AU2006252310B2

AU2006252310B2 - Method for determining an output signal

Info

Publication number: AU2006252310B2
Application number: AU2006252310A
Authority: AU
Inventors: Ralf Koenig; Timo Kuehn; Steffen Ullmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-12-23
Filing date: 2006-12-22
Publication date: 2012-09-20
Anticipated expiration: 2026-12-22
Also published as: AU2006252310A1; DE102005062125A1; FR2895505A1

Abstract

In this inventive method for determining an output signal (46) of a magneto-resistive angle sensor, a 5 periodic error component is determined for at least one raw signal (20, 22), with the period length of the at least one raw signal (20, 22) corresponding to an integer multiple of the period length of the periodic error component. This periodic error component in the at least 10 one raw signal (20, 22) is compensated during signal processing. 15/12/06,16166 specification,2

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL TO BE COMPLETED BY APPLICANT Name of Applicant: ROBERT BOSCH GMBH Actual Inventors: STEFFEN ULLMANN TIMO KUEHN RALF KOENIG Address for Service: CALLINAN LAWRIE, 711 High Street, Kew, Victoria 3101, Australia Invention Title: METHOD FOR DETERMINING AN OUTPUT SIGNAL The following statement is a full description of this invention, including the best method of performing it known to us:- -2 METHOD FOR DETERMINING AN OUTPUT SIGNAL DESCRIPTION The invention relates to: a method for determining 5 an output signal, a device, a magneto-resistive angle sensor, a computer program, and a computer program product. Third, fourth, and fifth generation steering-angle 10 sensors are based on the measuring principles of AMR (anisotropic magneto-resistive) and GMR (giant magneto resistive) technology, in which a large error component is attributable to an anisotropic error in the AMR or GMR elements of the steering-angle sensors. This error 15 component is expressed in a not-insignificant error amount in the angle and angular velocity output signals from steering-angle sensors. DE 103 06 127 Al relates to a method and a circuit 20 arrangement for determining the direction of a magnetic field. According to this document, the effect of anisotropic errors of GMR sensors on 3600 analysis can be curbed by suitable measures, particularly by suitable design of a transfer function. 25 EP 1 308 696 A2 relates to an angle measuring system with offset compensation and also to a method for compensating offset drift in the angle-measuring system. In this invention, an angle being measured is determined 30 on the basis of corresponding sinusoidal and cosinusoidal signals. For offset compensation, first the amplitude of the cosinusoidal and/or sinusoidal signal is determined, then an associated offset value is determined on the 15/12/06,16166 specification,2 -3 basis of the amplitude value determined. Thus, it is possible to correct the sinusoidal and cosinusoidal signals produced by the angle-measuring system, and hence to provide a corrected angle measurement value. 5 SUMMARY OF THE INVENTION According to the present invention, there is provided a method for determining an output signal for a magneto resistive angle sensor, in which a periodic error 10 component is determined for at least one raw signal, with the period length of the at least one raw signal corresponding to an integer multiple of the period length of the periodic error component, and in which, during signal processing, this periodic error component of the 15 at least one raw signal is compensated. ADVANTAGES OF THE INVENTION In the inventive method for determining an output signal of a magneto-resistive angle sensor, a periodic 20 error component for at least one raw signal is determined, in which the period length of the at least one raw signal corresponds to an integer multiple of the period length of the periodic error component. This periodic error component is compensated during signal 25 processing of the at least one raw signal. The inventive device for determining an output signal of a magneto-resistive angle sensor has a compensation element for correcting a periodic error 30 component of a raw signal, with the period length of the raw signal corresponding to an integer multiple of the period length of the periodic error component. 15/12/06,16166 specification,3 -4 It is advantageous if the device has a means for storing data representing the raw signal's periodic error component that is to be compensated. These data can, in particular, be measured at the completion of fabrication 5 of the angle sensor, and made available - if applicable, in computer-modified form - to the storage means in the device. The inventive magneto-resistive angle sensor has at 10 least one such inventive device. The invention also relates to a computer program with program code means for executing all the steps of a method according to the present invention, when the 15 computer program is executed on a computer or corresponding processing-unit, particularly in a device according to the invention. In addition, the invention relates to a computer 20 program product, with program code means stored on a computer-readable data-carrier, to execute all the steps of the inventive method, when the computer program is executed on a computer or corresponding processing-unit, particularly in a device according to the invention. 25 The inventive method makes it possible to largely compensate an anisotropic error of the magneto-resistive angle sensor or of a corresponding steering-angle sensor - and hence too of an AMR (anisotropic magneto-resistive) 30 or GMR (giant magneto-resistive) element. By compensating the anisotropic error, it is possible to improve the accuracy of angle sensors and their output signals (such as angle and angular velocity). 15/12/06,16166 specification,4 -5 The anisotropic error of GMR elements is attributable to a "120' error component" in the raw sinusoidal and cosinusoidal signals. A "120' error component" is to be understood as meaning a periodic 5 error component repeating every 1200: i.e., in a full 3600 revolution of a GMR element, three periods of this 120' error component occur. In an AMR element, the anisotropic error manifests 10 itself in a 60' error in the raw sinusoidal and cosinusoidal signals. However, because the GMR element has twice the measuring range of the AMR element, the same considerations apply regarding the raw signal, because the full period of the desired signal is 1800. 15 For this reason, only the GMR element with a measuring range of 3600 will be referred to in the discussion below. Spectral components of the raw signal of a GMR 20 element considered by way of example have been determined metrologically, and are listed in Table 1 below. Here the spectral components of the raw signals of the GMR element are standardized to a respective desired signal, in this case a 3600 spectral line. 15/12/06,16166 specification,5 -6 Spectral Analysis of Raw Signals Spectral Line Sinusoidal Raw Cosinusoidal Raw Signal Signal 3600 1 1 1800 0.0138 0.0138 1200 0.0672 0.0579 900 0.0004 0.0008 720 0.0025 0.0026 600 0.0006 0.0002 51.40 0.0004 0.0003 450 0.0002 0.0003 400 0.0004 0.0005 360 0.0002 0.0002 Table 1 As can be clearly seen in Table 1, the 1200 error 5 component is preponderant here. In this example, the amplitude of the 1200 error component in the raw sinusoidal signal is 6.72% of the amplitude of the desired signal, while in the raw cosinusoidal signal, this value is 5.79% of the amplitude of the desired 10 signal. By means of an additional compensation element, in an algorithm in a prior-art signal processing method, the 1200 error components of the respective raw signals can 15 be largely compensated. 15/12/06,16166 specification,6 -7 In a novel, expanded, signal processing method, the periodic error components are dealt with using the following algorithms for the raw sinusoidal signal (1) and the raw cosinusoidal signal (2): 5 X2 = Xi - CX (4 X 1 3 + 3 Xi) (1) where X 2 is an anisotropy-corrected sinusoidal value and Xi is an offset-corrected sinusoidal value for the 10 initially-measured raw sinusoidal signal, and CX is the correction factor for the periodic error component of the raw sinusoidal signal, and Y2 1 - Cy (4 Y13 + Yi), (2) 15 where Y 2 is an anisotropy-corrected cosinusoidal value and Yi is an offset-corrected cosinusoidal value for an initially-measured raw sinusoidal signal, and Cy is a correction factor for the periodic error component of the 20 raw sinusoidal signal. In equations (1) and (2), CX and Cy are constants which are determined e.g. at an end-of-belt test stand, i.e. after completed fabrication of the angle sensor, and 25 can be stored in a suitable manner in the angle sensor's inventive signal processing device, particularly a computing-type processing unit in the angle sensor. These two constants have values in the range of the standardized amplitude of the respective 1200 error 30 component. A good way of determining these constants CX and Cy at the end-of-belt test stand, or as part of a 15/12/06,16166 specification,7 -8 final inspection, is to use a least squares estimator, according to the least squares method, whereby a total angle error can be minimized. 5 A preferred embodiment of the present invention is usable in all products such as magneto-resistive angle sensors or corresponding steering-angle sensors whose raw signals have an additional error component with a period length corresponding to a third of the period length of 10 the desired signal. In third and fourth generation steering-angle sensors, the desired signal is a 180' signal, due to the AMR technology employed; and therefore, with the present invention, a 600 error component in the raw signal is compensatable. In fifth 15 generation steering-angle sensors, the desired signal is a 3600 signal, due to the GMR technology employed; and therefore, with the present invention, a 1200 error component is compensatable. The hitherto-uncompensated anisotropic errors with AMR and GMR elements can now be 20 largely compensated, thereby increasing the accuracy of steering-angle sensors with regard to their angle and angular velocity output signals. Further advantages and developments of the invention 25 will emerge from the description and the attached drawings. It will be appreciated that the features mentioned above and those yet to be explained below can be used not 30 only in the combination mentioned but also in other combinations or alone, without going beyond the scope of the present invention. 15/12/06,16166 specification,8 -9 An example of the invention will now be diagrammatically represented in the drawings, and will be described thoroughly below with reference to the drawings. In the drawings: 5 Fig. 1 is a flow diagram of signal processing in the prior art; Fig. 2 is a graph with an output angle-signal 10 exhibiting non-linearities; Fig. 3 is a flow diagram of expanded signal processing in a preferred form of implementation of a method according to the invention; and 15 Fig. 4 is a graph comparing angle errors for angles determined by a prior-art method and angles determined with a preferred form of implementation of a method according to the invention. 20 In Fig. 1, which is a flow diagram of signal processing according to the prior art, a raw sinusoidal signal 2 and a raw cosinusoidal signal 4 each undergo offset correction in an offset element 6. Raw signals 25 that have been offset-corrected in this way then undergo amplitude and phase correction in component 8. Then, in component 10, arctangent determination is performed, thereby supplying an angle 12 as the output signal of this method. 30 Fig. 2 shows, against a vertical axis 16, an output signal 18 plotted over a horizontal axis 16, as a reference measure. Such an output signal 18 is determined 15/12/06,16166 specification,9 -10 by the method shown in Fig. 1, and results in non linearities which can be clearly recognized in the output signal 18. Furthermore, there is an additional error amount in an angular velocity derived from the output 5 signal 18. Fig. 3 is a flow diagram showing a preferred form of implementation of an expanded signal processing method according to the invention. In this method, a raw 10 sinusoidal signal 20 undergoes offset correction in an offset-correction element 24, which results in an offset corrected sinusoidal value 26 for the raw sinusoidal signal 20. Correspondingly, a raw cosinusoidal signal 22 undergoes offset correction in an offset-correction 15 element 25, resulting in an offset-corrected cosinusoidal value 28 for the raw cosinusoidal signal 22. These two offset-corrected values 26, 28 each have an additional 1200 error component of approx. 5% of the 20 amplitude of the respective desired signal. Then, in the expanded signal processing operation (Fig. 3), the offset-corrected sinusoidal value 26 undergoes anisotropic i.e. 1200 correction in a compensation element 30, and the offset-corrected cosinusoidal value 25 28 likewise undergoes anisotropic i.e. 1200 correction in a compensation element 32. The constants CX and Cy used in these 1200 corrections 30, 32 are determined using a least squares estimator, and pass into a compensation element in the expanded signal processing operation. The 30 values of the two constants CX and Cy in this example are identical, because both raw signals 20, 22 have the same 1200 error component of approx. 5%. 15/12/06,16166 specification, 10 -11 During the performance of the 1200 corrections 30, 32 in the inventive method, an anisotropy-corrected sinusoidal value 34 and an anisotropy-corrected cosinusoidal value 36 are produced. In a subsequent step, 5 the anisotropy-corrected sinusoidal value 34 and the anisotropy-corrected cosinusoidal value 36 undergo amplitude and phase correction in component 38. This results in a desired cosinusoidal signal 40 and a desired cosinusoidal signal 42. Then, on the basis of these 10 desired signals 40, 42, and with arctangent determination by means of component 44, an output signal 46 for an angle is produced. In the graph in Fig. 4, an angle error 52 such as 15 results from the prior-art signal processing is plotted against a first, lefthand, vertical axis 48, over the horizontal axis 50. Against the second, righthand, vertical axis 54, an angle error 56 such as results from the expanded signal processing according to the invention 20 is plotted over the horizontal axis 50. Comparison of these angle errors 52, 56 shows that, with the prior-art signal processing, the 1200 error component in the raw signals leads to a 900 error component in the angle error 52. A reason for this transformation to another spectral 25 part is the non-linear arctangent function. With a transformed 120' error component in the raw signals, the expanded signal-processing leads, on the other hand, to a 450 error component in the angle error 56. 30 An advantage of the expanded signal-processing can be seen in the amplitudes of the angle errors 52, 56. In Fig. 4, it can be seen that, with the prior-art signal processing, the angle error 52 is up to 2.8660. With the 15/12/06,16166 specification, 11 -12 expanded signal-processing, on the other hand, the angle error is reduced to an amplitude of only 0.02150 (righthand vertical axis 54). This means that the angle error 52 with the prior-art signal processing is greater 5 by a factor 133 than the angle error 56 with the expanded signal-processing of the present invention. The angle error 52 can thus be drastically reduced. With the method according to the present invention, the accuracy of the value of an angular velocity derived from 10 the angle is considerably improved. 15/12/06,16166 specification, 12

Claims

1. A method for determining an output signal for a magneto-resistive angle sensor, wherein a periodic error 5 component is determined for at least one raw signal, with the period length of the at least one raw signal corresponding to an integer multiple of the period length of the periodic error component, and wherein, during signal processing, this periodic error component of the 10 at least one raw signal is compensated.

2. The method as claimed in claim 1, wherein a periodic error component whose period length corresponds to one third the period length of the raw signal is compensated. 15

3. The method as claimed in claim 1 or 2, wherein, during signal processing, the error component is compensated by means of a compensation element. 20

4. The method as claimed in any one of the preceding claims, wherein, during signal processing, an anisotropy corrected sinusoidal value X 2 is determined according to the following algorithm: X2 = XI - CX (4 X 1 3 + 3 XI), 25 where X 1 is an offset-corrected sinusoidal value of an initially-measured raw sinusoidal signal, and CX is a correction factor for the periodic error component of the raw sinusoidal signal, and in which, during signal processing, an anisotropy-corrected cosinusoidal value Y 2 30 is determined according to the following algorithm: Y2 1 - Cy (4 Y 1 3 + Yi), 15/12/06,16166 specification, 13 -14 where Yi is an offset-corrected cosinusoidal value of an initially-measured raw sinusoidal signal, and Cy is a correction factor for the periodic error component of the raw sinusoidal signal. 5

5. The method as claimed in claim 4, wherein, for the at least one periodic error component, a constant value is used for CX and Cy respectively. 10

6. The method as claimed in any one of the preceding claims, wherein a value for the error component is measured at the completion of fabrication of the angle sensor. 15

7. The method as claimed in any one of the preceding claims, wherein the error component is determined using a least squares estimator, which minimizes a total angle error. 20

8. The device for determining an output signal for a magneto-resistive angle sensor, with at least one compensation element for correcting a periodic error component of at least one raw signal, wherein the period length of the at least one raw signal corresponds to an 25 integer multiple of the period length of the periodic error component.

9. A device as claimed in claim 8, further including a device for storing data representing the periodic error 30 component in the raw signal. 15/12/06,16166 specification,14 - 15

10. A magneto-resistive angle sensor having a device as claimed in claim 8 or 9.

11. A computer program with program code means, to 5 execute all the steps of a method as claimed in any one of claim 1 to 7, when the computer program is executed on a computer or corresponding processing unit, particularly in a device as claimed in claim 8 or 9. 10

12. A computer program product stored on a computer readable data carrier, to execute all the steps of a method as claimed in any one of claims 1 to 7, when the computer program is executed on a computer or corresponding processing unit, particularly in a device 15 as claimed in claim 8 or 9.

13. A method for determining an output signal for a magneto-resistive angle sensor substantially as hereinbefore described with reference to the accompanying 20 drawings.

14. A device for determining an output signal for a magneto-resistive angle sensor substantially as hereinbefore described with reference to the accompanying 25 drawings.

15. A magneto-resistive angle sensor substantially as hereinbefore described with reference to the accompanying drawings. 15/12/06,16166 specification,15