Method for determining an angular position on a pair of poles of an encoder

Abstract

The invention relates to a method for determining an angular position on a pair of poles of an encoder having a track capable of emitting a magnetic field having two tangential (Ct) and normal (Cn) components, said method providing for using a sensor capable of delivering two pseudo-sinusoidal analog signals in quadrature SIN and COS representative of respectively a component (Ct, Cn), said method providing a preliminary procedure for establishing laws of evolution of respectively the amplitude and the phase of a harmonic of each SIN and COS signal as a function of its amplitude, said method then providing for the periodic determination of the angular position by: measuring the SIN and COS signals; determining the amplitude of the SIN and COS signals; calculating the measured angular position; applying the laws of evolution and using said measured angular position to determine SINc and COSc signals corrected for the corresponding harmonic;calculating the angular position by means of said corrected signals. Figure 2;

Description

Title of the invention: Method for determining an angular position on a pair of poles of an encoder

[0001] The invention relates to a method for determining an angular position on a pair of poles of an encoder having an angular succession of pairs of North and South magnetic poles, as well as a method for calculating a torque applied between two members rotating around a geometric axis of rotation.

[0002] The invention applies in particular to the determination of a torque applied between two members integrated in a transmission of a motor torque to a vehicle, for example between the electric motor or the pedal assembly and the mechanical transmission of an electrically assisted bicycle.

[0003] To do this, it is known to use a test body having two portions integral in rotation with a member respectively, each of said portions carrying an encoder and said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing angular movement between said portions.

[0004] In particular, each of the encoders forms a multipolar magnetic track capable of emitting a magnetic field having a tangential component and a normal component, a sensor being arranged at a reading distance from each of said tracks and being capable of delivering two pseudo-sinusoidal analog signals in quadrature SIN and COS which are representative of the respectively tangential and normal magnetic component of the corresponding track.

[0005] Thus, it is possible to determine the angular position on a pair of poles of each of the encoders, in particular by calculating the ATAN(SIN / COS) function, to obtain by subtraction an angular difference making it possible to calculate the torque as a function of said difference.

[0006] However, each of the determined angular positions, and therefore the calculated torque, are affected by an error induced by the fact that the components of the magnetic field emitted by the multipolar track are not purely sinusoidal.

[0007] In particular, when the reading distance is reduced, the magnetic field tends to have a square shape for the normal component and a triangular shape for the tangential component, which generates harmonics in the SIN and COS signals delivered by the sensor. Furthermore, at a significant reading distance, the magnetic field rapidly decreases in amplitude, which makes the measurement more subject to external noise.

[0008] Thus, in particular at low reading distances, the precision is not sufficient, in particular in relation to an angular difference of the order of 1° to calculate a torque with a precision of 1%.

[0009] The invention aims to solve the problems of the prior art by proposing in particular a method for determining an angular position, for example with a view to calculating a torque, the precision of which is improved, in particular with regard to possible differences in reading distance of the multipolar magnetic stripe and their variation during operation.

[0010] To this end, according to a first aspect, the invention proposes a method for determining an angular position on a pair of poles of an encoder having an angular succession of pairs of North and South magnetic poles forming a multipolar magnetic track capable of emitting a magnetic field having a tangential component and a normal component, said method providing for the use of a sensor arranged at a reading distance from said track, said sensor being capable of delivering two pseudo-sinusoidal analog signals in quadrature SIN and COS which are each representative of one of the tangential or normal magnetic components, said method providing a prior procedure for establishing laws of evolution of the amplitude and the phase of at least one harmonic of each of the signals SIN and COS as a function of the amplitude of said signal, said method then providing for the periodic determination of the angular position by: - measuring SIN and COS signals; - determining the amplitude of the SIN and COS signals; - calculating the measured angular position by means of said SIN and COS signals; - applying the laws of evolution and using said measured angular position to determine SINc and COSc signals corrected for the corresponding harmonic; - calculating the angular position by means of said corrected signals.

[0011] According to a second aspect, the invention proposes a method for calculating a torque applied between two members rotating around a geometric axis of rotation, said method providing for the determination of an angular position of two encoders by implementing a method according to the first aspect, said encoders being carried by respectively a portion of a test body integral in rotation with a member, said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing an angular movement between said portions, said method providing for subtracting the two determined angular positions and calculating the torque as a function of the angular difference thus obtained.

[0012] Other objects and advantages of the invention will appear in the following description, given with reference to the appended figures, in which:

[0013] [Fig-1] schematizes the tangential and normal components of the magnetic field emitted by the multipolar magnetic strip of an encoder,

[0014] [Fig. la] representing the evolution of these components;

[0015] [Fig.2] schematizes the implementation of a method according to the invention to determine a torque applied between two organs rotating around a geometric axis of rotation.

[0016] A method for determining an angular position on a pair of poles of an encoder 1, 1a, 1b having an angular succession of pairs of North N and South S magnetic poles is described below.

[0017] In relation to figures 1 and 1a, the encoder 1 forms a multipolar magnetic track 2 capable of emitting a magnetic field having a tangential component Ct (along the x direction) and a normal component Cn (along the z direction).

[0018] In particular, each of these components Ct, Cn has a pseudosinusoidal evolution with a period of one pair of poles. Furthermore, these magnetic components Ct, Cn are in quadrature, i.e. phase shifted by 90°, and can be likened to a sine for one and a cosine for the other, which is in phase advance.

[0019] The determination method provides for using a sensor 3, 3a, 3b arranged at a reading distance from the multipolar track 2, 2a, 2b, said sensor being capable of delivering two pseudo-sinusoidal analog signals in quadrature SIN and COS which are each representative of one of the tangential magnetic components Ct or normal Cn, in particular of the tangential magnetic component Ct for the SIN signal and normal Cn for the COS signal.

[0020] The sensor 3, 3a, 3b may comprise a pattern of sensitive elements, in particular a plurality of aligned sensitive elements as described in documents FR-2 792 403, EP-2 602 593 and EP-2 602 594.

[0021] The sensitive elements may be based on a magnetoresistive material whose resistance varies according to the magnetic signal of track 2, 2a, 2b to be detected, for example of the AMR, TMR or GMR type, or a Hall effect probe.

[0022] The sensitive elements can be uniaxial, sensitive to one or other component Ct, Cn of the magnetic field, which are positioned and / or combined so as to punctually give the signals SIN and COS. According to another embodiment, the sensitive elements are multiaxial (2D or 3D), sensitive to both the tangential Ct and normal Cn components of the magnetic field.

[0023] By measuring the SIN and COS signals delivered by the sensor 3, 3a, 3b, in particular in real time and as soon as the method is implemented, it is possible to calculate the angular position on the detected N, S pole pair. According to one embodiment, the angular position is calculated with the ATAN(SIN / COS) function.

[0024] The sinusoidality defects of the components Ct, Cn of the magnetic field delivered by the encoder 1, 1a, 1b induce the appearance of harmonics in the signals SIN and COS, that is to say that each of said signals is the sum of a fundamental and harmonics of rank 3, 5, ...

[0025] To correct the errors induced by these defects on the accuracy of the determined position, the method provides a procedure prior to the periodic determination, in which laws of evolution of the amplitude and the phase of at least one harmonic of each of the SIN and COS signals are established respectively as a function of the amplitude of said signal. In particular, the amplitude of the SIN and COS signals is representative of the reading distance.

[0026] According to one embodiment, the laws are established, for example on a measuring bench, by measuring the SIN and COS signals, for example on a lathe, at different reading distances from the sensor 3, 3a, 3b, then by carrying out an angular Fourier analysis of said measured signals.

[0027] In particular, the amplitude of a harmonic of a SIN or COS signal is established by a polynomial law as a function of the amplitude of said signal, in particular by a polynomial law of order 2. With regard to the phase of a harmonic of a SIN or COS signal, it can be advantageously established by a constant law as a function of the amplitude of said signal.

[0028] Once the evolution laws (or charts) have been established for a harmonic, and for example stored in the form of a table (for example of the LUT type: Look-Up Table) or a function (polynomial or other), these make it possible to approximate and interpolate the points obtained during the phase of establishing the laws.

[0029] The periodic determination of the angular position is then carried out by determining the amplitude Ampl of the SIN and COS signals after their measurement by the sensor 3, 3a, 3b, then by calculating the angular position measured by means of said SIN and COS signals, in particular with the function ATAN(SIN / COS).

[0030] Then, the determination is carried out by applying the laws and using the measured angular position to determine SINc and COSc signals corrected for the corresponding harmonic, before calculating said angular position by means of said corrected signals, in particular with the function ATAN(SINc / COSc).

[0031] In particular, the calculation is carried out in real time, at each sampling period of the measurement of the SIN and COS signals, and this without filtering but simply by applying charts which correct the measurements without delay.

[0032] Advantageously, the preliminary procedure is designed to eliminate the third harmonic, since it is the one which most disturbs the sinusoidality of the SIN and COS signals at short reading distance.

[0033] According to one embodiment, the preliminary procedure is provided for establishing evolution laws for several harmonics, said evolution laws being applied successively to correct each of said harmonics.

[0034] The preliminary procedure may also provide for establishing a law of evolution of the phase of the fundamental PhaseAmpl) of each of the SIN and COS signals as a function of the amplitude of said signal, said law of evolution also being applied to determine the corrected signals SINc and COSc.

[0035] In relation to the corrections formulated below for the third harmonic with its laws AmplH3(Ampl) and PhaseAmpl) for respectively the amplitude and the phase as a function of the amplitude Ampl of the corresponding SIN or COS signal, the calculation of the measured angular position anglmeas by means of the SIN and COS signals is used to determine the following SINc and COSc signals:

[0036] COSC = COS - AmplH3(Ampl) *co^3*anglemeas + Phase (Ampl) - 3*Phasem (Ampl))

[0037] SINcorr-SIN - Ampl H3 (Ampl)*c <x^3*angle +Phase H3( Ampl) -3*Phasem(Ampl) -y-)

[0038] According to one application, the determination of the angular position described above can be used to calculate a torque applied between two members rotating around a geometric axis of rotation, for example integrated into a transmission of a motor torque to a vehicle, in particular between the electric motor or the pedal assembly and the mechanical transmission of an electrically assisted bicycle.

[0039] According to [Fig.2], the calculation method provides for the determination (steps 5) of an angular position of two encoders 1a, 1b according to the method described to subtract at least one harmonic from the SIN and COS signals used.

[0040] The encoders 1a, 1b are carried by a portion of a test body secured in rotation to a member, said portions being connected by a deformable structure 4 which is arranged to transmit the torque between the members while allowing an angular movement between said portions. In particular, the maximum angular movement is less than the angular sector represented by a pair of poles N, S.

[0041] Thus, by subtracting the two angular positions determined by a sensor 3a, 3b respectively (step 6), it is possible to obtain an angular difference (step 7), then to calculate the torque as a function of the angular difference thus obtained (step 8). In particular, the angular difference corresponds to the torsion angle which, knowing the stiffness of the deformable structure 4, makes it possible to calculate the applied torque.

[0042] According to one embodiment, the test body may have an inner ring integral in rotation with means for mounting said test body on one member, and an outer ring extending around the inner ring while having means for mounting said test body on the other member, said rings being connected by at least one deformable arm.

[0043] As a variant, the deformable structure 4 may be in the form of at least one torsion bar, each end of which has a portion secured to a respective member, said bar being arranged to deform in torsion as a function of the torque applied between said members.

[0044] According to one embodiment, the calculation method provides a calibration procedure. In relation to [Fig. 2], the calibration is illustrated by means of at least one sensor 3b which can deliver a calibration pulse S3, in particular at least once per rotation of the test body.

[0045] In particular, the calibration procedure may provide for: - rotate the test body at least one revolution under a constant, and in particular substantially zero, calibration torque between the components; - define calibration values ​​of the angular gap between the portions as a function of the rotation angle of the test body.

[0046] Thus, the subsequent calculation of the applied torque can be carried out by correcting the angular deviation determined at a given angle with the corresponding calibration value, so as to be able to eliminate errors originating from possible relative defects between the portions, the encoders 1a, 1b and / or the sensors 3a, 3b.

Claims

Claims

1. Method for determining an angular position on a pair of poles (N, S) of an encoder (1, 1a, 1b) having an angular succession of pairs of North (N) and South (S) magnetic poles forming a multipolar magnetic track (2, 2a, 2b) capable of emitting a magnetic field having a tangential component (Ct) and a normal component (Cn), said method providing for using a sensor (3, 3a, 3b) arranged at a reading distance from said track, said sensor being capable of delivering two pseudosinusoidal analog signals in quadrature SIN and COS which are each representative of one of the tangential (Ct) or normal (Cn) magnetic components, said method providing a prior procedure for establishing laws of evolution of the amplitude and the phase of at least one harmonic of each of the SIN and COS signals respectively as a function of the amplitude of said signal,said method then providing for the periodic determination of the angular position by: - ​​measuring the SIN and COS signals; - determining the amplitude of the SIN and COS signals; - calculating the measured angular position by means of said SIN and COS signals; - applying the evolution laws and using said measured angular position to determine SINc and COSc signals corrected for the corresponding harmonic; - calculating the angular position by means of said corrected signals.,

2. Determination method according to claim 1, characterized in that the angular positions are calculated with the function ATAN(SIN / COS) for the measured angular position and ATAN(SINc / COSc) for the determined angular position.

3. Determination method according to one of claims 1 or 2, characterized in that the preliminary procedure provides for establishing a law of evolution of the phase of the fundamental of each of the SIN and COS signals as a function of the amplitude of said signal, said law of evolution also being applied to determine the corrected signals SINc and COSc.

4. Determination method according to any one of claims 1 to 3, characterized in that the evolution laws are established by measuring the SIN and COS signals at different reading distances from the sensor (3, 3a, 3b).

5. Determination method according to claim 4, characterized in that the establishment of the evolution law comprises an angular Fourier analysis of the measured SIN and COS signals.

6. Determination method according to any one of claims 1 to 5, characterized in that the amplitude of a harmonic of a SIN or COS signal is established by a polynomial law as a function of the amplitude of said signal.

7. Determination method according to claim 6, characterized in that the polynomial law is of order 2.

8. Determination method according to any one of claims 1 to 7, characterized in that the phase of a harmonic of a SIN or COS signal is established by a constant law as a function of the amplitude of said signal.

9. Determination method according to any one of claims 1 to 8, characterized in that the evolution laws are stored in the form of a table or function.

10. Determination method according to any one of claims 1 to 9, characterized in that the preliminary procedure is provided to suppress the third harmonic.

11. Determination method according to any one of claims 1 to 10, characterized in that the preliminary procedure is provided for establishing evolution laws for several harmonics, said evolution laws being applied successively to correct each of said harmonics.

12. Method for calculating a torque applied between two members rotating around a geometric axis of rotation, said method providing for the determination of an angular position of two encoders (1a, 1b) by implementing the method according to any one of claims 1 to 11, said encoders being carried by respectively a portion of a test body integral in rotation with a member, said portions being connected by a deformable structure (4) which is arranged to transmit the torque between the members while allowing an angular movement between said portions, said method providing

13. to subtract the two determined angular positions and calculate the torque based on the angular difference thus obtained. Calculation method according to claim 12, characterized in that it provides a calibration procedure for defining calibration values ​​of the angular deviation as a function of the angle of rotation, the subsequent calculation of the torque being carried out by correcting the angular deviation determined at a given angle with the corresponding calibration value.

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