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961.
962.
963.
为了能够有效地从轴承早期故障激励的高频振动信号中提取出故障特征信息,基于最优小波包基选取方法和峭度值最大筛选原则,提出了一种改进的小波包分解(WPD)、峭度值指标(KVI)与Hilbert变换相结合的滚动轴承早期故障特征识别方法。计算选取最优小波包基,确定分解层数;采用WPD方法对轴承故障振动信号进行分解,获得若干个Node分量;基于峭度值指标最大原则筛选出有效的Node分量进行信号重构;对重构信号进行包络解调分析,提取出故障特征频率对轴承故障进行诊断。采用建立的方法对凯斯西储大学滚珠轴承外圈、内圈故障实验数据和自行开展的滚棒轴承外圈、滚动体故障实验数据进行了分析与诊断。研究结果表明:该方法能够有效提高故障信号高频分辨率、保留周期性冲击成分,并能准确有效提取出滚珠和滚棒轴承故障特征频率的1~7倍频及其与轴转频调制的系列边频带频率,实现对滚动轴承故障特征的精准识别与故障诊断。 相似文献
964.
To resolve problems of complicated clutter, fast-varying scenes, and low signal-clutterratio (SCR) in application of target detection on sea for space-based radar (SBR), a target detection approach based on adaptive waveform design is proposed in this paper. Firstly, complicated sea clutter is modeled as compound Gaussian process, and a target is modeled as some scatterers with Gaussian reflectivity. Secondly, every dwell duration of radar is divided into several sub-dwells. Regular linear frequency modulated pulses are transmitted at Sub-dwell 1, and the received signal at this sub-dwell is used to estimate clutter covariance matrices and pre-detection. Estimated matrices are updated at every following sub-dwell by multiple particle filtering to cope with fast-varying clutter scenes of SBR. Furthermore, waveform of every following sub-dwell is designed adaptively according to mean square optimization technique. Finally, principal component analysis and generalized likelihood ratio test is used for mitigation of colored interference and property of constant false alarm rate, respectively. Simulation results show that, considering configuration of SBR and condition of complicated clutter, 9 dB is reduced for SCR which reliable detection requires by this target detection approach. Therefore, the work in this paper can markedly improve radar detection performance for weak targets. 相似文献
965.
渐开螺旋面啮合误差的广义圆柱坐标测量原理 总被引:1,自引:0,他引:1
石照耀 《航空精密制造技术》2003,39(2):34-36
论述了渐开螺旋面啮合误差测量的新方法——广义圆柱坐标法,给出了测量原理与实现方法、数学模型和数据处理算式;同时,指出了迄今一些文献中论述啮合误差测量时存在的错误。 相似文献
966.
967.
论述基于经营过程再造的大中型企业MIS设计思想,介绍该系统的结构和功能,给出了在具体实现过程中的关键技术、技术途径和重点难点,提出企业进行管理信息系统设计的新的出发点。 相似文献
968.
针对追求整体协调要求的车身曲面宏观形状测量问题,开发了相应的以激光技术,传感技术、伺服控制技术以及工程应用光学等为基础的自动测量,文章对自动测量的原理、测头随动准则,测头扫描规则以及测点坐标数据采集、传输和处理等内容,均作了较为详细的探讨。 相似文献
969.
970.
A number of advancements for X-ray inspection systems have recently been implemented in the image presented to the operator. Advances in the use of color and image fusion techniques have been developed to maximize the information available in the initial view shown on the monitor. Different techniques are appropriate depending upon the size of the inspection item. Inspection of checked and carry-on baggage requires imaging methods that would not be appropriate for use on larger, more complex objects such as cargo containers or whole trucks. Color-coded presentation of CT images of baggage imposes yet other demands. Comparative images and analyses are presented to support choices for imaging on L-3 Communications systems in terms of the conflicting requirements of cost, sensitivity, resolution, and penetration. A number of enhancements are available to the operator and their influence on system performance is explored. Some experimental enhancements are demonstrated and their trade-offs discussed. The imaging system is ultimately based on hardware, and the choice of detectors, amplifiers, and sampling methods plays an important role in overall performance. Image degradation can be caused by deficiencies in the imaging hardware. Effects such as detector cross-talk and afterglow will negatively impact system performance. Recognition of these factors and steps to mitigate them are discussed. The effect of X-ray source choices such as beam voltage, milliamps, and sampling rate has a direct influence on the image quality and bag dose. Results of theoretical modeling as well as results on actual systems are presented. For a given bag dose, the trade-off between sensitivity, resolution, and penetration are considered. Possibilities for future advancements in imaging for X-ray inspection systems are explored. 相似文献