A test and analysis method for shaft voltage in bearing electric corrosion

Abstract

The first aspect of the present application provides a kind of test device for bearing electric corrosion in shaft voltage, including rotating shaft, a pair of bearings are installed on the rotating shaft, the rotating shaft one end is connected with servo motor by magnetic coupling, the servo motor is connected with frequency converter, the rotating shaft is connected with function signal generator, the voltage measuring point of the bearing is connected with oscilloscope, adjustable resistance is connected in series between the voltage measuring point of bearing outer diameter and oscilloscope, the oscilloscope is connected with host computer by data switch;Based on the above device, the second aspect of the present application provides a kind of test and analysis method for bearing electric corrosion in shaft voltage, the data collected by oscilloscope, according to the discharge event of bearing capacitor, the corresponding identification algorithm is designed, and then the common-mode voltage and the shaft voltage measured are applied, the bearing capacitor, breakdown voltage, discharge energy, discharge frequency are calculated, and then the data support is provided for the prediction of subsequent motor bearing fault and the evaluation of life.

Description

Technical Field

[0001] This invention belongs to the field of motor bearing testing technology, and particularly relates to a method for testing and analyzing shaft voltage in bearing electro-corrosion. Background Technology

[0002] Bearings are widely used in modern machinery industry and are essential mechanical parts in motors. The quality of the bearing's electrical performance directly affects the severity of shaft voltage problems in motors. Bearings mainly serve to support and transmit power, maintaining a constant air gap between the stator and rotor cores of the motor while effectively transferring load. A bearing consists of five parts: inner raceway, outer raceway, balls, cage, and lubricating grease. In recent years, due to the widespread use of electric vehicles, the problem of bearing electro-corrosion in motors has become increasingly acute. Shaft voltage is a key parameter in bearing electro-corrosion; different shaft voltages affect the oil film thickness and the number of oil film breakdowns between the inner and outer raceways. The oil film thickness and the number of oil film breakdowns are related to the bearing's equivalent capacitance and equivalent resistance, respectively. Currently, the measurement methods and data processing for shaft voltage, a key electrical parameter of bearings, are not precise enough, and there is a lack of effective means to obtain the number of discharges and the discharge power during the electro-corrosion process of motor bearings. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for testing and analyzing shaft voltage during bearing electro-corrosion, aiming to detect and collect discharge voltage, discharge frequency, and discharge power during the electro-corrosion process of motor bearings, thereby providing data support for the prediction of subsequent motor bearing failures and the assessment of their lifespan.

[0004] Technical Solution: To achieve the above objectives, the first aspect of this invention proposes a testing device for the axial voltage in bearing electro-corrosion, comprising a rotating shaft, on which a pair of bearings are mounted, the pair of bearings being fixed to a test bench via bearing seats, one end of the rotating shaft being connected to a servo motor via a magnetic coupling, the servo motor being connected to a frequency converter, the other end of the rotating shaft being connected to a function signal generator via brushes, voltage measurement points being provided on the inner and outer diameters of the bearings, an oscilloscope being connected to each voltage measurement point, an adjustable resistor being connected in series between the voltage measurement point on the outer diameter of the bearing and the oscilloscope, and the oscilloscope being connected to a host computer via a data exchange.

[0005] Preferably, the test bench is a rubber-insulated tabletop, and a pair of bearing seats are fixedly installed on the rubber-insulated tabletop.

[0006] Preferably, the adjustable resistor is a precision adjustable resistor, which is immersed in an insulating coolant.

[0007] Based on the above-mentioned testing device, a second aspect of the present invention proposes a method for testing and analyzing shaft voltage in bearing electro-corrosion, comprising the following steps:

[0008] Step 1: ， A uniform lubricating grease is sprayed between the internal balls and the inner and outer raceways of the bearing. A common-mode voltage is applied to the shaft through a function signal generator, and the shaft is driven to rotate by a servo motor.

[0009] Step 2: Obtain the shaft voltage signal on the bearing using an oscilloscope and upload it to the host computer via a data exchange;

[0010] Step 3: The host computer obtains the bearing erosion parameters based on the applied common-mode voltage and the measured shaft voltage. The erosion parameters include the bearing equivalent capacitance, discharge energy, number of discharges, and average discharge power. The analysis results are then compiled into a dataset.

[0011] Step 4: Change the servo motor speed using a frequency converter, and change the amplitude and frequency of the common-mode voltage using a function signal generator. Repeat steps 1-3.

[0012] Step 5: Analyze the impact of common-mode voltage and rotational speed on bearing erosion based on the erosion parameter data in the database.

[0013] Preferably, in step 1, the common-mode voltage has an amplitude of 50V-100V and a frequency of 2kHz, 4kHz, 6kHz, 8kHz, or 10kHz as a square wave.

[0014] Preferably, in step 3, the bearing erosion parameters are sampled once per hour, and the sampling result is used as the average value for the hour.

[0015] Preferably, in step 3, the process of obtaining the equivalent capacitance of the bearing includes converting the bearing and the adjustable resistor into an RC circuit, wherein the voltage across the equivalent capacitance of the bearing satisfies the following equation:

[0016]

[0017] In the formula u m (t) represents the capacitor voltage, U s Let τ be the power supply voltage, and τ be the time constant of the RC circuit, where τ = RC.

[0018] Based on the bearing voltage waveform data sequence [u m (T-3Δt), u m (T-2Δt), u m (T-Δt), u m (T)],u m (T)=V bd , bring in Calculate the time constant τ, and then determine the bearing capacitance C and V during this discharge. bdIt indicates the magnitude of the bearing voltage, reflecting the voltage changes inside the bearing caused by electro-corrosion.

[0019] Preferably, in step 3, the process of obtaining the number of discharges includes: when the bearing is in a capacitor state, the function signal generator charges the capacitor through an adjustable resistor; when the host computer detects that the peak voltage of the bearing is higher than the set threshold voltage, it considers that a discharge event has occurred in the bearing.

[0020] Preferably, in step 3, the process of obtaining discharge energy includes: evaluating the discharge energy using discharge power, calculated using the following formula:

[0021]

[0022] In the formula, C is the bearing capacitance and U is the voltage at which the oil film breaks down.

[0023] Preferably, in step 3, the expression for the average discharge power is:

[0024]

[0025] In the formula, R c U is the charging resistor, T is the time for one charge / discharge cycle of the capacitor, τ is the discharge time constant of the circuit, and U m,i This is the capacitor voltage.

[0026] Beneficial effects:

[0027] Compared with the prior art, the present invention can achieve the following technical effects:

[0028] This invention applies different excitation signals to the bearing using a function generator to simulate a more accurate actual common-mode voltage. Furthermore, the entire shaft voltage circuit of this invention contains only one capacitor—a capacitor with the raceway and rolling elements as metal plates and the oil film as the insulating medium—avoiding the influence of other stray capacitors. This allows for better study of the discharge of capacitors at both ends of the bearing and provides more effective data support for the study of bearing electro-corrosion. Attached Figure Description

[0029] Figure 1 This is a schematic diagram for measuring the electrical parameters of a bearing.

[0030] Figure 2 Circuit diagram for applying shaft voltage.

[0031] Figure 3 This is a comparison chart of the number of discharge cycles at different voltages for the left bearing at 35°C.

[0032] Figure 4 This is a comparison chart of the number of discharges of the right bearing at different voltages under 35°C.

[0033] Figure 5A comparison chart of the average discharge power of the left bearing at different voltages under 35°C.

[0034] Figure 6 This is a comparison chart of the average discharge power of the right bearing at different voltages under 35℃.

[0035] The components include: 1. Shaft; 2. Bearing housing; 3. Bearing; 4. Servo motor; 5. Frequency converter; 6. Oscilloscope; 7. Data exchange; 8. Host computer; 9. Adjustable resistor; 10. Coolant; 11. Function generator; 12. Magnetic coupling; 13. Test bench. Detailed Implementation

[0036] 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.

[0037] This invention first proposes a testing device for shaft voltage in bearing electro-corrosion, such as... Figure 1 As shown, the test setup includes a rotating shaft 1, on which a pair of bearings 3 are mounted. The pair of bearings 3 are fixed to the test bench 13 via bearing seats 2. One end of the rotating shaft 1 is connected to a servo motor 4 via a magnetic coupling 12. The servo motor 4 is connected to a frequency converter 5. The other end of the rotating shaft 1 is connected to a function signal generator 11 via brushes. Voltage measurement points are provided on the inner and outer diameters of the bearings 3. An oscilloscope 6 is connected to each voltage measurement point. An adjustable resistor 9 is connected in series between the voltage measurement point on the outer diameter of the bearing 3 and the oscilloscope 6. The oscilloscope 6 is connected to a host computer 8 via a data exchange 7.

[0038] The measurement circuit is connected to the inner ring of the bearing 3 via a brush installed at the end of the rotating shaft 1, thus connecting to the rotating shaft. The two bearings 3 are connected in series through the rotating shaft 1, which simultaneously supplies power to the two bearings 3 (simulating common-mode voltage) and provides a shaft voltage measurement point.

[0039] A servo motor 14 and a rotating shaft 1 are connected by a magnetic coupling 12 to drive the rotation of the bearing 3. At the same time, a frequency converter 5 is used to control the speed, acceleration, and running time of the rotating shaft, which facilitates the extraction and analysis of bearing capacitance parameters under different test conditions.

[0040] The rotating shaft 1 and bearing 3 are fixed by the corresponding bearing seat 2. At the same time, the entire test table is made of rubber tabletop, which facilitates the insulation of voltage and current on bearing seat 2, making the measured data more accurate.

[0041] Based on the above testing device, this invention proposes a method for testing and analyzing shaft voltage in bearing electro-corrosion, comprising the following steps:

[0042] Step 1: Spray uniform lubricating grease between the inner balls and the inner and outer raceways of the bearing 3, apply a common-mode voltage to the rotating shaft 1 through the function signal generator 11, and drive the rotating shaft 1 to rotate through the servo motor 4 at the same time;

[0043] Shaft voltage measurement refers to the voltage between the inner raceway and the base of the bearing. The measurement method is as follows: A brush is used at the end of the shaft, with two wires leading from each end of the brush. The two wires at one end of the brush are simultaneously fixed to the inner raceway of the bearing, while the two wires at the other end are connected to a function generator and an oscilloscope, respectively. The wire connected to the function generator applies an amplitude V to the bearing. g A square wave with a voltage range of 50-100V and frequencies of 2kHz, 4kHz, 6kHz, 8kHz, and 10kHz is used to simulate shaft voltage; the wire connected to the oscilloscope is a measurement current for the shaft voltage. A suitable precision adjustable resistor R1 (R2) needs to be connected in series between the function generator and the bearing. This resistor functions to limit current when the bearing is in a resistive state and to supply capacitance C to the bearing when it is in a capacitive state. tot The purpose of charging is to ensure that precision adjustable resistors connected in series are completely immersed in coolant to achieve cooling and heat dissipation.

[0044] The bases are completely isolated from each other. The internal balls of the bearing and the inner and outer raceways of the bearing need to be sprayed with a uniform amount of lubricating grease. This grease acts as insulation and lubrication before the oil film is damaged by electrical discharge.

[0045] Step 2: Obtain the shaft voltage signal on bearing 3 using oscilloscope 6, and upload it to host computer 8 via data exchange 7;

[0046] Step 3: The host computer 8 obtains the bearing electrical erosion parameters based on the applied common-mode voltage and the measured shaft voltage. The electrical erosion parameters include the bearing equivalent capacitance, discharge energy, discharge times, and average discharge power. The analysis results are then compiled into a dataset.

[0047] Based on data acquired using an oscilloscope, a corresponding identification algorithm is designed to identify bearing capacitance discharge events. Then, by applying the common-mode voltage and measuring the shaft voltage, the bearing capacitance, breakdown voltage, discharge energy, and number of discharges are calculated. The method is as follows:

[0048] Bearing capacitance calculation: After the bearing oil film is established, a capacitance is formed with the raceway and rolling elements as metal plates and the oil film as the insulating medium. The measuring device uses a resistor R... c The bearing capacitor is charged. When the voltage across the capacitor exceeds the oil film voltage breakdown threshold, the energy stored in the bearing capacitor discharges to the raceway and rolling elements, forming an EDM current. Figure 2 As shown.

[0049] The amount of energy released depends on the breakdown voltage and the bearing capacitance during this discharge. It can be assumed that the energy stored in the bearing capacitance is completely released to the raceway and rolling elements, causing electrical damage. The magnitude of the bearing capacitance can be calculated using data from the charging phase of the bearing voltage waveform. During the charging phase, the voltage source U... s When charging an RC series circuit, the voltage across the capacitor satisfies the following equation.

[0050]

[0051] In the formula u m (t) represents the capacitor voltage, U s Let τ be the power supply voltage, and τ be the time constant of the RC circuit, τ = RC. Based on the bearing voltage waveform data sequence [u m (T-3Δt), u m (T-2Δt), u m (T-Δt), u m (T)],u m (T)=V bd Substituting these values ​​into the equation above allows us to calculate the time constant τ, which in turn determines the bearing capacitance C and V during that discharge. bd It indicates the magnitude of the bearing voltage, reflecting the voltage changes inside the bearing caused by electro-corrosion.

[0052] Discharge Count Calculation: Since bearing discharge events are random, the number of discharges over a period of time is calculated. A high-capacity, high-sampling-rate oscilloscope recorder is used to collect bearing voltage data. The bearing voltage time series is transmitted to a host computer via Ethernet for analysis. The host computer software sets voltage thresholds based on different operating conditions; when the bearing voltage exceeds the threshold, it is considered a discharge event. This is used to average the short-term frequency of discharge events. When the bearing is in a capacitive state, the power supply flows through the load resistor R. L When the capacitor is charged, the algorithm detects the peak voltage of the bearing. When the peak voltage is higher than the threshold voltage, it is considered that a discharge event has occurred in the bearing.

[0053] Discharge energy: The bearing capacitance for each discharge event can be identified through the bearing voltage sequence. The energy released during discharge is evaluated using the discharge power, and the calculation formula is shown below:

[0054]

[0055] Where C is the bearing capacitance and U is the voltage at which the oil film breaks down.

[0056] The expression for calculating the average discharge power is as follows:

[0057]

[0058] In the formula, Rc U is the charging resistor, T is the time for one charge / discharge cycle of the capacitor, τ is the discharge time constant of the circuit, and U m,i This is the capacitor voltage.

[0059] During the test, the bearing was continuously subjected to electrical erosion, and the sampling frequency was once per hour, with the statistical result of that sampling taken as the average value for the hour.

[0060] The relevant parameters, such as the number of effective discharges, total discharge energy, and average discharge power, are statistically analyzed and calculated from the dataset.

[0061] Step 4: Change the speed of servo motor 4 through frequency converter 5, and change the amplitude and frequency of common mode voltage through function signal generator 11. Repeat steps 1-3.

[0062] Step 5: Analyze the impact of common-mode voltage and rotational speed on bearing erosion based on the erosion parameter data in the database.

[0063] like Figures 3-6 As shown in the results, the analysis of the test results at 35℃ indicates that the number of discharges and the discharge power increase significantly with increasing voltage. This is because the electric field strength also increases with increasing voltage. The stronger the electric field strength, the stronger the interaction force between charges, and the easier it is for the molecular structure of the dielectric to be destroyed, leading to discharge.

[0064] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of the present invention is defined only by the appended claims.

Claims

1. A test device for the shaft voltage in bearing electric corrosion, characterized in that, The utility model relates to a test bench for bearing electro-erosion test, including pivot (1), a pair of bearings (3) are installed on pivot (1), a pair of bearings (3) are fixed on test bench (13) through bearing seat (2), pivot (1) one end is connected with servo motor (4) through magnetic coupling (12), servo motor (4) is connected with frequency converter (5), pivot (1) other end is connected with function signal generator (11) through brush, function signal generator (11) applies different excitation signal to bearing, thereby simulating actual common mode voltage, the inner diameter and outer diameter of bearing (3) are equipped with voltage measuring point, voltage measuring point is connected with oscilloscope (6), the voltage measuring point of bearing (3) outer diameter is connected with adjustable resistance (9) between oscilloscope (6) in series, oscilloscope (6) is connected with host computer (8) through data switcher (7).

2. The testing device for bearing electrochemical voltage in bearing electrocorrosion according to claim 1, characterized in that, The test bench (13) is a rubber insulated desktop, and a pair of bearing seats (2) are fixedly installed on the rubber insulated desktop.

3. The test device for bearing electrochemical voltage in bearing electrocorrosion according to claim 1, characterized in that, The adjustable resistance (9) is a precision adjustable resistance, and the precision adjustable resistance is immersed in the insulating cooling liquid (10).

4. A method for testing and analyzing the spindle voltage in electrochemical machining of a bearing using the apparatus of claim 1, characterized by The utility model relates to a test bench for bearing electro-erosion test, including the following steps: Step 1: spray uniform lubricating grease between the inner ball of bearing (3) and the inner and outer raceways of bearing, apply common mode voltage to pivot (1) through function signal generator (11), and drive pivot (1) to rotate through servo motor (4); Step 2: obtain the shaft voltage signal on bearing (3) through oscilloscope (6), and upload to host computer (8) through data switcher (7); Step 3: obtain bearing electro-erosion parameters according to the applied common mode voltage and the measured shaft voltage, the electro-erosion parameters include bearing equivalent capacitance, discharge energy, discharge frequency, average discharge power, and form a data set according to the analysis results; Step 4: change the speed of servo motor (4) through frequency converter (5), change the amplitude and frequency of common mode voltage through function signal generator (11), and repeat steps 1-3; Step 5: analyze the influence of common mode voltage and speed on bearing electro-erosion according to the electro-erosion parameter data in the database.

5. The method of claim 4, wherein the method further comprises: In step 1, the amplitude of the common mode voltage is 50V-100V, and the frequency is 2kHz, 4kHz, 6kHz, 8kHz, and 10kHz square wave.

6. The method of claim 4, wherein the step of applying a voltage to the bearing is performed by applying a voltage to the bearing that is less than 100 volts. In step 3, the bearing electro-erosion parameters are sampled once every hour, and the sampling results are taken as the average value within an hour.

7. The method of claim 4, wherein the step of applying a voltage to the bearing is performed by applying a voltage to the bearing that is less than 100 volts. In step 3, the process of obtaining the bearing equivalent capacitance includes that the bearing and adjustable resistance (9) are equivalent to an RC circuit, and the voltage across the bearing equivalent capacitance satisfies the following equation: ； wherein u m ( t ) is the capacitor voltage, U s is the power supply voltage, In step 3, the process of obtaining the discharge frequency includes that when the bearing is in a capacitive state, function signal generator (11) charges the capacitor through adjustable resistance (9), and host computer (8) detects that the peak voltage of the bearing is higher than the set threshold voltage, then it is considered that the bearing has a discharge event. is the RC circuit time constant, In step 3, the process of obtaining the discharge energy includes that the discharge energy is evaluated by the discharge power, and the calculation formula is as follows: = RC; According to the bearing voltage waveform data sequence[ u m ( T -3Δ t ), u m ( T -2Δ t ), u m ( T -Δ t ), u m ( T )], u m ( T )= V bd , into calculation time constant In step 3, the expression of the average discharge power is as follows: , and then determine the bearing capacitance C at this time, wherein, V bd represents the size of the bearing voltage, reflecting the voltage changes due to the internal electric corrosion phenomenon of the bearing.

8. The method of claim 4, wherein the method further comprises: ​ 9. The method of claim 4, wherein the method further comprises: ​ ； wherein C is the bearing capacitance, U is the voltage at oil film breakdown.

10. The method of claim 4, wherein the method further comprises: ​ ； wherein is the charging resistance, T is the time for one charge-discharge cycle of the capacitor, τ is the discharge time constant of the circuit, is the capacitor voltage.

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