System for determining at least one rotational parameter of a rotating member - Patents.com

Abstract

To provide a system for determining at least one rotation parameter of a rotating member.SOLUTION: A coder has alternating N poles 2n and S poles 2s separated by transitions 3 extending along a helix of pitch p and of angle α. A magnetic track 2 has pairs of N and S poles 2n, 2s and a polar width Lp, expressed as Lp=p×cos(α), as measured along a normal to the transitions 3. A sensor is capable of detecting a rotating magnetic field in a plane perpendicular to the magnetic track and to the transitions by means of a mounting of at least two magnetic sensing elements. The mounting is disposed at a radial reading distance from the magnetic track 2 and in relation to one another to deliver signals in quadrature.SELECTED DRAWING: Figure 2

Description

Detailed Description of the Invention

[0001] The present invention relates to a system for determining at least one rotation parameter of a rotating member, said system comprising a coder that outputs a periodic magnetic field and a sensor capable of detecting said magnetic field.

[0002] In many applications, it is desirable to identify at least one rotational parameter of a rotating member (eg, the position, velocity, acceleration, or direction of movement of the rotating member) in real time with optimal quality.

[0003] To do this, document WO 2006 / 064169 proposes the use of a coder intended to be integrated with a moving part, on which a magnetic track is formed that is able to output a quasi-sinusoidal magnetic field at a reading distance from a sensor that includes several sensing elements.

[0004] Advantageously, each sensing element may comprise at least one pattern with a Tunnel Magneto Resistance (TMR) substrate whose resistance varies depending on the detected magnetic field, as described, for example, in document WO 2004 / 083881.

[0005] To determine the movement parameters of the movable mass in response to changes in the detected magnetic field, document WO 2006 / 064169 provides a combination of signals representative of the resistance of each sensing element, thereby delivering two signals in quadrature and with the same amplitude, which can be used to calculate said parameters.

[0006] Document WO2018 / 051011 proposes a determination system in which the coder track has alternating north and south poles separated by transitions, each pole extending along an Archimedes spiral. With regard to the axial reading of the magnetic field emitted by the coder, this embodiment can separate the number of poles, the width of the poles, and the diameter of the coder. It is therefore possible to have few poles while still having a magnetic signal with good sinusoidal properties.

[0007] Furthermore, in some applications, particularly due to constraints regarding the available space, a radial reading of the magnetic field emitted by the coder is necessary. To achieve this, coders are known that comprise a body having a cylindrical periphery on which a magnetic track is formed, said track having magnetic transitions aligned with the axis of rotation.

[0008] In this embodiment, the pole width is the ratio of the circumference to the number of poles. Coders with small pole pairs, typically less than six, present problems because the pole width becomes substantial (specifically, about 10 millimeters).

[0009] These wide poles produce magnetic signals with poor sinusoidal properties at small read air gaps. They are rich in odd harmonics and are unsuitable for accurate angle measurements. Therefore, it is necessary to space the sensing element away from the magnetic track, which conflicts with increasing the signal amplitude and therefore is not well detected by the sensing element.

[0010] Furthermore, to maintain sufficient sine wave and amplitude of the magnetic signal, wider poles require the encoder to be substantially thicker, which is undesirable for integrating encoders in reduced dimensions, and which complicates the magnetization method since a larger thickness must be magnetically saturated.

[0011] Document JP200397971 describes a system in which two sensors are arranged relative to a magnetic track, measuring the same unidirectional component of the magnetic field at two positions, the positions being measured so that the signals emitted by the sensors are in quadrature.

[0012] The present invention aims to complete the state of the art by notably proposing a determination system by radial reading of the magnetic field emitted by a coder, in which a compromise between periodicity and amplitude of the detected magnetic field can be satisfied without inducing any particular size constraints on the coder, in particular for magnetic coders with a small number of pole pairs.

[0013] In particular, a coder with radial reading according to the present invention has a pole width for each pole that is independent of the number of pole pairs, and therefore a small number of pole pairs can be matched with appropriate positioning of the sensing elements relative to the sinusoidal nature and amplitude of the magnetic field to be detected.

[0014] To this effect, the invention proposes a system for determining at least one rotation parameter of a rotating member, said system comprising a coder and at least one sensor, The coder is configured to operate in conjunction with the rotating member to rotate therewith, the coder comprising a body having a cylindrical periphery with a radius a about an axis of rotation, the periphery having alternating north and south poles with a width l separated by transitions, each of the transitions extending along a helix of pitch p and angle α to form a multi-pole magnetic track capable of outputting a periodic magnetic field, the track having a N pole with a N pole and a S pole. pp pair and the polar width L to the transition measured along the normal N p N pp =πa / l and L p= p·cos α, the periodic magnetic field rotating in a plane perpendicular to the magnetic track and the transition, the sensor being capable of detecting the rotating periodic magnetic field output by the coder by means of an implementation of at least two sensitive magnetic elements, the implementations being positioned at a radial reading distance from the magnetic track and arranged to emit quadrature signals.

[0015] Other features and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings. [Fig. 1a] (perspective view) and [Fig. 1b] (side view) each show a schematic representation of a coder of a determination system of the present invention. [Fig. 2] is a plan view of the cylindrical periphery of the coder of Fig. 1a and Fig. 1b. [Fig. 3] shows a schematic representation of an embodiment of a sensing element implementation at a radial read distance relative to a coder of the present invention. [Fig. 4] is a diagram of an implementation of a sensing element of an embodiment of the present invention. [Fig. 5] shows the quadrature signals emitted by the implementation of Fig. 4. [Fig. 6] shows a schematic representation of an embodiment of two sensing element implementations at a radial read distance relative to a coder of the present invention. [Fig. 7] is an integral diagram of the implementation of Fig. 6 in a subtraction device. [Fig. 8] is a curve showing the filtering of the third harmonic as a function of the distance between the sensing elements of a sensor implementation.

[0016] In connection with these figures, a system for determining at least one rotational parameter of a rotating member relative to a fixed structure is described, in particular the parameter of the rotating member may be selected from the position, velocity, rotation direction, acceleration or direction of movement (in particular axial direction) of said rotating member.

[0017] In a particular application, the system may be used in connection with the control of a brushless DC electric motor, in particular to identify the absolute angular position of a pair of motor poles, the rotor relative to the stator.

[0018] The determination system comprises a coder 1 intended to be integrated with a rotating member so as to move together with the rotating member. The coder comprises a body having a cylindrical periphery with a radius a and centered on a rotation axis X, on which a magnetic track 2 is formed. The magnetic track 2 is capable of outputting a periodic magnetic field indicative of the rotation of the coder. In particular, the output magnetic field may be sinusoidal or pseudo-sinusoidal, i.e., the magnetic field has at least one portion that can be accurately approximated by a sine wave.

[0019] The track 2 has alternating north and south poles 2n and 2s of width l separated by transitions 3, each of which extends along a helix of pitch p and angle α.

[0020] Therefore, the magnetic track is made up of N and S poles. pp pair and the polar width L measured along the normal N to the transition 3 p N pp = πa / l, and L p = p cos α. Magnetic track 2 is λ = 2.L p The spatial period is along the normal N. In particular, the periodic magnetic field emitted by the magnetic track 2 rotates in a plane that is perpendicular to the magnetic track and the transition 3.

[0021] The magnetic field generated by the coder 1 on a pair of magnetic poles 2n, 2s is a combination of the perfect fundamental sinusoidal component and some odd harmonics (third, fifth, etc.) that are sought to be measured to determine the parameters.

[0022] Assuming that the coder 1 rotates at a constant rotational speed ω, the magnetic field can be written as follows:

[0023]

number

[0024] The amplitude H3 of the third harmonic may typically represent 5% of the amplitude H1 of the fundamental. Depending on the sensor location and reading distance, this ratio of the amplitude H3 of the third harmonic may be much larger.

[0025] According to the helical shape of the magnetic track 2, in particular, the number N of pairs of magnetic poles 2n, 2s pp and pole width L p can be selected independently of the radius R of the magnetic track 2. With reference to Figures 1a and 1b, the coder 1 comprises four pairs of magnetic poles 2n, 2s and is particularly suitable for controlling electric motors with four magnetic pole pairs. The system provides an absolute angle (i.e., a 90° mechanical position) on a pair of motor poles.

[0026] According to one embodiment, the coder 1 is formed by a magnet having a multi-pole magnetic track 2 executed on its cylindrical periphery. In particular, the magnet may be formed by an annular matrix made from a base material of plastic or elastomeric material, in which magnetic particles (in particular particles of ferrite or rare earths such as NdFeB) are dispersed.

[0027] The determination system comprises at least one sensor adapted to be integrally mounted on a fixed structure, capable of detecting the rotating periodic magnetic field output by the coder 1. To do this, the sensor comprises implementations 4 of at least two magnetic sensing elements 5, which are arranged at a radial reading distance from the magnetic track 2 so as to emit quadrature signals representative of the rotation of the coder 1.

[0028] Each of the sensing elements 5 may in particular be selected from among magnetically sensitive sensors, for example probes based on the Hall effect, tunneling magnetoresistance (TMR), anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) capable of measuring each one of two components of a magnetic field (normal (perpendicular) or tangential to the coder 1).

[0029] In particular, as described for example in document WO 2004 / 083881, each element 5 comprises a stack of a reference magnetic layer, an insulating isolation layer and a magnetic layer sensitive to the magnetic field to be detected, thereby forming a tunnel junction, the resistance of which is a function of the relative magnetization directions of the magnetic layers.

[0030] Advantageously, each sensing element 5 may comprise at least one pattern based on a magnetoresistive material whose resistance varies depending on a magnetic field (in particular, having a tunneling effect). A sensing element 5 may comprise a single motif or a group of motifs connected in series or in parallel.

[0031] In order to be able to determine the rotational parameters of the rotating member, the signals emitted by the sensing elements 5 must be in quadrature, i.e. they must be geometrically offset by Npp over 90° (90° / Npp). It is known that by using such quadrature signals, in particular in the sensor or in an associated computer, it is possible to determine the angular position of the coder 1, for example by direct calculation of the arctangent function by means of a "Look-up Table" (LUT) or by a CORDIC-type method.

[0032] To do this, with reference to Figure 4, the implementation 4 may include two Wheatstone bridge circuits of four sensing magnetic elements 5 arranged in a plane perpendicular to the magnetic track 2 to detect the magnetic field output from said track and rotating in said plane.

[0033] In particular, according to the tilt angle γ of the magnetic field, FIG. 5 shows that the quadrature signals V 01 and V 02 V 01 and V 02 is shown as follows: V 01 =(+V 01)-(-V 01 ) V 02 =(+V 02 )-(-V 02 )

[0034] In the context of the application of a system for controlling electric motors, good sinusoidality of the signals sent to the control computer makes it possible, in particular, to: Better performance, especially during start-up (e.g. time to reach set speed or position); "Smoother" operation without torque jerking at steady state; Lower energy consumption; Lower operating temperatures; More substantial maximum torque.

[0035] In particular, FIG. 3 shows the mounting 4 in a central position on the periphery of the coder 1, separated as far as possible from the edges of said coder.

[0036] With reference to Figure 6, the quadrature signals V 01 , V 02 and V' 01 , V' 02 by emitting .theta., the system comprises two sensors whose mountings 4, 4' are spaced apart by a distance e measured along the normal N to the transition 3. The system further comprises a device for subtracting the signals to form quadrature sine and cosine signals.

[0037] One embodiment is shown in Figure 7. The signals formed are shown as follows: SIN=(+SIN)-(-SIN); +SIN is (+V 01 )-(+V' 01 ) -SIN is equal to (-V 01 )-(-V' 01 ). COS=(+COS)-(-COS); +COS is (+V 02 )-(+V' 02). -COS is equivalent to (-V 0s )-(-V' 02 ).

[0038] This embodiment allows filtering of noise from outside (eg from the motor or adjacent wiring).

[0039] By separating the mountings 4, 4' by a distance e measured along the normal N to the transition (the distance e can be shown by the formula below) and placing the mountings 4, 4' at magnetic phases φ1 and φ2 (the relationship between φ1 and φ2 is shown below), the signals V1 = +COS or +SIN and V2 = -COS or -SIN can be shown by the formula below.

[0040]

number

[0041]

number

[0042] G is the assumed identical gain of the implementations 4 and 4'. ω is the rotation speed. H i is the amplitude of the fundamental corresponding to i=1 and the amplitude of the i-th harmonic corresponding to i=3, 5, etc.

[0043] The subtractor circuit calculates the difference between the sine and cosine of the following equation:

[0044]

number

[0045] Regarding Figure 6, e=L p modulo 2L p (i.e., the implementation is offset 180° modulo 360°), and the difference (V1(t)-V2(t)) is given as:

[0046]

number

[0047] It can be seen that the third and fifth harmonics are retained and have the same gain of 2 as the fundamental after the subtraction operation.

[0048] To accurately determine rotation parameters, it is desirable to measure signals from which at least the third harmonic has been filtered. However, it is difficult to provide any fixed compensation for the errors caused by harmonics, since the errors depend, among other things, on the measurement conditions (air gap, sensor position). Furthermore, it is difficult to predict the calibration in high-volume, low-cost applications.

[0049] FIG. 8 shows the filtering of the third harmonic depending on the value of the offset:

[0050]

number

[0051] Distance e is 2 / 3L p or 4 / 3L p modulo 2L p When V1(t) is substantially equal to V2(t), the difference (V1(t)-V2(t)) is given by:

[0052]

number

[0053] In the above case, the third harmonic is cancelled and the gain of the fundamental and fifth harmonic after the subtraction operation is 1.73. Next, spatial filtering of the third harmonic was performed while still retaining 86.5% of the fundamental.

[0054] 8, consider the case where the third harmonic filter generally serves to remove at least 3 dB from the third harmonic without filtering the fundamental amplitude. This requires the following relationship:

[0055]

number

[0056] Therefore, in terms of distance, to obtain filtering of the third harmonic, the mountings 4, 4' must be spaced apart by a distance e measured along the normal N to the transition 3, i.e., the following relationship is required: 0.55L p <e<0.82L p , modulo 2L p ,or, 1.18L p <e<1.45L p , modulo 2L p .

[0057] In particular, the distance e between the mountings 4, 4' may be varied within the ranges mentioned above to optimize the joint filtering gain. Furthermore, depending on the available space, the mountings 4, 4' may be aligned along the normal N to the transition 3 (offset along the axis X or in the circumferential direction (FIG. 6)).

[0058] Suppression or at least attenuation of the third harmonic in the processed signal for determining the rotation parameters is beneficial for improving the accuracy of said determination, and is also beneficial for signal processing algorithms that result in: Removal of offsets in the above signals; Equalization of the amplitude of the above signals; Phase correction between signals. [Brief explanation of the drawings]

[0059] [Figure 1a] 1 is a perspective view showing a schematic representation of a coder of the decision system of the present invention; [Figure 1b] 1 is a side view of a schematic representation of a coder of the decision system of the present invention; [Figure 2] FIG. 2 is a plan view of the cylindrical periphery of the coder of FIGS. 1a and 1b. [Figure 3] 10A and 10B show schematic diagrams of the placement of an embodiment of a sensing element implementation for a coder of the present invention at a radial read distance; [Figure 4] FIG. 1 is a diagram of an implementation of a sensing element according to an embodiment of the present invention. [Figure 5] 5 shows the quadrature signals delivered by the implementation of FIG. 4. [Figure 6] 10 shows a schematic representation of an embodiment of the arrangement of two implementations of sensing elements for a coder of the present invention at a radial reading distance. [Figure 7] FIG. 7 is an integral diagram of the implementation of FIG. 6 in a subtraction device. [Figure 8] 10 is a curve showing filtering of the third harmonic as a function of the distance between the sensing elements of a sensor implementation.

Claims

1. 1. A determination system for determining at least one rotational parameter of a rotating member, comprising: A coder (1) and two sensors, the coder is configured to operate in conjunction with the rotating member to rotate with the rotating member; the coder comprises a body having a cylindrical periphery with a radius a centered on an axis of rotation (X); the periphery having alternating north poles (2n) and south poles (2s) with width l separated by transitions (3); each of said transitions extending along a helix of pitch p and angle α forms a multi-pole magnetic track (2) capable of outputting a periodic magnetic field; The magnetic track is cylindrical and has a north pole (2n) and a south pole (2s). ｐｐ pairs and the polar width L measured along the normal (N) to the transition (3) ｐ and N ｐｐ = πa / l and L ｐ = p cos α, the periodic magnetic field rotates in a plane perpendicular to the axial direction of the magnetic track; the two sensors have a first mounting (4) and a second mounting (4') of at least two sensing magnetic elements (5), and the first mounting (4) and the second mounting (4') of the at least two sensing magnetic elements (5) are capable of detecting a rotating periodic magnetic field output by the coder; The first mounting (4) and the second mounting (4') are arranged at a radial reading distance from the magnetic track (2), and furthermore, each signal (V ０１ , V ０２ ; V' ０１ , V' ０２ ) and the first and second mountings (4) of the two sensors are spaced apart by a distance e along a normal (N) to the transition (3); A determination system in which an apparatus for generating quadrature signals (sinusoidal, cosinusoidal) receives the signals (V01, V02; V'01, V'02) from the first implementation (4) and the second implementation (4'), respectively, and generates quadrature signals (sinusoidal, cosinusoidal) by subtracting the second signal (V'01, V'02) received from the second implementation (4') from the first signal (V01, V02) received from the first implementation (4).

2. The first mounting (4) and the second mounting (4') comprise two Wheatstone bridge circuits of four sensing magnetic elements (5), 2. The determination system according to claim 1, wherein the circuit is arranged in a plane perpendicular to the axial direction of the magnetic track (2) and detects the magnetic field output from the magnetic track and rotating in said plane.

3. 3. A determination system according to claim 1 or 2, wherein each sensitive magnetic element (5) comprises at least one pattern of tunnel magnetoresistive material whose resistance changes in response to the detected magnetic field.

4. The determination system of claim 1 , wherein the distance e has the following relationship: e=L ｐ modulo 2L ｐ 。

5. The determination system of claim 1 , wherein the distance e has the following relationship: 0.55L ｐ < e < 0.82 L ｐ , modulo 2L ｐ ;or, 1.18L ｐ <e<1.45L ｐ 、modulo 2L ｐ 。

6. The distance e is 2 / 3L ｐ or 4 / 3L ｐ modulo 2L ｐ The determination system of claim 5 , wherein the determination system is substantially equal to

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