) comprising: - a detection head (1) according to any one of claims 1 to 7; and - a handle (110) mounted on the detection head (1).

9. A method for manufacturing a sensing head (1) according to any one of claims 1 to 7, comprising the following steps S1: providing a chassis (2) comprising a first face (2a) and supports (3) extending from the first face (2a); S2: mounting an inductive sensor (4) on the supports (3) of the chassis; S4: placing the assembly formed of the chassis (2) and the inductive sensor (4) in a mold; and S5: injecting under pressure a plastic material into the mold so as to embed the chassis (2) and the inductive sensor (4) in the plastic material to obtain the sensing head (1).

10. A manufacturing method according to claim 9, wherein, during step S2, the method further comprises mounting an electronic board (8) on the supports (3) of the chassis (2), the inductive sensor (4) being carried by the electronic board (8).

11. A manufacturing method according to claim 10, wherein the inductive sensor (4) is printed on the electronic board (8).

12. A manufacturing method according to any one of claims 10 and 11, further comprising, prior to step S4, a step S3 of electrical connection of a connector (17) of an electrical cable (16) with the electronic board (8).

13. A manufacturing method according to claim 12, wherein the electrical cable (16) comprises a sheath (18) fixed to the electrical cable (16) near the connector (17), and the chassis (2) comprises an orifice configured to receive the sheath (18), the method further comprising, during step S3, the mechanical fixing of the sheath (18) in the orifice.

14. A manufacturing method according to any one of claims 10 to 13, wherein the chassis (2) comprises walls (15) extending from the first face (2a) positioned so as to delimit chambers (20) around electronic components (10) of the electronic board (8), the walls (15) being positioned relative to an injection orifice (19) of the plastic material into the mold so as to reduce a flow of the plastic material entering the chambers (20).

15. A manufacturing method according to any one of claims 10 to 14, wherein an injection orifice (19) of the plastic material opens into a central area of ​​the inductive sensor (4), at a distance from electronic components (10) of the electronic board (8).

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