TW202409509A - Inductive sensor for performing dimensional and/or distance measurements - Google Patents

Abstract

Inductive sensor for measuring dimensions and/or distances, comprising a ferromagnetic core in which a winding is housed, a body to which the core is fixed, and a closing and protection element fixed to the core and/or to the body of the sensor by welding. The closing and protection element is made of non-magnetic metal and encloses the core and winding while ensuring a high immunity to external chemical agents and a reduced and better controllable dependence on thermal drift.

Description

Inductive sensors for size and/or distance measurements

The invention relates to an inductive sensor for measuring dimensions and/or distances.

The present invention is advantageously used in environments where adverse thermal and chemical conditions exist, such as in industrial settings or generally in applications (laboratory or non-laboratory) using chemical reagents.

In industrial scenarios, such as in a workshop environment, applications involving the use of machine tools often require the use of rugged sensors that are chemically resistant to various types of coolants and as immune as possible to thermal drift due to temperature fluctuations in the production area and temperature variations associated with the type of machining operations being performed and the coolants that may be used.

The inductive sensor according to the invention can be used, for example, in a machine tool to detect runout deviations of a spindle tool holder. Due to the presence of coolant and metal swarf in the sensor's working area, the sensor must have a robust design.

In laboratory applications, the sensor according to the invention can be used, for example, in a dilatometer which, depending on the type of application, can operate in the presence of chemical reagents.

In industrial practice, it is known that sensors need to be protected from external reagents, such as coolants or lubricants of various chemical compositions, which may affect the sensors or even prevent them from operating correctly. Usually, the protection function is provided by plastic plugs or resin coatings, which enclose the sensitive components of the sensor, such as windings and ferromagnetic cores.

These materials are not guaranteed to maintain their sealing properties over time: typically, with aging and continued exposure to coolants or other chemical agents, both resins and plastics deteriorate and allow liquid or gaseous components to pass through. The use of glue, resin or plastic in the construction of measurement sensors can also adversely affect their performance, which can be affected by thermal drift.

It is also known to protect the sensor by using a metal casing, which however significantly changes the correct functioning of the sensor itself and often renders the solution unusable in practice.

For example, patent number US10240908B2 mentions the disadvantage of using a metal housing for an inductive sensor, because eddy currents are inevitably generated in the metal and cause the sensitivity of the sensor to drop sharply. On the contrary, the patent proposes an advantageous inductive sensor in which the winding is embedded in one or more ceramic layers.

However, building such a sensor requires specific standardization of production procedures, which significantly increases costs and greatly reduces design flexibility.

The object of the present invention is to provide an inductive sensor for measuring dimensions and/or distances which overcomes the above-mentioned disadvantages while having a high immunity to external chemical reagents and a reduced and more controllable dependence on thermal drifts.

The object is achieved by a sensor as claimed, provided with a closing and protection element made of non-magnetic metal and surrounding the core and the windings housed therein. This allows the sensor to be very tightly sealed and resistant to external reagents without significantly affecting its sensitivity. The closing and protection element is fixed to the core and/or body of the sensor by welding.

The presence of closing and protective elements surrounding the core and windings also allows the windings to be held and fixed in place without the use of glue or resin, making the sensor less affected by temperature changes and simplifying the production procedure.

Preferably, the sensor's ferromagnetic core is made of ^MuMETAL® . The use of MuMETAL allows the closure and protection element to be applied to the sensor through laser welding performed between the core and the closure and protection element. As an alternative to using MuMETAL, other nickel-iron or iron-silicon metal alloys can be used.

According to a preferred embodiment of the invention, the closing and protective element has the form of a cover.

An inductive sensor for measuring dimensions and/or distances according to the invention is shown in FIG. 1 and is designated overall by the reference symbol 10 .

The sensor 10 includes a body 4 to which a ferromagnetic core 1 is fixed. The winding 2 is housed in the core 1 and more specifically the winding 2 is arranged around at least a part of said core.

Preferably, the core 1 is a pot core and the windings 2 are made of self-bonding copper.

A closing and protective element 3 made of non-magnetic metal is applied to the core 1 and/or the body 4 of the sensor 10 and is hermetically fixed by welding. The area of the sensor 10 where the welding is performed is roughly indicated by the reference symbol 5 in FIG. 1 .

The closing and protective element 3 preferably has the form of a protective cover.

Furthermore, the closing and protection element 3 is rigid to ensure protection against shocks.

Preferably, an elastically deformable sealing element 6, such as an annular seal also called an O-ring, is placed between the core 1 and the winding 2, more specifically positioned in the part of the core 1 accommodating the winding 2, between the inner surface of the core 1 and the winding 2, so as to keep the winding 2 pressed against the inner surface of the closing and protective element or protective cover 3.

Preferably, the sensor 10 is provided with an electronic circuit 7 connected to the winding 2 and via cables to a processing unit of known type not visible in the figure.

According to a preferred embodiment, the closing and protection element 3 is made of non-magnetic steel.

According to a further preferred embodiment, the core 1 is made of MuMETAL and the closing and protective elements are welded to the core 1 and/or the body 4 of the sensor 10 by means of laser welding.

The use of MuMETAL as the material for the ferromagnetic core and through the use of laser welding facilitated the use of metal for the protective cover.

However, different materials with similar properties to the materials mentioned above can be used, such as nickel-iron alloy for the core.

A very important difference between the present invention and the prior art is the use of non-magnetic metals for the closure and protection elements of the sensor 10 . This option allows the sensor to be hermetically sealed and to be far more robust to chemical attacks and influences, which is possible using known techniques such as resin coating of the sensitive elements of the sensor (i.e. core and windings). This is not possible at all levels.

In order to compensate for any reduction in the sensitivity of the sensor 10 that may be involved in the use of metallic materials for the manufacturing of the closing and protective element 3, appropriate measurements are taken during the design of the sensor 10, for example, with respect to the thickness of the closing and protective element 3 as well as the sensor The signal 10 is electronically adjusted relative to the measurement in order to maximize the overall sensitivity of the sensor 10 as much as possible.

More specifically, it is known that the presence of metal between the sensor and the surface in relation to which the measurement is performed (also simply called the target) causes a decrease in the sensitivity of the sensor due to induced eddy currents and an increase in the distance between the core and the target . Therefore, when designing a sensor, you usually want to avoid this situation.

In the sensor according to the invention, these disadvantages are overcome in the following manner.

First, the sensor 10 is tuned using low frequencies so that the protective cover made of non-magnetic metal is almost transparent to the electromagnetic field generated by the sensor. In other words, the inductive sensor is supplied with a sinusoidal AC voltage with a frequency less than 50kHz. The signal output by the sensor 10 is acquired and demodulated using known demodulation techniques, such as product, peak and integral demodulation. The measurements obtained are compared with previously obtained maps to provide a very precise indication of the distance between the sensor and the target. Using low frequencies, eddy currents in non-magnetic metal layers with a thickness of tens of millimeters (mm) are almost negligible. Low frequency adjustments can negatively affect the sensitivity of the system, albeit in an acceptable way. However, by properly designing the sensor geometry, it is possible to optimize the sensor characteristics and compensate for the reduction in sensitivity. From this point of view, the use of MuMETAL to manufacture ferromagnetic cores is highly advantageous because MuMETAL is an easily machined material and allows the use of machine tools to manufacture ferromagnetic cores according to optimal geometries with great precision.

Secondly, since the reduction in sensitivity is also due to the increased distance between the sensor and the target caused by the presence of the non-magnetic metal protective cover, the thickness of the latter should be as small as possible while maintaining appropriate strength and rigidity characteristics. Using appropriate manufacturing techniques, it is possible to produce protective covers with a thickness of less than 0.5 mm and a diameter of more than 10 mm.

It can be seen from the graph shown in Figure 2 that within the common operating range of the two sensors, the inductance value of the sensor with a protective cover progresses very much with that of the sensor without a protective cover. near. In other words, the graph shows the inductance as a function of distance between the target and the sensor, comparing the first data related to the sensor without the protective cover (darker color curve) and the Secondary data related to the sensor with protective cover (lighter color curve). For better understanding, in the second profile (lighter color curve), an offset factor is included along the x-axis to compensate for the gap caused by the presence of the protective cover. In other words, the second document takes into account the fact that in a sensor with a protective cover, there is a spatial deviation between the target and the sensor corresponding to the thickness of the protective cover. This deviation results in a slight reduction in the operating range of the sensor along its initial part compared to the operating range of the sensor without the protective cover. However, the reduction in the operating range is acceptable and does not significantly affect the functionality of the sensor and the performance of the required measurements.

The similarity between the two curves along the part where they both exist is evident, apart from the small decrease in sensitivity due, albeit small, to the eddy currents generated in the metal of the cover itself, which can be achieved when the protective cover is fitted The progression of the sensor's inductance is seen.

As previously mentioned, the protective cover is fixed to the core 1 and/or body 4 of the sensor 10 by welding, without the need for glue or other fixing means. The absence of a bonding system also avoids thermal drift problems, which are usually caused by resins and glues and affect the normal operation of the sensor in an uncontrolled way.

Furthermore, it greatly simplifies the production of the sensor 10: the deposition of the resin and the thermal curing of the resin require specific equipment and relatively long processing and waiting times.

In the sensor according to the invention, it is also possible to dispense with fixing the core 1 to the body 4 of the sensor 10: once welded, the protective cover 3 already ensures that the core 1 is positioned and fixed without having to fix it beforehand ( For example, by bonding or welding) to the body of the sensor.

In summary, the main advantages provided by the inductive sensor according to the present invention compared to the use of inductive sensors according to the prior art are as follows: •     Resistance to shocks and chemical reagents •     Reduction of thermal drift of the sensor •     Simplification of the manufacturing process due to the absence of bonding/resin coating process

FIG. 1 shows a possible configuration of a sensor 10 according to the present invention, other configurations are possible.

For example, a sensor according to the invention can be used in comparators to check the form and/or internal or external dimensions of mechanical components such as plug, snap or ring gauges, as well as in various types of measuring cells or measuring heads. use sensors. In this application, the use of a sensor according to the invention leads to significant application advantages in terms of resistance to external agents.

Figure 3 shows a possible alternative embodiment, in which a sensor according to the invention is used in a comparator or gauge for checking the shape and/or dimensions of a mechanical part, for example for measuring the outer diameter.

Components common to the embodiments shown in Figures 1 and 3 are designated by the same reference characters.

FIG3 shows only a portion of the gauge, shown very schematically, namely a mechanical armset 11 comprising two arms 12, each arm having a movable hand probe 14 suitable for contacting a mechanical part, a fulcrum or pivot point 13 to be measured, so as to enable the arms 12 to be moved relative to a support (not shown) to which the armset 11 is connected, and an inductive sensor 10 according to the invention is placed between the arms 12 of the armset 11.

Different from the general pot-shaped sensor that is shaped like a hollow cylinder made of ferromagnetic material, closed at the bottom, containing windings inside, and having only one sensing surface opposite to the bottom, the sensor used in this embodiment has Two sensing surfaces.

The sensor 10 shown in Figure 3 actually consists of a ferromagnetic core 1 with two parts of different diameters, substantially concentric and mechanically separated from each other. More specifically, the core consists of an inner barrel and an outer ring, has no base, and is "open" on both sides, that is, has two open sides. These open sides of the core define the sensing side of the core. A winding 2 made of, for example, self-joining copper is housed between said two parts of the core, ie between the outer ring and the inner barrel of the core 1 .

Two closing and protective elements or protective covers 3 made of non-magnetic metal are fixed to the ferromagnetic core 1 by welding on said open sides of the core 1 ; the sensor 10 is roughly indicated in FIG. 3 by the reference symbol 5 welding area. Each open side of the core 1 is closed by one of the closing and protective elements 3 .

Since there is no seat or other connecting surface between the inner cylinder and the outer ring, the core is mechanically fixed only by the presence of two protective covers mounted on the two "open" sides of the core and which give it mechanical stability, strength and tightness.

Preferably, two elastically deformable sealing elements 6, such as annular seals, also known as O-rings, are located between the windings and the inner surface of each protective cover 3 in order to secure the windings in the configuration so assembled. 2 location.

A matching element 15 made of ferromagnetic material with a substantially flat surface or plate is connected to each arm 12 and is arranged so that it faces one of the closing and protective elements, ie one of the sensing sides of the core. More specifically, each sensing side of the core 1 faces and is arranged at a distance from the corresponding plate 15 . During the inspection operation, due to the movement of the plate and core toward or away from each other after contact between the detector and the workpiece, the distance changes, causing the sensor to generate an electrical measurement signal 10 .

Preferably, the core 1 and/or the matching element 15 consists of Made of MuMETAL.

Additionally, the welding that secures the protective cover to the core is laser welding.

According to an alternative embodiment, the protective cover 3 has a special geometry at the edge (not shown), such as a beveled surface, which facilitates the application of welding and correct fixing of the protective cover 3 during the production process.

In the embodiments described so far, the core 1 and the body of the sensor 10 constitute two separate components of the sensor 10 . However, it is possible to make them as one piece.

1:Core 2: Winding 3: Closing and protecting elements; protective cover 4: Ontology 5: Reference symbols 6: Elastically deformable sealing element 7: Electronic circuit 10: Sensor; electrical measurement signal 11:Arm set 12: arm 13: Fulcrum or Pivot Point 14: Movable contacts 15: Matching components; corresponding board

The invention will now be described with reference to the accompanying drawings, which illustrate non-limiting examples of embodiments of the invention, in which: [Fig. 1] is a schematic cross-sectional view of an inductive sensor according to the present invention; [Fig. 2] is a graph comparing the inductance trends of an inductive sensor according to the present invention and an inductive sensor without closing and protection components; and [Fig. 3] is a schematic cross-sectional view of a portion of a gauge incorporating an alternative embodiment of an inductive sensor according to the present invention.

1: Core

2: Winding

3: Closing and protection components; protective cover

4: Ontology

5: Reference symbols

6: Elastically deformable sealing element

7: Electronic circuit

10: Sensor; electrical measurement signal

Claims (11)

An inductive sensor (10) for measuring size and/or distance comprises: a body (4); a ferromagnetic core (1) fixed to the body (4); a winding (2) arranged around a portion of the core (1); and a closing and protective element (3) fixed to the core (1) and/or the body (4) of the inductive sensor to surround the core (1) and the winding (2); wherein the closing and protective element (3) is made of non-magnetic metal and is fixed to the core (1) and/or the body (4) of the inductive sensor (10) by welding. An inductive sensor (10) as claimed in claim 1, wherein said closure and protection element (3) is in the form of a cover. The inductive sensor (10) of claim 1 or claim 2, wherein the ferromagnetic core (1) is made of MuMETAL. An inductive sensor (10) as claimed in claim 1 or claim 2, wherein said closure and protection element (3) is made of non-magnetic steel. An inductive sensor (10) as claimed in claim 1 or claim 2, wherein the closing and protection element (3) is fixed by laser welding. The inductive sensor (10) of claim 1 or claim 2, wherein the inductive sensor (10) is adjusted by using low frequency. An inductive sensor (10) as claimed in claim 6, which is suitable for being supplied with a sinusoidal alternating voltage with a frequency less than 50kHz. The inductive sensor (10) of claim 1 or claim 2, wherein the closing and protecting element (3) has a thickness of less than 0.5 mm. An inductive sensor (10) as claimed in claim 1 or claim 2 comprises an elastically deformable sealing element (6) placed between the core (1) and the winding (2), which is suitable for keeping the winding (2) pressed against the inner surface of the closing and protective element (3). An inductive sensor (10) as claimed in claim 1 or claim 2, wherein: the core (1) comprises two parts, which have different diameters, are substantially concentric and mechanically separated from each other, and have two open sides; and the winding (2) is arranged between the two parts of the core (1); the inductive sensor (10) comprises two closing and protective elements (3), which are fixed to the core (1) at the open sides of the core (1), and each open side of the core (1) is closed by one of the closing and protective elements (3). A gauge for checking the shape and/or size of a mechanical part, comprising a support, a mechanical arm set (11) connected to the support and comprising two arms (12), each arm having a movable probe (14) suitable for contacting the mechanical part, and a fulcrum (13) suitable for moving the arm (12) relative to the support, wherein the gauge comprises an inductive sensor (10) as claimed in claim 10, which is placed between the arms (12) of the mechanical arm set (11); and each arm (12) is provided with a matching element (15), the matching element (15) having a substantially flat surface, made of ferromagnetic material and arranged to face one of the closing and protective elements (3).

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