Shaft Vibration Monitoring System for Rotating Machinery

Transcription

1 2016 Sixth International Conference on Instrumentation & Measurement, Computer, Communication and Control Shaft Vibration Monitoring System for Rotating Machinery Zhang Guanglin School of Automation department, Southwest University,China, Qi Qian, Yu Zhihao School of Automation department, Southwest University,China, Abstract Monitoring of rotating machinery plays an essential role in industry. The basic software and hardware structure of the shaft vibration monitoring system of rotating machinery is introduced in this paper. The vibration signals caused by different reasons were analyzed. The national standard is based on vibration vibration velocity amplitude as the evaluation standard, but can not determine what is the cause of the abnormal vibration. By experiment we made analysis method of acceleration frequency or acceleration envelope frequency, amplitude and frequency setting monitoring, to determine the cause of the abnormal vibration of rotating machinery. Keywords Hardware composition; System structure; Frequency band; Rotor unbalance; External periodic impact; Bearing damage; Envelope; Frequency domain. I. PREFACE Many domestic experts and scholars have carried out research work of shaft vibration monitoring of rotating machinery. Zhu Fujia of Tsinghua University, [2], the nonlinear dynamic behavior of rotor system of rotating machinery in common between rotor and stator rubbing, loose parts, a rotating shaft crack fault of experimental research, significant progress has been made in the diagnosis and localization of the common faults of rotating machinery.nanjing University of Aeronautics and Astronautics of Li Shunming [3], the traditional methods of amplitude domain analysis method, Fourier transform, correlation analysis and modern methods of spectrum analysis, wavelet analysis, blind source separation transformation are studied and summarized. Certain progress has been made. II. COMPOSITION OF MONITORING SYSTEM FOR ROTATING MACHINERY We first set up the hardware part of the rotating machinery monitoring system:the vibration monitoring system device is mainly demonstrated for rotating shaft vibration monitoring in the condition monitoring, can simulate the mechanical imbalance, bearing damage, cycle impact of three different causes of vibration[4]. And through the data monitoring analysis to find the different reasons.the experiment table is mainly composed of two parts. Mechanical part is composed of servo motor, coupling and its axis of rotation, acceleration sensor, ball bearings, fan blade, a blocking piece, a counterweight block. The electric part is composed of DC power supply, CPU processor, X2X bus transmitter, X2X bus receiver, analog output module, servo drive module and so on. Fig.1 Information processing flow of rotating shaft vibration monitoring test bed /16 $ IEEE DOI /IMCCC

2 This vibration monitoring system mainly simulates three kinds of different vibration conditions. 1) rolling element bearing damage 2) the quality of the rotor is not uniform. 3) the axis of rotation of the object outside the scratch III. ANALYSIS AND TREATMENT OF VIBRATION SIGNAL CAUSED BY UNEVEN QUALITY OF ROTOR The use of international standards of vibration ISO2372 should be in this experiment, the scope of this standard is the operation speed of the low speed rotating machinery. As shown in fig.2. Among them: A. the effective value of the vibration rate in the area is normal, and the machine can be used normally. B. the machine can continue to use without any restraint. C. the status of the machine in the area is not suitable to be used again, it can only be maintained for a limited period of time. It is suggested that we can detect and repair the next maintenance. D. the effective value of the vibration rate in the area is dangerous, and the machine is likely to be damaged at any time. Acceleration time domain filtering signal Speed time-domain signal In Fig.3, the above figure for the original acceleration time-domain signal figure and the figure below ground acceleration signal integration and speed time domain signal graph, you can see the rate of vibration velocity signal in time domain in the mm / s sine form jumping, using the root mean square value (RMS) calculated the vibration velocity of the valid values for mm / s in area C class I small motor intermediate (Figure 3), Zone A and B two normal vibration rate exceeds the effective value, under the condition of this vibration, rotating machinery is not suitable for continued use, it can only be maintained for a limited period of time. The unbalance of the rotor is caused by a force from the maximum unbalance point of the center island of the motor shaft, and the effect of the unbalance of the rotor is the same as that of the speed of a motor shaft. So the measured value of the rotor unbalance = 1 * motor shaft speed. (Note: the measured value of the x = 2 motor shaft speed) principle as shown in fig.4. Fig.4 Mass unbalance principle diagram Fig.2 ISO 2372 Rotating machinery vibration classification The time domain signal of the vibration acceleration is the figure of the relationship between the acceleration and the time of the vertical axis. The changes of response signal with time. Continue with the rotor unbalance A1 acceleration sensor data acquisition, for example, vibration acceleration time domain diagram as shown in fig.5. Fig.3 Acceleration time domain signal integral for velocity time domain signal Fig.5 Time domain diagram of rotor unbalance A1 acceleration 48

3 First, the original acceleration signal is filtered[5]. According to the collected vibration signal, in order to suppress and prevent the interference noise, we first make the smoothing filter. Because we need the low-frequency signal frequency processing, smoothing filter is the enhancement of the low spatial domain filtering technique, eliminating high frequency noise affect the retention of the low frequency signal, so we use the filter for smoothing filter. After the A1 acceleration signal smoothing effect as shown in Fig.6. From the filtered image and filtering the image contrast, we obviously found, filtering the image effect is very good, less than we need 100Hz low-frequency signal peak retention and highlights the, high frequency signal was mostly filtered, is very conducive to the vibration signal frequency band analysis.in order to achieve the effect of rotor imbalance, in fan films install only a magnetic counterweight block the rotor unbalance, the motor control to speed = 638RPM 10.6Hz, group A and group B accelerometer vibration frequency domain was observed in the treatment (Fig.21 and Fig.22) and in XYZ direction selection in which a vibration signal is most clear discussion frequency chart. The X axis of which A1 and B1 received the most obvious signal, so we choose A1 and B1 to discuss. Below is A1, B1 vibration frequency domain Fig.8 and 9. Fig.6 A1 Contrast diagram of acceleration signal before and after filtering A1 Acceleration time domain original signal A1 Acceleration time domain filtered signal In addition, we note that our time-domain signal changes to the frequency domain through the FFT[6], 0Hz near the DC signal is very large. Will seriously affect the numerical analysis of other frequencies, but also for the cause of our abnormal vibration analysis does not help. So when we transform FFT, the first of the acceleration signal to the trend (to eliminate the influence of acceleration DC offset), and then FFT transform. The A1 acceleration signal after filtering of FFT transform, as shown in Fig.7 below, the acceleration frequency domain direct FFT processing without filtering the original acceleration signal. Fig.8 Fig.9 A1 Rotor imbalance spectrum A1 Rotor imbalance acceleration spectrum A1 Rotor imbalance acceleration envelope spectrum B1 Rotor imbalance spectrum B1 Rotor imbalance acceleration spectrum B1 Rotor imbalance acceleration envelope spectrum Fig.7 Frequency domain map of time domain signal FFT The frequency domain of the non filtered acceleration signal The frequency domain of acceleration signal after filtering Observed two figures, in which the left side of the yellow band Unbalance rotor unbalance vibration bands = 1 shaft rotation frequency = 10.64Hz, bandwidth is ± 2Hz. As can be seen in the acceleration spectrum, the amplitude of the rotor unbalance Unbalance band anomalies, and acceleration envelope frequency domain amplitude vibration frequency Unbalance on the obvious, almost zero. Therefore, in this experiment, the rotor unbalance vibration frequency amplitude should analyze acceleration frequency domain.after acceleration integrated frequency domain filtering process, the rate of vibration of rotating machinery vibration RMS 49

4 reach 2.853mm / s, vibration state reached C region is mainly due to the unbalanced rotor mass, leading to cause the X-axis direction A1 and B1 the vibration rate is too high. IV. ANALYSIS AND TREATMENT OF VIBRATION SIGNAL CAUSED BY EXTERNAL PERIODIC SHOCK Mechanical shock have generated in many ways, defective parts or foreign body contact fan can generate periodic impact. And analysis of load balance using acceleration frequency chart is that analysis using periodic impact signal is enveloped acceleration value diagram in frequency domain, the Taichung the fan baffle plate caused by external periodic impact vibration, and the experimental equipment of a total of eight blades, so the baffle block blades caused by periodic impulse measurement value = 8 x motor shaft speed. The principle is shown in fig.10. Fig.11 Fig.12 A1 External periodic shock vibration spectrum A1 Frequency domain of external periodic shock acceleration A1 The frequency domain of the envelope of the external periodic shock acceleration B1 External periodic shock vibration spectrum B1 Frequency domain of external periodic shock acceleration B1 The frequency domain of the envelope of the external periodic shock acceleration Fig.10 Number of shocks per lap Set a piece of the shaft is rotated by periodic vibration, control of motor speed is 425RPM = 7.86Hz the blades are eight by 8 shocks per lap so. We were still observed in the group A and group B acceleration sensor vibration frequency chart (see Fig.23 and Fig.24 external periodic impact six accelerometer vibration acceleration value) and in XYZ direction choice which a vibration signal is most clear discussion frequency chart selection. Wherein the X-axis vibration cyclical impact of A1 and B1 receives the most obvious, so we chose A1 and B1 will be discussed. Below is A1, B1 vibration frequency domain Fig.11 and 12. Observation of two figure, in which the blue band shock Periodic for the external cycle shock Band = 8 x axis rotation frequency = 61Hz, bandwidth is ± 2Hz, the impact on the spectrum periodic vibration frequency, vibration spectrum of A1 is not B1 spectrogram clearly observed in Fig. 5.2b spectrum B1, periodic shock acceleration in the amplitude spectrum is scarcely observed and the acceleration spectrum envelope amplitude at 61Hz has a strong amplitude, with the amplitude and the abscissa is increased periodically the frequency diminishes. It can be obtained in this experiment external cyclical impact analysis acceleration envelope spectrum more efficiently. Integrated acceleration enveloping frequency domain analysis, rotating machinery vibration rate exceeds international standards in the normal A and B areas was observed after six acceleration sensor acceleration enveloping frequency domain in the frequency domain band Periodic shock, much larger than the amplitude of the vibration amplitude B1 of other frequencies, it can be concluded that: the vibration and the vibration direction of the abnormal vibration is caused by periodic shocks nearby B at the main X-axis direction B1. 50

5 V.ANALYSIS AND TREATMENT OF VIBRATION SIGNAL CAUSED BY DAMAGE OF BALL BEARING Ball bearing damage is mechanical shock, can produce periodic impact and generates a periodic impact signal, the Taichung rotation shaft on the left and right two groups bearing seat and the XYZ axis acceleration sensor, of which the right side of the bearing of the bearing for bearing damage to simulate the bearing damage caused by vibration, the left bearing intact, in order to identify bearing damage we use and measurement of periodic impact as the method, different is impact of each circle is number 8 is supplied by the manufacturer of the bearing characteristic value (over rolling frequency on outer ring) alternative, on the bench, bearing characteristics of the use of value of Bearing cycle impact measuring value = 3.89 x Fig.14 A2 Frequency domain vibration of bearing damage A2 Frequency domain of bearing damage acceleration A2 Frequency domain of bearing damage acceleration envelope Fig.15 B2 Frequency domain vibration of bearing damage B2 Frequency domain of bearing damage acceleration B2 A2 Frequency domain of bearing damage acceleration envelope motor shaft speed. As shown in fig.13. Fig.13 Bearing cycle impact measurement concept map Replace the bearing of the accelerometer on the right side of the B with a damaged bearing, which causes the shaft to rotate when the bearing is damaged. The control motor speed is 810RPM = 13.5 Hz due to the bearing damage caused by the periodic vibration and bearing characteristic value of the bearing, the damage of the bearing outer ring characteristic value is Were observed in the group A and group B accelerometer vibration frequency chart (see Fig.25 and Fig.26 bearing damage state six accelerometer vibration acceleration value) and in XYZ direction choice which a vibration signal is most clear discussion frequency chart. Wherein the periodic shock and vibration A2 and B2 Y axis release party received the most obvious, so we choose A2 and B2 are discussed. Below is A2, B2 vibration frequency domain Fig.14 and 15. Observe the two figure, the middle green band Outer Ring rotor unbalance vibration frequency = 3.86 X axis rotation frequency = 52Hz, bandwidth is + 2Hz. In the spectrum of periodic vibration frequency, vibration spectrum of A2 spectrum of B2 was not. To observe the 6.2b B2 spectrum, acceleration spectrum amplitude in 0-100Hz is very small to analyze. The spectrum of acceleration envelope in Ring amplitude Outer frequency band in 52Hz has a strong amplitude and amplitude independent around no vibration band. It can be concluded that it is more effective to analyze the vibration of bearing damage in this experiment. Comprehensive group of six accelerometer acceleration envelope value frequency chart (Annex 3) and in the vibration can be through the B1 and B2 of the outer ring frequency with amplitude was significantly greater than that of other frequency on the amplitude of the phenomenon analysis of the vibration is caused by the right bearing B damage and vibration direction is perpendicular to the axis of the radial direction. VI. SUMMARY In this experimental system, the vibration state is analyzed from the detection of the 51

6 vibration to the last through the frequency domain: 1 the vibration acceleration signal is integral to the vibration rate, and compared with the vibration condition, the vibration state is safe. 2 For a large amount of vibration, the first to understand the different causes of vibration caused by the vibration frequency and set different vibration frequency bands. The frequency domain of the frequency domain of the unbalance of the rotor is in the frequency domain of the acceleration value, while the frequency domain of the external periodic shock and bearing damage is in the frequency domain of the acceleration envelope. 3 the original acceleration value filter and FFT are transformed into frequency domain, and the amplitude of different frequency band in frequency domain is observed. REFERENCE [1] Li Luping. Fault diagnosis technology for steam turbine. Beijing:China Electric Power Press,2001. [2] Zhu Fujia, Peng Zhike. modern signal processing methods. mechanical fault diagnosis in Beijing: Science Press, [3] Li Shunming.Review of vibration signal processing methods.chinese Journal of Scientific Instrument, [4] Li jinxue,guo xin. DCS system PC simulation training software development environment. Petrochemical Automation, [5] SA Riga. Bias filtering and smoothing.national Defence Industry Press, [6] R.Kokila. FFT Based Image Registration using Corner Response,