Optimal five-axis tool path generation algorithm based on double scalar fields for freeform surfaces

In order to generate efficient tool path with given precision requirements, scallop height should be kept under a given limit, while the tool path should be as short as possible to reduce machining time. Traditional methods generate CC curves one by one, which makes the final tool path far from being globally optimal. This paper presents an optimal tool path generation model for a ball-end tool which strives to globally optimize a tool path with various objectives and constraints. Two scalar functions are constructed over the part surface to represent the path intervals and the feedrate (with directions). Using the finite element method (FEM), the tool path length minimization model and the machining time minimization model are solved numerically. The proposed method is also suitable for tool path generation on mesh surfaces. Simulation results show that the generated tool path can be direction parallel or contour parallel with different boundary conditions. Compared to most of the conventional tool path generation methods, the proposed method is able to generate more effective tool paths due to the global optimization strategy.     

Triangulated surface flattening based on the physical shell model

Journal of Mechanical Science and Technology - Triangulated surface flattening plays an important role in the surface shape design of a complex product, such as a vehicle, a train and an air plane....     

Tool path generation by offsetting curves on polyhedral surfaces based on mesh flattening

Polyhedral surfaces are used as representation model for CAM and process planning purposes because of its simplicity for data exchange and geometric computation. However, there are few tool path planning strategies for such surfaces but isoplanar method. This paper presents a contour offset approach to tool path generation for three-axis ball-end milling of polyhedral surfaces, based on a novel method for offsetting curves on polyhedral surfaces. One of its salient features is to reduce the task of removing complex interfering of offsets from 3D physical surfaces to 2D plane by flattening mesh surfaces and avoid costly 3D Boolean set operations and relatively expensive distance calculation. Moreover, in practical implement, the procedures of calculating offset points and removing interfering loops are merged and carried out simultaneously results in an efficient tool path generation method. Empirical examples illustrate the feasibility of the proposed method.     

基于FreeForm的CAD模型细节添加与修改

分析了FreeForm造型的特点及优势,并针对FreeForm在造型过程中的细节添加与修改功能进行了详细论述,将传统CAD建模与触觉交互造型有机结合起来,提出了一种基于FreeForm的CAD模型细节添加与修改方法,并给出了应用实例.     

Measurement of nonrigid freeform surfaces by coordinate measuring machine

Nonrigid part could be subjected to significant distortion after the removal of manufacturing forces. This condition, known as free-state variation, is principally due to weight and flexibility of the part and the release of internal stresses resulting from fabrication. The present work deals with the inspection of freeform surfaces belonging to nonrigid parts. A manufactured aeronautic component, named Mid Cowling, is considered as case study. The design of an appropriate fixture equipment will be firstly presented: it enables both to simulate the mating part interface and to locate the part in coordinate measuring machines working volume. Then, a method for evaluation of a freeform surface with respect to the nominal one will be presented. This evaluation is based on Euclidean distance between actual and nominal surfaces. Finally, an analysis of the part deformation presented in order to evaluate the measurement process in terms of interaction of the measurement system with the inspected part will be proposed. The adopted method, based on a finite element analysis, was proposed in order to evaluate the interaction, due to the measuring force, between the touch probe and the inspected surface and thus its effect on the measurement result.     

Path planning of multi-patched freeform surfaces for laser scanning

In this paper, a new method for scanning a complex surface model with multiple patches is proposed. In scanning of freeform-shaped models, it is difficult to generate a measuring plan by human intuition due to the complexity of the part. The developed method calculates the number of scans, scan direction, and scan path for a stripe-type laser scanner. The user can designate the surface patches that need to be scanned. In generating the scan plan, surface information is first extracted from the CAD model automatically. Other information such as, design knowledge, functionality and machine parameters are provided interactively. Based on this information, the original surface model is sampled in the u, v parameter domain and the sampled points are grouped using the view angle of the laser scanner. The scan direction is determined by calculating the global mean vector of the sampled points that belong to a group. The range of the view angle can be varied to enhance the quality of captured point data. The optical scan paths for each scan direction are calculated by projecting the sampled points onto a 2D plane. The optical constraints are also verified to guarantee the generated scan plan.     

Constrained deformation of freeform surfaces using surface features for interactive design

There is an increasing demand in conceptual design for more intuitive methods for creating and modifying freeform curves and surfaces in CAD modeling systems. The methods should be based not only on the change of the mathematical parameters but also on the user's specified constraints and shapes. This paper presents a new surface representation model for freeform surface deformation representation. The model is a combination of two functions: a displacement function and a function for representing an existing NURBS surface called a parent surface. Based on the surface model, the authors develop several novel deformation methods which are named SingleDef (Single-point constraint based deformation method), MultiDef (Multiple-points constraints based deformation method), CurDef (Curve constraints based deformation method) and FeatDef (Feature constraint based deformation method). The techniques for freeform surface deformation allow conceptual designers to modify a parent surface by directly applying point constraints, curve constraint or a surface constraint to the parent surface. The deformation methods are implemented in an experimental CAD system. The results show that designers can easily and intuitively control the surface shape.     

An accurate surface error optimization for five-axis machining of freeform surfaces

This paper presents an accurate surface error interpolation algorithm for five-axis machining of freeform surfaces. One of the most important steps in the interpolation process is to calculate the next cutter contact (CC) point according to the present one. In this paper, the next CC point is calculated by an accurate chord evaluation method. This method is developed based on the cutting simulation process, which can be vividly described as firstly planting dense grasses on the tool path curve and then cutting them when the tool moves by. The left lengths of the grasses either positive or negative are considered to be the machining error. The method is accurate also because the tool geometry and the tool orientation changes during five-axis machining are taken into consideration. With this method, the chord errors between CC points are controlled uniform along the tool path. The proposed interpolation algorithm is compared with the commercial CAM systems like PowerMILL and UG. The results show that the proposed algorithm can significantly reduce the number of cutter locations meanwhile confine the chord error. A real cutting experiment is implemented, and the result indicates its promising value in industrial applications.     

Fast tool servo diamond turning of optical freeform surfaces for rear-view mirrors

The International Journal of Advanced Manufacturing Technology - Optical freeform surfaces have been applied in optoelectronic systems more and more widely, but it is difficult to fabricate this...     

基于迁移学习的滚抛磨块优选模型

在选择滚抛磨块时,针对案例推理技术在案例相似性较低情况下无法选定有效滚抛磨块的问题,提出基于迁移学习的滚抛磨块优选方法.通过缩小源案例和新问题的分布差异,将源案例的信息迁移到新问题的求解中,优选得到滚抛磨块.首先,通过分析大量实际加工工艺案例构建案例特征E-R图;然后,对不同类型的案例特征值进行归一化预处理,经过集成流...     

光学自由曲面金刚石车削CNC仿真程序编译系统

为了解决光学自由曲面金刚石车削(DTOFS)NC代码的验证问题,保证NC代码的正确性和合理性,将计算机仿真技术应用到DTOFS加工中。利用面向对象的编程语言Visual C++为平台,结合OpenGL库函数,开发了DTOFS CNC仿真程序编译系统。根据所提取的刀具坐标信息,建立了刀具运动轨迹方程,以实现刀具的插补过程。研究结果表明,该系统能够对数控加工程序进行检查,提前发现程序中的错误并及时地进行修改。与传统插补方法相比,本系统极大地提高了仿真精度。     

基于扫描线数据自由曲面在AutoCAD中的构建

这里提出一种AutoCAD环境下自由曲面的三维重建方法,根据测量得到的三维扫描线数据,通过反算得到控制顶点,用Add3Dmesh方法在AutoCAD中创建双三次B样条曲面实现了自由曲面三维模型的自动重建,提高了自由曲面建模和设计的效率。     

基于反射线模型修改NURBS曲面不光顺性

反射线模型是一种评估曲面光顺性的强有力工具.提出了一种基于反射线模型修改NURBS曲面局部不光顺性的新方法,将反射线不规则部分用期望形状的5次B样条曲线替换,通过指定新反射线部分点的入射线方向,将所得反射线修改模型对应的非线性方程组转化成线性方程组,大大简化了问题的复杂性.新NURBS曲面具有指定的反射线形状,某些点具有间接确定的法线方向.该方法直观、适用于实时交互设计.最后以实例验证了算法的有效性.     

基于自由曲面的空间光学系统偏振像差分析

针对含有自由曲面的空间光学系统中偏振像差对探测精度和成像质量的影响,基于琼斯表示法,提出以条纹泽尼克多项式为表征函数的自由曲面离轴光学系统偏振像差分析方法,构建了自由曲面反射光学系统偏振像差解析模型,分析了条纹泽尼克多项式低阶系数对视场离轴光学系统偏振像差分布的影响;通过全视场偏振光线追迹仿真及系统引入自由曲面前后的对...     

A robust surface fitting and reconstruction algorithm for form characterization of ultra-precision freeform surfaces

Ultra-precision freeform surfaces are non-rotational symmetric surfaces possessing sub-micrometer form accuracy and nanometric surface finish. Although they can be fabricated accurately by ultra-precision machining technology, their surface quality is difficult to be characterized. Surface reconstruction is a vital task in the form characterization of ultra-precision freeform surfaces. This paper presents a robust surface fitting algorithm to reconstruct a high fidelity surface from measured discrete points while the surface smoothness can be ensured as well. A fitting threshold named confidence interval of fitting error is proposed to strike the balance between fitting accuracy and surface smoothness in the fitting process. The fitting algorithm is in two steps. In the first step, bidirectional sampling method is developed to extract a curve network from measured points cloud to construct an initial surface. In the second step, the fitting error of the initial surface is minimized to meet the prescribed fitting error threshold. A series of experimental work has been conducted and the results show that the proposed algorithm is able to provide effective means for increasing the accuracy in the form characterization of ultra-precision freeform surfaces.     

Large-area profile measurement of sinusoidal freeform surfaces using a new prototype scanning tunneling microscopy

This paper presents large-area profile measurement of ultra-precision diamond turned sinusoidal surfaces by using a specially developed scanning tunneling microscopy (STM). The new prototype of STM system employs a long stroke PZT servo actuator as the Z-directional scanner, an integrated capacitance displacement sensor to accurately measure the Z-directional profile height, a motorized stage with long traveling stroke for carrying out large-area scanning. A simple method for self-calibration of the inevitable sample tilt is proposed in order to achieve large-area measurement without tip-crashing or losing of tip-sample interaction. Several types of ultra-precision machined sinusoidal freeform surfaces with different geometrical parameters are measured by the new STM system over large scanning areas at the scale of millimeters. Specially, a sinusoidal surface with peak-valley amplitude of 22 μm and periodical wavelength of 550 μm is successfully measured and imaged by the STM system. The measurement repeatability error, repeatability standard deviation and measured profile deviation are also evaluated. It is confirmed that the new STM system is capable of carrying out large-area as well as large-amplitude measurement of the ultra-precision machined sinusoidal surfaces.     

NURBS output based tool path generation for freeform pockets

A robust method is proposed to generate tool paths for NURBS-based machining of arbitrarily shaped freeform pockets with islands. Although the input and output are all of higher-degree NURBS curves, only one simple category of geometric entities, i.e., line segments, is required for initial offsetting and for detecting and removing self-intersecting loops. Furthermore, using those linear non-self-intersecting offsets as the legs of NURBS control polygons, NURBS-format tool paths can be smoothly reconstructed with G¹-continuity, no overcutting, no cusps, and global error control. Since all operations involved in computing tool path curves are linear geometric calculations, the method is robust and simple. Examples with integrated rough and finish cutting tool paths of pockets demonstrate the usefulness and effectiveness of this method.     

基于正方形网格能量模型的能量均衡策略

延长网络生命周期是无线传感器网络的一个重要的目标。不均衡的能耗在很大程度上影响了网络生命周期。在正方形网格能量模型的基础上,使传感节点以一定的概率直接传输到基站节点或经过中继节点多跳传输到基站,提出基于能量均衡消耗的延长无线传感网络的生命周期的算法,并进行了相关的计算推导。