FR2800457A1 - Manufacture of non-contact analog position sensor for car includes applying printed circuit material to substrate; circuit includes spiral coil and metallic layer(s) with magnetic properties - Google Patents

Abstract

Manufacture of a non-contact analog position sensor includes applying to a substrate a multi layer printed circuit material including a spiral coil. At least one layer is metallic with specific magnetic properties. The circuit may have a ferromagnetic material on both faces of layers of copper. An insulating material covers an external face of the coil and extends between its windings. The metallic layer is applied to an external face of the printed circuit.

Description

The invention is in the field of position sensors. It relates in particular sensor used in the automotive field to detect the position of motor elements or control elements, such as steering column, control levers lights, wipers, etc..

In the automotive field in particular, there is a significant need for knowledge of mobile joystick position, for example for vehicle control commands, or levels, for example of gasoline or other engine fluids. In addition, there is today, with the increase in the electronic content of vehicles, a desire to know more operating parameters of all the elements of the engine, with for example the position of controls or actuators, the torque applied to the steering bar, gear lever position etc.

Precise position sensors, economical to achieve and small are therefore more and more essential.

Resistive potentiometers are commonly used in this field. For reasons of reliability, it is desirable to replace this type of sensor by non-contact sensors, without increasing their cost.

In addition, contactless inductive position sensors are already known. Particularly in this field, reference can be made to document 5.204.621 (Position Sensor Employing a Soft Magnetic Core) which describes a device comprising a measuring coil framed by two excitation coils of opposite polarity arranged on a cylinder (or on a flat sheet). ) which comprises an internal sheet V of ferromagnetic material, in which is movable in translation a small magnet.

The magnet generates in the nucleus a saturation zone which interrupts the field lines created by the excitation coils, modifying the part of each of them in the signal measured at the terminals of the measuring coil. The magnet is then attached to the moving part whose displacement is to be measured. In the case of planar device, the small magnet is movable in contact with a protective and sliding layer in front of two coils and the measurement is performed differentially also.

It is understood that this device is not suitable for remote position measurement or through a wall. moreover, it is relatively complex in the case of embodiment in cylinder, leads to undesirable friction phenomena in the case of planar device.

The present invention has to overcome the aforementioned drawbacks, by providing an analog position sensor without economic contact to achieve, simple to implement, and adapted to measure a position through a wall.

For this purpose, the invention proposes a method of producing a non-contact analog position detector of the multilayer printed circuit type comprising at least one elongate spiral coil deposited on a substrate, characterized in that it comprises at least one metal layer constituted by material of predetermined magnetic characteristics.

It will be understood that the principle of the invention is a multilayer printed circuit, at least one metal layer of which is made of ferromagnetic material instead of copper.

In a preferred mode of implementation, the method comprises steps of creating a multilayer printed circuit comprising at least one elongated spiral coil deposited on a substrate, covering these coils on their outer face with an insulating layer, a material filler being introduced between the tracks of the coils, and adding on at least one outer face of this multilayer printed circuit of a layer of said core material of predetermined magnetic characteristics. This application is filed together with a group of patent applications "Non-Contact Analog Position Sensor", "Non-Contact Analog Position Sensor with Variable Width Core Layer", - "Differential-Coupled Contactless Analog Position Sensor". The following drawings will help to better understand the aims and advantages of the invention. It is clear that this description is given only by way of example, and is not limiting in nature. In the drawings - Figure 1 schematically shows a position sensor made by a method according to the invention; - Figure 2 shows an elongate spiral coil used in the detector; FIG. 3 is a sectional view of the components of the detector with two parallel windings; - Figure 4 illustrates similarly the case of four parallel windings; - Figure 5 is a sectional view of the detector and the movable magnet - Figure 6 illustrates a top view of the saturation zone generated by the magnet during its movement; Figure 7 shows in section the elements of a sensor; FIG. 8 illustrates a variant comprising electronic components; - Figure 9 shows a particular implementation of the invention.

The fundamental principle of the sensor for which the method is used is the implementation of an inductance coil disposed on a thin substrate, sandwiched between two layers (by default only one) of mumate type material (with high permeability magnetic). In the remainder of the description, the term mumetal will be used to designate more generally materials having similar magnetic characteristics, ie high magnetic permeability, for example of the order of 100,000 x that of air, and low saturation field, for example 0.8 Tesla) The mumetal behaves as an amplifier of the inductance L measured at the terminals of the coil (magnetic field storage effect). When a magnet passes in front of the mumetal sheet, its magnetic field causes a local saturation of said mumetal (which we have seen to be chosen such that it is saturated by a relatively weak field), whose magnetic permeability collapses on the saturated surface.

This results in a decrease in the value of the inductance L, proportional to the coil area covered by saturated mumetal.

This fall in inductance is naturally measurable at the terminals of said inductance, and an estimate of the surface of the coil covered by saturated mumetal is deduced therefrom.

It is also possible to use two coils arranged in parallel between the mumetal layers, one fed by an alternating current and the other connected to the terminals of a voltage measuring device. In case, the coupling between two coils is favored by the presence of the mumetal. Saturation last by the magnetic field of the magnet causes a variation of this coupling, proportional to the coil surface covered by saturated mumetal, which is measurable across the second coil.

By choosing a shape and a judicious arrangement of the coil, the meter and the magnet, an electrical signal (function of the inductance or coupling variation) related to a displacement of the magnet in a predetermined direction is obtained.

As can be seen in FIG. 1, a sensor produced by a method according to the invention, in its implementation in the form of a longitudinal sensor, comprises two parts of which the first part 1 constitutes the detector itself, and the second part 2 is integral with the moving part whose displacement is to be measured.

The detector 1 is a conventional multilayer printed circuit made from a sheet of substrate material 3 of any type conventional in this field, for example epoxy glass (rigid), or polyimide (flexible). In this non-limiting example, the substrate sheet has a length of a few centimeters for a width of about 1 centimeter and a thickness of 0.1 mm.

This substrate sheet 3 carries a flat coil 4 (Figure 2) elongated spiral type, for example ten times longer than wide. This coil preferably comprises a large number of turns (turns), since it knows that the inductance is proportional to the square of the number of turns. A spiral coil is used to cause an addition of the magnetic fields created by the concentric turns and not their subtraction two by two.

In the sensor described there is used a coil 4 having a plurality of windings 7 connected in series and arranged physically in parallel layers, so as to increase the mutual inductance of the windings to reduce the effects of non-linearity in the folding zones 5. On the other hand, it is known that the multiplication of coil and substrate thicknesses leads to an increase in both the cost of production and also the magnetic resistance of the assembly. However, the inductance is inversely proportional to this magnetic resistance. It is therefore desirable to restrict the number of layers of insulation.

In the present example, a coil 4 is used with two parallel windings 7A, 7B (FIG. 3) arranged on either side of the substrate sheet 3. It is clear that four-winding coils can be used. 7 or more as needed. (Figure 4).

The detector 1 then comprises two layers 8A, 8B of ferromagnetic material (called core layers in the remainder of the description), typically in mumetal, arranged on either side of the printed circuit board 3,4. An insulating material of conventional type (not shown) previously inserted between the tracks of the windings 7 of the coil and above said windings 7.

The thickness of each core layer 8A, 8B is small, between 20 and 50 microns, to prevent the appearance of eddy currents. The thickness of these core layers 8 can range from a few angstroms to a few tens of microns. To obtain an extremely low thickness, such a core layer 8 may optionally be obtained by vacuum deposition, at least for certain types of ferromagnetic material.

As regards the ferromagnetic material used, three or more families of materials compatible with stated conditions are known or less. First, the mumetal family itself is made of a nickel-iron alloy. A second family uses an amorphous metal obtained by ultra fast quenching. Finally, a third family uses a nanocrystalline material based on cobalt. Such materials are for example known under the tradenames of Permaloy, Ultraperm, Finmec.

It is desirable that the two core layers 8 be as close as possible to one another. As a result, a coil 4 and very thin insulators 3 are used.

The second part 2 (movable) of the displacement sensor comprises a magnet 9 which generates a saturation zone 10 (generated field greater than the saturation field of the core layer or layers 8) in the plane of the mumetal layers 8, the surface of which is similar to the surface of the mumetal layer 8 (FIGS. 5 and 6).

The method for manufacturing the sensors described above, in their various constitutions, comprises in principle the creation of a sandwich comprising a multilayer printed circuit supporting at least one core layer 8 of ferromagnetic material with predetermined magnetic characteristics.

The insulating substrate 3 which carries the coil or coils 4 is for example of the epoxy or polyimide synthetic material type. As an order of magnitude, this substrate 3 may be a few centimeters long, for about 1 centimeter wide and 0.1 mm thick. It is clear that this layer can naturally be chosen to be flexible or rigid (with a greater thickness), depending on the implementation constraints of the sensor in each application.

In a particular embodiment, the coils 4 are made by etching in the form of very elongated copper tracks deposited on a substrate plate 3. They typically have half a dozen turns.

These coils 4 are covered on their outer face by a new insulating layer 3 ', 3 ", similar to the substrate 3 both in dimensions and in material.A filling material 11 of a type known to those skilled in the art is naturally introduced between the tracks. coils 4, before depositing the new insulating layer 3 ', 3 ", for example by gluing or any other conventional means.

The realization of this multilayer printed circuit comprising two coils 4, 4 'of conventional nature and is therefore not detailed here above. Then a core layer 8 made of material with a high permeability (typically greater than a factor of 100,000 relative to air) and a low saturation field (typically 0.8 T) is deposited on at least one outer face of the insulating composite 3 + coils 4, 4 '(Figure 7).

The high permeability material used is, for example, mumetal itself (nickel-iron alloy), or an amorphous alloy (also called metal glass), or a nanocrystalline alloy based on cobalt typically.

The core layer 8 is of the order of 20 to 50 microns, to allow saturation by a weak external magnetic field). According to the type of sensor that one wishes to realize different forms of core layer are feasible: core layer in the form of triangle, or having width bearings, or local narrowing, core layer arc optionally tapered circle, core layer having hatching or grains larger or smaller and more or less tight.

The core layer 8 is for example made by chemical process (deposition), or by bonding, while being precut and then bonded in a conventional manner.

Alternatively, the deposition process is a roll forming, the shape of the core layer 8 being obtained for example by an additive or subtractive method of known type according to the form required by the application of the sensor.

A deposit by etching or screen printing is finally used, according to methods known to those skilled in the art.

To improve its electrical conductivity or weldability, the ferromagnetic material may optionally and selectively be covered by another metal in a manner known to those skilled in the art. This is particularly useful if the mumetal is to be used as a conductive track.

Of course, it is advantageous to carry out a treatment improving its adhesion to the support before bonding, for example with a deposit of a thin layer of gold, then copper, and then a step of oxidation of the copper.

A protective varnish of the core layer 8 is preferably applied, so as to reduce the mechanical stress and to isolate the ferromagnetic layer. In an alternative method of deposition of the ferromagnetic layer, the material used is pulverized and mixed with a polymer paste, so that it is then easily deposited on the coils.

It is also possible alternatively to modify after deposition the magnetic characteristics of a core layer 8, whether by local mechanical stress, or by laser treatment, the local heating destroying the magnetic properties of the mumétai in particular. Such a treatment is for example adapted to correct manufacturing errors (linearity errors or adjustment of the detector output value).

It is also clear that bonding circuit assemblies of elementary sub-circuits obtained by the method described above are feasible, with bonding methods known to those skilled in the art.

In an alternative embodiment reducing the number of layers of ferromagnetic material to be manufactured, the circuit is chosen of very flexible type, two coils 4, are produced side by side on a substrate 3, a core layer is deposited on the other side of the substrate 3, then the printed circuit is folded in two after deposition of the core layer 8, the two coils then being parallel in screws, separated by a thickness of adhesive, so as to obtain a core layer on both sides of the coils 4, 4. A separation is created between both sides of the core layer 8.

The detector assembly 1 is typically made in the form of a sheet of small thickness, for example about 0.5 mm.

It is clear that it is possible to use the same multilayer circuit, outside the zone comprising the coils 4, 4 'and the core layers 8A, 8B, to trace conductive tracks adapted to the production of electronic circuits, components 13 being then implanted on or both sides of the printed circuit.

In an alternative embodiment, a new insulating layer 12 is deposited on a core layer 8, and conductive copper tracks are etched therein, so as to allow the implementation of components 13 (Figure 8).

In another embodiment not shown, at least a portion of a core layer 8 is used as a component support 13 (with appropriate treatment), outside the area comprising the coils 4, 4 '. In this case, the first part of the core layer 8 used in the position detector function is connected to the ground of the electronic signal processing device, while the second part which supports components 13 and conductive tracks is not connected to this same mass. Two different zones are then created side by side in the core layer 8, with a separation.

Advantageously, in the case of a flexible sensor (with a thin substrate 3), comprising a first actual position detector zone, with two core layers 8A, 8B (FIG. 9), and a second zone 14 in which components 13 are implanted on a substrate supporting a layer of ferromagnetic material, the circuit is folded around these components 13, so as to provide them with excellent electromagnetic shielding.

It is clear that these components 13 may for example constitute the electronic signal processing circuit of the position detector 1.

The scope of the present invention is not limited to the details of the above embodiments considered by way of example, but instead extends to modifications within the scope of those skilled in the art.

Claims (1)

1. A method of producing a multilayer printed circuit contactless analog position detector comprising at least one elongate spiral coil deposited on a substrate, characterized in that it comprises at least a metal layer made of material of predetermined magnetic characteristics. Process according to claim 1, characterized in that it comprises the production of a multilayer printed circuit comprising a layer of ferromagnetic material, surrounded on both sides by layers of copper. 3. Method according to claim 1, characterized in that it comprises steps of creating a multilayer printed circuit comprising at least one elongated spiral coil deposited on a substrate, covering these coils on their outer face with an insulating layer. , a filling material being introduced between the tracks of the coils and adding on at least one outer face of this multilayer printed circuit of a layer of said core material of predetermined magnetic characteristics. 4. Method according to any one of claims 1 to 3, characterized in that the coils are formed by etching in the form of highly elongated copper tracks, deposited on the substrate plate. 5. Method according to any one of claims 1 to 4, characterized in that the core layer 8 is made by pre-cutting and then bonding. 6. Method according to any one of claims 1 to 4, characterized in that the core layer 8 is made by etching. Process according to any one of Claims 1 to 4, characterized in that the core layer 8 is produced by screen printing. 8. Method according to any one of claims 1 to 7, characterized in that the core layer is selectively covered by another metal. 9. A method according to any one of claims 1 to 7, characterized in that a deposit of a thin layer of gold, then copper, and a copper oxidation step is performed on the core layer. 10. Method according to any one of claims 1 to 9, characterized in that it comprises a step of applying a protective varnish core layer 8. 11. A method according to any one of claims 1 to 10 , characterized in that the core material has a permeability typically greater than 100,000 factor relative to air and a saturation field typically 0.8 T. Process according to any one of claims 1 to 11, characterized in that the core material is mu-metal. 13. Method according to any one of claims 1 to 11, characterized in that the core material is an amorphous alloy (also called metal glass). Process according to any one of claims 1 to 10, characterized in that the core material is a nanocrystalline cobalt-based alloy. 15. Method according to any one of claims to 14, characterized in that the layer of core material has a thickness in the order of 20 to 50 microns. Method according to any one of claims 1 to 15, characterized in that it also comprises steps of depositing a new layer of insulation on a layer of core material, and etching conductive tracks on this layer of insulation, in order to allow the implantation of components. Method according to any one of claims 16, characterized in that at least a portion of the mumetal surface used as conductive tracks and component support. 8. A method according to claim 17, characterized in that it comprises creating two distinct areas of core material, a first portion of the core material layer which is useful in the position sensor function being connected to the mass of an electronic signal processing device, and second part supporting components and conductive tracks not being connected to the same mass. A method according to any one of claims 1 to 18, characterized in that in the case of a flexible sensor (with a thin substrate), comprising a position sensor area proper, with two mumetal layers and a zone in which components are implanted above a mumetal layer, the method includes a step of folding the circuit around these components, so as to provide them with excellent electromagnetic shielding.