机床几何精度的在线激光测量与快速校准技术

为了改善机床的几何精度,达到高精度的三维空间定位,必须对它的垂直度误差与直线度误差进行测量与校正.传统的激光测量方法花费时间长,成本高.由ISO及ASME提出并由波音公司等应用的体对角线测量方法虽然速度快、成本低,但不能有效分离误差源.现介绍一种由美国光动公司发明的基于体对角线分步(或矢量)激光测量方法,该方法速度快、准确度高、成本低,可以分离误差源并对其提供补偿与校正.     

Load spectra of CNC machine tools

Load spectra of CNC machine tools are described in this paper; 112 CNC machine tools have been traced for 3 years. Data including machining parameters and conditions, drawings and NC programs of parts, process cards and specifications of each individual CNC machine tool are gathered. A database containing this information is designed. The loads of CNC machine tools are calculated and the distribution parameters of loads are estimated. A fuzzy multicriteria comprehensive evaluation method is applied to evaluate the fitness of the distribution model. This methodology lays a foundation for the reliability designs of CNC machine tools. Copyright © 2000 John Wiley & Sons, Ltd.     

基于极小极大算法的双臂机器人精度提升方法

针对双臂机器人绝对精度和协作精度的指标要求,基于激光跟踪仪测量的双臂末端三靶球点位数据,使用极小极大的搜索算法,提出了鲁棒的双臂机器人运动学几何参数校准方法.该方法分两步:首先,分别对左右两臂的几何参数进行校准,在左(右)臂末端安装三个靶球,以三个测量点中的最差绝对定位误差为指标函数建立非线性优化问题,确保校准结果的鲁...     

基于原始误差项快速辨识的空间几何误差补偿

在误差补偿中,误差项辨识和误差补偿一直是研究的重点,国内外许多学者对此开展了许多工作,但总的来说,仍然缺乏一种高精度并能够快速获得机床几何误差信息的测量仪器．目前的误差补偿方法,由于机床误差产生的原因很多,难以找到合适的通用数学模型进行误差分解,故难以推广应用．本文设计并实现了一种基于原始误差项快速辨识的空间几何误差补偿方法,使得在精度等级稍低的机床上实现更高精度等级加工的效果．     

Optimal maintenance schedule decisions for machine tools considering the user's cost structure

This paper proposes a model for obtaining optimal preventive repair and replacement intervals of a machine tool subassembly considering the user's cost structure and the effect of major overhauls. Corrective actions are considered as minimal, whereas preventive repair and major overhauls are considered as imperfect in this paper. The objective is to obtain optimal repair/replacement decisions for the machine tool subassembly such that the expected life-cycle cost contribution over the whole life of the system is minimised. The proposed strategy improves over other existing strategies since it simultaneously considers the effects of the user's cost structure and major overhauls, while optimising the preventive repair and replacement intervals. A numerical illustration is provided to demonstrate the general application of the proposed approach.     

A polynomial algorithm for the two machine job-shop scheduling problem with a fixed number of jobs

It is shown that the job-shop problem with two machines and a fixed number ofk jobs with makespan criterionJ2¦n=k¦C ^max is polynomially solvable. Sotskov and Shakhlevich (1993) have shown that problemJ3¦n=3¦C _maxisNP-hard. Furthermore it is well known that J¦n=2¦C _maxin polynomially solvable. Thus, our result settles the remaining open question concerning the complexity status of job-shop problems with fixed numbers of jobs and machines.Supported by Deutsche Forschungsgemeinschaft, Project Jop-TAG     

Key performance indicators for assessing inherent energy performance of machine tools in industries

Increasing attention has been paid toward enhancing energy retrofitting in machine tools due to its enormous energy consumption and high energy-saving potential. Developing energy-efficient machine tools and selecting appropriate machine tools in procurement processes are two effective approaches for saving energy. However, existing studies on the evaluation of energy performance to support the design and selection of machine tools, rarely consider various process controls, which have considerable impact on the energy performance of machine tools. This study proposes a group of key performance indicators, which are referred to as ‘inherent energy performance’ (IEP) indexes, to support the design and selection of machine tools with the consideration of the main process controls in the usage phase and their interaction. A systematic method is introduced to acquire the IEP indexes. The method involves a simplified measurement of basic data and the calculation of the indexes from the data. A case study indicates that the proposed indicators succeed in obtaining the energy demand information of almost all machine system activities and can be used to provide basic data for developing energy information labels, selecting matching machine tools, and designing energy-efficient machine tools.     

A new algorithm for improving the accuracy of periodic signalanalysis

Digital periodic signal analysis often requires synchronized sampling with the signal being analyzed. In certain practical situations, however, this condition is difficult to satisfy. As a result, a number of undesirable effect such as the spectral leakage associated with the discrete Fourier transform (DFT), and the truncation errors in digital wattmeters arise and degrade system performance. This paper presents a new approach which attempts to remedy the underlying problem. The basic idea of the proposed method is to modify the actual sampled sequence such that it becomes an ideal sample sequence which is synchronized with the signal subjected to sampling. A simple algorithm for modifying the sampled sequence on-line is derived based on interpolation. The proposed approach requires quite modest additional computational burden which makes it suitable for real-time signal professing. To illustrate the practical applicability of the proposed algorithm, the paper considers two distinct but common cases. First, it shows how the proposed method can be used in the case of DFT analysis of harmonic signals, and secondly, it considers the digital wattmeter application area in electrical power-system measurement. Results show that the proposed algorithm is capable of reducing both the leakage effect in DFT analysis and truncation errors in digital wattmeters     

A data acquisition system for machine tool condition monitoring

A flexible, generically applicable and inexpensive data acquisition system (DAS), for machine tool condition monitoring, has been designed, constructed and installed as part of a European Union sponsored project. The DAS is more than just a data logger and an array of sensors. It also consists of a methodology for analysing data logging requirements and a relational database that supports this methodology. The database is held on a central ‘maintenance management’ computer. The monitoring to be carried out by the DAS is specified through this database, which contains detailed information about the DAS's facilities. This feature makes it simple to reconfigure the DAS to implement new monitoring requirements and to customize its operation to meet the needs of different machines. The information in the database is transformed into a look-up table that is read by the software that sets up and controls the data logging processes.     

A data acquisition system for machine tool condition monitoring. Part 2—some of the signals acquired

This paper presents some of the machine tool condition monitoring signals logged by the data acquisition system (DAS) designed and implemented as part of the European Union research project BREU-CT91–0463. Cause and effect relationships between machine components and signal features are highlighted, along with a demonstration of the suitability of vibration signal kurtosis as a measure of machine tool spindle bearing condition.     

A radius compensation method of barrel tool based on macro variables in five-axis flank machining of sculptured surfaces

Barrel tool radius compensation is very important to improve the five-axis CNC machining precision and efficiency of sculptured surfaces. By combining macro variables and math function of CNC controller, a radius compensation method of barrel tool based on macro variables in five-axis flank machining of sculptured surfaces was presented. The basic principle of barrel tool radius compensation in five-axis flank machining was firstly investigated. For a specific five-axis CNC machine tool with dual rotary tables, a relationship equation between compensated cutter location (CL) data and machine control (MC) data could be derived. A post-processor with the function of five-axis barrel tool radius compensation was then developed by using the C++ language, which could generate the NC programme with macro variables of barrel tool radius compensation. Finally, the NC programme was obtained automatically by the developed post-processor for the aero-engine blade surface machining. The machining process was simulated on the software VERICUT, and machining experiments were also conducted on the five-axis machine tool. Both the simulation and experimental results showed that the proposed method could perform the function of barrel tool radius compensation in the NC programme for five-axis flank machining.     

A morphology proposal in commercial-off-the-shelf reconfigurable machine tools

Global manufacturing is continuously facing changing demands, the unpredictable part family supply that a machine tool user has to deal with needs varying machine morphologies. The reconfigurable manufacturing system paradigm proposes the need for the right capacity, for the right demand with an economical ramp-up period. The machinist needs to have a systematic manner of configuring the machines, given a set of modules that will be configured and reconfigured for the various demands in the lifespan of a manufacturing system. In this article, the author proposes how the machinist can go about identifying the different morphologies in advance. The method is simple and user-friendly in consideration of the main users who may have basic skills being deficient in sophistication and complexity; it further assists in the determination of the capability the manufacturer has with the available modules.     

A heuristic algorithm to minimise the control places of a Petri net for the control of shared machines

This paper proposes a design methodology of a controller based on a Petri net for the shared machines of manufacturing systems. A conflict occurs when several manufacturing systems require the same shared machines at the same time. In this case, we have two issues; the scheduling of jobs on shared machines and the construction of a control procedure for scheduling. The scheduling of production on machines has been extensively studied over the past years by researchers. In this paper, our concern is not the scheduling problem but the construction of a control procedure for the production schedule. We propose a design of a Petri net based controller for the shared machines of manufacturing systems such that the number of control places in the Petri net is minimised. The experimental results show that the proposed algorithm performs better than an upper bound in terms of optimality. Also, the proposed algorithm is computationally more efficient than the optimal algorithm. Finally, we present the application of the proposed algorithm to a realistic batch process system shown in the literature.     

A multilevel genetic algorithm for the optimum design of structural control systems

A multilevel genetic algorithm (MLGA) is proposed in this paper for solving the kind of optimization problems which are multilevel structures in nature and have features of mixed‐discrete design variables, multi‐modal and non‐continuous objective functions, etc. Firstly, the formulation of the mixed‐discrete multilevel optimization problems is presented. Secondly, the architecture and implementation of MLGA are described. Thirdly, the algorithm is applied to two multilevel optimization problems. The first one is a three‐level optimization problem in which the optimization of the number of actuators, the positions of actuators and the control parameters are considered in different levels. An actively controlled tall building subjected to strong wind action is considered to investigate the effectiveness of the proposed algorithm. The second application considers a combinatorial optimization problem in which the number and configuration of actuators are optimized simultaneously, an actively controlled building under earthquake excitations is adopted for this case study. Finally, some results and discussions about the application of the proposed algorithm are presented. Copyright © 2002 John Wiley & Sons, Ltd.     

并联机床的动力学特性对加工精度影响的分析

为了提高并联机床的加工精度,分析了并联机床的动力学特性对加工精度的影响。根据牛顿—欧拉方程,得到并联机床的动力学方程,解得连杆的驱动力;根据杆件轴向伸长量与受力之间的关系,得到连杆的长度误差;以无长度误差的连杆长度为优化目标,用优化的方法,得到动平台的位姿,并与连杆有长度误差时动平台的位姿比较,得动平台的位姿误差;根据刀具在动平台坐标系中位置,得刀具加工位置误差及对被加工零件精度的影响。结果表明：并联机床连杆的长度误差,引起刀具加工位置误差,使被加工零件产生形位误差和尺寸误差;并联机床电主轴偏心引起连杆的长度误差的扰动,产生刀具加工位置的扰动误差,影响被加工零件的表面粗糙度。     

专用数控机床中的工件定位误差自动补偿技术

专用数控机床由于能够较好地满足大批量、高效率、高精度生产的需求而在现代加工领域中获得了广泛的应用。工件定位误差自动补偿技术是其高效率、高精度生产的重要保证，本文讨论了专用数控机床中的工件定位误差自动补偿技术及其实现方法，并介绍了该技术的一个应用实例。     

A polychromatic sets approach to the conceptual design of machine tools

Currently very few computer-aided conceptual design systems are available to support the initial development of a machine tool and its structure (concept, calculation, design) and the verification of the prototype. In recent years, polychromatic sets have emerged as a promising approach for mathematical modelling. The theory, techniques, and approaches of polychromatic sets are capable of playing an important role in the conceptual design of a variety of products including machine tools. In this paper, the concept of polychromatic sets is introduced, and a polychromatic sets approach for the conceptual design of machine tools is proposed. The usefulness of the proposed method is illustrated by a conceptual design example of a machining centre of drilling, milling, and boring. Applying the proposed approach to machine tools helps to make right decisions in the conceptual design stage. Due to its powerful mathematical modelling capability, the polychromatic sets technique proposed in this paper may possibly be extended and applied to design evaluation problems encountered in other design tasks in manufacturing systems including process planning.