Angular position sensor

Abstract

An angular position sensor (1) for sensing the angular position of a rotor (R) rotating on an axis (A) relative to a stator (S), comprising a ferromagnetic target (C) of substantially oval cross-section and a sensitive element, the target rotating together with one of the rotor (R) or the stator (S), the sensitive element comprising a first group (J1) of coils (L11, L12, L13, L14) uniformly distributed in angle, rotating together with the other of the rotor (R) or the stator (S), the coils (L11, L12, L13, L14) being arranged in a straight line with the target (C) so as to be able to measure the distance to the target (C), so that the angular position of the rotor (R) relative to the stator (S) can be derived therefrom.

Description

Technical Field

[0001] The invention relates to an angular position sensor. Background Art

[0002] In order to measure, for example, the angular position of the rotor relative to the stator, it is known practice to use a resolver. Such a resolver comprises a primary coil carried by the rotor. The primary coil requires a complex power supply / excitation circuit. The stator comprises at least a first secondary coil. The first secondary coil has a voltage at its terminals that varies sinusoidally according to the angular position of the primary coil and the rotor. Advantageously, the stator comprises a second secondary coil, which is offset by a certain angle, advantageously by 45° or 90°. The second secondary coil has a voltage at its terminals similar to the voltage of the first secondary coil, which is orthogonally phase-shifted relative to the angle. Therefore, the amplitude of the signal of the first secondary coil indicates the sine of the angle of the angular position of the rotor relative to the stator, while the amplitude of the signal of the second secondary coil indicates the cosine of the angle of the angular position of the rotor relative to the stator.

[0003] This solver is expensive. Also, it is difficult to integrate due to its large size. Another disadvantage is that it has no alternative power supply solution.

[0004] It is also known practice to use anisotropic magnetoresistive AMR sensors or tunnel magnetoresistive TMR sensors. Such sensors are able to detect the position of a magnet. Therefore, a magnetic target is usually mounted on the periphery of the rotor, and the AMR or TMR sensor is able to detect the angular position of the magnetic target.

[0005] The use of additional magnets results in significant additional costs both in terms of material and integration.

[0006] Therefore, an alternative solution is sought that makes it possible to measure the angular position. Summary of the invention

[0007] To this end, a subject of the invention is an angular position sensor for sensing the angular position of a rotor rotating on an axis relative to a stator, comprising a ferromagnetic target of substantially oval cross section, which rotates with one of the rotor or the stator, and a sensitive element, which comprises a first set of angularly uniformly distributed coils, which rotate with the other of the rotor or the stator, the coils being arranged in line with the target so as to be able to measure the distance to the target, so that the angular position of the rotor relative to the stator can be deduced therefrom.

[0008] Specific features or embodiments that may be used alone or in combination are:

[0009] - the cross section of the target comprises a number of protrusions equal to half the cardinality of the group;

[0010] - the sensitive element further comprises a second group of coils having the same cardinality as the first group, the coils of the second group being angularly uniformly distributed relative to each other and interposed angularly in between the coils of the first group;

[0011] - The coils are arranged radially relative to the axis;

[0012] - A group of coils are connected in a paramagnetic manner;

[0013] - The cross section of the target has two symmetrical protrusions;

[0014] - the cardinality of the first group or the second group is equal to 4, and the coils of the first group or the coils of the second group are connected in a Wheatstone bridge,

[0015] - between the two first diagonal points, supplying two square wave signals of anti-phase to the Wheatstone bridge;

[0016] - on a Wheatstone bridge, taking a measurement between two second diagonal points, said two second diagonal points being different from the two first diagonal points;

[0017] - the sensor further comprises a differential amplifier for processing the measurements taken between the two second diagonal points;

[0018] - the sensor further comprises a resonator comprising a first capacitor arranged between two second diagonal points and a second capacitor arranged between two first diagonal points;

[0019] - the coil is a surface mounted SMD coil, which is mounted on a printed circuit, arranged perpendicular to the axis;

[0020] - The sensor also comprises a measurement processing unit of the resolver type.

[0021] In a second aspect of the present invention, a DC brushless motor assembly includes a DC brushless motor and such an angular position sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will be better understood by reading the following description, given by way of example only, and with reference to the accompanying drawings, in which:

[0023] Figure 1 shows the arrangement of the coils as seen at the end of the shaft;

[0024] Figure 2 The wiring of a set of coils is shown;

[0025] Figure 3 Shows the principle of wiring to the processing unit;

[0026] Figure 4 Shows detailed wiring;

[0027] Figure 5 , Figure 6 and Figure 7 The measurement signals obtained for the angular positions 0°, 45°-Δ and 90° are shown. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, an angular position sensor 1 capable of measuring the relative angular position between a rotor R and a stator S comprises a target C on the one hand and a sensitive element on the other hand, wherein the rotor R rotates with an axis A. The target C is ferromagnetic, for example made of steel, so as to change the magnetic field in the coil, and has an oval cross section relative to the axis A. The target C rotates with the rotor R, as shown in FIG. Figure 1 As shown, or according to an alternative embodiment, the target C rotates together with the stator S. The sensitive element comprises a first group J1 of coils L11, L12, L13, L14. Figure 1 As shown, the group J1 rotates with the stator S or, according to an alternative embodiment, with the rotor R. Preferably, the target C rotates with the rotor R. In particular, it is easier to connect the coils L11, L12, L13, L14 from the stator to the processing electronics. The coils L11, L12, L13, L14 are evenly distributed around the axis A, i.e. every 360° / n, where n is the cardinality of the number of coils / groups. Thus, 2 (n=2) coils are arranged at 180°, diametrically opposite each other. 3 (n=3) coils are arranged at 120°. As shown, 4 (n=4) coils are arranged at 90°. 8 (n=8) coils are arranged at 45°. The coils L11, L12, L13, L14 are arranged in line axially with the target C so that the distance to the target C and its variation can be measured so as to deduce the angular position of the rotor R relative to the stator S therefrom.

[0029] The cross section of the target C has a variable radius, so that the air gap seen by the coil varies continuously with the angular position. Advantageously, this cross section is repeated over a certain axial length, which is sufficient to be seen by the coil and allows to tolerate possible axial displacements of the coil. However, the coils are theoretically all arranged on the same cross section, in the same plane.

[0030] Compared to a resolver in which the equivalent of the target is a primary coil, the fact that the target C is passive makes it possible to omit an expensive excitation circuit for said primary coil. This excitation circuit comprises a sinusoidal voltage generator which usually comprises an audio amplifier. The invention makes it possible to omit such a circuit and to reduce costs accordingly.

[0031] The radius of the cross section of the target C preferably varies continuously in order to produce a continuous variation of the measured value. The measured value is advantageously sinusoidal, although the magnetic variation is quadratic.

[0032] The radius of the cross section of the target C varies between a minimum value and a maximum value, wherein the target C has a protrusion E. According to another feature, the target C comprises a plurality of protrusions E, the number of which is equal to half the cardinality n of the groups J1, J2. Thus, in the example shown, the target C comprises 2 protrusions E and each group J1, J2 comprises 4 coils. According to one embodiment, the cross section of the target C is elliptical.

[0033] Thus, in theory, the principle of the invention is applicable to a sensor comprising a target C with a single protrusion E having at least one set J1, J2 of coils comprising 2 coils. Such an embodiment complicates the manufacture of a target C having an eccentric cam shape. The presence of 2 coils per set J1, J2 significantly reduces the sensitivity of the sensor. In addition, the 2 coils prevent the above-mentioned very advantageous feature of the Wheatstone bridge.

[0034] This feature also has the consequence that the cardinality of the groups J1, J2 must be even.

[0035] According to another feature, the sensitive element also includes a second group J2 of coils L21, L22, L23, L24. The cardinality of the second group J2 is the same as that of the first group J1. The coils L21, L22, L23, L24 of the second group J2 are similar to the coils of the first group J1 and are angularly equally distributed relative to each other. In addition, they are angularly inserted in the middle between the coils L11, L12, L13, L14 of the first group J1. Therefore, each coil L21, L22, L23, L24 of the second group J2 is arranged in the middle between two coils of the first group J1. Therefore, the second group J2 is angularly offset by 360° / 2n relative to the first group J1. Therefore, for a configuration in which each group J1, J2 has n=4 coils, the 4 coils of the second group J2 are arranged at 45° to the 4 coils of the first group J1.

[0036] According to another feature, the coils L11 , L12, L13, L14, L21 , L22, L23, L24 are arranged to have maximum sensitivity to variations in the air gap or distance to the target C. This is obtained by a radial arrangement, wherein the axes of the coils are arranged radially relative to the axis A.

[0037] Likewise, there is the question of the physical direction / orientation of the coils of the same set J1, J2. The coils of the same set J1, J2 can be arranged in a configuration in which all coils of the set J1, J2 have the same magnetic polarity, i.e. inmagnetic series. Alternatively, in the case of an even cardinality n, the magnetic polarity of one coil out of every two coils within the same set J1, J2 can be alternated in a magnetically opposite configuration. Both configurations, paramagnetic or magnetically opposite, are possible and functional. However, simulations have shown that for the connection of the coils of the same set J1, J2 in a paramagnetic manner, a better sensitivity of the sensor is obtained. Therefore, this configuration is preferred.

[0038] exist Figure 2 and 4 In the figure, the points next to the coils L1, L2, L3, L4 mark the ends of the coils facing the target C.

[0039] According to another feature, the cross section of the target C has two symmetrical protrusions E. This preferred configuration is as Figure 1 Symmetry requires that the two protrusions are identical and radially opposite. Here, the cross section is advantageously elliptical.

[0040] Advantageously, the cardinality of the first group J1 is equal to 4. Therefore, the cardinality of the second group J2 is equal to 4. According to another particularly advantageous feature, the four coils L11, L12, L13, L14 of the first group J1 are connected in a Wheatstone bridge. Likewise, advantageously, the four coils L21, L22, L23, L24 of the second group J2 are connected in a Wheatstone bridge.

[0041] exist Figure 2 and Figure 4 In the figure, four coils are represented by L1, L2, L3, and L4, and respectively represent the coils L11, L12, L13, and L14 of the first group J1 or the coils L21, L22, L23, and L24 of the second group J2.

[0042] exist Figure 3 In FIG. 1 , the Wheatstone bridge and a set of four coils are represented by solid diamonds.

[0043] This Wheatstone bridge configuration makes it possible to attenuate thermal drifts of the components, to increase the sensitivity of the measurement and to compensate for any coil positioning tolerances.

[0044] Advantageously, this configuration allows the same set of coils J1 , J2 to themselves generate the magnetic flux through the target C. The target C can thus be passive, which is advantageous with respect to a resolver.

[0045] Powering all coils simultaneously creates a magnetic flux through target C whose sum is approximately constant.

[0046] According to Figure 2-4 Another feature visible in FIG. 1 is that, for each of the Wheatstone bridges in each of the groups J1 , J2 , between the two first diagonal points Vsp, Vsn, the Wheatstone bridge is supplied with two square wave signals of anti-phase.

[0047] The power supply / excitation signal SE applied at Vsn is a square wave signal that varies between a low voltage, such as 0 V, and a high voltage, such as 5 V. It varies periodically with a period of, for example, 20 μs / 50 kHz (corresponding to the resonant frequency of the sensor 1 ), as described below, with a duty cycle of 50%. The complementary signal applied at Vsp is a complementary 5V signal or an inverted signal.

[0048] Advantageously, the power supply / excitation signal SE is generated by a processing unit U which processes the signals S1, S2 measured between Vp and Vn from the coils to produce the angular position. The same excitation signal SE can advantageously be used to excite the two Wheatstone bridges of the two groups J1, J2.

[0049] like Figure 2-4 According to another feature, on a Wheatstone bridge, measurements S1, S2 are taken between two second diagonal points Vp, Vn, which are different from the first two diagonal points Vsp, Vsn for power supply / excitation. This is done for each of the groups J1, J2 to obtain two measurement signals S1, S2.

[0050] like Figure 3-4 As shown, according to another feature, the two potentials measured at the two second diagonal points Vp, Vn are sent to the differential amplifier AOP for differential processing of the measured values. Figure 4 In the example, amplifiers AOP1 and AOP2 implement a differential amplifier, which is equivalent to Figure 3 AOP.

[0051] According to another feature, each Wheatstone bridge / group J1, J2 has a resonant frequency. Assuming that the 4 coils of the group J1, J2 are identical, this resonant frequency is equivalent to the resonant frequency of the coils. Therefore, advantageously, the excitation signal SE applied to the Wheatstone bridge has a frequency equal to this resonant frequency. This makes it possible to avoid too high a winding excitation current for the output ports of the processing unit U.

[0052] To this end, the sensor 1 comprises a resonator. For each Wheatstone bridge / group J1, J2, the resonator comprises a first capacitor C1 for the excitation SE of the group J1, J2, arranged between the two second diagonal points Vp, Vn, and a second capacitor C2 for the measurement S1, S2, arranged between the two first diagonal points Vsp, Vsn. This enables self-excitation by resonance of the coil. The values ​​of the capacitors C1, C2 are matched to the operating frequency of the sensor. Thus, for example, for 50 kHz, C1=C2=100 nF.

[0053] These capacitors C1 , C2 are advantageously supplemented by resistors R10 , R11 connected in series to the points Vsp, Vsn. These resistors make it possible to reduce the excitation current SE from the processing unit U.

[0054] All this (with respect to the coils of the groups J1 , J2 ) makes it possible to “round off” the square wave signal injected as excitation SE to produce sinusoidal measurement signals S1 , S2 .

[0055] According to another feature, the coils L11, L12, L13, L14, L21, L22, L23, L24 are surface mounted or SMD coils. Such SMD coils are mounted on a printed circuit. This allows mounting on a flat printed circuit, which is advantageously arranged perpendicular to the axis A.

[0056] According to another advantageous feature, the printed circuit coincides with that of the processing unit U or computer and allows to greatly simplify the integration. Thus, for a resolver that must be placed at the end of a shaft and therefore cannot be integrated close to the processing unit U, a 6-wire cable is required between the processing unit U and the resolver. The feature of the SMD coil integrated on the printed circuit of the processing unit U advantageously makes it possible to omit this 6-wire cable.

[0057] Figure 5 , 6 7 show on the one hand a square wave excitation signal SE and on the other hand a signal S1, S2 measured for each of the groups J1, J2 of coils. The excitation signal is a square wave signal with a frequency of 50 kHz. The signals S1 and S2 are sinusoidal signals, with opposite phases relative to each other and with the same frequency, equal to the frequency of the excitation signal SE. Figure 5 The signals SE, S1, S2 are shown when the angle / angular position between the rotor R and the stator S is equal to 0°. The maximum amplitudes of the signals S1 and S2 are observed. Figure 6 The signals are shown when the angle / angular position between the rotor R and the stator S is almost equal to 45°. Minimum amplitudes close to zero are observed for the signals S1 and S2. Figure 7The signals are shown when the angle / angular position between the rotor R and the stator S is equal to 90°. The maximum amplitude of the signal S1 and the signal S2 is observed, but relative to Figure 5 The same signals S1 and S2 at the / 0° position have opposite phases.

[0058] It can be noted that the mechanical and electrical assembly of the coils results in that it is possible to distinguish between when the projection E faces the coils L11, L13 or the coils L12, L14. However, due to the mechanical and electrical symmetry, it is not possible to distinguish between when the projection E faces the coils L11, L13 and the coils L13, L11 and likewise it is not possible to distinguish between when the projection E faces the coils L12, L14 and the coils L14, L12. The angular position determined by the sensor 1 is therefore obtained modulo 180° in its configuration with 4 coils per group J1, J2.

[0059] The measurement signals S1, S2 obtained by the sensor 1 are sinusoidal signals in phase quadrature and whose amplitude indicates the angular position. In this respect, they are identical to the signals from the resolver (usually called sine and cosine). Therefore, according to another characteristic, these signals S1, S2 can advantageously be processed by a processing unit U for the resolver. The sensor 1 advantageously comprises such a processing unit U for processing / conditioning measurements of the resolver type in order to convert the measurement signals S1, S2 into angular position.

[0060] The invention also relates to a DC brushless motor assembly comprising a DC brushless motor and an angular position sensor 1 according to the invention. Due to the fact that the measurements are obtained modulo 180°, such a motor assembly is easily adaptable as long as the motor comprises an even number of poles at least equal to 4 poles.

[0061] The present invention has been illustrated and described in detail in the drawings and the above description. This should be considered illustrative and given by way of example, rather than limiting the present invention to only this description. Many variations are possible.

[0062] Reference numerals list

[0063] 1: Sensor

[0064] A: Axis

[0065] AOP: Operational Amplifier

[0066] C: Target

[0067] C1, C2: capacitors

[0068] E: protrusion

[0069] J1, J2: coil assembly

[0070] L1, L2, L3, L4, L11, L12, L13, L14, L21, L22, L23, L24: Coil

[0071] R: Rotor

[0072] S: stator

[0073] U: Processing Unit

[0074] Vp, Vn, Vsp, Vsn: points.

Claims

1. An angular position sensor for sensing the angular position of a rotor rotating on an axis relative to a stator, comprising a ferromagnetic target of oval cross-section and a sensitive element, wherein the target rotates together with one of the rotor or the stator, and the sensitive element comprises a first group of coils uniformly distributed in angle, which rotates together with the other of the rotor or the stator, each of the coils of the first group being arranged in line with the target so as to be able to measure the distance to the target, so that the angular position of the rotor relative to the stator can be deduced therefrom; the sensor is characterized in that: the sensitive element further comprises a second group of coils having the same cardinality as the first group, the coils of the second group being angularly uniformly distributed relative to each other and interposed angularly in between the coils of the first group, The cardinality of the first group or the second group is equal to 4, and the coils of the first group or the coils of the second group are connected in a Wheatstone bridge, respectively, the sensor further comprises a resonator, the resonator being designed to achieve self-excitation through resonance of the coil, the resonator comprising a first capacitor arranged between two second diagonal points for exciting the first group and the second group, and a second capacitor arranged between the two first diagonal points for measuring a signal to generate an angular position, The first group and the second group have a resonant frequency, • The excitation signal applied to the Wheatstone bridge has a frequency equal to the resonant frequency.

2. The sensor according to claim 1, wherein: The cross-section of the target includes a plurality of protrusions, the number of which is equal to half of the base number.

3. The sensor according to claim 1 or 2, wherein: The first and second groups of coils are arranged radially relative to the axis.

4. The sensor according to claim 1 or 2, wherein: The first and second groups of coils are connected in a paramagnetic manner.

5. The sensor according to claim 1 or 2, wherein: The cross section of the target has two symmetrical protrusions.

6. The sensor according to claim 1, wherein: Between the two first diagonal points, two square wave signals of anti-phase are supplied to the Wheatstone bridge.

7. The sensor according to claim 6, wherein: On the Wheatstone bridge, measured values ​​are taken between two second diagonal points which are different from the two first diagonal points.

8. A sensor according to claim 6 or 7, further comprising a differential amplifier for processing measurements taken between two second diagonal points.

9. The sensor according to claim 1 or 2, wherein: The coils of the first and second groups are surface mounted SMD coils mounted on a printed circuit, which are arranged perpendicular to the axis.

10. A sensor according to claim 1 or 2, comprising a measurement processing unit of the resolver type.

11. A DC brushless motor assembly comprising a DC brushless motor and an angular position sensor according to any one of claims 1 to 10.

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