共查询到20条相似文献,搜索用时 78 毫秒
1.
为了克服传统网格曲面变形对模型的特征只能进行近似控制的缺陷,提出一种精确的特征控制方法,使得模型特征在整体曲面变形中保持原有形状。首先提取形状特征的位置信息,将其作为变形过程中的刚性约束;再根据改进的离散拉普拉斯算子,建立反映网格曲面微分特性的柔性约束;对刚性约束条件引入拉格朗日乘子,结合柔性约束条件建立线性方程组,利用最小二乘法求出最优解,从而实现在保持形状特征的情况下网格曲面的整体变形。最后,通过实践应用证明了上述算法的合理有效性。 相似文献
2.
Kunjin He Zhengming Chen Lihua Zhao 《The International Journal of Advanced Manufacturing Technology》2011,57(1-4):271-283
Representation and parameterization of freeform feature is one key issue in CAD. Based on the idea of layering freeform feature and feature global shape (FGS), a novel method for classification and parametric representation of freeform feature is proposed. Firstly, freeform features are classified in use of a multi-side method which combines FGS, approaches for surface generation, types of characteristic curves and their topological structures. Secondly, freeform feature is parameterized step by step from global to local shape, from basic to fine characteristic, and from high to low level, thus its representation can be unified. Lastly, the framework of three-level structures and two-grade mappings is put forward to define freeform feature so that parametric semantics can be clearer and it is convenient for users to edit and modify surface by intuitive parameters. It is shown in the examples that the method can effectively improve classification and parameterization of freeform feature. It can be applied to surface feature-based design and other domains as well. 相似文献
3.
This paper investigates the tool-workpiece contact mechanism in the disc polishing process, where the soft polishing disc touches the rigid freeform workpiece with a small tilt angle. The developed contact force model can explain how the contact parameters, including the disc contact depth, the disc tilt angle, the radii of curvature of the disc and the workpiece, affect the normal contact force. Under some reasonable geometric and mechanical assumptions of the disc and the workpiece, an approximated contact force equation is derived in a simple power-law form similar to the Hertzian contact model. The contact force is found to be positively related to the disc contact depth and the disc radius, while negatively related to the disc tilt angle and the workpiece normal curvature that is orthogonal to the feed direction. Both finite element simulations and experiments verify the effectiveness of the proposed contact force model. Furthermore, the material removal process is analyzed and a model-based process parameter planning method is developed to achieve uniform material removal considering the variation of workpiece curvatures. 相似文献
4.
This paper presents a novel method for mapping a texture for machining onto a freeform surface. When a grain texture designed on a 2D plane is projected onto a freeform surface simply, the texture is distorted along the curvature of the surface in the projection direction. Therefore, a method is required to suppress this distortion. The algorithm proposed in this paper rapidly generates a point cloud that represents a texture with less distortion on a simply connected parametric surface. Specifically, four equations that express local geometry constraints instead of conventional parameterization methods are presented to reduce the distortion between adjacent points on the point cloud. Solving these equations can generate grain textures on freeform surfaces. This paper examines two grain images mapped to two freeform surfaces that were prepared as case studies to demonstrate the effectiveness of the proposed method. 相似文献
5.
The trend towards product miniaturisation and multi-functionality constitutes a driving force for the application of complex surfaces in many fields such as advanced optics. The precision measurement of these surfaces should be carried out at multiple scales, of which process commonly involves several datasets obtained from different sensors. This paper presents a weighted least square based multi-sensor data fusion method for such measurement. The method starts from unifying the coordinate frames of the measured datasets using an intrinsic feature based surface registration method. B-spline surface is used to fit linear surface model to each identified overlapping area of the registered datasets, respectively. By forming a common basis function, the fitted surface models and the corresponding residuals are then combined to construct a weighted least square based data fusion system which is used to generate a fused surface model. An analysis of the uncertainty propagation in data fusion process is also given. Both computer simulation and actual measurement on various freeform surfaces are conducted to verify the validity of proposed method. The results indicate that the proposed method is capable of fusing multi-sensor measured datasets with notable reduction of the measurement uncertainty. 相似文献
6.
基于遗传算法的非线性控制系统参数优化方法 总被引:4,自引:0,他引:4
甘俊英 《工业仪表与自动化装置》2000,(4):11-15
本文针对非线性控制系统参数优化问题,结合非线性控制系统理论、最优化理论及遗传算法,提出了一种新的仿真优化方法,该方法利用遗传算法来求解非线性控制系统参数优化问题,由于遗传算法是在解空间的多个区域内进行搜索,能以较大的概率跳出局部最优,因此可技巧以整体最优解。仿真结果表明,该方法是一种有效的非线性控制系统参数优化方法。 相似文献
7.
Shuo-Jen Lee Dar-Yuan Chang 《The International Journal of Advanced Manufacturing Technology》2006,31(5-6):474-482
In this paper, an integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve the system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead-space problem in the single-point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution is around 50 μm, and the system performs well in terms of stability and repeatability. The sensor system could be mounted on the NC machine or on the X–Y platform for freeform surface digitization. 相似文献
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9.
针对异构参数化特征模型难以检索重用的问题,建立了基于本体的特征表示模式,提出一种新的特征本体映射方法,将产品模型特征信息进行统一的语义描述,建立基于本体的特征模型库以有效地支持异构参数化特征模型的检索和重用.本体映射在系统特征本体和公共特征本体之间进行,基于相似性评价指标进行的特征概念匹配能够实现一对一、一对多和多对一的映射,并利用本体的推理能力和语义网规则描述语言对匹配结果进行检查,以保证本体映射的准确性.编程实现了本体映射算法,通过实例检验了方法的可行性和有效性. 相似文献
10.
JaeSung Kim KwangSoo Kim JaeYeol Lee JaeHun Jeong 《The International Journal of Advanced Manufacturing Technology》2005,26(1-2):131-137
In this paper, we propose a new joint-based assembly modeling method. In joint-based assembly modeling, the assembly constraints are specified on the components, but not on the geometric elements of the components. The proposed method generates assembly models from kinematic joint constraints by applying three procedures (1) to extract all feasible JMFs (Joint Mating Feature) for each mating component using information on joint constraints, (2) to derive mating alternatives for each pair of mating components after reducing the number of JMFs using the pruning criteria, and (3) to generate an assembly model by choosing the intended one from the mating alternatives for each pair of mating components and solving the JMF constraints. Since the joint constraints are expressed in terms of the relations between components rather than relations between geometric elements, the proposed method is more intuitive and natural for assembly modeling and supports modeling activities effectively by minimizing user interactions. By using joint mating constraints for assembly modeling, moreover, the kinematic behaviors of assemblies determined in the conceptual design stage can be directly applied and consistently maintained up to the detailed design stage. In the proposed method, it is also not necessary to re-input the mating constraints even when the component topology is changed. 相似文献
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12.
This paper presents a motion coordination of a two-cooperating robot arm when there are unknown system parameters and bounded
input disturbances. The order of the model of the two-arm system is reduced. To control this, a force/position control scheme
based on an inverse dynamics control scheme is devised. On the top of the control scheme, an adaptive control scheme to take
care of parametric uncertainties, and a robust control scheme to compensate coupling forces between two arms and input disturbances
are devised. The adaptive and the robust control scheme are derived based on a devised Lyapunov function. The adaptive control
algorithm is practical since it does not require the feedback of the second derivative of joint angles and interacting forces.
The robust control scheme guarantees that the tracking error of the leader arm and the interacting forces between two arms
are confined in a certain region. Numerical examples using dual 3 degree of freedom robot arm are shown. 相似文献
13.
Karl Janssens Peter GajdatsyLudo Gielen Peter MasLaurent Britte Wim DesmetHerman Van der Auweraer 《Mechanical Systems and Signal Processing》2011,25(4):1321-1338
Since its first publication in the beginning of the 1980s, transfer path analysis (TPA) has evolved into a widely used tool for noise and vibration troubleshooting and internal load estimation, for single source and multivariate problems. One of the main bottlenecks preventing its even more widespread use in the vehicle development process is the test time needed to build the full data model, requiring not only in-operation tests but also extensive frequency response function (FRF) measurements.As a consequence, several new approaches, such as operational TPA, have appeared over the past years attempting to circumvent this limitation. These methods attract quite some attention as they only require operational data measured at the path references and target locations. However, despite being time-efficient, these methods suffer from several limitations that can lead to incorrect path contribution interpretations and wrong engineering decisions.Hence, a new TPA approach is proposed, providing a good compromise between path accuracy and measurement time. The method is referred to as OPAX as it essentially uses in-operation data complemented with a minimal set of extra tests with forced excitation. The key idea of OPAX is the use of parametric models for identifying the operational loads. This makes the method scalable, enabling the engineer to use a simple model based on a small amount of measurement data for quick troubleshooting or increase accuracy using a more complex model together with additional measurements. 相似文献
14.
Su-Jin Kim Min-Yang Yang 《The International Journal of Advanced Manufacturing Technology》2006,28(3-4):314-320
In this paper, we present a cutter location (CL) surface deformation approach for constant scallop height tool path generation
from triangular mesh. The triangular mesh model of the stereo lithography (STL) format is offset to the CL surface and then
deformed in accordance with the deformation vectors, which are computed by the slope and the curvature of the CL surface.
In addition, the tool path, which is computed by slicing the deformed CL surface, is inversely deformed by those same deformation
vectors to a tool path with a constant scallop height. The proposed method is implemented, and a tool path is generated and
tested by simulation and by numerical control (NC) machining. The scallop height was found to be constant over the entire
machined surface, demonstrating much better quality than that of mesh slicing, under the same constraints for machining time. 相似文献
15.
变结构体参数化设计一直是参数化设计中的难题,在研究现有变结构体参数化设计中的主要方法一变结构变参数设计和模块化变参数设计的基础上,提出了一种基于样条化变参数设计的新设计方法,分析比较了这三种设计方法的优缺点.研究表明,基于样条化变参数设计方法具有数据储存量小、只需生成某一类型的参数设计样板即可实现一类零件的变结构体变参数设计的优点,用VC++6.0开发环境编制了实现程序,验证了样条化变参数设计方法的可行性. 相似文献
16.
17.
Calculation of the unit normal vector using the cross-curve moving mask method for probe radius compensation of a freeform surface measurement 总被引:1,自引:0,他引:1
This paper proposes a cross-curve moving mask method to calculate the unit normal vector based on 5 or 9 data points of a freeform surface measurement for probe radius compensation. This is done in order to simplify the calculation and thus, produce a more efficient and time-saving process. Passing through the middle point and 4 or 8 neighboring points, two crossed curves – longitude and latitude can be constructed. The unit normal vector at the middle point can be determined by calculating the cross product of two tangent vectors along these two crossed curves. Different curve fitting methods for the curves passing through 5 or 9 data points, such as Bézier and B-spline methodologies, have been investigated. Three kinds of surfaces, namely, a spherical surface, a cosine-like surface and a shoe-shaped surface (hereby termed “shoe last”) are selected for evaluating the accuracy of the calculated unit normal vectors. 相似文献
18.
A new 3D-CAD system for set-based parametric design 总被引:3,自引:0,他引:3
Y.-E. Nahm H. Ishikawa 《The International Journal of Advanced Manufacturing Technology》2006,29(1-2):137-150
So far, there has been an extraordinary development of computer-aided tools intended to generate, present or communicate 3D
models. But there has not been a comparable progress in the development of 3D-CAD systems intended to assist designers in
representing and manipulating both geometric and non-geometric design information based on solid models, thus facilitating
concurrent engineering (CE). Design objects continue to be produced by traditional means using the computer as little more
than a drafting tool. In addition, the state-of-the-art 3D-CAD systems are incapable of encoding engineering uncertainties
since only precise single-valued assignments are allowed for their modeling operations. Recently, set-based CE (SBCE) has
been attracting public attention as an emerging CE paradigm. Such a set-based design (SBD) approach presents many possibilities
in handling the uncertainties that are intrinsic at the early phases of design. This paper addresses a novel concept – set-based
parametric design (SBPD) – which combines the SBD practice with the parametric modeling technique widely used in most 3D-CAD
systems. A preference set-based design (PSD) model and a design information solid (DIS) model are proposed to incorporate
the SBPD concept into the current 3D-CAD systems. Finally, a prototype system is implemented to illustrate the potential
to achieve a SBPD practice. 相似文献
19.
Hyun-Jang Shin Heui-Jae Pahk 《The International Journal of Advanced Manufacturing Technology》2007,33(7-8):643-651
This paper discusses the development of a new precision motor stage, where a new magnet array is proposed and a new robust
controller is implemented. Several planar motor parameters, such as the air gap flux density and flux linkage, are analytically
evaluated by the scalar potential, and, thus, about a 5–8% increase is observed for the proposed magnet array. A new robust
controller is also proposed using the parametric uncertainty model, which can effectively control the movement during both
stable and cogging positions. The performance of the robust controller is evaluated, and it shows much higher robustness and
about a 200% higher position accuracy when compared with the conventional PID controller. Therefore, the developed planar
motor stage is successfully designed and implemented, and, thus, proposes great potential for most of the positioning applications
in the field of semiconductor equipment and machine tools. 相似文献
20.
高效率的三角网格模型保特征简化方法 总被引:1,自引:0,他引:1
部分三角网格模型因数据量庞大而导致其不便于存储、分析和显示,本文提出了一种结合网格精细化方法的三角形折叠网格简化算法以解决此问题。首先通过3~(1/2)网格细分法确定待折叠三角形三个顶点的修正坐标,并根据修正坐标初步确定折叠点位置,然后引入折叠点的拉普拉斯坐标和原三角形法向信息来更新折叠点位置,最后由三角形折叠后该区域的体积误差和被折叠三角形的平展度共同确定折叠代价,从而使网格优先从较为平坦和特征点较少的区域开始依次进行三角形折叠简化。对多个模型进行了实验测试和数据分析,结果表明该方法能够有效精简网格数据,与3个不同类型的简化方法相比,该方法的简化效率最高,而且能有效保持原网格模型的几何特征并控制简化三角形的质量。 相似文献