压电式微定位工作台及其控制系统

为了提高机床的定位精度，研究、设计了一种以柔性铰链为导向元件、压电陶瓷为驱动器的微定位工作台。微定位工作台在滚珠丝杠副驱动的基础上，对工作台进行了二次精定位。给出了工作台的设计简图，并对其动力学模型进行了分析，结合检测装置和微机控制系统，设计了基于前馈控制同数字PID反馈控制相结合的复合控制的微定位控制系统。实测表明，微定位工作台定位分辨率可达到0．01μm，可满足精密、超精密加工的需要。     

精密导轨的光电测试

长刻机具有精密丝杆、精密导轨和工作台。用光电自准值仪和桥板测试导轨，给出了三台刻机导轨的测试结果，还对一台长刻机和另两台机床的工作台进行了测试工作。     

IC加工及检测装备超精密工作台自标定技术研究

在对超精密工作台自标定相关文献综述的基础上,基于刚体运动方程和非线性最优化方法,提出了一种超精密工作台自标定算法。仿真结果表明:该算法可以实现超精密工作台的标定,并且其最终标定精度与辅助测量装置精度无关,只受自标定过程中随机测量噪声的影响。     

微细加工用双足式大行程微动工作台的研究

大行程微动工作台是微细加工设备的重要组成部分,针对当前微动工作台行程小,或行程较大而其检测控制复杂等不足,提出了一种“双足式移动”的新原理,并研制了一台双足式大行程微动工作台。该工作台由两套进给和支承微位移器来实现进给和支承,在研究中,提出了玫套检测控制系统,可对工作台的移动位移大小和方向进行实时控制,这种检测控制系统可以使工作台按照任意的路径进给。该工作台还具有很多优点：比如分辨率高、无导轨、无     

弹簧导轨在超精密工作台上的应用

本文根据大规模、超大规模集成电路微细加工超精密工作台的要求,提出了一种能作严格直线运动的微位移工作台,这种工作台由八根弹簧片组成的弹簧导轨支承。文中给出了这种导轨静位移的计算方法,并分析了其预紧力的要求。     

采用实心铁磁体的磁悬浮工作台的系统辨识

在超精密磁悬浮工作台中，作为衔铁被悬浮的工作台，如果可以不采用硅钢片而直接使用实心铁磁材料，则可以大大简化加工工艺，并提高工作台的刚度，但实心铁磁材料的电涡流效应对工作台性能的影响需要由实验加以确定。针对这一问题，对一个工作台采用电工纯铁的实际系统进行了研究。实验数据及系统辨识表明，由于电涡流效应，实际物理系统的特性与理论模型有明显的差异，如果不考虑这些差异，将很难获得令人满意的控制效果。另一方面，只要对系统实施辨识，并根据辨识的结果设计磁悬浮控制器，即使采用实心铁磁材料，仍可获得良好的控制性能。     

超精密位移台计量特性的差动式平面镜干涉溯源分析

超精密纳米位移台常用于扫描探针显微镜、光学显微镜等高精度分析仪器中,其纳米机械性能的精密计量和校准对显微测量系统的性能起着关键作用.基于一种双通道结构差动式平面镜干涉测量与校准方法(英国国家物理实验室),文中对一种超精密位移台的关键计量特性进行了定量研究.构建了基于现场可编程门阵列(FPGA)和LabView的高精度稳频激光干涉数据采集和数据解码系统,使其可溯源超精密纳米位移台的准静态校准计量特性.进一步地,利用该干涉测量系统对超精密位移台的计量特性进行了校准和分析.测试结果显示,该激光干涉校准系统在准开放环境中的背景噪声低于10 pm/√Hz;该超精密位移台具有优良的纳米机械性能,其线性度低于1.2×10-4,分辨率达40 pm,重复性和稳定性较好.上述对校准设备准静态性能和对纳米位移台计量特性的测试结果表明,所提出的方法和系统能够对纳米位移台进行计量,从而用于小于几皮米的皮米级压痕测量以及原子尺度上的大范围测量.     

变频技术在精密磨加工上的应用

变频技术在精密磨加工上的应用王永强（跃进汽车集团公司转向器厂，南京，２１００１２）我厂现有６台精密螺纹磨床，用于生产转向器的心脏部件螺母和螺杆。由于头架、工作台传动部分使用直流电机驱动，调速部分使用的是可控硅分立元件调压调速系统，因此调速性能差，加上...     

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.     

掩模移动曝光系统精密定位工件台研制

为满足掩模移动曝光技术制作微光学元件的要求,研制了接近式曝光系统中使用的x-y二维精密移动工件台.该工件台由x-y二维整体手动工作台子系统、x-y二维掩模精密移动台子系统和承片台子系统组成.利用一个方导轨和两对V形导轨组成的滚动导轨副实现了x向和y向精密移动的导向功能;利用驱动器、电机、光栅、细分卡、单片机构成的闭环控制系统保证了x和y向的运动精度;在气浮的作用下,利用掩模版靠平基片实现了调平功能;利用差动螺旋机构和1∶2杠杆缩小机构实现了间隙的调整功能.经检测,工件台在8 mm的工作行程范围内,沿x,y方向移动的直线性分别达到了4"和3",两个方向的正交性达到了10",运动定位精度达到了1.2 μm.     

High-frequency nonlinearity analysis of common-emitter anddifferential-pair transconductance stages

Equations describing the high-frequency nonlinear behavior of common-emitter and differential-pair transconductance stages are derived. The equations show that transconductance stages using inductive degeneration are more linear than those using capacitive or resistive degeneration, and that the common-emitter transconductance stages are more linear than the differential-pair transconductance stages with the same bias current and transconductance. The nonlinearity equations can also be used to explain the class AB behavior of the common-emitter transconductance stage with inductive degeneration     

A four-stage FM broadcast audio peak limiter

The design of a peak limiter processor for FM broadcast audio is described. The limiter has four gain control stages. The basic peak limiting function is performed in the first and second stages by a slow-attach-slow-release stage followed by a fast-attack-fast-release stage. Preemphasis control is performed in the third and fourth stages, which are part of a filter that emulates the transmitter preemphasis network. A peak clipper at the output of the preemphasis controller provides protection from overmodulation by short duration peaks that are not controlled by the four limiter stages     

Common-mode rejection ratio of differential amplifiers

The common-mode rejection ratio (CMRR) of differential amplifier stages is treated by means of the matrix analysis of networks with the amplifier gain elements represented as four-pole devices. Two generalized CMRR equations are obtained in terms of imbalances in the transconductance and open-circuit voltage gain parameters of the composiste devices for both the resistor-loaded stage and the current-mirror-loaded stage, respectively. The nonlinear characteristic of the current mirror load has also been derived, and it is demonstrated that the high load sensitivity of CMRR in stages loaded by current mirrors is due to the mirror's nonlinearity. The effects of the second stage of an operational amplifier on its CMRR are considered. The CMRR expressions for a number of typical stages incorporating source resistances are given, and the experimental results with these stages are discussed in detail.     

Comparison of Replacement Strategies for Items that Fail

Replacement strategies applicable to items which fail with monotonically increasing failure rate are considered. In particular, the important characteristics of n-stage and 1-stage strategies are compared. This study, though somewhat tutorial in nature, reveals interesting properties which are useful in selecting an appropriate strategy. In general, n-stage strategy has economic advantage over the corresponding 1-stage strategy. The advantage is obtained by transferring failures from stages where failure costs are high to stages where these costs are low. In many cases, a quick examination of the system will reveal whether n-stage strategy will be advantageous or not. Subsequently, based on a detailed study an appropriate n-stage strategy can be designed. The more stages the greater would be the economy, up to where practical considerations and increasing transfer costs will limit the number of stages.     

Forms of probability-density functions obtainable from summed m sequences

The letter discusses the sums of m sequences generated by a feedback shift register where the summed sequences are not necessarily from successive stages. A method for obtaining all the possible probability-density functions is given. The particular case of five stages is studied in detail. It is found that, for this case and a number of other cases tested, the rth moment (or central moment) is identical for all the situations in which there are at least r interdependent stages in the sum.     

A Timing-Driven Approach to Synthesize Fast Barrel Shifters

In modern digital signal processing and graphics applications, the shifter is an important module, consuming a significant amount of delay. This brief presents an architectural optimization approach to synthesize a faster barrel shifter block, which can be useful to reduce the delay of the design without significantly increasing the area. We have divided the problem of generating the shifter into two steps: (i) timing-driven selection of multiple stages for merging, and (ii) the design of the merged stage. In our proposed method, we define the notion of dual merged stage, where two stages are merged and the triple merged stage, where three stages are merged into a single composite stage. These merged stages are identified by using a timing-driven algorithm and are used in conjunction with some single stages of the traditional barrel shifter. The use of these merged stages helps reduce the depth of the proposed barrel shifter architecture, thereby improving the delay. The timing-driven nature of our algorithm helps produce a faster implementation for the overall shifter block. We have evaluated the performance of our design by using a number of technology libraries, timing constraints and shifter bit-widths. Our experimental data shows that the shifter block generated by our algorithm is significantly faster (10.19% on average) than the shifter block generated by a commercially available datapath synthesis tool. These improvements were verified on placed-and-routed designs as well.     

On stages of knowledge growth in the management sciences

The authors invoke Rostow's theory of economic development, the kinetics of chemical reactions, and the empirically based theory of the evolution of technologies, to address, by analogy, the stages of knowledge development in management science. They show that different strategies dominate research at the various stages of its development. The stages are related to the level of knowledge accumulated and the relative difficulty of teaching/learning the accumulated knowledge     

DC-20 GHz N×M passive switches

High-order, bidirectional, DC-20-GHz switch networks are discussed. Single-chip 1×2, 1×4, and 2×2 switch MMICs have been demonstrated. Multiple chips have been used to demonstrate 4×4 and 1×16 switches. The switches all use a combination of series and shunt passive FET switching elements. The 1×4 switch is made of a single stage of switching elements, rather than the usual two stages of 1×2 switches. The 2×2 switch is comprised of two stages of 1×2 switches. The multiple-chip 4×4 switch is made of four stages of 1×2 switches (using the 2×2 switch MMICs). Two stages of 1×4 switches are used to make the 1×16 switch     

Buffer-based switched-capacitor gain stages

New unity-gain buffer-based switched-capacitor S/H circuit and gain stages are described which have low sensitivity to buffer gain and offset voltage, and are only moderately sensitive to stray capacitances. The circuits are simple, require fewer switches and less capacitance and offer higher speed, lower noise and lower DC power consumption than op-amp based gain stages     

癌细胞细胞周期的紫外吸收特性

对了宫颈癌细胞(Hela细胞)在细胞周期G1、S、G2和M期的紫外吸收光谱特性差异进行了分析.在细胞周期各时相的光谱峰值存在位移,这些位移说明Hela在细胞周期变化过程中芳香族氨基酸生色刚发生的变化导致了不同时相的紫外吸收光谱的差异.从而得出结论:细胞周期各时相的紫外吸收光谱存在显著差异,能够反映细胞生长变化过程中蛋白质的变化.