挠性航天器姿态机动控制的主动振动抑制

针对喷嘴作为执行机构的挠性航天器大角度姿态机动时帆板的振动抑制问题,提出了伪速率(PSR)调制式喷气控制和基于压电陶瓷(PZT)材料的主动振动控制技术相结合的复合控制方法。首先,基于Lyapunov方法设计PD反馈控制器保证姿态的渐近稳定和模态振动的衰减性;为了减少喷嘴的非线性开关控制激起的挠性结构振动,采用PSR的准线性调制技术使喷嘴产生所需要的控制力矩的脉冲序列,从而在完成大角度姿态机动的同时抑制振动幅值较大的挠性模态的振动;通过设计正位置反馈(PPF)补偿器以增加结构的阻尼来进一步抑制挠性结构残余振动。最后,将该方法应用于航天器大角度rest-to-rest(静止到静止)姿态机动的仿真研究,结果表明:该方法不仅能够使航天器完成对姿态的机动,而且能够抑制帆板的挠性振动。     

A statistical analysis of weight and cost parameters of spacecraft with special reference to ‘Aryabhata’

The available data on the weights of several NASA and ESRO spacecraft have been statistically analysed using the regression analysis technique and empirical relationships of the type W_T = AW{kx/β} have been established, where W_T is the total weight of the spacecraft, W_x is the weight of one of its chosen subsystems andA and β are constants for the chosen subsystem. It is found that the weight data ofAryabhata show a fairly good fit with these empirical relationships. Further, using an established statistically derived relationship for NASA satellites, involving the cost of a spacecraft and its weight parameters, it is found that the cost ofAryabhata is much lower than that of other NASA satellites of comparable weight. The implications of these results are briefly discussed.     

Video imaging of debris clouds following penetration of lightweight spacecraft materials

The structure of debris clouds following hypervelocity penetration of thin materials is of special interest to spacecraft designers--it forms the basis for damage equations from meteoroids, orbital debris, and other kinetic energy threats. Today, video imaging offers the experimenter a new view into the structure and development of debris clouds following penetration of these thin materials. This technique is of special interest in its application to lightweight, thin, or other low density target materials whereflash x-ray experimental imaging has proven difficult to apply, including fibrous materials (such as Nextel and Kevlar), multi-layer insulation (MLI), aluminum foam, and so on.

This paper has two purposes: (1) to describe new developments in video imaging of debris clouds using high-speed multi-frame cameras (with frame rates of up to one million frames per second) and still video cameras with extremely high shutter speeds (as short as 3 nanoseconds), and (2) to present video images of debris clouds from light gas gun testing of aluminum and nylon spheres penetrating at 5 to 7 km/sec through thin aluminum plates, aluminum foam, and multi-layer insulation materials. The paper then compares the video images results to previous flash x-ray images (Piekutowski, 1997) and comments on similarities and new features that may be observed using this improved experimental technique.     

视轴偏心三轴跟踪机架指向精度分析

本文分析了实现大范围空间光电跟踪的视轴偏心三轴跟踪机架的轴系误差.在刚体动力学的基础上,利用姿态变换的方法对视轴偏心的这种新型跟踪机架进行分析,推导出了机架指向精度的具体算法,探索了计算视轴偏心的三轴跟踪机架误差及误差分配的新方法,并针对一跟踪架的具体误差进行了指向精度计算.其中,垂直度误差对指向精度影响最大.     

一种灰度成像扩展目标跟踪方法

灰度图像色彩信息贫乏会导致易陷于局部相似,使跟踪点发生漂移。针对此问题,提出了基于目标成像空间域与特征域分布的改进直方图模式扩展目标跟踪算法。以基于像素位置和像素灰度值的直方图模式作为目标模式;相似度测量采用基于Bhattacharyya系数定义的距离;用均值偏移迭代进行匹配区域搜索;通过建立卡尔曼预测跟踪策略解决目标被遮挡时的跟踪问题。试验结果表明,采用该算法,跟踪点漂移由原来十几个像素的波动减少到仅偶有1个像素的抖动。     

Broadband holography applied to eddy current imaging by using signals with multiplied phases

In this paper an eddy current imaging method for nondestructive testing purposes is presented which utilizes the concept of broadband holography. An eddy current coil which is used simultaneously as an antenna for eddy current generation and as a probe for detection of response of interaction between eddy currents and flaws, respectively, is moved along a synthetic aperture during the imaging procedure generating synthetic eddy current pulses by scanning a certain frequency range. In terms of wave propagation phenomena the penetration depth (range) of eddy currents in conducting media is small compared to the equivalent wavelength of this type of fields. Therefore, adequate resolution can only be obtained in the reconstructed cross-sectional images by phase multiplication of received multifrequency signals, which is equivalent to a fictitious reduction of wavelengths. Experimental results verify the imaging capability of this method with improved resolution compared to conventional eddy current testing methods.     

Time-of-flight neutron imaging at a continuous source: Proof of principle using a scintillator CCD imaging detector

Energy resolved imaging has recently gained attention for the potential of spatially resolved texture, crystallographic phase and strain investigations. Especially a time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources is currently in the focus of investigations. Here, we present results of corresponding TOF measurements recorded at the continuous source of Helmholtz Center Berlin. The critical component for TOF imaging is however the availability of a high resolution imaging detector capable of the required time resolution. Here, a gated time-integrating detector without the corresponding continuous time resolution has been used and the measurements therefore have to be interpreted as proof-of-principle experiments as will be discussed. Measurements of different series of samples revealing structural differences related to their crystalline structure will be presented as well as a strain measurement on a dieless drawn wire.     

泵氧型铈锆固溶体参比氧传感器的制备

传统片式浓差型氧传感器存在陶瓷成型工艺复杂、成本高等问题。为解决此类问题,利用铈锆固溶体储氧材料的储氧特性,将其作为固体氧参比材料代替空气参比,研制铈锆固溶体参比氧传感器,探讨不同化学组成和厚度的CeO2-ZrO2固溶体对传感器氧敏信号的影响。并通过增加泵氧单元以抑制氧敏信号衰减,解决了实际使用中因铈锆固溶体中氧消耗而导致的氧传感器输出信号衰减问题,可满足车用氧传感器的正常工作需要。     

Estimation of attitudes from a low-cost miniaturized inertial platform using Kalman Filter-based sensor fusion algorithm

Due to costs, size and mass, commercially available inertial navigation systems are not suitable for small, autonomous flying vehicles like ALEX and other UAVs. In contrast, by using modern MEMS (or of similar class) sensors, hardware costs, size and mass can be reduced substantially. However, low-cost sensors often suffer from inaccuracy and are influenced greatly by temperature variation. In this work, such inaccuracies and dependence on temperature variations have been studied, modelled and compensated in order to reach an adequate quality of measurements for the estimation of attitudes. This has been done applying a Kaiman Filter-based sensor fusion algorithm that combines sensor models, error parameters and estimation scheme. Attitude estimation from low-cost sensors is first realized in a Matlab/Simulink platform and then implemented on hardware by programming the micro controller and validated. The accuracies of the estimated roll and pitch attitudes are well within the stipulated accuracy level of ±5‡ for the ALEX. However, the estimation of heading, which is mainly derived from the magnetometer readings, seems to be influenced greatly by the variation in local magnetic field     

Multimodal atomic force microscopy: Biological imaging using atomic force microscopy combined with light fluorescence and confocal microscopies and electrophysiologic recording

Because the atomic force microscope (AFM) allows molecular resolution imaging of hydrated specimens, it provides a unique window to the microscopic biological world. A high signal-to-noise ratio in AFM images sets them apart from the images obtained from other techniques: One does not need extensive image analyses often required by other techniques to obtain high-resolution information. AFM can provide molecular details on crystalline as well as amorphous materials. However, it is often limited in providing identity of the imaged structures, especially in a complex system such as a cellular membrane. AFM's application for biological imaging will rely on an unambiguous identification of imaged structures. For mixed macromolecules, it may be essential to make critical comparisons of the same structural features imaged with AFM and other techniques such as light fluorescence and confocal microscopies, electron microscopy and X-ray diffraction, and biochemical, immunologic, and pharmacologic techniques and electrophysiologic recordings. Significantly, the simple design of AFM allows it to be integrated with other techniques for simultaneous multimodal imaging. Recent combined multimodal imaging include light fluorescence, confocal, and near-field optical imaging as well as electrophysiologic recordings. Preliminary studies from such multimodal imaging include 1) an independent identification of macromolecules in a complex specimen using appropriately labeled markers such as fluorescent-dye labeled antibodies or dark-field microscopy; 2) imaging real-time reorganization of surface features using laser confocal and AFM; 3) a direct correlation of structural features and ion transfer via pores in a membrane; and 4) macromolecular complexes such as receptor-ligand and antigen-antibody. These features of a multimodal imaging system will provide new and significant avenues for a direct real-time structure-function correlation studies of biological macromolecules. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 293–300, 1997     

Simultaneous removal of odor and particulate using plasma-treated polymer filters

Polymer filters treated by plasma-assisted graft polymerization (PG), nonthermal plasma (NTP) and PG followed by NTP treatment are developed for use as multifunctional filters that can simultaneously remove odor and particulate. A NTP-treated filter can adsorb a large amount of a typical odor component, ammonia (NH₃). However, the performance of the NTP-treated filter deteriorates significantly after one month whereas that of a PG followed by NTP-treated filter deteriorates only slightly. The particulate collection efficiency of a both-side PG-treated filter is higher than that of an untreated filter whereas that of the NTP-treated filter is slightly lower.     

First study of macroscopic neutron dark field imaging using scattering grids

Instead of using the phase grating concept for dark field imaging, macroscopic scattering grids were employed at the ANTARES neutron imaging facility. Two Cadmium grids with a 1 mm gap and 1.2 mm bar were adjusted in a distance of only a few cm in order to block the direct beam. Thus, by placing the samples between these two grids only neutrons that were scattered at the samples were transmitted. A linear motion of the coupled grids allowed scanning across the samples and obtaining complete scattering projections, which delivered surprisingly sharp images. The geometric relation between grids permits determination of the transmitted scattering angles.     

Characterization of plasma sprayed coatings using thermal wave infrared video imaging

A pulsed (time-domain) thermal wave infrared video imaging technique, using an IR camera, a video image processor, and a flash lamp, is described. This system is applied to the imaging of interfacial defects in plasma sprayed coatings on metallic substrates. Results are compared with the conventional point-scanned cw infrared thermal wave imaging technique.     

Monte Carlo study of a 3D Compton imaging device with GEANT4

In this paper we investigate, with a detailed Monte Carlo simulation based on Geant4, the novel approach of Lenti (2008) [1] to 3D imaging with photon scattering. A monochromatic and well collimated gamma beam is used to illuminate the object to be imaged and the photons Compton scattered are detected by means of a surrounding germanium strip detector. The impact position and the energy of the photons are measured with high precision and the scattering position along the beam axis is calculated. We study as an application of this technique the case of brain imaging but the results can be applied as well to situations where a lighter object, with localized variations of density, is embedded in a denser container. We report here the attainable sensitivity in the detection of density variations as a function of the beam energy, the depth inside the object and size and density of the inclusions. Using a 600 keV gamma beam, for an inclusion with a density increase of 30% with respect to the surrounding tissue and thickness along the beam of 5 mm, we obtain at midbrain position a resolution of about 2 mm and a contrast of 12%. In addition the simulation indicates that for the same gamma beam energy a complete brain scan would result in an effective dose of about 1 mSv.     

月球机器人高精度定位模糊神经网络直接自适应控制

针对常规模糊控制的不足,提出一种模糊神经网络直接适应控制,它结合了模型控制、神经网络控制和自适应控制的优点,实现了模糊控制的智能化,并将其应用于月球机器人的定位控制中。仿真证明了该方案的优越性、有效性和可行性。     

Maintenance-free soft sensor models with time difference of process variables

In industrial plants, soft sensors are widely used to estimate process variables that are difficult to measure online. However, their predictive accuracy gradually decreases with changes in the state of the plants. Although regression models are reconstructed with database which includes newest data to solve this problem, some problems remain in practice. Therefore, we have attempted to reduce the effects of deterioration with age on soft sensor models without maintenance of the models. By constructing models based upon the time difference of an objective variable and that of explanatory variables, the effects of drift and gradual changes can be handled. We verified the superiority of the proposed method over traditional ones with simulation data and applied this method to actual industrial data. It was confirmed that the proposed method could achieve almost the same predictive accuracy as the updating model for 3 years without reconstruction of the model.     

Development of scanning measurement of tooth flankform of generated face mill hypoid gear pair with reference to the conjugate mating tooth flank form using 2 axes sensor

The three diamensional (3D) scanning measurement method of tooth flank form of generated face mill gear pair is proposed, which is based on the conjugate mating tooth flank form. In this method, deviation sensor is placed at the position which has certain offset from the gear axis and synchronized to the gear rotation. This method realizes the 3D tooth flank form measurement and multi points scanning measurement by using 2 axes sensors. Based upon this proposal of the measurement method, tooth flank form measuring machine was developed and the experimental measurements were carried out. It is confirmed that this method is capable of high speed and high resolution measurement of fine waviness and it has high repeatability. It is confirmed that the proposed method, is capable of 3D scanning tooth form measurement of generated face mill hypoid gear pairs with high repeatability at high speed.     

Fabrication of high-speed polyimide-based humidity sensor using anisotropic and isotropic etching with ICP

A novel high-speed, high-sensitivity capacitive-type humidity sensor is fabricated by using a new microfabrication process involving combination of directional and isotropic etching with inductively coupled plasma (ICP) etcher and a localized curing of polyimide films on a micro-hotplate. The polyimide humidity sensor is found to have a sensitivity of 0.75 pF/%RH, a linearity of 0.995, a hysteresis of 1.32%RH, a time response of 3 s, and a temperature coefficient of 0.22%RH/°C. This high-sensitivity and high-speed device is achieved using the locally-cured polyimide and a sensor structure having many holes and allowing moisture to diffuse through the top and side surfaces of polyimide film.     

Enhancing radiographic imaging of cementitious materials in composite structures with photon attenuating inclusions

This article investigates the use of photon attenuating inclusions (PAI) for enhancing radiographic imaging of cementitious materials in composite structures. By targeting characteristic high attenuation regions in the photon energy spectrum, PAI can improve void detection in the parent material by increasing contrast in radiographic images. Radiographic imaging of cementitious grout specimens with 5% and 15% weight fractions of candidate PAI materials (Fe, BaCO₃, BaSO₄) was performed to characterize X-ray attenuation. Virtual radiography simulations were then conducted to evaluate the application of PAI to grout void detection in post-tensioned concrete construction. The simulations demonstrate that grout void detection is most effective when the high energy region of the emission spectrum is near the K-edge of the PAI material.