This application claims priority of German patent application No. 10 2014 115 179.8, filed on 17 Oct. 2014. The entire disclosure of German patent application No. 10 2014 115 179.8 is hereby incorporated herein by reference.
Field of the Invention
The present invention relates to a method and an apparatus for computing a rotation angle of a rotor in a motor.
Brief Description of the Related Art
For the correct measurement of the rotor position the direct current motors 100 must be calibrated. This calibration is initially effected in a known manner by external sensors, i.e. Hall sensors, placed in the front field of the motor 100 and with a permanent magnet fixed to the rotor 50.
In the state of the art also patent publications are known which disclose sensors for capturing the rotor position in a direct current motor. For example, the Japanese patent application No. JP 2005/308430 of the Matsushita Electric company teaches a contactless detector for the rotation angle which can be used in the direct current motor.
However, these known solutions do not permit a calibration of the sensor during operation. Such a calibration would permit both greater mounting tolerances in the manufacture of the motor and positional changes of the motor or of the sensors during operation. Moreover, an automatic calibration enables a continuous compensation of static and dynamic interference fields in the vicinity of a running motor, which otherwise influence the measurement of the rotation angle.
A method for determining the rotation angle of a rotor with the aid of sensors in a motor is described. The method comprises the measurement of reference values by reading signal values from the angle sensors after the rotor was brought to a predetermined rotor position. The signal values of a magnetic field are measured during at least one full revolution (360°) of the rotor 50 and offset values of the sensors are computed by forming the average value from the peak values of the magnetic field. A computation of corrected signal values is effected by subtracting the offset values from the measured signal values, and amplitude difference values are computed from the difference of the peak values of the magnetic field. Normalized/standardized signal values and reference values are computed by division in each case of the corrected signal values and reference values with a divisor corresponding to half of the amplitude difference values, and subsequently a correction angle is computed by using the ARCTAN value of the normalized/standardized reference values. The rotation angle is then determined by computing the ARCTAN value of the normalized/standardized amplitude values in the X direction and in the Y direction after deduction of the correction angle.
This method can be effected constantly or continuously, such that an automatic determination of the rotation angle and consequently the calibration of the motor can be effected also during operation.
An apparatus for determining the rotor position of a motor is also described. This apparatus comprises at least one sensor for capturing the magnetic field value and a processor for computing the rotor position for carrying out the method of the invention.
This apparatus and method are used in a synchronous motor having a stator with a plurality of switchable coils and a rotor that is rotatably held in the stator. A permanent magnet is mounted on an axle that is connected to the rotor. This permanent magnet generates the magnetic field used for capturing the rotor position.
For a better understanding of the invention, an exemplary embodiment will now be explained with reference to the following Figures, wherein the invention is not limited to this exemplary embodiment.
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:
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.
For a better understanding of the system 100 some coordinate systems are defined which are shown in
An optimal arrangement of the sensor array 10 is shown in
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)
The rotation angle θ is consequently computed as follows:
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:
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:
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 Ax,ref and Ay,ref in the corresponding X and Y directions at a defined rotor position θref. From equation 8 the correction angle is then computed:
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.
In the subsequent step 620 the orthogonal signal values Ax and Ay 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 Ax and Ay are normalized and the correction angle is computed with the aid of equation 9 in the step 660.
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.
In
During ongoing operation, the rotation angle of the rotor 50 is computed in step 710 with the aid of the method represented in
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.
Number | Date | Country | Kind |
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10 2014 115 179 | Oct 2014 | DE | national |
Number | Name | Date | Kind |
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5198738 | Blaser | Mar 1993 | A |
5493219 | Makino | Feb 1996 | A |
6249094 | Zeh | Jun 2001 | B1 |
6279375 | Draxelmayr | Aug 2001 | B1 |
20140225596 | Nakamura | Aug 2014 | A1 |
Number | Date | Country |
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197 07 263 | Aug 1998 | DE |
198 44 663 | Apr 2000 | DE |
2005308430 | Nov 2005 | JP |
9837386 | Aug 1998 | WO |
Entry |
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“Brushless electric motor,” Wikipedia. |
Number | Date | Country | |
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20160109264 A1 | Apr 2016 | US |