放音磁头的轮廓效应

本文介绍了录音机放音磁头轮廓效应的基本原理及其形成的规律性，轮廓效应影响的定量计算和克服其不良影响的基本方法，及轮廓效应和放音低频响应的关系。     

Virtual CNC system. Part II. High speed contouring application

This paper presents a trajectory planning strategy for maintaining the tool positioning accuracy in high speed cornering applications. A 3D contour error estimation algorithm is presented for determining the geometric deviation from arbitrarily shaped toolpaths. Two spline fitting strategies are developed for smoothening sharp corners. The under-corner approach reduces the toolpath length, and therefore the cornering time. This technique yields successful results when used with a high bandwidth servo controller (such as sliding mode control), capable of accurately tracking the commanded toolpath. The over-corner approach is based on stretching out the sharp corner with a smooth curve, which counteracts the ‘undercut’ caused by the large phase lag in low bandwidth servo controllers (such as P–PI control). The cornering feedrate is adjusted in the Virtual CNC platform, developed in the first part of this article, to ensure that contour error violation does not occur. The achieved cornering accuracy is verified in experiments, which are in close agreement with predictions obtained with the Virtual CNC.     

Gravitational clustering

This paper introduces and describes an algorithm or technique, called gravitational clustering, for performing cluster analysis on Euclidean data. The paper describes the physical gravitational model, an abstract generalized model, and several specific gravitational models. It illustrates clustering by one of these models using several sample data sets, and compares the results with those obtained using two other well-known nongravitational clustering methods. The paper also illustrates four graphical techniques to aid in the analysis of a clustering.     

A FORTRAN IV program for interpolating irregularly spaced data using the difference equations for minimum curvature

The interpolation of potential field data is a common problem in geophysics. It is accomplished each time a contour map or profile is drawn. These operations can be difficult and subjective if the data points are irregularly spaced. The method described here produces a “numerical surface”, or grid of values, that approaches the smoothest surface passing through the control points. Such a grid can be contoured automatically by standard routines, producing acceptable results. Alternatively, sections can be drawn through the surface on any azimuth—a more satisfactory procedure for constructing profiles than projecting the data points onto straight lines.     

基于形状特征点匹配的CT断层图象表面重建

当切片间距离较大时，如何快速，准确地重构出复杂器官的表面并显示它，在医学临床应用中已变得越来越重要。本文首先提出了一种保持轮廓形状特征的自适应特征点采样算法，该算法大大减少了后续处理的存储量和计算量，其次，在于对图象特性的分析，提出了一种特殊点匹配算法，该算法考虑到了特征点在原图象上的灰度，梯度幅值，梯度方向和位置对匹配的影响，提高了重建表面的准确度。实验结果证明了上述算法的有效性。     

Closed contour extraction application to meteorological pictures

This paper deals with the problem of closed contour extraction for noisy images whose boundaries are very fuzzy. The method used relies on simple arguments: reduction by adaptive quantization, filtering of the reduced-levels image contours and spots detection. Application of this method to meteorological satellite images proved to be successful while classical methods would have failed.     

A novel cross-coupling control design for Bi-axis motion

A new structure of cross-coupling controller for precise tracking in motion control is proposed in this paper. When compared with the conventional cross-coupling system, this new structure has the advantage that the compensators in CCC have a simpler design process than conventional ones and so does its stability analysis. The proposed compensator (or controller) is evaluated and compared experimentally with a traditional uncoupled controller on a microcomputer controlled dual-axis positioning system. The experimental results show that the new structure of cross-coupling controller remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine.     

基于变换域数字图像水印技术的研究

以数字图像水印为研究对象,在介绍典型的最低有效位LSB空间域图像水印算法优缺点的基础上,对DFT、DCT、DWT、Ridgelet变换域数字图像水印技术进行了研究,然后重点分析了Contourlet变换新技术,Contourlet变换通过各向异性基实现了图像的多尺度多方向性分解,更能捕获图像的曲线奇异性和匹配人类视觉特性,这一新技术在数字图像水印领域有广阔地应用前景,最后指出了数字水印的发展方向.     

A two-layered cross coupling control scheme for a three-dimensional motion control system

A two-layered modeling and compensation scheme is proposed to reduce the contouring error of a three-dimensional motion control system. In the proposed scheme, the contouring error model of the three-dimensional motion control system is divided into two layers: the top layer and the bottom layer. The proposed multi-layered structure of the contouring error model presents more flexibility in the control system design because the cross coupling controllers in different layers can be designed separately. In this paper, a nonlinear PI controller and a position error compensator are designed in the bottom layer in order to achieve high contouring accuracy in the XY plane, while a unilateral compensator is designed in the top layer to further reduce contouring error in the three dimensional space. Finally, experiments are performed to verify the performance of the proposed two-layered modeling and compensation scheme. Experiment results show that the designed two-layered cross coupling controller can obtain higher contouring accuracy than traditional cross coupling controller both in the XY plane and in the XYZ space.     

Precise contour following for biaxial systems via an A-type iterative learning cross-coupled control algorithm

This paper proposes an A-type iterative learning cross-coupled control (CCC) algorithm for biaxial systems. An algebraic equation based contour error model is used as the CCC input. This model has the advantage that it is zero if and only if the real value vanishes. The iterative learning CCC is designed to make its input converge to zero. Hence, it is expected to that the contour error will converge to zero as well. After analyzing the control algorithm convergence condition in the frequency domain, the proposed method is implemented on a motion stage. Experimental results show that the algorithm perfectly follows contours as the cycles approach infinity regardless of whether tracking errors are small or large.