外文翻译液压密封完整性调查研究

1、Mechanical Systems and Signal Processing, 2007, 21: 11151126A study of hydraulic seal integrityP. Chena, P.S.K. Chua, G.H. LimAbstract:The work described in this paper involved on-line detection of seal defects in a water hydraulic cylinder. An obvious effect of seal defect is internal leakage.There

2、fore,the approach used was to detect the internal leakage using suitable technique. The technique used involved detecting the acoustic emission (AE) due to the internal leakage. This paper evaluated various parameters of AE signals in terms of their capability in estimating the internal leakage rate

3、 in a water hydraulic cylinder. Experiments were carried out to study the characteristics of AE parameters at different internal leakage rates,the parameters including the root-mean-square (rms) value, the count rate, the peak magnitude of power spectral density and the energy.The correlations betwe

4、en these parameters and the internal leakage rate were analysed carefully. The results show that energy-based AE parameters,especially the rms value, are more suitable to interpret AE signals generated by internal leakage.Keywords: Acoustic emission; Water hydraulic cylinder; Internal leakage; AE co

5、unt rate; Root mean square; Power spectral density; AE energy1. IntroductionModern water hydraulics, using tap water as the hydraulic fluid, has gained much interest in the past decade due to its inherent advantages compared to oil hydraulics. These advantages include environment friendliness,good p

6、roduct compatibility and no fire hazards 1,2. However, some problems with modern water hydraulics are still to be addressed. One of the most common problems is the relatively large internal leakage in water hydraulic components. For example, a water hydraulic cylinder could suffer from internal leak

7、age across the piston seals. This is due to the very low viscosity of water in comparison with that of hydraulic oil 1,3. Therefore, it is important to monitor the internal leakage to achieve optimal performance and reliable and safe operations of water hydraulic systems.The work presented in this p

8、aper is part of a project that aims to develop a quantitative model to estimate the internal leakage flow rate in a water hydraulic cylinder by means of AE. It is focused on the internal leakage smaller than 1.0 L/min. In order to model the AE signal generated by the internal leakage, suitable param

9、eters must first be selected to interpret the signal. Therefore, experiments were conducted to study the characteristics of various AE parameters in terms of their effectiveness in estimating the internal leakage rate,as described in this paper.2. Acoustic emissionAE is defined as the transient elas

10、tic waves that are generated by the rapid release of energy from localised sources. It has been found that AE signals can be generated by fluid leakage. Pollock and Hsu 10 studied the physical origin of these signals in detail and Goodman et al. 12 reported a variety of AE source mechanisms associat

11、ed with leakage from vessels, tanks and pipelines. In the case of internal leakage in water hydraulic cylinders, the generation of AE signals is largely attributed to the turbulence induced by the internal leakage. AE signals can be categorised into two basic types. The burst-type AE refers to AE si

12、gnals corresponding to individual AE events, while the continuous-type AE refers to an apparently sustained signal level from rapidly occurring AE events 16. AE signals generated by internal leakage in water hydraulic cylinders are of continuous type, as shown in Fig. 1. AE counts are widely used as

13、 a practical measure of AE activity. This parameter is defined as the number of times the signal exceeds a counter threshold. For continuous-type AE, AE count rate is often used to measure the variation of AE counts with time. The root-mean-square (rms) value is often used to measure the energy cont

14、ent of AE signals. For an AE signal consisting ofx 0， x 1, , x N1 , its rms value isThe advantage of energy measurement is that the energy content of the AE signal can be directly related to important physical parameters associated with the energy release at the AE source 14. The above parameters ha

15、ve been used to describe AE signals in a variety of applications 11,17,18.The aforementioned parameters are measured in the time domain. Besides, parameters measured in the frequency domain are also of interest, such as the frequency and magnitude of the dominant frequency component and the energy c

16、ontained within frequency bands. For the continuous-type AE, these parameters can be obtained through spectral analysis using Fourier transform. The power spectral density (PSD) of AE signals can be computed using the following equation 19:where P k is the power spectral density, X k is the discrete

17、 Fourier transform (DFT) of an AE signal xn, andT is the sampling period. The PSD represents the distribution of the signal power over frequencies. Some studies of AE signals in the frequency domain can be found in Refs. 10,13,20,21.3. ExperimentationDue to the complexity of AE phenomena, analytical

18、 methods are not well established. Therefore,experimental methods are introduced to investigate AE. In order to study the characteristics of AE signals generated by internal leakage in water hydraulic cylinders, experiments were deliberately designed, as described below.For each record of AE signal,

19、 the AE count rate, denoted as _N AE was calculated by dividing the AE counts by the signal duration. Both a fixed threshold and a floating threshold were used for counting. Since there was no well-defined procedure to choose the threshold value, a wide range of values were tried. For the fixed thre

20、shold, a value of 0.04V yielded the best results, as shown in Fig. 6a. It is noted that the AE count rate drops fast as the internal leakage rate decreases. For the floating threshold, the threshold value was set to be proportional to the rms value of the signal. The resulting AE count rate remained

21、 at a constant level, no provide a desirable simulation of the dynamic processes existing in a cylinder subject to internal leakage. Thusin the present work, efforts have been made to simulate the real internal leakage in hydraulic cylinders. In the following, the leakage mechanism is first studied;

22、 then, the simulation of the leakage is presented.In order to simulate scores created by the abrasive action of solid particulates, a file was used, in the presentwork, to make scores on the piston seal surfaces of a water hydraulic cylinder. Fig. 2 shows the scored pistonseals used in the experimen

23、ts. These seals lead to an internal leakage smaller than 1.0 L/min for the pressure range of 070 bar. Sixteen scores were equally distributed along the circumference of the seals. The dimensions of these scores were measured with a non-contact optical measurement system. Fig.3shows the profile of a

24、score taken by the measurement system. Along the edge of the score, five key points were selected and their coordinates were measured. The width and depth of the score were then measured. In addition, a circular arc fit to these five points was calculated. Thus, an approximate radius of the score co

25、uld be obtained.Fig. 2. The 16-score piston seals.Fig. 3. The profile of a score.4. Experimental resultsIn the experiment, 100 sets of data were acquired at different internal leakage rates, with each set consisting of 40 records of AE signals measured at a certain leakage rate. Each record of AE si

26、gnal contained 4096 points sampled at 5 MHz, from which AE parameters were calculated. For each AE parameter, results obtained from the 40 records were then averaged. In the following, all the results are the average values.For each record of AE signal, the AE count rate, denoted as _N AE, was calcu

27、lated by dividing the AE counts by the signal duration. Both a fixed threshold and a floating threshold were used for counting. Since there was no well-defined procedure to choose the threshold value, a wide range of values were tried. For the fixed threshold, a value of 0.04V yielded the best resul

28、ts, as shown in Fig. 4a. It is noted that the AE count rate drops fast as the internal leakage rate decreases. Fig. 4. AE count rate versus internal leakage rateFor the floating threshold, the threshold value was set to be proportional to the rms value of the signal. The resulting AE count rate rema

29、ined at a constant level, nom atter how the leakage rate varied. This is shown in Fig. 4b, where the AE count rate was obtained with the threshold equal to the rms value of the signal. It can be seen that there is no desirable trend in the AE count rate with respect to the leakage rate.5. Predict th

30、e internal leakage rateAs has been shown in the above, the energy content of AE signal is closely related to the internal leakage rate in the water hydraulic cylinder. Therefore, it may be used to predict the internal leakage rate. The error of prediction, then, is of interest. In the following, an

31、empirical model is built to predict the internal leakage rate based on measured AE signals and the error of prediction is analysed with statistical methods. Due to the simplicity in calculation, the rms value Vrms is chosen instead of the energy Ef to characterise AE signals. From the previous exper

32、imental data, the relationship between the AE rms value Vrms and the internal leakage rate Qi is obtained using the least squares method, given byQi=7.86Vrms+0.14.For a measured AE rms value, the internal leakage rate may be predicted with Eq.(7). Suppose the measured AE rms value is Vrms0. A 95% pr

33、ediction interval for the true value of the internal leakage rate,denoted asQi0, is given bywhere Qi is the internal leakage rate predicted by Eq. (7) based on the measured Vrms0 and d is a measure of the width of the prediction interval. Note that d is not a constant but varies with the measured AE

34、 rms value Vrms0. For the range of the internal leakage rates smaller than 1.0 L/min, d is about 0.078 L/min. Eq. (8) means that for the measured AE rms value Vrms0, the true value of the internal leakage rate Qi0 lies inside the intervale Qi d; Qi t dT with 95% confidence. 6. ConclusionsThis paper

35、analysed the characteristics of AE signals generated by internal leakage in a water hydraulic cylinder. Experiments were carefully designed, including the simulation of the internal leakage across the piston seals in a water hydraulic cylinder and the measurement of the internal leakage rate. AE sig

36、nals obtained from the experiments were analysed, in which several AE parameters were extracted from the AE signals and their effectiveness for predicting the internal leakage rate were studied.From the analysis results,some conclusions can be made, as follows:(1) AE signals are sensitive to small i

37、nternal leakage in a water hydraulic cylinder and AE-based methods are able to predict the internal leakage that is smaller than 1.0 L/min.(2) Energy-based AE parameters, whether measured in the time domain or in the frequency domain, are more suitable than the AE count rate and the peak PSD magnitu

38、de to interpret AE signals generated by the internal leakage.References1 G.W. Krutz, P.S.K. Chua, Water hydraulicstheory and applications 2004, in: Proceedings of the Workshop on Water Hydraulics,Agricultural Equipment Technology Conference (AETC 04), Louisville, KY, USA, February 810, 2004.2 E. Tro

39、stmann, Water Hydraulics Control Technology, Marcel Dekker, New York, USA, 1996.3 W. Backe , Water- or oil-hydraulics in the future, in: Proceedings of the Sixth Scandinavian International Conference on Fluid Power,Tampere, Finland, May 2628, 1999, pp. 5164.4 J. Watton, Condition Monitoring and Faul

40、t Diagnosis in Fluid Power Systems, Ellis Horwood, New York, USA, 1992.5 T.T. Le, J. Watton, D.T. Pham, An artificial neural network based approach to fault diagnosis and classification of fluid powersystems, Proceedings of the Institution of Mechanical Engineers, Part I, Journal of Systems and Cont

41、rol Engineering 211 (1997)307317.6 T.T. Le, J. Watton, D.T. Pham, Fault classification of fluid power system using a dynamics feature extraction technique and neuralnetworks, Proceedings of the Institution of Mechanical Engineers, Part I, Journal of Systems and Control Engineering 212 (1998)8797.7 G

42、. Thompson, G. Zolkiewski, An experimental investigation into the detection of internal leakage of gases through valves byvibration analysis, Proceedings of the Institution of Mechanical Engineers, Part E, Journal of Process Mechanical Engineering 211(1997) 195207.8 M. Pietola, R. Ma kinen, P. Va yr

43、ynen, S. Kesanto, J. Varrio, Using a high resolution thermograph in predictive maintenance andfault diagnosis of fluid power components and systems, in: Proceedings of the Fourth Scandinavian International Conference onFluid Power, Tampere, Finland, September 2629, 1995, pp. 719725.机械系统与信号处理, 2007,

44、21: 11151126液压密封完整性调查研究P. Chena, P.S.K. Chua, G.H. Lim摘要：本文中所涉及在液压缸的上线检测密封缺陷. 一个明显的影响密封的缺陷是内部泄漏。因此，所采用的办法是使用合适的技术探测内部泄漏. 所采用的技术涉及由于检测声发射（ AE ）内部泄漏.本文评估了AE信号的各种各样的参量,根据他们估计液压缸内部漏出率。实验分析了AE参量不同的内部漏出率，参量包括根均方(rms)值，计数率、繁忙程度功率谱密度和能量的特征。分析了这些参量和内部漏出率之间的交互关系。结果表示，基于能量的AE参量，特别是均方根值，是更加适当解释内部漏出引起的AE信号。关键词：声

45、发射；液压缸；内部泄漏；声发射计数率；均方根功率谱密度；AE能量1 引言现代水利使用自来水作为液压油，在过去几十年中，由于液压油其固有的优势相比。这些优势包括环境，友善，良好的产品兼容性，并没有发生火警的危险。但是，一些问题，与现代水力仍有待解决。其中最常见的问题是比较大的内部渗漏水液压元件。举例来说，一个水上液压缸可能遭受横跨活塞封印的内部漏出。这归结于非常低粘度的水力液压油。因此，重要的是要监测内部漏出以达到最佳性能和水液压机构的可靠和安全。本文提出的是打算开发一个定量模型通过AE估计在水液压缸的内部漏出流速项目的一部分。它集中于内部漏出小于1.0 L /min。为了塑造AE发信号引起由内

46、部漏出，适当的参量必须首先选择解释信号。所以，试验根据他们的在估计内部漏出率的有效率做了各种各样的AE参量的特征，正如本文所描述。2. 声发射AE被定义作为由迅速能量的释放从局部性引起的瞬变弹性波。AE信号产生液体泄漏。可。波洛克和古德曼等人详细研究了这些信号的物理起源，并且Goodman等报告了各种各样的AE来源机制与从船、坦克和管道的漏出相关。在液压缸的内部漏出情况下，AE信号主要归因于内部漏出导致的动荡。声发射信号可分为两种基本类型。爆裂型声发射是指声发射信号所对应的个人声发射事件，而连续型声发射指的显然是持续的信号水平迅速发生声发射活动。声发射信号的产生是由内部渗漏水液压缸连续型，如图

47、1所示。图1：AE信号所产生的内部渗漏水液压缸一般来说，直接观察的连续声发射信号很少关于AE信号源资料。为了提取更多有用的信息，由声发射信号，首先应该适当地解释信号，通常涉及描绘他们与有些参量。为定量AE调查，任何一个数学模型进行之前参数必须加以界定，。各项参数已用于AE信号特性，无论是在时域和频域。以下简单地描述有些用途广泛的参量连续式AE发信号。AE计数用途广泛，是作为AE活动一项实用措施。当次数信号超出逆门限，这个参量被定义。对于连续式AE， AE计数率是常用的测量AE计数的变异与时间的。均方根(rms)是常用的测量AE信号能量内含。对于包括N样品的AE信号，它的rms值 x 0， x

48、1， x N1其有效值为（1）能量测量的优点是AE信号的能量内含可以直接地与重要物理参量释放能量。上述参量被广泛应用于描述AE信号。上述的参量在时间界域被测量。其外，在频域测量的参量也是利益，例如在频带内和巨大包含的统治频率组分和能量的频率。使用傅立叶变换，对于连续式AE，这些参量可以通过光谱分析得到。功率谱密度（ PSD ）的声发射信号，可使用以下公式连续计算(2)其中P k 是功率谱密度，X k是分离傅立叶变换(DFT) AE信号x n，T是取样周期。PSD的代表分布的信号功率超过频率。AE信号的有些研究在频域的可以在Refs找到。3. 实验由于AE现象的复杂，没有固定得分析方法。所以，介

49、绍实验法调查AE。为了学习AE信号的特征在液压缸的内部漏出引起的，实验设计，如下所述：在液压缸的内部漏出通过连接流量控制阀模仿了与圆筒平行。人工介绍的内部漏出流经了阀门而不是液压缸。这种的优点是模仿漏出率可能容易地是受控的。然而，模仿的有效性要求进一步调查。相信这种方法不可能提供存在于圆筒的动态过程的中意的模仿受内部漏出支配。因此，在当前工作，努力被做了模仿在液压缸的真正的内部漏出。首先研究下面漏出机制然后，然后提出漏出的模仿。为了模仿坚实微粒物质的磨蚀行动创造的比分，文件在当前工作在活塞被用于，做密封水液压缸的表面。图2显示用于实验的被计分的活塞封印。这些封印带领内部漏出070酒吧的压力范围的小于1.0升/分钟。16个得分沿封印的圆周平等地被分布了。维度这些比分测量了与一个没有接触的光学测量系统。图3显示测量系统采取的比分的外形。沿比分的边缘，五个关键被选择了，并且测量了他们的座标。然后测量了得分