Inductive sensor for performing size and / or distance measurements

Abstract

Inductive sensor for measuring dimensions and / or distances, comprising a ferromagnetic core having windings mounted therein, a body to which the core is secured, and a closure and protection assembly secured by welding to the core and / or to the body of the sensor. The closure and protection component is made of a non-magnetic metal and surrounds the core and winding while ensuring a high immunity to external chemicals and a reduced and more controllable dependency on thermal drift.

Description

Technical Field

[0001] The invention relates to an inductive sensor for measuring dimensions and / or distances.

[0002] The invention is advantageously used in environments where adverse thermal and chemical conditions exist, such as in industrial environments or generally in applications (laboratory or non-laboratory) where chemical reagents are used.

[0003] In industrial scenarios, such as in a shop environment, applications involving the use of machine tools often require the use of robust 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 site and temperature variations associated with the type of machining operations being performed and the coolant that may be used.

[0004] The inductive sensor according to the invention can be used, for example, in machine tools to detect runout deviations of a spindle tool holder. Due to the presence of coolant and metal chips in the sensor's working area, the sensor must be of a robust design.

[0005] 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. Background Art

[0006] In industrial practice, it is known that sensors need to be protected from external agents, such as coolants or lubricants of various chemical compositions, which may affect the sensors or even prevent them from functioning properly. Typically, the protection function is provided by plastic plugs or resin coatings that encase sensitive components of the sensor, such as windings and ferromagnetic cores.

[0007] These materials do not ensure that their sealing properties are maintained over time: As a rule, both resins and plastics deteriorate with age and with continued exposure to coolants or other chemical agents and allow the passage of liquid or gaseous components. The use of glue, resin or plastic in the construction of measuring sensors can also have a negative impact on their performance, which can be affected by thermal drift.

[0008] It is also known to protect the sensor by using a metal housing, which however significantly alters the correct functioning of the sensor itself and often makes said solution unusable in practice.

[0009] 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 sensor sensitivity to drop sharply. In contrast, the patent proposes an advantageous inductive sensor in which a winding is embedded in one or more ceramic layers.

[0010] However, building such sensors requires specific standardization of production procedures, which significantly increases costs and greatly reduces design flexibility. Summary of the invention

[0011] 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 agents and a reduced and more controllable dependence on thermal drifts.

[0012] Said object is achieved by the claimed sensor, which is provided with a closing and protection assembly made of non-magnetic metal and surrounding the core and the windings contained therein. This allows the sensor to be very tightly sealed and resistant to external agents without significantly affecting its sensitivity. The closing and protection assembly is fixed to the core and / or the body of the sensor by welding.

[0013] The presence of a closing and protective assembly 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 susceptible to temperature variations and simplifying production procedures.

[0014] Preferably, the ferromagnetic core of the sensor consists of The use of a high permeability alloy allows the closure and protection assembly to be applied to the sensor by laser welding performed between the core and the closure and protection assembly. As an alternative to the use of a high permeability alloy, other nickel-iron or iron-silicon metal alloys may be used.

[0015] According to a preferred embodiment of the invention, the closing and protecting assembly has the form of a cover. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will now be described with reference to the accompanying drawings, which illustrate non-limiting examples of embodiments of the invention, in which:

[0017] Figure 1 is a schematic cross-sectional view of an inductive sensor according to the present invention;

[0018] Figure 2 is a graph comparing the inductance trends of an inductive sensor according to the present invention and an inductive sensor without a closure and protection assembly; and

[0019] Figure 3 is a schematic cross-sectional view of a portion of a measuring instrument comprising an alternative embodiment of an inductive sensor according to the invention. DETAILED DESCRIPTION

[0020] The inductive sensor for measuring size and / or distance according to the present invention is Figure 1 1 and denoted as a whole by reference numeral 10.

[0021] The sensor 10 comprises a body 4, wherein a ferromagnetic core 1 is fixed to the body 4. A winding 2 is housed in the core 1, more specifically, the winding 2 is arranged around at least a portion of said core.

[0022] Preferably, the core 1 is a pot-shaped core and the winding 2 is made of self-bonding copper.

[0023] The closing and protection component 3 made of non-magnetic metal is applied to the core 1 and / or the body 4 of the sensor 10 and is sealed and fixed by welding. The area of ​​the sensor 10 where the welding is performed is Figure 1 In the figure, it is roughly indicated by the reference symbol 5.

[0024] The closing and protection assembly 3 preferably has the form of a protective cover.

[0025] Furthermore, the closing and protection assembly 3 is rigid so as to ensure protection against shocks.

[0026] Preferably, an elastically deformable sealing assembly 6, such as an annular seal also called an O-ring, is arranged 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 assembly or protective cover 3.

[0027] Preferably, the sensor 10 is provided with an electronic circuit 7 connected to the winding 2 and via a cable to a processing unit of known type not visible in the figure.

[0028] According to a preferred embodiment, the closing and protection assembly 3 is made of non-magnetic steel.

[0029] According to a further preferred embodiment, the core 1 is made of a high permeability alloy and the closing and protection assembly is welded to the core 1 and / or the body 4 of the sensor 10 by laser welding.

[0030] The use of metal for the protective cover is facilitated by the use of a high permeability alloy as the material for the ferromagnetic core and by the use of laser welding.

[0031] However, different materials having similar properties to those described above may be used, such as a nickel-iron alloy for the core.

[0032] A very important difference between the present invention and the prior art is the use of non-magnetic metal to manufacture the closing and protective components of the sensor 10. This choice allows the sensor to be hermetically sealed and to be far more robust against chemical attack and influence, which is not possible using known techniques such as resin coating of the sensitive components of the sensor (i.e. the core and windings).

[0033] In order to compensate for any reduction in the sensitivity of the sensor 10 that may be involved in using metal materials to manufacture the closing and protective component 3, appropriate measures are taken during the design of the sensor 10, for example, measurements relating to the thickness of the closing and protective component 3 and to the electronic conditioning of the signal of the sensor 10, so as to maximize as much as possible the sensitivity of the sensor 10 as a whole.

[0034] More specifically, it is well known that the presence of metal between the sensor and the surface on which the measurement is performed (also referred to as the target) can lead to 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, it is usually desirable to avoid this situation.

[0035] In the sensor according to the invention, these disadvantages are overcome in the following manner.

[0036] First, the sensor 10 is conditioned by using a low frequency 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 alternating voltage with a frequency of 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 obtained measurement results are compared with the previously obtained map in order to provide a very accurate indication of the distance between the sensor and the target. Using low frequencies, eddy currents in a non-magnetic metal layer with a thickness of tens of millimeters are almost negligible. Low-frequency conditioning has a negative impact on the sensitivity of the system, albeit in an acceptable manner. However, by properly designing the geometry of the sensor, it is possible to optimize the sensor characteristics and compensate for the reduction in sensitivity. From this point of view, it is very advantageous to use a high-permeability alloy to manufacture the ferromagnetic core, because the high-permeability alloy is a material that is easy to machine and allows the use of machine tools to manufacture the ferromagnetic core with extremely high precision according to the preferred geometry.

[0037] 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 stiffness 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.

[0038] from Figure 2As can be seen in the graph shown, the variation of the inductance value of the sensor with the protective cover is very close to that of the sensor without the protective cover within the common operating range of both sensors. In other words, the graph shows the variation of the inductance as the distance between the target and the sensor changes, comparing a first profile (darker colored curve) associated with the sensor without the protective cover and a second profile (lighter colored curve) associated with the sensor with the protective cover. For a better understanding, in the second profile (lighter colored 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 data takes into account the fact that in the sensor with the protective cover there is a spatial deviation between the target and the sensor corresponding to the thickness of the protective cover. This deviation causes 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 functioning of the sensor and the performance of the required measurements.

[0039] The similarity between the two curves along the section where they are both present is obvious, apart from a small reduction in sensitivity due to the eddy currents, however small, generated in the metal of the cover itself, which can be seen in the variation of the inductance of the sensor fitted with the protective cover.

[0040] As mentioned above, the protective cover is fixed to the core 1 and / or body 4 of the sensor 10 by welding, without the use of 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.

[0041] 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 handling and waiting times.

[0042] In the sensor according to the invention, it is also possible to dispense with fixing core 1 to body 4 of sensor 10 : once welded, protective cap 3 already ensures that core 1 is positioned and fixed, without having to previously fix it (for example by bonding or welding) to the body of the sensor.

[0043] In summary, the main advantages provided by the inductive sensor according to the present invention compared to the use of an inductive sensor according to the prior art are as follows:

[0044] Resistant to shock and chemical agents,

[0045] Reduce thermal drift of sensors,

[0046] · Since there is no bonding / resin coating process, the manufacturing process is simplified.

[0047] Figure 1 A possible configuration of a sensor 10 according to the invention is shown, other configurations are possible.

[0048] For example, the sensor according to the invention can be used in comparators to check the form and / or internal or external dimensions of mechanical parts (such as plug gauges, caliper gauges or ring gauges), and in various types of measuring cells or measuring heads. In such applications, the use of the sensor according to the invention results in significant application advantages in terms of resistance to external agents.

[0049] Figure 3 A possible alternative embodiment is shown in which the sensor according to the invention is used in a comparator or measuring instrument for checking the shape and / or size of a mechanical part, for example for measuring an outer diameter.

[0050] Figure 1 and Figure 3 Components common to the illustrated embodiments are denoted by the same reference characters.

[0051] Figure 3 Only a part of the measuring instrument is 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 arm 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 arranged between the arms 12 of the armset 11.

[0052] Unlike a general pot-shaped sensor which is in the shape of a hollow cylinder made of ferromagnetic material, closed at the bottom, contains a winding inside and has only one sensing face opposite to the bottom, the sensor used in this embodiment has two sensing faces.

[0053] Figure 3 The sensor 10 shown actually comprises a ferromagnetic core 1 having two parts with different diameters, substantially concentric and mechanically separated from each other. More specifically, the core comprises an inner cylinder 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-bonding copper is housed between the two parts of the core, i.e. between the outer ring and the inner cylinder of the core 1.

[0054] Two closing and protective components 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; Figure 3 The welding area of ​​the sensor 10 is roughly indicated in FIG. 1 by the reference symbol 5 . Each open side of the core 1 is closed by one of the closing and protection components 3 .

[0055] Since there is no seat or other connection 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 properties.

[0056] Preferably, two elastically deformable sealing members 6 , such as annular seals, also called O-rings, are located between the winding and the internal surface of each protective cover 3 , so as to fix the position of the winding 2 in the thus assembled configuration.

[0057] A matching component 15 made of ferromagnetic material and having a substantially flat surface or plate is connected to each arm 12, arranged so that it faces one of the closing and protection components, namely one of the sensing sides of the core. More specifically, each sensing side of the core 1 faces the corresponding plate 15 and is arranged at a distance therefrom. During the inspection operation, due to the movement of the plate and the core towards or away from each other after the contact between the probe and the workpiece, the distance changes, causing the sensor to generate an electrical measurement signal 10.

[0058] Preferably, the core 1 and / or the matching component 15 are made of a high magnetic permeability alloy.

[0059] Furthermore, the welds that secure the protective cover to the core are laser welds.

[0060] According to an alternative embodiment, the protective cover 3 has a special geometry at the edge (not shown), such as an inclined surface, which facilitates the application of welding and correct fixing of the protective cover 3 during the production procedure.

[0061] 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, they may be made as one body.

Claims

1. An inductive sensor (10) for measuring size and / or distance, comprising: Ontology(4); a ferromagnetic core (1) fixed to the body (4); a winding (2) arranged around a portion of the core (1); as well as a closing and protection assembly (3) fixed to the core (1) and / or the body (4) of the inductive sensor so as to surround the core (1) and the winding (2); It is characterized in that The closing and protection component (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.

2. The inductive sensor (10) according to claim 1, characterized in that in, The ferromagnetic core (1) is made of a high magnetic permeability alloy.

3. The inductive sensor (10) according to claim 1 or claim 2, characterized in that: in, The closing and protection assembly (3) is made of non-magnetic steel.

4. The inductive sensor (10) according to any one of the preceding claims, characterized in that The closing and protecting assembly (3) is in the form of a cover.

5. The inductive sensor (10) according to any one of the preceding claims, characterized in that in, The closing and protection assembly (3) is fixed by laser welding.

6. The inductive sensor (10) according to any one of the preceding claims, characterized in that in, The inductive sensor (10) is conditioned by using a low frequency.

7. The inductive sensor (10) according to claim 6, characterized in that It is configured to be supplied with a sinusoidal alternating voltage with a frequency less than 50 kHz.

8. The inductive sensor (10) according to any one of the preceding claims, characterized in that The thickness of the closing and protecting component (3) is less than 0.5 mm.

9. The inductive sensor (10) according to any one of the preceding claims, characterized in that include: An elastically deformable sealing component (6) is arranged between the core (1) and the winding (2) and is configured to keep the winding (2) pressed against the inner surface of the closing and protection component (3).

10. The inductive sensor (10) according to any one of the preceding claims, wherein: The core (1) comprises two parts having different diameters, substantially concentric and mechanically separated from each other, and having two open sides; and The winding (2) is arranged between the two parts of the core (1); The inductive sensor (10) is characterized by comprising: Two closing and protection components (3) are fixed to the core (1) at the open sides of the core (1), each open side of the core (1) being closed by one of the closing and protection components (3).

11. A measuring instrument 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) configured to contact the mechanical member, and a fulcrum (13) configured to move the arm (12) relative to the support, It is characterized in that The measuring instrument comprises an inductive sensor (10) according to claim 10, which is arranged between the arms (12) of the robot arm set (11); and Each arm (12) is provided with a matching component (15) having a substantially flat surface, made of ferromagnetic material and arranged facing one of the closing and protection components (3).

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