共查询到19条相似文献,搜索用时 125 毫秒
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大型3维板类件多点闭环成形的研究 总被引:11,自引:1,他引:10
以多点成形技术为核心,为CAD/CAM/CAT为基础,提出了3维板类件的多点闭环成形。在多点成形过程中,3维曲面形状的离散傅里叶变换描述能够反映成形件的整体变形特性。以此为基础,给出多点成形过程的传递函数,并通过非参数化系统辨识方法获得每次循环中成形过程的非参数模型,从而预测出下次成形的基本体群形状,实现板类件的多点闭环成形。实验研究表明,在不考虑材料非线性、几何非线性和成形条件的情况下,金属板材通过闭环成形快速收敛的目标形状,实现了3维曲面的精确柔性造型。 相似文献
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为了能够自动而且快速地获取唇读系统中所必需的唇形轮廓特征,提出了将正交压缩变换的方法用于唇形轮廓的特征提取,并对得到的唇形轮廓曲线进行了分析研究。通过离散傅里叶变换(DFT)和离散余弦变换(DCT)分别得到描述唇形轮廓特征的傅里叶描述子和离散余弦变换描述子,然后将两类描述子作为唇形轮廓的特征向量,采用隐马尔可夫模型(HMM)进行学习和识别。基于独立汉字发音的实验表明:在达到40%的识别率时,刻画唇形轮廓特征所需的离散余弦变换描述子数目为15个,傅里叶描述子数目为20个。在相同的识别效果时,刻画唇形轮廓特征所需的离散余弦变换描述子数目少于傅里叶描述子,可减少数据运算量和运算所需时间。 相似文献
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根据龙贝格方法推导了离散傅里叶交换算法,并给出了其快速计算方法和计算实例,其结果优于常规的离散傅里叶变换算法. 相似文献
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频谱泄漏和栅栏效应是影响衰减信号离散傅里叶变换精度的主要因素。为了提高多频衰减信号离散傅里叶变换频谱参数的校正精度,提出一种加窗两点矢量插值校正算法。对信号加M阶余弦窗并计算加窗后信号的离散傅里叶变换,利用真实频率附近的两根谱线的矢量比建立方程,通过求解方程获得频率偏移量和衰减因子,利用上述获得的两个参数计算出信号的频率、幅值和相位。余弦窗的最大旁瓣衰减特性能有效的降低频谱泄漏的影响,两点矢量频域插值可以消除栅栏效应,两者结合极大地提高了算法的参数校正精度。仿真和试验结果表明,算法具有较高的参数校正精度和稳定性,且计算效率较高,适用于实时处理及对计算资源要求苛刻的场合,为多频衰减信号的特征提取提供了一种可选的方法。 相似文献
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采用信号处理的方法来考察快速成形技术,将其分层制造所产生的特有的结果——阶梯效应理解为把输入的原型表面轮廓曲线函数改造成为阶梯函数,因此可以将快速成形设备理解为滤波器组。分别采用傅里叶变换、窗口傅里叶变换和小波变换描述了快速成形的轮廓信息变化过程,认为只有小波变换可以兼具处理非平稳信号和构建出阶梯波的特点,因此最适合用于建立表征快速成形过程的数学模型。针对分层制造的特点,以单位方波作为尺度函数构建出能够反映阶梯波特性的小波基函数,即Haar小波函数,并利用其间断性的特点,建立了快速成形过程的数学模型,其作用就是将输入的零件轮廓波形通过基于Haar基函数的小波变换改造成为阶梯波。 相似文献
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动平衡是旋转机械必须解决的一个基本共性问题,传统动平衡方法主要从硬件的滤波和离散傅里叶变换算法来提取振动的基频信号,但傅里叶变换算法无法分析信号显著局部特征,硬件滤波容易受干扰。采用小波理论的软件滤波方法,以ATmega64芯片为核心来实现振动信号的滤波,并取得很好的效果。 相似文献
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三维网格模型盲提取水印算法 总被引:2,自引:1,他引:1
基于离散傅里叶变换(DFT)技术和扩频通信技术提出三维模型稳健水印嵌入算法.算法利用扩频通信技术将原始的一维二值水印序列生成可直接嵌入的水印信息;利用主成分分析(PCA)方法,将原始模型变换到仿射(旋转、平移和均匀缩放)不变空间中,选取模型项点到其中心距离作为水印嵌入单元,采用单极性量化嵌入单元离散傅里叶变换系数幅度的方法实现水印的盲提取.对算法进行了仿真,结果表明嵌入的水印信息具有不可见性,且能够抵抗模型的旋转、平移、均匀缩放等常见攻击. 相似文献
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Jianjun Wu Xin Wu Liangcai Deng Hakim Naceur 《The International Journal of Advanced Manufacturing Technology》2014,71(5-8):843-855
For some shortcomings in the use of standard radial length development in the blank development for forming sheet metal parts, an improved radial length normal spreading approach considering outside normal direction is developed to resolve blank development in sheet metal forming. Moreover, a comprehensive spreading method, which combines radial length normal spreading and orthogonal length development method, is presented in this paper to avoid the overlapping problem which happens sometime in the spreading process related to severely curved sheet parts. To deal with holes and gaps which exist in some sheet metal parts, dummy elements are used to calculate the intercepting line’s length precisely. Finally, a multistep spreading and merging strategy is adopted to handle some special sheet metal parts with vertical free edges that should be jointed or not. Through practical applications, the effectiveness and the usefulness of this approach are evaluated, and the unfolded result is more reasonable; meanwhile, the obtained blank shape should be a better initial guess in the application of the so-called one-step quick analysis for sheet metal forming simulation. 相似文献
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Zhong-Yi Cai Dong-Bo Guan Mi Wang Ming-Zhe Li 《The International Journal of Advanced Manufacturing Technology》2014,73(9-12):1807-1814
To effectively manufacture three-dimensional sheet metal parts with various curvatures produced in small-batch quantity, a continuous roll forming (CRF) process is proposed and investigated. The sheet metal is compressed between pairs of bended rolls and formed into a doubly curved surface. The shapes of forming rolls and the gap between the two rolls are piecewise controlled at a series of points. The two bended rolls and the nonuniformly distributed roll gap between them make the sheet metal bent in longitudinal and transverse directions simultaneously after the sheet metal passes through the roll gap, and a three-dimensional surface is formed continuously with the rotation of forming rolls. The relation between longitudinal elongation distribution and longitudinal bending deformation is discussed, and the lateral spreading in CRF process is analyzed; the method to compute the roll gap and the curved profiles of forming rolls are presented. Forming experiments for torus-shaped surface parts were carried out, and the experiment results demonstrate the feasibility and validity of CRF process and the presented methods. 相似文献
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Formability analysis on the process of multi-point forming for titanium alloy retiary sheet 总被引:2,自引:2,他引:0
Tan Fuxing Li Mingzhe Cai Zhongyi Li Xiangji 《The International Journal of Advanced Manufacturing Technology》2009,41(11-12):1059-1065
The multi-point forming (MPF) process of spherical surface parts of titanium alloy retiary sheet and titanium alloy sheet metal with different thickness and curvature radius was simulated by an explicit finite element software. Contradistinctive analysis between retiary sheet and sheet metal forming parts with different modes were done. The simulation results show that under the same forming conditions, titanium alloy retiary sheet is not easy to wrinkle and springback, whereas it is easy to form. The reason for differences in the formability of above-mentioned sheet metal is also analyzed. A non-wrinkling limited graph and a fracture critical graph for spherical surface parts of retiary metal sheet and metal sheet were obtained. Finally a forming test of titanium alloy cranial prosthesis was done in MPF press. Testing results indicate the customized 3D curved surface of prosthesis can be adequately shaped and the forming quality was guaranteed. 相似文献
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通过理论分析及实验,阐明了曲面零件成型极限的意义,提出了成型极限危险点-起皱关键点及破裂关键点的概念,给出了起皱极限及破裂极限判据表达式,并得到了实验验证。 相似文献
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Numerical investigation of multi-point forming process for sheet metal: wrinkling, dimpling and springback 总被引:2,自引:2,他引:0
Zhong-Yi Cai Shao-Hui Wang Ming-Zhe Li 《The International Journal of Advanced Manufacturing Technology》2008,37(9-10):927-936
Multi-point forming (MPF) is a new flexible technique for manufacturing three-dimensional sheet metal parts. In this procedure, a pair of opposed matrices of punch elements substitute for the conventional fixed shape die sets, and the sheet metal can be formed rapidly between the matrices. Extensive numerical simulations of the processes for forming spherical and saddle-shaped parts were carried out by dynamic explicit finite element analysis. The contacting process between sheet metal and punch elements in MPF was investigated, and the variations of forming force with respect to the tool travel were analyzed. The wrinkling processes were simulated, and the MPF limit curves without wrinkles for spherical and saddle-shaped parts were obtained. Dimple is a particular defect in MPF, through the comparison of the thickness strains calculated by solid FE and shell FE, the finite elements appropriate for the numerical analysis of dimpling were detected, and the limit forming force without dimples was determined. Springback processes of MPF were simulated based on explicit-implicit algorithm. The springbacks and their distributions under different conditions were investigated. 相似文献
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Zemin Fu Xiuli Tian Wei Chen Bingkun Hu Xingyan Yao 《The International Journal of Advanced Manufacturing Technology》2013,69(5-8):1639-1647
The three-roll bending forming of sheet metal is an important and flexible manufacturing process due to simple configuration. It is suitable for forming large sheet parts with complex, curved faces. Most researches on roll bending forming of large workpiece are mainly based on experiments and explain the process through macroscopic metal deformation. An analytical model and ABAQUS finite element model (FEM) are proposed in this paper for investigating the three-roll bending forming process. A reasonably accurate relationship between the downward inner roller displacement and the desired springback radius (unloaded curvature radius) of the bent plate is yielded by both analytical and finite element approaches, which all agree well with experiments. Then, the three-roll bending forming process of a semi-circle-shaped workpiece with 3,105 mm (length)?×?714 mm (width)?×?545 mm (height) is simulated with FEM established by the optimum tool and process parameters. Manifested by the experiment for three-roll bending forming of this workpiece, the numerical simulation method proposed yields satisfactory performance in tool and process parameters optimization and workpiece forming. It can be taken as a valuable mathematical tool used for three-roll bending forming of large area sheet metal. 相似文献
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An improved method of contact treatment is developed in which both the FEM (finite element method) mesh and the tool surfaces are described with parametric patches which have C1 continuity or more. The FEM mesh at the current configuration is globally converted into smooth surface patches of net form. A continuous sheet surface normal scheme is devised by using the globally smoothed mesh surface. A robust and efficient contact search algorithm is also developed in connection with the proposed continuous contact treatment. As an improved version of conventional membrane element, the BEAM (abbreviated from Bending Energy Augmented Membrane) element is newly developed based on node spring. In order to verify the effectiveness of the proposed continuous contact treatment and BEAM element, deep drawing processes of complicated parts including actual auto-body panel are analysed. Comparisons with the available experiment and analysis show that the proposed continuous contact treatment in connection with BEAM elements can be effectively applied to the analysis of sheet metal forming processes for arbitrarily curved parts with deformation regions in which the bending effect must be taken into account. 相似文献
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Jun Wang Chunming Wang Xuanxuan Meng Xiyuan Hu Yangchun Yu Shengfu Yu 《Journal of Mechanical Science and Technology》2011,25(6):1529-1533
Hybrid plasma is an important physical phenomenon in fiber laser-MIG hybrid welding. It greatly affects the stability of the
process, the quality of the weld, and the efficiency of energy coupling. In this paper, clear and direct proofs of these characteristics
are presented through high-speed video images. Spectroscopic analysis is used to describe the characterization of hybrid plasma.
The hybrid plasma forms a curved channel between the welding wire and the keyhole during the fiber laser-MIG hybrid welding
process. The curved channel is composed of two parts. The laser-induced plasma/vapor expands due to the combined effect of
the laser and the MIG arc, forming an ionization duct, which is one part of the curved channel. The resistance of the duct
is smaller than that of other locations because of the rise in electrical conductivity. Consequently, the electrical arc is
guided through the duct to the surface of the material, which is the other part of the curved channel. The spectral intensities
of metal elements in laser-MIG hybrid welding are much stronger than those in MIG-only welding, whereas the spectral intensities
of shielding gas element in laser-MIG hybrid welding are much weaker. 相似文献