VIBRATION SENSOR

Abstract

Vibration sensor comprising a housing (1) with a central axis (Z) in which a PCB circuit (2) is arranged. The PCB circuit (2) has a central portion (20) centered on the central axis (Z) and from which extend distinct lateral portions (21a-21d), flexible zones (22a-22d) connecting the central portion (20) to the lateral portions (21a-21d), each lateral portion (21a-21d) forms an angle greater than or equal to 90° relative to the central portion (20). At least two MEMS sensitive elements (3a-3c) for vibration detection mounted on the inner faces (210a-210c) of the lateral portions (21a-21c) of the circuit (2), the sensitive axes (30a-30c) of the MEMS sensitive elements (3a-3c) are parallel to the inner face (210a-210d) of the corresponding lateral portion (21a-21d) and form a three-dimensional reference frame. Figure for abstract: Fig 2.

Description

Title of the invention: VIBRATION SENSOR Technical field

[0001] The invention relates to the field of MEMS-based vibration sensors (micro-electro-mechanical systems in English, or micro-electro-mechanical systems in French), intended to be installed on or coupled to a test structure subjected to vibrations. Prior art

[0002] A vibration sensor can be used to monitor the vibration state of a structure, such as industrial equipment such as a machine tool, a pump, a motor, etc. Vibration detection can be obtained by means of accelerometer-type sensors based on a piezoelectric sensitive element or a MEMS sensitive element.

[0003] Furthermore, vibration sensors intended to be installed in or on industrial equipment must generally meet industrial standards imposing, for example, their dimensions, their compactness being generally sought.

[0004] For the vibration measurement of industrial equipment exhibiting high-frequency vibrations, the use of sensors based on a piezoelectric sensitive element is preferred. Indeed, this type of piezoelectric sensor generally has the advantage of being usable over a very wide frequency range with a large dynamic range, and is well suited for the detection of high-frequency vibrations, in particular for frequencies greater than or equal to 10 kHz. This type of sensor generally takes the form of a cylindrical housing composed of a base provided with means for mounting the housing on the industrial equipment, as well as a cylindrical casing provided with a through hole suitable for a signal output.The base and the cylindrical casing delimit a volume in which the piezoelectric sensitive element is arranged as well as the electronic card integrating electronic components, the electronic card being further coupled to a signal output connector. Due to the dimensions imposed by industrial standards, the piezoelectric sensitive element and the electronic card are generally arranged in stages in the direction of the height of the cylinder so as to limit the size. In addition, the small surface area available on the electronic card generally does not allow the integration of components converting the analog signal into a digital signal. The integration of an analog-digital converter in the housing would require increasing the size of the housing, which would degrade the sensor measurements in the high frequencies. In addition, fixing to a . The bearing surface of industrial equipment is usually achieved by stud mounting (screw coupling and non-through central tapped hole in the base), so that the fixing axis coincides with the central axis of the cylinder and is perpendicular to the bearing plane. This type of mounting is preferred to ensure adequate transmission of high-frequency vibrations and to reduce the contribution of parasitic vibrations.

[0005] Silicon MEMS sensitive elements, also called MEMS chips, can also be used instead of piezoelectric sensitive elements. Indeed, compared to piezoelectric elements, MEMS elements can be manufactured collectively on a silicon wafer and have a reduced footprint compared to piezoelectric devices. The integration of MEMS chips in modules intended for measuring vibrations in industrial equipment therefore has a definite advantage. In particular, it is possible to produce vibration sensors along 3 axes having a reduced footprint and with a digital signal output.

[0006] Some manufacturers of 3-axis MEMS vibration sensors propose in particular to keep the cylindrical shape of the housing by positioning the MEMS sensitive elements on a printed circuit board whose surface carrying the MEMS sensitive elements contains the central axis of the cylinder and is oriented perpendicular to the transfer plane of the equipment. To allow measurement along 3 axes, certain sensitive axes of these MEMS sensitive elements are thus oriented out of plane (i.e. perpendicular to the surface of the printed circuit). Due to the constraints linked to the manufacture of the MEMS sensitive element from silicon wafer, this out of plane orientation of the sensitive axes reduces the bandwidth of the sensor and therefore restricts the use of the 3-axis MEMS vibration sensor to low frequencies. Generally, the bandwidth of this type of sensor in 3-axis mode is less than 10 kHz.

[0007] To meet the needs of high-frequency vibration measurement along the 3 measurement axes, for example for measuring vibrations on a machine tool, some manufacturers propose to position on the industrial equipment a module integrating several single-axis MEMS vibration sensors, each adapted to high frequencies. To optimize the size and use at high frequencies, this type of module is generally parallelepipedal and must be fixed to the industrial equipment by means of four screws. However, this type of fixing is not easily adjustable on all industrial equipment. In addition, the volume occupied by the sensors for measurement along the 3 measurement axes remains significant. Statement of the invention

[0008] In this context, the present invention thus aims to propose an alternative solution vibration sensor based on MEMS sensitive elements suitable for high frequency measurements, particularly greater than or equal to 10kHz.

[0009] The invention also aims to propose a 3-axis vibration sensor suitable for high-frequency measurements on the 3 measurement axes.

[0010] The vibration sensor advantageously has suitable dimensions meeting in particular the various industrial standards for integration into industrial equipment.

[0011] The invention thus relates to a vibration sensor comprising: - a housing with a central axis comprising a base coupled to a cover defining an internal volume in which a PCB (Printed Circuit Board) circuit support is arranged, the base comprising a central protrusion projecting into the internal volume and being configured to ensure the fixing of the housing to a vibrating structure; - the PCB circuit support has at least flexible zones, and is formed of at least one central portion centered on the central axis and from which at least two distinct lateral portions extend, said flexible zones electrically connecting the central portion to the lateral portions, each lateral portion forming an angle greater than or equal to 90° relative to the central portion; - at least two MEMS vibration detection sensitive elements mounted on the internal faces of the lateral portions of the circuit support, and positioned so that the sensitive axes of the MEMS sensitive elements are parallel to the internal face of the corresponding lateral portion and form a three-dimensional reference frame; and - signal output means.

[0012] For example, the signal output means may comprise a signal output connector centered on the central axis, attached to the central portion and opening outside the housing through a through hole in the cover.

[0013] Thus, unlike the vibration sensors of the prior art in which at least one sensitive detection axis coincides with the central axis of the housing, all of the sensitive axes of the invention are offset relative to the central axis of the housing. The MEMS sensitive elements are thus transferred not to a plane including the central axis of the housing, but to one or more surfaces substantially parallel to a plane including the central axis of the housing. In other words, the sensitive axes are distant from the central axis Z of the housing. The PCB circuit support may for example have four lateral portions, substantially forming with the central portion a cube or a parallelepiped open on one of its sides. The lateral and central portions are thus preferably quadrangular.

[0014] Each central and lateral portion has an internal face and an opposite external face. The internal face of the central portion being that opposite the protrusion central and the internal faces of the lateral portions being those facing the central axis.

[0015] The PCB circuit support is preferably in the form of a printed circuit (or PCB) of the flex-rigid type, that is to say that it is made in a single piece from a material and certain zones are thinned allowing the PCB to be folded at the level of these thinned zones. Thus, these thinned zones form the flexible zones connecting the lateral portions to the central portion. The thickness of each flexible zone is thus less than that of the lateral and central portions.

[0016] In practice, the formation of the angle between a side wall and the central portion is achieved by folding at these thinned areas. Due to the elastic properties of these thinned areas, the thinned areas will more or less return to their initial shape after deformation, so that the side portions can be slightly inclined relative to the central axis of the housing.

[0017] Thus, the angle formed between a lateral portion and the central portion can be between 90° and 95°.

[0018] Furthermore, due to this elastic return of the flexible zones, certain parts of the lateral portions may come into abutment on the internal wall of the housing, and in particular on the internal wall of the cover. Indeed, when inserting the folded PCB circuit support into the cover, the lateral portions tend to move away from the central axis due to this elastic return. By dimensioning the internal volume of the cover, and therefore of the housing, relative to the surface area of ​​the PCB circuit necessary to accommodate all of the MEMS sensitive elements and electronic components, the verticality or quasi-verticality of these lateral portions is ensured, and therefore the orthogonality of the sensitive axes.In other words, unlike existing solutions in which the PCB circuit is held on a specific support inside the housing by gluing or screwing, the PCB circuit can be held in place in the housing by taking advantage of the restoring force effect of the flexible zones ensuring the immobilization in abutment of the vertical edges on the internal wall.

[0019] Thus, a portion of the outer face of each side portion may be in contact with (or abut on) an area of ​​the inner wall of the lid. For example, the vertical edges of the side walls may abut on the inner surface of the lid. It is also possible to provide protruding protrusions on the inner wall of the lid and / or the base, for example in the form of wedges or ribs, acting as stops for the outer faces of the side portions.

[0020] In practice, to finish immobilizing the circuit support in the housing, the internal volume can be filled with a resin. Encapsulation with the resin also makes it possible to protect the PCB support, as well as the elements attached to this support, from possible corrosion or condensation phenomena.

[0021] In practice, the resin can be injected into the internal volume of the housing via through holes provided for this purpose and made in the base.

[0022] Advantageously, all or part of the electronic components associated with these MEMS sensitive elements are transferred to the internal face of the central portion.

[0023] For example, these electronic components may include a controller and an analog-to-digital converter for generating digital signals at the output of the sensor. The signal output connector may be attached to the outer surface of the central portion to open at the output of the sensor through the through-hole of the cover, and electrical connections of the via type may be provided for electrically connecting the connector to the electronic components disposed on the inner face of the central portion.

[0024] In a variant, depending on the available surfaces, it is also possible to mount electronic components on all or part of the side walls.

[0025] Preferably, the MEMS sensitive elements are of the micro-electro-mechanical device type with interdigitated capacitive combs produced in a substrate with sensitive axis(es) in the plane, i.e. parallel to the plane of the substrate. Each MEMS sensitive element can thus comprise one sensitive axis or two sensitive axes.

[0026] Advantageously, the external profile of the housing is hexagonal in shape. This profile is particularly preferred to facilitate the fixing of the sensor on industrial equipment with existing tools.

[0027] The vibration sensor may further have one or more of the following characteristics: - the vibration sensor is a 3-axis sensor suitable for high-frequency measurements (greater than or equal to 10kHz), according to the 3 measurement axes; - the vibration sensor comprises three single-axis MEMS sensitive elements, each distributed over a lateral portion, the sensitive axes being oriented so as to form a three-dimensional, preferably orthonormal, reference frame; - the vibration sensor comprises a single-axis MEMS sensitive element mounted on one of the lateral portions, and a 2-axis MEMS sensitive element mounted on another of the lateral portions, and the sensitive axes being oriented so as to form a three-dimensional, preferably orthonormal, reference frame; - the vibration sensor comprises two 2-axis MEMS sensitive elements each distributed over a lateral portion, the sensitive axes being oriented so as to form a three-dimensional, preferably orthonormal, reference frame; - the central protrusion is configured to ensure stud mounting; - the central protrusion is a blind hole tapped and open to the outside of the housing; - the central outgrowth defines an axis of fixation which coincides with the central axis, and the distance of the internal faces of the lateral portions from this fixing axis is of the order of 7mm; - the signal output connector can be replaced by an electrical cable directly to the central portion and exiting the housing through the through hole in the cover. This type of connection without physical connector is little used in the industrial world of vibration metrology, but allows to obtain a sensor with good high frequency behavior while reducing the size of the sensor; - the sensor can integrate electronic components necessary for signal transfers according to the communication protocol used; - the housing may be made of a metallic material suitable for the intended application, for example steel, aluminum or titanium; - the base can be metallic and the cover can be made of thermoplastic material to allow radio waves to pass through, a radio antenna can thus be integrated into the housing. This configuration makes it possible to do without the output connector or the electrical cable; - the external diameter of the case can be around 25mm; - the height of the housing is preferably less than or equal to 20mm, which allows the first resonance mode to be greater than 20kHz; - the assembly of the cover to the base can be carried out by any means, for example by screwing, welding, gluing or even stamping, in order to seal the housing and protect the electronic components from electromagnetic disturbances which are very present on industrial equipment.

[0028] The invention thus takes advantage of the use of MEMS sensitive elements perfectly suited for high-frequency vibration measurements and whose dimensions are much smaller than those of a piezoelectric sensitive element. Due to their reduced dimensions, it is thus possible to decenter or offset the sensitive axes from the fixing axis or the central axis without impacting the performance of these sensitive elements, nor on the transmission of vibrations, nor on the overall size of the assembly.

[0029] The invention thus makes it possible to produce a 3-axis vibration sensor suitable for high-frequency measurements on the 3 measurement axes, and meeting the dimensional constraints dictated by the various industrial standards. Brief description of the drawings

[0030] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, in which:

[0031] [Fig.l] [Fig.l] is a schematic representation of the sensor according to a mode of realization of the invention;

[0032] [Fig.2] [Fig.2] is an exploded view of the sensor of [Fig.l];

[0033] [Fig.3] [Fig.3] is a sectional view of the sensor of [Fig.l] along the sectional plane AA;

[0034] [Fig.4] [Fig.4] is a schematic representation of a non-PCB circuit carrier folded, according to one embodiment of the invention;

[0035] [Fig.5] [Fig.5] is a section of the sensor of [Fig.l] along the section plane BB;

[0036] [Fig.6] [Fig.6] is a sectional view of the sensor of [Fig.l] along the sectional plane AA, wherein the side portions abut the inner surface of the housing;

[0037] [Fig.7] [Fig.7] is a schematic representation of an angle according to a variant;

[0038] [Fig.8] [Fig.8] is a schematic representation of an angle following another variant;

[0039] [Fig.9] [Fig.9] is a sectional view of the sensor of [Fig.l] along the sectional plane CC;

[0040] [Fig. 10] [Fig. 10] is a sectional view of the sensor of [Fig.l] along the plane of CC cut, according to another embodiment;

[0041] [Fig.11] [Fig.11] is a perspective view of the sensor of [Fig.10]. Description of an embodiment

[0042] A 3-axis vibration sensor suitable for high-frequency measurements on the 3 measurement axes, according to embodiments illustrated in Figures 1 to 11, is described below.

[0043] The vibration sensor thus comprises a housing 1 formed by the assembly of two parts, a first part forming the cover 11 or hood and a second part forming the base 10. The housing 1 has a central axis Z as well as an internal volume 12.

[0044] The sensor further comprises a PCB circuit support 2 arranged in the internal volume 12 of the housing 1. The PCB circuit support 2 is formed of at least one central portion 20 centered on the central axis Z and from which at least two lateral portions 21a-21d extend. For example, the PCB support circuit 2 illustrated in [Fig.4] comprises four lateral portions 21a-21d. In particular, flexible zones 22a-22d are located between the central portion 20 and the lateral portions 21a-21d, and in particular make it possible to electrically connect the central portion 20 to the lateral portions 21a-21d. These flexible zones 22a-22d connecting the lateral portions 21a-21d to the central portion 20 are configured to be folded or curved so that each lateral portion 21a-21d forms with the central portion 20 an angle a less than 180° and greater than or equal to 90°.Each central portion 20 and lateral portion 21a-21d thus has an internal face 200, 210a-210d and an opposite external face, the external faces being those facing the internal wall of the housing 1.

[0045] In practice, the PCB circuit support 2 is in the form of a printed circuit (or PCB) of the flex-rigid type, that is to say that it is made in a single piece from a material and certain zones are thinned to allow folding. Thus, these thinned zones form the flexible zones 22a-22d connecting the lateral portions 21a-21d to the central portion 20. The thickness of each flexible zone 22a-22d is thus less than that of the lateral portions 21a-21d and central 20. The central 20 and lateral 21a-21d portions may have different shapes, for example quadrangular. As illustrated in [Fig.4], the PCB circuit support 2 may have four lateral portions 21a-21d, and once folded, forms a cube or a parallelepiped open on one of its sides.Thus, when the folded PCB circuit support 2 is positioned in the internal volume 12, the central portion 20 is centered on the central axis Z and perpendicular to this central axis Z, and the faces of the lateral portions 21a-21d each form an angle a of between 90° and 95° with the central portion 20.

[0046] To enable vibration detection, at least two MEMS sensitive elements 3a-3c for vibration detection suitable for high-frequency measurements are mounted on the internal faces 210a-210c of the lateral portions 21a-21c of the PCB circuit support 2. The MEMS sensitive elements 3a-3c are advantageously of the microelectromechanical device type with interdigitated capacitive combs made in a substrate with sensitive axis(es) in the plane, i.e. parallel to the plane of the substrate. Each MEMS sensitive element 3a-3c can thus comprise a single sensitive axis or two sensitive axes. The sensitive axes 30a-30c of the MEMS sensitive elements 3a-3c are parallel to the internal face 210a-210d of the lateral portion 21a-21d on which the sensitive element is mounted and form a three-dimensional reference frame. The set of sensitive axes 30a-30c is therefore distant from the central axis Z of the housing. For example, as illustrated in [Fig.4], three single-axis MEMS sensitive elements 3a-3c are each mounted on the internal face of a lateral portion 21a-21c. Thus, when the angle a formed between each lateral portion 21a-21d and the central portion 20 is equal to 90° ( [Fig.7]), the sensitive axes 30a-30c form an orthonormal three-dimensional reference frame. In practice, due to the elastic properties of the thinned zones 22a-22d, these thinned zones will more or less return to their initial shape after deformation, so that the lateral portions 21a-21d can be slightly inclined ([Fig.8]) relative to the central axis Z of the package. Due to this elastic return of these flexible zones 22a-22d, certain parts of the lateral portions 21a-21d can come into abutment ([Fig.6]) on the internal wall of the housing 1, for example on the internal wall 111 of the cover 11.Indeed, when inserting the folded PCB circuit support 2 into the cover 11, the lateral portions 21a-21d tend to move away from the central axis Z due to this elastic return. By sizing the internal volume of the cover 11, and therefore of the housing 1, relative to the surface area of ​​the PCB circuit 2 required to accommodate . the set of MEMS sensitive elements 3a-3c and electronic components, the verticality or quasi-verticality of these lateral portions 21a-21d is ensured, and therefore the orthogonality of the sensitive axes 30a-30c. Thus, the PCB circuit 2 is not held by gluing or screwing on a specific support of the housing, but is advantageously held in place in the housing by the effect of the restoring force of the flexible zones 22a-22d which ensures the immobilization in abutment of the vertical edges 211 of the lateral portions 21a-21d on the internal wall ([Fig.5] and [Fig.6]). In addition, all of the sensitive axes 30a-30c are distant from the central axis Z of the housing.

[0047] In a variant illustrated in Figures 10 and 11, the internal wall of the housing 1 may be provided with projecting protrusions in the form of ribs 5, so that the external faces of the lateral portions 21a-21d come into abutment on these ribs 5. In [Fig.l 1], the lateral portion 21a is not shown to allow a better visualization of the ribs 5. In practice, these protrusions 5 may have different profiles insofar as they are configured to ensure the function of a stop and thus limit the opening angle of the lateral portions 21a-21d.

[0048] Electronic components associated with the MEMS sensitive elements 3a-3c may be transferred to the internal face 200 of the central portion 20, and / or to free areas of the lateral portions 21a-21d. For example, these electronic components may include a controller and an analog-digital converter for generating digital signals at the output of the sensor.

[0049] To ensure the output of the signals, a signal output connector 4 can be fixed to the external surface of the central portion 20 to open at the output of the sensor through a through hole 110 of the cover 11, and electrical connections of the via type can be provided to electrically connect the connector to the electronic components arranged on the internal face 200 of the central portion 20.

[0050] According to another variant, the output of the signals can be ensured by an electric cable adapted to signal transfers according to an industrial communication protocol. This cable is connected directly to the central portion 20 and exits the housing 1 through the through hole 110 of the cover 11. According to another variant, the sensor can integrate wireless communication means.

[0051] In practice, to finish immobilizing the PCB circuit support 2 in the housing, the internal volume 12 can be filled with a resin. In practice, the resin can be injected into the internal volume 12 of the housing via through holes provided for this purpose and made in the base 10, after assembly of the cover 11 with the base 10.

[0052] The assembly of the cover 11 to the base 10 can be carried out by any means, for example by screwing, welding, gluing or even stamping, in order to seal the housing and protect the electronic components from electromagnetic disturbances which are very present on industrial equipment. Thus, the base 10 and the cover 11 may have thicker areas to allow assembly by screwing. For example, the base may include through holes in its thick areas for the passage of screws, and the cover 11 may also include threaded holes in its thick areas configured to cooperate with screws. In practice, the outer profile of the housing is hexagonal in shape, this profile facilitating the fixing of the sensor on industrial equipment with existing tools.

[0053] To fix the sensor on a vibrating structure, a central protrusion 100 is provided at the base 10. This central protrusion 100 projects into the internal volume 12 of the housing and is for example in the form of a tapped blind hole open to the outside of the housing 1. In practice, the central protrusion 100 defines a fixing axis which coincides with the central axis Z.

[0054] The sensor can be mounted as follows: - production of the PCB 2 circuit support integrating the various electronic components as well as the sensitive modules 3a-3c; - bending of the PCB support 2 at the flexible zones 22a-22d; - insertion of the PCB support 2 thus folded into the cover 11 with fixing to the connector when the connector is provided; - depending on the dimensions of the cover, and due to the elastic return of the flexible zones 22a-22d, the lateral portions 21a-21d move apart slightly to come into abutment on the internal wall of the cover 11; - assembly of the cover 11 with the base 10, for example by screwing; and - pouring the resin into the internal volume of housing 1 to fix and protect the assembly.

[0055] The invention thus makes it possible to produce a 3-axis vibration sensor integrating MEMS sensitive elements whose sensitive axes are offset from the central axis of the sensor, and adapted to industrial equipment.

Claims

Claims

1. Vibration sensor characterized in that it comprises: - a housing (1) with a central axis (Z) comprising a base (10) coupled to a cover (11) defining an internal volume (12) in which a PCB circuit support (2) is arranged, the base (10) comprising a central protrusion (100) projecting into the internal volume (12) and being configured to ensure the fixing of the housing (10) to a vibrating structure; - the PCB circuit support (2) has at least flexible zones (22a-22d), and is formed of at least one central portion (20) centered on the central axis (Z) and from which extend at least two distinct lateral portions (21a-21d), said flexible zones (22a-22d) electrically connecting the central portion (20) to the lateral portions (21a-21d), each lateral portion (21a-21d) forms an angle (a) greater than or equal to 90° with respect to the central portion (20);- at least two MEMS sensitive elements (3a-3c) for vibration detection mounted on the internal faces (210a-210c) of the lateral portions (21a-21c) of the circuit support (2), and positioned so that the sensitive axes (30a-30c) of the MEMS sensitive elements (3a-3c) are parallel to the internal face (210a-210d) of the corresponding lateral portion (21a-21d) and form a three-dimensional reference frame; and - signal output means.;

2. A vibration sensor according to claim 1, wherein the signal output means comprises a signal output connector (4) centered on the central axis (Z), fixed to the central portion (20) and opening outside the housing (1) through a through hole (110) of the cover (11).

3. A vibration sensor according to claim 1 or 2, wherein the angle (a) formed between a lateral portion (21a-21d) and the central portion (20) is between 90° and 95°.

4. Vibration sensor according to one of claims 1 to 3, in which a part of the outer face of each lateral portion (21a-21d) is in contact with an area of ​​the inner wall (111) of the cover (11).

5. Vibration sensor according to one of claims 1 to 4, in which the internal volume (12) is filled with a resin.

6. Vibration sensor according to one of claims 1 to 5, in which all or part of the electronic components associated with these elements

7.

8.

9. sensitive MEMS (3a-3c) are transferred to the internal face (200) of the central portion (20). Vibration sensor according to one of claims 1 to 6, in which the MEMS sensitive elements (3a-3c) are of the microelectromechanical device type with interdigitated capacitive combs produced in a substrate with sensitive axis(es) in the plane. Vibration sensor according to one of claims 1 to 7, wherein the outer profile of the housing (1) is hexagonal in shape. Vibration sensor according to one of claims 1 to 8, wherein the sensor is configured for vibration measurements at frequencies above 10kHz.

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