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 components, tangential (Ct) and normal (Cn), said method providing for the use of a sensor capable of delivering two analog pseudo-sinusoidal quadrature signals SIN and COS representing respectively a component (Ct, Cn), said method providing for a preliminary procedure for establishing evolution laws for respectively the amplitude and phase of a harmonic of each signal SIN and COS as a function of its amplitude, said method then providing for the periodic determination of the angular position by: measuring the signals SIN and COS; determining the amplitude of the signals SIN and COS; calculating the measured angular position; applying the evolution laws and using said measured angular position to determine signals SINc and COSc corrected for the corresponding harmonic;calculating the angular position using 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 elements rotating around a geometric axis of rotation.

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

[0003] To do this, it is known to use a test body having two portions fixed in rotation to respectively an organ, 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 organs while allowing an angular deflection 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 disposed at a reading distance from each of said tracks being capable of delivering two quadrature pseudo-sinusoidal analog signals SIN and COS which are representative of the tangential and normal magnetic components respectively 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 function ATAN(SIN / COS), to obtain by subtraction an angular deviation allowing the torque to be calculated as a function of said deviation.

[0006] However, each of the determined angular positions, and therefore the calculated torque, is 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 large reading distance, the magnetic field decreases rapidly in amplitude, making the measurement more susceptible to external noise.

[0008] Thus, in particular at short reading distances, the accuracy is not sufficient, especially in relation to an angular deviation of the order of 1° to calculate a torque with an accuracy 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 in order to calculate a torque, the accuracy of which is improved, in particular with regard to the possible differences in reading distance of the multipolar magnetic track 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 North and South magnetic pole pairs 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 disposed at a reading distance from said track, said sensor being capable of delivering two quadrature pseudo-sinusoidal analog signals SIN and COS, each of which is representative of one of the tangential or normal magnetic components, said method providing for a preliminary procedure for establishing laws of evolution of the amplitude and 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 angular position measured using 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 using said corrected signals.

[0011] According to a second aspect, the invention proposes a method for calculating a torque applied between two elements 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 respectively by a portion of a test body fixed in rotation to an element, said portions being connected by a deformable structure which is arranged to transmit the torque between the elements while allowing an angular displacement between said portions, said method providing for subtracting the two determined angular positions and calculating the torque as a function of the angular deviation thus obtained.

[0012] Other objects and advantages of the invention will become apparent from the following description, made with reference to the accompanying figures, in which:

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

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

[0015] [Fig.2] schematically illustrates 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, la, 1b having an angular succession of pairs of magnetic poles North N and South S is described below.

[0017] In relation to figures 1 and a, 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 exhibits a pseudosinusoidal evolution with a period of one pole pair. Furthermore, these magnetic components Ct, Cn are in quadrature, that is, phase-shifted by 90°, and can be approximated by a sine wave for one and a cosine wave for the other, which is in phase lead.

[0019] The determination method involves using a sensor 3, 3a, 3b disposed at a reading distance from the multipolar track 2, 2a, 2b, said sensor being capable of delivering two quadrature pseudo-sinusoidal analog signals 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 include 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 can 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 type AMR, TMR or GMR, or a Hall effect probe.

[0022] The sensing elements can be uniaxial, sensitive to one or the other component Ct, Cn of the magnetic field, which are positioned and / or combined so as to provide pointwise SIN and COS signals. According to another embodiment, the sensing 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, particularly in real time and from the start of the process, it is possible to calculate the Angular position on the N, S pole pair detected. In one embodiment, the angular position is calculated using the ATAN(SIN / COS) function.

[0024] The sinusoidal defects of the components Ct, Cn of the magnetic field delivered by the encoder 1, la, 1b induce the appearance of harmonics in the SIN and COS signals, 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 includes a procedure prior to the periodic determination, in which laws are established for the evolution of the amplitude and phase of at least one harmonic of each of the SIN and COS signals 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, and then performing 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. As regards the phase of a harmonic of a SIN or COS signal, it can advantageously be 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 type LUT: Look-Up Table) or a function (polynomial or other), these allow us 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, and then by calculating the angular position measured by means of said SIN and COS signals, in particular with the function ATAN(SIN / COS).

[0030] Next, 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 using said corrected signals, in particular with the ATAN(SINc / COSc) function.

[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 just by application of nomograms which correct the measurements without delay.

[0032] Advantageously, the preliminary procedure is provided to suppress the third harmonic, since it is the one that most disturbs the sinusoidality of the SIN and COS signals at short reading distances.

[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 signals SIN and COS 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 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 organs 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 crankset and the mechanical transmission of an electric assisted bicycle.

[0039] According to [Fig.2], the calculation method involves determining (steps 5) an angular position of two encoders la, 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 respectively carried by a portion of a test body fixed in rotation to a component, said portions being connected by a deformable structure 4 which is arranged to transmit the torque between the components while allowing angular deflection between said portions. In particular, the maximum angular deflection is less than the angular sector represented by a pair of poles N, S.

[0041] Thus, by subtracting the two angular positions determined respectively by a sensor 3a, 3b (step 6), it is possible to obtain an angular deviation (step 7), and then to calculate the torque as a function of the angular deviation thus obtained (step 8). In particular, the angular deviation corresponds to the angle of torsion 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 fixed in rotation to means for mounting said test body on one component, and an outer ring extending around the inner ring and having means for mounting said test body on the other component, said rings being connected by at least one deformable arm.

[0043] Alternatively, the deformable structure 4 can be in the form of at least one torsion bar, each end of which has a portion attached to a member respectively, said bar being arranged to deform in torsion according to the torque applied between said members.

[0044] According to one embodiment, the calculation method includes a calibration procedure. With reference 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 include: - rotate the test body through at least one revolution under a constant calibration torque, and in particular substantially zero, between the components; - define calibration values ​​for the angular gap between 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 arising from possible relative defects between the portions, the encoders la, 1b and / or the sensors 3a, 3b.

Claims

Demands

1. A method for determining an angular position on a pair of poles (N, S) of an encoder (1, 1a, 1b) having an angular succession of North (N) and South (S) magnetic pole pairs 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 comprising using a sensor (3, 3a, 3b) disposed at a reading distance from said track, said sensor being capable of delivering two quadrature pseudo-sinusoidal analog signals SIN and COS, each of which is representative of one of the tangential (Ct) or normal (Cn) magnetic components, said method comprising a prior procedure for establishing evolution laws for the amplitude and phase of at least one harmonic of each of the SIN and COS signals as a function of the amplitude of said signal,said method subsequently 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 using 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 using said corrected signals.

2. Method of determination 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. Method of determination according to claim 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 signals SIN and COS 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. Method of determination 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. Method of determination according to claim 4, characterized in that the establishment of the evolution law includes an angular Fourier analysis of the measured SIN and COS signals.

6. A method for determining 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. Method of determination according to claim 6, characterized in that the polynomial law is of order 2.

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

10. A method for determining according to any one of claims 1 to 9, characterized in that the preliminary procedure is provided for removing the third harmonic.

11. A method for determining 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. A method for calculating a torque applied between two elements rotating about a geometric axis of rotation, said method comprising determining the angular position of two encoders (1a, 1b) by implementing the method according to any one of claims 1 to 11, said encoders being carried respectively by a portion of a test body fixed in rotation to an element, said portions being connected by a deformable structure (4) which is arranged to transmit the torque between the elements while allowing angular deflection between said portions, said method comprising

13. subtract the two determined angular positions and calculate the torque as a function of the resulting angular deviation. Calculation method according to claim 12, characterized in that it provides for a calibration procedure to define 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.

Images