共查询到14条相似文献,搜索用时 3 毫秒
1.
G2 Continuity for Multiple Surfaces Fitting 总被引:1,自引:0,他引:1
J.-Y. Lai W.-D. Ueng 《The International Journal of Advanced Manufacturing Technology》2001,17(8):575-585
Fitting 3D known data into sculptured surfaces has received extensive attention. However, most algorithms available are suitable only for an isolated surface. A part typically contains multiple surface regions that must be blended to a degree of continuity. The conventional approach based on blending, lofting, stitching, etc. cannot guarantee the quality of the surface near the jointed area. The purpose of this work is to present a surface-fitting algorithm for multiple sets of data, concentrating on G 2 continuity across the boundary of the fitted surfaces. The proposed surface-fitting algorithm essentially fits several sets of data simultaneously, and yields a B-spline surface for each set of data. The G 0 ,G 1 , and G 2 continuity conditions between B-spline surface patches were addressed. Based on these results, additional constraints were specified to achieve G 2 continuity across the surface boundary. A successful demonstration of the proposed strategy is provided also. 相似文献
2.
E. Capello Q. Semeraro 《The International Journal of Advanced Manufacturing Technology》2000,16(4):250-258
The paper proposes the harmonic fitting (HF) approach for the selection of the number of sampled points when measuring a plane geometry. HF is the spatial frequency correspondent of the least squares method (LSM) and it will be demonstrated that following HF, the estimated errors can be evaluated as a function of the number of sampled points with closed analytical formulae. This is the basis for the development of a parsimonious sampling for coordinate measuring machines (CMMs). 相似文献
3.
基于B样条曲面的点云孔洞拟合填充 总被引:1,自引:0,他引:1
为了后续曲面重构的需要,针对有孔洞的点云数据,提出了一种孔洞拟合填充的自适应方法。由于孔洞与其周围离散点有一定的连续性,该算法首先从孔洞周围已有的点云数据中选取离散点,用新的参数化方法对得到的离散点参数化后,用最小二乘法进行自适应曲面拟合,对得到的拟合曲面通过迭代法逐步逼近优化,考虑曲率变化的影响在曲面上取点,实现了孔洞光滑填充。实例表明,改进的参数化方法使算法的复杂度减低,进一步迭代优化提高了曲面拟合精度,在面上取点时考虑了曲率变化,因此该方法可以应用于具有复杂曲面形状的点云中的孔洞填充。 相似文献
4.
5.
H.B. Jung K. Kim 《The International Journal of Advanced Manufacturing Technology》2000,16(11):784-790
A new method is proposed for the parameterisation of data points in NURBS surface global interpolation. In this method, the
parameter value at the maximum of each rational B-spline basis function is defined as the parameter value of the associated
data point. Some advantages of this method in geometric modelling are:
1. It selects the knot vectors freely, regardless of the distribution of data points.
2. It is invariant under affine transformations of the data points.
3. It allows multiple data points. 相似文献
6.
B. Lauwers J.P. Kruth P. Dejonghe 《The International Journal of Advanced Manufacturing Technology》2001,17(11):799-804
Multi-axis milling of sculptured surfaces with cylindrical or toroidal cutters has many advantages compared to the use of
three-axis milling with ball nose cutters. Surfaces to be machined are often of complex shape and characterised by convex,
concave and saddle areas. Today, CAM-systems do not support the user in the selection of the different operations in order
to finish the workpiece. This paper describes an operation planning system, which facilitates process planning for the multi-axis
machining of sculptured surfaces. The core of the system is surface analysis, which divides the surfaces into regions, each
characterised by a preferred milling direction and tool diameter. Further, for each region or set of regions, a drive surface
is constructed that is used as the basis for the tool-path calculation. The drive surface approximates to the original workpiece
as closely as possible, and the isoparametric lines which will be the tool-path feed direction lie in the preferred milling
direction. 相似文献
7.
已有的五轴联动数控加工系统往往忽略刀轴矢量插补问题,只是简单地通过对线性轴进行插补、对旋转轴进行跟随的方式来实现刀具轨迹的控制,导致产生非线性误差和刀具碰撞与干涉等问题。为此,提出一种基于刀轴矢量插补的刀具轨迹控制算法。该算法采用大圆弧插补法对加工过程中的刀轴矢量进行控制,同时采用NURBS曲线拟合方法对控制过程中产生的中间点进行处理,并通过对拟合而成的NURBS曲线进行插补来实时计算各运动轴的位置。该算法不仅能够有效地提高五轴联动数控加工的精度,而且可以有效减小数据存储量。仿真和实际加工验证了算法的有效性和实用性,证明算法具有轨迹过渡平稳、非线性误差小的特点。 相似文献
8.
W.Y. Zhang S.B. Tor G.A. Britton 《The International Journal of Advanced Manufacturing Technology》2002,19(6):454-460
Modelling as a means of knowledge acquisition has been proposed by some workers in artificial intelligence. In this paper
the authors describe an approach using two-level knowledge modelling that employs the concepts of a functional model (extended
FEBS model) and an object model to capture domain-specific functional design knowledge. The functional model serves as a basis
for communication between domain experts and a knowledge engineer. The object model is used to bridge the gap between the
functional model and an executable knowledge base. The approach is viewed as an important method for building a function-laden
knowledge base that is useful for developing a knowledge-based functional design expert system. The proposed knowledge acquisition
method is applied to an automatic assembly system for manufacturing electronic connectors to illustrate the general idea. 相似文献
9.
W.Y. Zhang S.B. Tor G.A. Britton 《The International Journal of Advanced Manufacturing Technology》2002,19(4):235-244
This paper presents a knowledge-based approach for automating the functional design of mechanical systems. By using our proposed
automated functional reasoning strategy, which is based on a heuristic search method, a set of physical behaviours can be
reasoned out automatically from the desired functions. The interconnection of these behaviours is possible when the functional
outputs of one are compatible to the corresponding functional requirements of the next one. Though the design space for behavioural
configuration is very large, by defining its heuristic evaluation function as a fuzzy multicriteria decision-making (FMCDM)
problem, the proposed heuristic search method can lead to a near optimum design solution in a reasonable time. A case study
for the automated functional design of an automatic assembly system is given to illustrate the operation of the proposed heuristic
search method, and to show its effectiveness in functional reasoning and optimizing the final design. 相似文献
10.
C. Tournier E. Duc 《The International Journal of Advanced Manufacturing Technology》2002,19(5):318-324
The machining of sculptured surfaces such as moulds and dies in 3-axis milling relies on the chordal deviation, the scallop
height parameter and the planning strategy. The choice of these parameters must ensure that manufacturing surfaces respect
the geometrical specifications. The current strategies for machining, consist primarily in driving the tool in parallel planes
which generates a tightening of the tool paths. A constant scallop height planning strategy has been developed to avoid this
tightening. In this paper, we present a new method of constant scallop height tool-path generation based on the concept of
the machining surface. The concept of the machining surface is developed and its use to generate constant scallop height tool
paths is described. The approach is compared with existing methods in terms of precision and in particular its aptitude to
treat curvature discontinuities. 相似文献
11.
针对直线与参数空间NURBS曲线、直线与NURBS曲面求交问题,提出了一种改进的基于仿射算术和区间运算的直线与NURBS曲线/曲面求交的有效方法。该方法将基于边曲率或面曲率的子域分解方法应用到求交算法中,快速定位预迭代区间,减少不必要的迭代求交判断。与传统区间迭代算法相比,该求交算法为超线性收敛的快速迭代算法,在一定程度上解决了传统区间运算的“保守性”。另外,该方法放宽了对初始区间的要求,减少迭代次数,提高了迭代算法效率。通过计算区间算子判断给定直线与NURBS曲线/曲面有无交点和存在交点时的交点数目,保证了求解交点精度,为解决直线与曲线/曲面多交点判断及内外环或内外域判断等问题提供了有利条件。数值算例验证了该方法的有效性、计算精度和效率。 相似文献
12.
J.-M. Redonnet W. Rubio F. Monies G. Dessein 《The International Journal of Advanced Manufacturing Technology》2000,16(6):383-391
End-milling of free-form surfaces on 5-axis NC machine tools is a complex problem which has been studied by a large number
of research scientists. When end-milling non-convex surfaces there is a risk of interference between the tool and the surface.
Using a 5-axis NC machine tool enables the tool to be oriented in any spatial direction to access a given point. This means
interference can be avoided and the position of the tool can be optimised so as to minimise residual material. Here, a new
method is presented for tool positioning in end-milling of free-form surfaces based on evaluating the interference for a set
of test points distributed around the circumference of the tip of the tool. Distinction is made between the cases of semi-finishing
and finishing which can be performed using a large diameter flat-end tool and a toroidal tool, respectively. Further, all
developments are implemented for interactive use in a CAD/CAM software environment. 相似文献
13.
F. Xi Y. Liu H.-Y. Feng 《The International Journal of Advanced Manufacturing Technology》2001,18(3):211-216
In this paper, the problem of compensation of 3D line laser scanning data for improved inspection accuracy is addressed. This
problem is important, as a 3D line laser scanner is about one order less accurate than a touch probe. The approach taken is
to compensate through error characterisation. In other words, a software compensation is performed, instead of a hardware
compensation, which is probably more expensive. To do so, the errors associated with a 3D line laser scanning system are first
characterised. With error characterisation, an empirical formula is obtained relating the errors to the influencing factors
including the projected angle and the scan depth. This empirical formula is used to compensate for the digitised surface data
obtained by the corresponding laser scanning system. The results show that the proposed approach effectively improves inspection
accuracy. 相似文献