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The author uses the computer's multimedia sound card to replace the expensive commercial data acquisition card, which ensures the development and real-time of the gear noise signal acquisition, greatly reduces the development cost, and develops a set of spectrum analysis based on LabVIEW as the software development platform. The technical gear breakage fault identification virtual instrument.
1 Gear breaking mechanism The broken tooth is the most important and most serious form of damage to the gear failure [1]. The vibration system of the gear and gearbox is a complex non-linear system. The manufacture, installation and gear stiffness of the gears are subject to certain conditions, and a pair of new gears will also vibrate during the meshing motion. Therefore, it is necessary to analyze the gear broken tooth excitation source from the gear vibration model and the dynamic equation, and further perform the broken tooth analysis. The gear pair transmission is used as a vibration system. According to the vibration theory, the dynamic equation of the gear meshing physical model is: d2xdt2 Cdxdt k(t)x F(t)(1) where the relative displacement of the gear on the x mesh line; C gear meshing damping ; k(t) meshing stiffness; M equivalent mass; Mm1m2m1 m2; F(t) external excitation.
The dynamic load F(t) applied to the gear includes the excitation generated by all faults of the gear, and its change is affected by the change of gear tooth stiffness and transmission error, and also related to the change of the frictional direction of the tooth surface.
The failure of the gear pair is related to the dynamic load F(t). When the gear pair transmits the movement and the load, the force of the driving wheel and the reaction force of the driven wheel are respectively applied to the teeth of the opposite teeth through the contact points. When the contact point is located at the top of the teeth, the teeth are like this. A cantilever beam that produces the greatest bending stress at the root of the tooth after loading.
If F(t) suddenly changes (overload or shock), it is easy to generate an overload fracture at the root. Even if there is no F(t) mutation, when the gear teeth are repeatedly loaded, fatigue cracks often occur due to stress concentration at the root of the tooth, and gradually expand, and finally develop to finally make the gear can no longer bear the dynamic load F(t). And cause broken teeth. The vibration signal impact energy is also maximized when the teeth are broken.
2 signal characteristics [3] (1) frequency domain characteristics of the normal gear The signal of the normal gear is reflected in the power spectrum, there is the meshing frequency fm and its harmonic components, that is, there are nfm (n1, 2), and the meshing frequency component is Mainly, its higher harmonics are successively reduced. At the same time, at the low frequency there is the gear shaft rotation frequency fz and its higher harmonics mfz (m1, 2).
(2) When the frequency domain characteristics of the uniformly worn gear are uniformly worn, the meshing frequency and its harmonic components remain unchanged, but the magnitude of the amplitude changes, and the amplitude of the higher harmonics increases relatively. In the analysis, at least three or more harmonic changes must be analyzed to detect such wear from the spectrum. In addition, as the wear is intensified, fractional harmonics of 1/k (k2, 3, 4) may also be generated, and sometimes jumps of nonlinear vibration characteristics may occur at the time of lifting and lowering.
(3) Frequency characteristics of local anomalous gears Local anomalies of gears have a wide range of meanings, including large cracks at the root of the tooth, local tooth surface wear, broken teeth, and local tooth shape errors. For gears with local anomalies, due to the influence of cracks, breaks or tooth profile errors, the frequency of rotation will be the main frequency characteristic, ie mfz(m1,2).
(4) Frequency characteristics of gear pitting During the meshing process, when the gear is turned into contact with the pitting part, due to the sudden increase of the friction force, one or several impact phenomena will occur, the meshing vibration is modulated, and the frequency domain is expressed as a signal. A series of equally spaced frequency clusters appear in the spectrum, especially on both sides of the high frequency meshing frequency, and a series of sidebands spaced at a rotational frequency are often distributed, which is the fault characteristic of pitting corrosion.
3 system formation 3.1 hardware components in the hardware must use the data acquisition card, and the acquisition of sound signals on the data acquisition card requirements mainly have two aspects: First, the sampling frequency, that is, the number of sound samples collected per second. The higher the sampling frequency, the more accurate the recorded sound waveform and the higher the fidelity. The second is the number of samples, that is, the number of bits of the sound converted from analog to digital. The higher the number of bits, the greater the number of acoustic amplitudes that can be represented in a certain range, and the better the analysis of the signal.
The price of the dedicated data acquisition card is generally high. Considering that the sound card of the computer itself is a good data acquisition card, especially in the collection of sound signals, the level of the dedicated data acquisition card is basically reached. Generally, the meshing frequency of the gear will not be higher than 10 kHz, and the highest sampling frequency of the sound card can reach 44.1 kHz. According to the sampling law, the highest signal frequency that can be acquired is 22.05 kHz, so the sound card completely satisfies the sampling accuracy requirement of the noise signal; most data acquisition The number of samples for the card is 1216 bits, and the number of samples for the sound card is 16 bits, which also satisfies the requirements of the number of samples. I chose the innovative ACc97 sound card integrated on the computer motherboard as the sound signal data acquisition card. Other hardware has sound sensors (using a normal microphone to meet the requirements) and a personal computer [4].
3.2 Software composition According to the functions to be realized by the system, the software compiled includes the following sub-programs: 1 The sound card-based lathe noise signal acquisition program. Noise signal power spectrum analysis program. Transmission gear meshing frequency calculation program. Word report generator.
(1) Noise signal acquisition program subroutine box.
Since the system needs to realize the data acquisition of the gear noise signal, it is necessary to select the sound card parameters according to the actual situation: 1 The sound quality is mono (single channel) or stereo (stereo). The sampling frequency is 11025, 22050 or 44100kHz. The sampling digits are 8 or 16bit. The default settings for the system are mono (single channel), 22050kHz and 16bit. The SIConfig node and SIStart node are placed outside the loop to set the sound card parameters and digital sound. Format and drive the sound card to start collecting data. The SIClear node is also placed outside the loop and is controlled by the data flow to release the resources occupied by the sound card when the program stops. After data acquisition, stop the data acquisition with the SIStop node and enter the power spectrum analysis program. After the data processing is completed, continue the data acquisition cycle, and re-drive the sound card to collect data with the SIStart node. The SIRead node reads mono data containing 16 bits. It should be noted that the number of data points read by the sound card is 8192, that is, the array dimension read by the SIRead node is 8192 lines. After the program runs, the data collection and processing loops until the user thinks that the analysis is completed, when the user confirms that it is no longer Data collection and analysis, the program automatically generates a Word report.
(2) Power Spectrum Analysis Program This program calls the NI Sound Vibration Toolkit (SoundandVibrationToolkit4.
Some of the function modules in 0), the main functions include: 1 maximum sound pressure level (dB) peak and automatic display of the corresponding peak frequency (ie with automatic peak finding function). The power [Pa2rms] 2 frequency (Hz) map or the sound pressure level (dB) 2 frequency (Hz) map can be switched by selecting the ON/OFF of the /dB0 button. You can find out the operating status of the program by running the status indicator.
(3) The subroutine block diagram of the Word report program is shown in Fig. 3. In order to facilitate the long-term preservation of the measurement results, the report generation program is set.
This program calls NI LabVIEWReportGener2ationToolkit toolkit, enters relevant information in the test device information settings, and this information is automatically loaded into the Word file.
4 Example Vibration test analysis of a certain automobile transmission. When testing, the transmission is operated in 2nd gear, the input gear meshing gear ratio is 38/26, the output end is 20/41. The input shaft speed is measured as 1800 rev/min, and the calculation is performed. The characteristic frequencies are obtained.
Take 360460kHz (near the meshing frequency of the output end) as the analysis bandwidth, and perform detailed demodulation analysis on the radial vibration speed signal (sampling frequency of 5000kHz) near the output shaft bearing housing to obtain a refinement power spectrum refinement multiple of 50 times.
The output shaft frequency shift and its frequency doubling component indicate that there is a significant modulation phenomenon in the vibration signal that the output shaft frequency is the modulation frequency and the meshing frequency is the carrier wave, so that the output shaft end gear can be judged to be faulty. After disintegration, it was found that the output shaft end gear had obvious peeling.
The synthetic displacement trajectory of the particle is an ellipse.
At r3.953mm, the direction of rotation of the ellipse is reversed, and this guided wave energy is mainly concentrated on the outer wall of the pipe, which decays rapidly with increasing depth. This is in agreement with the experimental observations. If the internal defect echo amplitude is observed to be about 16.4 dB lower than the external defect, the oil is applied to the ultrasonic propagation path of the outer wall of the tube, or the finger is pressed with the eucalyptus oil, causing echo. (including SC echo and internal and external defect echo) the amplitude is reduced by more than 90, while the inner wall is oiled or filled with water, causing the amplitude of the echo to decrease by no more than 10; the roughness of the outer surface of the pipe significantly reduces the amplitude of the echo. Theoretical analysis and experimental observations show that the vibration and propagation characteristics of the first-order mode guided wave are similar to Rayleigh waves in many respects, such as displacement distribution, particle motion trajectory and no obvious dispersion, so it is considered that this is A quasi-Rayleigh wave [6].
It should be noted that although the displacement of the inner surface is very low, the defect at the inner wall can still be detected, which is related to the reflection and scattering of the guided wave at the defect. The presence of defects in the inner wall destroys the morphology of the guided wave of the mode, resulting in a reflected wave of the mode. However, the current theory of guided wave reflection and scattering is not perfect and cannot be quantitatively compared with the test results.
3 Conclusions (1) The experimental observation and theoretical analysis of a circumferential guided wave propagating in the wall of a small-diameter thin-walled tube are carried out. It is pointed out that the guided wave is a first-order mode guided wave, and the energy is mainly concentrated on the outer surface of the pipe. nearby.
(2) The SC echo phenomenon was observed in the test. The mechanism of SC echo generation was proposed and confirmed by experiments. This echo has a high value in ensuring the reliability of the flaw detection.
(3) Using this guided wave to detect small-diameter thin-walled tubes, it can simultaneously detect the longitudinal defects of the inner and outer walls of the pipe. The detection sensitivity is comparable to that of the water immersion focusing method, and it has greater operational flexibility for in-situ inspection. , to make up for the lack of water immersion focusing method is not suitable for in situ detection. At the same time, this guided wave detecting method has the same disadvantages as other types of guided wave detecting techniques in that internal and external wall defects cannot be distinguished.