面向数控加工组合自由曲面过渡技术

从数控加工的角度研究了组合自由曲面的过渡技术并建立过渡面的方法。该过渡技术充分考虑了与数控加工关系密切的组合曲面的曲率情况,避免了以往ＣＡＤ造型中过渡圆角半么牟盲目性,使得在加工过程中,不同过渡面 而无法加工或更换半径更小 刀具而降低加工效率。该方法为曲面过渡技术提供了新的思路,同时有利于ＣＡＤ／ＣＡＭ一体化的实现。     

复杂曲面重构中的倒圆技术

介绍复杂曲面重构中的曲面倒圆圆角和有关倒圆术语的定义 ,研究曲面倒圆的基本算法 ,概述曲面倒圆的方法 ,并给出曲面倒圆技术的应用实例及部分结论     

基于径向基函数和自适应单元分解的大规模散乱点云快速重构

径向基函数用于散乱数据的插值和拟合具有精确和稳定的优点,但是它不适合大规模点集的曲面重构。把径向基函数和单元分解原理综合起来,提出一种大规模散乱点云的隐式曲面快速重构算法。把整体定义域自适应细分成一系列稍微重叠的子域,基于径向基函数在各子域上计算局部表面,最后采用单元分解函数对局部表面进行加权混合得到全局的重构表面。方法适于处理数量较大和分布密度变化较大的点云数据重构。     

分形表面特征信息的复合评定方法

提出一种表面特征信息的复合评定方法,识别和分析不同尺度下的表面特征信息分量,理解工程表面宏观功能特性。许多工程表面具有统计自相似和自组织等分形特性,针对这种分形工程表面,提出一种基于小波的表面特征模型。利用小波的变焦特性,观察和分析不同尺度下的工程表面形貌。采用分形维方法,确定特征信息的小波分量尺度,从原始表面形貌中提取粗糙度、形状误差和波纹度等特征信息。     

Freeform texture representation and characterisation based on triangular mesh projection techniques

Texture characterisation for freeform non-Euclidean surfaces is becoming increasingly important due to the widespread of the use of such surfaces in different applications, e.g. the additive manufacturing. Four main steps are required to analyse and characterise those surfaces which include new surface representation, surface filtration and decomposition, texture representation methods and finally the calculation of the surface parameters. Recently, the representation, as well as the filtration and decomposition, of freeform surfaces have been investigated and some algorithms have been proposed. This paper, however, shed the light on how to represent the texture of freeform non-Euclidean surfaces before calculating the parameters. A novel model for freeform surface parameterisation is introduced; this new model proposes the use of a projection algorithm before the actual calculation of the parameters. Different projection algorithms have been adopted from the mesh projection techniques found in the field of computer graphics. The results of applying those algorithms to represent the texture of both simulated and bio-engineering surfaces are shown, also a comparison between those algorithms has been carried out. Furthermore, examples of calculating some of the surface parameters for freeform surfaces are given.     

基于表面法矢的散乱数据分割与几何特征提取

使用区域增长法进行散乱数据的区域分割以及二次曲面几何特征的提取.算法首先自动地布置种子区域,然后通过迭代/拟合这一循环过程来实现区域的增长.为了提高算法的可靠性,提出基于散乱数据表面法矢的二次曲面直接拟合方法.该方法根据特定类型二次曲面的几何性质,应用线性最小二乘技术求解其几何参数,从根本上解决以往二次曲面拟合算法因几何参数初值的设置精度不高而导致的求解效率低,进而失败的问题.试验结果表明提出的算法实现简单,且稳定可靠.     

Surface-texture measurement and characterisation with applications to machine-tool monitoring

In this paper, a comprehensive review is given of surface-texture measurement methods, characterisation of surfaces, surface finish and machine-condition monitoring using surface-texture information. A comparative evaluation of surface-texture modelling is provided. Directions in the areas of surface-texture research are also identified.     

Surface offsetting using distance volumes

Proposed in this paper is a new approach for offset surface construction using three- dimensional (3D) distance volumes. After converting an original compound surface into a triangular mesh, the approach creates a distance volume of the triangular mesh. With this distance volume and a given offset value, it extracts the offset points in each slice to create a sequence of two dimensional (2D) cross-sections. The approach then performs offset surface construction using the serial cross-sections. For more accurate and efficient computation of the distance volume, the concept of space division is combined with the concept one of distance propagation to the whole space of interest. The resulting offset surface is a G¹ composite surface consisting of three kinds of surfaces: skinned, capped, andor branched surfaces. The proposed approach provides offset surfaces that are accurate and free of degeneracy. Some experimental results demonstrate its usefulness and quality.     

Fiber optic displacement sensor for imaging of tooth surface roughness

A simple and inexpensive method using fiber optic displacement sensor is proposed for measurements of tooth surface roughness based on the intensity modulation technique. A light beam was launched onto a tooth surface via a bundled fiber. The reflected light from the surface was collected and measured as a function of lateral distance to estimate the roughness of the surface. The system’s roughness measurement capability was successfully tested on teeth surfaces of varying surface texture. In the measurement, the average surface roughness, R_a for the canine, molar, hybrid composite resin and artificial teeth surfaces were estimated to be approximately 121, 62.6, 39 and 37.6 μm, respectively. The experimental results indicated the capability of implementation of the displacement sensor for the imaging of the tooth surface profile as well as a micron-size roughness estimator with a measurement error of less than 2.35%.     

G2 Continuity for Multiple Surfaces Fitting

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.     

曲面间最小距离及其在曲面求交中的应用

为了计算曲面间的最小距离 ,首先在两曲面上分别划分网格 ,选择两曲面上对应于最小距离的一对网格点作为初始点 ,利用曲面的几何特性进行数值迭代求取两曲面间的最小距离。在此算法的基础上 ,对采用跟踪法求曲面交线时如何确定初始跟踪点进行了深入研究。为了获得用于跟踪全部交线的初始跟踪点 ,将一张曲面分割成一组小曲面片 ,利用曲面间的最小距离检测各曲面片与另一曲面的相交性 ,并采用二分法求初始跟踪点。计算结果表明 ,本文算法效率高 ,稳定性好 ,实用性强。     

Surface texture generation using high-feed milling with spindle speed modulation

This paper presents a new surface texturing technique using ball-end milling with high feed speed and spindle speed modulation. The ratio between feed-rate and cutting tool radius is in the range of 0.2–0.4, which is much larger than the ratio in conventional milling. Sinusoidal modulation signal is added, so the spindle speed becomes time-varying in order to generate different texture profiles. The cutting tool kinematics are modeled considering the tool-tip run-out and deflection due to cutting forces. The effects of amplitude and frequency of the modulation signal on tool-tip trajectories and surface textures are simulated and analyzed. The relationship between the micro features of the surface texture and the process parameters are investigated. Surface texturing experiments are conducted based on the proposed technique, and tribology tests are performed on the textured surface. It is shown that the textured surfaces present frictional anisotropy, which depends on the process conditions and modulation parameters. The proposed technique is able to achieve fast generation of various surface textures without additional instrumentation, and the final texture geometry is controllable based on the presented kinematics model.     

A Freeform Surface Modelling System Based on Laser Scan Data for Reverse Engineering

Reverse engineering technology starts with a measurement process, inspecting the surface contour of the object, and applies a CAD geometric modelling technique to construct the surface model. The purpose of this study is to develop a freeform surface modelling system involving the functions of data reorganisation and surface construction of reverse engineering. An important task in reverse engineering is the process of reducing the large amount of coordinate data derived by measurement devices. Reduction methods in common use include uniform deviation, division by a factor, spatial sampling, chordal deviation and interpolated sampling. Each of the above modes has its advantages and weaknesses, and suitable application areas. A new data reduction mode, which integrates the space concept and height characteristic, is proposed, called the height decision method. This method can achieve the aim of data simplification while maintaining the curve characteristics of the model. The CAD modelling system is developed by an AutoLISP program with MDT v4.0 software. An egg model is presented in this paper for explanation and verification.     

Reverse Engineering of Sculptured Surfaces by Four-Axis Non-Contacting Scanning

To deal with the complex-sculptured-surface data extraction problem, an efficient four-axis non-contacting surface data scanning system, which integrates a PC-based XYZ table, a laser displacement meter (LDM), and a personal computer is developed. In this four-axis system, an LDM, an XYZ table and a PC are used as a displacement sensor, sensor carrier and central controller, respectively. In extracted data processing, we apply the medium filter technique to smooth data points, and propose a simple algorithm to discard efficiently those redundant measured points according to the required degree of accuracy. While in the surface reconstruction, we first try to convert all eliminated column or row data into spline curves. Methods for 2D spline (u, v directions) curve construction are described. Non-meshed 2D spline curves are then blended to a spline surface in terms of a sparse matrix data structure. Experimental results show that the proposed four-axis surface data scanning machine can be programmed to measure most of the complex sculptured surfaces which is not possible using a three-axis machine. The proposed extracted data-processing method can reduce the surface reconstruction time substantially, for only the cost of a little extracting time and minor modelling errors.     

Reverse engineering from uni-directional CMM scan data

The design and manufacture of sculptured surfaces using the reverse engineering (RE) approach is popular in industry. RE requires the definition of surfaces, a process that is usually performed using a coordinate measuring machine (CMM). However, the present methods for surface model reproduction require a high density of data points, resulting in increased manufacturing times.This paper proposes a method to reduce the manufacturing times. In this method constrained least-square fitting techniques are employed. The splines are then blended to a surface model by a spline segment matching and subdividing algorithm. A model refinement method is proposed, that uses only a fraction of the data points. Experimental results and future developments are also included.     

A Wavelet–Fractal-Based Approach for Composite Characterisation of Engineering Surfaces

Many types of engineering surfaces have been seen to have fractal characteristics. A good model of the properties can be produced using wavelet-based expansions. For multiscale analysis of surface topography, a difficulty exists in determining quantitatively the feature separation index for comprehensively characterising roughness, waviness, and form errors from a primary surface structure. In this project, we utilise the fractal dimension, which has proved to be an intrinsic parameter capable of measuring surface irregularities, to quantify the feature separation index in the wavelet transform for a composite characterisation of engineering surfaces. The effectiveness of the proposed method is validated in the computational testing of 2D and 3D surfaces. ID="A1"Correspondance and offprint requests to: Dr Y. Gao, Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: meygao@ust.hk     

The development of a technique for 3D complex surface reconstruction from unorganized point cloud

In this paper, we propose a new neural network based on our two-level adaptive hierarchical clustering algorithm. The algorithm is to manage unorganized points, so that the triangular mesh models can be correctly obtained by applying the triangular mesh creation algorithm. We also develop adaptive self-flipping triangle edges to improve triangular mesh structure. Only one parameter, the maximal edge length of triangle, is needed in the neural network. The proposed two-level consists of the first level for clustering the cloud of points that has same order of the maximal edge length into a same cluster and the second level for generating triangular surface model or drape surfaces over the points of the same cluster. The normal vector for the generated triangular 3D surface model can be obtained from the second level. This helps to generate the STL file or stereolithography format. From the experimental results it can be shown that the proposed method is very effective for clustering unorganized point clouds for generating a triangular mesh of complex surfaces.     

An Improved Sculptured Part Surface Design Method with Jerk Continuity Consideration for Smooth Machining

This paper presents an investigation of jerk continuity in milling operations for sculptured surfaces of mechanical parts. It has been realised that chattering in machining operations can cause detrimental effects on the quality of machined parts as well as on the life of the cutting tool. One of the major reasons of chattering is known to be the rough transition of cutter accelerations when traversing through desired part sur-faces. The problem becomes serious when machining sculptured surfaces of parts. In this work, an effective computer-aided sculptured surface design technique is proposed. The ultimate goal is to achieve smooth and near chattering-free machining for producing precision parts. The proposed surface design scheme models the part’s sculptured surfaces in such a way that it warrants a smooth "jerk" transition at the boundaries of common surface patches on the part. This results in a drastic reduction of large step changes of cutter accelerations during machining operations which will in turn eliminate a good portion of the chattering effects. Three theorems concerning the necessary jerk continuity conditions for surface patches connections are developed and their proofs are presented. Examples of an aerofoil and a concept car model are implemented, using the proposed modelling approach, to demonstrate its effectiveness.     

复杂曲面自动铺丝轨迹规划算法设计

针对复杂曲面自动铺丝轨迹生成问题,提出一种可自动生成铺丝轨迹的经线包络法,即按照曲面形态,自适应生成一族包络整个曲面的经线,然后以此作为参考线,根据复合材料铺丝束纤维的宽度、数量等工艺数据,生成与对应参考线成固定铺放角度的铺丝轨迹。该算法适用于采用参数方法描述的复杂曲面,仿真实例表明该算法可行且有效。     

Measurement of in-plane deformation by surface inclusion (proposed measuring method and some experimental results)

A new measuring technique is proposed for measuring the in-plane deformation of soft metal surfaces when indented by a hard indenter, using the displacement of inclusions on the soft metal surface as sensors. In in-plane deformation, the soft metal surface flows along the hard indenter surface. In this paper, the principle of this new measuring technique is explained and some example measurements obtained from the experiments with aluminum and copper beryllium alloy plates, are presented.