CN116298369A - Device and method for measuring motor speed based on non-contact magnetic rotary position sensor - Google Patents

Abstract

The invention discloses a motor rotating speed measuring device and method based on a non-contact magnetic rotating position sensor, and belongs to the field of motor rotating speed measurement. The method comprises the following steps: 1. collecting pulse signals of the motor rotating for one circle, and roughly calculating a motor rotating speed value; 2. combining the rough speed value to obtain a pulse frequency and selecting a sampling frequency; 3. based on the sampling frequency, collecting the voltage value of the pulse signal output by the A/B pin of the sensor, and processing the sampled data in real time; 4. performing FFT (fast Fourier transform) on the processed data, performing complex modular value operation on the conversion result, obtaining the amplitude of each point, and selecting a sequence n of the point with the maximum amplitude to obtain the frequency F of the pulse signal; 5. and (3) carrying out speed conversion according to the frequency F to obtain a motor rotation speed value. The invention uses an analog quantity acquisition method, converts a time domain signal into a frequency domain signal through an FFT (fast Fourier transform) algorithm, and then converts a frequency value of a pulse into the rotating speed of the motor, thereby improving the precision of rotating speed calculation and the speed measuring range.

Description

A motor speed measuring device based on a non-contact magnetic rotary position sensor and its method

technical field

The invention relates to the technical field of motor speed measurement, in particular to a motor speed measurement device and method based on a non-contact magnetic rotation position sensor.

Background technique

With the rapid development of industrial automation and artificial intelligence, motors have been widely used and developed in today's industrial automation devices or household appliances. The speed is an extremely important state parameter of the motor, and its measurement accuracy will directly affect the accuracy of testing other related parameters and characteristics of the motor, as well as fault detection and diagnosis.

The current main measurement methods include centrifugal tachometer test method, tachometer generator speed measurement method, flash speed measurement method, photoelectric code disc speed measurement method, Hall element speed measurement method, etc. In the above-mentioned methods, most of the sensors are required to be installed coaxially and the coaxiality is required to be high, so the installation is relatively difficult. A slight skew will affect the final reading. And they are all hard connections, which not only cause mechanical wear, but also reduce the service life of the encoder and the system. Although the Hall element speed measurement method does not require hard connection, it needs to process a special speed measurement turntable and fix it with a hole on the spindle. The installation process is more complicated and the accuracy is not high. It is only suitable for occasions with general accuracy requirements.

Commonly used digital speed acquisition and calculation methods mainly include the following three types: M method (frequency method), T method (period method), and M/T method (frequency/period method). Among them, the M method has higher measurement accuracy when the measured speed is high or the number of speed pulse signals sent by the motor rotates a circle is large, so the M method is suitable for high-speed measurement; T method, when the measured Only when the speed is low (the time of two adjacent speed pulse signals is relatively large) can the measurement accuracy be higher, so the T method is suitable for low-speed measurement; the M/T method is to simultaneously measure the detection time and the photoelectric The speed is determined by the number of speed pulse signals generated by the pulse generator. Since the two pulse signals are counted at the same time, only when the "simultaneity" is properly handled can the M/T method have a high speed measurement accuracy.

After retrieval, patent publication number CN 104426439 A, title of invention: method and device for monitoring the rotational position of a motor, the application monitors the signal output from the pulse-type rotational position sensor and is used for the control of the motor The reference signal to which the signal is associated. Determining the position of the rotor of the electric motor consistent with the reference signal based on the nominal rotor position, the nominal rotational speed of the rotor and the time between the reference signal and the falling edge of the signal output from the pulse-type rotary position sensor . The signal acquisition method used in this application is to capture the number of sensor pulse signals within a period of time, and the speed calculation method is the M/T method. Therefore, this application has the problem that it is suitable for low-resolution pulse-type rotary position sensors, the measurement accuracy is not high, and the measurement range is small, so it is not suitable for high-speed measurement. The ringing effect of the pulse signal at high speed will lead to inaccurate measurement.

Contents of the invention

1. The technical problem to be solved by the invention

Aiming at the problems existing in the motor speed measurement scheme in the prior art, the speed measurement accuracy is poor, the speed measurement range is small, the controller system is required to be strictly synchronized, and the installation requirements are high, the present invention provides a non-contact magnetic rotation position sensor A motor speed measuring device and method. The present invention uses an analog quantity acquisition method, that is, acquires the signal voltage, and converts the time-domain signal into a frequency-domain signal through a fast Fourier transform (FFT) algorithm, and then converts the frequency value of the pulse into the rotational speed of the motor, thereby improving the rotational speed. The precision of the calculation.

2. Technical solution

In order to achieve the above object, the technical scheme provided by the invention is:

A kind of motor speed measuring method based on non-contact magnetic rotary position sensor of the present invention, its steps are:

Step 1. Collect the pulse signal output by the motor for one revolution, and roughly calculate the motor speed value based on the pulse signal;

Step 2. Combine the rough speed value of the motor to obtain the pulse frequency output by the A/B pin of the sensor, and select the sampling frequency based on the pulse frequency;

Step 3. Based on the sampling frequency, collect the pulse signal voltage value output by the A/B pin of the non-contact magnetic rotation position sensor, and process the sampled data in real time;

Step 4. Perform FFT transformation on the data processed in step 3, and then perform complex modulo calculation on the transformation result to find the amplitude of each point, and select the sequence n of the point with the largest amplitude, and obtain the sensor based on the sequence number The frequency F of the pulse signal output by the A/B pin;

Step 5: Perform speed conversion according to the frequency F of the pulse signal output by the A/B pin of the sensor to obtain the motor speed value.

Furthermore, in step 1, install the radially magnetized circular magnet of the magnetic rotary position sensor in the non-magnetic circular bushing, fix the bushing on the motor shaft and keep the axis center consistent; install it on the motor shaft The magnet on the magnet outputs a pulse signal every time it rotates, and the Index pin of the magnetic rotation position sensor collects the pulse signal, uses the interrupt function of the single-chip microcomputer pin to collect the pulse signal of the sensor Index pin, and records the pulse signal of two adjacent pulses. time interval ΔT, then the rough speed value of the motor

Furthermore, in step 2, first determine the resolution PPR of the magnetic rotary position sensor, and combine the rough speed value of the motor to obtain the pulse frequency f=PPR*V output by the A/B pin of the sensor, and select a pulse frequency greater than 2 times f as the sampling frequency f _s .

Furthermore, in step 3, the pulse signal voltage value output by the A/B pin of the collected sensor is sequentially stored in the sampling buffer according to the sampling time sequence, and the value of the current sampling point is stored in real time from the sampling buffer. The position is the starting point, and the value of 2048 sampling points is selected forward to perform limiting filtering.

Furthermore, step five divides the frequency F of the pulse signal output by the A/B pin of the sensor by the resolution of the sensor to convert to obtain the motor speed value.

Furthermore, after the sampling data is transformed by FFT, the real part and imaginary part of the corresponding frequency point amplitude are obtained, and the corresponding phase angle of the A/B phase is obtained based on the real part and imaginary part, and the phase angle is used to judge Direction of motor rotation.

Furthermore, in step four, the radix-2FFT algorithm selected by time is used to transform the signal from the time domain to the frequency domain.

A motor speed measuring device based on a non-contact magnetic rotation position sensor of the present invention includes a power supply module, a main control chip, a magnetic rotation position sensor, a display screen and a communication module. The magnetic rotation position sensor adopts a non-contact rotation The encoder SC60104 uses its quadrature A/B output mode; the main control chip adopts AT32F403ACGT7 single-chip microcomputer, and the ADC module inside the single-chip microcomputer collects the voltage value of the pulse signal output by the A/B pin of the sensor chip; the speed and direction of the motor are real-time The ground is displayed on the display screen, the single-chip microcomputer communicates with the host computer or a specific terminal through the RS-485 communication interface, and the power module is powered by an external power supply or a lithium battery.

3. Beneficial effect

Compared with the existing known technology, the technical solution provided by the invention has the following remarkable effects:

(1) A kind of motor rotational speed measurement method based on non-contact magnetic rotary position sensor of the present invention, on pulse signal acquisition, abandons the method of traditional acquisition pulse number, changes to acquisition pulse signal voltage. The traditional method of collecting the number of pulse signals is suitable for low-resolution sensors, and the accuracy is not high, so software filtering cannot be performed. The invention collects the pulse signal voltage, belongs to an analog quantity collection method, can use a high sampling rate, is suitable for a high-resolution sensor, and has high precision.

(2) In view of the fact that the sampling accuracy of the motor is low when the motor is at a low speed, the present invention adopts a variable sampling frequency method, that is, real-time calculation of the number of pulse signals of the sensor Index pin, first roughly calculating the motor speed value, and according to this rough Select the appropriate sampling frequency, so that when the motor rotates at low speed, the low sampling frequency is automatically selected, and when the motor rotates at a high speed, the high sampling frequency is automatically selected. In this way, under the premise of ensuring the integrity of the signal, an appropriate number of sampling points can be selected to participate in the subsequent FFT operation, thereby saving memory overhead and speeding up the operating speed of the system.

(3) A kind of motor speed measuring device based on non-contact magnetic rotary position sensor of the present invention adopts non-contact rotary encoder, which is easy to install and improves measurement efficiency. The analog voltage value of the pulse signal output by the B pin improves the sampling speed and accuracy, and the FFT transformation algorithm is used to improve the accuracy of the speed calculation.

Description of drawings

Fig. 1 is a kind of hardware structure schematic diagram of the motor speed measuring device based on non-contact magnetic rotary position sensor of the present invention;

FIG. 2 is a flow chart of a method for measuring the rotational speed of a motor based on a non-contact magnetic rotary position sensor according to the present invention.

Detailed ways

In order to further understand the content of the present invention, the present invention will be described in detail in conjunction with the accompanying drawings and embodiments.

Example 1

Referring to FIG. 1 , a motor speed measurement device based on a non-contact magnetic rotational position sensor in this embodiment includes a power module, a main control chip, a magnetic rotational position sensor, a display screen, and a communication module. The magnetic rotary position sensor adopts the non-contact rotary encoder SC60104. This sensor is a system-on-chip, which integrates integrated Hall components, analog front-end and data processing functions in a single chip. The chip provides 3 available incremental output modes, including quadrature A/B output (quadrature A/B mode), LSB output (step/direction mode), pulse width modulation output, and quadrature A/B is its missing province mode. The quadrature A/B output mode used in this device does not need to be configured.

Regarding the installation of the magnetic rotary position sensor, in this embodiment, a radially magnetized circular magnet with a diameter of 6 mm is installed in a non-magnetic circular bushing, and then the bushing is fixed on the motor shaft to keep the axis center consistent. Keep the center of the magnetic rotary position sensor coaxial with the center of the magnet, and the error is within 0.485mm. The surface of the magnet is 2mm away from the surface of the sensor, and this distance can be properly adjusted according to the magnetic field strength of the magnet.

This embodiment can be powered by an external power supply or a lithium battery, and the power conversion chip is RT6150AGQW. The power chip is a high-efficiency, fixed-frequency Buck-Boost DC/DC converter that can work when the input voltage is higher than, lower than or equal to the output voltage. The circuit topology integrated in it can perform continuous voltage conversion in various working modes, making it very suitable for occasions powered by single-cell lithium-ion batteries, multi-cell alkaline batteries or nickel-metal hydride batteries, and solves the problem that the output voltage is in the battery voltage range voltage conversion problem.

The main control chip adopts AT32F403ACGT7 single-chip microcomputer, which integrates single-precision floating-point unit (FPU) and digital signal processor (DSP), and has rich on-chip peripherals and flexible clock control mechanism.

In order to complete the long-distance data communication with the host computer, and meet the stable and reliable requirements of the application site. The present invention adopts RS485 communication, and adopts optocoupler isolation circuit to realize this function. The RS485 chip model is MAX13487E, and this series of chips contains a state machine and a receiving comparator inside. By configuring the external hardware, the chip can automatically enable or disable the driver and receiver to keep the bus in the correct working state, thereby saving the I/O pins of the microcontroller.

In this embodiment, the traditional method of collecting the number of pulses is abandoned in collecting the pulse signal, and the voltage of the pulse signal is collected instead. The traditional method of collecting the number of pulse signals is suitable for low-resolution sensors (encoders), the accuracy is not high, and software filtering cannot be performed. This embodiment collects the pulse signal voltage, which belongs to an analog quantity collection method, can use a high sampling rate, is suitable for a high-resolution sensor (encoder), and has high precision.

In this embodiment, the ADC module inside the AT32F403ACGT7 microcontroller is used to collect the voltage value of the pulse signal output by the A/B pin of the sensor chip. At the same time, in order to improve the accuracy, the use of high-resolution sensors and high sampling frequency can better restore the original signal. In order to better analyze the signal characteristics, the signal is converted from the time domain to the frequency domain. The fast Fourier transform (FFT) algorithm has a small amount of calculation, combined with high-speed hardware, it can realize real-time processing of the signal, and has the best performance. This embodiment converts the time domain signal into a frequency domain through the fast Fourier transform (FFT) algorithm. signal, and then convert the frequency value of the pulse into the rotational speed of the motor. By judging the A/B phase difference, the direction of motor rotation can be identified. The speed and direction of rotation of the motor are displayed on the local OLED display in real time. It can also be uploaded to the host computer or a specific terminal through the RS-485 communication interface, and the Modbus-RTU protocol is used for communication.

Example 2

Referring to FIG. 2 , a method for measuring motor speed based on a non-contact magnetic rotational position sensor in this embodiment takes the pulse signal of the A-phase pin of the non-contact magnetic rotational position sensor as an example, and the principle of the B-phase is the same. First of all, 10K word memory unit is defined in the RAM of the single-chip microcomputer. This 10K word memory unit is called a sampling buffer, which is used to store the sampling point data after the voltage value of the pulse signal is converted by AD. The measurement steps of the present embodiment are as follows:

Step 1. Use the interrupt function of the single-chip microcomputer pin to collect the pulse signal of the Index pin of the sensor (the pulse signal output by the Index pin is the rotation of the magnet installed on the motor shaft, that is, the motor rotates a circle to generate a pulse signal), record the time interval ΔT between two adjacent pulses, that is, the time it takes for the motor to rotate one circle, then the rough speed value of the motor

Step 2. According to the characteristics of the non-contact magnetic rotary position sensor, when the magnet rotates one circle, the phase A pin of the sensor outputs 256 pulse signals, that is, the resolution PPR of the sensor is 256. Combined with the rough speed value of the motor obtained in step 1, the pulse frequency f=PPR*V output by the A-phase pin of the sensor can be further calculated. Select the appropriate sampling frequency f _s , and the A-phase pin of the sensor whose f _s is greater than 2 times outputs the pulse frequency f. According to the selected sampling frequency f _s , the pulse signal output by the A-phase pin of the sensor is sampled for the analog voltage value, and the values of the sampling points are stored in the sampling buffer in sequence according to the sampling time.

It is worth noting that, in view of the fact that the sampling accuracy is low when the motor rotates at a low speed, this embodiment adopts a variable sampling frequency method. That is, when the motor rotates at a low speed, a low sampling frequency is automatically selected, and when the motor rotates at a high speed, a high sampling frequency is automatically selected. In this way, under the premise of ensuring the integrity of the signal, an appropriate number of sampling points can be selected to participate in the subsequent FFT operation, thereby saving memory overhead and speeding up the running speed of the system, and can improve the accuracy at low speed. The implementation principle of this embodiment is to calculate the number of pulse signals output by the Index pin of the sensor in real time, first roughly calculate the motor speed value, and select an appropriate sampling frequency according to this rough value.

The magnet installed on the motor shaft, the Index pin of the sensor will output a pulse signal every time it rotates one circle. Use the interrupt function of the AT32F403ACGT7 single-chip microcomputer to collect the Index pulse signal, and then record the time interval between two adjacent pulse signals, that is, the time taken by the motor to rotate a circle, and the motor speed can be simply and roughly calculated. This method is simple but very practical.

Step 3, real-time processing of the sampled data of the A-phase pin output pulse signal of the sensor, the data here is the pulse signal voltage value of the sensor A-phase pin output collected by f _s sampling frequency, that is, from the sampling buffer , from the position where the value of the new sampling point is stored, select 2048 sampling point values from the value that has been stored in the buffer before, and perform limiting filtering to remove some unreliable sampling point data, which can better restore the signal , to ensure the continuity and integrity of the signal.

Step 4: Perform FFT transformation on the values of the selected 2048 sampling points to transform the signal from the time domain to the frequency domain. Fast Fourier transform is another method to solve discrete Fourier transform (DFT). FFT algorithm classification includes: time decimation method (DIT) and frequency decimation method (DIF). In this embodiment, the radix-2FFT algorithm selected by time is selected.

其中f_s是已知的采样频率，n是幅值最大点的序列数，N为已知的参与变换运算选取的采样点数。For the FFT transformation result, the complex number modulo operation is performed to obtain the amplitude of each point, and the sequence n of the point with the largest amplitude is selected. The pulse signal is a rectangular wave, also known as a square wave. For a square wave, it is formed by the superposition of infinite sine waves, and the first one with the highest amplitude is the frequency of the square wave, that is, the frequency of the A phase pin of the sensor. Pulse signal frequency F. The calculation formula of the pulse signal frequency F of the sensor A phase pin is:

Where f _s is the known sampling frequency, n is the sequence number of the point with the maximum amplitude, and N is the known number of sampling points selected to participate in the transformation operation.

其中速度V'的单位是RPS(转/每秒)，F是传感器A相引脚的脉冲信号频率，PPR是传感器的分辨率，本实施例中传感器的分辨率PPR是256。Step 5. Perform speed conversion according to the calculated frequency F of the pulse signal of the A phase pin of the sensor. The conversion formula is

Wherein the unit of the speed V' is RPS (rotation per second), F is the pulse signal frequency of the A phase pin of the sensor, and PPR is the resolution of the sensor, and the resolution PPR of the sensor in this embodiment is 256.

此速度值是精度较高的电机转速值。If you want to convert the speed unit to RPM, you need V=60*V', that is

This speed value is the motor speed value with high precision.

After the sampling point is transformed by FFT, the real part and the imaginary part of the amplitude of the corresponding frequency point can be obtained. The phase calculation formula is as follows:

P _n =atan 2(b,a)

In the formula: P _n is the radian value of the phase, rad; a is the real part of the frequency point; b is the imaginary part of the frequency point. Bring the real part and imaginary part of the maximum amplitude point into the above formula, and the corresponding phase angle of A/B phase can be obtained.

The unit of the phase value calculated by the above formula is radian rad, which needs to be converted into an angle value. The conversion formula is as follows:

In the formula: θ _n is the phase angle value, °; P _n is the phase radian value, rad.

The motor rotation direction judgment formula is as follows:

Δθ＝θ _A -θ _B

Where: Δθ is the phase difference, °; θ _A is the phase angle value, °; θ _B is the phase angle value, °.

When Δθ=90°, that is, the phase of channel A leads the phase angle of channel B by 90°, and the motor (magnet) rotates clockwise; when Δθ=-90°, that is, the phase of channel B leads the phase of channel A by 90° , the motor rotates counterclockwise.

The above schematically describes the present invention and its implementation, which is not restrictive, and what is shown in the drawings is only one of the implementations of the present invention, and the actual structure is not limited thereto. Therefore, if a person of ordinary skill in the art is inspired by it, without departing from the inventive concept of the present invention, without creatively designing a structural mode and embodiment similar to the technical solution, it shall all belong to the protection scope of the present invention .

Claims (10)

1. A motor rotating speed measuring method based on a non-contact magnetic rotation position sensor is characterized by comprising the following steps:

step one, collecting a pulse signal output by one turn of motor rotation, and roughly calculating a motor rotation speed value based on the pulse signal;

step two, combining the rough speed value of the motor to obtain pulse frequency, and selecting sampling frequency based on the pulse frequency;

step three, based on sampling frequency, collecting pulse signal voltage values output by an A/B pin of the non-contact magnetic rotation position sensor, and processing sampled data in real time;

performing FFT (fast Fourier transform) on the data processed in the step three, performing complex modular value operation on the transformation result, obtaining the amplitude of each point, selecting a sequence n of points with the maximum amplitude, and obtaining the frequency F of the pulse signal based on the sequence number;

and fifthly, performing speed conversion according to the pulse signal frequency F to obtain a motor rotation speed value.

2. The method for measuring the motor rotation speed based on the non-contact magnetic rotation position sensor according to claim 1, wherein the method comprises the following steps: in the first step, radial magnetized circular magnets of a magnetic rotary position sensor are arranged in a non-magnetic circular bushing, and the bushing is fixed on a motor shaft and keeps the axle center consistent; the magnet is arranged on the motor shaft, a pulse signal is output every time the magnet rotates for one circle, the Index pin of the magnetic rotation position sensor acquires the pulse signal, the interrupt function of the singlechip pin is used for acquiring the pulse signal of the Index pin of the sensor, the time interval delta T of two adjacent pulses is recorded, and then the rough speed value of the motor is obtained

3. A method for measuring the rotational speed of a motor based on a non-contact magnetic rotational position sensor as claimed in claim 2, wherein: in the second step, firstly, determining the resolution PPR of the magnetic rotation position sensor, combining the rough speed value of the motor to obtain the pulse frequency f=ppr×v, and selecting the pulse frequency f which is more than 2 times as the sampling frequency f _s 。

4. A method of measuring motor speed based on a non-contact magnetic rotational position sensor as defined in claim 3, wherein: and thirdly, sequentially storing the acquired pulse signal voltage values into a sampling buffer area according to a sampling time sequence, and selecting 2048 sampling point values forwards from the sampling buffer area in real time by taking the position storing the current sampling point value as a starting point, and performing amplitude limiting filtering.

5. The method for measuring the motor rotation speed based on the non-contact magnetic rotation position sensor according to claim 4, wherein the method comprises the following steps: in the fourth step, the calculation formula of the pulse signal frequency F is:

wherein f _s For sampling frequency, N is the number of sequences of the maximum points of amplitude, and N is the number of sampling points selected by the known conversion operation.

6. The method for measuring the motor rotation speed based on the non-contact magnetic rotation position sensor according to claim 5, wherein the method comprises the following steps: and fifthly, dividing the pulse signal frequency F by the resolution of the sensor, and converting to obtain a motor rotating speed value.

7. The method for measuring the motor rotation speed based on the non-contact magnetic rotation position sensor according to claim 6, wherein the method comprises the following steps: after FFT conversion, the sampling data obtain real and imaginary parts of corresponding frequency point amplitude, and based on the real and imaginary parts, the phase angle of corresponding A/B phase is obtained, and the rotation direction of the motor is judged according to the phase angle.

8. The method for measuring the motor rotation speed based on the non-contact magnetic rotation position sensor according to claim 7, wherein the method comprises the following steps: and step four, converting the signal from the time domain to the frequency domain by using a time-decimated base-2 FFT algorithm.

9. A motor rotation speed measuring device based on non-contact magnetic rotation position sensor is characterized in that: the apparatus performs the motor rotation speed measurement method according to any one of claims 1 to 8.

10. A motor speed measurement device based on a non-contact magnetic rotational position sensor as claimed in claim 9, wherein: the magnetic rotation position sensor adopts a non-contact rotary encoder SC60104 and uses an orthogonal A/B output mode thereof; the main control chip adopts an AT32F403ACGT7 singlechip, an ADC module in the singlechip collects the voltage value of a pulse signal output by an A/B pin of the sensor chip; the rotating speed and the rotating direction of the motor are displayed on a display screen in real time, the singlechip is communicated with the upper computer or the specific terminal through the RS-485 communication interface, and the power supply module supplies power by using an external power supply or a lithium battery.

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