EP0845097B1 - Mine-clearing coil and device using same - Google Patents

Abstract

PCT No. PCT/FR97/01105 Sec. 371 Date Mar. 17, 1998 Sec. 102(e) Date Mar. 17, 1998 PCT Filed Jun. 19, 1997 PCT Pub. No. WO97/48965 PCT Pub. Date Dec. 24, 1997A demining coil to be fastened to a demining vehicle, which coil comprises a magnetic core and wherein the ratio of length to the largest transversal dimension of the core of the coil is greater than or equal to 4. The core of the coil may be fluted in shape and/or magnetically laminated. A demining device utilizes a plurality of demining coils spaced in different directions to maximize the area of detection.

Description

The technical field of the invention is that of coils used in mine clearance operations.

We know in particular by the patents DE3444037 and FR2701105 demining devices that use at least one induction coil powered by an electrical circuit.

Known devices generally use coils substantially flat and devoid of core.

Indeed, this technology allows to place the coils directly on the glacis of a tank by limiting disturbances of the magnetic field that the mass of the tank could generate.

However, these coils have the main disadvantage of being very heavy (the usual mass of a demining coil is 80 kg), and the field generated remains of relatively small amplitude (of the order of 5 micro tesla at 5 m). By way of illustration, we will mention patent EP-0574967 which describes a device for demining comprising a coil made integral with a vehicle minesweeper which has a magnetic core and a wire conductor wrapped around the core. The role of this coil is activate the various mine detection systems.

In addition, the magnetic field generated is oriented essentially along a single axis (the axis of the coil) which decreases the effectiveness of the demining device.

It is a first aim of the invention to propose a demining reel whose size is reduced and the efficiency is improved compared to known coils.

It is another object of the invention to propose a demining device using one or more of these demining coils, a device with higher efficiency to that of known demining devices.

Thus, the subject of the invention is a demining coil equipped with a magnetic core, intended in particular to be secured to a demining vehicle, reel characterized in what the core is of the laminated or grooved type to limit the eddy currents and in that the ratio of the length over the largest transverse dimension of the coil core is greater than or equal to 4.

The material of the magnetic core will have preferably a relative permeability greater than or equal to 100 and a saturation induction greater than or equal to 2 you're here.

The demining coil may be surrounded by a case protection made of non-magnetic material and not driver.

According to another characteristic of the invention, the coil may include a connecting means for allow its fixation on a support placed to a part front of a demining vehicle, the connecting means being shaped so as to allow an angular displacement of the axis of the coil relative to the support.

Thus, the connection means may include a base having at least two fixing systems separated by a part made of flexible synthetic material.

According to another embodiment, the means of connection may include at least two elastic wedges, arranged between the coil and the protective case, shims which ensure flexible positioning of the coil substantially at the axis of the case.

According to another embodiment, the means of link may include at least three rings concentric, pivots being provided between a ring intermediate and the other two rings, pivots positioned so as to allow the pivoting of an internal ring carrying the coil along at least two orthogonal axes.

The invention also relates to a device for mine clearance using at least three coils and characterized in that the coils are fixed on a support placed at a front part of the demining vehicle, the axes of the coils being distributed so as to form two at two at least two non-parallel planes.

According to another embodiment, the coils are fixed on a support placed at a front part of the vehicle of demining, and the axes of the coils are distributed along at least two different directions.

The axes of the coils can be distributed according to at least three different directions.

• la figure 1a représente en coupe longitudinale une bobine de déminage selon un premier mode de réalisation de l'invention,
• la figure 1b est une vue de cette bobine en coupe transversale suivant le plan repéré en AA sur la figure la,
• la figure 2a représente en coupe longitudinale une bobine suivant un deuxième mode de réalisation de l'invention,
• la figure 2b est une vue de cette bobine en coupe transversale suivant le plan repéré en BB sur la figure 2a,
• la figure 3a représente en coupe longitudinale une bobine suivant un troisième mode de réalisation de l'invention,
• la figure 3b est une vue de cette bobine en coupe transversale suivant le plan repéré en CC sur la figure 3a,
• la figure 4 représente schématiquement un dispositif de déminage suivant l'art antérieur,
• la figure 4a montre schématiquement l'orientation des lignes de champ autour d'une bobine d'induction,
• la figure 5 représente schématiquement un dispositif de déminage suivant un premier mode de réalisation de l'invention,
• la figure 6 représente schématiquement un dispositif de déminage suivant un deuxième mode de réalisation de l'invention,
• les figures 7a et 7b représentent schématiquement un dispositif de déminage suivant un quatrième mode de réalisation de l'invention, la figure 7b étant une vue du dispositif suivant la direction repérée F sur la figure 7a,
• la figure 8 représente schématiquement un dispositif de déminage suivant une variante de l'invention.

The invention will be better understood on reading the description which follows of different embodiments, description made with reference to the accompanying drawings and in which:

• FIG. 1a represents in longitudinal section a demining coil according to a first embodiment of the invention,
• FIG. 1b is a view of this coil in cross section along the plane marked in AA in FIG. la,
• FIG. 2a represents in longitudinal section a coil according to a second embodiment of the invention,
• FIG. 2b is a view of this coil in cross section along the plane marked in BB in FIG. 2a,
• FIG. 3a represents in longitudinal section a coil according to a third embodiment of the invention,
• FIG. 3b is a view of this coil in cross section along the plane marked in CC in FIG. 3a,
• FIG. 4 schematically represents a demining device according to the prior art,
• FIG. 4a schematically shows the orientation of the field lines around an induction coil,
• FIG. 5 schematically represents a demining device according to a first embodiment of the invention,
• FIG. 6 schematically represents a demining device according to a second embodiment of the invention,
• FIGS. 7a and 7b schematically represent a demining device according to a fourth embodiment of the invention, FIG. 7b being a view of the device in the direction marked F in FIG. 7a,
• FIG. 8 schematically represents a demining device according to a variant of the invention.

Referring to Figure 1, a demining coil 1 according to the invention is intended to be fixed to a part front of a demining vehicle (not shown).

This coil includes a winding 2 of a wire conductor 3, winding comprising a number of concentric layers. This winding is carried out around of a magnetic core 4. The winding is connected by connections not shown to control electronics, for example of the type described by the patent FR2701105.

The nucleus 4 has a parallelepiped shape which has been chosen for manufacturing facilities. He is flaky consisting of a stack of soft iron sheets isolated from each other by an oxide layer. The different oxide layers act as insulation electric which limits the action of currents of Foucault.

Alternatively, we could use a kernel bearing longitudinal grooves penetrating radially in the nucleus. These grooves also make it possible to limit eddy currents.

We will choose the material of the sheets such that it has a relative permeability µr greater than or equal to 100. This limit value is sufficient because magnetic induction created by the coil at 4 m no longer believes with µr when this one exceeds 100.

Induction to saturation of the core material (maximum magnetic induction allowed by its material) must also be as high as possible in order to limit the non-linearities of the magnetic induction that is created depending on the current. This optimizes the yield.

We practically choose a saturation induction greater than or equal to 2 tesla.

We could for example use an iron core standard sweet whose µr is around 1000 and the saturation induction is 2 tesla. Wire 3 of the winding will be copper wire. We will choose the length of wire and therefore the number of concentric layers depending on the desired performance for the coil.

The coil is dimensioned so that its core has a ratio of its length L to its largest transverse dimension (here the diagonal of the section square) greater than 4.

Such an arrangement makes it possible to optimize the yield constraints, mass and size of the coil.

Indeed, the field projected out of the coil will be all the more important as the core of the coil will long, this is because the field lines get close between the two North (N) and South (S) poles of a coil (see fig 4a). They will close much more away from the coil if it or its core is long.

At the same time, the value of the coil inductor must stay relatively small to make it possible to inject current into it. Now the value of the self increases with diameter.

Finally the mass of the coil is proportional to its volume.

The essential parameter for the definition of a coil effective is therefore the L / D ratio (length over diameter or length over greatest transverse dimension for a parallelepipedic nucleus).

The coil is arranged inside a case of protection 5 made of a non-magnetic material and not conductor (e.g. plastic or coiled filamentary) and closed by covers 6a, 6b. This case protects the coil against external aggressions.

This coil carries at one of its ends a connecting means 15 which is intended to allow its fixing on a support placed at a front part of a vehicle demining.

This connecting means is formed by a base having at least two fixing systems 16a, 16b (here rods threaded) separated by a part 17 made of a material flexible synthetic (eg rubber).

Each threaded rod 16a, 16b is integral with a plate metal on which the intermediate part is molded 17.

The connection means is flexible and allows a angular displacement of the axis 24 of the coil 1 by support.

So when moving the vehicle, the coil will subject to vibrations which will modify randomly the spatial components of the field magnetic generated.

This results in an improvement in the efficiency of the demining.

It is of course possible to fix on a vehicle the coil according to the invention by means rigid connection.

By way of example, a coil according to the invention, having a winding of 150 m of wire and having a plus large section dimension (D) of 80 mm for a length L of 550 mm, has a mass of 18 kg. She creates at a point given a magnetic field of intensity double that of generated by a known type air coil having the same number of turns and whose mass is 35 kg.

With equivalent electrical power, 4 coils to air of this type will create a field of 6 micro teslas at 5 m, and 4 core coils will generate a field of 15 micro teslas.

Figures 2a and 2b show a second mode of production of a coil according to the invention

This embodiment differs from the previous one in that the core 4 carrying the wire winding 2 is positioned substantially coaxial to case 5 by two shims elastic bands 18a and 18b which thus form the connecting means flexible coil.

The shims 18a, 18b are produced for example in rubber. Each wedge has a central part annular 19 which is positioned at a rod cylindrical 20 integral with the laminated core 4.

Each end of the core 4 carries such a rod 20 which may be made of plastic (non-magnetic) and fixed to the core 4 for example by thread.

The central part 19 of the wedge is connected to a peripheral part 21 by three arms 22. The thickness and the shape of the arms 22 are determined so as to give the bond the desired flexibility.

The peripheral part 21 of each wedge is adjusted to the internal surface of the case 5.

The shims 18a, 18b are fixed to the rods 20 and to the case 5 for example by gluing.

The case 5 itself will be fixed to the vehicle by means of a threaded rod 23 integral with the cover 6a.

The advantage of this embodiment is that the coil 1 is suspended by its two ends at the level of the axis 24 of the protective case 5. It can therefore be animated by more complex vibration movements than those allowed by the previous embodiment.

This results in an even more random variation in the magnetic field generated and higher efficiency.

In addition, the flexible mounting method is protected by case 5.

It is of course possible to provide variants of realization and to modify for example the forms of shims, number of arms, shim material. It is also possible to provide reinforcement inserts at the level of the central and peripheral parts. It is possible to provide a third wedge arranged substantially in the middle of the coil.

It is finally possible to combine the modes of realization of figures 1 and 2 by associating a coil suspended by shims 18a, 18b and the case of which is fixed to the vehicle by flexible connection means 16,17.

Figures 3a and 3b show a third mode of production of a coil according to the invention.

According to this embodiment the coil is linked to the case 5 (which allows its attachment to the carrier vehicle) via a compass assembly which includes a outer ring 25, an intermediate ring 26 and a ring internal 27. The intermediate ring 26 is linked to the ring outer 25 by two pivots 28a, 28b (shown schematically) which allow a rotation of the ring intermediate to the outer ring around a axis 29 perpendicular to the axis of the case.

The intermediate ring 26 is linked to the internal ring 27 by two other pivots 30a, 30b (shown schematically) which allow a rotation of the ring internal 27 relative to the intermediate ring 26 around an axis 31 perpendicular to the axis of the case and to the axis 29.

The coil is integral with the inner ring 27.

It results from this mounting a possibility of pivoting of the axis 24 of the coil around the axes 29 and 31.

When moving the carrier vehicle, the axis of the reel constantly changes orientation which varies the magnetic field randomly and improves the effectiveness of mine clearance.

Stops may be provided to adjust the maximum values of the angular deflections of the axis 24.

Figure 4 shows a demining device according to prior art.

This device comprises two coils 7a, 7b arranged on a bar 8 secured to a front part of a vehicle 9.

The coils are arranged so that their axes are substantially vertical (here perpendicular to the plan of the figure).

In a known way, a coil generates a field magnetic whose vector is tangent to lines equipotentials which are substantially parallel to the axis of the coil inside it and which close outside the coil.

Figure 4a shows schematically (for the record) a coil 11 in longitudinal section with the field lines 10 that she creates and some B magnetic field vectors positioned on the field lines.

So the field vectors are not perfectly parallel to the axis of the coil outside of it.

The minesweeper coils having their axes substantially vertical, they generate in front of the demining vehicle a magnetic field which has a vertical component and a horizontal component.

The field seen at a point A located in front of the Minesweeper is a composition of the field created by the two coils. This field therefore has a vertical component and two horizontal components (represented by the BH1 and BH2 notations).

However, the field seen at a point B located laterally at the minesweeper sees only one component horizontal (BH3), and which corresponds practically to the single action of the nearest coil (attenuation of the field generated by a coil being proportional to the cube distance).

This results in lower efficiency with respect to mines disposed laterally at the minesweeper.

Referring to FIG. 5, a device for demining according to a first embodiment of the invention comprises four coils 1 of the type of those described with reference to Figures la and 1b. These coils have their axes substantially vertical and are arranged along two pairs 12a, 12b.

Each pair of coils is attached to a wing 13a, 13b of a support 14 secured to the vehicle 9. The wings 13a and 13b are not coplanar and therefore form an angle .

From a geometric point of view we can say that the axes coils of each pair materialize a plane which corresponds to a wing 13a or 13b, and the two planes 13a, 13b materialized by the coils are not parallel.

Advantageously, a blade will be adopted as support 14 which is usually used on demining vehicles.

Such an arrangement greatly improves the efficiency of the demining device.

Indeed, if a point A placed in front of the vehicle 9 sees a magnetic field with two components horizontal BH1, BH2, a point B arranged laterally at vehicle also sees a magnetic field with two horizontal components BH4 and BH5. Each point therefore sees two different coils located at distances which are of the same order of magnitude, these coils generate field lines with slightly different shapes, their actions combine.

As a variant it is of course possible to use only three coils, two arranged on one wing 13a and one on wing 13b, or one on each wing and the third at the intersection of the two wings 13a, 13b.

Figure 6 shows another embodiment of the demining device according to the invention in which the support 14 also has two side wings 13a and 13b forming an angle.

In order to improve the distribution of the magnetic field along three orthogonal components Bx, By and Bz, two coils 1a and 1b are oriented with their vertical axis, two coils 1c and 1d have their horizontal axis, and the axis of the coil 1c is perpendicular to that of the coil 1d.

Each coil generating a field at ground level magnetic whose maximum intensity component is substantially that which is parallel to the axis of the coil, we are assured with the configuration of figure 6 to generate a resulting magnetic field which has components along the three orthogonal directions.

This results in better mine clearance efficiency.

Figures 7a and 7b show another mode of embodiment of the invention in which in order to distribute the intensity of the magnetic field in three directions orthogonal we have arranged on the support 14 two coils 1a and 1b with vertical axis and two coils 1c and 1d whose axes respective D4 and D5 form an angle, both with the vertical (angle β visible in Figure 7b), and with the direction Δ of vehicle progression (angle α visible at Figure 7a).

An appropriate adjustment of the angles α and β makes it possible to generate a magnetic field with a given intensity along each of the three orthogonal directions.

Alternatively the four coils may also be fixed to a flat support, the double inclination α and β ensuring for any point in space surrounding the vehicle the presence of three components of the magnetic field.

It is also possible to provide a means of individual adjustment of the angles of each of the coils. We can then (using charts) adjust so specifies each of the components of the magnetic field generated. The adjustment can optionally be controlled so manual or automatic from the demining vehicle in order to adapt demining to a particular configuration ground.

All embodiments of the invention shown in Figures 5 to 7 can be implemented with coils fixed to the support 14 in a rigid manner.

They can also be implemented with coils having flexible connecting means such as those described with reference to Figures 1, 2 and 3.

The flexible connection means can make it possible not to use for example that coils having practically the same orientation.

We can thus consider Figure 8 which shows a support formed by a clearing blade which has two wings 13a, 13b and on which are fixed two coils 1 to parallel axes. These coils are linked to the support by a flexible connection means of the type for example of Figures 1, 2 or 3.

In this case, the variation of the field components which is given by the flexible connection is sufficient to ensure the effectiveness of mine clearance.

Claims (11)

1. A demining coil (1) provided with a magnetic core (4), intended in particular to be made integral with a demining vehicle, a coil characterized in that the core (4) is a magnetic laminated or fluted core to restrict the eddy currents and in that the ratio of length to the largest transversal dimension of the core of the coil is greater than or equal to 4.
2. A demining coil according to Claim 1, characterized in that the constitutive material of the magnetic core (4) has a relative permeability greater than or equal to 100.
3. A demining coil according to Claim 2, characterized in that the constitutive material of the magnetic core (4) has a saturation induction greater than or equal to 2 tesla.
4. A demining coil according to one of Claims 1 to 3, characterized in that the it is surrounded by a protective casing (5) made of a non-magnetic, non-conductive material.
5. A demining coil according to one of Claims 1 to 4, characterized in that it incorporates linking means (15) intended to enable its fastening onto a support placed at a front part of a demining vehicle, the linking means being formed so as to allow an angular displacement of the coil axis with respect to the support.
6. A demining coil according to Claim 5, characterized in that the linking means incorporate a base having at least two fastening systems (16a, 16b) separated by a part (17) made of a flexible synthetic material.
7. A demining device according to Claims 4 and 5, characterized in that the linking means incorporate at least two elastic shims (18a, 18b), arranged between the coil (1) and the protective casing (5), shims which ensure flexible positioning of the coil substantially level with the casing axis.
8. A demining coil according to Claim 5, characterized in that the linking means incorporate at least three concentric rings (25, 26, 27), pivots (28a, 28b, 30a, 30b) being provided between a middle ring (26) and the two other rings, pivots positioned so as to allow an inner ring (27) carrying the coil (1) to pivot following at least two orthogonal axes (29, 31).
9. A demining device implementing at least three coils according to any one of Claims 1 to 8, characterized in that the coils (1) are fastened onto a support (14) placed on a front part of the demining vehicle, the coil axes being spaced so as to form two by two at least two non parallel planes.
10. A demining device implementing at least three coils according to any one of Claims 1 to 8, characterized in that the coils (1) are fastened onto a support (14) placed on a front part of the demining vehicle, the coil axes being spaced along at least two different directions.
11. A demining device according to Claim 10, characterized in that the coil axes are spaced along at least three different directions.

Images