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, a magnetic track (2) 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 at least one sensor capable of detecting a rotating magnetic field in a plane perpendicular to the track and the transition zone by means of mountings (4, 4') of at least two sensitive magnetic elements (5), the mountings being disposed at a radial reading distance from the track (2) and arranged 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.

[0011] We also know from document JP-2003-97971 a system in which two sensors are arranged relative to the track for measuring the same unidirectional component of the magnetic field at two positions, said positions being determined such that the signals delivered by said sensors are orthogonal. Summary of the invention

[0012] 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.

[0013] 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.

[0014] To this end, the present invention proposes a system for determining at least one rotation parameter of a rotating component, the system comprising:

[0015] - an encoder intended to be rotationally associated with a rotating member in such a way as to move together with the rotating member, the encoder comprising a body having a cylindrical periphery with a radius a around the axis of rotation, the periphery having alternating north and south magnetic poles of width l separated by transition zones, each of the transition zones extending along a helix of pitch p and angle α so as to form a multipolar track capable of emitting a periodic magnetic field rotating in a plane perpendicular to the track and the transition zones, the 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;

[0016] - At least one sensor capable of detecting the rotating magnetic field emitted by the encoder by means of at least two mounts of sensitive magnetic elements, the mounts being deployed at a radial reading distance from the tracks and arranged to deliver quadrature signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features and advantages of the present invention will appear from the following description with reference to the accompanying drawings, in which:

[0018] [ 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;

[0019] [ Figure 2 ]yes Figure 1a and 1b A plan view of the cylindrical periphery of the encoder;

[0020] [ Figure 3 ] schematically shows an embodiment of the arrangement of the mounting of the sensitive element at the radial reading distance relative to the encoder according to the invention;

[0021] [ Figure 4 ] is a diagram of a mounting member for a sensitive element according to an embodiment of the present invention;

[0022] [ Figure 5 ] shows that according to Figure 4 of orthogonal signals delivered through the mounting;

[0023] [ Figure 6 ] schematically shows an embodiment of the arrangement of the mountings of two sensitive elements at a radial reading distance relative to the encoder according to the invention;

[0024] [ Figure 7 ] Figure 7 yes Figure 6 Figure 2. Integration diagram of the mounting in a device for subtraction.

[0025] [ Figure 8 ] Figure 8 is a graph showing the filtering of the third order harmonics as a function of the distance between the mountings of the sensitive element of the sensor. DETAILED DESCRIPTION

[0026] 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).

[0027] 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.

[0028] 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.

[0029] The track 2 has an alternation of 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.

[0030] 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 In particular, the periodic magnetic field delivered by the track 2 rotates in a plane perpendicular to the track and the transition region 3 .

[0031] 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.

[0032] If it is assumed that the encoder 1 rotates at a constant rotational speed ω, the magnetic field can be expressed as follows:

[0033] H(t)=H1.sinωt+H3.sin3ωt+H5.sin5ωt+…

[0034] The amplitude H3 of the third harmonic may 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 may be much higher.

[0035] 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 1bThe 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.

[0036] 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.

[0037] The system for determination comprises at least one sensor intended to be integrated with a fixed structure, said sensor being able to detect the rotating magnetic field emitted by the encoder 1. To this end, the sensor comprises a mount 4 of at least two sensitive magnetic elements 5, said mount being arranged at a radial reading distance from the track 2 so as to deliver a quadrature signal representative of the rotation of the encoder 1.

[0038] Each of the sensitive elements 5 can in particular be selected from magnetically sensitive probes, such as Hall, Tunnel Magneto-Resistance (TMR), Anisotropic Magneto-Resistance (AMR) or Giant Magneto-Resistance (GMR) probes that can measure each of the two components of the magnetic field (perpendicular and tangential to the encoder 1 ).

[0039] In particular, as described in document WO-2004 / 083881, each element 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.

[0040] Advantageously, each sensitive element 5 may include 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 5 can include a single motif or a group of motifs connected in series or in parallel.

[0041] In order to be able to determine the rotational parameters of the rotating member, the signals delivered by the mounting 4 of the sensitive element 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.

[0042] For this reason, relative to Figure 4 The mounting 4 may comprise two Wheatstone bridge circuits with four sensitive elements 5, said circuits being arranged in a plane perpendicular to the track 2 so as to detect the magnetic field emitted by said track rotating in said plane.

[0043] In particular, according to the inclination angle γ of the magnetic field, Figure 5 shows the quadrature signal V delivered by the bridge 01 and V 02 , which makes:

[0044] V 01 =(+V 01 )–(-V 01 );

[0045] V 02 =(+V 02 )–(-V 02 ).

[0046] 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:

[0047] - Better performance, especially at startup, e.g. in terms of time to reach a speed setting or position setting;

[0048] -More "gentle" operation, no torque shift in steady state;

[0049] - Less energy consumption;

[0050] - Lower operating temperature;

[0051] -Higher maximum torque.

[0052] In particular, Figure 3 The mounting 4 is shown in a mid-position of the periphery of the encoder 1 so as to be as far away from the edge of said encoder as possible.

[0053] about Figure 6 The system for determining comprises two sensors, the mountings 4 and 4' of which deliver orthogonal signals V 01 、V 02 and V' 01 、V' 02 Spaced apart a distance e measured along a normal N to the transition zone 3, the system also comprises means for subtracting the signals so as to form orthogonal SIN, COS signals.

[0054] Figure 7 An embodiment is shown, where the signal formed is:

[0055] SIN=(+SIN)–(-SIN);

[0056] +SIN is equal to (+V 01 )–(+V' 01 ),

[0057] -SIN is equal to (-V01 )–(-V' 01 );

[0058] COS = (+COS) – (-COS);

[0059] +COS is equal to (+V 02 )–(+V' 02 ),

[0060] -COS is equal to (-V 02 )–(-V' 02 ).

[0061] This embodiment allows filtering noise coming from the outside, for example from a motor or adjacent interconnections.In fact, if the magnetic field comprises the same noise component on the different mounts 4, 4', this same noise component will be subtracted from the output signals SIN, COS.

[0062] By positioning the mountings 4, 4' at the magnetic phases φ1 and φ2, respectively, ie by spacing them apart by a distance e measured along the normal N to the transition zone 3, The delivered signals V1 = +COS or +SIN and V2 = -COS or -SIN can be written as:

[0063]

[0064]

[0065] G is the assumed equal gain of the mounts 4, 4', 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, and so on.

[0066] The subtractor circuit calculates the SIN or COS difference, which is then written as:

[0067]

[0068] about Figure 6 , e=L p mod 2L p , i.e. the mounting is offset by 180° mod 360°, the difference being written as:

[0069]

[0070] 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.

[0071] 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.

[0072] Figure 8 shows the offset value according to Filtering of third-order harmonics.

[0073] When the distance e is substantially equal to 2 / 3L p mod 2L p or 4 / 3L p mod 2L p , the difference is written as:

[0074]

[0075] 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.

[0076] Generally speaking, about Figure 8 , 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:

[0077]

[0078] or

[0079] Expressed in distance, in order to obtain filtering of the third order harmonics, it is therefore required that the mountings 4, 4' are spaced apart by a distance e measured along the normal N of the transition zone 3, which is such that:

[0080] 0.55L p mod 2L p <e<0.82L p mod 2L p ;or

[0081] 1.18L p mod 2L p <e<1.45L p mod 2L p

[0082] In particular, the distance e between the mountings 4, 4' can be varied within the ranges mentioned above in order to optimize the coupling filter-gain. Furthermore, depending on the available space, the mountings 4, 4' can be aligned along the normal N of the transition zone 3, along the axis X or along a circumferential offset ( Figure 6 ).

[0083] 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:

[0084] - remove the offset of said signal;

[0085] - balancing the amplitude of said signals;

[0086] - Phase correction between the signals.

Claims

1. A system for determining at least one rotation parameter of a rotating component, the system comprising: - An encoder (1) intended to be rotationally associated with a rotating member in such a way as to move together with the rotating member, the encoder comprising a body having a cylindrical periphery with a radius a around an axis of rotation (X), the periphery having alternating north (2n) and south (2s) magnetic poles of width l separated by transition zones (3), each of the transition zones extending along a helix of pitch p and angle α so as to form a multipolar track (2), the multipolar track (2) being able to emit a periodic magnetic field rotating in a plane perpendicular to the track and the transition zones, the 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 , so that: N pp =πa / l and L p = p * cos α; - two sensors, each capable of detecting the rotating magnetic field emitted by the encoder by means of at least two mounts (4, 4') of sensitive magnetic elements (5), the mounts being arranged at a radial reading distance from the magnetic track (2) and each of the mounts of the two sensors being arranged to deliver a quadrature signal (V 01 、V 02 ; V' 01 , V' 02 ), the mountings (4, 4') of the two sensors being spaced apart by a distance e measured along a normal (N) to the transition zone (3); - means for subtracting the signals of the two mountings (4, 4') of the two sensors in order to form quadrature signals (SIN, COS).

2. The system for determining according to claim 1, characterized in that The mounting (4, 4') comprises two Wheatstone bridge circuits with four sensitive magnetic elements (5), arranged in a plane perpendicular to the track (2) so as to detect the magnetic field emitted by the track rotating in said plane.

3. System for determining according to one of claims 1 or 2, characterized in that Each sensitive magnetic element (5) comprises at least one pattern having a tunnel magnetoresistive material substrate, the electrical resistance of which varies according to a detected magnetic field.

4. The system for determining according to claim 1, characterized in that The distance e is such that: e=L p mod2L p .

5. The system for determining according to claim 1, characterized in that The distance e is such that: 0.55L p mod 2L p <e<0.82L p mod 2L p ;or <h2 style=";text-align:left;direction:ltr">1.18L<h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> mod 2L<h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"><e<1.45L <h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> mod 2L<h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> 。 6. The system for determining according to claim 5, characterized in that The distance e is substantially equal to 2 / 3L p mod 2L p or 4 / 3Lp mod 2L p .

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