大型凹球面数控加工工艺研究

以压力杆和支座两类零件的加工为例,分析了大型凹球面的数控加工方法.选择以铣代车的加工工艺方案,对不同的刀具、走刀路线进行了分析比较,得到合理的铣削加工方案,并进行了实际加工验证.结果表明:采用合理的以铣代车工艺可提高生产效率和零件加工表面的质量,降低加工成本.     

Versatile resonance-tracking circuit for acoustic levitation experiments

Objects can be levitated by radiation pressure forces in an acoustic standing wave. In many circumstances it is important that the standing wave frequency remain locked on an acoustic resonance despite small changes in the resonance frequency. A self-locking oscillator circuit is described which tracks the resonance frequency by sensing the magnitude of the transducer current. The tracking principle could be applied to other resonant systems.     

凹球面激光直写系统电控误差分析

高精度激光直写技术是光、机、电综合运用的前沿技术,广泛应用于精密仪器、设备等高新技术领域.而减小电控误差是凹球面激光直写技术的难点.介绍了凹球面自动调焦激光直写系统原理,分析了步进电机驱动的凹球面激光直写系统的电控误差,步进电机的步距误差,动态误差以及传动间隙空走误差等.同时给出了理论公式,并结合实例进行了精度对比分析;针对各个误差源,提出了提高步距角精度、避开共振频率、补偿空走误差等减小误差的方法.最后给出了激光直写纬线程序流程图.     

Interaction of acoustic surface waves induced by inter-digital transducer with wall thinning defect in pipe structure

Most structural health monitoring (SHM) systems require transducers permanently attached to or integrated with the monitored structure to form a type of smart structure. It is difficult to permanently attach traditional ultrasonic transducers for non-destructive testing of structures for health monitoring. However, inter-digital transducers (IDTs) can be considered for on-site SHM because of the small size and economic efficiency of the IDT sensor. In this paper, an alternative sensor approach is proposed using IDT rather than conventional transducers to identify the interaction of surface acoustic waves (SAWs) with a wall-thinning defect. The SAWs generated by IDT sensors are modeled using the finite element analysis method. Acoustic wave propagation behavior in plate and pipe structures was reviewed, and the effect of the curvature of curved plate was investigated. From the interaction behavior observed between SAWs and a wallthinning defect in the pipe, which was determined using numerical simulation and tests, a novel concept is proposed for characterizing wall-thinning defects in pipelines.     

Excitation of a circular-aperture transducer with an echo pulse reflected from a spherical surface

A theoretical model is suggested that allows one to explain peculiarities of the frequency response of echo signals at the output of a receiving transducer versus geometrical parameters of reflecting surfaces. It is shown that the way the instantaneous frequency of signals at the output of the receiving transducer changes depends on the curvature radius of reflected wavefront at the receivingtransducer aperture. It has been established that the frequency modulation of the pulsed echo signal is due to nonuniformity of the distribution of the phase of acoustic signal at the receiving-transducer aperture; this can be characterized by the radii of Fresnel zones that correspond to the reflected wavefront in relationship to the aperture radius of the circular transducer. Data on the frequency modulation of pulsed echo signals expressed in terms of dimensionless parameters (normalized frequency deviations) that were obtained experimentally and calculated by the suggested theoretical model demonstrate fair qualitative and quantitative agreement.     

Absolute interferometric test for high numerical-aperture spherical concave surfaces: Gravitational effect

Spherical concave surfaces with high numerical apertures are required in industry for lithography optics at ultraviolet and X-ray wavelengths. Among the systematic errors in these spherical-surface test, the gravitational deformation has not been separated from the other optical aberrations. We utilized a two-surface comparison method to quantify the gravitational deformation in a vertical Fizeau interferometer. Certain aberrations vary with rotation around the optical axis. We averaged the ordinary aberrations and isolated the aberration caused by gravitational deformation. Experimental results show that a 4-in concave surface with an F-number 0.75 reveals to have a gravitational deformation of 7 nm peak-to-valley.     

Broadband electrostatic acoustic transducer for ultrasonic measurements in liquids

A broadband capacitive electrostatic acoustic transducer (ESAT) has been developed for use in a liquid environment at megahertz frequencies. The ESAT basically consists of a thin conductive membrane stretched over a metallic housing. The membrane functions as the ground plate of a parallel plate capacitor, the other plate being a dc biased electrode recessed approximately 10 mum from the electrically grounded membrane. An ultrasonic wave incident on the membrane varies the membrane-electrode gap spacing and generates an electrical signal proportional to the wave amplitude. The entire assembly is sealed for immersion in a liquid environment. Calibration of the ESAT with incident ultrasonic waves of constant displacement amplitude from 1 to 15 MHz reveals a decrease in signal response with increasing frequency independent of membrane tension. The use of the ESAT as a broadband ultrasonic transducer in liquids with a predictable frequency response is promising.     

斜角进刀旋风铣削外球表面

一种斜角进刀旋风铣削加工外球表面的工艺方法,可以有效地提高生产效率和外球的尺寸精度,降低外球表面的形状误差.     

随钻声波发射换能器宽频阻抗匹配设计及实验

发射换能器是随钻声波测井仪器的核心部件,其工作带宽及辐射声波能量的强弱是仪器的关键技术指标。换能器是一个非线性容性负载,可以采用阻抗匹配的方式增强有功功率并拓宽工作频带。本文将换能器多模态等效电路与阻抗匹配网络结合,利用电路网格方程对元件参数进行求解。最终在消声水池进行声场测试,观测换能器有功功率、声场辐射声压、发射电压响应等电、声特性,综合评估阻抗匹配网络的效果,为后续的随钻仪器研发及实验测试提供帮助和指导。实验结果表明,本文所设计的阻抗匹配网络能够明显改善换能器的声波辐射性能,频带宽度拓宽3.3倍,有功功率提高1.7倍,声压增强1.8倍,发射电压响应提高5 dB,在12～16 kHz的频带内发射电压响应最高可达125 dB。     

大尺寸球面加工装置

球面加工一直是决定轴流泵产品质量的关键因素。充分利用卧式车床的结构特点，设计了一种新型的大尺寸球面加工装置，并对其结构特点、工作原理、使用注意事项进行了介绍。     

激光直写凹球面网栅的电控实现

凹球面网栅激光直写系统采用同心结构及稳光控制保证了光强不变,提出了周期纬线纬纬相交形成网栅的图形结构,应用调节角速度的控制算法,确保激光直写光斑在不同的纬度以不同角速度扫描,始终保持线速度和曝光量恒定,实现了在凹球面上以恒定曝光量激光直写网栅。分析了网格周期、角速度和纬线弧长等关键参数,设计了控制程序。在通光孔径60 mm的普通玻璃凹球面进行了多组激光直写试验,设定周期450 mm~800 mm,线速度1 mm /s ~20 mm/s,经显影、定影后由读数显微镜测得网格实际周期与设定周期误差在±3%以内,原子力显微镜测得线宽小于5 mm,线条侧壁陡直、平行,具有较好的均匀性,满足设计要求。     

内球面旋风铣削

铣刀旋转轴线与工件旋转轴线交叉成斜角,铣刀边旋转边沿旋转轴线进给加工内球面。分析结果表明,可以有效地提高生产效率和内球面的尺寸精度,降低内球表面的形状误差。     

Fowler-Nordheim theory for a spherical emitting surface

In tests on a field emitter whose dimensions and work function were known, Fowler-Nordheim (F-N) theory as usually stated for a planar emitter was found to give poor agreement with observations. The effect of curvature of the emitting surface has been modelled by including (a) non-linear variation of potential with distance from the surface; (b) the consequent changes in the exponent and pre-exponential terms in the F-N expression for current; and (c) the variation of current density over the surface, modelled by an effective solid angle. Application of the resulting expression to the measured data gives estimates for apex radius which agree much more closely with the measured value than the value from planar theory does.     

同心扫描法制作凹球面等距网栅的误差分析

纬线与纬线相交可形成球面等距网栅,而采用"同心扫描"的运动方式可在凹球面上生成纬线。"同心扫描"要求直写物镜光轴、直写物镜水平转轴、工件回转轴和工件分度轴四轴交于工件凹面球心。采用两两相交误差几何分析的方法,得到了同心误差与离焦量和栅距误差的变化关系:随着同心误差增加,系统离焦量和栅距误差也增加,且二者的变化趋势基本一致。因为网栅线宽一般要求达到微米量级,与之匹配的栅距则往往为几百微米,所以栅距误差与栅距相比可以忽略,系统离焦量对网栅线宽的影响却必须认真考虑。采用几何光学基本公式对物镜系统的进一步分析表明,为了制作细且均匀的网栅线条,必须采用小光斑,而小光斑对应的焦深也小,从而要求离焦量小,对同心误差要求严格;反之,则可放宽对同心误差的要求。     

自攀爬式幕墙清洗机器人设计

以国家大剧院椭球壳体的清洗为应用背景,设计了首台复杂曲面自攀爬式机器人样机。首先简单介绍了机器人系统的机械结构组成;控制系统采用基于CAN总线的网络结构,并以P80C592单片机为核心构成分布节点控制器,软件采用模块化设计;在此基础上对机器人运动功能实现进行了讨论。作业实验表明样机系统的组成原理合理,机械结构和控制系统方案成功可靠。     

Design of a piezoelectric transducer cylindrical phase modulator for simulating acoustic emission signals

To conveniently carry out the pipeline leak experiment in a laboratory, leak acoustic signals are simulated by using the converse piezoelectric effect of a piezoelectric transducer (PZT) cylindrical phase modulator. On the basis of the piezoelectric equations and electromechanical equivalence principle, the transfer function of a PZT cylindrical phase modulator is delivered. A PZT cylindrical phase modulator is designed, and the numerical simulation is conducted. Results prove that the PZT cylindrical phase modulator can effectively simulate leak acoustic emission signals when the frequency is lower than 25 KHz. __________ Translated from Journal of Beijing University of Technology, 2006, 32(8): 683–687 [译自: 北京工业大学学报]     

用于钢管缺陷检测的电磁超声传感器优化设计研究

电磁铁是电磁超声传感器的重要组成部分，它与钢管构成的磁场是电磁超声传感器产生超声波的基础。本文建立磁感应强度与分子振动幅值的关系函数，用均匀实验设计对电磁超声传感器进行优化设计，实现了电磁超声传感器的小型化。实验研究证明，优化设计方法是正确的。     

Evaluation of discrete displacement transducer by spectral analysis of surface roughness

A discrete displacement transducer using an optical technique and attached to a commonly used stylus instrument is described. The proposed transducer plays an important role in generating a digital output of surface profile from the viewpoint of sampling error. The working accuracy is discussed with reference to the spectral analysis of surface roughness.