共查询到19条相似文献,搜索用时 171 毫秒
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针对复杂结构毛坯的小余量数控加工中很容易出现局部加工余量不足的问题,基于毛坯表面的点云测量数据,提出了一种层次化快速约束配准算法,从而实现加工余量的优化分配。首先通过建立一个知识向导模型并应用局部微分信息,自动分离出毛坯上需要分配余量的各待加工表面,并分别施加最小余量约束,在确定各待加工表面上参与约束配准优化的初始点集的基础上,采用广义乘子法将初始配准点集与设计数模进行约束匹配;然后采用迭代方法将不满足余量约束的测点追加到当前配准点集中,直到所有待加工表面的测点满足余量约束。实验结果表明,该配准算法在最大程度满足余量约束的前提下,显著提高了点云数据的配准效率。 相似文献
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鉴于复杂曲面误差评估问题中,不同配准方法往往导致不同的评估结果,在精度要求较高或误差形势较严峻时,恰当的配准位姿具有重要意义,提出一种面向复杂曲面误差评估的最小区域包容配准算法。为解决计算复杂性,采用凝聚函数一致光滑逼近不连续的极差函数,并利用高效有限存储拟牛顿算法求解大规模无约束非线性问题。最近点迭代算法为最小区域包容配准方法提供了收敛条件,同时加快了收敛速度,而且算法容易实施,对复杂曲面扫描数据点云有效。通过仿真平面和实测钣金件的误差评估配准实验说明了所提算法的有效性。 相似文献
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高速飞行器薄壁异形零件加工余量的数字化分析与优化 总被引:2,自引:0,他引:2
《计算机集成制造系统》2016,(6)
针对高速飞行器中非圆、薄壁异形结构件加工超差、壁厚不均等导致的报废率较高的问题,提出一种以毛坯/零件三维模型匹配对准为核心的工件加工余量数值分析方法。以精密测量技术获取毛坯实例的三维点云模型,建立了毛坯/零件点云的空间匹配对准基本方法,并以包容、对齐、均匀等约束条件进行加强,实现了毛坯/零件的匹配对准及三维加工余量的优化分析。通过运用基准转换原则实现了数值分析中的虚拟基准向零件加工中的实体基准的转换,为数值余量分析结果的加工应用奠定了基础。以某型复杂薄壁异形舱段零件的毛坯件加工为例对研究方法进行了工程验证,结果表明了该方法在工作效率、加工精度等方面的技术优势及其有效性。 相似文献
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航空叶片属于复杂异形曲面,作为航天发动机的重要零件之一,其形状结构的高精度检测必不可少。复杂异形曲面由于其边缘曲率复杂,使得目前的点云配准技术尚无法满足其高精度配准需求,针对航空发动机叶片复杂异形曲面高精度配准的要求,提出了基于多尺度描述子的空间角度差分阈值筛除误配准对的配准算法,创新性的通过多尺度特征与空间角度差分阈值筛除算法相结合的方法实现高精度的异形曲面配准。该方法可以有效降低误匹配点和噪声点对配准效果的影响。实验表明,本算法对于航空叶片复杂异形曲面具有很好的配准效果,配准精度高,且具有良好的鲁棒性。 相似文献
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为减小钛合金薄壁件切削加工过程中的变形,提出了一种新型的非均匀余量设计策略。建立了基于Rayleigh-Ritz法的薄壁件铣削加工变形预测数学模型,提出了离散化的余量体积单元设计思路并完成了工件的非均匀余量设计,最后对比分析了不同余量设计策略对薄壁悬臂结构件加工变形的影响。研究结果表明:所提出的基于Rayleigh-Ritz法的离散余量体积单元非均匀余量设计策略对工件自身刚度利用率高,表面加工误差分布一致性好,且对控制最大表面加工误差具有更优的效果。 相似文献
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An unconstrained approach to blank localization with allowance assurance for machining complex parts
Gaoshan Tan Liyan Zhang Shenglan Liu Nan Ye 《The International Journal of Advanced Manufacturing Technology》2014,73(5-8):647-658
In machining large complex parts with critical stock allowance, even small deviations in the blank parts or slight inadequacy in the fixturing may result in local shortage of material (i.e., insufficient stock allowance). This paper presents an optimal localization algorithm that aligns the measured points from a blank part with the nominal model to assure the weakest allowance area with as much material to be cut as possible. Instead of exploiting extra constraints to force the allowance at each point larger than a specific value, which is a popular strategy for allowance assurance in the previous localization algorithms, we formulate the blank localization problem as an unconstrained max-min problem. To deal with the unsmoothness exhibiting in the max-min objective function, a method based on the entropy optimization principle is adopted to convert the non-differential objective function to an unconstrained differential one, which can be efficiently solved using the conventional Quasi-Newton algorithms. The unconstrained optimization result finally gives rise to localization with the maximum allowance margin. For the blank parts that the material shortage is inevitable, the method can still efficiently achieve reasonable localization results, which confine the material shortage to a least extent. The proposed method is easy to be implemented and works well for both sparse sample points and dense-scanned points. Case studies included justify the superiority of the proposed scheme over the existing non-linear constrained optimization solutions. 相似文献
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针对非圆齿轮加工中,由齿坯节曲线曲率变化所引起的分次进刀过程中齿面加工余量分布不均的问题,提出一种匀化非圆齿轮齿面加工余量的工艺方法。以非圆齿轮插削工艺为研究对象,基于插齿加工原理,对齿面加工余量分布不均的成因进行了分析;在此基础上建立了非圆齿轮匀化工艺插削联动模型,通过实时调整插刀与齿坯的几何位置关系,实现了非圆齿轮齿面加工余量的匀化;开发了非圆齿轮插齿CAM系统,利用CAM系统对齿面加工余量匀化工艺进行了仿真验证,仿真结果表明,所提工艺方法正确、可行;将匀化工艺集成到自主开发的齿轮加工数控系统中,进行了非圆齿轮插削加工试验,试验结果表明,所提工艺方法能够有效匀化齿面加工余量;对加工出的非圆齿轮齿面进行了三维形貌检测,检测结果表明,所提工艺方法能够显著提高非圆齿轮的加工精度与表面质量。 相似文献
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Xiaohui Zhang Dong Yu Taotao Song 《The International Journal of Advanced Manufacturing Technology》2012,62(9-12):1179-1189
The existing interpolation algorithm cannot meet the need of high-speed and high-accuracy machining of a free-form surface. So this paper proposed a correcting and compressing interpolation algorithm. Depending on the distance and angle evaluated from the adjacent command points, the machining path of free form can be divided into two machining types. For those regions where the accurate figure is critical such as corners, the convention linear interpolation is performed exactly between the adjacent command points. For those regions having a large radius of curvature where the smooth figure is critical, firstly, the interior point selection method based on circle transition is derived to reduce the tolerance between the machining path and the original surface; secondly, the interior point correction method based on the least-square method is proposed to reduce the calculation error and round-off error in the interior point and estimate the first- and second-order derivative vectors of the interior point; thirdly, the shape-defining point is selected by the bend direction of the machining path and fitted to a quintic spline curve which has the C2 continuity; fourthly, the fitting accuracy controlling method is proposed to ensure the machining accuracy; lastly, the curve interpolation is performed on the fitted smooth curve. Machining tests carried out on a vertical machining center show that the proposed algorithm can improve the machining efficiency and machining quality of a free-form surface. 相似文献
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Accurate evaluation of free-form surface profile error based on quasi particle swarm optimization algorithm and surface subdivision 总被引:2,自引:2,他引:0
Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline(NURBS) for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system(DCS) and measurement coordinate system(MCS) for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization(QPSO) is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface. 相似文献
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复杂曲面加工检测中的精确定位方法 总被引:3,自引:0,他引:3
测量数据的精确定位是实现复杂曲面加工检测的关键,针对其在初始变换估计和最近点计算等方面存在的问题,提出一种快速、精确的定位方法.该方法以曲面的曲率为联系特征,建立起满足角度、距离约束的对应关系,能够实现测量数据的初始定位,从而为后续迭代算法向全局最优收敛提供一个良好的初始变换.进而以Bernstein多项式算术运算为基础,给出一种新的最近点计算方法,能够克服传统方法需要给定初始迭代点的不足.最后利用基于最小二乘的迭代算法完成测量数据定位的精确调整,达到全局最优的目标.试验结果显示,所提出的方法快速、可靠,并且具有良好的定位精度. 相似文献
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Zhengji Teng Hsi-Yung Feng Abdullahil Azeem 《The International Journal of Advanced Manufacturing Technology》2006,30(3-4):254-260
This paper presents a method of generating efficient three-axis ball-end milling tool paths directly from point cloud data. The primary objective is to achieve high efficiency in the machining of free-form surface geometry having isolated complex machining area. The high machining efficiency is attained by segmenting the entire machining domain into distinct areas according to the geometric complexity of the data points and by using cutters of different sizes for the segmented machining areas. An iterative numerical procedure is derived to determine the critical complexity that separates the data points with higher complexity (the complex points) from those with lower complexity (the non-complex points). A larger and more efficient ball-end mill is used to machine the area defined by the non-complex points. The gouging condition of all the data points is then evaluated with respect to the given ball-end mill. The isolated complex machining area is established by enclosing both the complex points and the gouge points. The smaller and gouge-free ball-end mill for the isolated complex machining area is subsequently selected from the standard commercial cutter series. Implementation of the presented method clearly demonstrates the high efficiency of the generated tool paths. 相似文献