System for determining at least one rotation parameter of a rotating component

Abstract

The present disclosure relates to a system for determining at least one rotation parameter of a rotating member. The present invention relates to a system comprising: an encoder having alternating north magnetic poles (2n) and south magnetic poles (2s) separated by transition zones (3) extending along a helix with a pitch p and an angle α, the magnetic track having N pp to the north pole (2n) and the south pole (2s), and having a pole width L measured along the normal (N) of the transition region (3) p , which makes: N pp =πa / l and L p =p*cosα; and a sensor capable of detecting a periodic magnetic field emitted by the encoder by means of at least two sensitive magnetic elements (41, 42; 51, 52), the at least two sensitive magnetic elements being arranged at a radial reading distance from the track (2), the sensitive elements being arranged relative to each other to deliver orthogonal signals.

Description

Technical Field

[0001] The invention relates to a system for determining at least one rotation parameter of a rotating member, said system comprising an encoder emitting a periodic magnetic field and a sensor capable of detecting said magnetic field. Background Art

[0002] In many applications, it is desirable to know at least one rotation parameter of a rotating component, such as its position, its velocity, its acceleration or its direction of movement, in real time and with optimal quality.

[0003] To this end, document WO-2006 / 064169 proposes the use of an encoder intended to be integrated with a mobile member and forming thereon a magnetic track capable of emitting a pseudo-sinusoidal magnetic field at a reading distance from a sensor comprising several sensitive elements.

[0004] Advantageously, each sensitive element may comprise at least one pattern having a tunnel magnetoresistive (TMR) material substrate, the electrical resistance of which varies as a function of the magnetic field detected, as described, for example, in document WO-2004 / 083881.

[0005] In order to determine a movement parameter of a mobile member from the variation of the magnetic field detected, document WO-2006 / 064169 provides for the combination of the signals representative of the resistance of each sensitive element so as to deliver two signals, orthogonal and of equal amplitude, which can be used to calculate said parameter.

[0006] Document WO-2018 / 051011 proposes a system for determination in which the track of the encoder has alternating north and south magnetic poles separated by transition zones, each extending along an Archimedean spiral. With regard to the axial reading of the magnetic field delivered by the encoder, this embodiment makes it possible to separate the number of poles, the width of the poles and the diameter of the encoder. It is thus possible to have very few poles while still having a magnetic signal whose sinusoidal properties are good.

[0007] Furthermore, some applications require a radial reading of the magnetic field delivered by the encoder, in particular due to restrictions on available space. To this end, an encoder is known comprising a body having a cylindrical periphery with a magnetic track formed thereon, the magnetic track having a magnetic transition zone aligned with the axis of rotation.

[0008] In this embodiment, the pole width is the ratio of the circumference to the number of poles, which causes problems for encoders with a small number of pole pairs (typically less than 6) because the pole width becomes quite large, in particular around ten millimeters.

[0009] These wide poles provide a poorly sinusoidal magnetic signal that has a low read gap, becomes full of odd harmonics, is not suitable for accurate angle measurement, requires the sensitive element to be far from the track, which is detrimental to the amplitude of the signal and therefore its good detection by the sensitive element.

[0010] In addition, the wide poles require the encoder to be thicker in order to keep the sinusoidal and amplitude of the magnetic signal sufficient. This is not conducive to the integration of the encoder on a small area and complicates the magnetization method because a larger thickness of material must be magnetically saturated. Summary of the invention

[0011] The present invention aims to complete the prior art by proposing a system for making determinations by radial reading of the magnetic field delivered by an encoder, wherein a compromise can be reached between the periodicity and the amplitude of the detected magnetic field without imposing any specific dimensional constraints on the encoder, which is particularly relevant for magnetic encoders with a small number of pole pairs.

[0012] In particular, the encoder with radial reading according to the invention makes the pole width of each pole independent of the number of pole pairs, thereby enabling a small number of pole pairs with appropriately positioned sensitive elements to be coordinated with respect to the sinusoidality and amplitude of the magnetic field to be detected.

[0013] To this end, the present invention proposes a system for determining at least one rotation parameter of a rotating component, the system comprising:

[0014] - an encoder intended to be associated in rotation with a rotating member in such a way as to move together with the rotating member, said encoder comprising a body having a cylindrical periphery with a radius a around the axis of rotation, said periphery having alternating north and south magnetic poles of width l separated by transition zones, each of said transition zones extending along a helix of pitch p and angle α so as to form a multipolar magnetic track capable of emitting a periodic magnetic field representative of the rotation of said encoder, said track having N pp to the north and south poles, and having a pole width L measured along the normal of the transition region p , so that: N pp =πa / l and L p = p * cos α;

[0015] - a sensor capable of detecting a periodic magnetic field emitted by the encoder by means of at least two sensitive magnetic elements disposed at a radial reading distance from the tracks, the sensitive elements being disposed relative to each other so as to deliver orthogonal signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other features and advantages of the present invention will appear from the following description with reference to the accompanying drawings, in which:

[0017] [ Figure 1a ]and[ Figure 1b ] respectively in perspective view ( Figure 1a ) and side view ( Figure 1b ) schematically shows an encoder of a system for determining according to the present invention;

[0018] [ Figure 2 ]yes Figure 1a and 1b A plan view of the cylindrical periphery of the encoder;

[0019] [ Figure 3a ]and[ Figure 3b ] respectively schematically show alternative embodiments of the arrangement at the radial reading distance relative to the sensitive element of the encoder according to the invention;

[0020] [ Figure 4a ]and Figure 4b ] respectively schematically show alternative embodiments of the arrangement at the radial reading distance of the sensitive elements in groups relative to the encoder according to the invention;

[0021] [ Figure 5a ]、[ Figure 5b ]and[ Figure 5c ] respectively schematically show alternative embodiments of the arrangement at the radial reading distance of the sensitive elements in groups relative to the encoder according to the invention;

[0022] [ Figure 6 ] is a curve showing filtering of third-order harmonics according to the distance between sensitive elements of a group. DETAILED DESCRIPTION

[0023] In conjunction with these figures, a system for determining at least one rotation parameter of a rotating component relative to a fixed structure is described. In particular, the parameter of the rotating component can be selected from its position, its speed, the direction of its rotation, its acceleration or the direction of its movement (in particular the axis).

[0024] In a particular application, the system may be used in connection with the control of a brushless DC motor, in particular to make known the absolute angular position of a pair of motor poles of the rotor relative to the stator.

[0025] The system for determining comprises an encoder 1 intended to be formed integrally with a rotating member so as to move therewith, said encoder comprising a body having a cylindrical periphery of radius a around an axis of rotation X, on which a magnetic track 2 is formed, capable of emitting a periodic magnetic field representative of the rotation of said encoder. In particular, the emitted magnetic field can be sinusoidal or pseudo-sinusoidal, ie having at least one portion that can be correctly approximated by a sine.

[0026] The track 2 has alternating north and south magnetic poles 2n, 2s of width l separated by transition zones 3, each of which extends along a helix with pitch p and angle α.

[0027] Therefore, the track has N pp to the north and south poles and having a pole width L measured along the normal N of the transition region 3 p , so that: N pp =πa / l and L p =p*cosα. Track 2 delivers a pseudo-sinusoidal magnetic signal whose spatial period along the normal N is equal to λ=2*L p .

[0028] In particular, the magnetic field generated by the encoder 1 on a pair of magnetic poles 2n, 2s is a combination of a perfect fundamental sine wave component and several odd order harmonics (3rd, 5th, etc.) to be measured for the purpose of determining the parameter.

[0029] If it is assumed that the encoder 1 rotates at a constant rotational speed ω, the magnetic field can be expressed as follows:

[0030] H(t)=H1.sinωt+H3.sin3ωt+H5.sin5ωt+…

[0031] The amplitude H3 of the third harmonic can typically represent 5% of the amplitude H1 of the fundamental wave. Depending on the location of the sensor and the reading distance, this ratio of the amplitude H3 of the third harmonic can be much higher.

[0032] The spiral geometry of the track 2 is such that the number N of magnetic pole pairs 2n, 2s is pp And the pole width L p Can be selected independently of the radius a of the track 2. Figure 1a and 1b The encoder 1 comprises four pairs of magnetic poles 2n, 2s, which is particularly suitable for controlling a motor having four pairs of magnetic poles. The system provides an absolute position on one pair of motor magnetic poles, i.e., a 90° mechanical angle.

[0033] According to an embodiment, the encoder 1 is formed by a magnet on the cylindrical periphery executing a multipolar track 2. In particular, the magnet can be formed by an annular matrix, for example made of a substrate of plastic or elastomeric material, in which magnetic particles are dispersed, in particular particles of ferrite or rare earth such as NdFeB.

[0034] The system for determination comprises a sensor intended to be integrated with a fixed structure, said sensor being able to detect a periodic magnetic field emitted by the encoder 1. To this end, the sensor comprises at least two sensitive magnetic elements 4, 5, arranged at a radial reading distance from the track 2 so that each magnetic element delivers a signal representative of the rotation of the encoder 1, said sensitive elements being arranged relative to each other so as to deliver orthogonal signals.

[0035] Each of the sensitive elements 4, 5 can in particular be selected from magnetically sensitive probes, such as Hall, tunnel magnetoresistance (TMR), anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) probes that can measure each of the two components of the magnetic field (perpendicular and tangential to the encoder 1).

[0036] In particular, as described in document WO-2004 / 083881, each element 4, 5 forms a tunnel junction by a stack comprising a reference magnetic layer, an insulating isolation layer and a magnetic layer sensitive to the field to be detected, the resistance of the stack depending on the relative orientation of the magnetizations of the magnetic layers.

[0037] Advantageously, each sensitive element 4, 5 may comprise at least one pattern having a magnetoresistive material substrate, in particular a pattern having a tunnel effect, the resistance of which varies according to the magnetic field, and the sensitive element 4, 5 can comprise a single motif or a group of motifs connected in series or in parallel.

[0038] Alternatively, Hall elements may be used, for example, to measure only the normal component of the magnetic field delivered by the encoder 1. Using the normal field alone is advantageous because it is more sinusoidal than the tangential field.

[0039] In order to be able to determine the rotational parameters of the rotating member, the signals delivered by the sensitive elements 4, 5 must preferably be orthogonal, ie geometrically offset by 90° divided by N. pp In particular, it is known to determine the angular position of the encoder 1 by using such quadrature signals in the sensor or in an associated calculator, for example using a look-up table (LUT) or a CORDIC type method by directly calculating the inverse tangent function.

[0040] For this reason, relative to Figure 3a and 3b The sensor comprises at least two sensitive elements 4, 5 which are spaced apart by a distance d measured along the normal N of the transition zone 3, the distance d being equal to L p / 2mod L p In other words, when the sensitive element 4 is positioned facing the transition zone 3 , another sensitive element 5 is positioned on a spiral parallel to said transition zone and spaced apart therefrom by a distance d measured along the normal N.

[0041] Thus, a good compromise is obtained between sinusoidality and amplitude of the detected signal. In particular, pole widths L between 2 mm and 6 mm can be used. p , and then even using encoder 1's N pp (This number is less than 6) pairs of magnetic poles 2n, 2s to obtain the optimal positioning.

[0042] Regarding the application of the system in controlling electric motors, the signal delivered to the control computer has a good sinusoidal nature allowing in particular:

[0043] - Better performance, especially at startup, e.g. in terms of time to reach a speed setting or position setting;

[0044] -More "gentle" operation, no torque shift in steady state;

[0045] - Less energy consumption;

[0046] - Lower operating temperature;

[0047] -Higher maximum torque.

[0048] In particular, Figure 3a Two sensitive elements 4, 5 are shown, which are aligned along the normal N of the transition region 3, said elements being Figure 3b Mid-circumferential alignment, in particular in the middle of the periphery of the encoder 1, so as to be separated as much as possible from the edge of said encoder. Alternatively, the two sensitive elements 4, 5 can be aligned along the axis X of rotation.

[0049] Relative to Figures 4a to 5c The sensor comprises at least two groups of two sensitive elements 41, 42; 51, 52, wherein the center of gravity of one group of sensitive elements 41, 42; 51, 52 is separated from the center of gravity of the other group of sensitive elements 41, 42; 51, 52 by a distance d measured along the normal N of the transition zone 3, d being equal to L p / 2mod L p .

[0050] Therefore, relative to Figure 3a and 3b This repetition of the sensitive elements 4, 5 of the embodiment of the two groups allows filtering of noise coming from the outside, for example from an electric motor or an adjacent interconnection.

[0051] Indeed, assuming that the sensor also comprises means for subtracting the signals (V1, V2) delivered by the two sensitive elements 41, 42; 51, 52 of each of these groups, if the magnetic field comprises the same noise component on the different sensitive elements 41, 42; 51, 52, this same noise component will be subtracted from the output signal.

[0052] By positioning a set of sensitive elements 41, 42; 51, 52 at the magnetic phases φ1 and φ2, respectively, i.e. by spacing them apart by a distance e measured along the normal N to the transition zone 3, such that The signal V1, V2 delivered by each of the sensitive elements 41, 42; 51, 52 can be written as:

[0053]

[0054]

[0055] G is the assumed same gain of the sensitive elements 41, 42; 51, 52, ω is the speed of rotation, H i is the amplitude of the fundamental frequency for i=1 and the amplitude of the i-th harmonic for i=3, 5, etc.

[0056] The subtractor circuit calculates the difference, which is then written as:

[0057]

[0058] about Figure 4a and 4b , e=L p mod 2L p , that is, a set of sensitive elements 41, 42; 51, 52 are offset by 180° mod 360°, the difference being written as:

[0059]

[0060] It can be seen that after the subtraction operation, the third and fifth order harmonics are retained and have the same gain of 2 as the fundamental.

[0061] In order to obtain an accurate determination of the rotation parameters, filtered signals of at least the third harmonic are measured. However, it is difficult to make any fixed compensation for the error generated by the harmonics, especially since it depends on the measurement conditions (gap, position of the sensor). Moreover, calibration is difficult for large-volume and low-cost applications.

[0062] Figure 6 shows the offset value according to Filtering of third-order harmonics.

[0063] Regarding the distance e which is substantially equal to 2 / 3L p mod 2L p or 4 / 3L p mod 2L p of Figures 5a to 5c , the difference is written as:

[0064]

[0065] In this case, the third order harmonic is cancelled, and after the subtraction, the gain between the fundamental and fifth order harmonic is 1.73. A third order harmonic spatial filter is then performed while still retaining 86.5% of the fundamental.

[0066] Generally speaking, about Figure 6 , considering that a third-order harmonic filter would work if it removed at least 3dB from its value without filtering relative to the amplitude of the fundamental, thus requiring:

[0067]

[0068]

[0069] or

[0070] Expressed in terms of distance, in order to obtain filtering of the third order harmonics, it is therefore required that a set of sensitive elements 41, 42; 51, 52 be spaced apart by a distance e measured along the normal N of the transition zone 3, which is such that:

[0071] 0.55L p mod 2L p <e<0.82L p mod 2L p ;or

[0072] 1.18L p mod 2L p <e<1.45L p mod 2L p

[0073] In particular, the distance e between a group of sensitive elements 41, 42; 51, 52 can be varied within the range mentioned above in order to optimize the coupling filter-gain. In addition, depending on the available space, a group of sensitive elements 41, 42; 51, 52 can be arranged along the normal N ( Figure 4a and 5b ) or along the circumference ( Figure 5c ) alignment. Alternatively, one set of sensitive elements 41, 42; 51, 52 may be circumferentially offset relative to those of the other set ( Figure 4b and 5a ).

[0074] Suppressing or at least attenuating the third order harmonics in the processed signal to determine the rotation parameter is not only beneficial with respect to the accuracy of said determination, but also for the signal processing algorithm that performs the following operations:

[0075] - remove the offset of said signal;

[0076] - balancing the amplitude of said signals;

[0077] - Phase correction between the signals.

Claims

1. A system for determining at least one rotational parameter of a rotating component, the system comprising: - an encoder (1) intended to move with the rotating member in such a manner as to move with the rotating member Rotationally associated, the encoder comprises a body with a cylindrical periphery having a radius a around an axis of rotation (X), the periphery having alternating north magnetic poles (2n) and south magnetic poles (2s) of width l separated by transition zones (3), each of the transition zones extending along a helix of pitch p and angle α to form a multipolar magnetic track (2), the multipolar magnetic track (2) being capable of capable of emitting a periodic magnetic field representing the rotation of the encoder, the magnetic track having N pp to the north magnetic pole (2n) and the south magnetic pole (2s), and having a pole width L measured along the normal (N) of the transition region (3) p , such that: N pp =πa / l and L p =p*cosα; - a sensor capable of sensing magnetic fields with the aid of at least two sensitive magnetic elements (4, 5; 41, 42; 51, 52) detect the periodic magnetic field emitted by the encoder, the at least two sensors Sensitive magnetic elements are disposed at a radial reading distance from the magnetic track (2), said sensitive magnetic elements being disposed relative to each other to deliver quadrature signals, - wherein the sensor comprises at least two groups of two sensitive magnetic elements (41, 42; 51, 52), wherein a group of sensitive magnetic elements (41, 42; 51, 52) has a gravitational The center of gravity of another group of sensitive magnetic elements (51, 52, 41, 42) is separated along The distance d measured from the normal (N) of the transition zone (3) is equal to L p / 2mod L p .

2. The system for determining according to claim 1, characterized in that The sensor also comprises means for subtracting the signals (V1, V2) delivered by the two sensitive magnetic elements (41, 42; 51, 52) of each of the groups.

3. The system for determining according to claim 1, wherein: A set of sensitive magnetic elements (41, 42; 51, 52) are spaced apart by a distance e measured along the normal (N) of the transition zone (3) such that: e=L p mod 2L p .

4. The system for determining according to claim 1, wherein: A set of sensitive magnetic elements (41, 42; 51, 52) are spaced apart by a distance e measured along a normal (N) to the transition region (3) such that: 0.55L p mod 2L p <e<0.82L p mod 2L p ;or 1.18L p mod 2L p <e<1.45L p mod 2L p 。 5. The system for determining according to claim 4, characterized in that The distance e is substantially equal to 2 / 3L p mod 2L p or 4 / 3L p mod 2L p .

6. The system for determining according to claim 1, wherein: The sensitive magnetic elements (41, 42; 51, 52) are aligned.

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