EP1417457A2 - Detection device - Google Patents

Detection device

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Publication number
EP1417457A2
EP1417457A2 EP02794567A EP02794567A EP1417457A2 EP 1417457 A2 EP1417457 A2 EP 1417457A2 EP 02794567 A EP02794567 A EP 02794567A EP 02794567 A EP02794567 A EP 02794567A EP 1417457 A2 EP1417457 A2 EP 1417457A2
Authority
EP
European Patent Office
Prior art keywords
magnetic circuit
transformer
detection device
transformers
input
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02794567A
Other languages
German (de)
French (fr)
Inventor
Nicolas Martin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Universite de Liege ULG
Original Assignee
Universite de Liege ULG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Universite de Liege ULG filed Critical Universite de Liege ULG
Priority to EP02794567A priority Critical patent/EP1417457A2/en
Publication of EP1417457A2 publication Critical patent/EP1417457A2/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
    • G01D5/2013—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils by a movable ferromagnetic element, e.g. a core
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/22—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils
    • G01D5/225—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils
    • G01D5/2258—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils by a movable ferromagnetic element, e.g. core
    • G01D5/2266—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils by a movable ferromagnetic element, e.g. core specially adapted circuits therefor

Definitions

  • the present invention relates to a device for detecting a displacement of an object, comprising a ferromagnetic material and which can move along a path, which device comprises a magnetic circuit generator, provided with a first and '' a second ferromagnetic material core as well as an excitation coil and a measurement coil, which magnetic circuit generator is connected to a detection unit arranged to detect a change in reluctance caused in the circuit by the displacement of the object and deduce a position from the object.
  • the magnetic circuit generator comprises two U-shaped cores and ferromagnetic material arranged back to back in the same plane.
  • the measuring coil is formed by a single coil winding in phase opposition around the central part of each core.
  • the excitation coil is itself wound in series around the two cores.
  • the detection device is mounted in such a way that the object moves perpendicular to the plane in which the two cores are located.
  • the object whose displacement is to be detected is itself formed by a series of ferromagnetic material elements which are each arranged at a predetermined distance from each other.
  • the magnetic circuit formed by this core surrounded by the excitation coil will form. Since an alternating current is injected into the excitation coil, the latter will create a magnetic field in the ferromagnetic cores. The elements which move along the path will modify the flux induced in the magnetic circuit, thus modifying the reluctance of the latter. Measuring this change in reluctance using the detector then makes it possible to determine the rate of displacement of the object.
  • a disadvantage of the known device is that the magnetic circuit generator is of complex construction. Indeed, the way in which the excitation coil and the measurement coil are arranged requires covering the cores in ferromagnetic material on each side with a shielding plate in non-magnetic material. Thus, the excitation coil is separated from the measurement one. This complexity therefore requires having to build the entire device without being able to use components generally used to detect a variation in the magnetic field.
  • a device is characterized in that the magnetic circuit generator comprises a first and a second transformer with open magnetic circuit, said first transformer having the first core and the second transformer having the second core, said transformers being juxtaposed and each comprising an axis which extends through their respective core, said axes extending substantially perpendicular to said path, said excitation coil comprising a series connection of two coils which form the primaries of the first and second transformer and said measuring coil comprising a series connection of two coils which form the secondaries of the first and second transformer, said secondaries being connected in phase opposition.
  • the choice of the first and second transformer allows the use of generally used components. Since the transformers are open circuit and their axes extend substantially perpendicular to the path along which the object is moves, the movement of the object along the path will cause the magnetic circuit to close when the object, which contains ferromagnetic material, crosses one of the axes. It being understood that the excitation coil forms the primaries of the two transformers, the voltage applied to the excitation coil will induce a voltage in the secondary when the magnetic circuit closes due to the movement of the object. This secondary induced voltage will change as the object moves along the path. Since the secondaries form the measuring coil, the change in voltage measured in the secondaries will make it possible to deduce the displacement and therefore the position of the object. Thus, the use of transformers allows a reliable measurement of the position of the object.
  • a first embodiment of a detection device is characterized in that the transformers are separated from the object by a metal wall which is weakly conductive of electric current. Displacement detection can thus also be carried out through a wall. Such an application is particularly useful when the object moves in an environment which must remain isolated such as for example a chemical or nuclear reactor.
  • a second embodiment of a detection device is characterized in that each transformer comprises a ferrite screw placed in each of said axes and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
  • the use of ferrite screws offers a simple and reliable solution to compensate for the difference in magnetic characteristic.
  • a third embodiment of a detection device is characterized in that said primaries are connected to a first input of the detector and the secondary in opposition to a second input of the detector, which detector comprises an operational amplifier connected to the second input and one output of which is connected via a phase shift circuit to a first input of a multiplier, which multiplier comprises a second input connected to the first of the detector, an output of the multiplier being connected to a low-pass filter.
  • the detector comprises linearization means connected to the output of the low-pass filter and arranged to linearize the output signal of the filter.
  • linearization means are intended in particular to compensate for the effects of variations in ambient temperature which can influence the value of the filter output signal.
  • the coils of the transformers used in the device according to the invention being made up of metallic wires, generally copper or steel, the effects of temperature on the physical properties of these wires are felt on the signal measured at the secondary coils of the transformers and therefore on said filter output signal.
  • These linearization means may consist in applying to this filter output signal, directly or after subsequent processing of the signal, an interpolation polynomial, preferably of the 6 th order.
  • FIG. 1 shows an overall view of an embodiment of a device according to the invention
  • Figure 2 schematically illustrates an embodiment of a device according to the invention and Figures 2b and 2c illustrate the voltage measured in the secondary before and after linearization
  • Figure 3 schematically illustrates the device with its detector
  • Figures 4 and 5 illustrate with a graph the displacement and rotation of the object
  • FIG. 6 schematically illustrates another embodiment of a device according to the invention.
  • the device 1 for detecting a displacement of an object 4 comprises, as illustrated in FIG. 1, a first 2 and a second 3 transformer which are juxtaposed in parallel with one another.
  • Each transformer has a ferromagnetic core and is part of a magnetic circuit generator.
  • a first axis ai and a second axis a2 extend respectively through the first core and the second core of the first and second transformers, as illustrated in FIG. 2.
  • the two transformers are with open magnetic circuit and their axes extend substantially perpendicular to the path 7 that the object 4 travels when it moves on the support 5.
  • the axes ai and a2 intersect the path of the object.
  • object 4 includes ferromagnetic material.
  • the support 5 for its part is made of non-magnetic material so as not to disturb the generator of the magnetic circuit as will be described below.
  • a metal wall 6, which is weakly conductive of electric current, separates the object 4 from the transformers 2 and 3. Thus, the displacement of the object 4 can even be detected through this wall.
  • the presence of this wall is not essential for the operation of the detection device.
  • the primaries 2-1 and 3-1 of the first and second transformer are connected in series.
  • the secondary 2-2 and 3-2 of the two transformers are also connected in series.
  • the primary forms an excitation coil and the secondary forms a measurement coil.
  • a source 8 of alternating voltage, controlled by an oscillator, is connected to the primaries as well as to a first input 9-1 of a detection unit 9.
  • the oscillator preferably provides a wave having a frequency situated between 3KHz and 6KHz .
  • a second input 9-2 of the detector 9 is connected to the secondary ones, which are connected in phase opposition with respect to the primary ones.
  • the two transformers 2 and 3 each have a ferrite screw (indicated by the arrow in the secondary) placed in the axis of the primary and secondary and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
  • a sinusoidal voltage is applied using the source 8 to the primary 2-1 and 3-1 transformers. Since the transformers are at open magnetic circuit and their axes ai and a2 intersect the trajectory of the object, which contains a ferromagnetic material, the crossing of one of the axes ai or a2 by the object will cause the closing of the magnetic circuit whose axis is cross. This closing of the magnetic circuit will in turn cause that the voltage Vi injected into the primaries, which form an excitation circuit, will induce a voltage Vs in the secondary which form a measurement circuit.
  • the movement of the object will cause a variation of reluctance in the magnetic circuit of the transformers. It is the measurement of this change in reluctance which will make it possible to determine, using the detection unit 9, the relative or absolute position of the object on its trajectory.
  • the presence of the two transformers and the winding connected in series allows detection of the direction of movement.
  • the voltage Vs induced in the secondary 2-2 and 3-2 is collected at the second input 9-2 of the detection unit. This latter voltage is slightly out of phase with respect to the excitation voltage (Vi) which is applied to the input 9-1 of the detection unit 9.
  • Vi excitation voltage
  • a preferred embodiment of this detection unit is illustrated in the Figure 3.
  • the secondary are connected to an operational amplifier 11 whose output is connected to a phase shift circuit 12.
  • the primary are connected to a trapezoid-shaped voltage generator, which generator is controlled by an oscillator 13 whose signal is also supplied to a second input of a multiplier 14.
  • a first input of the multiplier 14 is connected to the output of the phase shift circuit 12.
  • An output of the multiplier 14 is connected to an input of a low-pass filter 15 whose output is connected via a digital analog converter 16 to a display unit 17 arranged to display the position of the object. Since the secondaries are connected to the operational amplifier 11 in phase opposition, the operational amplifier performs an operation on a subtraction result.
  • the multiplier 14 carries out the multiplication between the voltages Vi and Vs and thus functions as a synchronous detector.
  • FIG. 2b In order to obtain a displacement value, it is necessary to linearize the signal V1 obtained at the output of the low-pass filter and illustrated in FIG. 2b.
  • an interpolation polynomial preferably of the 6th order, is applied to the digital signal supplied at the output of the analog digital converter 16.
  • the result (V2) of this linearization applied to the signal V1 is illustrated in FIG. 2c.
  • the voltage V2 is then equal to a constant (k) multiplied by the position x of the object. From this value the position x can then be determined.
  • FIG. 4 illustrates the position x of the object as a function of the value V2 determined.
  • FIG. 5 illustrates the rotation of the object which can also be determined from the voltage V2, in a similar manner to the linear displacement of the object.
  • FIG. 6 illustrates another embodiment of a device according to the invention. This is distinguished from that illustrated in Figure 2 by the application of a capacitor 10 connected in parallel to the secondary. The value of this capacitor is chosen so as to produce a parallel resonant circuit with the coils 2-2 and 3-2 secondary. The addition of this capacitor makes it possible to raise the level of the useful signal before synchronous detection and to increase higher in frequency for reasons of response time.

Abstract

The invention concerns a device for detecting the displacement of an object comprising a ferromagnetic material. Said device comprises a magnetic circuit generator provided with first and a second cores made of ferromagnetic material and an excitation coil and a measurement coil. The magnetic circuit generator is connected to a detecting unit designed to detect a reluctance variation brought about in the circuit by the displacement of the object and to deduce therefrom its position. In said device the magnetic circuit generator comprises first and second transformers with open magnetic circuit, said transformers being juxtaposed and comprise each an axis extending across their respective core, said axes extending substantially perpendicular to said path. The excitation coil comprises two coils connected in series which form the primary windings of the first and second transformers. The measurement coil comprises two coils connected in series which form the secondary windings of the first and second transformers, said primary and secondary windings being connected in opposite phase.

Description

DISPOSITIF DE DETECTION DETECTION DEVICE
La présente invention concerne un dispositif de détection d'un déplacement d'un objet, comprenant une matière ferromagnétique et qui peut se déplacer le long d'un trajet, lequel dispositif comporte un générateur de circuit magnétique, pourvu d'un premier -et d'un deuxième noyau en matière ferromagnétique ainsi que d'une bobine d'excitation et d'une bobine de mesure, lequel générateur de circuit magnétique est relié à une unité de détection agencée pour détecter une variation de reluctance provoquée dans le circuit par le déplacement de l'objet et en déduire une position de l'objet.The present invention relates to a device for detecting a displacement of an object, comprising a ferromagnetic material and which can move along a path, which device comprises a magnetic circuit generator, provided with a first and '' a second ferromagnetic material core as well as an excitation coil and a measurement coil, which magnetic circuit generator is connected to a detection unit arranged to detect a change in reluctance caused in the circuit by the displacement of the object and deduce a position from the object.
Un tel dispositif est connu du brevet US-A-5117181. Dans le dispositif connu, le générateur de circuit magnétique comporte deux noyaux en forme de U et en matière ferromagnétique disposés dos à dos dans un même plan. La bobine de mesure est formée par un seul enroulement bobine en opposition de phase autour de la partie centrale de chaque noyau. La bobine d'excitation est quant à elle bobinée en série autour des deux noyaux. Le dispositif de détection est monté de telle façon que l'objet se déplace perpendiculairement par rapport au plan dans lequel sont situés les deux noyaux. L'objet dont le déplacement est à détecter est quant à lui formé par une série d'éléments en matière ferromagnétique qui sont chaque fois disposés à une distance prédéterminée l'un de l'autre. Lorsque l'objet se déplace le long de son trajet et qu'un des éléments s'approche de la branche du noyau disposé en face du trajet, le circuit magnétique formé par ce noyau entouré de la bobine d'excitation va se former. Puisqu'un courant alternatif est injecté dans la bobine d'excitation, cette dernière va créer un champ magnétique dans les noyaux ferromagnétiques. Les éléments qui se déplacent le long du trajet vont modifier le flux induit dans le circuit magnétique, modifiant ainsi la reluctance de ce dernier. La mesure de cette variation de reluctance à l'aide du détecteur permet alors de déterminer le taux de déplacement de l'objet.Such a device is known from US-A-5117181. In the known device, the magnetic circuit generator comprises two U-shaped cores and ferromagnetic material arranged back to back in the same plane. The measuring coil is formed by a single coil winding in phase opposition around the central part of each core. The excitation coil is itself wound in series around the two cores. The detection device is mounted in such a way that the object moves perpendicular to the plane in which the two cores are located. The object whose displacement is to be detected is itself formed by a series of ferromagnetic material elements which are each arranged at a predetermined distance from each other. When the object moves along its path and one of the elements approaches the branch of the core placed opposite the path, the magnetic circuit formed by this core surrounded by the excitation coil will form. Since an alternating current is injected into the excitation coil, the latter will create a magnetic field in the ferromagnetic cores. The elements which move along the path will modify the flux induced in the magnetic circuit, thus modifying the reluctance of the latter. Measuring this change in reluctance using the detector then makes it possible to determine the rate of displacement of the object.
Un désavantage du dispositif connu est que le générateur de circuit magnétique est de construction complexe. En effet, la façon dont la bobine d'excitation et la bobine de mesure sont disposées nécessite de recouvrir les noyaux en matière ferromagnétique de chaque côté d'une plaque de blindage en matière amagnétique. Ainsi, la bobine d'excitation est séparée de celle de mesure. Cette complexité nécessite donc de devoir construire l'ensemble du dispositif sans pouvoir faire appel à des composants généralement utilisés pour détecter une variation du champ magnétique.A disadvantage of the known device is that the magnetic circuit generator is of complex construction. Indeed, the way in which the excitation coil and the measurement coil are arranged requires covering the cores in ferromagnetic material on each side with a shielding plate in non-magnetic material. Thus, the excitation coil is separated from the measurement one. This complexity therefore requires having to build the entire device without being able to use components generally used to detect a variation in the magnetic field.
L'invention a pour but de réaliser un dispositif de détection d'un déplacement qui est plus simple à fabriquer sans pour autant réduire la précision de la mesure à faire. A cette fin, un dispositif suivant l'invention est caractérisé en ce que le générateur de circuit magnétique comporte un premier et un deuxième transformateur à circuit magnétique ouvert, ledit premier transformateur ayant le premier noyau et le deuxième transformateur ayant le deuxième noyau, lesdits transformateurs étant juxtaposés et comportant chacun un axe qui s'étend à travers leur noyau respectif, lesdits axes s'étendant sensiblement perpendiculairement audit trajet, ladite bobine d'excitation comportant une connexion en série de deux bobines qui forment les primaires du premier et deuxième transformateur et ladite bobine de mesure comportant une connexion en série de deux bobines qui forment les secondaires du premier et deuxième transformateur, lesdits secondaires étant raccordés en opposition de phase. Le choix du premier et deuxième transformateur permet d'utiliser des composants généralement utilisés. Puisque les transformateurs sont à circuit ouvert et que leurs axes s'étendent sensiblement perpendiculaire au trajet suivant lequel l'objet se déplace, le mouvement de l'objet le long du trajet va provoquer la fermeture de circuit magnétique lorsque l'objet, qui comporte une matière ferromagnétique, croise l'un des axes. Etant entendu que la bobine d'excitation forme les primaires des deux transformateurs, la tension appliquée à la bobine d'excitation va induire une tension dans les secondaires lorsque le circuit magnétique se fermera à cause du mouvement de l'objet. Cette tension induite dans les secondaires va se modifier au fur et à mesure que l'objet se déplace le long du trajet. Puisque les secondaires forment la bobine de mesure, le changement de tension mesuré dans les secondaires va permettre d'en déduire le déplacement et donc la position de l'objet. Ainsi, l'emploi des transformateurs permet une mesure fiable de la position de l'objet.The object of the invention is to provide a displacement detection device which is simpler to manufacture without reducing the accuracy of the measurement to be made. To this end, a device according to the invention is characterized in that the magnetic circuit generator comprises a first and a second transformer with open magnetic circuit, said first transformer having the first core and the second transformer having the second core, said transformers being juxtaposed and each comprising an axis which extends through their respective core, said axes extending substantially perpendicular to said path, said excitation coil comprising a series connection of two coils which form the primaries of the first and second transformer and said measuring coil comprising a series connection of two coils which form the secondaries of the first and second transformer, said secondaries being connected in phase opposition. The choice of the first and second transformer allows the use of generally used components. Since the transformers are open circuit and their axes extend substantially perpendicular to the path along which the object is moves, the movement of the object along the path will cause the magnetic circuit to close when the object, which contains ferromagnetic material, crosses one of the axes. It being understood that the excitation coil forms the primaries of the two transformers, the voltage applied to the excitation coil will induce a voltage in the secondary when the magnetic circuit closes due to the movement of the object. This secondary induced voltage will change as the object moves along the path. Since the secondaries form the measuring coil, the change in voltage measured in the secondaries will make it possible to deduce the displacement and therefore the position of the object. Thus, the use of transformers allows a reliable measurement of the position of the object.
Une première forme de réalisation d'un dispositif de détection suivant l'invention est caractérisée en ce que les transformateurs sont séparés de l'objet par une paroi métallique qui est faiblement conductrice de courant électrique. La détection du déplacement peut ainsi également être réalisée à travers une paroi. Une telle application est particulièrement utile lorsque l'objet se déplace dans un milieu qui doit rester isolé comme par exemple un réacteur chimique ou nucléaire.A first embodiment of a detection device according to the invention is characterized in that the transformers are separated from the object by a metal wall which is weakly conductive of electric current. Displacement detection can thus also be carried out through a wall. Such an application is particularly useful when the object moves in an environment which must remain isolated such as for example a chemical or nuclear reactor.
Une deuxième forme de réalisation d'un dispositif de détection suivant l'invention est caractérisée en ce que chaque transformateur comporte une vis en ferrite placée dans chacun desdits axes et agencée pour compenser une différence de caractéristique magnétique dans le circuit magnétique de chaque transformateur. L'usage de vis en ferrite offre une solution simple et fiable pour compenser la différence de caractéristique magnétique.A second embodiment of a detection device according to the invention is characterized in that each transformer comprises a ferrite screw placed in each of said axes and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer. The use of ferrite screws offers a simple and reliable solution to compensate for the difference in magnetic characteristic.
Une troisième forme de réalisation d'un dispositif de détection suivant l'invention est caractérisée en ce que lesdits primaires sont reliés à une première entrée du détecteur et les secondaires en opposition à une deuxième entrée du détecteur, lequel détecteur comporte un amplificateur opérationnel relié à la deuxième entrée et dont une sortie est connectée via un circuit de déphasage à une première entrée d'un multiplicateur, lequel multiplicateur comporte une deuxième entrée reliée à la première du détecteur, une sortie du multiplicateur étant reliée à un filtre passe-bas. Une telle réalisation du détecteur permet une détermination fiable de la position de l'objet à partir de la tension d'excitation et de la tension prélevée aux secondaires. De préférence, le détecteur comporte des moyens de linéarisation reliés à la sortie du filtre passe-bas et agencés pour linéariser le signal de sortie du filtre. Ceci permet de linéariser la valeur mesurée et de déterminer de façon linéaire la position, ce qui correspond à la position effective de l'objet. Ces moyens de linéarisation ont en particulier pour but de compenser les effets des variations de température ambiante qui peuvent influencer la valeur du signal de sortie du filtre. Les bobines des transformateurs utilisés dans le dispositif selon l'invention étant constituées de fils métalliques, généralement de cuivre ou d'acier, les effets de la température sur les propriétés physiques de ces fils se ressentent sur le signal mesuré aux bobines secondaires des transformateurs et dès lors sur ledit signal de sortie du filtre. Ces moyens de linéarisation peuvent consister en l'application à ce signal de sortie du filtre, directement ou après un traitement subséquent du signal, d'un polynôme d'interpolation, de préférence du 6eme ordre.A third embodiment of a detection device according to the invention is characterized in that said primaries are connected to a first input of the detector and the secondary in opposition to a second input of the detector, which detector comprises an operational amplifier connected to the second input and one output of which is connected via a phase shift circuit to a first input of a multiplier, which multiplier comprises a second input connected to the first of the detector, an output of the multiplier being connected to a low-pass filter. Such an embodiment of the detector allows a reliable determination of the position of the object from the excitation voltage and the voltage taken from the secondary. Preferably, the detector comprises linearization means connected to the output of the low-pass filter and arranged to linearize the output signal of the filter. This allows the measured value to be linearized and the position to be determined linearly, which corresponds to the actual position of the object. These linearization means are intended in particular to compensate for the effects of variations in ambient temperature which can influence the value of the filter output signal. The coils of the transformers used in the device according to the invention being made up of metallic wires, generally copper or steel, the effects of temperature on the physical properties of these wires are felt on the signal measured at the secondary coils of the transformers and therefore on said filter output signal. These linearization means may consist in applying to this filter output signal, directly or after subsequent processing of the signal, an interpolation polynomial, preferably of the 6 th order.
De préférence, l'oscillateur est agencé pour produire une fréquence inférieure à 50 khz, plus préférablement inférieure à 30 khz, plus préférablement encore située entre 3KHz et 6KHZ. Des expériences ont fait apparaître que ces valeurs de fréquences donnent un résultat fiable. L'invention sera maintenant décrite plus en détail à l'aide des dessins qui illustrent des formes de réalisation préférentielles d'un dispositif de détection suivant l'invention. Dans les dessins : la figure 1 montre une vue d'ensemble d'une forme de réalisation d'un dispositif suivant l'invention; la figure 2 illustre schématiquement une forme de réalisation d'un dispositif suivant l'invention et les figures 2b et 2c illustrent la tension mesurée dans les secondaires avant et après linéarisation; la figure 3 illustre schématiquement le dispositif avec son détecteur; les figures 4 et 5 illustrent à l'aide d'un graphique le déplacement et la rotation de l'objet; et la figure 6 illustre schématiquement une autre forme de réalisation d'un dispositif suivant l'invention.Preferably, the oscillator is arranged to produce a frequency of less than 50 kHz, more preferably less than 30 kHz, more preferably still situated between 3 kHz and 6 kHz. Experiments have shown that these frequency values give a reliable result. The invention will now be described in more detail using the drawings which illustrate preferred embodiments of a detection device according to the invention. In the drawings: FIG. 1 shows an overall view of an embodiment of a device according to the invention; Figure 2 schematically illustrates an embodiment of a device according to the invention and Figures 2b and 2c illustrate the voltage measured in the secondary before and after linearization; Figure 3 schematically illustrates the device with its detector; Figures 4 and 5 illustrate with a graph the displacement and rotation of the object; and FIG. 6 schematically illustrates another embodiment of a device according to the invention.
Dans les dessins, une même référence a été attribuée à un même élément ou à un élément analogue.In the drawings, the same reference has been assigned to the same element or to an analogous element.
Le dispositif 1 de détection d'un déplacement d'un objet 4 suivant l'invention comporte, comme illustré à la figure 1, un premier 2 et un deuxième 3 transformateur qui sont juxtaposés en parallèle l'un par rapport à l'autre. Chaque transformateur comporte un noyau en matière ferromagnétique et fait partie d'un générateur de circuit magnétique. Un premier axe ai et un second axe a2 s'étendent respectivement à travers le premier noyau et le deuxième noyau du premier et du deuxième transformateur, comme illustré à la figure 2. Les deux transformateurs sont à circuit magnétique ouvert et leur axes s'étendent sensiblement perpendiculaire au trajet 7 que l'objet 4 parcourt lorsqu'il se déplace sur le support 5. Ainsi, les axes ai et a2 coupent la trajectoire de l'objet. Tout comme les noyaux des transformateurs 2 et 3, l'objet 4 comporte une matière ferromagnétique. Le support 5 quant à lui est en matière amagnétique afin de ne pas perturber le générateur de circuit magnétique comme il sera décrit ci-dessous. Dans la forme de réalisation illustrée à la figure 1 , une paroi métallique 6, qui est faiblement conductrice de courant électrique, sépare l'objet 4 des transformateurs 2 et 3. Ainsi, le déplacement de l'objet 4 peut même être détecté à travers cette paroi. Toutefois, la présence de cette paroi n'est pas indispensable pour le fonctionnement du dispositif de détection.The device 1 for detecting a displacement of an object 4 according to the invention comprises, as illustrated in FIG. 1, a first 2 and a second 3 transformer which are juxtaposed in parallel with one another. Each transformer has a ferromagnetic core and is part of a magnetic circuit generator. A first axis ai and a second axis a2 extend respectively through the first core and the second core of the first and second transformers, as illustrated in FIG. 2. The two transformers are with open magnetic circuit and their axes extend substantially perpendicular to the path 7 that the object 4 travels when it moves on the support 5. Thus, the axes ai and a2 intersect the path of the object. Like the cores of transformers 2 and 3, object 4 includes ferromagnetic material. The support 5 for its part is made of non-magnetic material so as not to disturb the generator of the magnetic circuit as will be described below. In the embodiment illustrated in FIG. 1, a metal wall 6, which is weakly conductive of electric current, separates the object 4 from the transformers 2 and 3. Thus, the displacement of the object 4 can even be detected through this wall. However, the presence of this wall is not essential for the operation of the detection device.
Comme illustré à la figure 2a, les primaires 2-1 et 3-1 du premier et deuxième transformateur sont connectés en série. Les secondaires 2-2 et 3-2 des deux transformateurs sont également connectés en série. Les primaires forment une bobine d'excitation et les secondaires une bobine de mesure. Une source 8 de tension alternative, contrôlée par un oscillateur, est reliée aux primaires ainsi qu'à une première entrée 9-1 d'une unité de détection 9. L'oscillateur fournit de préférence une onde ayant une fréquence située entre 3KHz et 6KHz. Une deuxième entrée 9-2 du détecteur 9 est reliée aux secondaires, qui sont raccordés en opposition de phase par rapport aux primaires.As illustrated in FIG. 2a, the primaries 2-1 and 3-1 of the first and second transformer are connected in series. The secondary 2-2 and 3-2 of the two transformers are also connected in series. The primary forms an excitation coil and the secondary forms a measurement coil. A source 8 of alternating voltage, controlled by an oscillator, is connected to the primaries as well as to a first input 9-1 of a detection unit 9. The oscillator preferably provides a wave having a frequency situated between 3KHz and 6KHz . A second input 9-2 of the detector 9 is connected to the secondary ones, which are connected in phase opposition with respect to the primary ones.
Les deux transformateurs 2 et 3 comportent chacun une vis en ferrite (indiquée par la flèche dans les secondaires) placée dans l'axe du primaire et du secondaire et agencée pour compenser une différence de caractéristique magnétique dans le circuit magnétique de chaque transformateur.The two transformers 2 and 3 each have a ferrite screw (indicated by the arrow in the secondary) placed in the axis of the primary and secondary and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
Pour déterminer la position de l'objet 4 qui se déplace soit vers la gauche (7-L) soit vers la droite (7-R) le long du trajet 7, une tension sinusoïdale est appliquée à l'aide de la source 8 aux primaires 2-1 et 3-1 des transformateurs. Puisque les transformateurs sont à circuit magnétique ouvert et que leurs axes ai et a2 coupent la trajectoire de l'objet, qui comporte une matière ferromagnétique, le croisement d'un des axes ai ou a2 par l'objet va provoquer la fermeture du circuit magnétique dont l'axe est croisé. Cette fermeture du circuit magnétique va à son tour provoquer que la tension Vi injectée dans les primaires, qui forment un circuit d'excitation, va induire une tension Vs dans les secondaires qui forment un circuit de mesure. Ainsi, le déplacement de l'objet va provoquer une variation de reluctance dans le circuit magnétique des transformateurs. C'est la mesure de cette variation de reluctance qui va permettre de déterminer, à l'aide de l'unité de détection 9, la position relative ou absolue de l'objet sur sa trajectoire. La présence des deux transformateurs et le bobinage connectés en série permet une détection du sens de mouvement. La tension Vs induite dans les secondaires 2-2 et 3-2 est récoltée à la deuxième entrée 9-2 de l'unité de détection. Cette dernière tension est légèrement déphasée par rapport à la tension (Vi) d'excitation qui elle est appliquée à l'entrée 9-1 de l'unité de détection 9. Une forme de réalisation préférentielle de cette unité de détection est illustrée à la figure 3. Les secondaires sont reliés à un amplificateur opérationnel 11 dont la sortie est reliée à un circuit de déphasage 12. Les primaires sont reliés à un générateur de tension en forme de trapèze, lequel générateur est contrôlé par un oscillateur 13 dont le signal est également fourni à une deuxième entrée d'un multiplicateur 14. Une première entrée du multiplicateur 14 est reliée à la sortie du circuit de déphasage 12. Une sortie du multiplicateur 14 est reliée à une entrée d'un filtre passe-bas 15 dont la sortie est reliée via un convertisseur analogue numérique 16 à une unité d'affichage 17 agencée pour afficher la position de l'objet. Puisque les secondaires sont raccordés à l'amplificateur opérationnel 11 en opposition de phase, l'amplificateur opérationnel en effectue une opération sur un résultat de soustraction. Le multiplicateur 14 réalise la multiplication entre les tensions Vi et Vs et fonctionne ainsi comme un détecteur synchrone. Le filtre passe-bas 15 est utilisé pour éliminer la composante f1 + f2 des fréquences fournies au multiplicateur. En effet, la multiplication des signaux fi et f2 a fourni deux composantes fi = f2 et f1- f2. Puisque les fréquences f1 et f2 sont égales dans le présent cas, le résultat obtenu est 2f1 et 0 (DC). Le signal DC permet alors la détermination du déplacement.To determine the position of the object 4 which moves either to the left (7-L) or to the right (7-R) along the path 7, a sinusoidal voltage is applied using the source 8 to the primary 2-1 and 3-1 transformers. Since the transformers are at open magnetic circuit and their axes ai and a2 intersect the trajectory of the object, which contains a ferromagnetic material, the crossing of one of the axes ai or a2 by the object will cause the closing of the magnetic circuit whose axis is cross. This closing of the magnetic circuit will in turn cause that the voltage Vi injected into the primaries, which form an excitation circuit, will induce a voltage Vs in the secondary which form a measurement circuit. Thus, the movement of the object will cause a variation of reluctance in the magnetic circuit of the transformers. It is the measurement of this change in reluctance which will make it possible to determine, using the detection unit 9, the relative or absolute position of the object on its trajectory. The presence of the two transformers and the winding connected in series allows detection of the direction of movement. The voltage Vs induced in the secondary 2-2 and 3-2 is collected at the second input 9-2 of the detection unit. This latter voltage is slightly out of phase with respect to the excitation voltage (Vi) which is applied to the input 9-1 of the detection unit 9. A preferred embodiment of this detection unit is illustrated in the Figure 3. The secondary are connected to an operational amplifier 11 whose output is connected to a phase shift circuit 12. The primary are connected to a trapezoid-shaped voltage generator, which generator is controlled by an oscillator 13 whose signal is also supplied to a second input of a multiplier 14. A first input of the multiplier 14 is connected to the output of the phase shift circuit 12. An output of the multiplier 14 is connected to an input of a low-pass filter 15 whose output is connected via a digital analog converter 16 to a display unit 17 arranged to display the position of the object. Since the secondaries are connected to the operational amplifier 11 in phase opposition, the operational amplifier performs an operation on a subtraction result. The multiplier 14 carries out the multiplication between the voltages Vi and Vs and thus functions as a synchronous detector. The low-pass filter 15 is used to eliminate the component f1 + f2 from the frequencies supplied to the multiplier. Indeed, the multiplication of the signals fi and f2 provided two components fi = f2 and f1- f2. Since the frequencies f1 and f2 are equal in the present case, the result obtained is 2f1 and 0 (DC). The DC signal then allows the displacement to be determined.
Afin d'obtenir une valeur de déplacement, il est nécessaire de linéariser le signal V1 obtenu à la sortie du filtre passe-bas et illustré à la figure 2b. Pour cela un polynôme d'interpolation, de préférence du 6ème ordre, est appliqué sur le signal numérique fourni à la sortie du convertisseur analogue numérique 16. Le résultat (V2) de cette linéarisation appliquée sur le signal V1 est illustré à la figure 2c. La tension V2 est alors égale à une constante (k) multipliée par la position x de l'objet. A partir de cette valeur la position x peut alors être déterminée. La figure 4 illustre la position x de l'objet en fonction de la valeur V2 déterminée.In order to obtain a displacement value, it is necessary to linearize the signal V1 obtained at the output of the low-pass filter and illustrated in FIG. 2b. For this, an interpolation polynomial, preferably of the 6th order, is applied to the digital signal supplied at the output of the analog digital converter 16. The result (V2) of this linearization applied to the signal V1 is illustrated in FIG. 2c. The voltage V2 is then equal to a constant (k) multiplied by the position x of the object. From this value the position x can then be determined. FIG. 4 illustrates the position x of the object as a function of the value V2 determined.
De préférence, et comme illustré à la figure 4, la position x=0 est choisie au centre situé entre les deux axes ai et a2. La figure 5 illustre la rotation de l'objet qui peut également être déterminée à partir de la tension V2, de manière similaire au déplacement linéaire de l'objet.Preferably, and as illustrated in FIG. 4, the position x = 0 is chosen at the center located between the two axes ai and a2. FIG. 5 illustrates the rotation of the object which can also be determined from the voltage V2, in a similar manner to the linear displacement of the object.
La figure 6 illustre une autre forme de réalisation d'un dispositif suivant l'invention. Celle-ci se distingue de celle illustrée à la figure 2 par l'application d'un condensateur 10 branché en parallèle aux secondaires. La valeur de ce condensateur est choisie de telle façon à réaliser un circuit résonant parallèle avec les bobines 2-2 et 3-2 des secondaires. L'adjonction de ce condensateur permet de relever le niveau du signal utile avant détection synchrone et de monter plus haut en fréquence pour des raisons de temps de réponse. FIG. 6 illustrates another embodiment of a device according to the invention. This is distinguished from that illustrated in Figure 2 by the application of a capacitor 10 connected in parallel to the secondary. The value of this capacitor is chosen so as to produce a parallel resonant circuit with the coils 2-2 and 3-2 secondary. The addition of this capacitor makes it possible to raise the level of the useful signal before synchronous detection and to increase higher in frequency for reasons of response time.

Claims

REVENDICATIONS
1. Dispositif de détection d'un déplacement d'un objet comprenant une matière ferromagnétique et qui peut se déplacer le long d'un trajet, lequel dispositif comporte un générateur de circuit magnétique pourvu d'un premier et d'un deuxième noyau en matière ferromagnétique ainsi que d'une bobine d'excitation et d'une bobine de mesure, lequel générateur de circuit magnétique est relié à une unité de détection agencée pour détecter une variation de reluctance provoquée dans le circuit par le déplacement de l'objet et en déduire une position de l'objet, caractérisé en ce que le générateur de circuit magnétique comporte un premier et un deuxième transformateur à circuit magnétique ouvert, ledit premier transformateur ayant le premier noyau et le deuxième transformateur ayant le deuxième noyau, lesdits transformateurs étant juxtaposés et comportent chacun un axe qui s'étend à travers leur noyau respectif, lesdits axes s'étendant sensiblement perpendiculairement audit trajet, ladite bobine d'excitation comportant une connexion en série de deux bobines qui forment les primaires du premier et deuxième transformateur et ladite bobine de mesure comportant une connexion en série de deux bobines qui forment les secondaires du premier et deuxième transformateur, lesdits secondaires étant raccordés en opposition de phase.1. A device for detecting a displacement of an object comprising a ferromagnetic material and which can move along a path, which device comprises a magnetic circuit generator provided with a first and a second material core ferromagnetic as well as an excitation coil and a measurement coil, which magnetic circuit generator is connected to a detection unit arranged to detect a change in reluctance caused in the circuit by the movement of the object and in deduce a position of the object, characterized in that the magnetic circuit generator comprises a first and a second transformer with open magnetic circuit, said first transformer having the first core and the second transformer having the second core, said transformers being juxtaposed and each have an axis which extends through their respective core, said axes extending substantially perpendicular to Rement to said path, said excitation coil comprising a series connection of two coils which form the primaries of the first and second transformer and said measurement coil comprising a series connection of two coils which form the secondary of the first and second transformer, said secondary being connected in phase opposition.
2. Dispositif de détection suivant la revendication 1 , caractérisé en ce que les transformateurs sont séparés de l'objet par une paroi métallique qui est faiblement conductrice de courant électrique.2. Detection device according to claim 1, characterized in that the transformers are separated from the object by a metal wall which is weakly conductive of electric current.
3. Dispositif de détection suivant la revendication 1 ou 2, caractérisé en ce que ledit objet est monté sur un support en matière amagnétique.3. Detection device according to claim 1 or 2, characterized in that said object is mounted on a support made of non-magnetic material.
4. Dispositif de détection suivant l'une des revendications 1 à 3, caractérisé en ce que chaque transformateur comporte une vis en ferrite placée dans chacun desdits axes et agencée pour compenser une différence de caractéristique magnétique dans le circuit magnétique de chaque transformateur.4. Detection device according to one of claims 1 to 3, characterized in that each transformer comprises a screw made of ferrite placed in each of said axes and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
5. Dispositif de détection suivant l'une des revendications 1 à 4, caractérisé en ce que lesdits primaires sont reliés à une première entrée du détecteur et les secondaires en opposition à une deuxième entrée du détecteur, lequel détecteur comporte un amplificateur opérationnel relié à la deuxième entrée et dont une sortie est connectée via un circuit de déphasage à une première entrée d'un multiplicateur, lequel multiplicateur comporte une deuxième entrée reliée à la première du détecteur, une sortie du multiplicateur étant reliée à un filtre passe-bas.5. Detection device according to one of claims 1 to 4, characterized in that said primary are connected to a first input of the detector and the secondary in opposition to a second input of the detector, which detector comprises an operational amplifier connected to the second input and one output of which is connected via a phase shift circuit to a first input of a multiplier, which multiplier comprises a second input connected to the first of the detector, an output of the multiplier being connected to a low-pass filter.
6. Dispositif de détection suivant la revendication 5, caractérisé en ce que le détecteur comporte des moyens de linéarisation reliés à la sortie du filtre passe-bas et agencés pour linéariser le signal de sortie du filtre.6. Detection device according to claim 5, characterized in that the detector comprises linearization means connected to the output of the low-pass filter and arranged to linearize the output signal of the filter.
7. Dispositif de détection suivant la revendication 5 ou 6, caractérisé en ce qu'il comporte une source de tension alternative contrôlée par un oscillateur, ladite source étant connectée aux primaires.7. Detection device according to claim 5 or 6, characterized in that it comprises an alternating voltage source controlled by an oscillator, said source being connected to the primaries.
8. Dispositif de détection suivant la revendication 7, caractérisé en ce que ledit oscillateur est agencé pour produire une fréquence située entre 3KHz et 6KHZ. 8. Detection device according to claim 7, characterized in that said oscillator is arranged to produce a frequency between 3KHz and 6KHZ.
EP02794567A 2001-08-08 2002-08-06 Detection device Withdrawn EP1417457A2 (en)

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US20040169507A1 (en) 2004-09-02
AU2002333357A1 (en) 2003-02-24
WO2003014675A2 (en) 2003-02-20
WO2003014675A3 (en) 2003-07-31
JP2004537735A (en) 2004-12-16
US7132825B2 (en) 2006-11-07
EP1283409A1 (en) 2003-02-12

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