PROXIMITY SENSOR

Description

[0001] The present invention relates to a proximity sensor according to the preamble of claim 1.

[0002] Inductively operating proximity sensors are known in the prior art. US Pat. No. 8,188,730 B2 discloses a coil system with two coils mounted in a ferrite core. US Pat. No. 5,952,822 A discloses a proximity sensor in which shielding of the two coils is proposed on one, two, or three sides by means of a flat element. Furthermore, WO 2016 / 037597 A1 discloses an electrically conductive shielding of the coils of a proximity sensor, in which a shielding cup is provided that surrounds the coil arrangement laterally and on the rear side, with the shielding cup merging into an upper flange. Finally, a design of a proximity sensor has also become known from DE 10 057 773 A1, in which, in order to expand the proximity field, the secondary coils are divided into several partial coils arranged in the same plane, wherein the shielding of the primary coil is located symmetrically between the secondary coils.Proximity sensors are known from DE 2 356 783 A1 and DE 10 2012 214 330 B3.

[0003] Overall, there is still room for improvement regarding the detection and switching distance of proximity sensors, while simultaneously achieving a very compact and economical design. In particular, it is a recurring problem that the installation situation of a proximity sensor, due to the use of metallic fastening or cover elements, leads to partial shielding and thus to a change in the switching properties of the sensor. Therefore, the object of the present invention is to propose a proximity sensor that has an increased switching distance, improved installation properties, and a simple design.

[0004] The primary or transmitting coil and the at least one secondary coil are slightly spaced apart from one another in the direction of the axis. Ideally, in the case of wound coils, these are guided in grooves or depressions or arranged at a defined distance from one another by circumferential webs. The coil carrier has an end face and a base face, with the end face of the coil carrier directly opposite and / or resting against the inner surface of the front cap. Ideally, the end face of the coil carrier is connected, welded, or glued to the front cap. The first secondary coil is arranged closer to the end face or directly adjacent to it in the axial direction, while the primary coil is arranged closer to the base end.

[0005] The coil carrier is made of a non-conductive material with a low coefficient of expansion across the temperature range. In particular, the coil carrier is made of a glass-fiber-reinforced plastic and / or an epoxy resin.

[0006] The core of the invention is that a second secondary coil is provided on the coil carrier, which is wound or wound in opposite directions, and wherein the primary coil is arranged between the two secondary coils. Furthermore, a metallic shielding element is arranged at least in the axial region of the second secondary coil and enclosing it, and no metallic shielding element is provided in the axial region of the first secondary coil, which directly borders the end face or a closure cap.

[0007] Here, axis or axial direction refers to the theoretical, central (symmetry) axis, which is defined by the (printed) turns or windings of the coils and / or the geometry of the coil carrier.

[0008] In an advantageous embodiment, the metallic shielding element has a width that corresponds to at least a quarter of the height between the second secondary coil and the inner surface of the front cap; ideally, the width corresponds to at least half the height. The shielding element thus extends significantly beyond the second secondary coil in the axial direction without protruding into the detection area of ​​the first secondary coil, thereby achieving optimal switching properties.

[0009] An advantageous ratio between the height of the coil structure and the width of the shielding element is achieved when the width corresponds to 30% to 50% of the height of the coil structure.

[0010] A further improvement is that the shielding element has a width such that the primary coil is at least partially shielded in the axial direction, in particular completely shielded. Depending on the desired switching characteristics, an improvement is achieved if the width of the shielding element is greater than the outer distance between the coils and / or only projects beyond the respective coil edge in the axial direction toward the first secondary coil. In particular, the shielding element should not project into the axial area of ​​the front, first secondary coil, so as not to adversely limit its detection radius.

[0011] This partially shields the coils of the wound or printed multi-coil system of the inductive proximity sensor by shielding at least one of the coils used for signal generation and / or evaluation. This allows the proximity sensor to be mounted and installed flush with a metallic environment, even with a high, non-flush switching distance. The surrounding shielding simulates a typical installation condition, so that the behavior of the proximity sensor in a "worst-case" installation situation is already simulated during production and can be measured in the laboratory.

[0012] This design ensures that the internal partial shielding of the multiple coil system is precisely positioned at the optimal axial position relative to the individual coils by the spacer. Thus, with the selected optimal coil diameter, the resulting differential voltage is zeroed at the set switching point. Influences from metallic elements in the installation situation are thus largely eliminated, and a high switching distance is achieved.

[0013] The advantage is that the first secondary coil can be positioned in the immediate, maximum proximity to the detection zone, allowing a wide radius to be monitored and detected, while the influences from and on the second secondary coil and, if applicable, the primary coil are kept as low as possible. This achieves very high detection precision and immunity to external interference.

[0014] An improved embodiment involves applying the shielding element to the inner wall of the housing surrounding the second secondary coil or the pair of the second secondary coil and the primary coil and / or the surrounding inner wall of the cap, at least in sections, so that one and the same housing and shielding element can be provided to the greatest extent possible even for different coil diameters, which are dimensioned depending on the respective detection tasks. It is advantageous to provide the maximum possible distance between the shielding element and, in particular, the second secondary coil, for example, by having it rest against the inner wall of the housing or the front cap, whereby the diameter of the second secondary coil should be 60% to 70% of the diameter of the shielding element.

[0015] In an improved variant, at least one non-metallic, single- or multi-part spacer is arranged between the inner surface of the front cap and the shielding element, on which the shielding element rests at least partially and / or by which it is supported. This allows for the production of very easy-to-install and cost-effective variants of proximity sensors with different coil arrangements, in which the precise shielding of the primary coil can be very easily adjusted. Ideally, the spacer is a ring or rim, which is advantageously made monolithically from plastic.

[0016] An advantageous embodiment consists in the coil carrier being ring-shaped and thus having a free core and an inner wall. In this case, ring-shaped means any elongated hollow shape, as well as a piece of pipe with any cross-section, which is ideally round. The ring thickness in the circumferential direction and / or axial direction can vary. The core of this embodiment is a carrier element to which the circuit board is directly or indirectly attached. The carrier element has a guide and holding section with which it rests against the inner wall of the coil carrier and / or via which it is attached. In this way, a very compact and stable design is created, with a very good connection between the coil carrier and the circuit board or the processing and receiving unit.In particular, it can be easily pre-assembled and accessible from all sides and then inserted into the housing and / or onto the front cap.

[0017] A further improvement is that the circuit board is connected to or has a connector element via which the proximity sensor can be connected to external structures for data and / or power transmission. Such external structures are typically data and / or power cables leading to components of a network, in particular an Ethernet, a BUS system, I / O link, or the like. Advantageously, the connector element has a group of two or more adjacently arranged individual connectors, with the individual connectors ideally aligned parallel to the axis.

[0018] The connection between the circuit board and the coil carrier of the proximity sensor can be further improved if the plug element rests at least partially on the base surface of the coil carrier, thereby bridging the annular coil carrier, and / or the plug element rests on or is fastened to a web element of the carrier element, and this web element rests at least partially on the base surface of the coil carrier, partially bridging the annular coil carrier. The advantage of this design is a very stable support for the plug element while requiring the smallest possible installation space. The force required when attaching a connecting mating connector can be diverted to the front cap in a straight line, which greatly simplifies assembly.

[0019] Further details and advantages of the invention will now be explained in more detail with reference to embodiments shown in the drawings.

[0020] They show: Fig. 1a proximity sensor as a vertical sectional view, Fig. 2the proximity sensor from Figure 2 as a horizontal sectional view, Fig. 3 an exploded view of the sensor according to Figure 1 and 2 , Fig. 4 a vertical sectional view of another proximity sensor with three coils, Fig. 5 a vertical sectional view of another proximity sensor with printed secondary coils and a wound primary coil and Fig. 6 a vertical sectional view of another embodiment of a proximity sensor with three printed coils.

[0021] The Figure 1The proximity sensor 1 shown is oriented vertically downwards. The housing 2, sketched as a dashed line, has a front cap 3 at its lower end, on which the coil carrier 6 is centrally mounted. The coil carrier 6, with its end face 6.1, lies plane-parallel to the inner surface 3.1 of the front cap 3 and is glued, or is fastened in a form-fitting and / or force-fitting manner not shown. At least one upper, first secondary coil 8a and a second, lower secondary coil 8b are arranged in parallel grooves or slots of the coil carrier 6. A primary coil 7 (transmitting coil) is inserted between these two secondary coils 8a, b, which have oppositely oriented windings. The positional information with respect to gravity, such as in particular "top" or "bottom," is not to be understood as limiting and serves only to clarify the respective illustration.It is understood that the proximity sensor 1 can have any orientation, such as horizontal to the side, tilted, upwards or downwards, so that the information given herein is then to be understood analogously.

[0022] The coil carrier 6 is monolithic, designed as a ring or rim, and extends in the direction of the (symmetry) axis A, around which the secondary coils 8a, b and the primary coil 7 are also arranged concentrically. The coil carrier 6 is optimized with regard to the required coil diameters and, for this purpose, has sections with different free inner diameters in the axial direction A, so that the inner surface 6.2 has different rings or ring contours. Circumferential grooves or slots of varying depths are arranged on the outer side, in which, among other things, the primary coil 7 and the secondary coils 8a, b are mounted or inserted. The mode of operation and interaction of the excited coils when detecting an object 50 that appears in front of the free side of the proximity sensor 1 is basically known to those skilled in the art and will therefore not be described in more detail.

[0023] A connector element 9 is placed on the base surface 6.3 of the coil carrier 6, the individual connectors of which are aligned parallel to the axial direction A, so that no additional installation space is consumed and vertical forces are diverted via the coil carrier 6 to the front cap 3. This connector element 9, soldered to a printed circuit board 4, can be connected to an external control and evaluation unit 100. Control and evaluation unit 100 is understood to mean any external component and / or network to which the proximity sensor 1 can be connected for power and / or data transmission.

[0024] The shielding element 10 made of copper has a width B and is arranged enclosingly at the level of the primary coil 7 and the lower, second secondary coil 8b by being placed on a spacer body 11 designed as a plastic ring. In the embodiment shown, the Figures 1 to 4, the ratio between the width B of the shielding element and the height H of the coil structure is 45%, furthermore the diameter of the shielding ring 10 is 1 / 3 larger than the diameter of the second secondary coil 8b. Figure 2 shows proximity sensor 1 to Figure 1 as a vertical sectional view. It can be seen that the shielding element 10 is designed as a square frame, which rests against the inner wall 3.2 of the front cap 3 surrounding the coil carrier 6 and is held in the required axial position by the round spacer 11. The printed circuit board 4 is oriented lengthwise in the direction of axis A and is placed on the base surface 6.3 via the soldered connector element 9. In addition, the printed circuit board 4 is inserted and held in lateral guides 13, which are parts of the front cap 3. The compact design and good accessibility of the connector element 9 when the housing 2 is open are clearly visible.

[0025] Figure 3shows the proximity sensor 1 according to the Figures 1 and 2 as an exploded view, so the previous explanations apply analogously. In the illustration according to Figure 3It can be seen that a carrier element 12 is provided which has a guide and holding section 12.1 at the lower end and an upper end which is designed as a web element 12.2. The plug element 9 with the six individual plugs is attached to the web element 12.2, which rests on the base surface 6.3 of the coil carrier 6 and partially bridges the free core. The guide and holding section 12.1 of the carrier element 12 projects in the axial direction into the core of the coil carrier 6 and rests on its inner surface 6.2. In a variant not shown, the web element 12.2 and / or the guide and holding section 12.1 is locked and / or glued to the coil carrier 6. On the circuit board 4, two (micro-)electronic components 14 are indicated, which can be, for example, a µ-controller, a memory module, an ADC (analog-to-digital converter) or the like.

[0026] Fig. 4shows a coil carrier on which the two secondary coils 8a, b are arranged, which have opposite winding directions. The width B of the shielding element 10 is such that the primary coil 7 and the second secondary coil 8b are framed and shielded together, with the spacer element 11 made of a non-shielding plastic being arranged only in the area of ​​the first secondary coil 8a.

[0027] In the embodiment according to Figure 5The first secondary coil 8a is a printed coil that is part of a first circuit board 15 attached to the end face 6.1 of the coil carrier 6. The second secondary coil 8b is printed in a similar manner, as part of a second circuit board 16 attached to the base surface 6.3. The circuit boards 15, 16 have positioning holes 15.1, 16.1 into which receiving elements 6.4 of the central coil carrier 6 are inserted and secured. In the illustrated embodiment, the primary coil 7 is wound in grooves on the central coil carrier 6. The width of the shielding element 10 covers the second circuit board 16 with the printed, second secondary coil 8b and the wound primary coil 7 in the axial direction A.

[0028] The positioning holes 15.1, 16.1 in the printed circuit boards 15, 16 can have any suitable geometry, in particular also be designed as grooves or slots, wherein the respective receiving element 6.4 has a corresponding, complementary geometry. In the embodiments according to the Figures 5 and 6 the front cap 3 has a centering element 3.4, which is inserted in a form-fitting manner into a complementary receiving opening of both the head-side first circuit board 15 and the coil carrier 6 and is glued or fastened if necessary.

[0029] The Figure 6 shows a vertical sectional view of another embodiment of a proximity sensor 1 with three printed coils 7, 8a, 8b. Here, the first secondary coil 8a and the primary coil 7 are arranged on a common printed circuit board 15 on the respective opposite surfaces, which are analogous to the embodiment of the Figure 5rests on the inner surface 3.1 of the front cap 3 and is penetrated and held by a central receiving element 3.4. The coil carrier 6 comprises the spacer body 11, which is monolithically designed as a circumferential ring, edge, or a plurality of support bolts, and on whose upper edge the circumferential shielding element 10 is mounted. The second printed circuit board 16, on which the second secondary coil 8b is printed, has a central positioning bore 16.1, into which a central receiving element 6.4 of the coil carrier 6 is inserted. In both embodiments according to Figure 5 and 6 the width B is 50% of the height H. List of reference symbols

[0030] 1 Proximity sensor 2 Housing 3 Front cap 3.1 Surface 3.2 Inner wall 3.3 Centering element 4 Printed circuit board 5 Process and receiving unit 6 Coil carrier 6.1 End face 6.2 Inner surface 6.3 Base surface 6.4 Receptacle element 7 Primary coil (transmitting coil) 8a Secondary coil, first 8b Secondary coil, second 9 Plug element 10 Shielding element 11 Spacer body 12 Carrier element 12.1 Guide and holding section 12.2 Web element 13 Guide groove 14 Component, (micro-)electronic 15 Printed circuit board, first 15.1 Positioning hole 16 Printed circuit board, second 16.1 Positioning hole 50 Object 100 Control and / or evaluation unit A Axis B Width H Height

Claims

1. Proximity sensor (1) for inductive detection of objects (50), comprising - a housing (2) having a front cap (3) which forms the detection side of the proximity sensor (1), - a processing and receiving unit (5) which comprises a printed circuit board (4) and which can be connected to an external control and / or evaluation unit (100), - wherein a single-part or multi-part coil carrier (6) is provided, on which at least one primary coil (7) and at least one first secondary coil (8a) are arranged circumferentially wound or pressed and spaced apart in the direction of the axis (A), wherein an end surface (6.1) of the coil carrier (6) of the inner surface (3.1) of the front cap (3) is directly opposite and / or abuts against it, and the first secondary coil (8a) in the axial direction is closer to the end surface (6.1) than the primary coil (7), wherein a second secondary coil (8b) is provided on the coil carrier (6), which is wound in the opposite direction to the first secondary coil (8a), wherein the primary coil (7) is arranged between the two secondary coils (8a, b), wherein a metallic shielding element (10) is arranged in such a way that it encloses the second secondary coil (8b), and wherein the shielding element (10) does not extend into the axial area of the first secondary coil (8a) in order not to restrict its detection radius.

2. Proximity sensor (1) according to Claim 1, characterized in that the shielding element (10) has a width such that the primary coil (7) is also at least partially shielded, in particular is completely shielded, in the axial direction.

3. Proximity sensor (1) according to either one of Claims 1 and 2, characterized in that the width (B) of the shielding element (10) in the axial direction (A) on the front cap (3) is at least factor 0.25 of the height (H), wherein the height (H) is formed by the distance of the second secondary coil (8b) from the inner surface (3.1) of the front cap (3), the width (B) is ideally in the range of factor 0.3 to 0.5 of the height (H).

4. Proximity sensor (1) according to any one of the preceding claims, characterized in that the shielding element (10) bears at least in sections on the - inner wall (2.1) of the housing (2) and / or - inner cap wall (3.2) surrounding the second secondary coil (8b) or the pair consisting of second secondary coil (8b) and primary coil (7).

5. Proximity sensor (1) according to any one of the preceding claims, characterized in that the shielding ring (10) bears on the inside of the front cap (3), and wherein the diameter of the second secondary coil (8b) is a factor of 0.6 to 0.7 of the diameter of the shielding element (10).

6. Proximity sensor (1) according to any one of the preceding claims, characterized in that at least one non-metallic, single-part or multi-part spacer body (11) is arranged between the inner surface (3.1) of the front cap (3) and the shielding element (10), wherein the shielding element (10) rests on this spacer body (11) at least in sections and / or is carried thereby.

7. Proximity sensor (1) according to any one of the preceding claims, characterized in that the spacer body is a ring or an annulus, in particular a plastic ring or annulus.

8. Proximity sensor (1) according to any one of the preceding claims, characterized in that that the coil carrier (6) is annular and has an inner wall (6.2), wherein a carrier element (12) is provided, to which the printed circuit board (4) is attached, and the carrier element (12) bears by way of a guiding and holding portion (12.1) against the inner wall (6.2) of the coil carrier (6) and / or is attached thereto.

9. Proximity sensor (1) according to any one of the preceding claims, characterized in that the printed circuit board (4) is connected to a plug element (9) or comprises a plug element (9), via which the proximity sensor (1) can be connected to external structures so as to conduct data and / or current.

10. Proximity sensor (1) according to Claim 9, characterized in that the plug element (9) comprises a group of two or more individual plugs (9.1 ... 9.n) arranged next to one another, wherein the individual plugs (9.1 ... 9.n) are oriented parallel to the axis (A).

11. Proximity sensor (1) according to any one of Claims 9 and 10, characterized in that - the plug element (9) bears at least in sections on the foot surface (6.3) opposite to the end surface (6.1) of the coil carrier (6) and bypasses the annular coil carrier (6), or - the plug element (9) bears on or is attached to a web element (12.2) of the carrier element (12), which web element bears at least in sections on the foot surface (6.1) of the coil carrier (6) and bypasses the annular coil carrier (6).