Inductive angle sensor and torque sensor

Abstract

To achieve an improved measurement range, improved accuracy, and a reduced error compared to existing solutions having the same diameter of coupling elements.SOLUTION: An inductive angle sensor includes: a transmitter coil (TX) and an excitation circuit; a first set of receiver coils having a geometry with a first periodicity N; a first movable coupling element having a periodic geometry with the first periodicity N; a second set of receiver coils having a geometry with a second periodicity M smaller than the first periodicity N; and a second movable coupling element having a periodic geometry with the second periodicity M; where a ratio N / M of the first periodicity N to the second periodicity M is equal to 1.5. A torque sensor includes such inductive angle sensor and a torque bar. A printed circuit board includes the plurality of coils.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates generally to the field of inductive angle and torque sensors, and more particularly to inductive angle and torque sensors of the type comprising a transmitter coil, a first set of receiver coils, a first moveable coupling element, a second set of receiver coils, and a second moveable coupling element. The present invention also relates to a printed circuit board suitable for use in an inductive angle or torque sensor. [Background technology]

[0002] Inductive angle sensors are known in the art. They offer the advantage of being able to measure angular position without physical contact, thus avoiding problems such as mechanical wear, scratches, friction, etc. They typically comprise an excitation coil (also known as a "transmitter coil") and a number of detection coils (also known as "receiver coils"). The excitation coil generates an alternating magnetic field that is coupled to a set of receiver coils depending on the angular position of the coupling element. The signals obtained from the receiver coils are processed in electronic circuits and the angular position is determined based on these signals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2010 / 319467 [Patent Document 2] European Patent Application Publication No. 3885711 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention relates to an inductive angle sensor having two sets of receiver coils, two movable elements, and electronic circuitry for determining the angle between the movable elements, which, when connected to a torque bar, is related to the torque applied to the torque bar.

[0005] Patent Document 1 discloses an inductive torque sensor for automobiles, comprising at least one excitation coil, at least one oscillator circuit, a stator circuit board, at least two rotors, and an evaluation means.

[0006] There is always room for improvement or alternatives.

[0007] It is an object of embodiments of the present invention to provide an inductive angle sensor, a torque sensor comprising such an angle sensor, and a printed circuit board for use with such an angle sensor.

[0008] It is an object of embodiments of the present invention to provide an inductive angle sensor and / or torque sensor having one or more of the following features: the same or improved measurement range, the same or improved accuracy (e.g. the same or reduced error), and preferably all of these, compared to existing solutions having a similar size (e.g. coupling element of the same diameter).

[0009] It is an object of embodiments of the present invention to provide an inductive angle sensor and / or torque sensor having smaller dimensions (e.g. smaller diameter coupling elements) compared to existing solutions having a similar measurement range and / or similar accuracy (e.g. similar error).

[0010] It is an aim of embodiments of the present invention to provide an inductive angle and / or torque sensor that has similar dimensions and similar accuracy but is simpler and / or less expensive and / or easier to manufacture compared to existing solutions.

[0011] It is an object of embodiments of the present invention to provide an inductive and / or torque sensor suitable for use in an automotive environment.

[0012] It is an object of embodiments of the present invention to provide an inductive sensor and / or torque sensor suitable for use in an industrial or robotic environment.

[0013] These objectives are achieved by embodiments of the present invention. [Means for solving the problem]

[0014] According to a first aspect, the present invention provides an inductive angle sensor comprising at least one transmitter coil (e.g. TX) for generating an alternating magnetic field, at least one excitation circuit for generating an alternating signal for energizing the at least one transmitter coil, a first set of receiver coils (e.g. RX1a, RX1b, RX1c), each having a geometry with a first periodicity N, a second set of receiver coils (e.g. Rx2a, RX2b, RX2c), each having a geometry with a second periodicity M smaller than the first periodicity N, an evaluation circuit for evaluating signals obtained from the first set of receiver coils and the second set of receiver coils, and at least one transmitter coil (e.g. and a second movable coupling element (also referred to as a "second target") for providing inductive coupling between at least one transmitter coil and a second set of receiver coils (e.g., Rx2a, RX2b, RX2c), the second movable coupling element having a periodic geometry with a second periodicity M, wherein a ratio of the first periodicity N and the second periodicity M is equal to 1.5.

[0015] Surprisingly, the inventors have found that the accuracy of such an inductive angle sensor is much better than the accuracy of an inductive angle sensor having substantially the same angular range but with an integer ratio between the first and second periodicities, not only because the signal-to-noise ratio (SNR) is better, but especially because the crosstalk is much lower.

[0016] The second coupling element is movable relative to the first coupling element so as to form an angle between the second coupling element and the first coupling element.

[0017] At least one transmitter coil and multiple receiver coils may be implemented on a single substrate (eg, a printed circuit board, PCB) or may be implemented on two separate PCBs.

[0018] In an embodiment, the inductive angle sensor comprises only a single transmitter coil arranged to generate a magnetic field that is received by both the first set of receiver coils and the second set of receiver coils.

[0019] In an embodiment, the inductive angle sensor comprises two transmitter coils including a first transmitter coil for generating a magnetic field received by a first set of receiver coils and a second transmitter coil for generating a magnetic field received by a second set of receiver coils.

[0020] In an embodiment, the excitation circuit and the evaluation circuit are implemented in an integrated semiconductor device (also referred to as a "chip").

[0021] The evaluation unit may be configured to determine a first angle value based on signals obtained from the first set of receiver coils, to determine a second angle value based on signals obtained from the second set of receiver coils, and optionally also to determine an angular difference between the first and second angle values. The evaluation unit may also be configured to determine a torque value based on the angular difference.

[0022] The integrated semiconductor device may output one or more of the first angle value, the second angle value, the angle difference (if determined), and the torque value (if determined).

[0023] The inductive angle sensor may include a single transmitter coil that is commonly used for the first and second receiver coils, or alternatively, the inductive angle sensor may include two transmitter coils, one for the first set of receiver coils and one for the second set of receiver coils.

[0024] In an embodiment, the evaluation circuit is configured to determine a first angle value (α1) based on signals obtained from a first set of receiver coils, to determine a second angle value (α2) based on signals obtained from a second set of receiver coils, and to determine a difference between the first angle value (α1) and the second angle value (α2).

[0025] In an embodiment, the first periodicity N is equal to 6 and the second periodicity M is 4.

[0026] In an embodiment, the first periodicity N is equal to 9 and the second periodicity M is equal to 6.

[0027] In an embodiment, the first periodicity N is equal to 12 and the second periodicity M is equal to 8.

[0028] In an embodiment, the first periodicity N is equal to 15 and the second periodicity M is equal to 10.

[0029] In an embodiment, the first periodicity N is equal to 18 and the second periodicity M is equal to 12.

[0030] The combination with (N=6 or 9 or 12) is particularly useful for use in automotive applications since, in addition to the above advantages, it offers the following relatively wide measurement ranges: ±15° (for N=6, M=4), ±10° (for N=9, M=6), ±7.5° (for N=12, M=8).

[0031] The combination with (N=6 or N=9) is particularly advantageous since the measurement range not only includes the functional range (typically ±5%) but also includes an additional range for functional safety.

[0032] In an embodiment, the first set of receiver coils has a two-phase loop configuration and the second set of receiver coils has a two-phase loop configuration.

[0033] In an embodiment, the first set of receiver coils has a two-phase loop configuration and the second set of receiver coils has a three-phase loop configuration.

[0034] In an embodiment, the first set of receiver coils has a three-phase loop structure and the second set of receiver coils has a two-phase loop structure.

[0035] In an embodiment, the first set of receiver coils has a three-phase loop configuration, and the second set of receiver coils has a three-phase loop configuration.

[0036] In an embodiment, at least one of the first set of receiver coils and the second set of receiver coils has a three-phase loop structure, and the at least one transmitter coil, the first set of receiver coils, and the second set of receiver coils are implemented on a single multi-layer printed circuit board.

[0037] The second harmonic of the signal induced by one set of coils is seen by the other set of coils as 3.0 or 1.33 times the harmonic frequency, but an advantage of this embodiment is that it is insensitive to this frequency. Multilayer printed circuit boards may also include the integrated semiconductor devices described above.

[0038] Preferably, the multi-layer PCB is disposed between the first movable coupling element and the second movable coupling element, so that the distance between the coil and the corresponding movable coupling element can be reduced, while the received signal is large enough and the physical distance (air gap) between the PCB and the movable element is large enough to avoid contact.

[0039] In an embodiment, the multi-layer PCB is a six-layer PCB: a first set of receiver coils may be implemented primarily on two adjacent layers, a second set of receiver coils may be implemented primarily on two other adjacent layers, and the two inner layers may be used primarily for shielding purposes (e.g., to prevent or reduce crosstalk).

[0040] In an embodiment, the printed circuit board is a four-layer printed circuit board.

[0041] Surprisingly, it has been found that a three-phase loop structure is substantially insensitive to the third and ninth harmonics, so that a six-layer PCB is not required when the ratio between the periodicities is a factor of 1.5 and at least one of the first set of receiver coils and the second set of receiver coils is implemented in a three-phase loop structure, despite the fact that the second (and sixth) harmonics of the signal induced in the first set of coils may be experienced as third (and ninth) harmonic interference in the second set of coils (due to the ratio of 1.5).

[0042] According to a second aspect, the present invention also provides an inductive torque sensor comprising a torsion bar and an inductive angle sensor according to the first aspect, wherein a first moveable coupling element and a second moveable coupling element are connected to the torsion bar (e.g. at either end of the torsion bar).

[0043] The actual torque value may be calculated by the evaluation circuit and output by the integrated semiconductor device. Alternatively or additionally, the evaluation circuit may output the two angular positions and / or the difference between them, or the torque value may be calculated outside the evaluation circuit, for example in an electronic control unit (ECU) connected to the integrated semiconductor device.

[0044] According to a third aspect, the invention also provides a printed circuit board (e.g. suitable for use in an inductive angle sensor according to the first aspect or an inductive torque sensor according to the second aspect), comprising at least one transmitter coil (e.g. TX) for generating an alternating magnetic field, a first set of receiver coils (e.g. RX1a, RX1b, RX1c), each having a geometry with a first periodicity N, and a second set of receiver coils (e.g. Rx2a, RX2b, RX2c), each having a geometry with a second periodicity M smaller than the first periodicity N, wherein the printed circuit board comprises only four layers, and wherein a ratio N / M of the first periodicity N and the second periodicity M is equal to 1.5.

[0045] In an embodiment, the first periodicity N is equal to 6 and the second periodicity M is 4.

[0046] In an embodiment, the first periodicity N is equal to 9 and the second periodicity M is equal to 6.

[0047] In an embodiment, the first periodicity N is equal to 12 and the second periodicity M is equal to 8.

[0048] In an embodiment, the first periodicity N is equal to 15 and the second periodicity M is equal to 10.

[0049] In an embodiment, the first periodicity N is equal to 18 and the second periodicity M is equal to 12.

[0050] In an embodiment, the printed circuit board further comprises at least one excitation circuit for generating an alternating signal for energizing the at least one transmitter coil, and an evaluation circuit for evaluating signals obtained from the first set of receiver coils and the second set of receiver coils.

[0051] In an embodiment, at least one of the excitation circuit and the evaluation circuit are implemented in a single integrated circuit device mounted on a printed circuit board.

[0052] According to a fourth aspect, the present invention also provides an inductive angle sensor comprising at least one transmitter coil for generating an alternating magnetic field, at least one excitation circuit for generating an alternating signal for energizing the at least one transmitter coil, a first set of receiver coils, each having a geometry with a first periodicity N, a second set of receiver coils, each having a geometry with a second periodicity M smaller than the first periodicity N, an evaluation circuit for evaluating signals obtained from the first set of receiver coils and the second set of receiver coils, and a first movable coil for providing an inductive coupling between the at least one transmitter coil and the first set of receiver coils. and a second movable coupling element for providing inductive coupling between at least one transmitter coil and a second set of receiver coils, the first movable coupling element having a periodic geometry with the first periodicity N, the second movable coupling element having a periodic geometry with the second periodicity M, wherein a ratio N / M of the first periodicity N and the second periodicity M is a non-integer value selected from the group consisting of 4 / 3, 6 / 5, 5 / 2, and 7 / 2, and the at least one transmitter coil, the first set of receiver coils, and the second set of receiver coils are implemented on a single four-layer printed circuit board.

[0053] Optionally, at least one of the first set of receiver coils and the second set of receiver coils has a three-phase loop structure.

[0054] It can be shown that an inductive angle sensor with a first set of receiver coils and a second set of receiver coils with a ratio N / M equal to one of these values ​​has many of the same properties as an inductive angle sensor with N / M=1.5, especially with respect to negligible crosstalk. Thus, the multiple coils can be implemented on a four-layer PCB, since no shielding layers are required. This results in a solution that is easier to manufacture (compared to a six-layer PCB) and therefore cheaper.

[0055] According to a fifth aspect, the present invention also provides an inductive torque sensor comprising a torsion bar and an inductive angle sensor according to the fourth aspect, wherein a first moveable coupling element and a second moveable coupling element are connected to the torsion bar (e.g. at either end of the torsion bar).

[0056] The evaluation circuit may be configured to output a signal indicative of the actual torque (eg, the above-mentioned angular difference, which is typically proportional to the actual torque).

[0057] According to a sixth aspect, the present invention also provides a printed circuit board suitable for use in an inductive angle sensor according to the fourth aspect or an inductive torque sensor according to the fifth aspect, comprising at least one transmitter coil for generating an alternating magnetic field, a first set of receiver coils, each having a geometry with a first periodicity N, and a second set of receiver coils, each having a geometry with a second periodicity M smaller than the first periodicity N, wherein the printed circuit board comprises only four layers, and wherein the ratio N / M of the first periodicity N and the second periodicity M is a non-integer value selected from the group consisting of 3 / 2, 4 / 3, 6 / 5, 5 / 2 and 7 / 2.

[0058] Optionally, at least one of the first set of receiver coils and the second set of receiver coils has a three-phase loop structure.

[0059] In an embodiment, the first set of receiver coils has a three-phase loop structure and the second set of receiver coils has a two-phase loop structure.

[0060] In an embodiment, the first set of receiver coils has a two-phase loop configuration and the second set of receiver coils has a three-phase loop configuration.

[0061] In an embodiment, the first set of receiver coils has a three-phase loop configuration, and the second set of receiver coils has a three-phase loop configuration.

[0062] In an embodiment, the ratio is equal to 2.5, N is equal to 15, and M is equal to 6.

[0063] In an embodiment, the printed circuit board further comprises at least one excitation circuit for generating an alternating signal for energizing the at least one transmitter coil, and an evaluation circuit for evaluating signals obtained from the first set of receiver coils and the second set of receiver coils.

[0064] In an embodiment, at least one of the excitation circuit and the evaluation circuit are implemented in a single integrated circuit device mounted on a printed circuit board.

[0065] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0066] [Figure 1](A) shows a schematic diagram of a torque sensor according to an embodiment of the present invention, comprising an angle sensor according to an embodiment of the present invention and a torque bar mounted on an input shaft portion and an output shaft portion, (B) shows an illustrative example of a first coupling element having N lobes (in this example, N=9), (C) shows an illustrative example of a printed circuit board comprising a plurality of coils, and (D) shows an illustrative example of a second coupling element having M lobes (in this example, M=6). [Figure 2A] 1(B) shows an illustrative example of a first coupling element of FIG. 1(B) movably mounted to a substrate having at least one transmitter coil and a first set of receiver coils, the receiver coils having the same periodicity as the first coupling element (in this example, N=9). [Figure 2B] 1(D) shows an illustrative example of a second coupling element of FIG. 1(D) movably mounted to a substrate having at least one transmitter coil and a second set of receiver coils, the receiver coils having the same periodicity as the second coupling element (in this example, M=6). [Diagram 3] FIG. 1 shows a high level block diagram of an electronic circuit that may be used in an embodiment of the present invention. [Figure 4A] 1 shows a graph illustrating that an inductive angle sensor with (N=9, M=6) has the same measurement range (i.e., 20° or ±10°) as an inductive angle sensor with (N=18, M=9). [Figure 4B] Angular ranges are shown for five example combinations of N and M, as may be used in embodiments of the present invention. [Diagram 5] 4 shows a graph of a typical signal strength of a signal obtained from a receiver coil as a function of periodicity. [Figure 6] 4 shows curves illustrating the typical amount of noise (in arbitrary units) as a function of the periodicity (i.e., number of lobes) of the coupling element and the receiver coil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] The drawings are only schematic and non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. Any reference signs in the claims should not be construed as limiting the scope. In different drawings, the same or similar reference signs (e.g., the same modulo 100) typically refer to the same or similar elements.

[0068] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims.

[0069] The terms first, second, etc. in this specification and claims are used to distinguish between similar elements and not necessarily to describe an order, either temporally, spatially, sequentially, or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein are capable of operating in orders other than those described or illustrated herein.

[0070] Terms such as top, under, and the like in this specification and claims are used for purposes of description and not necessarily to describe relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in orientations other than those described or illustrated herein.

[0071] It should be noted that the term "comprising" used in the claims should not be interpreted as being limited to the means listed thereafter, and does not exclude other elements or steps. It is thus interpreted as specifying the presence of stated features, integers, steps or components mentioned, but does not exclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to a device consisting of only components A and B. This means that in the context of the present invention, the only relevant components of the device are A and B.

[0072] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, although they may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to one of ordinary skill in the art from this disclosure.

[0073] Similarly, in describing exemplary embodiments of the present invention, it should be understood that various features of the invention may be grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in understanding one or more of the various inventive aspects. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single disclosed embodiment above. Thus, the claims following the detailed description are expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the present invention.

[0074] Furthermore, although some embodiments described herein include some but not others features that are included in other embodiments, as will be understood by those skilled in the art, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0075] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0076] In this document, the terms "excitation coil" and "transmitter coil" have the same meaning.

[0077] In this document, the terms "receiver coil" and "detector coil" have the same meaning.

[0078] In this document, the terms "coupling element" and "target" and "rotor" have the same meaning.

[0079] In this document, the phrase "first coil set" may refer to a "first set of receiver coils" with or without at least one transmitter coil, depending on the context.

[0080] In this document, the phrase "second coil set" may refer to a "second set of receiver coils" with or without at least one transmitter coil, depending on the context.

[0081] In this document, the "periodicity" of a movable target may refer to the number of protrusions.

[0082] In this document, the "mechanical angle" of a moveable target may be calculated as the "electrical angle" of the moveable target divided by its periodicity.

[0083] In this document, sqrt() means the square root function.

[0084] The present invention relates to an inductive angle sensor having two sets of receiver coils and two movable coupling elements (for example of the type described in US Pat. No. 6,399,313). For ease of discussion, it is assumed that the first target has a first periodicity N (for example, N lobes) and the second target has a second periodicity M (for example, M lobes), where N and M are integer values. In US Pat. No. 6,399,313, the value of N is an integer multiple of M, and the preferred ratio of N / M is equal to 2.0. An example is given of an inductive sensor with an angular periodicity of 15° (N=30 and M=15) and another with an angular periodicity of 20° (N=18 and M=9). Such a combination is said to result in almost no measurement error.

[0085] The inventors hoped to find an inductive angle sensor that would have a similar measurement range without significantly increasing the measurement error.

[0086] They started to experiment and surprisingly found that, taking into account all relevant aspects, an inductive angle sensor of similar size (e.g., target of the same outer diameter) but with a ratio N / M equal to 1.5, provides a lower measurement error than a prior art sensor with the same measurement range (N / M=2). This was unexpected. Or, in other words, they found that an inductive angle sensor with the same measurement range and the same measurement error can be implemented in a smaller size or form factor and therefore at a lower cost. This was a big surprise, especially considering that the automotive market is a very competitive market and that US Pat. No. 6,233,339 was already published more than 12 years ago.

[0087] The principles of the invention are explained in more detail below.The above prior art sensor with N=18 and M=9 (ratio N / M=2) is called the "reference sensor".

[0088] Now, reference is made to the figure.

[0089] 1(A) shows a schematic diagram of a torque sensor 100 comprising an angle sensor 101 and a torque bar 141. The torque bar 141 may be connected to an input shaft 142 at one end and to an output shaft 143 at its other end.

[0090] The angle sensor 101 is at least one transmitter coil (for example only one transmitter coil or two transmitter coils Tx1, Tx2) for generating an alternating magnetic field, which may for example have a substantially circular shape, as illustrated in Figures 2A and 2B; at least one excitation circuit 321 (see, for example, FIG. 3 ) for generating an alternating signal (for example, a sinusoidal current) for energizing said at least one transmitter coil; a first set of receiver coils Rx1a, Rx1b, Rx1c each having a geometry with a first periodicity N, where for example in a two-phase system the two receiver coils are phase shifted by 90° with respect to each other, or in a three-phase system the two receiver coils are phase shifted by 120° with respect to each other, a second set of receiver coils Rx2a, Rx2b, Rx2c, each having a geometry with a second periodicity M smaller than the first periodicity N; an evaluation circuit 320 for evaluating the signals obtained from the first set of receiver coils and from the second set of receiver coils; a first movable coupling element 131 (also called "first target" or "first rotor") for providing inductive coupling between at least one transmitter coil and a first set of receiver coils, said first movable coupling element 131 having a periodic geometric shape with said first periodicity N, in the example of FIG. 1(D) having a shape with 9 lobes (N=9) angularly spaced at multiples of 360° / 9=40°; a second movable coupling element 132 (also called "second target" or "second rotor") for providing inductive coupling between at least one transmitter coil and a second set of receiver coils, the second movable coupling element 132 having a periodic geometric shape with said second periodicity M, in the example of Figs. 1(B)-1(D) having a shape with 6 lobes (M=6) angularly spaced at multiples of 360° / 6=60°, The ratio of the first periodicity N and the second periodicity M is equal to 1.5.

[0091] Note that a single transmitter coil is sufficient to excite both moveable targets.

[0092] In an embodiment, the transmitter coil has a generally circular shape. Alternatively, the transmitter coil has a generally C-shape.

[0093] As suggested in Fig. 1(A), the first target 131 is located at a distance "g" from the first set of coils and the second target 132 is located at a distance "g" from the second set of coils. In a preferred embodiment, "g" is equal to a value in the range of 0.1-5.0 mm, or a value in the range of 0.5-4.0 mm, for example a value in the range of 1.0-3.0 mm, or a value in the range of 1.5-2.5 mm, for example about 2.0 mm. The smaller the value "g", the larger the signal obtained from the receiver coils and thus the larger the signal-to-noise ratio (SNR), but the smaller (i.e. higher requirements) the mechanical tolerances to avoid mechanical friction.

[0094] 1(B) shows an illustrative example of a first coupling element having N lobes, where N is equal to 9 in the example shown.

[0095] Figure 1(C) shows an illustrative example of a printed circuit board PCB 110 comprising a number of coils (not explicitly shown in Figure 1(C) but see e.g. Figures 2A and 2B). The PCB may also comprise an excitation circuit 321 and an evaluation circuit 320, preferably integrated in a single semiconductor device 128 (e.g. as illustrated in Figure 3). The PCB is typically fixedly mounted to a frame (not shown).

[0096] FIG. 1(D) shows an illustrative example of a second coupling element having M lobes (in this example, M=6).

[0097] In the example shown in Figures 1(A) to 1(D), the first target 131 having periodicity N is located on the side of the output shaft 143, and the second target 132 having periodicity M is located on the side of the input shaft 142, but the present invention is not limited to this, and it is naturally possible to connect the first target 131 to the input shaft 142 and connect the second target 132 to the output shaft 143.

[0098] In the example of Fig. 1(B), the PCB has a particular shape with a rectangular portion at the bottom and a semicircular portion at the top, but the invention is not limited thereto and other shapes are possible. The PCB can be a single 6-layer PCB, with the first set of coils implemented on the two layers located on the left side of Fig. 1(A) near the first target 131, and the second set of coils implemented on the two layers located on the right side of Fig. 1(A) near the second target 132, with the two inner layers acting as shielding to reduce crosstalk between the first target and the coils of the first set on the one hand, and between the second target and the coils of the second set on the other hand.

[0099] Fig. 2A shows an illustrative example of the first coupling element 131, 231 of Fig. 1(B) movably mounted with respect to the transmitter coil Tx1 and the first set of receiver coils Rx1a, Rx1b, Rx1c. These coils may be mounted on a printed circuit board (for example, as illustrated in Fig. 1(C) but not explicitly shown in Fig. 2A). The receiver coils Rx1a, Rx1b, Rx1c have the same periodicity N as the first coupling element 231. In the specific example shown in Fig. 2A, the first periodicity N is equal to 9, but the invention is not limited thereto and values ​​other than N are also possible (see, for example, Fig. 4B).

[0100] In the example shown in FIG. 2A, the first set of receiver coils includes three receiver coils Rx1a, Rx1b, Rx1c spaced 120° apart from each other. The signals obtained from these three receiver coils can be decoded using a three-phase system. However, the invention is not limited thereto and it is also possible to use a first set of receiver coils having only two receiver coils (not shown) spaced 90° apart. The signals obtained from these two receiver coils can be decoded using a two-phase system. Two-phase and three-phase decoding systems are well known in the art and are not the main focus of the present invention and therefore need not be described in further detail here.

[0101] Fig. 2B shows an illustrative example of the second coupling element 132, 232 of Fig. 1(D) movably mounted with respect to the transmitter coil Tx2 and the second set of receiver coils Rx2a, Rx2b, Rx2c. These coils can be implemented on the same printed circuit board as the first set of receiver coils or on a separate printed circuit board. The receiver coils Rx2a, Rx2b, Rx2c have the same periodicity M as the second coupling element 232 (in this example M=6, but other values ​​are also possible, see for example Fig. 4B).

[0102] In the example shown in FIG. 2B, the second set of receiver coils includes three receiver coils spaced 120° apart from each other to form a three-phase coil system, however the invention is not limited in this respect and it is also possible to use a second set of receiver coils having only two receiver coils (not shown) spaced 90° apart.

[0103] In an embodiment, the first set of receiver coils includes two coils that are phase shifted 90° relative to each other, and the second set of receiver coils also includes two coils that are phase shifted 90° relative to each other.

[0104] In an embodiment, the first set of receiver coils includes two coils that are phase shifted 90° relative to each other, and the second set of receiver coils includes three coils that are phase shifted 120° relative to each other.

[0105] In an embodiment, the first set of receiver coils includes three coils that are phase shifted 120° relative to each other, and the second set of receiver coils includes two coils that are phase shifted 90° relative to each other.

[0106] In an embodiment, the first set of receiver coils includes three coils that are phase shifted 120° relative to each other, and the second set of receiver coils also includes three coils that are phase shifted 120° relative to each other.

[0107] Readers unfamiliar with coil layouts may refer to US Pat. No. 6,399,323, which is incorporated herein by reference in its entirety, although the invention is not limited thereto and other coil layouts may also be used.

[0108] FIG. 3 shows a high level block diagram of electronic circuitry that may be used in embodiments of the present invention, although the invention is not so limited and other circuits may also be used.

[0109] The electronic circuit of Fig. 3 comprises two main sub-circuits: an excitation circuit 321 and an evaluation circuit 320. In the example of Fig. 3, these sub-circuits are implemented in a single integrated semiconductor device 328, but this is not absolutely necessary and the excitation can also be performed by a separate circuit, for example a separate chip.

[0110] The electronic circuit of FIG. 3 is connected to at least one transmitter coil (schematically illustrated by a single black rectangle Tx), but as mentioned above, it is also possible to use two separate transmitter coils Tx1, Tx2. In that case, the two transmitter coils are preferably driven by a single excitation signal, for example by connecting them in series or in parallel. The transmitter coil TX may be part of the excitation circuit 321, but this is not absolutely necessary. The transmitter coil Tx may be excited with a frequency of about 1 MHz to about 20 MHz. The excitation frequency may be higher or lower than, or substantially equal to, the resonant frequency of the oscillator circuit. These aspects are well known in the art, but are not the main focus of the present invention and therefore do not need to be described in more detail here.

[0111] The electronic circuit of FIG. 3 is also connected to a first set of receiver coils (schematically illustrated by three black rectangles Rx1a, Rx1b, Rx1c) and a second set of receiver coils (schematically illustrated by three black rectangles Rx2a, Rx2b, Rx2c). Circuit 328 is configured to receive signals from each set of receiver coils, optionally amplify these signals using amplifiers 322a, 322b, and decode the received signals in a known manner (e.g., by demodulating the received signals to baseband signals). Demodulation may include synchronous rectification and low-pass filtering. The demodulated signals may be further processed using analog or digital circuitry, including, for example, an analog-to-digital converter 327, a digital processor 326 (e.g., DSP), and a controller 325 connected to a non-volatile memory 324 (e.g., flash).

[0112] The evaluation circuit 320 may be configured to determine a first mechanical angle value α1 based on signals obtained from a first set of receiver coils and a first periodicity N (e.g., by determining a first electrical angle based on the received signals and dividing this electrical angle by the first periodicity N) and to determine a second mechanical angle value α2 based on signals obtained from a second set of receiver coils and a second periodicity M (e.g., by determining a second electrical angle based on the received signals and dividing this electrical angle by the second periodicity M). A relative position between the two targets may be calculated based on the difference between the values ​​α1 and α2. This relative position is indicative of (e.g., proportional to) the torque applied to the torsion bar 141. The angle difference and / or the torque value may be calculated inside the evaluation circuit 320 and output to an external processor, for example an electronic control unit (ECU, not shown) connected to the circuit 328. Alternatively or additionally, angles α1 and α2 may be output and the angle difference and / or torque may be calculated by the external processor.

[0113] It should be noted that the electronic circuit architecture shown in FIG. 3 is just one example of how the signals obtained from the receiver coils may be processed to obtain angle values, but the invention is not limited thereto and other architectures may also be used.

[0114] 4A shows a graph not known from the prior art but presented by the present invention, illustrating the measurement range for several combinations of the first periodicity N and the second periodicity M. The inventors have found that the measurement range of an inductive angle sensor having a structure as shown in FIG. 1(A) with the first periodicity N and the second periodicity M can be expressed by the following equation: Measurement range = 360° / LCM(N,M)[1] where LCM is the least common multiple of the values ​​N and M.

[0115] More specifically, FIG. 4A shows two "curves": The upper curve (black) shows the measurement range as a function of the first periodicity N for a fixed value of the second periodicity M (equal to 6). As can be seen, this curve provides several relatively high peaks (indicated by "X"), namely for N=12 (2x6), and N=18 (3x6), and N=24 (4x6), etc.

[0116] - the lower curve (grey) shows the measurement range as a function of the first periodicity N for a fixed value of the second periodicity M (equal to 9). As can be seen, this curve also provides several relatively high peaks, i.e. peaks for N=18 (2×9), N=27 (3×9), etc.

[0117] The inventors have surprisingly found that the upper curve shows additional peaks for N=9 and M=6, where the ratio N / M is 1.5. As can be seen from Fig. 4A, the range ±10° obtained by the inductive angle sensor proposed by the present invention and shown by the circle with (N=9, M=6, ratio=1.5) is the same measurement range as the classical inductive angle sensor with (N=18, M=9, ratio=2), which is the same measurement range as the classical inductive angle sensor with (N=18, M=6, ratio=3).

[0118] This observation illustrates a first insight of the present invention, but does not provide any clues about the accuracy or error obtained by such guided angle systems.

[0119] Before describing the accuracy or error, Figure 4B provides a table listing the angular ranges for five illustrative combinations of N and M, as may be used in embodiments of the present invention. It can be seen that: i) the combination (N=6, M=4, ratio=1.5) as proposed by the present invention provides the same range (i.e. ±15°) as can be obtained by a classical sensor with (N=12, M=6, ratio=2); ii) the combination (N=9, M=6, ratio=1.5) as proposed by the present invention provides the same range (i.e. ±10°) as can be obtained by a classical sensor with (N=18, M=9, ratio=2); iii) The combination (N=12, M=8, ratio=1.5) as proposed by the present invention provides the same range (i.e. ±7.5°) as can be obtained by a classical sensor with (N=24, M=6, ratio=4).

[0120] From these examples, it can be seen that the same range can be achieved using a smaller periodicity with a ratio N / M=1.5 compared to prior art solutions using integer ratios N / M=2 or higher. This means that for an inductive angle sensor of comparable dimensions, a stronger signal results in lower noise and less sensitivity to misalignment, but with a slightly reduced resolution.

[0121] It should be noted that the measurement range may depend on the application. For example, for measurement of steering torque in automotive applications, a measurement range of at least 10°, or at least 15°, or at least 20° may be required. Narrower measurement ranges may be applicable in other fields, for example in certain robotics and / or industrial applications. In this respect, it should be noted that the list in FIG. 4B is not exhaustive and that further combinations of N and M (where N and M are integer values ​​having a ratio of 1.5) can easily be found.

[0122] However, a second key insight underlying the present invention is the ability to understand and quantify the error (or accuracy) of an inductive angle sensor of the type illustrated in FIG. 1(A) having various values ​​of first periodicity N and second periodicity M, e.g., as listed in FIG. 4B.

[0123] Existing solutions appear to select values ​​of N and M to maximize the resolution of the sensor for a given measurement range. A typical measurement range for automotive applications is ±10°. While "high resolution" is important, other factors that are also important to good performance of an inductive angle sensor are noise and crosstalk. Each of these factors is described in more detail below.

[0124] i) First factor: range and resolution The first set of receiver coils and the first moveable element have a first periodicity N. The second set of receiver coils and the second moveable element have a second periodicity M. As above, the measurement range is 360° divided by the least common multiple of N and M.

[0125] The resolution of the difference angle is determined by the smaller of the values ​​N and M, and therefore by M. The resolution is typically defined as the mechanical angle corresponding to 1 LSB (least significant bit). For a given evaluation circuit (e.g. with an ADC with a predefined number of bits, e.g. 12 bits), the higher the periodicity, the higher the resolution. More specifically, when using a 12-bit ADC, the minimum number may represent 0 and the maximum number may represent 4095, and the resolution, when expressed in mechanical degrees, may be defined as (360 / M) / 4096, or in general as resolution=(360° / M) divided by the K power of 2, where K=12 (for a 12-bit ADC).

[0126] Comparing the inductive angle sensor of the present invention with (N=9, M=6, ratio=1.5, range=±10°) with a classical inductive angle sensor with (N=18, M=9, ratio=2, range=±10°), the resolution of the sensor proposed by the present invention is only 1.5 times lower.

[0127] ii) Second factor: noise and signal strength Inductive sensors with high periodicity (i.e., larger N or M) have significant drawbacks: as the periodicity increases, the signal strength of the signal provided by the receiver coil decreases because the target protrusions (or teeth) become smaller and are not excited as efficiently, and the noise level increases (i.e., the signal-to-noise ratio, SNR, decreases).

[0128] This is illustrated in Figure 5, which shows a graph with typical signal strength as a function of periodicity. As shown, the greater the periodicity, the smaller the signal strength. The signal strength of an inductive sensor is highly dependent on its periodicity (readings: N and M) and size (e.g., radius). For a given size (e.g., radius), as the periodicity increases, the signal strength decreases.

[0129] FIG. 6 shows an illustrative curve showing a typical amount of noise (in arbitrary units) as a function of the periodicity (e.g., number of protrusions) of a coupling element and a receiver coil mounted at a predefined distance from the receiver coil, as can be obtained from measurements or computer simulations.

[0130] Noise is inversely proportional to the signal strength. Therefore, the noise performance of a sensor can be improved by increasing the signal level. Note that the "noise expressed in electrical degrees" is obtained as 1 / signal_strength. To get the "noise expressed in mechanical degrees", we need to divide the "noise in electrical degrees" by the periodicity.

[0131] The example of Figure 6 was obtained by computer simulation modeling the signal strength of an inductive angle sensor as illustrated in Figure 1(A) with a target coil diameter of 5.0 cm, positioned at an air gap "g" of 2.0 mm from the printed circuit board 110.

[0132] Comparing the inductive angle sensor of the present invention with (N=9, M=6, ratio=1.5, range=±10°) with a classical inductive angle sensor with (N=18, M=9, ratio=2, range=±10°), the noise of the former is typically about 29% lower than the latter, and as can be seen from FIG. 6, the noise associated with N=9 is about 32, and the noise associated with M=6 is about 34, so the total noise for (N=9 and M=6) is about 10% of that of the sensor proposed by the present invention.

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[0133] iii) The third factor: crosstalk Ideally, the first angle value (e.g., the angle value of the input axis) is independent from the second angle value (e.g., the angle value of the output axis) and vice versa, but in practice, to obtain independent measurements with a single printed circuit board, a shielding layer between the first set of coils and the second set of coils may be required to avoid crosstalk, which means that such a printed circuit board 110 (see FIG. 1(C)) needs to have at least six layers (two layers for the first set of receiver coils, two shielding layers, and two layers for the second set of receiver coils).

[0134] An inductive target with periodicity N, even if excited by a perfect sine wave, generates an alternating magnetic field containing a fundamental frequency and harmonics of the Nth, 2Nth, 3Nth, 4Nth, 5Nth, 6Nth, 7Nth, etc. order due to spatial modulations linked to the periodicity and / or geometry of the receiver coil and / or the movable target. Surprisingly, it has been found that the inductive angle sensor proposed by the invention, with an N / M ratio equal to 1.5, is particularly advantageous in terms of crosstalk.

[0135] Indeed, the inventors have surprisingly found that a two-phase coil system (wherein the two input signals have substantially the same amplitude but are phase shifted by 90°) is sensitive to odd harmonics, i.e., Nth, 3Nth, 5Nth, 7Nth, 9Nth, etc. harmonics, whereas a three-phase coil system (wherein the three input signals have substantially the same amplitude but are phase shifted by 120°) is sensitive to Nth, 5Nth, 7Nth, 11Nth, 13Nth, etc. harmonics, but is not sensitive to 3Nth, 9Nth, and other multiples of 3N.

[0136] When the second coil set (with periodicity M) transmits a signal with the base frequency, it is "seen" by the first coil set (with periodicity N=1.5×M) as a signal with a frequency 1.5 times the base frequency, but is not sensitive to this. When the second coil set transmits a second harmonic (2M), it is seen by the first coil set as (3N), but if the first coil set is a three-phase system, it is not sensitive to this frequency. When the second coil set transmits the third harmonic (3M), it is seen by the first coil set as (4.5N), but is not sensitive to this frequency. When the second coil set transmits the fourth harmonic (4M), it is seen by the first coil set as (6N), but is not sensitive to this frequency. When the second coil set transmits the fifth harmonic (5M), it is seen by the first coil set as (7.5N), but is not sensitive to this frequency. When the second coil set transmits the sixth harmonic (6M), it is seen by the first coil set as (9N), but if the first coil set is a three-phase system, it is not sensitive to this frequency, and so on.

[0137] Therefore, in the inductive angle sensor (with N / M=1.5) of the present invention, the first coil set (with periodicity N) experiences no crosstalk from the signal emitted by the second coil set (with periodicity M) when the first coil set is a three-phase system. In other words, the second coil set (with periodicity M) does not interfere with the signal of the first coil set (with periodicity N). In fact, simulations have shown that the crosstalk of the inductive angle sensor with N / M=1.5 is negligible not only in three-phase systems but also in two-phase systems.

[0138] Following similar reasoning, it can be shown that the second coil set (with periodicity M) also suffers no crosstalk from the signals emitted by the first coil set (with periodicity N). When the first coil set (with periodicity N) transmits a signal with the base frequency, it is "seen" by the second coil set (with periodicity M=N / 1.5) as a signal with a frequency of 0.67 times the base frequency, but is not sensitive to this frequency. When the first coil set transmits the second harmonic (2N), it is seen by the second coil set as (1.33×M), but is not sensitive to this frequency. When the first coil set transmits the third harmonic (3N), it is seen by the second coil set as (2M), but is not sensitive to this frequency. When the first coil set transmits the fourth harmonic (4N), it is seen by the second coil set as (2.66×M), but is not sensitive to this frequency. When the first coil set transmits the fifth harmonic (5N), it is seen by the second coil set as (3.33×M), but is not sensitive to this frequency. When the first coil set transmits the sixth harmonic (6N), it is seen by the second coil set as (4×M), but is not sensitive to this frequency and so on.

[0139] Therefore, in the inductive angle sensor of the present invention (with N / M=1.5), the second coil set (with periodicity M) experiences no crosstalk from the signal emitted by the first coil set (with periodicity N), regardless of whether the second coil set is implemented in a two-phase or three-phase system. In other words, the first coil set (with periodicity N) does not interfere with the signal of the second coil set (with periodicity M).

[0140] This is true even if the first set of receiver coils and the second set of receiver coils are implemented on a four-layer printed circuit board without the two shielding layers, which is less complicated to manufacture than a six-layer PCB and therefore much cheaper.

[0141] The mutual independence of the first set of coils and the second set of coils was quantitatively investigated through simulations using a model without shielding layers, with N=9, M=6, ratio=1.5, Tx coil diameter: 38mm, Rx coil outer diameter: 34mm, Rx coil inner diameter: 22mm, target outer diameter: 40mm, target inner diameter: 20mm, air gap between the first target and the first set of receiver coils: 2.0mm, air gap between the second target and the second set of receiver coils: 2.0mm, PCB thickness: 1.0mm, air gap between the first target and the second set of receiver coils: 3.0mm, air gap between the second target and the first set of receiver coils: 3.0mm, assuming a PCB thickness of 1.0mm, as depicted in FIG. 1(A) for example.

[0142] For the inductive angle sensor of the present invention having N=9 and M=6, the following results were found: a first movable target (with N=9) produced a 10 mV signal at the first receiver coil, a second movable target (with M=6) produced a 20 mV signal at the second receiver coil, a first target (with N=9) produced a signal of less than 10 μV at the second set of coils (with M=6), and a second target (with M=6) produced a signal of less than 10 μV at the first set of coils (with N=6), resulting in a differential angle error of less than 0.01°.

[0143] These simulations were also performed on a model of a classical inductive angle sensor with the same dimensions (d=5 cm, g=3 mm) and no shielding layer, N=18 and M=9, ratio=2. In this case, the second target (with M=9) produced a signal of 0.2 mV in the first set of coils (with N=18), resulting in a differential angle error of more than 0.1°.

[0144] In summary, it can be concluded that the above inductive angle sensor with first periodicity N and second periodicity M, where N / M=1.5, is a valid alternative to classical inductive angle sensors with first periodicity N and second periodicity M, where N / M is an integer value.

[0145] With a 6-layer PCB including two shielding layers, the proposed solution (with N / M=1.5) has a similar range, slightly (typically 1.5 times) lower resolution, and slightly (typically 1.29 times) lower noise due to the smaller periodicity value and the absence of significant crosstalk. Overall, this means a slightly better accuracy compared to the classical solution that is also implemented on a 6-layer PCB including two shielding layers and with the same range and dimensions.

[0146] With a four-layer PCB without two shielding layers, the proposed solution (with N / M=1.5) has a similar range, slightly (typically 1.5 times) lower resolution and slightly (typically 2.5 times) lower noise due to a smaller periodicity value but much lower crosstalk. Overall, this means a much better accuracy compared to the classical solution, which is also implemented on a four-layer PCB with the same range and the same dimensions without shielding layers.

[0147] Although the above discussion has been provided primarily for inductive angle sensors having N=9 and M=6, the same reasoning is also applicable to other inductive angle sensors with N / M=1.5 (e.g., having values ​​of N and M as illustrated in FIG. 4B).

[0148] Although an example having a 12-bit ADC has been used, the invention is not limited thereto and other ADCs (eg having 14-bit or 16-bit) may also be used. [Explanation of symbols]

[0149] 100 Torque sensor (equipped with angle sensor system and torque bar) 101 Angle sensor system (with multiple coils, two targets, and electronics) 110, 310 Printed Circuit Board (PCB) 320 Sensor Device 321 Oscillator Circuit 322 Amplifier 323 Demodulator or Rectifier & Filter 324 NV MEM (e.g. flash) 325 Controller 326 DSP 327 ADC 128, 328 Integrated semiconductor devices (ICs or chips) 131, 231, 331 First movable target 132, 232, 332 Secondary movable target 141 Torsion bar 142 Input shaft part 143 Output shaft part g Air gap N first periodicity M Second Periodicity TX Transmitter Coil RX1a, RX1b, RX1c First set of receiver coils RX2a, RX2b, RX2c Second set of receiver coils

Claims

1. It is an inductive angle sensor, - At least one transmitter coil (TX) for generating an alternating magnetic field, - At least one excitation circuit for generating an alternating signal to energize the at least one transmitter coil, - A first set of receiver coils (RX1a, RX1b, RX1c), each having a geometric shape with a first periodicity (N), - A second set of receiver coils (Rx2a, RX2b, RX2c) each having a geometric shape having a second periodicity (M) smaller than the first periodicity (N), - An evaluation circuit for evaluating the signals obtained from the receiver coil of the first set and the receiver coil of the second set, - A first movable coupling element for providing inductive coupling between at least one transmitter coil (TX) and the first set of receiver coils (RX1a, RX1b, RX1c), the first movable coupling element having a periodic geometry having a first periodicity (N), - A second movable coupling element for providing inductive coupling between at least one transmitter coil and the second set of receiver coils (Rx2a, RX2b, RX2c), comprising a second movable coupling element having a periodic geometry having a second periodicity (M), The ratio of the first periodicity (N) to the second periodicity (M) is equal to 1.5, The first periodicity and the second periodicity (N, M) are in the following combinations: i) The first periodicity (N) is equal to 6 and the second periodicity (M) is equal to 4, or ii) The first periodicity (N) is equal to 9 and the second periodicity (M) is equal to 6, or iii) The first periodicity (N) is equal to 12, and the second periodicity (M) is equal to 8, or iv) The first periodicity (N) is equal to 15 and the second periodicity (M) is equal to 10, or v) An inductive angle sensor characterized in that the first periodicity (N) is equal to 18 and the second periodicity (M) is equal to 12.

2. The induction angle sensor according to claim 1, wherein the evaluation circuit is configured to determine a first angle value (α1) based on the signal obtained from the first set of receiver coils and the first periodicity (N), determine a second angle value (α2) based on the signal obtained from the second set of receiver coils and the second periodicity (M), and determine the difference between the first angle value (α1) and the second angle value (α2).

3. The receiver coil of the first set has a two-phase loop structure, and the receiver coil of the second set has a two-phase loop structure, or The receiver coil of the first set has a two-phase loop structure, and the receiver coil of the second set has a three-phase loop structure, or The receiver coil of the first set has a three-phase loop structure, and the receiver coil of the second set has a two-phase loop structure, or The induction angle sensor according to claim 1 or 2, wherein the receiver coil of the first set has a three-phase loop structure, and the receiver coil of the second set has a three-phase loop structure.

4. At least one of the receiver coils of the first set and the receiver coil of the second set has a three-phase loop structure. The inductive angle sensor according to claim 1 or 2, wherein the at least one transmitter coil, the first set of receiver coils, and the second set of receiver coils are mounted on a single multilayer printed circuit board.

5. The induction-type angle sensor according to claim 4, wherein the printed circuit board is a four-layer printed circuit board.

6. It is an induction type torque sensor, Torsion bar and The system comprises an induction-type angle sensor according to claim 1 or 2, An inductive torque sensor in which the first movable coupling element and the second movable coupling element are connected to the torsion bar.

7. Printed circuit board, - At least one transmitter coil (TX) for generating an alternating magnetic field, - A first set of receiver coils (RX1a, RX1b, RX1c), each having a geometric shape with a first periodicity (N), - A second set of receiver coils (Rx2a, RX2b, RX2c) each having a geometric shape having a second periodicity (M) smaller than the first periodicity (N), - The printed circuit board contains only four layers, - The ratio of the first periodicity (N) and the second periodicity (M) is equal to 1.5, The first periodicity and the second periodicity (N, M) are in the following combinations: i) The first periodicity (N) is equal to 6 and the second periodicity (M) is equal to 4, or ii) The first periodicity (N) is equal to 9 and the second periodicity (M) is equal to 6, or iii) The first periodicity (N) is equal to 12, and the second periodicity (M) is equal to 8, or iv) The first periodicity (N) is equal to 15 and the second periodicity (M) is equal to 10, or v) A printed circuit board characterized in that the first periodicity (N) is equal to 18 and the second periodicity (M) is equal to 12.

8. - At least one excitation circuit for generating an alternating signal to energize the at least one transmitter coil, - The printed circuit board according to claim 7, further comprising: an evaluation circuit for evaluating signals obtained from the first set of receiver coils and the second set of receiver coils.

9. The printed circuit board according to claim 8, wherein the at least one excitation circuit and the evaluation circuit are mounted within a single integrated circuit device mounted on the printed circuit board.

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