(19)
(11)EP 3 249 363 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
04.12.2019 Bulletin 2019/49

(21)Application number: 15842860.7

(22)Date of filing:  11.09.2015
(51)Int. Cl.: 
G01D 3/036  (2006.01)
G01D 5/20  (2006.01)
(86)International application number:
PCT/CN2015/089405
(87)International publication number:
WO 2016/041466 (24.03.2016 Gazette  2016/12)

(54)

INDUCTIVE TRANSDUCER SHIELDING METHOD

ABSCHIRMVERFAHREN FÜR INDUKTIVEN WANDLER

PROCÉDÉ DE BLINDAGE DE TRANSDUCTEUR À INDUCTION


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 17.09.2014 CN 201410474732

(43)Date of publication of application:
29.11.2017 Bulletin 2017/48

(73)Proprietor: Shanghai Lanbao Sensing Technology Co., Ltd.
Shanghai 201404 (CN)

(72)Inventors:
  • XIE, Yong
    Shanghai 201404 (CN)
  • JIANG, Chunhua
    Shanghai 201404 (CN)

(74)Representative: Sun, Yiming 
HUASUN Patent- und Rechtsanwälte Friedrichstraße 33
80801 München
80801 München (DE)


(56)References cited: : 
WO-A1-2013/079347
CN-A- 101 140 169
CN-A- 102 713 655
CN-A- 104 266 665
CN-U- 204 116 623
DE-A1-102007 027 822
US-A1- 2012 206 132
WO-A2-97/13122
CN-A- 101 144 725
CN-A- 103 115 634
CN-U- 203 231 762
CN-Y- 2 594 785
JP-A- 2009 210 346
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    TECHNICAL FIELD



    [0001] The present invention relates to an inductive sensor, and more particularly, to shielding an inductive sensor.

    [0002] In particular the present invention relates to an inductive sensor, wherein an annular shielding coil is additionally arranged outside an annular detection coil, the shielding coil surrounds the detection coil, and the radial thickness of the shielding coil is smaller than that of the detection coil; the magnetic field generated by the shielding coil and the magnetic field generated by the detection coil are opposite in direction and partially offset, and the magnetic fields are attenuated or increased at the same time, such that the overlapped magnetic field strength can be kept constant.

    BACKGROUND ART



    [0003] US 2012/0206132 A1 discloses an inductive sensor of the generic type defined hereinabove.

    [0004] The existing common inductive sensors are divided into inductive sensors with ferrite pot cores and inductive sensors without ferrite pot cores.

    [0005] The inductive sensor with a ferrite pot core is used for detecting metal by using a coil system consisting of the ferrite pot core and a coil wound on the ferrite pot core. The ferrite pot core has a self-shielded structure and has only an opening in one direction, so that the magnetic field generated by the coil system is present only in the opening direction. As shown in Fig. 1a and Fig. 1b, the sensor comprises a housing 1.1, a connecting cable 1.3 and a coil system 1.8 which is formed by winding a coil 1.7 inside a ferrite pot core 1.5. This sensor has a magnetic field only on a front detection area 1.2 of the housing 1.1 of the housing. This sensor is not affected by slight electromagnetic interference, but if there is a strong electromagnetic interference near the sensor, such as a welding robot, this may affect the magnetic properties of the used ferrite to interfere with the sensor.

    [0006] As to the inductive sensor without a ferrite pot core, a coil is wound around a plastic pipe. Such sensor is relatively wide in magnetic field distribution. In order to obtain a directional magnetic field, metal rings or metal pipes having different thicknesses and favorable conductivity are additionally arranged around the coil of the sensor, for example, copper is used to completely surround the side surface of the coil to weaken the radial magnetic field of the detection coil, leaving only the magnetic field in front of the detection coil. As shown in Fig. 1a and Fig. 1c, the sensor comprises a housing 1.1, a connecting cable 1.3 and a coil system 1.8 which is formed by winding a coil 1.7 around the plastic pipe 1.10. The coil 1.7 is also surrounded by a copper ring 1.9, such that this sensor has a magnetic field only on a front detection area 1.2 of the housing 1.1 of the sensor. However, this sensor also reduces the influence of the surrounding metal on the sensor, and also weakens the magnetic field on a detection area 1.2 and reduces the sensitivity of the sensor.

    SUMMARY OF THE INVENTION



    [0007] An objective of the present invention is to provide an inductive sensor, which can improve the interference rejection of the inductive sensor to the external magnetic field and reduce the influence of the surrounding metal to the sensor without affecting the detection sensitivity of the inductive sensor.

    [0008] The present invention is realized by the following technical scheme:
    There is provided an inductive sensor, wherein an annular shielding coil is additionally arranged outside an annular detection coil, the shielding coil surrounds the detection coil, and the radial thickness of the shielding coil is smaller than that of the detection coil; the magnetic field generated by the shielding coil and the magnetic field generated by the detection coil are opposite in direction and partially offset, and the two magnetic fields are attenuated or increased at the same time, such that the overlapped magnetic field strength can be kept constant.

    [0009] There is provided an inductive sensor wherein a housing of the sensor is cylindrical, the detection coil is wound on a plastic pipe, and an insulating material is filled between the detection coil and the shielding coil, at least two annular detection coils which are successively arranged along an axial direction of the housing are provided inside the housing, an annular shielding coil at least surrounds each detection coil, and the radial thickness of the shielding coil is smaller that of the detection coil.

    [0010] The sensor further comprises a testing circuit. The testing circuit comprises resonant circuits, voltage dividing circuits, a shielding circuit and a differential amplifying circuit; the two detection coils are respectively connected in series with a resonant capacitor to form the resonant circuits and are then connected in parallel to the output end of a voltage source; the two groups of resonant circuits are identical in resonant frequency; the two groups of resonant voltages generated by the resonant circuits are respectively divided by the voltage dividing circuits having the same voltage division ratio, and are then connected to positive and negative input ends of the differential amplifying circuit; the two shielding coils are connected to the positive and negative input ends of the differential amplifying circuit respectively via a Voltage follower to form the shielding circuit; a ratio of the number of turns of the detection coil to the number of turns of the shielding coil surrounding the detection coil is proportional to the voltage division ratio of the voltage dividing circuit.

    [0011] The present invention has the beneficial effects that: the shielding coil is additionally arranged outside the original detection coil of the inductive sensor, magnetic fields generated by the two coils are opposite in direction and partially offset, and when interference exists, the magnetic fields generated by the two coils are influenced at the same time and are attenuated or increased by identical strength. Therefore, the overlapped magnetic field strength can be kept constant, resonance voltages cannot be attenuated, the interference rejection of the inductive sensor is improved, and the sensitivity of the inductive sensor is not influenced.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0012] 

    Fig. 1a is an external view of a prior art inductive sensor;

    Fig. 1b is an internal structure diagram of an inductive sensor with a prior art ferrite pot core;

    Fig. 1c is an internal structure diagram of an inductive sensor without a prior art ferrite pot core;

    Fig. 2a is a schematic view showing the internal structure of the inductive sensor of the present invention;

    Fig. 2b is a schematic cross-sectional view of Fig. 2a;

    Fig. 3 is a schematic diagram of a testing circuit without a ferrite pot core in the inductive sensor of the present invention;

    in which reference signs are as follows: 1.1-housing; 1.2-detection area; 1.3- cable; 1.4- metal around the sensor; 1.5-ferrite pot core; 1.6-magnetic field line; 1.7-coil; 1.8-coil system, 1.9-short circuit ring; 1.10-plastic pipe; 2.1-electronic switch; 2.2 and 2.3-detection coil; 2.4-microprocessor; 2.5-low-impedance output; 2.6 and 2.7 -resonant capacitor; 2.8 and 2.9-resonant voltage; 2.10-differential amplifier; 2.11-differential signal; 2.12 and 2.13-shielding coil; 2.14 Voltage follower-; 2.15-output signal.

    DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS



    [0013] The present invention will now be further described with reference to specific embodiments and the accompanying drawings.

    [0014] As shown in Figs. 2a and 2b, two detection coils 2.2 and 2.3 are connected in series and are then successively arranged inside a housing in the axial direction of a sensor, wherein the detection coil 2.2 is provided in front of the detection coil 2.3; the detection coil 2.3 is 5 mm away from the detection coil 2.2 in the front; the side surfaces of the two detection coils 2.2 and 2.3 are surrounded by shielding coils 2.12 and 2.13, and the number of turns of the coils 2.2 and 2.3 is larger than that of the shielding coils 2.12 and 2.13.

    [0015] As shown in Fig. 3, a testing circuit is used in an inductive sensor without a ferrite pot type core. A microprocessor 2.4 controls an electronic switch 2.1 connected to a power supply, such that the switching frequency is 250 kHz to provide a low-impedance output 2.5. The detection coil 2.2 and the resonant capacitor 2.6 constitute a first resonant circuit, the detection coil 2.3 and the resonant capacitor 2.7 constitute a second resonant circuit, and the two groups of resonant circuits are identical in resonant frequency and are connected in parallel to the low-impedance output 2.5. The resonant voltages 2.8 and 2.9 generated by the two groups of resonant circuits are respectively divided by comparison resistors R1 and R2 as well as comparison resistors R3 and R4, and are then connected to the positive and negative input ends of a differential amplifier 2.10. The shielding coil 2.12 surrounds the detection coil 2.2, the shielding coil 2.13 surrounds the detection coil 2.3, and the shielding coils 2.12 and 2.13 are also connected to the positive and negative input ends of the differential amplifier 2.10 respectively via a Voltage follower 2.14, that is, the voltage-divided resonant voltages 2.8 and 2.9 drive the shielding coils 2.12 and 2.13. The voltage division ratio of the comparison resistors R1 and R2 is the same as that of the comparison resistors R3 and R4. The number of turns of the detection coils 2.2 and 2.3 is larger than that of the shielding coils 2.12 and 2.13. A ratio of the number of turns of the shielding coils 2.12 and 2.13 to the number of turns of the detection coils 2.2 and 2.3 are identical and are proportional to the voltage division ratio of the comparison resistors R1 and R2.

    [0016] The magnetic fields generated by the detection coils 2.2 and 2.3 as well as the shielding coils 2.12 and 2.13 are opposite in direction and partially offset. By adjusting the ratio of the number of turns of the detection coils 2.2 and 2.3 to the number of turns of the shielding coils 2.12 and 2.13, the magnetic fields generated by the detection coils 2.2 and 2.3 as well as the shielding coils 2.12 and 2.13 are attenuated by the identical intensity when subjected to external interference, that is, the overlapped magnetic field strength of the detection coil 2.2 and the shield coil 2.12 and the overlapped magnetic field strength of the detection coil 2.3 and the shielding coil 2.13 are kept constant. The detection coils 2.2 and 2.3 and the resonant capacitors 2.6 and 2.7 in the two groups of resonant circuits are adjusted, so that the resonant voltages 2.8 and 2.9 are not attenuated, and basically remain constant.

    [0017] The resonant voltages 2.8 and 2.9 are identical when there is no metal near the detection area at the front end of the sensor, that is, the differential amplifier 2.10 has no output. When the metal is located near the detection area at the front end of the sensor, because the detection coil 2.2 is provided in front of the detection coil 2.3, the influences of the metal on the magnetic fields generated by the detection coils 2.2 and 2.3 are different, thus leading that the resonant voltages 2.8 and 2.9 are different. The differential amplifier 2.10 outputs a differential signal 2.11, and a microprocessor 2.4 distinguishes whether there is a metal near the sensor by judging the differential signal 2.11.


    Claims

    1. An inductive sensor, wherein an annular shielding coil (2.12, 2.13) is additionally arranged outside an annular detection coil (2.2, 2.3), the shielding coil surrounds the detection coil, and the radial thickness of the shielding coil is smaller than that of the detection coil; the magnetic field generated by the shielding coil and the magnetic field generated by the detection coil are opposite in direction and partially offset, and the magnetic fields are attenuated or increased at the same time, such that the overlapped magnetic field strength can be kept constant, characterized in that
    a housing (1.1) of the sensor is cylindrical, the detection coil is wound on a plastic pipe (1.10), and an insulating material is filled between the detection coil and the shielding coil,
    at least two annular detection coils which are successively arranged along an axial direction of the housing are provided inside the housing, an annular shielding coil at least surrounds each detection coil; the radial thickness of the shielding coil is smaller that of the detection coil, and
    the sensor further comprises a testing circuit; the testing circuit comprises resonant circuits, voltage dividing circuits, a shielding circuit and a differential amplifying circuit; the two detection coils are respectively connected in series with a resonant capacitor (2.6, 2.7) to form the resonant circuits and are then connected in parallel to the output end of a voltage source; the two groups of resonant circuits are identical in resonant frequency; the two groups of resonant voltages generated by the resonant circuits are respectively divided by the voltage dividing circuits having the same voltage division ratio, and are then connected to positive and negative input ends of the differential amplifying circuit; the two shielding coils are connected to the positive and negative input ends of the differential amplifying circuit respectively via a Voltage follower (2.14) to form the shielding circuit; a ratio of the number of turns of the detection coil to the number of turns of the shielding coil surrounding the detection coil is proportional to the voltage division ratio of the voltage dividing circuit.
     


    Ansprüche

    1. Induktiver Sensor, wobei eine ringförmige Abschirmspule (2.12, 2.13) zusätzlich außerhalb einer ringförmigen Erfassungsspule (2.2, 2.3) angeordnet ist, die Abschirmspule die Erfassungsspule umgibt und die radiale Dicke der Abschirmspule kleiner ist als diejenige der Erfassungsspule; das von der Abschirmspule erzeugte Magnetfeld und das von der Erfassungsspule erzeugte Magnetfeld entgegengesetzt und teilweise versetzt sind, und die Magnetfelder gleichzeitig gedämpft oder erhöht werden, so dass die überlappte Magnetfeldstärke konstant gehalten werden kann, dadurch gekennzeichnet, dass
    ein Gehäuse (1.1) des Sensors zylindrisch ist, die Erfassungsspule auf ein Kunststoffrohr (1.10) gewickelt ist und ein Isoliermaterial zwischen die Erfassungsspule und die Abschirmspule gefüllt ist,
    im Inneren des Gehäuses mindestens zwei ringförmige Erfassungsspulen vorgesehen sind, die nacheinander entlang einer axialen Richtung des Gehäuses angeordnet sind, wobei eine ringförmige Abschirmspule jede Erfassungsspule mindestens umgibt; die radiale Dicke der Abschirmspule kleiner als diejenige der Erfassungsspule ist, und
    der Sensor ferner eine Testschaltung umfasst; die Testschaltung Resonanzschaltungen, Spannungsteilerschaltungen, eine Abschirmschaltung und eine Differenzverstärkerschaltung umfasst; die beiden Erfassungsspulen jeweils in Reihe mit einem Resonanzkondensator (2.6, 2.7) verbunden sind, um die Resonanzschaltungen zu bilden, und dann mit dem Ausgangsende einer Spannungsquelle parallel verbunden sind; die beiden Gruppen von Resonanzschaltungen hinsichtlich einer Resonanzfrequenz identisch sind; die beiden Gruppen von Resonanzspannungen, die durch die Resonanzschaltungen erzeugt werden, jeweils durch die Spannungsteilerschaltungen, die das gleiche Spannungsteilungsverhältnis aufweisen, dividiert und dann mit positiven und negativen Eingangsenden der Differenzverstärkerschaltung verbunden sind; die beiden Abschirmspulen mit den positiven und negativen Eingangsenden der Differenzverstärkerschaltung jeweils über einen Spannungsfolger (2.14) verbunden sind, um die Abschirmschaltung zu bilden; ein Verhältnis der Windungszahl der Erfassungsspule zu der Windungszahl der Abschirmspule, die die Erfassungsspule umgibt, proportional zu dem Spannungsteilungsverhältnis der Spannungsteilerschaltung ist.
     


    Revendications

    1. Capteur inductif, dans lequel une bobine de blindage annulaire (2.12, 2.13) est additionnellement disposée à l'extérieur d'une bobine de détection annulaire (2.2, 2.3), la bobine de blindage entoure la bobine de détection, et l'épaisseur radiale de la bobine de blindage est inférieure à celle de la bobine de détection ; le champ magnétique généré par la bobine de blindage et le champ magnétique généré par la bobine de détection sont opposés en direction et partiellement décalés, et les champs magnétiques sont atténués ou augmentés simultanément de sorte que l'intensité de champ magnétique de chevauchement peut être gardée constante, caractérisé en ce que
    un boîtier (1.1) du capteur est cylindrique, la bobine de détection est enroulée sur un tuyau en plastique (1.10), et un matériau isolant rempli l'espace entre la bobine de détection et la bobine de blindage,
    au moins deux bobines de détection annulaires qui sont disposées successivement le long d'une direction axiale du boîtier sont fournies dans le boîtier, une bobine de blindage annulaire entoure au moins chaque bobine de détection ; l'épaisseur radiale de la bobine de blindage est inférieure à celle de la bobine de détection, et
    le capteur comprend en outre un circuit de test ; le circuit de test comprend des circuits résonnants, des circuits diviseurs de tension, un circuit de blindage et un circuit amplificateur différentiel ; les deux bobines de détection sont respectivement connectées en série avec un condensateur résonnant (2.6, 2.7) pour former les circuits résonnants et sont ensuite connectées en parallèle à l'extrémité de sortie d'une source de tension ; les deux groupes de circuits résonnants sont identiques en fréquence de résonnance ; les deux groupes de tensions de résonnance générées par les circuits résonnants sont respectivement divisés par les circuits diviseurs de tension ayant le même rapport de division de tension, et sont ensuite connectés à des extrémités d'entrée positive et négative du circuit amplificateur différentiel ; les deux bobines de blindage sont connectées à des extrémités d'entrée positive et négative du circuit amplificateur différentiel respectivement via un suiveur de tension (2.14) pour former le circuit de blindage ; un rapport entre le nombre de spires de la bobine de détection et le nombre de spires de la bobine de blindage entourant la bobine de détection est proportionnel au rapport de division de tension du circuit diviseur de tension.
     




    Drawing












    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description