Self-adjustment computing method for time-partition interpolation in motion trajectory control of CNC machine tools

For time-partition interpolation in computer numerical control of the motion trajectory of a machine tool, the trajectory in a sampling cycle is approximated by a line segment from the current position of the tool to another on the expected trajectory; and locating the terminal of the line is the goal of the interpolation. In this paper, a self-adjustment computing method applicable to any explicit curve type is proposed. With the method, the terminal of the linear moving path in a cycle is first estimated by the motion information in the previous cycle, then adjusted according to the ratio of the desired moving distance to the computed linear path length. The result of the computation is fairly accurate, and it can be further enhanced with more adjustments performed in a sampling cycle, which is demonstrated in the simulation results. Furthermore, an adaptive feedrate adjustment algorithm is also introduced to enable the proposed method to control the trajectory contour errors.     

The optimisation of the grinding of silicon carbide with diamond wheels using genetic algorithms

Modelling and optimisation are necessary for the control of any process to achieve improved product quality, high productivity and low cost. The grinding of silicon carbide is difficult because of its low fracture toughness, making it very sensitive to cracking. The efficient grinding of high performance ceramics involves the selection of operating parameters to maximise the MRR while maintaining the required surface finish and limiting surface damage. In the present work, experimental studies have been carried out to obtain optimum conditions for silicon carbide grinding. The effect of wheel grit size and grinding parameters such as wheel depth of cut and work feed rate on the surface roughness and damage are investigated. The significance of these parameters, on the surface roughness and the number of flaws, has been established using the analysis of variance. Mathematical models have also been developed for estimating the surface roughness and the number of flaws on the basis of experimental results. The optimisation of silicon carbide grinding has been carried out using genetic algorithms to obtain a maximum MRR with reference to surface finish and damage.Nomenclature C constant in mathematical model - C₁ constant in surface roughness model - C₂ constant in the number of flaws model - d depth of cut, m - dof degrees of freedom - f table feed rate, mm/min - M grit size (mesh) - MRR material removal rate, mm³/mm width-min - N_c number of flaws measured - R_a surface roughness measured, m - Y machining response - depth of cut exponent in mathematical model - ₁ depth of cut exponent in surface roughness model - ₂ depth of cut exponent in number of flaws model - feed rate exponent in mathematical model - ₁ feed rate exponent in surface roughness model - ₂ feed rate exponent in number of flaws model - grit size exponent in mathematical model - ₁ grit size exponent in surface roughness model - ₂ grit size exponent in number of flaws model     

一种基于遗传算法的装配序列优化方法

基于遗传算法建立了装配序列生成模型,对装配序列进行优化生成。为提高优化效率,该算法将装配方向作为已知数据给出,并引入子装配体进行分层规划。最后,以蜗轮减速器装拆序列规划为实例验证该方法的有效性。     

基于步距规的数控机床误差测量和补偿技术

提出一种在工业现场进行单轴高精度位置误差的测量系统.使用步距规,可以用来代替激光干涉仪进行轴线位置的高精度标定;安装简单,操作容易.对轴线位置误差的补偿结果表明,通过该方法,可以使机床实现"软"升级.     

Developing a genetic optimisation approach to balance an apparel assembly line

In apparel manufacturing, it is difficult to achieve line balance because the production rate of each workstation is different. This difficulty is particularly prominent in the labour-intensive assembly process. The development of a line balancing technique using genetic algorithms is thus proposed for optimising the assignment of operators in an assembly line. The impact of a different level of skill inventory SI_n on the assembly makespan is also investigated in order to find out the optimal number of task skills an operator should possess in the apparel assembly process. Experimental results will be discussed to demonstrate the performance of the proposed genetic optimisation approach.     

A Linear Cross-Coupled Control System for High-Speed Machining

We present a linear cross-coupled controller to improve highspeed contouring accuracy independently of tracking accuracy in a biaxial machine tool feed drive servomechanism. Unlike conventional cross-coupled controllers, the cross-coupled controller presented here is a linear system, so it is very easy to perform the stability and steady-state error analysis, and to optimise the controller parameters. The proposed controller is evaluated experimentally on a CNC LOM machine and compared to an uncoupled controller and a conventional cross-coupled controller. Controller performance is evaluated for a circular contour at a feedrate of 30 m min _1 . The experimental results show that the proposed controller can greatly reduce the contour error at large feedrates. The linear cross-coupled controller is simple to implement and is practical.     

数控机床切削负荷误差补偿装置的设计

以开放式数控系统-华中I型为平台研制了数控机床切削负荷误差补偿装置,介绍了这套基于电流检测和处理技术的负荷误差补偿装置的基本构架和设计方法,这套装置被用于数控铣削粗加工中,被证明是成功、有效的,它显著提高了机床加工效率和加工精度。     

数控机床精度评价和螺距误差补偿技术研究

建立了螺距误差补偿的数学模型，设计了利用光栅尺进行螺距误差补偿的装置。对补偿前后的螺距误差进行了精度评价，结果表明，经过螺距误差的补偿，数控机床位置误差降低，实现了机床精度的软升级。     

符合阿贝原则的数控机床几何误差建模

为提高现有数控机床空间误差分析方法的准确度,本文基于阿贝原则对齐次转换矩阵(HTM)几何误差补偿模型进行优化。首先,推导出XYFZ型三轴机床适用的HTM几何误差补偿模型并给出模型正确使用的前提条件;然后,基于阿贝原则分析了三轴机床的空间误差传递机理,指出阿贝误差对机床定位精度的影响,给出理论计算公式并在机床运动轴上进行实验验证;最后,基于阿贝原则和布莱恩原则对现有的HTM几何误差补偿模型进行优化,采用该模型拟合体对角线空间误差,并与实测机床体对角线误差进行对比验证。现有HTM几何补偿模型可将机床空间误差由41.15μm补偿至16.37μm,补偿率为60.22%;优化后的补偿模型可将机床空间误差补偿至5.32μm,补偿率为87.07%,提高了26.85%。实验结果表明,优化后的补偿模型更加合理,进一步改善了空间误差的补偿精度。     

PCB assembly planning using genetic algorithms

Printed circuit boards (PCB) are used extensively in industry for the manufacture of electronic and electromechanical products. One of the primary concerns in the manufacture of PCBs is the determination of the optimal assembly plan. This paper presents work that leads to the development of an approach to PCB assembly planning using genetic algorithms (GAs). The approach takes into consideration component insertion priority and sequencing decision rules. A polygamy reproduction mechanism with dual mutation has been proposed and implemented. Details of the approach are described. A PCB model extracted from the literature was used for performance evaluation. Details of the evaluation are presented.     

基于G代码修改的数控机床几何误差补偿方法

为减小数控机床的空间运动定位误差,研究了一种基于G代码修改的几何误差补偿方法。以多体系统理论为基础,构建起多轴数控机床的通用误差模型,并据此建立了三轴数控机床空间误差模型。提出三维空间内任意直线轨迹的直线插补补偿算法和可提高圆心位置精度的平面内圆弧插补补偿算法,且这2种补偿算法都可分别设定不同的插补精度。采用修改G代码方式实现补偿方法的通用性,在XZOY型三轴数控机床上开展了误差补偿实验,验证了其有效性。     

Stochastic U-line balancing using genetic algorithms

The advantages of U-type lines are very well known in industry. They offer improved productivity and quality, and are considered as one of the better techniques in implementing just-in-time (JIT) systems. There is a growing interest in the literature to organize traditional assembly lines as U-lines for improved performance. U-type assembly line balancing is an extension of the traditional line balancing problem, in which tasks can be assigned from both sides of the precedence diagram. Although there are many studies in the literature for the design of traditional straight assembly lines, the work on U-type lines is limited. Moreover, in most of the previous studies, task times are assumed to be deterministic. In this paper, a new multiple-rule-based genetic algorithm (GA) is proposed for balancing U-type assembly lines with stochastic task times.     

A geometrical approach to computer-aided process planning for computer-controlled machine tools

This paper documents part of a research program which has been under way at the CIM Centre at Swinburne University of Technology since 1989. The purpose of the research program was to develop an open-architecture machine tool control system and then to see how that system could be used to change the distribution of traditional manufacturing design, planning and control functions. This paper examines one part of that research program and focuses on a methodology which could prove to be useful in the machine tool selection, cutter selection and cutter path generation phases of process planning for cutting operations on workpieces in computer-controlled machine tools.It is suggested that a configuration space transform be used for each cutter/machine tool combination to find the volume that the combination could remove from the uncut workpiece without removing any of the material that will form the final workpiece. A method of comparing these volumes from different combinations is then outlined. The output of this method is a reasonable sequence of machine tools and cutters. Path planning can then be carried out for each of the chosen combinations using a method similar to the one used to find the possible volume to be removed.Possible implementation techniques, and their limitations on existing computer hardware, are discussed and the most promising of these are identified, based upon some properties of configuration space transforms.     

A new type of machine control system to replace traditional CNC

This paper discusses the rationale behind a new form of machine tool control system which has been developed at the Key Centre for Computer Integrated Manufacture (CIM Centre) in Melbourne Australia. The new control system is based upon standard computer hardware and is intended as a replacement for computer numerical control (CNC), which has severe limitations in the CIM environment. The paper also outlines the new CIM possibilities which are now available as a result of this development.     

A new 2D error separation technique for performance tests of CNC machine tools

The error separation technique is widely adopted for many machine tool performance tests. The most common applications include roughness measurement, straightness measurement and spindle measurement. In this paper, two error-separation technologies, the straightness reversal technique and the semi-reversal technique, are developed. The straightness reversal technique can be adopted for the straightness measurement of a linear axis. The semi-reversal technique can be adopted for setting error separation in a contouring test and in the spindle error measurement. In this paper, mathematical models have been developed. In order to verify the possibility of the semi-reversal technique, related experimental work has been carried out.     

Optimization of manual fabric-cutting process in apparel manufacture using genetic algorithms

In apparel manufacturing, experience and subjective assessment of production planners are used quite often to plan the production schedules in their fabric-cutting departments. The quantities of cut-pieces produced by fabric-cutting departments based on these non-systematic schedules cannot fulfil the cut-piece requirements of the downstream sewing lines and minimize the makespan. This paper proposes a genetic algorithms (GAs) approach to optimize both the cut-piece requirements and the makespan of the conventional fabric-cutting departments using manual spreading and cutting methods. An optimization model for the manual fabric cutting process based on GAs was developed. Two sets of production data were collected to validate the performance of the model and the experimental results were obtained. From the results, it can be found that both the makespan and cut-piece fulfilment rates are improved in which the latter is improved significantly.     

数控机床进给速度控制分析

分析了数控机床的进给速度控制方式及具体控制方法,得出数控机床进给速度控制是按工艺要求加工出合格零件的必要手段。     

基于RTLinux的全软件并联机床数控系统研究

并联数控装备的最大特点在于其结构简单而控制复杂，且不同构型的并联机构逆解方程和结构参数不尽相同，这对控制系统的灵活性和开放性提出了更高要求。由于在控制原理上存在较大差异，基于串联机构设计的传统数控系统无法直接应用于并联机床这类独特的场合。针对并联机床的控制要求和特点，本文提出采用全软件化集成式的数控结构来建造并联机床数控系统，研究了以RTLinux作为底层实日寸操作系统的软件数控系统开发方法。     

Using genetic algorithms for the optimization of mechanisms

This work examines the possibility of using genetic algorithms for the optimization of the loads transmitted in mechanisms. The variables of design are the relative positions of the various connections, considered in a comparative manner. The minimization of the loads transmitted in the connections is achieved by optimizing the respective positions of those lead to less expensive solutions for bearings and sections of beams. The examples show that using this stochastic method is an efficient way to minimize loads in mechanisms.