Apparatus and method for determining a rotation angle of a rotor

Abstract

A method and an apparatus for determining a rotation angle of a rotor in a motor with the aid of angle sensors by measurement of reference values and correction of the effected computations. The method is used, for example, in a synchronous motor.

Claims

1. A method for determining a rotation angle of a rotor with the aid of angle sensors in a motor, comprising: capturing of reference values by reading signal values from the angle sensors after the rotor was brought to a predetermined rotor position; measuring amplitude values of a magnetic field during at least one full revolution of the rotor; computing offset values of the angle sensors by forming an average value of peak values of the magnetic field; computing corrected amplitude values by subtraction of the offset values from the measured amplitude values; computing amplitude difference values from the difference of the peak values of the magnetic field; computing normalized/standardized amplitude values and of normalized/standardized reference values by division of the corrected amplitude values and the reference values with a divisor, corresponding to the half of the amplitude difference values; computing a correction angle by computing the ATAN value of the normalized/standardized reference values; and determining the rotation angle by computing the ATAN value of the normalized/standardized amplitude values in the X direction and in the Y direction and deduction of the correction angle.

2. The method according to claim 1, wherein the predetermined rotor position is determined by using the magnetic field.

3. The method according to claim 1, further comprising a constant measurement of the rotation angle.

4. The method according to claim 2, further comprising a constant measurement of the rotation angle.

5. An apparatus for determining the rotor position of a motor, comprising: at least one sensor for capturing a magnetic field value; and a processor for computing the rotor position, wherein the processor is configured to: capture of reference values by reading signal values from angle sensors after the rotor was brought to a predetermined rotor position; measure amplitude values of a magnetic field during at least one full revolution of the rotor; compute offset values of the angle sensors by forming an average value of peak values of the magnetic field; compute corrected amplitude values by subtraction of the offset values from the measured amplitude values; compute amplitude difference values from the difference of the peak values of the magnetic field; compute normalized/standardized amplitude values and of normalized/standardized reference values by division of the corrected amplitude values and the reference values with a divisor, corresponding to the half of the amplitude difference values; compute a correction angle by computing the ATAN value of the normalized/standardized reference values; and determine the rotation angle by computing the ATAN value of the normalized/standardized amplitude values in the X direction and in the Y direction and deduction of the correction angle.

6. The apparatus according to claim 5, wherein the processor is further configured to use a value of the magnetic field to determine the predetermined rotor position.

7. The apparatus according to claim 5, wherein the processor is further configured to constantly measure the rotation angle.

8. The apparatus according to claim 6, wherein the processor is further configured to constantly measure the rotation angle.

9. A synchronous motor, comprising: a stator with a plurality of switchable coils; a rotor rotatably held in the stator; a permanent magnet mounted on an axle connected to the rotor; and an apparatus for determining the rotor position of a motor, comprising: at least one sensor for capturing a magnetic field value; and a processor for computing the rotor position configured to: capture of reference values by reading signal values from angle sensors after the rotor was brought to a predetermined rotor position; measure amplitude values of a magnetic field during at least one full revolution of the rotor; compute offset values of the angle sensors by forming an average value of peak values of the magnetic field; compute corrected amplitude values by subtraction of the offset values from the measured amplitude values; compute amplitude difference values from the difference of the peak values of the magnetic field; compute normalized/standardized amplitude values and of normalized/standardized reference values by division of the corrected amplitude values and the reference values with a divisor, corresponding to the half of the amplitude difference values; compute a correction angle by computing the ATAN value of the normalized/standardized reference values; and determine the rotation angle by computing the ATAN value of the normalized/standardized amplitude values in the X direction and in the Y direction and deduction of the correction angle.

10. The synchronous motor according to claim 9, further comprising an electronic circuit for switching the switchable coils on and off.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considering in connection with the accompanying drawings, wherein:

(2) FIG. 1 is the arrangement of a sensor array;

(3) FIGS. 2A and 2B are views along the rotor axle in an optimal arrangement of the sensor array and the curve of the signal values of the sensor;

(4) FIG. 3A is a view along the rotor axle with a rotated sensor;

(5) FIG. 3B is a graph of the curve of the signal values of the sensor;

(6) FIG. 4A is a view along the rotor axle with a rotated and offset sensor;

(7) FIG. 4B is a graph of the curve of the measured signal values of the sensor;

(8) FIG. 5 is a conventional brushless direct current motor;

(9) FIG. 6 is the sequence of the method; and

(10) FIG. 7 is a diagram of the method of control of a brushless direct current motor.

DESCRIPTION OF THE EMBODIMENTS

(11) The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

(12) FIG. 1 shows the simplified arrangement of a direct current motor 100 having an axle 55 connected to the rotor in the direct current motor 100, and a permanent magnet 60 attached to the front of the axle 55. The permanent magnet 60 in this embodiment has a north pole N and a south pole S. The rotor in the direct current motor 100 rotates about a central axis 15. In the vicinity of the permanent magnet 60 a sensor 20 is attached, which measures the magnetic field B of the permanent magnet 60. The sensor 20 has one or a plurality of two-dimensional or three-dimensional Hall sensors, which can measure the orthogonal values of the magnetic field B in an X direction X.sub.h and in a Y direction Y.sub.h as sensor signals (two-dimensionally) and additionally in a Z direction Z.sub.h (three-dimensionally). The orthogonal values X.sub.h and Y.sub.h are forwarded to a microcontroller 40 via lines 45. The microcontroller 40 is connected to the electronic control 90 of the direct current motor 100 and can switch on and off the activatable coils 85 in the stator 80 of the direct current motor 100.

(13) For a better understanding of the system 100 some coordinate systems are defined which are shown in FIG. 1: stator coordinate system (referred to by a character S in subscript); rotating rotor coordinate system (referred to by a character R in subscript); rotating magnet coordinate system (referred to by a character M in subscript); and Hall coordinate system (referred to by a character h in subscript).

(14) An optimal arrangement of the sensor array 10 is shown in FIG. 2A, which shows the arrangement of the sensor array 10 along the central axis 15. In the arrangement shown in FIG. 2A, the center of the sensor 20 crosses the central axis 15, and the X and Y directions of the stator coordinate system (X.sub.S, Y.sub.S) are identical to the X and Y directions of the Hall coordinate system (X.sub.h, Y.sub.h). The magnetic field B has a signal value measured by the sensor 20 in the X direction of A.sub.x and in the Y direction of A.sub.y. FIG. 2B shows the curve of the measured signal values A.sub.x and A.sub.y over a full revolution of the rotor 50. In the X direction the measured signal value A.sub.x has a maximal value A.sub.x,max, which, in this ideal case, is identical to the maximal value of the signal value in the Y direction A.sub.y,max. The curves of the signal values A.sub.x and A.sub.y are identical and offset by 90°, since the signal values A.sub.x and A.sub.y are orthogonal. The rotation angle θ of the axle 55 is identical to the measured rotation angle δ of the sensor 20 and is computed with the aid of the arc tangent function as follows:

(15) $\begin{array}{cc}\theta =\delta ={\tan }^{-1}\left(\frac{A_y}{A_x}\right)& \left(1\right)\end{array}$

(16) FIG. 3A shows an arrangement of the sensor array 10 in which the center of the sensor 20 still lies in the central axis 15, but the sensor 20 itself and the Hall coordinate system is rotated. In other words, the X and Y directions of the stator 50 and of the sensor 20 are no longer identical. As can be seen from FIG. 3B, the curves of the signal values A.sub.x and A.sub.y measured in each case still have an identical shape in the X direction and the Y direction and are still offset by 90°, since the two directions are orthogonal. The zero point of the signal value in the Y direction A.sub.y is at the angle value α+β, as can be recognized in FIG. 3.

(17) The actual rotation angle θ of the axle 55 is consequently no longer equal to the measured rotation angle δ of the sensor 20, but must be corrected by the factor α+β (correction angle):
θ=δ−(α+β)  (2)

(18) The rotation angle θ is consequently computed as follows:

(19) $\begin{array}{cc}\theta ={\tan }^{-1}\left(\frac{A_y}{A_x}\right)-\left(\alpha +\beta \right)& \left(3\right)\end{array}$

(20) FIG. 4A shows the typical arrangement of the sensor array 10, in which the sensor 20 is rotated about a rotation point and is positioned at a distance (Δx, Δy) from the central axis 15. Moreover, FIG. 4A shows a stray field or interference field caused e.g. by an interfering conductor 70.

(21) FIG. 4B shows the curves of the read-out signal values in this case. As can be gathered from FIG. 4B, the curves have a different shape with different maximal values A.sub.x,max and A.sub.y,max due to the stray field influencing the orthogonal component differently. Likewise, the minimal values of the curves of the orthogonal components A.sub.x,min and A.sub.y,min have different values. In this case, offset values offx and offy must first be computed in the corresponding X and Y direction for correcting the signal values, before the rotation angle θ of the axle 55 can be computed. These offset values offx and offy are computed by forming the average value of the sum of the maximal and minimal values of the corresponding orthogonal components:

(22) $\begin{array}{cc}\mathrm{offx}=\frac{A_{x,\max }+A_{x,\min }}{2}& \left(4\right)\\ \mathrm{offy}=\frac{A_{y,\max }+A_{y,\min }}{2}& \left(5\right)\end{array}$

(23) The average values of the amplitude difference of the maximal and minimal values ampx in the X direction and ampy in the Y direction are computed according to the following equations:

(24) $\begin{array}{cc}\mathrm{ampx}=\frac{A_{x,\max }-A_{x,\min }}{2}& \left(6\right)\\ \mathrm{ampy}=\frac{A_{y,\max }-A_{y,\min }}{2}& \left(7\right)\end{array}$

(25) The rotation angle θ is now computed from equation 3 as follows, wherein the signal values are corrected by subtracting the corresponding offset values and normalization by the amplitude differences:

(26) $\begin{array}{cc}\theta ={\tan }^{-1}\left(\frac{A_x-\mathrm{offx}}{\mathrm{ampx}},\frac{A_y-\mathrm{offy}}{\mathrm{ampy}}\right)-\left(\alpha +\beta \right)& \left(8\right)\end{array}$

(27) In equation 8 the value of α+β (correction angle) is still unknown. However, this value can be computed from a one-off measurement of the signal values of the orthogonal components A.sub.x,ref and A.sub.y,ref in the corresponding X and Y directions at a defined rotor position θ.sub.ref. From equation 8 the correction angle is then computed:

(28) $\begin{array}{cc}\left(\alpha +\beta \right)={\tan }^{-1}\left(\frac{A_{x,\mathrm{ref}}-\mathrm{offx}}{\mathrm{ampx}},\frac{A_{y,\mathrm{ref}}-\mathrm{offy}}{\mathrm{ampy}}\right)-{\theta }_{\mathrm{ref}}& \left(9\right)\end{array}$

(29) Consequently, the rotation angle θ can be computed in any position of the rotor 50 even during ongoing operation by applying the equation 8. The computed values of the rotation angle θ can then be forwarded to the electronic control 90 of the direct current motor 100 in order to control an optimal commutation.

(30) FIG. 6 shows the sequence of the method, which starts in step 600. In a first step 610 the orthogonal reference values A.sub.x,ref and A.sub.y,ref of the Hall signal are read out from the sensor 20 at the known rotation angle θ.sub.ref. These reference values A.sub.x,ref and A.sub.y,ref are used for computing the correction angle α+β later on.

(31) In the subsequent step 620 the orthogonal signal values A.sub.x and A.sub.y are measured over at least one full revolution of the rotor 50, and in step 630 the offset values offx and offy are computed therefrom with the aid of the equations 4 and 5 for the further computation of the corrected signal values. In the step 640 subsequently the amplitude differences ampx and ampy are computed with the aid of the equations 6 and 7. In a further step 650 the corrected signal values A.sub.x and A.sub.y are normalized and the correction angle is computed with the aid of equation 9 in the step 660.

(32) After the computation of the correction angle, the rotor position can be measured at any given time with the aid of equation 8 in step 670.

(33) In FIG. 7 the control of the brushless direct current motor 100 is explained in simplified fashion. In a first step 700 the coils 85 in the stator 80 are switched suitably in order to generate a rotating field.

(34) During ongoing operation, the rotation angle of the rotor 50 is computed in step 710 with the aid of the method represented in FIG. 6. Further, the parameters (A.sub.x,min, A.sub.x,max, A.sub.y,min A.sub.y,max, α+β) required for computing the rotor position are measured red continuously (step 720), and when there exists an excessive, permanent variation, are correspondingly adjusted/recalibrated in order to ensure an efficient control of the motor during ongoing operation.

(35) The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.