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.     

A CNC machine tool interpolator for surfaces of cross-sectional design

A machining strategy for milling a particular set of surfaces, obtained by the technique of cross-sectional design is proposed. The surfaces considered are formed by sliding a Bezier curve (profile curve) along another Bezier curve (trajectory curve). The curves are located in perpendicular planes. The method employs a three-axis CNC milling machine equipped with suitable ball-end cutter and is based on the locus-tracing concept. The algorithm described, utilizes a real-time CNC interpolator providing the highest possible accuracy, of which the milling machine is capable. The surface quality is controlled by keeping the distance between scallops within a programmed value. Finally, the whole machining task can be programmed in a single block of the part program.     

CAXA在数控技术中的编程理论

本文通过阐述CAXA在数控技术中的编程理论,详细说明了用CAXA制造工程师实现数控加工的过程,并论述了数字化制造所特有的优越性,并为数控技术中的CAXA只要工程师在数字化制造过程提供了理论依据。     

Condition monitoring of CNC machining using adaptive control

In this work, an adaptive control constraint system has been developed for computer numerical control (CNC) turning based on the feedback control and adaptive control/self-tuning control. In an adaptive controlled system, the signals from the online measurement have to be processed and fed back to the machine tool controller to adjust the cutting parameters so that the machining can be stopped once a certain threshold is crossed. The main focus of the present work is to develop a reliable adaptive control system, and the objective of the control system is to control the cutting parameters and maintain the displacement and tool flank wear under constraint valves for a particular workpiece and tool combination as per ISO standard. Using Matlab Simulink, the digital adaption of the cutting parameters for experiment has confirmed the efficiency of the adaptively controlled condition monitoring system, which is reflected in different machining processes at varying machining conditions. This work describes the state of the art of the adaptive control constraint (ACC) machining systems for turning. AISI4140 steel of 150 BHN hardness is used as the workpiece material, and carbide inserts are used as cutting tool material throughout the experiment. With the developed approach, it is possible to predict the tool condition pretty accurately, if the feed and surface roughness are measured at identical conditions. As part of the present research work, the relationship between displacement due to vibration, cutting force, flank wear, and surface roughness has been examined.     

基于免疫遗传算法优化的模糊控制方法及其应用

在模糊控制器的设计过程中,为了使模糊控制器的性能达到全局优化,应用免疫遗传算法对模糊控制器参数进行优化设计;在综合考虑各种参数对控制器性能影响的基础上,给出了一种全面优化隶属度函数、比例因子和量化因子的优化方法;利用了免疫算法能保持个体的多样性和能对学习过程进行引导的特点,对模糊控制器的多个参数同时进行优化,从而显著提高了系统的收敛性、稳定性。应用该方法对数控铣削加工过程的模糊控制器的设计进行了仿真,并与其他方法进行比较和控制实例的验证,表明了该基于免疫遗传算法优化的模糊器能获得更优良的控制性能。     

Remote real-time CNC machining for web-based manufacturing

Today's machining shop floors, characterized by large variety of products in small batch sizes, require dynamic control and real-time monitoring capabilities that are responsive and adaptive to the rapid changes of production capability and functionality. It is especially true when the shop floors are combined with the e-manufacturing concept. However, a highly efficient infrastructure that can integrate the pieces of automated equipment together and link them to the e-manufacturing is still missing. The objective of this research is to develop an appropriate methodology with open architecture for real-time monitoring and remote control of networked CNC machines. A framework named Wise-ShopFloor (Web-based-integrated sensor-driven e-ShopFloor) is designed for this purpose. Within the context, this paper presents a new enabling technology to bring traditional CNC machine tools on-line with combined monitoring and control capability. Issues such as architecture design, methodology development, and prototype implementation are addressed through a milling machine case study. It is expected that the developed technology can be readily applied to real shop floor environments with increased productivity, flexibility, and responsiveness.     

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.     

Feed-rate and trajectory optimization for CNC machine tools

The key task performed by CNCs is the generation of the time-sequence of set-points for driving each physical axis of the machine tool during program execution. This interpolation of axes movement must satisfy a number of constraints on axes dynamics (velocity, acceleration, and jerk), and on process outcome (smooth tool movement and precise tracking of the nominal tool-path at the desired feed-rate). This paper presents an algorithm for CNC kernels that aims at solving the axes interpolation problem by exploiting an Optimal Control Problem formulation. With respect to other solutions proposed in the literature, the approach presented here takes an original approach by assuming a predefined path tracking tolerance—to be added to the constraints listed above—and calculating the whole trajectory (path and feed-rate profile) that satisfies the given constraints. The effectiveness of the proposed solution is benchmarked against the trajectory generated by an industrial, state-of-the-art CNC, proving a significant advantage in efficiency and smoothness of axes velocity profiles.     

基于嵌入式Linux的数控机床远程监控

为实现数控机床的网络化管理,针对目前一些老式机床无远程监控平台的问题,提出了基于嵌入式Linux的数控机床远程监控系统的设计与实现方案.该方案采用嵌入式Linux与ARM处理器为平台,软硬件结合,完成车间级监控主机与局域网内各机床之间的通信,并利用嵌入式数据库对机床状态信息进行实时备份,达到对局域网内多台机床进行集中监控管理的目的.该方案的智能控制模块可根据接收到的机床报警信息,向机床发送相应的控制命令,保护机床正常运行;车间级监控主机还可直接接入Intemet,以便将机床的数据发送到远程进行故障诊断.实验结果表明,该方案可以有效的对老式机床进行集中监控,实现了数控机床的网络化管理.     

A universal velocity limit curve generator considering abnormal tool path geometry for CNC machine tools

Non-linear parametric curves, such as B-spline curves, are becoming increasingly available in modern CNC (Computer Numerical Control) systems. The smoothness of parametric curves offers higher order of continuity and thus invokes less vibration in machines as compared to short line segments. Nevertheless, the computations for velocity limit curves, velocity profiles and interpolation points are quite complicated and time-consuming and therefore approximation methods are applied. Unnecessary accelerations and decelerations, which cost additional time of motion, can be caused by inaccurate computations of the velocity limits around tiny corners. To overcome the problem, the unit arc length increment scanning method (UALISM) is proposed to reduce the time of movement and to improve the efficiency. The scanning interval is fixed at 1 BLU (basic length unit) which is irrelevant to the type, size and shape of the tool path curve. The constraints of chord height errors and axis accelerations are considered and the velocity limit for the specified scanning point is computed using the coordinates of multiple scanning points near the specified scanning point. Simulation results show that the unnecessary accelerations and decelerations can be avoided and thus the total motion time can be reduced by UALISM.     

Virtual machining considering dimensional,geometrical and tool deflection errors in three-axis CNC milling machines

Virtual manufacturing systems can provide useful means for products to be manufactured without the need of physical testing on the shop floor. As a result, the time and cost of part production can be decreased. There are different error sources in machine tools such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors which have a big portion of the total error, need more attention. This paper presents a virtual machining system in order to enforce dimensional, geometrical and tool deflection errors in three-axis milling operations. The system receives 21 dimensional and geometrical errors of a machine tool and machining codes of a specific part as input. The output of the system is the modified codes which will produce actual machined part in the virtual environment.     

电火花加工中嵌入式脉冲电源的设计

针对CNC电火花加工机床,设计了一种基于单片机W78E58B和复杂可编程逻辑器件(CPLD)的新型嵌入式数控脉冲电源,该电源脉冲宽度和脉冲间隙数控可调,在软件中利用模糊控制算法实现对加工状态的闭环控制,试验证明间隙电压稳定可靠,系统高效节能。     

Process control in CNC manufacturing for discrete components: A STEP-NC compliant framework

With today's highly competitive global manufacturing marketplace, the pressure for right-first-time manufacture has never been so high. New emerging data standards combined with machine data collection methods, such as in-process verification lead the way to a complete paradigm shift from the traditional manufacturing and inspection to intelligent networked process control. Low-level G and M codes offer very limited information on machine capabilities or work piece characteristics which consequently, results in no information being available on manufacturing processes, inspection plans and work piece attributes in terms of tolerances, etc. and design features to computer numerically controlled (CNC) machines. One solution to the aforementioned problems is using STEP-NC (ISO 14649) suite of standards, which aim to provide higher-level information for process control. In this paper, the authors provide a definition for process control in CNC manufacturing and identify the challenges in achieving process control in current CNC manufacturing scenario. The paper then introduces a STEP-compliant framework that makes use of self-learning algorithms that enable the manufacturing system to learn from previous data and results in eliminating the errors and consistently producing quality products. The framework relies on knowledge discovery methods such as data mining encapsulated in a process analyser to derive rules for corrective measures to control the manufacturing process. The design for the knowledge-based process analyser and the various process control mechanisms conclude the paper.     

高性能运动控制在数控系统中的应用综述

分析了在高速高精度加工中设计高性能运动控制器时存在的问题及面临的挑战,评述 了高性能数控系统运动控制器设计方法的发展现状,对存在的主要问题和今后可能的发展方向作了进一步的探讨.     

柔性制造系统中CNC机床故障诊断机理研究

为了及时发现处理柔性制造系统数控机床的故障或异常现象,设计了CNC在线故障诊断测试系统。该系统不仅便于查找数控机床故障的一个或多个症结,可以快捷、准确地对CNC故障定位,而且解决了诊断处理与知识应用中的相关问题。为了对CNC设备终端提供可靠的故障排除建议,对伺服控制组件与后台服务关联关系进行深入剖析,并对故障数据库进行描述与测试程序设计,解决了系统维护、扩展与升级操作等问题。     

基于复杂曲面的多轴数控加工非线性误差的控制研究

通过分析非线性误差及其对多轴数控加工的影响,提出了基于复杂曲面的多轴数控加工中非线性误差的控制方法,以期为提高多轴数控机床的加工精度贡献力量。     

A methodology for the determination of foamed polymer contraction rates as a result of cryogenic CNC machining

The ability to produce products, suited to a particular individual is becoming more prevalent in today’s society. This requires more efficient and rapid methods for manufacturing of bespoke products. One such method being currently developed is the cryogenic CNC machining of soft materials for producing personalised shoe insoles and outsoles. A major element of cryogenic CNC machining is the freezing of the soft polymers, which subsequently contract. This paper describes a method for predicting and compensating for the effect of cryogenic material contraction for the commonly used shoe midsole foamed polymer, ethylene vinyl acetate (EVA). Using the linear coefficient of thermal expansion a scaling factor for EVA has been developed to enable it to be accurately cryogenically CNC machined. This factor is then applied to the X, Y and Z scaling within the Delcam CAM software to shrink the model. The process is tested for a series of EVA cube test pieces and the results provide a scaling factor, which shows that the linear scaled dimension are within 1% of the measured contracted X, Y and Z dimensions. The scaling factor is subsequently used on an example low density EVA orthotic insole, which is cryogenically machined and then compared dimensionally with the original CAD model. It was found that using the cryogenic contraction factor the cryogenically machined insole had a dimensional X, Y, Z error of less than 1% when compared and analysed with the original CAD model.     

Modeling and intellligent chatter control strategies for a lathe machine

In the active chatter control of machine tools, the most effective way to suppress the chatter is to place the actuator as close as possible to the tool tip. However, in practice, it is almost impossible to put the actuator at the same location of the tool tip. Also, in many machines the cutting tools are usually long and may be flexible. Both of these problems pose serious problems in machine chatter control. In order to control the chatter effectively and efficiently, a systematic methodology is proposed in this paper to deal with the modeling and control system design aspects of this challenging problem. Because of the flexibility effect in the tool shaft, conventional active control approaches may not perform in an efficient and effective manner. Here, two advanced control algorithms (LMS adaptive filter and fuzzy CMAC neural network) are proposed to counteract this problem. Experimental results on a lathe machine are also included. Approximately 20 dB reduction in chatter has been achieved.