Method for compensating for angle error

Abstract

The invention relates to a method for compensating for an angle error in determining an angle value of an arrangement having a permanent magnet and at least two magnetic field sensors, having a distance formed between the permanent magnet and the magnetic field sensors, in which sinusoidal and cosine signals are generated in the magnetic field sensors, the measurement and evaluation unit comprises two signals, and an evaluation signal corresponding to the angle value is formed from the two signals by means of an arc tangent function, an arrangement error and an error of the measurement and evaluation unit alters the shape of the evaluation signal and causes an angular deviation in the evaluation signal, and in order to minimize the angular deviation, the measurement and evaluation unit is configured to measure the angle value of the measurement and evaluation unit. An offset value of the signal is varied and determined by determining a density difference of measurement points of a first harmonic in the evaluation signal and / or a second harmonic in the signal and / or a Lissajous figure.

Description

Technical Field

[0001] The invention relates to a method for compensating for angular errors. Background Art

[0002] DE 10 2014 109 693 A1 discloses a method in which the angular position of a magnet arrangement having a rotation axis is determined by contactless measurement. The magnet arrangement has a magnet and at least three magnetic field sensors, wherein sine and cosine output signals are calculated from the signals of the magnetic field sensors by means of a transformation.

[0003] In the evaluation device, the angle of rotation (ie the angular position of a magnet or a sensor arranged on the axis of rotation) is calculated directly from the two output signals or from the instantaneous values ​​of the two output signals by means of an inverse tangent function.

[0004] By using at least three magnetic field sensors, magnetic interference fields can be compensated, wherein interference fields occur in particular in the application environment of automotive electronics. The device and the method are not limited to three magnetic field sensors. When more than three sensors are used, the angular position can be calculated more accurately.

[0005] However, such methods are not suitable for compensating for errors in positioning and orientation inaccuracies. For example, both the magnet arrangement and the sensor arrangement may be offset relative to one another in the axial direction or have a tilt or inclination due to tolerances.

[0006] In addition to non-ideal magnet properties, further errors in the signal and therefore in the angle determination are caused, in particular, by temperature changes and aging. Basically, errors can be divided into three types:

[0007] - an offset error caused by the DC component of the signal, and

[0008] - gain error, the deviation of the peak value of the signal amplitude causes the gain error, and

[0009] - Quadrature error, which is caused by deviations in the phase shift of the signals.

[0010] A further method for compensating errors is known from “Application Note APN000202_001EN.” The basic arrangement has components for carrying out the compensation method.

[0011] However, due to the multiplicity and superposition of error sources, such as, for example, axial misalignment between the magnet arrangement and the sensor arrangement associated with a tilting of the magnet, effects occur which cannot be corrected using known compensation methods. Summary of the invention

[0012] Against this background, the object of the present invention is to specify a method which expands the prior art.

[0013] This object is achieved by a method for compensating for angular errors having the features of claim 1. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0014] According to the described subject matter, a method for compensating for angular errors is provided.

[0015] The method is carried out to determine an angle value of an arrangement having a permanent magnet and at least two magnetic field sensors.

[0016] The two magnetic field sensors are connected to a measuring and evaluation device.

[0017] A gap is formed between the permanent magnet and the magnetic field sensor.

[0018] Sine and cosine signals are generated in the magnetic field sensor by means of a forced-guided mechanical movement or by means of a transformation.

[0019] An evaluation signal corresponding to the angle value is formed from these two signals by means of an inverse tangent function, wherein arrangement errors and errors of the measuring and evaluation unit change the shape of the evaluation signal.

[0020] In the evaluation of the signal, the error leads to an angular deviation, wherein in order to minimize the angular deviation, the value of the offset error for the correction signal, referred to below as offset value, is changed.

[0021] In this case, in one method step, the offset value is ascertained by determining the density differences of the measuring points of the first harmonic in the evaluation signal and / or the second harmonic in the signal and / or the Lissajous figure.

[0022] It should be noted that the measuring and evaluation unit generally does not determine the offset value, but uses the value for correcting the offset that has already been determined, for example, during calibration. Rather, the latter is performed outside the measuring and evaluation unit and is usually stored.

[0023] In other words, in particular the offset error, ie the DC component in the signal, is known before the method is carried out and is taken into account by the measuring and evaluation unit, ie the signal is corrected with respect to the DC component.

[0024] It should be noted that, unlike the prior art (in which, for example, the minimum and maximum values ​​of the signal are taken into account, whereby the resulting angular deviation may even increase rather than decrease in some cases), in the present invention, other methods are used to calculate the offset value in order to reliably correct the first-order angular deviation.

[0025] It goes without saying that the term “magnetic field sensor” includes in particular vertical Hall sensors and / or transverse Hall sensors and / or TMR and / or AMR and / or another type of magnetic field sensor. Furthermore, different types of magnetic field sensors can also be used in the arrangement.

[0026] It should be noted that in an embodiment with just two sensors, the sine and cosine signals can also be generated directly as measurement signals from the two magnetic field sensors or can only be derived by means of a transformation of the measurement signals. In particular, in the case of more than two magnetic field sensors, the sine and cosine signals can usually only be generated by means of a transformation.

[0027] If there are exactly two magnetic field sensors, a changeover may also be necessary depending on the arrangement of the two magnetic field sensors and / or when using different types of magnetic field sensors, for example if one of the two magnetic field sensors is designed as a TMR and the other as a Hall sensor.

[0028] It is to be noted that, with the aid of this method, the second harmonic in the signal is minimized by means of a change in the offset value.

[0029] The second harmonic can be determined directly in the signal or in the influences resulting therefrom, such as an angular deviation of the resulting evaluation signal or a density function of the Lissajous figures of the two signals.

[0030] It should be noted that in an alternative, the angular deviations which occur there as first harmonics are to be minimized in the evaluation signal. In other words, the first harmonics are minimized.

[0031] In a further alternative, density differences at the measuring points are compensated during the evaluation using Lissajous figures.

[0032] It should be noted that the previously described approaches for reducing the errors are equivalent to one another in terms of their effects.

[0033] It goes without saying that the error value can be determined and compensated directly in the signal and only then the offset value can be determined with the aid of the method according to the invention.

[0034] One advantage of this method is that errors caused by axial misalignment between the magnet arrangement and the sensor arrangement or tilting of the magnets and other error causes which lead to higher-order effects in the signal can be compensated.

[0035] In particular, the second harmonic can be determined in the sine and cosine signals as the first harmonic of the rotation angle value and the resulting rotation angle deviation. It goes without saying that it is advantageous to consider at least one 360° traversal here.

[0036] Furthermore, it should be noted that the method significantly expands the compensation of angle errors occurring in the form of the second harmonic of the signal.

[0037] As a result, on the one hand, the achievable accuracy of the angle measurement is increased, and on the other hand, the requirements for production tolerances can be reduced and the recovery rate or the cost when joining the device can be reduced. In other words, the costs in production can be reduced.

[0038] It goes without saying that the method is not limited to the measurement of the angle of rotation. The method can be used for all types of contactless displacement measurement (Wegemessung), in which at least one permanent magnet generates sine and cosine signals in combination with at least two magnetic field sensors. This also includes all types of linear motions, the magnetic structure of which is designed in a corresponding manner.

[0039] In one specific embodiment, after the angle value has been calculated by means of the inverse tangent function, the offset value is determined from the amplitude and phase of the sinusoidal component, ie the first harmonic of the resulting angular deviation of the 360° rotation.

[0040] In one specific embodiment, in order to determine the offset value from the density difference of the measurement points of the Lissajous figure, the measurement points are recorded with a fixed sampling rate at a constant period speed / frequency or rotational speed.

[0041] In a further specific embodiment, the offset value is determined from a component of the first harmonic in the resulting profile of the error of the rotation angle through 360° rotation, calculated by means of a DFT or FFT.

[0042] In one development, the offset value is determined from a change in the correction value already generated by other methods in conjunction with the second harmonic of the sine and cosine signals calculated by means of DFT or FFT.

[0043] In other words, with the method according to the invention, an offset value is calculated from the determination of the second harmonic after a correction has been made from the determination of the first harmonic in the signal.

[0044] In an extended solution, the DFT calculation is performed by means of the Goertzel algorithm or in an alternative solution, the first harmonic or the second harmonic is directly obtained by means of a sinusoidal fitting function. In other words, in the alternative solution, no FFT calculation or DFT calculation is performed. The advantage is that the computing power used to perform the method is reduced.

[0045] In one embodiment, it is preferred that the offset value is determined multiple times in an iterative manner, thereby further improving the accuracy of the angle calculation.

[0046] In one embodiment, the magnetic field sensors are spaced apart along the X direction.

[0047] In a further embodiment, the magnetic field sensors are arranged directly adjacent to one another in the X direction and / or partially or completely one above the other in the Z direction.

[0048] In a further embodiment, three magnetic field sensors are arranged in pixel units, wherein three different directions of the magnetic field are measured by the three magnetic field sensors. In a further development, the plurality of magnetic field sensors are preferably arranged linearly or on a circle in an XY plane.

[0049] According to a further development, after the correction value has been determined, the second harmonic is determined directly in the measured value by comparing the signal profile with an ideal sine profile and by comparing the signal profile with an ideal cosine profile.

[0050] The offset value is determined from the correction value that has been ascertained and the deviation from the ideal profile.

[0051] In one specific embodiment, the method is used to determine an angular position in an arrangement having a permanent magnet and a magnetic field sensor.

[0052] In this case, the arrangement has an axis with an end face and is the axis of at least one permanent magnet arranged on the end face or laterally on the axis.

[0053] The magnetic field sensor is arranged along an imaginary extension of the axis. Alternatively, the magnetic field sensor is arranged laterally, that is, spaced apart from the imaginary extension of the axis.

[0054] It goes without saying that a distance is formed between the axis and the magnetic field sensor.

[0055] The measuring and evaluation device is connected to the magnetic field sensor, wherein, in the event of a rotation of the axis, a sinusoidal or cosine signal is present at the output of the respective magnetic field sensor or is obtained by means of a transformation.

[0056] In one embodiment, the magnetic field sensors are arranged spaced apart in the X direction or arranged directly adjacent to one another in the X direction and / or partially or completely overlapping one another in the Z direction. If the magnetic field sensors are arranged adjacent to one another or overlapping one another, different directions of the magnetic field are measured by the two magnetic field sensors.

[0057] The measuring and evaluation device is provided to calculate an evaluation signal corresponding to the rotation angle value from the signal by means of an inverse tangent function.

[0058] Furthermore, the measuring and evaluation device is provided to calculate an offset value for evaluating the change of the signal in order to minimize the angular deviation.

[0059] In an alternative embodiment, the method is used in a different arrangement for ascertaining the angular value of the translational movement path.

[0060] Here, the further arrangement comprises a plurality of permanent magnet pairs arranged along the translational path and at least two magnetic field sensors arranged along the translational movement path.

[0061] It goes without saying that the magnetic field sensor is spaced apart from the permanent magnet pair and is arranged so as to be movable along a translational movement path.

[0062] Furthermore, a measuring and evaluation device is provided which is connected to the magnetic field sensor.

[0063] In the case of a translational movement of the permanent magnet pair or of the magnetic field sensor along the path, a sinusoidal signal or a cosine signal is present at the output of the respective magnetic field sensor, or both signals are generated by means of a transformation.

[0064] The measuring and evaluation device is provided to calculate an evaluation signal corresponding to the angle value from the signal by means of an inverse tangent function.

[0065] Furthermore, the measuring and evaluation device is provided to calculate an offset value for evaluating the change of the signal in order to minimize the angular deviation.

[0066] In a preferred specific embodiment, the measuring and evaluation device is provided to determine the offset value by means of a DFT or FFT evaluation.

[0067] In one embodiment, the measuring and evaluation device comprises a Goertzel filter or the measuring and evaluation device is designed to carry out a sinusoidal fitting function.

[0068] In an alternative development, the measuring and evaluation device is provided to determine density differences of the measuring points of the Lissajous figure.

[0069] In a preferred embodiment, the measuring and evaluation device is integrated with the magnetic field sensor monolithically or as a multi-chip solution in an IC housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The invention is explained in more detail below with reference to the drawings. Here, similar parts are labeled with the same names. The embodiments shown are highly schematic, that is, the spacings and the lateral and vertical extensions are not drawn to scale and, unless otherwise indicated, they do not have any derivable geometrical relationships with each other. It is shown therein:

[0071] Figure 1 Showing the sine and cosine signals with errors,

[0072] Figure 2 Display or analyze the spectrum of a signal,

[0073] Figure 3 A diagram showing the resulting angular error of the evaluation signal,

[0074] Figure 4 A diagram showing Lissajous figures of erroneous sine and cosine signals in the form of density changes at the measuring points,

[0075] Figure 5 shows a Goertzel filter,

[0076] Figure 6 The rotating device is shown.

[0077] Figure 7 Showing a linear device,

[0078] FIG. 8 shows a diagram of ideal sinusoidal and cosine signals. DETAILED DESCRIPTION

[0079] It should be pointed out that in the following figures, the illustrated sine and cosine signals of the two magnetic field sensors S1 and S2 are either present directly as measurement signals or only after a transformation.

[0080] Figure 1 The diagram of φ shows a view of the uncompensated sine and cosine signals as a function of the rotation angle value.

[0081] Here, the signals have three error types: A DC component 3 (often also referred to as an offset) can lead to a distortion of one or both measurement signals in the positive or negative direction.

[0082] The gain error 4 results in a difference in the peak values ​​of the two measured signals in the absence of a DC component.

[0083] The quadrature error 5 results in a phase shift in the signal that is not equal to 90°. The quadrature error describes the deviation of the two measured magnetic field vector components from the ideal 90° orientation.

[0084] exist Figure 2 The diagram in shows the spectrum of the signal. In the case of an analysis of the spectrum of the angular deviation of the signal, the deviation will appear in the form of the first harmonic 6. The resulting error is reduced by carrying out the compensation according to the invention.

[0085] The diagram is also used to show the spectrum of the measurement signal, in which the DC component 3, the gain error 4 and the quadrature error 6 have been balanced, and in which the second harmonic can always occur, which is usually also referred to as the first higher harmonic.

[0086] The first higher harmonic produces a difference to the first harmonic which forms the actual signal and is often also referred to as the fundamental wave.

[0087] In the inverse tangent calculation, this deviation results in an error ΔΨ in the resulting rotation angle Ψ.

[0088] The application of the method according to the invention changes the offset value and thereby minimizes the angular error ΔΨ which is caused by the second harmonic present in the signal.

[0089] The zeroth harmonic corresponds to the direct current component. The method according to the invention is characterized in that the offset value of the two measurement signals is varied.

[0090] It is inherent to this method that, in the presence of a second harmonic in the measurement signal, a further offset leads to a smaller resulting angle error than according to known corrections in which the offset is compensated directly in the signal.

[0091] Here, overcompensation may be mentioned. In other words, by means of the method according to the invention, overcompensation of the error coming from the second harmonic in the signal leads to an increase in the accuracy of the angle calculation.

[0092] exist Figure 3 The diagram in shows a typical variation of the angle error ΔΨ resulting from the evaluation of the signal. In this case, the error occurs as a first harmonic oscillation. In the characteristics shown, the deviation of the measurement signal is visible in the form of a clear second harmonic. It should be noted that an offset can also lead to the characteristics shown.

[0093] exist Figure 4 The figure shows the Lissajous figures of sine and cosine signals.

[0094] The diagram has no further deformation, which means that the three errors mentioned have been ideally balanced. However, the diagram does not have any equidistant measuring points 8 .

[0095] The density distribution shows the presence of the second harmonic in the measurement signal. Although a change in the offset will shift the plot, it will balance the density distribution and thereby minimize the resulting angular error ΔΨ.

[0096] exist Figure 5 In the map sample of , a second-order Goertzel filter is shown by way of example. The use of a Goertzel filter enables targeted determination of individual spectral components of a signal. A Goertzel filter is particularly suitable for carrying out, according to the invention, determination of the second harmonic of a signal.

[0097] exist Figure 6 A rotary device DV is depicted in the drawing, wherein the rotary device DV has a rotation axis DA formed in the Z direction and a permanent magnet PM arranged in the XY plane on the end side of the rotation axis DA. The permanent magnet PM has a north pole N and a south pole S. A first magnetic field sensor S1 and a second magnetic field sensor S2 are arranged on a carrier plate TR along an imaginary extension line of the rotation axis DA.

[0098] The two magnetic field sensors S1, S2 are spaced apart from one another in the X direction by a spacing x1. The two magnetic field sensors S1, S2 are also spaced apart from the head-side end of the rotation axis DA. In the event that the carrier plate with the two magnetic field sensors S1, S2 is tilted relative to the end face and / or the magnetic field sensors S1, S2 are misaligned, the signals are loaded with different errors.

[0099] In an embodiment not shown, the distance x1 between the two magnetic field sensors S1 and S2 is zero or very small, or the two magnetic field sensors S1 and S2 are arranged one above the other in the Z direction, wherein in the case of the one above the other arrangement the two magnetic field sensors preferably measure different components of the magnetic field.

[0100] exist Figure 7 The drawing shows the arrangement of permanent magnet pairs along a straight line.

[0101] By means of a linearly movable permanent magnet PM having magnetic pole pairs 10-16 arranged closely to one another, sine and cosine signals can be generated by spaced-apart magnetic field sensors S1, S2, respectively. Even in the case of linear motion, the compensation according to the invention for angular errors caused by second-order deviations in the measurement signal can also be used for translational displacement / position measurement.

[0102] The diagram of FIG. 8 shows an ideal profile of two signals, a sine signal 20 and a cosine signal 10 .

[0103] Not only the sine signal but also the cosine signal is ideal, that is, error-free.

Claims

1. A method for compensating for an angular error when determining an angular value of an arrangement having a permanent magnet (PM) and at least two magnetic field sensors (S1, S2), comprising: - a measuring and evaluation device connected to the magnetic field sensor (S1, S2), - a distance formed between the permanent magnet and the magnetic field sensor (S1, S2), - generating a sine signal and a cosine signal in the magnetic field sensor (S1, S2) by means of a forced mechanical movement, or generating the sine signal and the cosine signal by means of a transformation, and, An evaluation signal corresponding to the angle value is formed from the two signals using an inverse tangent function, wherein: - arrangement errors and errors of the measuring and evaluation unit change the shape of the evaluation signal and lead to angular deviations in the evaluation signal, and - in order to minimize the angular deviation, changing the offset value of the measurement signal, It is characterized in that The offset value is ascertained by determining a first harmonic in the evaluation signal and / or a second harmonic in the signal and / or a density difference of a measuring point in a Lissajous figure.

2. The method according to claim 1, characterized in that After the angle value has been calculated using the arc tangent, the offset value is determined from the amplitude and phase of the first harmonic of the resulting angle deviation of the 360° rotation.

3. The method according to claim 1, characterized in that In order to determine the offset value from the density differences of the measuring points of the Lissajous figure, the measuring points are recorded at a fixed sampling rate at a constant cycle speed.

4. The method according to claim 1, characterized in that The offset value is determined from the first harmonic component of the curve of the error of the rotation angle during a 360° rotation, which is calculated by means of a DFT or an FFT.

5. The method according to claim 1, characterized in that: The offset value is determined by varying the correction value already generated by other methods and the second harmonic of the sine and cosine signals calculated by means of DFT or FFT.

6. The method according to claim 4 or 5, characterized in that: The DFT calculation is performed with the aid of the Goertzel algorithm, or the first harmonic or the second harmonic is determined directly from a sinusoidal fitting function.

7. The method according to any one of the preceding claims, characterized in that The determination of the offset value is performed multiple times in an iterative manner.

8. The method according to any one of the preceding claims, characterized in that After the correction value has been determined, the second harmonic is determined directly in the signal by comparing the signal profile with an ideal sine profile and by comparing the signal profile with an ideal cosine profile, and the offset value to be set is determined from the correction value that has been determined and the deviation from the ideal profile.

9. The method according to any one of the preceding claims, characterized in that The magnetic field sensors (S1, S2) are spaced apart in the X direction, or the magnetic field sensors (S1, S2) are arranged one above the other in the Z direction.

10. Use of the method according to any one of the preceding claims for determining a rotation angle value, comprising: - having an axis with an end face and at least one permanent magnet arranged on the end face or laterally on the axis, at least two magnetic field sensors (S1, S2) arranged along an imaginary extension of the axis or arranged laterally with respect to the axis, wherein: A distance is formed between the axis and the magnetic field sensor (S1, S2), - a measuring and evaluation device connected to the magnetic field sensor (S1, S2), wherein: When the axis rotates, a sine signal or a cosine signal is present at the output of the corresponding magnetic field sensor, and the measuring and evaluation device is designed to calculate an evaluation signal corresponding to the rotation angle value from said signal by means of an inverse tangent function in order to minimize the angular deviation.

11. Use of the method according to any one of the preceding claims 1 to 8 for determining the angle value of a translational movement path, comprising: - a plurality of permanent magnet pairs arranged along the path of said translation, at least two magnetic field sensors arranged along the translational movement path, the magnetic field sensors being spaced apart from the permanent magnet pair and being arranged movably along the translational movement path, - a measuring and evaluation device connected to the magnetic field sensor (S1, S2), wherein: - During the translational movement of the permanent magnet pair or the magnetic field sensor (S1, S2) along the path, a sinusoidal signal or a cosine signal is present at the output of the magnetic field sensor (S1, S2), and the measuring and analyzing device is configured to calculate an analyzing signal corresponding to the angle value from the signal by means of an inverse tangent function in order to minimize the angular deviation.

12. Use of the method according to claim 10 or claim 11, characterized in that The measuring and evaluation device is provided to determine the offset value by means of a DFT or FFT evaluation.

13. Use of the method according to any one of claims 10 to 12, characterized in that The measuring and evaluation device comprises a Goertzel filter or is configured to carry out a sinusoidal fitting function.

14. Use of the method according to claim 10 or claim 11, characterized in that The measuring and evaluation device is configured to determine density differences at measuring points of a Lissajous figure.

15. Use of the method according to any one of the preceding claims, characterized in that The measuring and evaluation device is integrated with the magnetic field sensor monolithically or as a multi-chip solution in an IC housing.

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