FREEZE: A Celebration of Design in the Modern North

Brian Carter reports from Anchorage, in Alaska, where he co-curated an art and architectural event in early 2009 that set out to celebrate the climate, landscape and light of the icy north. Copyright © 2009 John Wiley & Sons, Ltd.     

基于电流变效应的超精密工件台研究与展望

通过分析超精密工件台系统的研究现状和存在问题及电流变液ERF的机理和应用现状,提出"基于ERF半主动阻尼的直线电机驱动-气浮/磁浮导轨"纳米级超精密工件台系统.介绍了国内外相关研究,分析了此工件台系统具有的特性及尚待解决的问题.     

转台伺服控制系统中数字化速度测量方法的研究

介绍了伺服系统的两大类测速方法,即模拟测速和数字测速。详细讨论了数字测速的方法实现和特点,并作了性能比较。最后对数字测速的方法提出了展望。     

纸盒模切板CAM系统中自动锯槽机的机械设计

自动锯槽机是纸盒模切板CAM系统的重要设备,为了保证加工精度和降低设备成本,故采用机械锯槽工艺和CNC技术相结合的方案,本文着重介绍了整机的结构和数控工作台的设计要点.     

永磁同步电机直接功率控制基本原理

在对永磁同步电机有功功率和无功功率与系统稳定运行所需转矩和磁链之间的内在关系进行分析的基础上,提出了永磁同步电机基于开关表的直接功率控制新方法.该方法通过计算瞬时有功功率和瞬时无功功率的两个滞环输出,并根据定子磁链所在的扇区,从瞬时功率开关表中查询出合适的开关电压矢量进行输出,从而对瞬时功率进行直接控制.本文以无功功率等于零为控制目标,即需把无功功率控制在零附近很小的范围内波动,使得在电机输出同样有功功率的条件下,提高了电机的功率因数,使无功功率降到最小,达到了节能的目的.仿真和实验结果证明了该控制方案的有效性和正确性,该方法在节能电机驱动系统中有着广阔的应用前景.     

基于信息熵最优约简算法的电网故障诊断模型

介绍粗糙集理论及信息熵约简方法,应用粗糙集理论对电网故障样本数据进行分析统计,建立决策表,采用信息熵约简算法对其进行条件属性约简,得到一组最小知识系统,再用粗糙集值约简方法对其进行简化,得到一组故障诊断的最小决策规则集,结合模型进行分析,证明该方法简便、快速、有效。     

Application of Cooling Water in Controlled Runout Table Cooling on Hot Strip Mill

The controlled runout table cooling is essential in determining the final mechanical properties and flatness of steel strip. The heat of a hot steel strip is mainly extracted by cooling water during runout. In order to study the heat transfer by water jet impingement boiling during runout, a pilot facility was constructed at the University of British Columbia. On this pilotfacility, the water jet impingement tests were carried out under various cooling conditions to investigate the effect of processing parameters, such as cooling water temperature, water jet impingement velocity, initial strip temperature, water flow rate, water nozzle diameter and array of water nozzles, on the heat transfer of heated strip. The results obtained contribute to the optimization of cooling water during runout.     

介绍一种声震动靶

文章介绍一种用CA-YD系列压电式加速度传感器来测试由雷管爆炸而引起的声震动,用此经过放大和处理的声震动信号来触发NLG202G型系列电子测时仪器,从而测出雷管的起爆时间,即所谓的声震动靶,简称声靶.此方法在长期的使用过程中证明是方便可行的,适用于雷管起爆时间等的测量.     

基于等效误差法的直线电机XY平台二阶滑模控制

对于直线电机驱动XY平台,系统动态的非线性、系统不确定性因素以及曲线轨迹的轮廓误差模型相对复杂等问题影响其轮廓加工精度。采用适用于多轴非线性运动系统轮廓控制的等效误差法,建立可用于一般曲线跟踪且容易计算的XY平台等效误差非线性模型。运用二阶滑模控制方法进行轮廓控制器的设计,通过连续控制量使滑模面及其时间导数在有限时间内趋近于零,削弱抖振的同时抑制不确定性因素对系统性能的影响,使直线电机XY平台达到高加工精度要求。理论推导与仿真结果表明,所设计控制系统能有效提高XY平台的轮廓加工精度。     

Power quality improvement using DPC controlled three-phase shunt active filter

This paper presents a new control method entitled direct power control (DPC) for shunt active power filter (APF), which is applied to eliminate line current harmonics and compensate reactive power. Its main goal is to rebuild active and reactive source powers to be compared to references values using hysteresis control. The active power reference is issue of DC-side of inverter and reactive power reference is set to zero for unity power factor. The outputs of hysteresis controllers associated with a switching table, control the instantaneous active and reactive power by selecting the optimum switching state of the voltage source inverter (VSI). A theoretical analysis with a complete simulation of the system and experimental results are presented to prove the excellent performance of the proposed technique.