交流伺服系统在高速数字化电阻焊机中的应用

基于总线形式由PLC与交流伺服系统组成的位置伺服同步跟踪系统能够使机器能快速同步，实现高速电阻焊机数字化过程控制。通过由PLC控制交流伺服电动机多轴联动系统取代传统的机械联动机构，实现机器各运动之间运动的协调，保证各个相关动作能够快速准确同步运行，不仅使各运动关系之间的“机械锁合”转变为“电子锁合”，同时简化凸轮、无级变速机和万向联轴器等复杂的机械结构，系统的可靠性，从而提高整机的工作性能。     

组大鼠毛细血管内的镧盐颗粒穿过血脑屏障进入到脑组

生长发育期铅接触可使血脑屏障通透性增加,脑毛细血管内皮细胞紧密连接蛋白occludin表达降低可能是血脑屏障通透性改变的主要分子机制之一;铅接触的同时适量补充铁元素,可保护由慢性铅接触所造成的血脑屏障紧密连接的损伤.Effects of iron suppleme     

Temperature uniformity of the glass panel heated in the infrared heating chamber

An analysis has been carried out to investigate the effect of the reflectivity on the temperature distribution of a glass panel by infrared radiant heating. Halogen lamps are used to heat the panel, located near the top and bottom of the rectangular chamber. The thermal energy is transferred from the lamps to the panel only by radiation and it is considered by using view factor. The conductive transfer is limited inside the panel. The results show that the uniformity of the temperature distribution of the panel is improved and, at the same time, the time for heating increases as the wall reflectivity increases. The temperature difference between the center and the corner reaches a maximum in the early stage of the heating process and then decreases until it reaches a uniform steady-state value.     

Characterization of 3D pore nanostructure and stress-dependent permeability of organic-rich shales in northern Guizhou Depression,China

The three-dimensional (3D) pore structures and permeability of shale are critical for forecasting gas production capacity and guiding pressure differential control in practical reservoir extraction. However, few investigations have analyzed the effects of microscopic organic matter (OM) morphology and 3D pore nanostructures on the stress sensitivity, which are precisely the most unique and controlling factors of reservoir quality in shales. In this study, ultra-high nanoscale-resolution imaging experiments, i.e. focused ion beam-scanning electron microscopy (FIB-SEMs), were conducted on two organic-rich shale samples from Longmaxi and Wufeng Formations in northern Guizhou Depression, China. Pore morphology, porosity of 3D pore nanostructures, pore size distribution, and connectivity of the six selected regions of interest (including clump-shaped OMs, interstitial OMs, framboidal pyrite, and microfractures) were qualitatively and quantitatively characterized. Pulse decay permeability (PDP) measurement was used to investigate the variation patterns of stress-dependent permeability and stress sensitivity of shales under different confining pressures and pore pressures, and the results were then used to calculate the Biot coefficients for the two shale formations. The results showed that the samples have high OM porosity and 85% of the OM pores have the radius of less than 40 nm. The OM morphology and pore structure characteristics of the Longmaxi and Wufeng Formations were distinctly different. In particular, the OM in the Wufeng Formation samples developed some OM pores with radius larger than 500 nm, which significantly improved the connectivity. The macroscopic permeability strongly depends on the permeability of OM pores. The stress sensitivity of permeability of Wufeng Formation was significantly lower than that of Longmaxi Formation, due to the differences in OM morphology and pore structures. The Biot coefficients of 0.729 and 0.697 were obtained for the Longmaxi and Wufeng Formations, respectively.     

石墨触点在交流接触器中的应用

通过作者参与研制的“新型交流接触器”滑动旋转结构,文章对开断电路时产生的电弧引起触点电蚀机理及削减不良能量变换进行了讨论,并给出了应用石墨替代贵金属作触点完成电路转换的方法。     

高压直流套管电压监测器的研究

介绍了高压直流套管用电压监测器的作用、计算原理、技术参数、结构特点、试验项目及结果。主要性能指标:输出两路110VAC/5VA信号电压,输出信号与高压交流分量关联精度≤3%,高压交流分量与输出信号电压相位偏差≤30°,输出三路继电器报警120 VAC/125VAC/130VAC。安装到BJR-±204/2 800高压直流套管上完成了联调。     

偏转线圈垂直绕线机的数控改造

介绍了偏转线圈垂直绕线机的数控改造方案及技术关键,给出了简单方便的垂直线圈绕线程序的编制方法。     

永磁直线电动机加速度反馈位置控制系统研究

分析了永磁交流同步直线电动机的数学模型,提出了基于扰动器的加速度反馈位置伺服控制系统,并研究了可选参数对其性能的影响。     

评价交流接地网施工及运行可靠性的相关问题分析

结合现场测试情况以及解决部分接地施工验收争议问题的经验,提出接地网评价的主要指标,如:电气完整性测试结果、接地电阻校核、接触及跨步电压校核、接地网导体通流容量验算、所处土壤的电阻率及pH值。以上指标均能定量,易于形成评价分值。对新建投运与运行多年两类情况,各指标所占权重应有差异。在运行中的发、变电站内,采用变频电流注入,可降低测试接触及跨步电压的不确定度。因土壤电阻率与入地电流频率间有关系,采用变频不宜偏离工频超过10Hz。在不同温、湿度条件下测量,接地网电阻有一定差异,这种差异有时会达到25%。     

方波信号发生器及场效应管驱动器

本文介绍方波信号发生器及场效应管驱动器的原理与设计。实验证明,设计的方波信号发生器与场效应管驱动器工作稳定可靠,所研制的方波交流高频弧焊电源已成功地对薄钢板进行了焊接。