DE102020105254A1 - Method for determining an angular position of a shaft - Google Patents

Abstract

The invention relates to a method for determining an angular position of a shaft (1), in a first step using an XMR sensor (2) arranged radially offset from the shaft (1) a signal representing an angular position of the shaft (1) with the Shaft (1) firmly connected magnet (3) is detected, and in a second step an analytical angle error compensation of this detected signal is carried out by, while driving the shaft (1) with constant speed, either by the XMR sensor (2) or by another reference angle sensor, the magnetic field of the magnet (3), which changes as a function of the angular position of the shaft (1), is scanned over at least one full revolution of the shaft (1), then a change in a gradient of an amplitude curve of the magnetic field is determined, then, using at least two gradient values present at different angles of rotation, a correction value is determined by means of which Ko correction value, an angle error of the angular position taken from the signal of the XMR sensor after the first step is determined, and finally the angular error is used to correct the angular position determined from the signal emitted by the XMR sensor (2).

Description

The invention relates to a method for determining an angular position of a shaft, preferably a rotor shaft of an electric motor / actuator, which is more preferably used for clutch actuation in a motor vehicle.

Generic methods are already sufficiently known from the prior art. For example, WO 2018/219 388 A1 discloses a method for determining an angular position of a rotating component, in particular an electric motor for a clutch actuation system of a vehicle. In this method, the angular position of the rotating component is picked up by a sensor system positioned radially at a distance from the axis of rotation of the rotating component, with a magnet ring that is fixedly and concentrically arranged on the rotating component building up a magnetic field that changes with respect to the sensor system and that is detected by the sensor system will. In addition, a signal picked up by the sensor system is evaluated with regard to the angular position. This evaluation of the signal picked up by the sensor system takes place with regard to amplitude information of the magnetic field, with this amplitude information being used to determine a correction parameter by means of which an angular error in the angular position obtained from the signal of the sensor system is determined. The angle error is then used to correct the angular position determined from the signal emitted by the sensor system.

Thus, methods for determining an angular position in so-called off-axis sensor arrangements, i.e. sensor arrangements in which a sensor is located radially offset from a shaft having a magnet, are already known from the prior art. WO 2018/219 388 A1 discloses a method for correcting the deviation of an amplitude curve, represented by an ellipse in a Lissajous representation, from a circle. The angle error can be determined by the quotient of the long to the short axis of the ellipse.

In practice, however, it has been found to be disadvantageous that this method can be relatively complex or even impractical, depending on the output value of the existing sensor. Furthermore, a usually separate and relatively complexly constructed Hall sensor is to be provided for this measurement.

It is therefore the object of the present invention to eliminate these disadvantages known from the prior art and to provide a method for determining an angular position of a shaft which enables the angular position to be determined more precisely with sensors that work as efficiently as possible and are of simple construction.

This is achieved according to the invention by the method according to claim 1. Accordingly, a method for determining an angular position of a shaft is claimed, in a first step using (precisely / exclusively) an XMR sensor arranged radially offset from the shaft, a signal representing an angular position of the shaft from a magnet firmly connected to the shaft is detected, and in a second step, an analytical angular error compensation of this detected signal is carried out by temporally before or after the first step, with the shaft being driven at constant speed, either by the XMR sensor or by a further reference angle sensor that changes depending on the angular position of the shaft Magnetic field of the magnet is scanned over at least one full revolution of the shaft, then a change in a gradient of an amplitude curve of the magnetic field is determined, then a correction value is determined using at least two gradient values present at different angles of rotation which correction value is used to determine an angle error of the angular position taken from the signal of the XMR sensor after the first step, and finally the angular error is used to correct the angular position determined from the signal emitted by the XMR sensor.

As a result, a method for determining an angular position of a shaft is implemented, which enables a reliable, error-corrected determination of the angular position independently of the output value of the existing XMR sensor.

Further advantageous embodiments are claimed with the subclaims and explained in more detail below.

It has been found to be useful if, in the second step, the shaft is driven at a lower speed than in the first step.

For the calculation, it is also useful if a first gradient value at an angular position of 0 ° and a second gradient value at an angular position of 90 ° are used in the second step to determine the correction value.

In practice, it is advantageous if the XMR sensor outputs an angle value in the first step.

Alternatively, it is also useful if the XMR sensor in the first step (considering in a (2D) coordinate system) outputs a first position value lying on an x-axis and a second position value lying on a y-axis oriented perpendicular to the x-axis.

In addition, it has proven to be useful if, in the last-mentioned case, an angle value is calculated on the basis of the two position values using an arctan2 function.

For this method, i.e. primarily for performing the first and second steps, it is preferred if only one sensor (preferably the XMR sensor) is used. This makes the process as easy to implement as possible.

Accordingly, it is also expedient if the scanning after the second step using the XMR sensor at the end of an assembly chain (end-of-line) of a measuring arrangement having the shaft, the XMR sensor and the magnet, preferably an actuator having the measuring arrangement, is carried out.

In other words, the performance of an XMR (AMR / GMR / TMR) angle sensor for an off-axis application is made possible by the electric motor, preferably without an additional sensor. The object of the invention is to determine a systematic error in an end-of-line or online measurement of a corresponding system by measuring with a reference angle sensor or directly with the existing XMR sensor and then to compensate for it accordingly during operation. Depending on the type of measured value, the invention proposes one of two calculation options for determining the error. Depending on the case, two values (gradient values) are determined for gradients G or G * at different angles, in particular at 0 ° and 90 °. The quotient of the elliptical axes is typically determined, but this is not determined directly. From this quotient, the error of the measured from the actual can then be determined according to a further formula. In one case an angle is measured and in another case the sine / cosine values of an angle are measured / output by the sensor. The shaft is typically driven at constant speed. The angular error can then be determined via an actually measured angular acceleration. For this purpose, the angular acceleration is measured by a sensor. From this a factor can then be determined which corresponds to the factor of a Lissajous figure. The error can then be calculated from this factor and then compensated.

The invention will now be explained in more detail below with reference to figures, in which context various exemplary embodiments are also shown.

• 1 ein Flussdiagramm zum Durchführen eines erfindungsgemäßen Verfahrens nach einem ersten Ausführungsbeispiel, wobei ein vorhandener XMR-Sensor direkt einen Winkelwert ausgibt,
• 2 ein Flussdiagramm zum Durchführen eines erfindungsgemäßen Verfahrens nach einem weiteren zweiten Ausführungsbeispiel, bei dem der XMR-Sensor einen x- und einen y-Wert ausgibt,
• 3 eine perspektivische Darstellung einer zum Durchführen des Verfahrens nach einem der 1 und 2 einsetzbaren Messanordnung,
• 4 eine Lissajous-Darstellung einer durch die Messanordnung nach 3 erfassten Messreihe zur Darstellung der von dem XMR-Sensor erfassten Amplitudenwerte entlang einer vollen Umdrehung einer durch den XMR-Sensor erfassten Welle,
• 5 ein Diagramm zum Darstellen eines Verhältnisses zwischen einem Winkel / einer Winkelposition und einer Auflösung / einem Gradienten der in 4 erfassten Messreihe,
• 6 ein Diagramm zum Veranschaulichen eines Verhältnisses zwischen einem ermittelten Korrekturwert ( ) in Abhängigkeit eines Verhältnisses zweier Gradientenwerte (G(90°) und G(0°), sowie
• 7 ein Diagramm zum Darstellen eines üblichen Verhältnisses zwischen einem Drehwinkel und einem gemessenen Winkel.

Show it:

• 1 a flowchart for performing a method according to the invention according to a first embodiment, an existing XMR sensor directly outputting an angle value,
• 2 a flowchart for performing a method according to the invention according to a further second exemplary embodiment, in which the XMR sensor outputs an x value and a y value,
• 3 a perspective view of a for performing the method according to one of the 1 and 2 usable measuring arrangement,
• 4th a Lissajous representation of a through the measuring arrangement according to 3 Recorded series of measurements to display the amplitude values recorded by the XMR sensor along a full revolution of a shaft recorded by the XMR sensor,
• 5 FIG. 13 is a diagram showing a relationship between an angle / an angular position and a resolution / a gradient of the FIG 4th recorded series of measurements,
• 6th a diagram to illustrate a relationship between a determined correction value () as a function of a ratio of two gradient values (G (90 °) and G (0 °), and
• 7th a diagram showing a usual relationship between a rotation angle and a measured angle.

The figures are merely of a schematic nature and are used exclusively for understanding the invention.

With 3 is first a common measurement setup 4th shown, which, as described below, has an off-axis arrangement. The measuring arrangement 4th exhibits a wave 1 on which a magnet that generates a permanently excited magnetic field 3 is firmly attached. This magnet 3 is as a concentric to the shaft 1 trained magnetic ring implemented. The magnet 3 sits on a radial outside of the shaft 1 and is firmly attached to this. Radially outside the shaft 1 (in relation to an axis of rotation 5 the wave 1 ) an XMR sensor is located according to the off-axis arrangement 2 that is used to capture one moving with rotation of the shaft 1 changing magnetic field of the magnet 3 serves to thus provide an angular position of the shaft 1 to investigate.

In this context, it should be pointed out that the preferred area of application of the measuring arrangement 4th is an actuator for clutch actuation, which further preferably has an electric motor with a rotor shaft. The wave 1 is preferably non-rotatably connected to the rotor shaft or formed directly by this rotor shaft.

As in 4th Shown by a Lissajous representation, according to a method according to the invention (in a calibration process) a determination of a time profile of several amplitude values of a measured magnetic field component takes place. To do this, the wave 1 driven at a constant speed / speed. Using one XMR sensor 2 or alternatively, the angular position of the magnet is determined by means of a further reference angle sensor 3 / the wave 1 scanned using the magnetic field.

With 4th is the relationship between the arrangement of the XMR sensor on which the calculation according to the invention is based 2 and an associated change in resolution along a direction of rotation / circumferential direction of the shaft 1 shown. Accordingly, due to the off-axis arrangement, an analysis of the amplitude values of the recorded signal curve occurs, as in FIG 4th illustrated in a Lissajous representation for forming a circle with different density (of the measuring points) / different angular gradients.

the 4th further shows that when looking at the angle with an XMR sensor 2 captured, the x and y information captured the Lissajous representation corresponds to a circle. An XMR sensor 2 , which only outputs an angle (without x, y information), primarily does not allow a Lissajous representation, but this can then be generated by an orthogonal decomposition, as described below. If the magnetic field is recorded with a 2D Hall sensor or by magnetic field scanning, then the Lissajous representation corresponds to an ellipse.

With 7th Finally, it becomes clear that the angular position thus measured during operation (in a first step of the method) can deviate from an actual angle of rotation and consequently a certain angular error is present. With the method described in detail below for determining the angular position of the shaft 1 this angle error is calculated and used to output the actual angular position of the shaft 1 with the previously measured signal from the XMR sensor 2 offset.

With 1 a first embodiment of the method according to the invention is shown. In a first step, exactly one XMR sensor 2 a signal representing the angular position of the shaft, here an angular signal / angular value is detected and output directly. The angle value is marked with the Greek letter.

This angle value is then used, in a second step, to calculate / display a gradient G * present for this angle value. An example of this is 5 refer to. The gradient G * is after 5 to be clarified exactly. For this purpose, one makes use of the previously mentioned fact that at a constant speed the measured angular velocity (angular gradient) is actually constant; with an XMR sensor 2 in the case of an off-axis arrangement, however, this gradient G * is not constant after all.

The gradient G * at the angular position is determined in this second step on the basis of the following equation 1: $$\frac{G*\left(90°\right)}{G*\left(0°\right)}=\mathrm{\gamma }$$

Thus, a first gradient value is preferably calculated at an angular position of 0 ° (G * (0 °)) and a second gradient value is calculated at an angular position of 90 ° (G * (90 °)), with which the correction value is then calculated.

The correction value determined is then used to adjust the value previously determined with the XMR sensor 2 to correct the detected angle value / the angle signal, which is represented by the angle error. A corrected angle value is thus ultimately output.

In this context, it should be noted that the method for determining the angular position of the shaft 1 principally end-of-line, ie takes place at the end of a corresponding assembly chain of the actuator, or alternatively online, ie can take place during operation / in the area of application of the actuator. However, the embodiment at the end of the assembly chain is preferred, in which case only one sensor in the form of the XMR sensor 2 is used to carry out the method according to the invention (ie both to carry out the first step and the second step). The gradient values are therefore preferably determined using the same XMR sensor after the second step 2 as in the first step, e.g. with the end-of-line measurement. Alternatively, according to further explanations, this is implemented with the reference angle sensor, which is not shown here for the sake of clarity.

Equation 2 shows further fundamental relationships between the Trigonometric functions and the correction value. This means that the angle error is calculated directly. $$\epsilon =arctan\left[\frac{\left(\mathrm{\gamma }-1\right)\cdot tan\left(\theta \right)}{\mathrm{\gamma }+ta{n}^2\left(\theta \right)}\right]$$

The angle error is subtracted from this angle value to correct the detected angle value.

$$S_{sin}=sin\left(\mathrm{\theta }\right)=cos\left(\mathrm{\theta +}\frac{\mathrm{\pi }}{2}\right)$$

According to a second embodiment 2 it is alternatively also possible that an XMR sensor 2 is used, which outputs x and y values. This is made possible by an orthogonal decomposition (see equations 3 and 4). $${\mathrm{S.}}_{cOs}=cOs\left(\mathrm{\theta }\right)$$

$${\mathrm{S.}}_{sin}=sin\left(\mathrm{\theta }\right)=cOs\left(\mathrm{\theta \; +}\frac{\mathrm{\pi }}{2}\right)$$

The two partial signals recorded according to this embodiment (x and y value) are shown in FIG 4th graphically illustrated. Normally, as already mentioned, the Lissajous representation of a magnetic field in an off-axis application should correspond to an ellipse with a short axis b and a long axis a. In addition, the resolution / gradient should be constant. The quotient of the two axes can thus be formulated according to equation 5 with the Greek letter. $$\mathrm{\gamma \; =}\frac{b}{a}$$

In comparison, the Lissajous representation corresponds to the XMR sensor 2 after the orthogonal decomposition a circle with a resolution that changes over the circumference. This change depends on which derivation is described below.

$${\theta }_{off}=\frac{1}{i}ln\left(\frac{\mathrm{\gamma }x+iy}{\sqrt{{\mathrm{\gamma }}^2{x}^2+y^2}}\right)$$

The resolution is mathematically defined as the first derivative of the angle. In addition, the angle can be determined with two pieces of orthogonal information using equation 6. For an off-axis system, the angle can thus be calculated using equation 7. $$\theta =atan2\left(y,x\right)=\frac{1}{i}ln\left(\frac{x+iy}{\sqrt{x^2+y^2}}\right)$$

$${\theta }_{Off}=\frac{1}{i}ln\left(\frac{\mathrm{\gamma }x+iy}{\sqrt{{\mathrm{\gamma }}^2{x}^2+y^2}}\right)$$

$$G*\left(90°\right)=\left(\begin{array}{c}\frac{\mathrm{\gamma }b}{b^2}\\ 0\end{array}\right)=\frac{\mathrm{\gamma }}{b}$$

$$G*\left(0°\right)=\left(\begin{array}{c}0\\ \frac{\mathrm{\gamma }a}{{\mathrm{\gamma }}^2{a}^2}\end{array}\right)=\frac{1}{\mathrm{\gamma }a}$$

The following relationships, as expressed by equations 8 to 10, return to equation 1 via the gradient. $$G*\left(\theta \right)=\nabla \theta =\left(\begin{array}{c}\frac{\partial \theta }{\partial x}\\ \frac{\partial \theta }{\partial y}\end{array}\right)=\left(\begin{array}{c}\frac{-\mathrm{\gamma }y}{{\mathrm{\gamma }}^2{x}^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="DE102020105254A1\_0013.png,DE102020105254A1\_0015.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}\\ \frac{\mathrm{\gamma }x}{{\mathrm{\gamma }}^2{x}^2+y^2}\end{array}\right)$$

$$G*\left(90°\right)=\left(\begin{array}{c}\frac{\mathrm{<figure-callout\; id="2"\; label="\gamma \; b\; b"\; filenames="DE102020105254A1\_0013.png,DE102020105254A1\_0015.png"\; state="\{\{state\}\}">\gamma </figure-callout>}b}{b^{}}\\ 0\end{array}\right)=\frac{\mathrm{\gamma }}{b}$$

$$G*\left(0°\right)=\left(\begin{array}{c}0\\ \frac{\mathrm{\gamma }a}{{\mathrm{\gamma }}^2{a}^2}\end{array}\right)=\frac{1}{\mathrm{\gamma }a}$$

die auf der Gleichung 1 basiert, bestimmt.At 90 ° the gradient G corresponds to the position of B according to 4th (x = 0, y = b). At G (0 °) the gradient G corresponds to the position of A (x = a, y = 0). Thus, the resolution of an off-axis system is in turn given by the equation $\frac{G*\left(90°\right)}{G*\left(0°\right)}={\mathrm{\gamma }}^2\frac{a}{b}=\mathrm{\gamma }\mathrm{,}$

which is based on Equation 1 is determined.

Furthermore, in 4th It can be seen schematically that the orthogonal decomposition has expanded the contour in the x direction by 1 / times. This means that the resolution in the y direction is increased by times. This is the resolution for the XMR sensor 2 , especially TMR sensor, intended for off-axis applications with equation 11. $$\frac{G\left(90°\right)}{G\left(0°\right)}=\frac{\mathrm{\gamma }\cdot G*\left(90°\right)}{G*\left(0°\right)}={\mathrm{<figure-callout\; id="2"\; label="\gamma "\; filenames="DE102020105254A1\_0013.png,DE102020105254A1\_0015.png"\; state="\{\{state\}\}">\gamma </figure-callout>}}^2$$

To 2 the gradient G is thus subsequently calculated in order to subsequently obtain the correction value again. On the basis of the correction value, the angle error is then in turn calculated and, ultimately, a corrected angle value is output.

• Wenn der XMR-Sensor 2 (z.B. TMR) nur die Winkelinformation liefert:
  • - Abtastung mit einer geringen Frequenz bei einer konstanten Drehzahl / Abtastung mit einem externen Referenzwinkelsensor
  • - Abbilden des Gradienten im Prozess G* cal
  • - Bestimmen von nach der Gleichung 1 im Prozess cal
  • - Bestimmen des Winkelfehlers nach der Gleichung 2 im Prozess cal
  • - Winkelfehlerkompensation
• Wenn der XMR-Sensor 2 (z.B. TMR) x und y Information liefert:
  • - Winkel bestimmen mit der Atan2 Funktion
  • - Abtastung mit einer geringen Frequenz bei einer konstanten Drehzahl / Abtastung mit einem externen Referenzwinkelsensor
  • - Abbilden des Gradienten im Prozess G cal
  • - Bestimmen von im Prozess cal
  • - Bestimmen des Winkelfehlers nach der Gleichung 2 im Prozess cal
  • - Winkelfehlerkompensation

In other words, a method according to the invention takes place either according to variant a) or b) as follows:

• When the XMR sensor 2 (e.g. TMR) only provides the angle information:
  • - Sampling with a low frequency at a constant speed / sampling with an external reference angle sensor
  • - Mapping the gradient in the G * cal process
  • - Determination of according to equation 1 in the process cal
  • - Determination of the angle error according to equation 2 in the process cal
  • - Angular error compensation
• When the XMR sensor 2 (e.g. TMR) x and y information provides:
  • - Determine the angle with the Atan2 function
  • - Sampling with a low frequency at a constant speed / sampling with an external reference angle sensor
  • - Mapping the gradient in the G cal process
  • - Determine in the process cal
  • - Determination of the angle error according to equation 2 in the process cal
  • - Angular error compensation

The (preferably TMR) angle sensor 2 in practice often does not provide the angle information directly; instead, it is broken down in an orthogonal coordinate system into a sine and cosine signal (S_cos and S_sin) according to equations 3 and 4. The letter corresponds to the measured angle. With an on-axis system, this decomposition produces ideal sine and cosine signals, while with an off-axis system, sine and cosine signals with harmonic interference are generated. The influence of this process can be recognized in a Lissajous representation, whereby the shape of the signals is transformed from an ellipse to a circle ( 4th ). With the representation of the calculated points, an inhomogeneity of the points can be observed; ie the resolution is different. In practice, this effect can be understood to mean that if a signal with a lower sampling frequency is recorded during a rotation at a constant speed, the temporal resolution is inconstant.

Another idea is an end-of-line process with an external angle sensor 2 record the points (LUT calibration), the gradient being inconstant. The change in the gradient is shown again in the 5 shown. Another observation shows that the maximum is at position A, while the minimum is at position B. Positions A and B are offset from one another by 90 °. Positions A and B correspond to the places where the long and short axes are located.

Therefore, a hypothesis can be defined that the quotient of the maximum A to the minimum B corresponds to the change in the gradient G of the parameter. The further simulation after 6th shows a linear relationship between the quotient of G and ² .

This result can also be proven mathematically. Because the Atan2 function can be formulated mathematically according to equation 6. Therefore, the Atan2 function for an amplitude difference / TMR off-axis application can be rewritten as equation 7. In addition, the gradient of the equation can be solved according to equation 8. Thus, the gradient for the angle 90 ° is to be determined according to equation 9 and for the position / angle 0 ° according to equation 10. Therefore, the quotient can be determined using Equation 1. Equation 1 corresponds to the state before the orthogonal decomposition (ellipse formed by star points in 4th ). After the orthogonal decomposition, the sensitivity in the x-direction will increase again by. Finally, equation 11 is obtained, which is identical to equation 1.

The signal flow diagrams of the two options are in the 1 and 2 shown.

List of reference symbols

1

wave

2

XMR sensor

3

magnet

4th

Measuring arrangement

5

Axis of rotation

Claims (8)

Method for determining an angular position of a shaft (1), in a first step using an XMR sensor (2) arranged radially offset from the shaft (1) a signal representing an angular position of the shaft (1) from a signal associated with the shaft (1) permanently connected magnet (3) is detected, and in a second step an analytical angle error compensation of this detected signal is carried out by, while driving the shaft (1) at constant speed, either by the XMR sensor (2) or by another reference angle sensor depending on the angular position of the shaft (1) changing magnetic field of the magnet (3) over at least a full revolution of the shaft (1) is scanned, then a change in a gradient of an amplitude curve of the magnetic field is determined, then, using at least two gradient values present at different angles of rotation, a correction value is determined, by means of which correction value an angle error continues to be determined the angular position taken from the signal of the XMR sensor after the first step is determined, and finally the angular error is used to correct the angular position determined from the signal emitted by the XMR sensor (2). Procedure according to Claim 1 , characterized in that in the second step the shaft (1) is driven at a lower speed than in the first step. Procedure according to Claim 1 or 2 , characterized in that a first gradient value at an angular position of 0 ° and a second gradient value at an angular position of 90 ° are used in the second step to determine the correction value. Method according to one of the Claims 1 until 3 , characterized in that the XMR sensor (2) outputs an angle value in the first step. Method according to one of the Claims 1 until 3 , characterized in that the XMR sensor (2) in the first step outputs a first position value lying on an x-axis and a second position value lying on a y-axis oriented perpendicular to the x-axis. Procedure according to Claim 5 , characterized in that an angle value is calculated based on the two position values using an arctan2 function. Method according to one of the Claims 1 until 6th , characterized in that exactly one sensor (2) is used in the second step. Method according to one of the Claims 1 until 7th , characterized in that the scanning is carried out after the second step using the XMR sensor (2) at the end of an assembly chain of a measuring arrangement (4) having the shaft (1), the XMR sensor (2) and the magnet (3) .

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