Speed measurement method and device of motor and test equipment

Abstract

The invention discloses a motor speed measurement method and device and test equipment, and relates to the field of test, and the method comprises the steps: obtaining current signals of a qualified motor and a fault motor; acquiring a current signal of the to-be-tested motor; based on the current signal of the fault motor and the current signal of the to-be-tested motor, determining whether the to-be-tested motor has a fault; if not, determining whether the to-be-tested motor is in steady-state operation or not based on the current signal of the qualified motor and the current signal of the to-be-tested motor; and if in steady-state operation, determining the rotating speed of the to-be-tested motor based on the current signal of the to-be-tested motor. According to the determined current signals of the qualified motor and the fault motor, whether the to-be-tested motor does not rotate or not is directly determined, if the to-be-tested motor has faults, it is proved that the rotating speed is not necessary to be determined, and the testing efficiency is improved. Furthermore, the rotating speed is determined only when the motor to be tested is in the steady state, and the defect that the rotating speed obtained through calculation in the non-steady state is inaccurate is overcome.

Description

Technical Field

[0001] This invention relates to the field of testing, and in particular to a method, apparatus, and testing equipment for measuring the speed of an electric motor. Background Technology

[0002] Speed ​​detection for BLDC (Brushless DC Motor) and PMDC (Permanent Magnet DC Motor) is a core aspect of online quality control on production lines. Current technologies often use Hall effect sensors or encoders to directly acquire speed signals, but these methods require additional sensor installation, increasing testing costs and operational complexity. and For motors that fail to rotate due to stalling, winding breakage, or other faults, the fault status is inferred solely from the speed calculation results without establishing a dedicated judgment logic. This leads to extended testing cycles and fails to meet the high-efficiency testing requirements of production lines. Summary of the Invention

[0003] The purpose of this invention is to provide a method, apparatus, and testing equipment for measuring the speed of an electric motor. Based on the current signals of a qualified motor and a faulty motor, the invention directly determines whether the motor under test has a fault such as not rotating. If a fault exists, it proves that there is no need to determine the speed, thus improving testing efficiency. Furthermore, the speed is determined only when the motor under test is in a steady state, reducing the drawback of inaccurate speed calculations obtained in non-steady-state conditions.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for measuring the speed of an electric motor, comprising:

[0005] Obtain the current signals of qualified and faulty motors;

[0006] Acquire the current signal of the motor under test;

[0007] The current signal of the faulty motor and the current signal of the motor under test are used to determine whether the motor under test has a fault.

[0008] If the motor under test does not have a fault, then it is determined whether the motor under test is in steady-state operation based on the current signal of the qualified motor and the current signal of the motor under test.

[0009] If the motor under test is operating in a steady state, the speed of the motor under test is determined based on the current signal of the motor under test.

[0010] On the other hand, before obtaining the current signals of qualified and faulty motors, the following steps are also included:

[0011] Determine the attribute data of the motor under test, including at least one of the following: motor type, rated supply voltage, and number of pole pairs of a DC permanent magnet brushless motor or number of commutator segments of a DC permanent magnet brushed motor.

[0012] Obtain the current signals of qualified and faulty motors, including:

[0013] Acquire current signals from qualified motors and faulty motors of the same type as the motor under test.

[0014] On the other hand, after obtaining the current signals of qualified and faulty motors, the process also includes:

[0015] Determine the stall current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, and the average value of the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor.

[0016] Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes:

[0017] The fault status of the motor under test is determined based on the average ratio of the stall current and open-circuit leakage current of the DC permanent magnet brushless motor and the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor.

[0018] On the other hand, determining whether the motor under test is faulty is based on the stall current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, the average ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor, and the current signal of the motor under test, including:

[0019] If the motor under test is a DC permanent magnet brushless motor, then if the current of the motor under test is greater than or equal to the stall threshold, or if the current of the motor under test is less than or equal to the open circuit threshold, then the motor under test is determined to be faulty. The stall threshold is positively correlated with the stall current, and the open circuit threshold is positively correlated with the open circuit leakage current.

[0020] If the motor under test is a DC permanent magnet brushed motor, then if the average ratio of the starting peak current to the steady-state current of the motor under test is less than the starting abnormal threshold, or if the steady-state current of the motor under test is less than or equal to the disconnection threshold, then the motor under test is determined to be faulty.

[0021] On the other hand, after obtaining the current signals of qualified and faulty motors, the process also includes:

[0022] Fast Fourier analysis is performed on the current signal of the qualified motor to obtain the ripple frequency signal;

[0023] Determine the mean and standard deviation of the ripple frequency signal;

[0024] Determine the dispersion of the current signal of the qualified motor;

[0025] Determine the steady-state speed range and the steady-state current range;

[0026] Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes:

[0027] The determination of whether the motor under test has a fault is based on the dispersion of the current signal of the qualified motor, the steady-state speed range, the steady-state current range, and the current signal of the motor under test.

[0028] On the other hand, before performing Fast Fourier Analysis on the current signal of the qualified motor to obtain the ripple frequency signal, the following steps are also included:

[0029] The theoretical frequency range is determined based on the steady-state speed range of the qualified motor and the type of the qualified motor.

[0030] The frequency band amplification ratio is determined based on the dispersion, and the dispersion is positively correlated with the frequency band amplification ratio.

[0031] The theoretical frequency range is adjusted based on the amplification ratio of the frequency band to obtain the target frequency band;

[0032] Determine the interference frequency band corresponding to the known interference frequency in the test environment where the motor under test is located;

[0033] If the target frequency band overlaps with the interfering frequency band, the overlapping interfering frequency band is removed, and the target frequency band is divided into multiple non-interfering sub-frequency bands, which are then used as screening frequency bands.

[0034] If there is no overlap, the target frequency band will be used directly as the selection frequency band.

[0035] The selected frequency band is used as the effective range for extracting the ripple main frequency when performing fast Fourier analysis on the current signal of the qualified motor.

[0036] On the other hand, if the motor under test is not faulty, then determining whether the motor under test is in steady-state operation is based on the current signal of the qualified motor and the current signal of the motor under test, including:

[0037] If the current signal of the motor under test is within the steady-state current range, and the current fluctuation amplitude within a first preset time is less than or equal to the preset fluctuation range, then the motor under test is determined to be in steady-state operation.

[0038] If the motor under test fails to reach steady-state operation within a second preset time after startup, it is directly determined to be faulty.

[0039] On the other hand, if the motor under test is operating in a steady state, the speed of the motor under test is determined based on the current signal of the motor under test, including:

[0040] The current of the motor under test is subjected to fast Fourier analysis, and the ripple frequency with the highest energy is selected within the preset target frequency band.

[0041] The speed of the motor under test is determined according to the type of motor under test;

[0042] If it is a DC permanent magnet brushless motor, then the speed of the motor under test is determined to be n = 10 × f0 / N;

[0043] Where n is the rotational speed in r / min, f0 is the ripple frequency in Hz, and N is the number of pole pairs.

[0044] If it is a DC permanent magnet brushed motor, then the speed of the motor under test is determined to be n = 60 × f0 / Z;

[0045] Where Z represents the number of commutator segments in a DC permanent magnet brushed motor.

[0046] To solve the above-mentioned technical problems, the present invention also provides a speed measuring device for an electric motor, comprising:

[0047] Memory, used to store computer programs;

[0048] A processor is used to implement the steps of the above-described method for measuring the speed of an electric motor when executing the computer program.

[0049] To address the aforementioned technical problems, the present invention also provides a testing device, including the aforementioned motor speed measuring device, and further including a filtering module connected to the processor, the filtering module being used to filter the current signal.

[0050] This application provides a method, apparatus, and testing equipment for measuring the speed of an electric motor, relating to the testing field. The method includes: acquiring current signals from a qualified motor and a faulty motor; acquiring the current signal of a motor under test; determining whether the motor under test is faulty based on the current signals of the faulty motor and the motor under test; if the motor under test is not faulty, determining whether the motor under test is in steady-state operation based on the current signals of the qualified motor and the motor under test; if the motor under test is in steady-state operation, determining the speed of the motor under test based on its current signal. By directly determining whether the motor under test has a fault such as not rotating based on the determined current signals of the qualified and faulty motors, and if a fault exists, it proves that determining the speed is unnecessary, thus improving testing efficiency. Furthermore, determining the speed only when the motor under test is in a steady-state state reduces the drawback of inaccurate speed calculations obtained in non-steady-state conditions. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 A flowchart of a method for measuring the speed of an electric motor provided by the present invention;

[0053] Figure 2 A schematic diagram of the spectrum of a BLDC provided for this invention;

[0054] Figure 3 A schematic diagram of the spectrum of a PMDC provided for this invention;

[0055] Figure 4 A schematic diagram of the structure of a speed measuring device for an electric motor provided by the present invention;

[0056] Figure 5 This is a schematic diagram of the structure of a testing device provided by the present invention. Detailed Implementation

[0057] The core of this invention is to provide a method, apparatus, and testing equipment for measuring the speed of an electric motor. Based on the current signals of a qualified and faulty electric motor, it first directly determines whether the motor under test has a fault such as not rotating. If a fault exists, it proves that there is no need to determine the speed, thus improving the efficiency of the test. Furthermore, the speed is determined only when the motor under test is in a steady state, reducing the drawback of inaccurate speed calculations obtained in non-steady-state conditions.

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Figure 1 The flowchart of a method for measuring the speed of an electric motor provided by the present invention includes:

[0060] S11: Obtain the current signals of qualified and faulty motors;

[0061] S12: Acquire the current signal of the motor under test;

[0062] Speed ​​detection for BLDC (Brushless DC Motor) and PMDC (Permanent Magnet DC Motor) is a core aspect of online quality control on production lines. Currently, related technologies for motors that fail to rotate due to stalling, winding breakage, or other faults rely solely on speed calculations to infer the fault state, lacking dedicated judgment logic. This leads to extended testing cycles and fails to meet the high-efficiency testing requirements of production lines.

[0063] Therefore, this application first obtains the current signals of qualified motors and faulty motors. Compared with related technologies that directly calculate the speed based on the current signal and then determine the cause of the fault based on the speed, this application first makes judgments in multiple ways based on qualified motors and faulty motors, and then proceeds to calculate the speed.

[0064] Specifically, the current signal of a qualified motor should be collected based on the rated supply voltage and rated load.

[0065] S13: Determine whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test; if not, proceed to step S14.

[0066] Prioritize excluding motors with stalled rotors or broken wires to reduce unnecessary speed measurement steps and significantly improve testing efficiency. If the waveform of the current of the motor under test is similar to that of the faulty motor, the motor under test is directly determined to be faulty without further judgment, thus improving testing efficiency.

[0067] S14: Determine whether the motor under test is in steady-state operation based on the current signal of the qualified motor and the current signal of the motor under test; if so, proceed to step S15.

[0068] Furthermore, if the motor under test has not entered a steady-state operating state, the calculated speed will also be inaccurate. The current signal of a qualified motor can be used to assist in confirming the current signal of the motor under test. If it is similar to the current signal of a qualified motor in a steady state, then it can be determined that the motor under test has entered a steady-state operating state, and at this time, the effective speed can be calculated.

[0069] S15: Determine the speed of the motor under test based on the current signal of the motor under test.

[0070] It should be noted that BLDC and PMDC are two different types of motors, so calculations can be performed separately based on their actual types. This application does not impose any restrictions on them here.

[0071] It should also be noted that DC permanent magnet brushless motors are divided into two main categories: those with position sensors and those without. The starting characteristics of brushless motors without position sensors are similar to those of brushed motors. The starting / steady-state operation characteristics of brushed motors can also be used as a reference to determine whether there is a stall fault.

[0072] This application provides a method for measuring the speed of an electric motor, relating to the testing field, including: acquiring current signals from a qualified motor and a faulty motor; acquiring the current signal of a motor under test; determining whether the motor under test is faulty based on the current signals of the faulty motor and the motor under test; if the motor under test is not faulty, determining whether the motor under test is in steady-state operation based on the current signals of the qualified motor and the motor under test; if the motor under test is in steady-state operation, determining the speed of the motor under test based on its current signal. By directly determining whether the motor under test has faults such as not rotating based on the determined current signals of the qualified and faulty motors, if a fault exists, it proves that determining the speed is unnecessary, thus improving testing efficiency. Furthermore, determining the speed only when the motor under test is in a steady-state state reduces the drawback of inaccurate speed calculations obtained in non-steady-state conditions.

[0073] Based on the above embodiments:

[0074] In some embodiments, before acquiring the current signals of the qualified motor and the faulty motor, the method further includes:

[0075] Determine the attribute data of the motor under test. The attribute data includes at least one of the following: motor type, rated supply voltage, and number of pole pairs of a DC permanent magnet brushless motor or number of commutator segments of a DC permanent magnet brushed motor.

[0076] Obtain the current signals of qualified and faulty motors, including:

[0077] Acquire current signals from qualified motors and faulty motors of the same type as the motor under test.

[0078] For the target motor model (BLDC or PMDC), complete the basic parameter calibration, threshold determination, and sample testing. All data is stored in the device's memory, specifically including:

[0079] Enter the core attributes of the motor, including motor type (BLDC / PMDC), number of pole pairs N in BLDC, number of commutator segments Z in PMDC, and rated supply voltage U, to ensure that the parameters match the model of the motor under test;

[0080] Based on the motor design standards and factory requirements, the steady-state speed range [n_min, n_max] and steady-state current range [I_min, I_max] are set.

[0081] Select more than 30 qualified samples of the same model and more than 10 typical faulty samples (including stalled rotor, broken winding, etc.), test them with this device and record their current signals.

[0082] In some embodiments, after acquiring the current signals of the qualified motor and the faulty motor, the method further includes:

[0083] Determine the stall current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, and the average value of the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor.

[0084] Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes:

[0085] The fault status of the motor under test is determined by the average ratio of the stall current and open-circuit leakage current of the DC permanent magnet brushless motor and the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor.

[0086] Qualified sample characteristic analysis: The steady-state current ripple signal of qualified samples is collected and analyzed by FFT (Fast Fourier Transform) to obtain the ripple frequency sample set {F_s}. The sample mean μ and standard deviation σ are calculated, and the dispersion Cv = σ / μ is calculated.

[0087] Record the minimum locked-rotor current I_block and the maximum open-circuit leakage current I_leak of the BLDC circuit.

[0088] Record a sample set of PMDC startup peak current to steady-state current ratios Ki, and calculate the mean Ki_avg as the benchmark for startup anomaly judgment.

[0089] In some embodiments, determining whether the motor under test is faulty is based on the locked-rotor current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, the average ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor, and the current signal of the motor under test, including:

[0090] If the motor under test is a DC permanent magnet brushless motor, then if the current of the motor under test is greater than or equal to the stall threshold, or the current of the motor under test is less than or equal to the open circuit threshold, then the motor under test is determined to be faulty. The stall threshold is positively correlated with the stall current, and the open circuit threshold is positively correlated with the open circuit leakage current.

[0091] If the motor under test is a DC permanent magnet brushed motor, then the motor under test is determined to be faulty when the average ratio of the starting peak current to the steady-state current of the motor under test is less than the starting abnormal threshold, or when the steady-state current of the motor under test is less than or equal to the disconnection threshold.

[0092] The current signal from the power supply bus of the motor under test is acquired and decomposed into DC current I_dc and AC ripple current I_ac by the signal conditioning module. The motor status is determined in two steps according to the "fault priority" principle to reduce invalid processes:

[0093] Step 1: Quick Fault Diagnosis (Highest Priority);

[0094] Based on the statistical threshold of fault samples, directly determine whether the motor has a non-rotation fault, with a determination period of ≤0.2 seconds. Specific standards:

[0095] BLDC fault determination: If I_dc≥3×I_max (locked rotor threshold, which is the P95 quantile of 50 locked rotor samples to ensure that 95% of locked rotor faults are covered) or I_dc≤0.1×I_min (wire break threshold, which is the maximum leakage current of 10 wire break samples to cover 99% of wire break faults), it is directly determined as "not rotating and unqualified".

[0096] PMDC fault diagnosis: Record the current change during the period from motor start-up to steady state (maximum 0.8 seconds). If the ratio of peak current to steady-state current Ki_test < 0.5 × Ki_avg (start-up abnormal threshold), or I_dc ≤ 0.1 × I_min (wire breakage threshold), it is directly judged as "not rotating, unqualified". The first current detection is performed within 0.1 seconds after start-up. If the threshold is met for 3 consecutive sampling cycles, a fault is judged. If the starting peak current briefly exceeds the threshold but falls back to the steady-state range within 0.2 seconds, and Ki_test meets the requirements, it is judged as normal start-up to avoid false judgments due to start-up impact.

[0097] In some embodiments, after acquiring the current signals of the qualified motor and the faulty motor, the method further includes:

[0098] Fast Fourier analysis is performed on the current signal of a qualified motor to obtain the ripple frequency signal;

[0099] Determine the mean and standard deviation of the ripple frequency signal;

[0100] Determine the dispersion of the current signal of a qualified motor;

[0101] Determine the steady-state speed range and the steady-state current range;

[0102] Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes:

[0103] The determination of whether the motor under test is faulty is based on the dispersion, steady-state speed range, and steady-state current range of the current signal of a qualified motor and the current signal of the motor under test.

[0104] Based on the type of motor, the theoretical ripple frequency range can be deduced from the acceptable speed range:

[0105] BLDC: Calculated using f=n×N / 10, the theoretical frequency range is obtained from [n_min,n_max]: [f_theo_min,f_theo_max]=[n_min×N / 10,n_max×N / 10].

[0106] PMDC: Calculated according to f=n×Z / 60, the theoretical frequency range is obtained from [n_min,n_max]: [f_theo_min,f_theo_max]=[n_min×Z / 60,n_max×Z / 60].

[0107] In some embodiments, before performing Fast Fourier Analysis on the current signal of a qualified motor to obtain the ripple frequency signal, the method further includes:

[0108] The theoretical frequency range is determined based on the steady-state speed range of a qualified motor and the type of motor.

[0109] The frequency band amplification ratio is determined based on the dispersion, and the dispersion is positively correlated with the frequency band amplification ratio.

[0110] The target frequency band is obtained by adjusting the theoretical frequency range based on the frequency band amplification ratio.

[0111] Determine the interference frequency band corresponding to the known interference frequency in the test environment where the motor under test is located;

[0112] If the target frequency band overlaps with the interfering frequency band, the overlapping interfering frequency band is removed, and the target frequency band is divided into multiple non-interfering sub-frequency bands, which are then used as the screening frequency bands.

[0113] If there is no overlap, the target frequency band will be used as the selection band directly.

[0114] The selected frequency band is used as the effective range for extracting the ripple main frequency when performing fast Fourier analysis on the current signal of a qualified motor.

[0115] Frequency band widening adjustment: The frequency band amplification ratio k is determined based on the dispersion Cv to balance frequency band coverage and anti-interference capability.

[0116] When Cv ≤ 0.3, k = 1 + 2 × Cv;

[0117] When Cv>0.3, k=1.5 (to avoid interference caused by an excessively wide frequency band).

[0118] If the target frequency band contains known interference frequencies (such as 45~55Hz and 100~110Hz corresponding to the 50Hz power supply harmonics), the interference frequency band is removed, and the target frequency band is divided into multiple non-interference sub-bands to ensure the accuracy of subsequent main frequency extraction.

[0119] In some embodiments, if the motor under test is not faulty, determining whether the motor under test is in steady-state operation based on the current signal of a qualified motor and the current signal of the motor under test includes:

[0120] If the current signal of the motor under test is within the steady-state current range, and the current fluctuation amplitude within the first preset time is less than or equal to the preset fluctuation range, then the motor under test is determined to be in steady-state operation.

[0121] If the motor under test fails to reach steady-state operation within the second preset time after startup, it is directly determined to be faulty.

[0122] If the motor is not identified as faulty, it is further determined whether it has entered steady-state operation: if I_dc∈[I_min,I_max], and the current fluctuation amplitude within 100ms is ≤±5%, it is determined to be in "steady-state operation" and proceeds to the subsequent speed measurement process. This judgment standard is based on steady-state test data of 30 qualified PMDCs, with 100ms as the minimum time threshold to reach steady state and ±5% as the maximum allowable range of steady-state current fluctuation, ensuring that 99% of qualified motors are accurately judged.

[0123] Based on the starting characteristics test of 30 PMDC motors, 99% of the qualified motors can reach steady state within 0.8 seconds (0.8 seconds is the maximum time taken from start to steady state, i.e., the P99 quantile). If the motor does not reach steady state within 0.8 seconds after start, it is judged as "unqualified", ensuring that the test time of a single motor is controlled within 1 second.

[0124] In some embodiments, if the motor under test is operating in a steady state, the speed of the motor under test is determined based on the current signal of the motor under test, including:

[0125] The current of the motor under test is subjected to fast Fourier analysis, and the ripple frequency with the highest energy is selected within the preset target frequency band.

[0126] Determine the speed of the motor under test based on its motor type;

[0127] If it is a DC permanent magnet brushless motor, then the speed of the motor under test is determined to be n = 10 × f0 / N;

[0128] Where n is the rotational speed in r / min, f0 is the ripple frequency in Hz, and N is the number of pole pairs.

[0129] If it is a DC permanent magnet brushed motor, then the speed of the motor under test is determined to be n = 60 × f0 / Z;

[0130] Where Z represents the number of commutator segments in a DC permanent magnet brushed motor.

[0131] For motors operating in steady state, accurate speed measurement is achieved through ripple signal processing, main frequency extraction, and speed calculation. Specific steps include:

[0132] Ripple signal FFT processing: FFT analysis is performed on the AC ripple current I_ac, and the quantization standards of the core parameters are as follows:

[0133] Sampling frequency Fs = 2 × f4 × 1.2 (satisfies the Nyquist sampling criterion, with 20% redundancy reserved to avoid aliasing);

[0134] Number of sampling points N_fft: Take the smallest power of 2 greater than or equal to Fs / Δf_target, where Δf_target≤0.5Hz (to ensure spectral resolution);

[0135] Window function: Hanning window is preferred to reduce the impact of spectral leakage on the extraction of the main frequency;

[0136] The spectral resolution Δf = Fs / N_fft.

[0137] Dominant frequency extraction: Within the target frequency band [f3, f4] (or non-interference sub-band), select the dominant frequency f0 with the highest energy. The energy of f0 must be at least 30 dB higher than the energy of the maximum interference frequency outside the band (ensuring a signal-to-noise ratio ≥ 1000:1). See [link to target frequency band and interference frequency spectrum distribution] for details. Figure 2 (BLDC) Figure 3 (PMDC), where the main frequency f0 can be clearly identified within the target frequency band marked by the solid line box.

[0138] Calculate the speed using the appropriate formula based on the motor type, and compare it with the acceptable range:

[0139] BLDC: Calculated as n = 10 × f0 / N;

[0140] PMDC: Calculated based on n = 60 × f0 / Z;

[0141] If n∈[n_min,n_max], it is determined that "speed is qualified"; otherwise, it is determined that "speed is unqualified".

[0142] The following is an explanation through a specific test process:

[0143] BLDC Implementation Example:

[0144] The motor under test is a BLDC motor with one pole pair (N=1), rated voltage of 24V, acceptable speed range of [2900, 3100] r / min, and acceptable current range of [1.8, 2.2] A.

[0145] Qualified samples: The ripple frequency sample set of 30 qualified samples has a mean μ=300Hz, a standard deviation σ=15Hz, and a dispersion Cv=σ / μ=0.05;

[0146] Fault samples: 11 typical fault samples (7 stalled rotor, 4 open circuit), among which the minimum stalled rotor current of the stalled rotor sample was 6.6A, and the maximum leakage current of the open circuit sample was 0.15A;

[0147] Fault thresholds: Stall threshold 3×I_max=6.6A (consistent with the P95 quantile of 50 BLDC stall samples of the same model), open circuit threshold 0.1×I_min=0.18A (covering the maximum leakage current of 0.15A of 4 open circuit samples).

[0148] Theoretical frequency range: calculated based on [2900×1 / 10, 3100×1 / 10] = [290, 310] Hz;

[0149] Relaxation ratio: Cv=0.05≤0.3, so k=1+2×0.05=1.1;

[0150] The final target frequency band is [290 / 1.1,310×1.1]≈[263.6,341]Hz. This frequency band does not contain 50Hz harmonic interference (45~55Hz) and does not need to be split.

[0151] Status determination: After the tested motor is powered on, the current sensor collects the current signal, which is decomposed by the signal conditioning module to obtain I_dc=2.0A (within the range of [1.8,2.2]A, and the fluctuation amplitude within 100ms is ≤±3%), which is determined to be "steady-state operation";

[0152] FFT analysis: Based on the quantization parameters, the sampling frequency Fs = 2 × 341 × 1.2 = 818.4 Hz, Δf_target = 0.5 Hz, Fs / Δf_target = 1636.8, and the smallest power of 2 is selected as 2048, so N_fft = 2048, and the spectral resolution Δf = 818.4 / 2048 ≈ 0.4 Hz; the maximum energy frequency f0 = 300 Hz is extracted within the target frequency band [263.6, 341] Hz, and its energy is 35 dB higher than the maximum interference frequency outside the band, which meets the signal-to-noise ratio requirement;

[0153] Speed ​​calculation and judgment: Based on n=10×300 / 1=3000r / min (within the qualified range of [2900,3100]r / min), it is judged as "qualified";

[0154] Comparative experiment: Using existing technology (taking the maximum main frequency of the full spectrum) to test the same motor, the 50Hz interference was mistakenly identified as the main frequency, and the calculated speed was 500r / min, with a misjudgment rate of 100%; the misjudgment rate of this solution was 0%, and the test time for a single unit was 0.8 seconds.

[0155] PMDC Implementation Examples:

[0156] The motor under test is a PMDC motor with Z=12 commutator segments, rated voltage 12V, acceptable speed range [3400, 3600] r / min, and acceptable current range [0.9, 1.1] A.

[0157] Qualified samples: The mean ripple frequency of 30 qualified samples is μ=700Hz, the standard deviation is σ=35Hz, and the dispersion is Cv=0.05; the ratio of peak starting current to steady-state current Ki is Ki_avg=8 in the sample set.

[0158] Fault samples: 10 typical fault samples (5 with abnormal startup, 5 with open circuit), among which the open circuit sample has a maximum leakage current of 0.08A;

[0159] Fault thresholds: Start-up abnormal threshold 0.5×Ki_avg=4, disconnection threshold 0.1×I_min=0.09A (covering the maximum leakage current of 0.08A for 5 disconnection samples).

[0160] Theoretical frequency range: calculated based on [3400×12 / 60, 3600×12 / 60] = [680, 720] Hz;

[0161] Relaxation ratio: Cv=0.05≤0.3, k=1.1;

[0162] The final target frequency band is [680 / 1.1, 720×1.1]≈[618.2, 792]Hz, with no interference from the frequency bands and no need for splitting.

[0163] Status determination: After the motor under test starts, the current is detected for the first time within 0.1 seconds, and the current drops from 7.5A to 1.0A within 0.5 seconds. Ki_test=7.5 / 1.0=7.5>4, I_dc=1.0A∈[0.9,1.1]A and the fluctuation within 100ms is ≤±2%, which is determined to be "steady-state operation".

[0164] FFT analysis: Sampling frequency Fs = 2 × 792 × 1.2 = 1900.8 Hz, Δf_target = 0.5 Hz, Fs / Δf_target = 3801.6, N_fft = 4096 (minimum power of 2), spectral resolution ≈ 0.46 Hz; the extracted main frequency within the target frequency band is f0 = 712 Hz, and the signal-to-noise ratio is ≥ 32 dB;

[0165] Speed ​​calculation and judgment: n is calculated according to n=60×712 / 12=3560r / min (which is within the qualified range of [3400,3600]r / min), and is judged as "qualified";

[0166] Comparative experiment: Existing technology mistakenly identified 250Hz (50Hz power frequency 5th harmonic) as the main frequency and calculated the rotational speed as 1250r / min (misjudgment); the misjudgment rate of this solution is 0%, and the test time is 0.7 seconds.

[0167] The following is used to automatically test the motor of this model, store and display the test data, and give the result of determining whether it is qualified.

[0168] Figure 2 A schematic diagram of the spectrum of a BLDC provided for this invention;

[0169] Figure 3 A schematic diagram of the spectrum of a PMDC provided for this invention;

[0170] The acceptable speed range for a certain type of single-pole BLDC motor is 2900–3100 r / min, and the acceptable DC current range is 1.8–2.2 A. The measured speed of a qualified motor sample was 3000 r / min. The full-frequency spectrum of the current ripple after FFT spectrum analysis is shown below. Figure 2 As shown in the graph, the maximum frequency of energy is 50Hz. If this maximum frequency is used as the rotational speed test, the incorrect result of 500r / min will be obtained.

[0171] Given the number of pole pairs N and rotational speed n of a BLDC generator, the corresponding frequencies in the spectrum of its current ripple after FFT transformation are:

[0172] f = n * N / 10, where n is the rotational speed in r / min, N is the number of pole pairs, and f is the frequency in Hz.

[0173] Figure 2 In the above calculations, the lower limit n1 of the acceptable speed range is 2900 r / min, and the upper limit n2 is 3100 r / min. The calculated frequencies corresponding to the dashed lines in the frequency spectrum are f1 = 290 Hz and f2 = 310 Hz. This can be achieved using... Figure 2 The similar graphs shown display the test analysis results on the screen. The frequency band settings related to speed, corresponding to the frequency points f3 and f4 in the solid spectrum box, can be determined according to the actual situation or adjusted based on the test results of a batch of qualified motors. In this embodiment, f3 is set to 180Hz and f4 is set to 420Hz. The main frequency in this band is 300Hz, and the calculated current speed is 3000r / min, which is considered qualified. For motors that fail to turn due to short circuits or mechanical jamming, a threshold for judging zero speed can be set between the measured DC current value and the upper limit of the qualified current. For motors that fail to turn due to open circuits, a threshold for judging zero speed can be set between the measured DC current value and the lower limit of the qualified current. When the measured DC current of the motor exceeds the above thresholds, a failure judgment of zero speed is given.

[0174] The acceptable speed range for a certain type of PMDC with 12 commutator segments per pair is 3400–3600 r / min, and the acceptable DC current range is 0.9–1.1 A. The measured speed of a qualified motor sample was 3560 r / min. The full-frequency spectrum of the current ripple after FFT spectrum analysis is shown below. Figure 3 As shown in the figure, the maximum frequency of energy in the spectrum is 1000Hz. If this maximum frequency is used as the speed test for calculation, the incorrect result of 5000r / min will be obtained.

[0175] Given the number of commutator segments Z and the rotational speed n of a PMDC converter, the corresponding frequencies in the frequency spectrum after FFT transformation of the current ripple are:

[0176] f = n * Z / 60, where n is the rotational speed in r / min, f is the frequency in Hz, and Z is the number of commutator segments.

[0177] Figure 3 In this context, the lower limit n1 of the acceptable speed range is 3400 r / min, and the upper limit n2 is 3600 r / min. Calculations show that the corresponding frequencies within the dashed frame of the frequency spectrum are f1 = 680 Hz and f2 = 720 Hz. This can be achieved using... Figure 3The similar graphs shown display the test analysis results on the screen. The frequency band settings related to speed, corresponding to the frequency points f3 and f4 in the solid spectrum box, can be determined according to the actual situation or adjusted based on the test results of a batch of qualified motors. In this embodiment, f3 is set to 360Hz and f4 is set to 900Hz. The main frequency in this band is 712Hz. The calculated current speed is 3560r / min, which is considered qualified. During the sampling process of good motors, the ratio Ki of the maximum starting current Im from the start of power-on to the steady-state operating current I0 is recorded. By observing the change value of the ratio Ki in the batch sampling, a Ki0 between 1 and Ki is selected as the basis for judging the motor operation. If the value exceeds the value, the speed is displayed as zero, and the speed is judged as unqualified. For faulty motors that do not turn due to short circuit or mechanical jamming, a threshold for judging the speed as zero can also be set between the measured DC current value and the upper limit of the qualified current; for faulty motors that do not turn due to wire breakage, a threshold for judging the speed as zero can be set between the measured DC current value and the lower limit of the qualified current. If the DC current of the motor exceeds the above threshold, a failure judgment of zero speed is given.

[0178] The current sensor A described in this application can be a Hall sensor, a resistor, a current transformer, etc., and its form is not limited. The current sensor A can be connected in series at any terminal of the DC power supply. The DC power supply device can be composed of an independent programmable DC power supply, whose operating voltage is set and whose start and stop are controlled by a measurement and control module.

[0179] Figure 4 This is a schematic diagram of the structure of a speed measuring device for an electric motor provided by the present invention. The speed measuring device for the electric motor includes:

[0180] Memory 21 is used to store computer programs;

[0181] The processor 22 is used to implement the steps of the above-described method for measuring the speed of an electric motor when executing a computer program.

[0182] The description of the speed measuring device for the electric motor provided in this application is given in the above embodiments and will not be repeated here.

[0183] Figure 5 The present invention provides a schematic diagram of a test device, which includes the aforementioned motor speed measuring device and a filtering module connected to a processor. The filtering module is used to filter the current signal.

[0184] Measurement and control module: The core processing unit adopts an ARM Cortex-M4 architecture microcontroller to perform parameter calculation, FFT signal analysis, and motor status determination logic. The operation speed is ≥100MHz to ensure real-time performance.

[0185] Signal conditioning module: Implements component separation and interference filtering of current signals.

[0186] The DC component I_dc is extracted by a low-pass filter (cutoff frequency 0.1Hz). This frequency was determined based on tests of 30 qualified motors of 20 different models (10 models of BLDC and 10 models of PMDC). This effectively filters out ripple interference and retains a stable DC component.

[0187] The difference between the original current and I_dc is the AC ripple current I_ac. The extracted AC ripple current I_ac is amplified by a precision amplifier circuit and then passed through a programmable bandpass filter to effectively improve the signal-to-noise ratio and RMS value of the signal (matching the target frequency band [f3,f4]) and filter out interference outside the frequency band.

[0188] Current sensor: A closed-loop Hall current sensor is selected, connected in series with the positive or negative terminal of the DC power supply, with a sampling range of 0~50A, sampling accuracy ≥0.5 grade, and linearity ≤0.1%, to ensure the accuracy of current signal acquisition;

[0189] Programmable DC power supply: Output voltage range 0~60V, current range 0~50A, output voltage (error ≤±1%) and start / stop are controlled by the measurement and control module via RS485 bus to meet the power supply requirements of different types of motors;

[0190] Storage: Uses an SD card with a capacity of ≥16GB to store test parameters (model, attributes, thresholds, etc.), test data and judgment results for a single motor, and supports data retention even after power failure;

[0191] Display: A 5-inch TFT touchscreen is used to display the test progress, current time-domain waveform, spectrum, speed value and pass / fail result in real time, and supports operation command input.

[0192] The measurement and control module activates the DC power supply to power the motor under test. The signal conditioning module decomposes the current signal into DC current and AC ripple current signals. The measurement and control module samples and processes these DC current and AC ripple signals according to the motor's characteristics. The processing result of the DC signal is used to determine whether the motor is operating in a steady-state state. The AC ripple signal undergoes FFT spectrum analysis to obtain a full spectrum distribution map. Within the relevant high and low limit frequency bands of this spectrum, the module searches for the dominant frequency with the highest energy and uses it to calculate the rotational speed. The process of setting the relevant high and low limit frequency bands is as follows: Based on the motor's manufacturing requirements, high and low threshold values ​​for the acceptable speed range are set, and the corresponding high and low frequency thresholds in the spectrum are calculated. These threshold values ​​are then appropriately relaxed to form the frequency bands required for calculating the rotational speed. By filtering out irrelevant frequencies in the spectrum, the signal-to-noise ratio of the speed-related current ripple is greatly improved, thereby enhancing the accuracy of speed measurement.

[0193] Under the unified coordination of the measurement and control module, the memory and display are used for human-machine interaction and to store relevant information. During the test project setup phase for the motor under test, information including motor model code, brushed / brushless attributes, number of commutator segments, number of pole pairs, operating voltage, acceptable thresholds for operating current / speed, and high / low frequency values ​​for the frequency bands calculated based on the motor's attributes from the full frequency spectrum generated by FFT spectrum analysis of the sample motor's current test data. It also needs to set the defective current threshold value (for BLDC) for motor samples that fail to rotate due to various factors, or the DC current threshold value (for PMDC) for detecting the decrease in current from startup to steady-state operation. When the test project is invoked for production testing, the memory and display, under the unified coordination of the measurement and control module, automatically test the motor of that model, store and display the test data, and provide a result indicating whether it is qualified or not.

[0194] The description of the testing equipment provided in this application is similar to that in the above embodiments and will not be repeated here.

[0195] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0196] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0197] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the speed of an electric motor, characterized in that, include: Obtain the current signals of qualified and faulty motors; Acquire the current signal of the motor under test; The current signal of the faulty motor and the current signal of the motor under test are used to determine whether the motor under test has a fault. If the motor under test does not have a fault, then it is determined whether the motor under test is in steady-state operation based on the current signal of the qualified motor and the current signal of the motor under test. If the motor under test is operating in a steady state, the speed of the motor under test is determined based on the current signal of the motor under test.

2. The method for measuring the speed of an electric motor as described in claim 1, characterized in that, Before obtaining the current signals of qualified and faulty motors, the following steps are also included: Determine the attribute data of the motor under test, including at least one of the following: motor type, rated supply voltage, and number of pole pairs of a DC permanent magnet brushless motor or number of commutator segments of a DC permanent magnet brushed motor. Obtain the current signals of qualified and faulty motors, including: Acquire current signals from qualified motors and faulty motors of the same type as the motor under test.

3. The method for measuring the speed of an electric motor as described in claim 1, characterized in that, After obtaining the current signals of qualified and faulty motors, the process also includes: Determine the stall current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, and the average value of the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor. Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes: The fault status of the motor under test is determined based on the average ratio of the stall current and open-circuit leakage current of the DC permanent magnet brushless motor and the ratio of the starting peak current to the steady-state current of the DC permanent magnet brushed motor.

4. The method for measuring the speed of an electric motor as described in claim 3, characterized in that, Based on the stall current and open-circuit leakage current of the DC permanent magnet brushless motor in the faulty motor, the average ratio of the starting peak current to steady-state current of the DC permanent magnet brushed motor, and the current signal of the motor under test, it is determined whether the motor under test has a fault, including: If the motor under test is a DC permanent magnet brushless motor, then if the current of the motor under test is greater than or equal to the stall threshold, or if the current of the motor under test is less than or equal to the open circuit threshold, then the motor under test is determined to be faulty. The stall threshold is positively correlated with the stall current, and the open circuit threshold is positively correlated with the open circuit leakage current. If the motor under test is a DC permanent magnet brushed motor, then if the average ratio of the starting peak current to the steady-state current of the motor under test is less than the starting abnormal threshold, or if the steady-state current of the motor under test is less than or equal to the disconnection threshold, then the motor under test is determined to be faulty.

5. The method for measuring the speed of an electric motor as described in claim 1, characterized in that, After obtaining the current signals of qualified and faulty motors, the process also includes: Fast Fourier analysis is performed on the current signal of the qualified motor to obtain the ripple frequency signal; Determine the mean and standard deviation of the ripple frequency signal; Determine the dispersion of the current signal of the qualified motor; Determine the steady-state speed range and the steady-state current range; Determining whether the motor under test is faulty based on the current signal of the faulty motor and the current signal of the motor under test includes: The determination of whether the motor under test has a fault is based on the dispersion of the current signal of the qualified motor, the steady-state speed range, the steady-state current range, and the current signal of the motor under test.

6. The method for measuring the speed of an electric motor as described in claim 5, characterized in that, Before performing Fast Fourier Analysis on the current signal of the qualified motor to obtain the ripple frequency signal, the following steps are also included: The theoretical frequency range is determined based on the steady-state speed range of the qualified motor and the type of the qualified motor. The frequency band amplification ratio is determined based on the dispersion, and the dispersion is positively correlated with the frequency band amplification ratio. The theoretical frequency range is adjusted based on the amplification ratio of the frequency band to obtain the target frequency band; Determine the interference frequency band corresponding to the known interference frequency in the test environment where the motor under test is located; If the target frequency band overlaps with the interfering frequency band, the overlapping interfering frequency band is removed, and the target frequency band is divided into multiple non-interfering sub-frequency bands, which are then used as screening frequency bands. If there is no overlap, the target frequency band will be used directly as the selection frequency band. The selected frequency band is used as the effective range for extracting the ripple main frequency when performing fast Fourier analysis on the current signal of the qualified motor.

7. The method for measuring the speed of an electric motor as described in claim 1, characterized in that, If the motor under test is not faulty, then based on the current signal of the qualified motor and the current signal of the motor under test, it is determined whether the motor under test is in steady-state operation, including: If the current signal of the motor under test is within the steady-state current range, and the current fluctuation amplitude within a first preset time is less than or equal to the preset fluctuation range, then the motor under test is determined to be in steady-state operation. If the motor under test fails to reach steady-state operation within a second preset time after startup, it is directly determined to be faulty.

8. The method for measuring the speed of an electric motor as described in any one of claims 1 to 7, characterized in that, If the motor under test is operating in a steady state, the speed of the motor under test is determined based on the current signal of the motor under test, including: The current of the motor under test is subjected to fast Fourier analysis, and the ripple frequency with the highest energy is selected within the preset target frequency band. The speed of the motor under test is determined according to the type of motor under test; If it is a DC permanent magnet brushless motor, then the speed of the motor under test is determined to be n = 10 × f0 / N; Where n is the rotational speed in r / min, f0 is the ripple frequency in Hz, and N is the number of pole pairs. If it is a DC permanent magnet brushed motor, then the speed of the motor under test is determined to be n = 60 × f0 / Z; Where Z represents the number of commutator segments in a DC permanent magnet brushed motor.

9. A speed measuring device for an electric motor, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the speed measurement method for an electric motor as described in any one of claims 1 to 8.

10. A testing device, characterized in that, The device includes a speed measuring device for an electric motor as described in claim 9, and further includes a filtering module connected to the processor, the filtering module being used to filter the current signal.

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