PL235653B1 - Method for measuring angular position of the direct current motor brushless shaft with the shaft position sensor - Google Patents

Abstract

The method of measuring the angular position of the shaft of a brushless DC motor with shaft position sensors by measuring the time at a constant engine speed between successive states of the shaft position sensors consists in starting the brushless DC motor and bringing it to a constant speed. The first times between successive states of the shaft position sensors for a full mechanical rotation of the shaft are measured and saved in the memory of the control device. The brushless DC motor is stopped. Then the brushless DC motor is started again at a constant speed and the times between successive states of the shaft position sensors for a full mechanical rotation of the shaft are measured again. They are compared with the first times between successive states of the shaft position sensors for a full mechanical rotation of the shaft and the angular position of the shaft of the brushless DC motor is determined on the basis of the compared times.

Description

Description of the invention

The subject of the invention is a method of measuring the angular position of a shaft of a brushless DC motor with shaft position sensors.

So far, a system for determining the position of a motor shaft is known from patent description No. US4086519 (A) based on an alternately magnetized rotating magnet together with the rotor and field sensors, the change of whose state provides information about the angular displacement of the rotor relative to the sensor.

From the description of patent application DE19949106 (A1) a method of measuring speed and position is known, which consists in placing shaft position sensors with different angular displacement, the signals of which constitute information about the angular position and can be used to calculate the engine speed.

Also known from patent description no. PL 223772 (B1) is a method of measuring the rotational speed of an electric motor, especially a brushless DC motor with compensation for the inaccuracy of the arrangement of sensors. It consists in calculating the differences between the times measured at a constant rotational speed of the motor, between subsequent states of the motor shaft position sensors and saving them in the memory of the control device. On their basis, the percentage error of the arrangement of the motor shaft position sensors is determined, while the speed of the motor shaft is determined on the basis of the time measured between subsequent states of the motor shaft position sensors, taking into account the measured corrective values.

The article entitled "Calculation of the brushless dc motor shaftspeed with allowances for incorrect alignment of sensors", Metrology and Measurement Systems Volume 22, Issue 3, 1 September 2015, pages 393-402 describes issues related to speed measurements of multi-pole BLDC motors. They indicate that the speed reading resolution possible for each measurement sector increases with the number of pole pairs. It indicates the basic methods of measuring the speed of BLDC motors using their position sensors. Additionally, the number of possible speed measurement points per mechanical shaft revolution is determined at p*6, where p is the number of pole pairs. In the tested motor, the number of pole pairs is 4, so the number of speed measurement points (sectors) is 4*6=24.

The problem to be solved is to determine the mechanical angular position of the motor shaft, in particular a brushless DC motor - BLDC with more than one pole pair, based on the state of the Hall sensors of the electronic commutator.

Previously known control methods allow determining the mechanical position of the motor shaft based on Hall sensors only for motors with one pair of poles - such in which the state of the Hall sensors unequivocally determines the position of the rotor. In the case of machines with the number of pole pairs equal to p, the same state of the sensors is repeated several times for one full mechanical revolution of the motor shaft, which makes it impossible to determine the mechanical position of the motor rotor.

The purpose of the invention is to determine the angular position of the engine each time it is started.

The essence of the method of measuring the angular position of the shaft of a brushless DC motor with shaft position sensors, by measuring the time at a constant engine speed between successive states of the shaft position sensors, is that the brushless DC motor is started and brought to a constant speed and the first times are measured between successive states of the shaft position sensors for a full mechanical rotation of the shaft, which are saved in the memory of the control device in the value table and by dividing them by the average value of the time of change of the state of the Hall sensors, the first - reference errors of the arrangement of sensors are determined, after which the brushless DC motor is stopped. Then the brushless DC motor is started at a constant speed and the error of the arrangement of sensors is measured again and for the selected combination of the state of the Hall sensors, the values of errors measured during the second start of the engine are subtracted from the first reference errors of the arrangement of sensors. In the case when the differences are equal to zero, the result of the displacement of the motor rotor relative to the reference position expressed in sectors is obtained. However, if the difference is other than zero, the table of values measured during the second start-up is rotated and the subsequent times measured during the second engine start-up are subtracted from the times among the first reference times, and this operation is repeated until the differences equal zero are obtained.

An advantageous effect of the invention is that by using the proposed method it becomes possible to determine the rotor position of a motor with more than one pair of poles without the need

PL 235 653 Β1 the possibility of using additional absolute rotor position sensors. Analysis of the distribution of Hall sensor layout errors of the motor, especially BLDC, and comparing it with the distribution saved in the memory, allows determining the actual angular position of the rotor in relation to that saved in the memory of the control device. This is crucial for many industrial applications that require repeatability of the device shaft position in specific operating states.

The subject of the invention in an example implementation is shown in the drawing, in which Fig. 1 shows the error distribution of a BLDC motor with four pairs of poles, Fig. 2 - error distributions for the state of sensors (H1=0, H2=0, H3=1) for a BLDC motor with four pairs of poles, Fig. 3 - speed measurement sectors of the Anaheim Automation BLY343S-48V-4200 motor.

The method of measuring the angular position of the shaft of a brushless DC motor with shaft position sensors in the example embodiment was implemented using a BLDC motor from Anaheim Automation type BLY343S-48V-4200 with four pairs of poles equipped with standard shaft position sensors. The engine was started, brought to the rated speed (3000 rpm), and then the times T1 between changes in the Hall sensor states were measured, which are shown in Table 1. On their basis, the speed for each interval for the given engine speed was calculated and compared with the rated speed value, determining the errors in calculating the speed for the individual sectors, which are shown in Fig. 1 of the drawing. This procedure was repeated 20 times. Depending on the initial shaft position (which was random), the distribution of errors for the known sensor state (H1=0, H2=0, H3=1) assumed one of the four distributions, which are shown in Fig. 2 of the drawing. After analyzing the error distribution, it was concluded that the rotor is shifted relative to the distribution stored in the controller memory for distribution 1 by 0°, for distribution 2 by 90°, for distribution 3 by 180°, and for distribution 4 by 270°. This allowed determining the mechanical position of the BLDC motor rotor.

Table 1

Hall sensor status Sector number Measured value of T1 sector time [MS] Calculated mean value of T2 sector time [με] Calculated Hall sensor placement error E1 [%] Achievable error distributions of E2 sensors H1 H2 H3 Distribution 1 Sh. 2 Distribution 3 Distribution 4 0 0 1 1 503 745.15 32.5 2,2 27.4 19.5 32.5 0 1 1 2 1050 -40.9 -19.9 -4.1 -9.0 -40.9 0 1 0 3 744 0,1 14.4 -16.9 7,8 0,1 1 1 0 4 518 30.5 -4.1 19.5 34.8 30.5 1 0 0 5 871 -16.9 -24.6 -9.0 -40.9 -16.9 1 0 1 6 649 12.9 8.7 -22.9 -0.9 12.9 0 0 1 7 729 2,2 27.4 19.5 32.5 2,2 0 1 1 8 893 -19.9 -4.1 -9.0 -40.9 -19.9 0 1 0 9 638 14.4 -16.9 7,8 o,1 14.4 1 1 0 10 776 -4.1 19.5 34.8 30.5 -4.1 1 0 0 11 928 -24.6 -9.0 -40.9 -16.9 -24.6 1 0 1 12 680 8.7 -22.9 -0.9 12.9 8.7 0 0 1 13 541 27.4 19.5 32.5 2,2 27.4 0 1 1 14 776 -4.1 -9.0 -40.9 -19.9 -4.1 0 1 0 15 871 -16.9 7,8 0,1 14.4 -16.9 1 1 0 16 600 19.5 34.8 30.5 -4.1 19.5 1 0 0 17 812 -9.0 40.9 16.9 24.6 -9.0 1 0 1 18 916 -22.9 -0.9 12.9 8.7 -22.9 0 0 1 19 600 19.5 32.5 2,2 27.4 19.5 0 1 1 20 812 -9.0 -40.9 -19.9 -4.1 -9.0 0 1 0 21 687 7,8 0,1 14.4 -16.9 7,8 1 1 0 22 486 34.8 30.5 -4.1 19.5 34.8 1 0 0 23 1050 -40.9 -16.9 -24.6 -9.0 -40.9 1 0 1 24 752 -0.9 12.9 8.7 -22.9 -0.9

Claims (1)

Patent claim 1. A method of measuring the angular position of a shaft of a brushless DC motor with shaft position sensors by measuring the time at a constant engine speed between successive states of the shaft position sensors, characterized in that the brushless DC motor is started and brought to a constant speed and the first times (T1) are measured between successive states of the shaft position sensors for a full mechanical rotation of the shaft, which are saved in the memory of the control device in a table of values and by dividing them by the average value of the time (T2) of the change in the state of the Hall sensors, the first - reference errors (E1) of the arrangement of the sensors are determined, after which the brushless DC motor is stopped, then the brushless DC motor is started at a constant speed and the error of the arrangement of the sensors (E2) is measured again and for the selected combination of the state of the Hall sensors, the error values measured during the second start-up of the motor are subtracted from the first reference errors of the arrangement of the sensors (E1) and in the case when the differences are equal to zero, the result of the displacement of the motor rotor relative to the reference position is obtained, expressed in sectors, whereas in the case of a difference other than zero, the table of values measured during the second start is rotated and the subsequent times measured during the second engine start are subtracted from the times among the first reference times (T1) and this operation is repeated until differences equal to zero are obtained.