Computerized laminagraphy

Laminagraphy is a radiographic technique used to image cross-sectional views through solid objects. Coplanar rotational laminagraphy (CRL) is a special case where the film and object rotate synchronously while the radiation source remains stationary. The orientation of the radiographic film corresponds to the cross-sectional slice through the object being imaged. The image formed on the exposed film is highly blurred owing to the continuous summation of radiographic projections taken at different angles through the object. Theoretical analysis of the image formation process shows that the resultant image is simply a convolution of the ideal cross-sectional image with a radially symmetric point spread function having the form r⁻¹. Direct deconvolution does not give good results since image noise becomes a significant factor owing to the high-frequency amplification of the deconvolution operator. A parametric filter based on the optimized Wiener restoration filter is shown to provide good results for a few selected specimens.     

基于负载观测的PMSM滑模抗扰动自适应控制

实际转速值是转角微分得到的,基于转速的观测器设计会引入微分突变．本文在滑模变指数趋近率控制的基础上,针对实际应用的永磁同步电机（permanent magnet synchronous motor, PMSM）提出了一种新的负载转矩降阶观测器设计方法,以可直接测量的转角为已知观测对象,避免引入微分突变,将观测到的负载转矩成比例地前馈补偿,以削弱负载扰动对控制性能的影响,实现滑模抗扰动自适应控制．一方面,通过理论推导,得出所提出策略的理论计算方法;另一方面,以一应用案例,建立了与实际逼近的离散仿真系统．仿真验证了观测器的无超调和快速响应特性,并通过与普通滑模控制对比分析,验证了采用该方法设计的PMSM调速系统具有动态响应快和抗外界干扰能力强的高鲁棒特性．     

Scheimpflug stereocamera for particle image velocimetry in liquid flows

A novel stereocamera has been developed based on the angular-displacement method, wherein the two camera axes are oriented in a nonorthogonal manner toward the object plane. The stereocamera satisfies the Scheimpflug condition such that the image plane, the object plane, and the lens plane are nominally colinear. A unique feature of the stereocamera is the introduction of a liquid prism between the object plane and the recording lens, which significantly reduces the radial distortions that arise when imaging through a thick liquid layer. The design of the camera and its computer optimization with geometric modeling are described. Results indicate that the use of a liquid prism reduces the amount of radial distortion by an order of magnitude. The results have been shown to agree very well with experiments.     

Topographic profiling and refractive-index analysis by use of differential interference contrast with bright-field intensity and atomic force imaging

A methodology is described for phase restoration of an object function from differential interference contrast (DIC) images. The methodology involves collecting a set of DIC images in the same plane with different bias retardation between the two illuminating light components produced by a Wollaston prism. These images, together with one conventional bright-field image, allows for reduction of the phase deconvolution restoration problem from a highly complex nonlinear mathematical formulation to a set of linear equations that can be applied to resolve the phase for images with a relatively large number of pixels. Additionally, under certain conditions, an on-line atomic force imaging system that does not interfere with the standard DIC illumination modes resolves uncertainties in large topographical variations that generally lead to a basic problem in DIC imaging, i.e., phase unwrapping. Furthermore, the availability of confocal detection allows for a three-dimensional reconstruction with high accuracy of the refractive-index measurement of the object that is to be imaged. This has been applied to reconstruction of the refractive index of an arrayed waveguide in a region in which a defect in the sample is present. The results of this paper highlight the synergism of far-field microscopies integrated with scanned probe microscopies and restoration algorithms for phase reconstruction.     

Third-order aberrations of a prism with spherically curved surfaces

A third-order analysis of a spherically curved prism in a converging beam shows that solutions exist that permit the beam to pass without aberration. A reflecting telescope with such a prism in front of the focus would form a high-throughput astronomical spectrometer for stellar sources. This configuration would yield diffraction-limited performance at a single wavelength. A LiF prism has been designed for a rocket telescope that will image Jupiter from 1216 to 1608 ? with a spatial resolution limited by the 0.5-arcsec pixels of the detector.     

DIC显微术及在大气颗粒物观察中应用的研究

微分干涉相衬(DIC)显微术使用诺马斯基棱镜完成光束的分割、合成,合成光束发生干涉,将样品上各部分折射率、厚度的变化率或表面起伏的不同转化为像面上光强的差别,故像面是物面的微分。DIC与无限远光学系统的结合,减小了棱镜、检偏器的插入引起的负面影响。将该DIC应用于PM2.5大气颗粒物的研究,得到了优于其它显微术的图像。     

Observation of Magnetic Fine Structures by Electron Differential Microscopy

New techniques for electron differential interferometry and microscopy that are free from the effect of distorted reference waves have been developed using an electron trapezoidal prism. This new prism, which replaces an electron biprism, makes a hologram with the object wave inclined and the reference wave perpendicular to the image plane. A differential interferogram can be produced from one double-exposed hologram. A differential phase image from two independently recorded holograms can also be easily achieved. These two techniques retain the advantages of conventional off-axis electron holography, that is, resolution and sensitivity. Their performance is evaluated by reconstructing the electrostatic potential around a charged polystyrene latex particle and by the observation of magnetic fine structures in a permalloy thin film. A two-dimensional vector map of the magnetic flux density enables an interpretation of the contrast of the Lorenz micrograph of the same specimen area.     

Implementation of a high-speed face recognition system that uses an optical parallel correlator

We implement a fully automatic fast face recognition system by using a 1000 frame/s optical parallel correlator designed and assembled by us. The operational speed for the 1:N (i.e., matching one image against N, where N refers to the number of images in the database) identification experiment (4000 face images) amounts to less than 1.5 s, including the preprocessing and postprocessing times. The binary real-only matched filter is devised for the sake of face recognition, and the system is optimized by the false-rejection rate (FRR) and the false-acceptance rate (FAR), according to 300 samples selected by the biometrics guideline. From trial 1:N identification experiments with the optical parallel correlator, we acquired low error rates of 2.6% FRR and 1.3% FAR. Facial images of people wearing thin glasses or heavy makeup that rendered identification difficult were identified with this system.     

发动机测功系统转速检测研究

转速信号是发动机测功系统十分重要的物理量，其检测方法与电路设计直接关系到测功系统的性能和测试控制精度。在详细分析M法、T法和M/T法等测速方法的基础上，本文设计了M／T法测速的硬件电路和自动量程切换的软件实现方法，利用磁电式转速传感器实现了发动机测功系统转速的高精度测量。测速系统实际运行表明，本文设计的非接触式转速测量系统结构简单、抗干扰能力强适用于交、直流全数字化调速系统的数字测速装置的工程设计实践中。     

A Double Refracting Interference Microscope with Continuously Variable Amount and Direction of Wavefront Shear

A double refracting interference microscope, which is capable of giving uniform and fringe interference field with both the amount and direction of image duplication continuously variable, has been developed. A combination of two simultaneously acting birefringent prisms, separated by a half-wave plate and inserted between a polarizer and analyser, is used. One of these prisms, of the Nomarski type, is incorporated in objectives and is rotatable round the objective axis. Rotation of this prism enables the amount and direction of image duplication to be changed. The other prism, of the Nomarski or Wollaston type, is placed in the microscope tube and can be slid in a direction perpendicular to the microscope axis. This translation serves for shifting the phase of interfering light waves, for measuring the optical path difference between an object under investigation and its surrounding medium. As a source of coherent light a slit diaphragm located in the front focal plane of a condenser is used. Both the slit diaphragm and half-wave plate, as well as the polarizer, are rotatable around the microscope axis when the objective birefringent prism is turned. Advantages and application possibilities of this system are discussed.     

Wiener filtering of interferometry measurements through turbulent air using an exponential forgetting factor

The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter.     

Eye rotation and vignetting in visual instruments

The eye can rotate to accommodate the angular position of an object and the distance of the object from it. The rotation of the eye inside its socket to align its visual axis in the direction of an off-axis image may introduce full or partial vignetting when one is looking through a visual instrument with a real exit pupil. We analyze the effects of vignetting owing to rotation of the eye in visual instruments with real exit pupils.     

Increased sensitivity to in-plane displacements in electronic speckle pattern interferometry

We describe an optical arrangement that increases the sensitivity to in-plane displacement in an electronic speckle-pattern interferometric system. This is accomplished by oblique illumination and observation along the direction of illumination. An anamorphic prism placed in front of the object is used to correct for the eccentricity in the image caused by the oblique observation. The sensitivity to in-plane displacement can be increased to a maximum of approximately λ/2. Experimental results including phase stepping are presented.     

机器人触觉识别系统的研究

介绍了一种机器人触觉识别系统。该系统具有智能抓握功能，能抓握各种机械零件及鸡蛋、玻璃器皿等易碎物体。在抓握物体的同时可自动获取、处理该物体的触觉图象，从而可以自动识别某些规则物体。该系统的建立将为智能机器人提供实用化技术。     

Achromatic 90° polarization rotating prisms

Half wave plates are often used to rotate the plane of polarization by 90° at one wavelength. To rotate the plane of polarization over a range of wavelengths, Fresnel rhombs may be used. Fresnel rhombs, however, exhibit significant deviation from precisely 180° retardation over any broad wavelength range. This note describes two prism (or mirror) designs which rotate the incident polarization exactly 90° at all wavelengths. In one case the incident beam direction is deviated by 90°, while in the other case the incident beam is transmitted undeviated.     

Oblique incidence and observation electronic speckle-pattern interferometry

In this paper we discuss an oblique incidence and observation electronic speckle-pattern interferometer, in which we use an anamorphic prism in front of the object. A collimated beam traveling through the prism is partly reflected at the base of the prism. The reflected light is the reference beam and the transmitted light illuminates the diffuse object, thereby generating the object beam. In this scheme the object and the reference beams are collinear. A new scheme that uses two prisms and permits phase stepping is also presented.     

新型火炮缠角测量系统设计

提出了一种基于投影法的新型火炮缠角测量系统。该系统主要由照明光源、反射锥镜、CCD相机和驱动机构组成。首先，用光源把身管内壁照亮，然后经过锥镜反射后内壁在CCD相机中成像，最后对该数字图像进行分析，计算得到缠角。本文阐述了测量火炮缠角的计算方法、系统硬件配置及软件设计，最后对该方法的技术特点进行了总结。     

Analytical solutions for image orientation changes in prisms

Optical prisms are most commonly employed because of their ability to output an image of different orientation relative to the input object. Previous papers have presented a systematic but numeric approximation for designing a single prism, which outputs an image with a specific image orientation. Instead of a numerical solution, an exact analytical solution for the same problem is offered. Further, how to design prism systems by using off-the-shelf right-angle prisms and roof prisms as building blocks to obtain an output image with a specific image orientation is addressed. Illustrative examples are given to verify the proposed approach and demonstrate its use.     

Optical levitation and trapping of a micro-optic inclined end-surface cylindrical spinner

Cylindrical micro-objects with inclined end surfaces have been observed to be optically trapped in a focused laser beam and to rotate about the beam's propagation direction. A simplified vector model is developed that accounts for the observed effect; the enhanced ray-optics model is used to simulate the behavior of time evolution for the cylindrical object in the beam. Experimental laser trap configurations are presented, along with a video image sequence of the cylinder's precession.     

Optical Filtering Approach to Regularized Tracking of an Object's Position and Orientation

We present a regularized nonlinear least-squares algorithm for tracking the position and the orientation of a known object by using an active camera and an optical correlator situated between digital preprocessing and postprocessing operations. The numerical minimization required by the regularized least-squares solution is implemented by use of a rapid look-up table method. Performance of the algorithm is evaluated through a Monte Carlo sensitivity analysis that incorporates models for lens blur, image noise, illumination variation, and partial occlusion. This analysis shows robust performance with respect to image noise, partial occlusion of the object, and errors in the camera pan and tilt used to follow the moving object. The limiting factors in the algorithm's performance are errors in the preprocessing step used to scale and rotate the input video images. These errors should be maintained within 6% and 3 degrees , respectively.