Device and method for determining a rotation angle of a rotor

Abstract

Method for determining a rotation angle of a rotor (50) using angle sensors (25) in a motor, comprising: - detecting reference values ​​by reading signal values ​​from the angle sensors after the rotor (50) has been brought into a predetermined rotor position (55); - detecting amplitude values ​​(Ax, Ay) of a magnetic field (B) during at least one full revolution of the rotor (50); - Calculation of offset values ​​(offx, offy) of the angle sensors (10) by forming an average of peak values ​​(A x,max , A y,max ) of the magnetic field (B); - Calculation of corrected amplitude values ​​by subtracting the offset values ​​(offx, offy) from the recorded amplitude values ​​(Ax, Ay); - Calculation of amplitude difference values ​​(ampx, ampy) from the difference of the peak values ​​(A x,max , A y,max ) of the magnetic field (B); - Calculation of normalised amplitude values ​​and of normalised reference values ​​by dividing the corrected amplitude values ​​and the reference values ​​by a divisor corresponding to half of the amplitude difference values; - Calculation of a correction angle by calculating the ATAN value of the normalized / standardized reference values; and - Determination of the angle of rotation by calculating the ATAN value of the normalized / normalized amplitude values ​​in the X-direction and in the Y-direction and subtracting the correction angle.

Description

[0001] The invention relates to a method and a device for calculating a rotation angle of a rotor in a motor.

[0002] Fig. 5 shows the structure of a conventional brushless DC motor 100. The brushless DC motor 100 has a rotor 50, which is implemented with a permanent magnet and is rotatably mounted within a stator 80. The stator 80 has a plurality of coils 85, which are controlled by an electronic circuit 90 in order to generate a rotating magnetic field within the stator 80. The rotating field causes a torque on the rotor 50. The commutation of the DC motor 100, i.e. the switching of the coils 85 on and off, takes place via the electronic control 90 and is usually dependent on the rotor position, the speed, and the instantaneous load on the rotor 50. Angular errors when detecting the rotor position of the rotor 50 lead to high power losses in the DC motor 100 and thus reduce the available maximum torque.These angular errors are often the cause of noise and vibration in DC motors 100.

[0003] To correctly detect the rotor position, the DC motors 100 must be calibrated. This calibration is performed in a conventional manner, initially using external sensors, including Hall sensors, placed in front of the motor 100, and a permanent magnet fixed to the rotor 50.

[0004] Patents are also known in the prior art that disclose sensors for detecting the rotor position in a DC motor. For example, Japanese patent application No. JP 2005 - 308 430 A from Matsushita Electric teaches a contactless detector for the angle of rotation that can be used in the DC motor.

[0005] DE 10 2012 219 146 A1 discloses a measuring device for the contactless determination of a rotation angle. The measuring device comprises a first component with a magnet. Furthermore, the measuring device comprises a second component with a magnet-sensitive element. The first component and the second component are mounted so as to be rotatable relative to each other about a common axis of rotation. The magnet-sensitive element is designed to determine a rotation angle value of the first component with respect to the second component as a function of a magnetic field of the magnet. The magnet is designed as a ferrite magnet.

[0006] DE 10 2015 211 252 A1 discloses a device and a method for adjusting signals from a rotary encoder. For this purpose, extreme values ​​are determined in the output signals of the rotary encoder, and the amplitude or offset of the output signal from the rotary encoder is calculated based on these extreme values. The rotary encoder signals are then normalized using the calculated amplitude and offset. This enables precise and standardized further processing for determining angular position and frequency.

[0007] However, these known solutions do not allow for calibration of the sensor during operation. Such calibration would allow for larger installation tolerances during motor manufacturing, as well as position changes of the motor or sensors during operation. Furthermore, automatic calibration enables ongoing compensation for static and dynamic interference fields in the vicinity of a running motor, which would otherwise affect the detection of the rotation angle.

[0008] A method for determining the rotation angle of a rotor using sensors in a motor is described. The method comprises detecting reference values ​​by reading signal values ​​from the angle sensors after the rotor has been brought into a predetermined rotor position. The signal values ​​of a magnetic field are detected during at least one full revolution (360°) of the rotor 50, and offset values ​​of the sensors are calculated by averaging the peak values ​​of the magnetic field. Corrected signal values ​​are calculated by subtracting the offset values ​​from the detected signal values, and amplitude difference values ​​are calculated from the difference between the peak values ​​of the magnetic field.Normalized signal values ​​and reference values ​​are calculated by dividing the corrected signal values ​​and reference values ​​by a divisor equal to half the amplitude difference values, respectively. A correction angle is then calculated using the ARCTAN value of the normalized reference values. The rotation angle is then determined by calculating the ARCTAN value of the normalized amplitude values ​​in the X direction and in the Y direction after subtracting the correction angle.

[0009] This procedure can be carried out continuously or continuously so that the angle of rotation can be determined automatically and thus the calibration of the motor can be carried out even during operation.

[0010] A device for determining the rotor position of a motor is also described. This device comprises at least one sensor for detecting the magnetic field value and a processor for calculating the rotor position by implementing the method according to the invention.

[0011] This device and method are used in a synchronous motor comprising a stator with a plurality of switchable coils and a rotor rotatably mounted within the stator. A permanent magnet is mounted on an axle connected to the rotor. This permanent magnet generates the magnetic field used to detect the rotor position.

[0012] For a better understanding of the invention, an embodiment will now be explained with reference to the following figures, whereby the invention is not limited to this embodiment.

[0013] They show: Fig. 1 the structure of a sensor arrangement; Fig. 2a and Fig. 2b a view along the rotor axis with an optimal setup of the sensor arrangement and the curve of the signal values ​​from the sensor; Fig. 3a and Fig. 3b a view along the rotor axis with a rotated sensor and the curve of the signal values ​​from the sensor; Fig. 4a and Fig. 4b a view along the rotor axis with a rotated and offset sensor and the curve of the recorded signal values ​​from the sensor; Fig. 5 a conventional brushless DC motor, and Fig. 6 the course of the procedure. Fig. 7 the control of a brushless DC motor

[0014] Fig. 1 shows the simplified structure of a DC motor 100 with an axle 55, which is connected to the rotor 50 in the DC motor 100, and a permanent magnet 60, which is attached to the end of the axle 55. The permanent magnet 60, in this embodiment, has a north pole N and a south pole S. The rotor 50 rotates about a central axis 15. A sensor 20 is attached near the permanent magnet 60, which detects the magnetic field B from the permanent magnet 60. The sensor 20 has one or a plurality of 2-dimensional or 3-dimensional Hall sensors 25, which measure the orthogonal values ​​of the magnetic field B in an X-direction X h and in a Y-direction Y h as sensor signals (2-dimensional) and additionally in a Z direction Z h (3-dimensional). The orthogonal values ​​X h and Y hare forwarded via lines 45 to a microcontroller 40. The microcontroller 40 is connected to the electronic control 90 of the DC motor 100 and can switch the switchable coils 85 in the stator 80 of the DC motor 100 on and off.

[0015] For a better understanding of the system 100, some coordinate systems are defined, which are Fig. 1 are shown: Stator coordinate system (denoted by a subscript letter S) Rotating rotor coordinate system (denoted by a subscript letter R) Rotating magnetic coordinate system (denoted by a subscript letter M), and Hall coordinate system (denoted by a subscript letter h).

[0016] An optimal design of the sensor arrangement 10 is shown in Fig. 2a, which shows the structure of the sensor arrangement 10 along the central axis 15. In the Fig. In the structure shown in Figure 2a, the center point of the sensor 20 crosses the central axis 15 and the X and Y directions of the stator coordinate system (X s , Y s ) are identical to the X and Y directions of the Hall coordinate system (X h , Y h ). The magnetic field B has a signal value detected by the sensor 20 in the X-direction of A x and in the Y direction of A y . Fig. 2b shows the curve of the recorded signal values ​​A x and A y over one full revolution of the rotor 50. In the X-direction, the recorded signal value A x a maximum value of A x,max , which in this ideal case is identical to the maximum value of the signal value in the Y direction A y,max The curves of the signal values ​​A x and A y are identical and offset by 90°, since the signal values ​​A x and A yare orthogonal. The angle of rotation θ of axis 55 is identical to the angle of rotation δ detected by sensor 20 and is calculated using the arctangent function as follows: θ=δ=tan−1(AyAx)

[0017] Fig. Figure 3a shows a configuration of the sensor arrangement 10 in which the center of the sensor 20 is still located on the central axis 15, but the sensor 20 itself and the Hall coordinate system are rotated. In other words, the X and Y directions of the stator 50 and the sensor 20 are no longer identical. As can be seen from Fig. As can be seen in Figure 3b, the recorded curves of the signal values ​​A x and A y in the X-direction and the Y-direction they still have an identical shape and are offset by 90°, since the two directions are orthogonal. The zero point of the signal value in the Y-direction A y is at the angle value α + β, as in Fig. 3 can be seen.

[0018] The actual angle of rotation θ of the axis 55 is therefore no longer equal to the measured angle of rotation δ of the sensor 20, but must be corrected by the factor α + β (correction angle): θ=δ−(α+β)

[0019] Thus, the angle of rotation θ is calculated as follows: θ=tan−1(AyAx)−(α+β)

[0020] Fig. Figure 4a shows the typical structure of the sensor arrangement 10, in which the sensor 20 is rotated about a pivot point and positioned at a distance (Δx, Δy) from the central axis 15. In addition, Fig. 4a a stray or interference field caused, for example, by an interference conductor 70.

[0021] Fig. 4b shows the curves of the read signal values ​​in this case. As the Fig. As can be seen in Figure 4b, the curves have a different shape with different maximum values ​​A x,max and A y,maxdue to the stray field, which affects the orthogonal component differently. Likewise, the minimum values ​​of the curves of the orthogonal components A x,min and A y,min different values. In this case, offset values ​​offx and offy must first be calculated in the respective X and Y directions to correct the signal values ​​before the rotation angle θ of axis 55 can be calculated. These offset values ​​offx and offy are calculated by averaging the sum of the maximum and minimum values ​​of the respective orthogonal components: offx=Ax,max+Ax,min2 offy=Ay,max+Ay,min2

[0022] The mean values ​​of the amplitude difference of the maximum and minimum values ​​ampx in the X-direction and ampy in the Y-direction are calculated according to the following formulas: ampx=Ax,max−Ax,min2 ampy=Ay,max−Ay,min2

[0023] The angle of rotation θ is now calculated from formula 3 as follows, where the signal values ​​are corrected by subtracting the respective offset values ​​and normalizing by the amplitude differences: θ=tan−1(Ax−offxampx,Ay−offyampy)−(α+β)

[0024] In formula 8, the value of α + β (correction angle) is still unknown. However, this value can be determined from a single measurement of the signal values ​​of the orthogonal components A x,ref and A y,ref in the respective X and Y directions at a defined rotor position θ ref The correction angle is then calculated from formula 8: (α+β)=tan−1(Ax,ref−offxampx,Ay,ref−offyampy)−θref

[0025] Thus, for any position of the rotor 50, the angle of rotation θ can be calculated even during operation by applying formula 8. The calculated values ​​of the angle of rotation θ can then be passed on to the electronic control 90 of the DC motor 100 in order to control optimal commutation.

[0026] Fig. Figure 6 shows the flow of the method, which begins in step 600. In a first step 610, the orthogonal reference values ​​A x,ref and A y,ref of the Hall signal from the sensor 20 at the known angle of rotation θ ref These reference values ​​A x,ref and A y,ref are later used to calculate the correction angle α + β.

[0027] In the following step 620, the orthogonal signal values ​​A x and A yover at least one full revolution of the rotor 50 and, in step 630, using formulas 4 and 5, the offset values ​​offx and offy are calculated for the further calculation of the corrected signal values. In step 640, the amplitude differences ampx and ampy are then calculated using formulas 6 and 7. In a further step 650, the corrected signal values ​​A x and A y normalized and the correction angle is calculated using formula 9 in step 660.

[0028] After calculating the correction angle, the rotor position can be determined at any time using formula 8 in step 670.

[0029] In Fig. Figure 7 provides a simplified explanation of the control of the brushless DC motor 100. In a first step 700, the coils 85 in the stator 80 are suitably connected to generate a rotating field.

[0030] During operation, the Fig.6, the angle of rotation of the rotor 50 is calculated in step 710. Furthermore, the parameters required to calculate the rotor position (A x,min , A x,max , A y,min A y,max , α + β) is continuously recorded (step 720) and, if the permanent deviation is too large, is adjusted / recalibrated accordingly in step 730 in order to ensure efficient control of the motor during operation. Reference symbol 10 Sensor arrangement 15 Central axis 20 sensors 25 Hall sensor 40 microcontrollers 45 lines 50 rotor 55 Axis 60 permanent magnet 70 interference conductors 80 Stator 85 spools 90 electronic control 100 brushless motor

Claims

[1] Method for determining a rotation angle of a rotor (50) using angle sensors (25) in a motor, comprising: - detecting reference values ​​by reading signal values ​​from the angle sensors after the rotor (50) has been brought into a predetermined rotor position (55); - detecting amplitude values ​​(Ax, Ay) of a magnetic field (B) during at least one full revolution of the rotor (50); - Calculation of offset values ​​(offx, offy) of the angle sensors (10) by forming an average of peak values ​​(A x,max , A y,max ) of the magnetic field (B); - Calculation of corrected amplitude values ​​by subtracting the offset values ​​(offx, offy) from the recorded amplitude values ​​(Ax, Ay); - Calculation of amplitude difference values ​​(ampx, ampy) from the difference of the peak values ​​(A x,max , A y,max ) of the magnetic field (B); - Calculation of normalised amplitude values ​​and of normalised reference values ​​by dividing the corrected amplitude values ​​and the reference values ​​by a divisor corresponding to half of the amplitude difference values; - Calculation of a correction angle by calculating the ATAN value of the normalized / standardized reference values; and - Determination of the angle of rotation by calculating the ATAN value of the normalized / normalized amplitude values ​​in the X-direction and in the Y-direction and subtracting the correction angle. [2] Method according to claim 1, wherein the predetermined rotor position (55) is determined by using the magnetic field (8). [3] Method according to claim 1 or 2, further comprising continuously detecting the angle of rotation. [4] Device (10) for determining the rotor position (55) of a motor (100) comprising: - at least one sensor (25) for detecting a magnetic field value (Bx, By); and - a processor (40) for calculating the rotor position (55) by carrying out the method according to one of claims 1 to 3. [5] Synchronous motor (100) comprising: - a stator (80) with a plurality of switchable coils (85); - a rotor (50) rotatably mounted in the stator (80); - a permanent magnet (60) mounted on an axle (55) connected to the rotor (50); and - a device according to claim 4. [6] Synchronous motor (100) according to claim 5, further comprising an electronic circuit (230) for switching the switchable coils (220) on and off.

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