MINIATURIZED INDUCTIVE PROXIMITY SENSOR AND METHOD FOR DETECTING A SENSING BODY

Description

[0001] The present invention relates to an inductive proximity sensor according to the preamble of claim 1 and a detection method according to the preamble of claim 12.

[0002] Inductive proximity sensors are known in the prior art. One such arrangement is shown, for example, in DE 10 2006 053 023 A1, which proposes a planar transmitting coil arrangement with a transmitting coil generating an alternating magnetic field. Furthermore, DE 10 2006 053 023 A1 proposes providing the coil windings in a printed manner on a carrier board. The shared compensation coil and the external field and its field lines generated by it compensate for the field lines of the transmitting coil in the surrounding area, so that the overall flux in the surrounding area can be brought to zero or essentially zero. According to DE 10 2006 053 023 A1, the receiving coil is arranged between the transmitting coil and the compensating transmitting coil.

[0003] US 2017 / 302273 A1 discloses a sensor element for an inductive distance sensor. US 2017 / 345548 A1 describes a stacked coil for a wireless charging structure.

[0004] It has been found that such coils can only be miniaturized to a very limited extent because the disturbing influences, for example from line paths or adjacent contact points, become disproportionately large.

[0005] It is the object of the present invention to propose an improved design for very small inductive proximity sensors which avoids the aforementioned disadvantages.

[0006] This object is achieved according to the invention by a miniaturized, inductive proximity switch according to the features of claim 1 and a detection method according to the features of claim 11. Advantageous embodiments are specified in the respective associated subclaims.

[0007] According to this, the problem is solved by an inductive proximity sensor for detecting a sensing body, comprising two receiving coils and one transmitting coil, each formed from a group of at least two individual coils on carrier boards, which are aligned parallel to one another and arranged axially offset as a stack along a common sensor axis, wherein the transmitting coil is arranged between the two receiving coils, and wherein the carrier boards of the individual coils have a diameter of less than or equal to 10 mm. The winding of the receiving coil and / or transmitting coil has a cross-sectional geometry in which the ratio of height to base width is in the range of 0.2 to 0.3, ideally between 0.23 and 0.27.

[0008] The coil arrangement is excited by an oscillator and / or a generator to an oscillating alternating field; in particular, the circuit is designed in such a way that a self-exciting alternating field oscillating at resonant frequency is formed.

[0009] Advantageously, the height of the winding does not exceed 0.05mm, in particular it is a maximum of 0.04mm.

[0010] In state-of-the-art coil systems, windings are printed with a base width of approximately 0.14 mm and a height above the carrier board of 0.014 mm. It has been found that it is advantageous not to reduce the cross-section linearly, based on the cross-sections known in the prior art, but to provide a proportionally larger height. This prevents excessive ohmic resistance in the respective coils and allows for tighter windings.

[0011] In the following, the terms "single coil" and "carrier board" (with a turn of a single coil attached there) are used synonymously unless explicitly stated otherwise.

[0012] An improved embodiment provides that the number of turns of at least one individual coil of the receiving coils is equal to or greater than 3, ideally 4 or 5, in particular all individual coils of the receiving coils are equal to or greater than 3, ideally 4 or 5. Not surprisingly, it has been shown that this represents an optimum for building up sufficient inductance with very limited occupancy areas. Furthermore, a further improved embodiment consists in that the number of turns of at least one individual coil of the transmitting coil is equal to or greater than 3, ideally 3 or 4, in particular all individual coils of the receiving coils are equal to or greater than 3, ideally 3 or 4.

[0013] Here, the number of turns is not to be understood as an even number of absolute 360° revolutions; rather, a number of turns X means x times the revolution of 360° plus a portion of 360°. In other words, for example, the number of turns "4" also includes absolute turns / revolution numbers of 4.25 or 4.5, but no longer means the number of turns / revolutions "5."

[0014] Advantageously, the stack formed from individual coils and carrier boards is arranged symmetrically to a central plane of symmetry arranged vertically to the sensor axis, whereby a central individual coil of the transmitting coil can be located in the plane of symmetry. In this case, a mechanical-structural plane of symmetry can be arranged somewhat differently in terms of its axial position than a parallel, electrical plane of symmetry, which can be formed by an individual coil. This difference can be compensated by adjusting the differential voltage using parallel-connected, particularly adjustable, resistors.

[0015] Advantageously, the circuit also includes or is connected to a measuring and control circuit, by means of which a resistance to ground can be coupled via at least one individual coil, in particular the one adjacent to or opposite the end plate, to compensate for phase shifts in particular. The measuring and control circuit advantageously includes a potentiometer. In this way, manufacturing tolerances and material influences, particularly in the conductor paths and coils, can be compensated for in order to ensure the zero difference of the induced voltages in the receiving coils during normal operation. The integration of only the terminal individual coil of the receiving coil, opposite the end plate, has the great advantage that the short conductor paths, which primarily run strictly parallel to the stack axis, have no or only very minimal influence on the magnetic field.

[0016] In this case, a particularly well-regulated and controllable embodiment consists in the fact that the transmitting coil has a number of n individual coils and the two receiving coils together have a number of at least n+1 individual coils.

[0017] Here, the term "plane" is not to be understood in the mathematical sense as a purely two-dimensional structure, but can also be a very flat, theoretical space or corridor that encompasses and / or accommodates the respective elements.

[0018] To further reduce space, it is advantageous if at least one of the carrier boards is designed as a double carrier board, which has a single coil or the coil windings on both surface sides. Advantageously, the at least one carrier board designed as a double carrier board is designed as a single coil of the receiving coil on one side and as a single coil of the transmitting coil on the other surface side.

[0019] A header board is provided that serves as an interface with connection pads, in particular exactly four connection pads, for the electrically conductive connection to a circuit comprising an oscillator and / or generator, and which does not have a (single) coil. In a further improved embodiment, the header board can have additional connection or contact pads for one or more measuring points and / or a measuring and control circuit into which at least one individual coil, in particular the individual coil adjacent to the header board, is integrated.

[0020] Because the negative influence of all metallic surfaces and conductors (tracks) on the magnetic field increases significantly with the increasing miniaturization of inductive sensors and individual coils, ideally no individual coils are designed to converge conductors or conducting paths outside of the direct connection to neighboring or associated individual coils. Only the header board has metallic connection pads for connecting to the circuitry encompassing the oscillator, and only the header board accommodates multiple conductors or tracks from different (individual) coils. "Multiple" here means that more than just two adjacent or correlating individual coils are conductively connected.

[0021] Therefore, no conductor paths running transversely to the coil axis are provided on each individual coil, particularly on the outer individual coils of the receiving coil, for forwarding or connecting purposes. In particular, the connections between two individual coils are always made by a connecting line or through-hole parallel to the coil axis. For this purpose, the carrier boards advantageously have a plurality of holes or through-holes that are aligned along the coil axis and, in particular, together form a type of channel or shaft for the conductor paths running across multiple boards. Electrical conductors are routed through some of the aligned holes or shafts, or the holes or shafts are filled with an electrically conductive material.Advantageously, at least four of the slots extend into the header board designed as an interface and end directly at a connection pad or are connected to one of the connection pads on the back, i.e. on the side facing away from the board stack, via a conductor track.

[0022] The hole on the side of the carrier board on which a (single) coil to be connected is located serves as a soldering and connection point, or is designed as such. The respective individual coil is connected in a known manner via a conductor track to the conductor routed parallel to the stack axis in the holes or the shaft.

[0023] The head circuit board advantageously has exactly four connection pads, two connection pads each for the supply and discharge of the series-connected receiving coils and two connection pads each for the supply and discharge of the transmitting coil. As explained above, additional connection pads can be provided for measuring points and / or at least one measuring and control circuit. Forming a self-exciting system is particularly advantageous in terms of energy. A particularly advantageous embodiment provides for only one oscillator without an (active) generator. An LC resonator is formed via the transmitting coil, which acts as an inductor, and a parallel capacitor. This LC resonator is connected in series with the amplifier and the sensor coils or the associated compensation coils to form an LC oscillator, whereby an alternating field can be generated. This alternating field is, in particular, a self-exciting alternating field oscillating at a resonant frequency.

[0024] The invention further encompasses a method for detecting a sensing body using an inductive proximity sensor having an outer diameter of less than or equal to 10 mm and configured according to one of the aforementioned embodiments. The proximity sensor comprises a header board that serves as an interface with connection pads for connection to a circuit comprising a generator and / or oscillator and that does not have a coil.

[0025] Further details and advantages of the invention will now be explained in more detail with reference to an embodiment shown in the drawings.

[0026] They show: Fig. 1 shows the proximity sensor with a single coil and the associated circuitry, Fig. 2 shows a single carrier board, Fig. 3 shows a coil stack in a sectional view, Fig. 4 shows the individual coils of a coil stack as a top view, and Fig. 5 shows a head board in top view.

[0027] Fig. 1 shows a schematic structure of the proximity sensor 1, which is constructed from three groups of individual coils. These are two receiving coils 2, between which a transmitting coil 3 is arranged. This inductive proximity sensor 1 is used to detect a metallic object 50 and comprises a housing 11, which generally has a cylindrical or square base. As shown in the Figure 1As can be seen, the proximity sensor 1 is connected to a circuit 21 and a self-exciting alternating field is generated by an oscillator 9 via a transmitting coil 3, which, as an inductance, together with a capacitor 17, forms an LC resonant circuit of the oscillator 9. A typical oscillation signal is in the range of 3 - 10 MHz. The two counter-wound receiving coils 2 are arranged in a direct differential circuit. The resulting differential alternating voltage of the two receiving coils 2 is supplied to the input of the amplifier 9 and detected by the voltmeter 8. The receiving coils 2 are designed by their spatial position on the two mutually parallel planes and the respective number of turns such that the differential alternating voltage UD becomes zero when a trigger approaches the desired response distance, whereby the changes in the oscillation states are detected in a manner not shown and converted into a switching signal.Such circuits are generally known to those skilled in the art, for example, from DE 44 29 314 B4 or DE 40 31 252 C1. The design of such circuits for different operating modes for material-dependent detection (metallic, non-metallic) of different objects 50 is also known to those skilled in the art, for example, from the aforementioned DE 44 29 314 B4.

[0028] In the present example, a measuring and control unit 51 is provided, which comprises a potentiometer and, in a manner not shown in detail, integrates a single coil of the front receiving coil 2 into the measuring and control circuit 52, so that a phase shift between the two receiving coils with opposite current flow can be compensated. This is achieved by controlling corresponding resistors, in particular ohmic resistors.

[0029] The special feature is that the individual windings 2.1, 3.1 have a cross-sectional geometry with a ratio of height H to the base width B of the individual winding of 0.25. In the present example, the base width is 0.14 mm and the height is 0.035 mm. Such conductor track structures are applied using a printing process. The carrier board 4 is made of a non-conductive material, such as a PCB material. In the example shown, the diameter D of the carrier board is 8 mm and it has a height X of 0.068 mm.

[0030] As shown in the detailed drawing below, the innermost winding 2.1, 3.1 is connected to an inner conductor track 13 provided on the surface and in the bore 22, so that the soldering and connection point 15 is formed on the surface. The outer end of the winding 2.1, 3.1 is also connected to a soldering and connection point 15 and an outer conductor track in the example shown, which continues in a bore or via (not shown) leading upwards to be connected to the individual coil above it (not shown). It is understood that spatial specifications such as "above" or "below" are not to be understood as limiting and are to be understood analogously depending on the overall orientation of the proximity sensor. Outer and inner conductor tracks refer to their radial positions relative to the respective individual coil or its windings.

[0031] In the Figure 21 shows a plan view of a single carrier board 4 of an individual coil 2.1 of the receiving coil 2. Of the seven holes 22 or vias in the carrier board 4, which can be provided for all carrier boards 4 of the sensor stack 20, only one is used for supplying this carrier board 4, so that it is designed on the surface as a soldering and connection point 15 and is in conductive connection with an outer conductor track 14 and the winding of the individual coil 2.1. The other six holes 22 serve as conductor tracks parallel to the stack axis 20 for connecting other individual coils or remain without function. The opposing flattened areas 4.2 serve to stabilize the position and as an insertion aid, whereby alternatively other geometries such as grooves, edges or guide fingers can also be provided, which interact in a form-fitting manner with a housing or support and guide element (not shown).

[0032] The Figure 3Sensor stack 20, shown in a sectional view, illustrates the avoidance of metallic surfaces and elements on the surfaces of carrier plates 4 and individual coils designed as double carrier plates 4.1. Layers L1 to L3 are part of or form the first receiver coil 2, and layers L9 to L11 form the second receiver coil 2. The transmitter coil 3, which comprises layers L4 to L8, is arranged in between. The layers are defined by the individual coils. Dielectrics are arranged between the individual coils, which either represent carrier plates 4 carrying a single coil, or double carrier plates 4.1 with individual coils on both sides. Furthermore, to create a strictly symmetrical structure, dielectrics are also provided as pure spacer elements 16, on whose surface no individual coil is applied.The layer 12 does not have a coil, but is essentially formed by the connection pads 7, soldering and connection points 15 and transverse conductor tracks located there, which are used for the connection to the circuitry 21 (not shown) and / or the measuring and control section 52 (. Fig. 1 ). The respective correlating individual coils 2.1, 3.1 are each grouped together with a curly bracket. The individual coil of layer 6 forms the electrical symmetry plane 30 in this case, with the structural-mechanical symmetry plane 30, shown as a dot-dash line, being formed by the middle plane between layers L1 and L12 and located between layers L6 and L7. An end plate 18 is provided at each end of the stack 20.

[0033] In the present example, the structural-mechanical symmetry axis of the boards is determined by the mechanical design and is 0.822 mm high. For the functionality and tunability of the coil system to an induced differential voltage at the desired switching point of 0 mV, the number of layers and total number of turns for the receiving coils L2 and L3 must ideally be identical or nearly identical, and the distances between the transmitting coil 3 and the two receiving coils 2 must be identical or nearly identical.

[0034] A certain difference can be compensated by adjusting the differential voltage using resistors connected in parallel, ideally designed as adjustable resistors or integrated into a control loop. This allows a defined output state to be imposed on the proximity sensor.

[0035] The part, or rather the individual coil, of the transmitting coil 3, which is laid out in position L6, forms the "electrical" plane of symmetry.

[0036] As in the Figure 3 and especially in Figure 4 As can be clearly seen, no transverse connection or coupling is routed on any carrier board 4 outside of the direct line connection to the respective individual coil 2.1, 3.1. The outer conductor track 14 shown on the left, which is routed through holes 22 to the stack axis 20, serves to connect to an external supply and is routed through the dielectric of the header board 5 to its rear. Only there is it connected to the connection pad 7, which is usually done by soldering. The connection from the header board 5 to the individual coil is made in a similar manner on layer L11.

[0037] Furthermore, in the example shown, the carrier board 4.1 for layers L3 and L4 is designed to have a dual function, in that the individual coil of layer L3 functionally belongs to the first receiving coil 2, and the lower individual coil of layer L4 functionally belongs to the transmitting coil 3. The continuous bore 22 or via connects 10 of the 11 layers and is a line connection that serves only for the purpose of measurement and provides access to a measuring point (not shown).

[0038] Figure 4 shows in detail the conductive connection 14.1 between the individual coils and also to the header board 5 and its connection pad 7.1. The flattened portions 4.2 on both sides serve to stabilize the position and as an insertion aid. The individual coils shown in plan view correlate with the layers L1 to L11, or layer L12 of the header board 5, as shown in the Figure 3indicated. From the connection pad 7.1, the outer conductor track 14.1 runs to the individual coil of layer L1 and is then guided via the conductor tracks 13.1, 14.2 and the individual coils of layers L2, L3 via a conductor track to the individual coil of layer L9 and, after passing through the individual coils of layers L10, L11 and via the conductor tracks 13.3, 14.5 and 13.4, back to a soldering and connection point which is connected to the connection pad 7.2 of the header board 5. The transmitting coil 3 is connected to the individual coil on layer L4 via the outer conductor track 14.3 to the connection pad 7.3 of the header board 5 and the return takes place after analogous conduction through the individual coils and conductor tracks from the individual board / coil of layer L8 via the outer conductor track 14.4 to the connection pad 7.7. For reasons of space, the soldering and connection points on the header board 5 are partly outside the actual connection pads, as can be seen for the connection pads 7.2, 7.4.

[0039] In an embodiment not shown, a measuring and control system is provided, as in Figure 1 sketched, into which the individual coil is integrated on the lowest layer L11. Furthermore, at least one measuring point is arranged, for example, in conductor track 13.2 or the outer conductor track 14.2, which interacts with the measuring and control system or is encompassed by it. This allows tolerances, for example, in the structure, the conductor tracks, or the coils that influence the differential voltage and phase position to be compensated.

[0040] In this case, the left receiving coil 2 and the middle transmitting coil 3 carry the same current direction, namely counterclockwise in the direction indicated by the arrows. The right receiving coil 2 carries the opposite current direction, clockwise in the example shown. Due to the oscillation, the current directions naturally alternate regularly.

[0041] In the Figure 5a) and 5b ) two head boards 5 are shown. The head board of the Figure 5a has two flattened portions 5.1, similar to the flattened portions 4.2 of the individual circuit boards 4, to ensure a defined alignment, guidance and position in a housing 11. The larger diameter D1 = 8 mm and the width at the flattened areas D2 = 7.5 mm. The smaller of the two head circuit boards 5 of the Figure 5b has a diameter D1 of 5.5 mm and a width at the flattened points D2 of 5.0 mm.

[0042] In these sensor dimensions, the switching distance is approximately 4 mm with a carrier board diameter D1 of 8 mm, with a diameter D1 of 5.5 mm the switching distance is approximately 2 mm and with a diameter D1 of 3 mm the switching distance is approximately 1 mm.

[0043] In an embodiment not shown, a generator is additionally provided that excites the oscillator 9, consisting of the transmitting coil 3 and the capacitor 17, at its resonant frequency. Alternatively, if the capacitor 17 is omitted, an additional generator can excite the transmitting coil 3 at any desired frequency. List of reference symbols

[0044] 1 Proximity switch 2 Receiver coil 2.1 Single coil 3 Transmitter coil 3.1 Single coil 4 Carrier board 4.1 Double carrier board 4.2 Flattening 5 Head board 5.1 Flattening 6 Voltmeter 7 Connection pad 8 Voltmeter 9 Oscillator 10 Amplifier 11 Housing 12 Measuring point 13 Holes 14 Conductor track (also 14.1 ... 14.n) 15 Soldering and connection point 15.1 Conductor track 16 Spacer element, dielectric 17 Capacitor 18 End plate 19 .. 20 Stacking axis 21 Connection 22 Holes 30 Plane of symmetry, mechanical 31 Plane of symmetry, electrical 50 Object 51 Measuring and control unit 52 Measuring and control section B Width D Diameter, also D1, D2 H Height X Height

Claims

1. Inductive proximity sensor (1) for detecting a sensing body (50), comprising two receiving coils (2) and one transmitting coil (3), each of which is formed from a group of at least two individual coils on carrier boards (4), which are arranged parallel to each other and axially offset in the form of a stack (10) along a common sensor axis (20), wherein the transmitting coil (3) is arranged between the two receiving coils (2), characterized in that the carrier boards (4) have a diameter (D) which is less than or equal to 10 mm, wherein the turn (2.1, 3.1) of the receiving coil (2) and / or the transmitting coil (3) has a cross-sectional geometry in the case of which the ratio of height (H) to foot width (B) lies in the range of from 0.2 to 0.3, ideally between 0.23 and 0.27, wherein a head board (5) is provided, which serves as an interface with connection pads (7) for connection with a circuit (100) comprising a generator and / or oscillator (90) and which does not have a coil.

2. Device according to Claim 1, characterized in that the height (H) does not exceed 0.05 mm, in particular does not exceed 0.04 mm.

3. Device according to either of Claims 1 and 2, characterized in that the number of turns of at least one individual coil from amongst the receiving coils (2) is equal to or greater than 3, ideally is 4 or 5, in particular all individual coils from amongst the receiving coils (2) is equal to or greater than 3, ideally is 4 or 5.

4. Device according to any of the preceding claims, characterized in that the number of turns of at least one individual coil of the receiving coil (3) is equal to or greater than 3, ideally is 3 or 4, in particular all individual coils from amongst the receiving coils (2) is equal to or greater than 3, ideally is 3 or 4.

5. Device according to any of the preceding claims, characterized in that the stack (10) formed from individual coils and carrier boards (4) is arranged symmetrically to a central plane of symmetry (30) arranged vertically in relation to the sensor axis (20), wherein a central individual coil of the transmitting coil (3) can lie in the plane of symmetry (30).

6. Device according to any of the preceding claims, characterized in that the transmitting coil (3) has a number of n individual coils and the two receiving coils (2) together have a number of at least n+1 individual coils.

7. Device according to any of the preceding claims, characterized in that at least one carrier board (4) is in the form of a double carrier board, which has an individual coil on both faces.

8. Device according to Claim 7, characterized in that the at least one carrier board (4) in the form of a double carrier board has an individual coil of the receiving coil (2) on one face and an individual coil of the transmitting coil (3) on the other face.

9. Device according to any of the preceding claims, characterized in that a head board (5) has precisely four connection pads (7), two connection pads (7) for the receiving coils (2) and two connection pads (7) for the transmitting coil (3).

10. Device according to any of the preceding claims, characterized in that, on each individual coil, in particular on the outer individual coils of the receiving coil (2), no conduction paths (14) running transversely to the coil axis (20) for forwarding or connection to a only one in each case one conduction path (14) a head board (5) is provided, which serves as an interface for connection with the circuit (21) and which does not have a coil.

11. Method for detecting a sensing body (50) by means of an inductive proximity sensor (1), wherein the inductive proximity switch (1) has an outside diameter (D1) of equal to or less than 10 mm and is designed according to any of the preceding claims.