【正文】 設(shè)計(jì) 第 4頁 共 13頁 井岡山大學(xué)外文翻譯用紙 leakage in hydraulic cylinders. In the following, the leakage mechanism is first studied。 Root mean square。 Internal leakage。機(jī)電 工程學(xué)院 機(jī)械系機(jī)械設(shè)計(jì)制造及其自動(dòng)化班 學(xué)生 毛祖慶 畢業(yè)設(shè)計(jì) 第 1頁 共 13頁 井岡山大學(xué)外文翻譯用紙 Mechanical Systems and Signal Processing, 2020, 21: 1115–1126 A study of hydraulic seal integrity P. Chena, . Chua, . Lim Abstract: The work described in this paper involved online detection of seal defects in a water hydraulic cylinder. An obvious effect of seal defect is internal leakage. Therefore, 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 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 rootmeansquare (rms) value, the count rate, the peak magnitude of power spectral density and the energy. The correlations between these parameters and the internal leakage rate were analysed carefully. The results show that energybased AE parameters, especially the rms value, are more suitable to interpret AE signals generated by internal leakage. Keywords: Acoustic emission。 Water hydraulic cylinder。 AE count rate。 Power spectral density。 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 present work, to make scores on the piston seal surfaces of a water hydraulic cylinder. Fig. 2 shows the scored piston seals used in the experiments. These seals lead to an internal leakage smaller than L/min for the pressure range of 0–70 bar. Sixteen scores were equally distributed along the circumference of the seals. The dimensions of these scores were measured with a noncontact optical measurement system. shows the profile of a 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 could be obtained. Fig. 2. The 16score piston seals. Fig. 3. The profile of a score. 機(jī)電 工程學(xué)院 機(jī)械系機(jī)械設(shè)計(jì)制造及其自動(dòng)化班 學(xué)生 毛祖慶 畢業(yè)設(shè)計(jì) 第 5頁 共 13頁 井岡山大學(xué)外文翻譯用紙 4. Experimental results In 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 signal 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 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 welldefined procedure to choose the threshold value, a wide range of values were tried. For the fixed threshold, a value of yielded the best results, 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 rate For the floating threshold, the threshold value was set to be proportional to the rms value of the signal. The resulting AE count rate remaine