通用刀具扫描体隐式曲面建模方法

提出五轴加工仿真中基于隐式曲面理论的通用刀具扫描体建模方法。为了提高布尔减运算时间性能,采用隐式曲面能够高效判断扫描体与工件体素数据场点集的位置关系,避免耗时的空间相交计算。定义通用刀具体的隐式曲面模型;根据刚体运动框架理论,建立工件框架与刀具框架的映射关系,利用逆向运动法确定曲面边界范围,将刀具体线性位移和旋转角度作线性插补,推导出工件框架中刀具扫描体的隐函数曲面方程;在分析刀具各部分扫描体方程实数根情况的基础上,给出基于隐式曲面的扫描体构造算法。以典型刀具和运动类型为例,分析扫描体构建过程,试验结果验证方法的正确性和较好的时间性能,方法应用于数控系统中的材料去除仿真。     

NC验证中通用铣刀扫描体生成方法

根据数控程序计算刀具扫描体对于复杂曲面数控铣削程序的验证具有重要意义。文章提出了一种用于生成刀具扫描体的有效方法。基本思想是：计算刀具相对于工件运动时，刀轴形成的扫描面；然后，根据刀具几何形状和刀轴扫描面计算刀具扫描体，并举例说明了本文方法的正确性。     

Research on an algorithm for an NC machining hypoid pinion

Based on the flexibility characteristics of the NC machine tool, which means that various motions can be performed arbitrarily on NC machine tools, a new algorithm for manufacturing a hypoid pinion is proposed. This gets rid of the limitation of traditional mechanical machine tools and their algorithms. When the cutter tilt method is combined with the modification method, a method of manufacturing the pinion with a prescribed-size cutter on an NC machine tool can be realised. This helps to simplify cutter specifications and realise the error compensation of the cutter size. In this paper the algorithm is derived. According to the equations of cutting, the machine settings are calculated.     

Tool path optimization in postprocessor of five-axis machine tools

Generally, tool path is generated in a computer-aided manufacturing software considering only the geometry of machining parts. It is converted into numerical control (NC) codes in the postprocessor based on the particular machine kinematics. For some special types of five-axis machine tools, e.g., non-orthogonal five-axis machine tools, the generated NC codes may produce unqualified parts because of the existence of the non-linear error. Conventional commercialized postprocessors usually do not have the function of non-linear error checking. Observing that the tool path is a non-smooth trajectory full of corners and a series of connected line segments, cubic spline interpolation is applied to smooth the tool path at regular points in this study. The cutter tip center points are computed by the cubic spine interpolation, while the cutter posture vectors are obtained via linear interpolation. At the splines (for regular points) and the line segments (feature points), more points are chosen to be converted into NC codes to reduce the non-linear error, which is called data densification. Using the cubic spline to smooth the tool path and the data densification to reduce the non-linear error, a novel tool path optimization algorithm in postprocessor is proposed. Experiments were carried out on an inclined rotary spindle axis non-orthogonal five-axis machine tool. It shows that the proposed tool path optimization provides improved accuracy and surface quality.     

工作台旋转式五轴加工中扫掠轮廓线的求解

国内外对五轴数控加工中的扫掠轮廓线的研究往往集中于主轴摆动式机床。本文给出了实际生产中应用广泛的工作台旋转式五轴加工中环形刀具上扫掠轮廓线的显式表达式,分析了扫掠轮廓线在刀具曲面上的几何特性。所用的计算方法高效精确,为复杂曲面加工过程的动态模拟和加工误差的控制奠定了数学基础。     

机械制造业数控机床几何误差自动控制

为了降低数控机床几何误差,提升加工精度,提出机械制造业数控机床几何误差自动控制方法。通过激光跟踪仪辨识机械制造业数控机床的几何误差,采用快速定位补偿算法与圆弧插补补偿算法相结合的方法补偿数控机床几何误差。利用计算机辅助制造软件生成刀位文件,依据刀位文件生成数控机床加工程序,通过补偿控制器生成数控机床各轴运动的控制指令,数控机床伺服系统接收控制指令后,自动控制数控机床各轴运动,以达到数控机床几何误差自动控制的目的。实验结果表明,采用该方法自动控制数控机床几何误差后,方向与角度的几何误差分别低于0.03 mm与0.1°,实际应用效果较好。     

复杂曲面的数控加工误差分析

针对复杂曲面的多轴数控加工,应用数学知识建模,从理论上分析了平底铣刀刀具加工复杂曲面时的误差,得出了影响数控加工精度的主要因素并提出了误差补偿方法,为控制多轴数控加工的误差提供了理论依据与补偿算法,对高精度复杂曲面的数控加工具有借鉴意义。     

从测量的散乱数据点云直接生成数控刀具路径的研究

提出了一种直接从测量的散乱数据点云用球头刀对自由曲面进行三轴数控加工时生成刀具路径的方法。不同于现有散乱点云基于逆向工程的刀具路径生成方法,本法考虑并估计了曲面加工误差和粗糙度。将散乱数据点云向XY平面投影,以获得的投影边界为刀具路径的主方向,然后根据曲面所需的加工误差和残留高度要求划分该投影数据点云,得到一系列刀位网格单元。通过最小化每个刀位网格单元的加工误差以确定每个刀位网格的节点位置,加权平均相关联刀位网格节点来对齐相邻刀位网格单元的边缘。为了缩短加工时间,裁去刀位路径上多余的线段,最终生成高效合理的数控加工刀具路径。已用实测的数据点云验证了本法直接生成刀具路径的有效性。     

通用刀具扫描体的快速造型

以实体造型仿真和工程应用为目的,以包络理论为理论基础,结合离散造型法和实体造型法这两种造型方法的优点,提出刀具扫描体快速造型的新方法。该方法主要由四个有序部分组成：第一部分是对刀具进行离散采样的预处理;第二部分是刀具上的离散采样点沿着扫描路径运动,生成扫描元曲线;第三部分是利用在扫描路径上建立起来的若干截平面与扫描元曲线相交后得到的交点集,构造平面网格,求解出平面网格的外轮廓顶点后将其分组,分别进行曲线拟合后再组合成刀具扫描体的包络曲线;第四部分则是通过这些包络曲线进行放样,构建刀具扫描体的包络曲面,最终完成刀具扫描体的完整构造。与现有方法相比,该方法能快速有效地对刀具扫描体进行造型,在减少计算量的同时保证了造型的准确性,因而具有广泛的应用价值。     

A new approach to generating arc length parameterized NURBS tool paths for efficient three-axis machining of smooth, accurate sculptured surfaces

With the development of a new function of computer numerical control controllers, nonuniform rational B-spline (NURBS) interpolation, NURBS tool path generation for sculptured surface machining is under extensive research. The common procedures of the current NURBS tool path planning methods are as follows: first, to find a group of cutter contact points on a sculptured surface; second, to calculate their corresponding cutter locations (CLs); then, to fit a NURBS tool path to the CLs within a prescribed tolerance; and finally, to inspect the tool path for possible gouge by the tool and delete the invalid path segments, if any. However, the NURBS tool path has the following problems: (a) although it passes through the discrete CLs of the theoretical CL path, the deviation along the two paths could be larger than the tolerance; (b) its parameter is not the arc length of the path; and (c) it is difficult to detect gouge along the NURBS path and to remove the invalid segments from it. Consequently, NURBS tool paths generated with the current methods of commercial computer-aided design/computer-aided manufacturing (CAD/CAM) software cannot be used to make smooth and accurate surfaces. To address these problems, this work proposes a new approach to generating arc length parameterized NURBS tool paths with high accuracy in terms of the theoretical CL paths and without gouge and interference. Two practical examples in this work clearly demonstrate the feasibility of this approach and the advantages of the generated NURBS tool paths. Therefore, this approach can be implemented into the CAD/CAM software to promote NURBS machining in industry.     

Design and implementation of a real-time NURBS surface interpolator

In recent years, various parametric curve interpolators have been proposed for high-speed and high-accuracy machining. However, these methods are based on a constant cutter location (CL) velocity. Hence, the cutter contact (CC) velocity along the surface tends to vary, resulting in a nonuniform machining performance. Furthermore, machining complex surfaces requires the provision of a large number of tool paths and therefore the associated NC data files are generally very large. To overcome these limitations, the current study presents a novel real-time NURBS surface interpolator which ensures a constant CC velocity along the CC paths and its intervals. A PC-based real-time motion control network utilizing SSCNET is developed to achieve the goal of multi-axis synchronous motion. In this study, both the NURBS surface interpolator algorithms and the SSCNET communication protocols are realized by Embedded XP with the RTX real-time kernel. The experimental results confirm that the proposed real-time NURBS surface interpolator is capable of achieving a satisfactory performance.     

NC toolpath generation for arbitrary pockets with Islands

This paper presents an efficient algorithm for generating cutter paths for the NC milling of arbitrary pockets with multiple islands. In this algorithm, the pocket border and island profiles are made up of concave or convex segments comprising linear and circular arc elements. For the generation of NC tool paths, the algorithm is divided into four stages, namely, profile pre-processing stage, offset calculation, determination of the termination condition, and determination of the path sequence. Compared with the other pocketing algorithms, the main aspect of this work is that the pocket border and island profiles are pre-processed in the first stage of the algorithm. Making use of contour bridges in the profile pre-processing stage, the island profiles are connected to the pocket border profile to form a closed path. This then simplifies the calculations in cutter offsets and eliminates the problem of nesting which occurs in some other pocketing algorithms.     

Post-Processor Development of a Hybrid TRR-XY Parallel Kinematic Machine Tool

A hybrid 5-degrees-of-freedom parallel kinematic machine tool constructed using the TRR-XY mechanism has been used to investigate the theory of post-processing. The effects of the cutter shapes and machine construction on the post-processing are investigated. Some specific parameters only are required to modify the post-processing for the different tools used in real cutting. The tilt angle and yaw angle of the cutter relative to the normal direction of the cutting surface are included in the investigation. The parametric representations of different cutter shapes defined by the DIN standard were also adopted in the derivation. The generality of the post-processor theory developed was then increased. Finally, NC code has been generated using LABVIEW software. Simulations are performed to verify the correctness of the work based on several designed tool paths.     

数控机床的数字化全闭环控制

针对发展国产高精度数控机床的需求，提出一种数字化全闭环控制方法，开发出新型数字化全闭环位置控制系统，实现了以数字驱动、数字检测和数字位控为特征的全数字化刀具轨迹控制，有效保证了数控机床的加工精度。该系统已在多种国产数控机床上进行了应用，在复杂精密零件加工方面取得良好效果。     

基于光线跟踪法的多轴铣削加工仿真研究

在数控加工中．对数控代码进行集成的几何仿真和物理仿真，可以快速检验加工代码的正确性并对加工参数进行优化。运用光线跟踪法研究了多轴数控铣削加工的几何仿真和物理仿真问题，运用解析法对工件和刀具扫描体进行求交离散．依据数控代码提取刀位信息并计算刀具扫描体。工件与扫描体的布尔减运算，一方面可获得每一步切削结果并进行实时的立体显示，另一方面可依据材料切削速率模型实时计算切削力。     

基于VERICUT的五轴数控加工仿真与优化

虚拟加工平台的构建、数控加工程序的正确性验证及加工过程的仿真与优化及是五轴数控机床实现高效加工的重要基础技术。基于VERICUT数控加工仿真与优化平台,以非正交五轴数控机床DMC70ev为研究对象,构建了数控加工仿真平台;以曲面加工为例,建立了基于恒定体积去除率和恒定切屑厚度的优化设计数学模型,进行了刀位轨迹的优化。应用表明:研究成果实现了五轴数控加工过程仿真及数控加工程序的正确性验证,减少了刀具磨损,提高了加工效率与加工质量,可以较好地提升企业数控加工技术的应用水平、应用质量,推动现代制造技术的发展。     

五轴数控加工中刀具扫掠轮廓线的计算和分析

给出了五轴联动数控加工中环形刀具扫掠轮廓线的表达式,分析了扫掠轮廓线在刀具曲面不同部分的几何特性.所用的计算方法高效精确,并可进一步推广到任意形状的刀具在不同形式的数控机床上扫掠轮廓线的计算和分析.     

多轴NC加工仿真中的刀具扫描体计算

基于微分几何理论建立了刀具扫描体的精确数学表达，可用于任意形状的刀具，并将其用于ＮＤ铣削加工的真实感图形仿真，可提高多轴ＮＤ程序较验和图形计算的精度。     

基于OpenGL的数控铣削仿真研究

通过数控代码的正确性检验,生成刀具运动轨迹,针对数控铣削加工过程,将毛坯表面按照Delaunay准则进行三角剖分,用离散矢量求交法实现毛坯的逐步切削,应用三维图形接口标准OpenGL实现了加工过程仿真。     

Post-Processor Development for a Six Degree-of-Freedom Parallel-Link Machine Tool

A coordinate system with multiple non-orthogonal axes, defined for a parallel-link machine tool is very different from that for a conventional serial-type machine. Therefore, a special post-processor that can automatically transfer the cutter location data (CL-data) into machine specific NC commands is essential for real machining applications of a parallel-link machine tool. Parallel-link machine tools have been investigated by many previous workers. However, work on the theory of post-processors for this machine tool is very sparse, and most is focused on the orthogonal serial motion. The potential benefits of the parallel-link machine tools make work necessary and urgent on the transformation of the CL-data from a CAD/CAM system into NC commands for special parallel-link machine tools. A six degrees-of-freedom (DOF) parallel-link machine tool constructed as a 6-3-3 mechanism was selected in this work to investigate the theory of post-processing, and the effects of the cutter shapes and the machine construction on it. The parametric representations of different cutter shapes defined by the DIN standard were adopted in the work, increasing the usefulness of the post-processor theory developed. Specific parameters must be modified in the post-processor for different tools applied for real cutting. The tilt angle and yaw angle of the cutter, relative to the normal direction of the cutting surface, is also included in the theory. Finally, the NC code is generated using LabVIEW software, and simulations were performed to investigate the correctness based on several designed tool paths.