Feed-rate control using fuzzy reasoning for NC machine tools

In this article, a 3D design and machining system based on an NC machine tool with a rotary unit is first introduced to effectively produce attractive paint rollers. A post-processor is proposed to transform a base tool path called cutter location data (CL data) to NC data, mapping the y-directional pick feed to the rotational angle of the rotary unit. The 3D machining system with the postprocessor allows us easily to transcribe a relief design on a flat model surface to a cylindrical model surface. The postprocessor has another function that systematically adjusts the feed-rate according to the curvature of each design to prevent the machined surface from being chipped. The post-processor generates suitable feed-rate codes by using a simple fuzzy reasoning method while checking the edges in relief designs. Experimental results show that wooden paint rollers with attractive relief designs can be successfully machined without undesirable edge chipping. Next, the proposed fuzzy feed-rate generator is further applied to a mold-polishing robot, so that the polishing time can be reduced by about 30% compared with the case without the generator. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Intelligent desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance control capability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots. Tools attached to the tip of the z-axis are ball-end abrasive tools. The control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feed-forward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Further, the position feed-forward loop leads the tool tip along cutter location data. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash that causes the position inaccuracy at the tip of an abrasive tool, through a simple position/force measurement. Through a similar measurement and a surface following control experiment along a lens mold, the basic position/force controllability with high resolutions is demonstrated. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

五轴后置处理转角选解优化及奇异区域处理方法的研究

五轴后置处理是将CAM 软件系统产生的刀位文件转换成数控机床加工程序的关键 环节。基于五轴后置处理过程中转角选解、优化以及奇异区域加工数据处理的问题,提出了一种 集合转角选解、优化及奇异区域处理的方法,解决了因后置处理中选解不当引起的碰撞、旋转轴 在相邻刀位之间摆幅过大以及在奇异区域旋转轴产生急速转动、非线性误差过大等问题。该方法 应用C++语言开发了相应的后置处理系统,通过读取CATIA 刀位文件,生成可执行数控加工程 序,经Vericut 仿真验证该算法可行。     

Development of universal environment for constructing 5-axis virtual machine tool based on modified D–H notation and OpenGL

For construction of a universal 5-axis virtual machine simulation system, a new methodology is proposed in this paper. The OpenGL library is used to render the virtual environment and to display all motions of the virtual machine tool. In order to achieve the universal construction procedures, the D–H notation is adopted. The user interfaces are developed to help users to select the configuration of machine tool. Once the configuration is decided, the motion directions between adjacent links are known and the kinematic parameters are described by D–H notation. Then the post-processor is derived by D–H notation. Finally, the motion control simulation of the virtual machine tool is executed by D–H transformation matrix. This new methodology can assist developers in constructing the simulation system for the universal 5-axis virtual machine tool efficiently and effectively.     

微处理机控制铣床刀具补偿进给

本文介绍了用微处理机实现数控机床刀具补偿的一个应用实例,叙述了用于刀具补偿的 专用单板计算机的软件和硬件设计思想,介绍了以通用单板机为手段的简易开发方法.     

A novel methodology for cross-technology interoperability in CNC machining

In CNC part programmes, the lack of standardisation for representing part geometry and semantics of manufacturing operations leads to the necessity for existence of a unique part programme for each machine. Generating multiple programmes for producing the same part is not a value adding activity and is very time consuming. This wasteful activity can be eliminated if users are given the ability to write an NC program for a specific machine and robustly convert the program to syntax suitable for another CNC machine with a different structure. This, cross-technology interoperability, would enable for parts manufactured on old CNC machines using legacy code to be manufactured on new CNC machines by automatically converting the programmes. Every NC programme is written based on various categories of information such as: cutting tool specifications, process planning knowledge and machine tool information. This paper presents an approach for cross-technology interoperability by refining high-level process information (i.e., geometric features on the part and embedded manufacturing resource data) from NC programmes. These refined items of information stored in compliance with the ISO14649 (STEP-NC) standard may then be combined with new manufacturing resource information to generate NC code in a format that is compatible with machines based on different technologies. The authors provide a framework for this process of identification, semantic interpretation and re-integration of information. The focus of this paper is on asymmetric rotational components as the initial application area. To demonstrate the proposed cross-technology interoperability approach, a C-axis CNC turn–mill machine and a 4 axis CNC machining centre have been used with a simple test component.     

Inverse kinematics for optimal tool orientation control in 5-axis CNC machining

The problem of determining the inputs to the rotary axes of a 5-axis CNC machine is addressed, such that relative variations of orientation between the tool axis and surface normal are minimized subject to the constraint of maintaining a constant cutting speed with a ball-end tool. In the context of an orientable-spindle machine, the results of a prior study are directly applicable to the solution of this inverse-kinematics problem. However, since they are expressed in terms of the integral of the geodesic curvature, a discrete time-step solution is proposed that yields accurate rotary-axis increments at high sampling frequencies. For an orientable-table machine, a closed-form solution that specifies the rotary-axis positions as functions of the surface normal variation along the toolpath is possible. In this context, however, the feasibility of a solution is dependent upon the surface normal along the toolpath satisfying certain orientational constraints. These inverse-kinematics solutions facilitate accurate and efficient 5-axis machining of free-form surfaces without “unnecessary” actuation of the machine rotary axes.     

Estimation of NC machining time using NC block distribution for sculptured surface machining

The estimation of NC machining time is of importance because it provides manufacturing engineers with information to accurately predict the productivity of an NC machine, as well as its production schedule. NC programs contain various machining information, such as tool positions, feed and speed rates, and other machine instructions. Nominal NC machining time can easily be obtained based on the NC program data. Actual machining time, however, cannot simply be found due to the dynamic characteristics of a NC machine controller, such as acceleration and deceleration effect. Hence, this study presents an NC machine time estimation model for machining sculptured surfaces, considering such dynamic characteristics of the machine. The proposed estimation model uses several factors, such as the distribution of NC blocks, angle between the blocks, federates, acceleration and deceleration constants, classifying tool feed rate patterns into four types based on the acceleration and deceleration profile, NC block length, and minimum feed rate. However, there exists an error for the actual machining time due to the lack of the measurement equipment or tools to gauge an exact minimum feed rate. Thus, this paper proposes a machining time estimation model using NC block distributions, lowering down the error caused by the inaccurate minimum feed rate. The proposed machining time estimator performs at around 10% of mean error.     

Tool orientation adjustment for improving the kinematics performance of 5-axis ball-end machining via CPM method.

For 5-axis ball-end machining, it is desired to maintain the expected cutting performance of tool orientation when adjusting tool orientation for improving the motions of rotary axes of 5-axis machine. For this purpose, a cutting performance maintained (CPM) method is proposed to adjust the tool orientations, the objective of which is to minimize the sum of the absolute deviations between the initial and adjusted coordinates of the rotary axes while improving the kinematics performance of the rotary axes and ensuring no machining interferences. In order to speed up the solving of the optimization objective, the analytical linear representations for the drive limits of rotary axes and especially irregular geometry feasible domains (GFDs) of tool orientations are first discussed in detail. The nonlinearity of the objective function is then eliminated by introducing two new auxiliary variables for further simplifying the computation of optimal tool orientation. After rewriting the drive limits and GFD constraints with the two auxiliary variables, the linear objective function can be efficiently solved by the simple linear programming method. The tool orientations adjusted by the proposed CPM method can not only improve the interference-free motions of the rotary axes, but also can maintain the expected cutting performance. Finally, the computer simulation and real milling were conducted to validate the proposed method.     

Automated surface subdivision and tool path generation for -axis CNC machining of sculptured parts

As an innovative and cost-effective method for carrying out multiple-axis CNC machining, -axis CNC machining technique adds an automatic indexing/rotary table with two additional discrete rotations to a regular 3-axis CNC machine, to improve its ability and efficiency for machining complex sculptured parts. In this work, a new tool path generation method to automatically subdivide a complex sculptured surface into a number of easy-to-machine surface patches; identify the favorable machining set-up/orientation for each patch; and generate effective 3-axis CNC tool paths for each patch is introduced. The method and its advantages are illustrated using an example of sculptured surface machining. The work contributes to automated multiple-axis CNC tool path generation for sculptured part machining and forms a foundation for further research.     

数控机床进给伺服系统故障诊断的人工智能实现

以FANUC 0i数控机床为研究对象,对进给系统的典型故障现象和原因进行深入分析. 提出一种模糊神经网络和专家系统互补的数控机床进给系统故障诊断方法及原理, 并给出采用VC.NET实现的具体方案.     

五坐标数控技术的联动原理

本文通过对五坐标数控技术的坐标运动规律进行分析研究,揭示了五坐标数控技术的联 动原理.即建立了从CAD中的理想轨迹的几何特性(包括位置、切矢、曲率)和五坐标联动的 运动动力学特性(包括位移、进给速度、各坐标理想速度和加速度)之间的通用数学模型.从 而可根据被加工零件表面的几何形状和机床的进给速度确定联动过程中各坐标的理想速度 和理想加速度.     

Adaptive learning control for thermal error compensation of 5-axis machine tools

The research presented in this paper shows an adaptive approach for long-term thermal error compensation of 5-axis machine tools (MT). A system of differential equations is used to compute the model based compensation values. The model can predict thermal displacements of the tool center point (TCP) based on changes in the environmental temperature, load-dependent changes and boundary condition changes and states, like machining with or without cutting fluid. The model based compensation of the rotary axis of a 5-axis MT is then extended by on-machine measurements. The information gained by the process-intermittent probing is used to adaptively update the model parameters, so that the model learns how to predict thermal position and orientation errors and to maintain a small residual error of the thermally induced errors of the rotary axis over a long time. This approach not only increases the MT accuracy but also reduces the amount of time spent on preproduction model parameter identification. Additionally an algorithm has been developed to dynamically adjust the length of the on-machine measurement intervals to maintain a high productivity and a constant deviation of the machined parts.Experimental results confirm that the adaptive learning control (ALC) for thermal errors shows a desirable long-term prediction accuracy.     

Correlation between machining direction,cutter geometry and step-over distance in 3-axis milling: Application to milling by zones

Computer-Aided Manufacturing (CAM) occupies an increasingly important role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. The present study addresses machining of free-form surfaces on a 3-axis NC machine tool. There have recently been a large number of studies devoted to planning tool paths on free-form surfaces with various strategies being adopted. These strategies are intended to increase efficiency by reducing the overall length of machining. Often, the choice of the cutter is arbitrary and the work focuses on planning. In order to boost productivity, the present work offers assistance in choosing the cutting tool, the machining direction and cutting by surface zones, adopting a milling strategy by parallel planes. To do so, a comparison is made between milling using a spherical end milling cutter and a torus end milling cutter with the same outer radius. This comparison relates to the radius of curvature of the trace left by the cutter at the point of contact between the tool and the workpiece in relation to the direction of feed motion.     

Graphics-assisted Rolling Ball Method for 5-axis surface machining

In this paper, a graphics hardware-assisted approach to 5-axis surface machining is presented that builds upon a tool positioning strategy named the Rolling Ball Method presented in an earlier paper by the present authors [Comput. Aided Des. 35 (2003) 347]. The depth buffer of the computer's graphics card is used to compute the data needed for the Rolling Ball Method, which generates gouge-free 5-axis curvature-matched tool positions. With this approach, the tool path for a workpiece can be computed with triangulated data instead of parametric surface equations. It also permits the generation of tool paths for multiple surface patch workpieces that have only positional continuity. The method is easy to implement and it is robust since every tool position is computed with the same algorithm regardless of the type of surface. For illustration, tool paths were generated for a workpiece with two bi-cubic surface patches, connected with only position continuity. Simulations for gouge-checking and machining tests were performed. Workpiece cusp heights were measured using a coordinate measuring machine. The maximum undercutting measured in the machining examples was 0.07 and 0.05 mm, which is within the expected NC machine accuracy and measuring capabilities for surfaces.     

基于面向对象的虚拟数控系统的研究

提出了虚拟数控机床的基本系统结构,引入面向对象程序设计的基本概念于虚拟数控机床的设计.根据数控机床各零部件在加工过程中的特点,把它们分成静态类、运动类和动态类3类.在此基础上,利用3维实体CAD（computer aided design）软件系统进行虚拟数控机床加工过程中非变形物体（静态类与运动类）的外形设计并转换成STL（stereolithography）文件,对动态变形物体采用特征造型方法,与设计的成员函数即该零部件的运动函数有机地集成起来,构成类,最终实现数控机床各机构的动态仿真.引入了四元数的基本概念,并将其应用于系统设计与实现.上述方法为虚拟数控系统的研究提供了基本框架.实验结果证明,上述方法是可行的,具有很好的实用价值和参考价值.     

基于六坐标数控侧铣加工仿真系统的研究与实现

在六坐标数控机床上采用圆柱型刀具侧铣加工,本文从机床的结构设计到通过了一个数控面加工仿真显示系统模拟了圆柱型刀具面加工的过程。系统采用了一种独特的切削模拟及三维图形显示方法,并依据走刀最短加工路线、一次性走刀和选择切入切出方向等原则,可以在微机上动态模拟出刀具面加工运动的轨迹,采用三维图形和多视图模拟数控面加工的全过程。     

基于六坐标数控侧铣加工仿真系统的研究与实现

在六坐标数控机床上采用圆柱型刀具侧铣加工．本文从机床的结构设计到通过了一个数控面加工仿真显示系统模拟了圆柱型刀具面加工的过程。系统采用了一种独特的切削模拟及三维图形显示方法,并依据走刀最短加工路线、一次性走刀和选择切入切出方向等原则,可以在微机上动态模拟出刀具面加工运动的轨迹,采用三维图形和多视图模拟数控面加工的全过程。     

Reverse engineering applications for recovery of broken or worn parts and re-manufacturing: Three case studies

Damaged or broken parts are generally too expensive to replace, or are no longer available. RE can be defined as: ‘Systematic evaluation of a product with the purpose of replication. This involves design of a new part, copy of an existing part, recovery of a damaged or broken part, improvement of model precision and inspection of a numerical model. Advantages of the technique include immediate feedback, data reduction, direct generation of geometry and higher precision of the final product. This paper shows some possibilities of use and benefit from utilising the RE-methodologies and techniques in production process, especially in the case when exists parts without 3D-CAD support.This paper, which defines obtaining CAD data step by step from damaged three different parts to reproduce or make a new design for some recoveries, has not get any technical drawings. When these parts had been recovered, some problems occurred. These problems have been solved by referring to some practical approaches. Establishing continuity across curve and surface patches is an important concept in the free form surface modeling. The CAD models were recovered and reconstructed to consider parametric and geometric continuity. The iso-phote method was used for surface continuity analysis. Hence, in this work, not only occurring problems but also solving methods were explained. Firstly, CAD models are created from damaged and broken parts by data digitization method by using CMM and the process was explored in detailed. Later, CAD models that had been obtained earlier are transferred into CAM module of the software and G codes are taken by the NC post-processor, and finally, the parts are manufactured by means of CNC milling machine. Additionally, this paper presents a review of the part digitization techniques available for reverse engineering.     

汽轮机叶片五轴数控加工的一种实用方法

提出了一种汽轮机叶片五轴数控加工的实用方法 ,对于叶背和叶盆采用中凹盘形铣刀 ,基于密切曲率法给出优化刀位轨迹的计算方法 ;而对于进、排汽边圆弧采用无干涉侧铣加工方法 ,根据误差估算自动进行刀位排布 .通过这两种加工方法的有机结合 ,在保证精度的前提下 ,大大提高了加工效率 ,对于汽轮机叶片多轴数控加工具有实用价值 .