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1、1A new approach to CNC tool path generation The feedrate is one of the most important factors to machining efficiency and quality. Current methods for tool path generation adopt a constant velocity along the cutter location path and do not satisfy the desired feedrate along the sculptured surface. T
2、his paper presents a new approach to tool path generation so as to cope with this problem. Methods base on linear, curve, and surface interpolators are presented and analyzed. 1998 Elsevier science ltd. All rights reserved. Keyword: computer numerical control, tool path generation, interpolator Intr
3、oduction Computer-aided manufacturing (CAM) system as well as computer numerical control (CNC) machine tools are widely used in todays manufacturing industries. To produce the desired part, The CAM system generates the tool path for the CNC machine tool so that it can cut the Surfaces of the part. I
4、n the current approach1-4, the CAM system first computes the cutter contact (CC) points and then offsets these points the cutter location (CL) points. The CC points are a set of points located on the sculptured surface so that the edge of the tool is scheduled to pass through, while the CL points ar
5、e a set of points that the center (or the bottom tip ) of the tool is scheduled to pass through. In this paper the CC path and the CL path are defined as the paths passing through the CC points and the CL points, respectively. In addition, the CC velocity and the CL velocity are defined as the veloc
6、ities along the CC path and the CL path, respectively.The CL path is in practice the tool path. Conventionally, the CL path is represented by a set of consecutive linear segments (that connect the CL points), and then fed to the CNC machine that adapts a linear interpolator. The interpolator impleme
7、nted in the CNC machine can convert the cutter path to motion trajectories of all the axes in order to coordinate 一种生成数控机床刀路新方法一种生成数控机床刀路新方法进给率是影响机械加工效率和质量的最 重要因素之一。目前产生刀具路径采用的是 一种沿刀具路径的等速的方法，但不能满足 沿自由曲面进给率的要求。本文提出了一种 新的产生刀具路径的方法来解决这个问题。 分别提出并分析基于直线、曲线和曲面的加 工方法。关键词：计算机数控，刀具路径生成，插补绪论绪论 计算机辅助制造（CAM）系统
8、和计算 机数控（CNC）机床广泛应用于当今制造行 业。为了生产出所需零件，计算机辅助制造 系统为数控机床产生刀具路径，以便数控机 床加工出零件面。当前的加工方法是计算机 辅助制造系统首先计算刀具连接点（CC） ， 然后偏置这些刀具连接点而得到刀具位置点 即刀位点（CL） 。刀具连接点是一系列在自 由曲面上刀具切削加工时刀具边缘通过的点， 而刀位点则是一系列刀具中心（刀具底心） 通过的点。本文中，刀具连接路径和刀位路 径分别被定义为通过刀具连接点的路径和通 过刀位点的路径。此外，刀具连接速度和刀 位速度分别被定义为沿着刀具连接路径的速 度和沿着刀位路径的速度。刀位路径实际上就是刀具路径。通常，
9、刀位路径被视为一组连续的直线段（即连接 刀位点的线段） ，然后，输入到采用直线插 补器的数控机床。为了调整刀具在多轴加工 中的运动，数控机床中的插补器能将刀具路 径转化成机床所有轴的运动轨迹。因为为了 这些直线运动命令，上面的方法要求大量的 刀位文件，且导致沿刀具路径进给率的波动，2their motion in multi-axis machining. Because the above method requires a large CL file for these linear motion commands and results in feedrate fluctuation a
10、long the cutter path5, parametric curves are recommended to represent the CL path. To achieve this purpose, curve interpolators are continuously being developed6-9.The feedate is one of the most important cutting conditions that determine the machining efficiency and quality. Because the production
11、rate is proportional to the feedrate, a large feedrate is recommended. However, on the basis of cutting principles as well as experts experiences, the feedrate must be small enough so as to achieve a quality machining that is in terms of dimension accuracy and surface integrity10-12. The feedrate de
12、notes the velocity that the cutter edge moves along the part and is in practice the CC velocity defined above. In the existing approach, the CL path together with a preset (usually constant) CL velocity is fed to the CNC machine. Although the preset CL velocity is usually called the feedrate in a lo
13、t of literature, it is not the real one related to the machining efficiency and quality. For this reason, the existing approach to tool path generation can not satisfy the desired feedrate (i.e.,CC velocity) requirement, and consequently, may result in low efficient and/or low quality machining.This
14、 paper presents a new approach to tool path generation so as to cope with the above problem. Three methods based on linear, curve, and surface interpolators are developed and analyzed, respectively. Existing approach The exiting approach to tool path generation can be depicted by figure 1. In this a
15、pproach, the first step is to schedule the CC paths for the cutter edge to follow. The path interval (or side step) between two neighboring CC paths is determined based on the limit of the scallop height3. Current CAM systems frequently adopt the isoparametric machining method that assigns the CC pa
16、th along the u-or the ，因此参数曲线被用来表达刀位路径。为了 达到这种目的，曲线插补被不断开发。进给率是最重要的切削条件之一，它决 定着机械加工的效率和质量。因为产品的生 产率和进给率是成正比的，所以需要一个较 大的进给率。尽管如此，基于切削原理和专 家的经验，进给率必须足够小以便在尺寸精 度和表面质量方面达到机械加工的质量。进 给率指的是刀具沿零件的边缘的移动速度， 实际上是上面被定义的刀具连接速度。在现 有的加工方法中，刀位路径和预先设定好的 刀具速度（通常是恒速）被传送到数控机床 中。虽然在很多文章中把预先设定好的刀位 速度通常称为进给率，但它不是一个真正关 系到机械加工效率和质量的因素。因此现有 的刀具路径生成方法不能满足理想的进给率 （也就是刀具连接速度）的要求，从而导致 了低效率和/或低质量。本文提出一种刀具路径生成的新方法以 便解决上面的问题，分别提出并加以分析了
